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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | RUNTIME MANAGEMENT COMMANDS | ACTIVE-STANDBY FOR HIGH AVAILABILITY | LOGICAL FLOW TABLE STRUCTURE | DROP SAMPLING | COLOPHON |
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ovn-northd(8) OVN Manual ovn-northd(8)
ovn-northd - Open Virtual Network central control daemon
ovn-northd [options]
ovn-northd is a centralized daemon responsible for translating
the high-level OVN configuration into logical configuration
consumable by daemons such as ovn-controller. It translates the
logical network configuration in terms of conventional network
concepts, taken from the OVN Northbound Database (see ovn-nb(5)),
into logical datapath flows in the OVN Southbound Database (see
ovn-sb(5)) below it.
--ovnnb-db=database
The OVSDB database containing the OVN Northbound Database.
If the OVN_NB_DB environment variable is set, its value is
used as the default. Otherwise, the default is
unix:/ovnnb_db.sock.
--ovnsb-db=database
The OVSDB database containing the OVN Southbound Database.
If the OVN_SB_DB environment variable is set, its value is
used as the default. Otherwise, the default is
unix:/ovnsb_db.sock.
--dry-run
Causes ovn-northd to start paused. In the paused state,
ovn-northd does not apply any changes to the databases,
although it continues to monitor them. For more
information, see the pause command, under Runtime
Management Commands below.
n-threads N
In certain situations, it may be desirable to enable
parallelization on a system to decrease latency (at the
potential cost of increasing CPU usage).
This option will cause ovn-northd to use N threads when
building logical flows, when N is within [2-256]. If N is
1, parallelization is disabled (default behavior). If N is
less than 1, then N is set to 1, parallelization is
disabled and a warning is logged. If N is more than 256,
then N is set to 256, parallelization is enabled (with 256
threads) and a warning is logged.
database in the above options must be an OVSDB active or passive
connection method, as described in ovsdb(7).
Daemon Options
--pidfile[=pidfile]
Causes a file (by default, program.pid) to be created
indicating the PID of the running process. If the pidfile
argument is not specified, or if it does not begin with /,
then it is created in .
If --pidfile is not specified, no pidfile is created.
--overwrite-pidfile
By default, when --pidfile is specified and the specified
pidfile already exists and is locked by a running process,
the daemon refuses to start. Specify --overwrite-pidfile
to cause it to instead overwrite the pidfile.
When --pidfile is not specified, this option has no
effect.
--detach
Runs this program as a background process. The process
forks, and in the child it starts a new session, closes
the standard file descriptors (which has the side effect
of disabling logging to the console), and changes its
current directory to the root (unless --no-chdir is
specified). After the child completes its initialization,
the parent exits.
--monitor
Creates an additional process to monitor this program. If
it dies due to a signal that indicates a programming error
(SIGABRT, SIGALRM, SIGBUS, SIGFPE, SIGILL, SIGPIPE,
SIGSEGV, SIGXCPU, or SIGXFSZ) then the monitor process
starts a new copy of it. If the daemon dies or exits for
another reason, the monitor process exits.
This option is normally used with --detach, but it also
functions without it.
--no-chdir
By default, when --detach is specified, the daemon changes
its current working directory to the root directory after
it detaches. Otherwise, invoking the daemon from a
carelessly chosen directory would prevent the
administrator from unmounting the file system that holds
that directory.
Specifying --no-chdir suppresses this behavior, preventing
the daemon from changing its current working directory.
This may be useful for collecting core files, since it is
common behavior to write core dumps into the current
working directory and the root directory is not a good
directory to use.
This option has no effect when --detach is not specified.
--no-self-confinement
By default this daemon will try to self-confine itself to
work with files under well-known directories determined at
build time. It is better to stick with this default
behavior and not to use this flag unless some other Access
Control is used to confine daemon. Note that in contrast
to other access control implementations that are typically
enforced from kernel-space (e.g. DAC or MAC), self-
confinement is imposed from the user-space daemon itself
and hence should not be considered as a full confinement
strategy, but instead should be viewed as an additional
layer of security.
--user=user:group
Causes this program to run as a different user specified
in user:group, thus dropping most of the root privileges.
Short forms user and :group are also allowed, with current
user or group assumed, respectively. Only daemons started
by the root user accepts this argument.
On Linux, daemons will be granted CAP_IPC_LOCK and
CAP_NET_BIND_SERVICES before dropping root privileges.
Daemons that interact with a datapath, such as
ovs-vswitchd, will be granted three additional
capabilities, namely CAP_NET_ADMIN, CAP_NET_BROADCAST and
CAP_NET_RAW. The capability change will apply even if the
new user is root.
On Windows, this option is not currently supported. For
security reasons, specifying this option will cause the
daemon process not to start.
Logging Options
-v[spec]
--verbose=[spec]
Sets logging levels. Without any spec, sets the log level
for every module and destination to dbg. Otherwise, spec is
a list of words separated by spaces or commas or colons, up
to one from each category below:
• A valid module name, as displayed by the vlog/list
command on ovs-appctl(8), limits the log level change
to the specified module.
• syslog, console, or file, to limit the log level
change to only to the system log, to the console, or
to a file, respectively. (If --detach is specified,
the daemon closes its standard file descriptors, so
logging to the console will have no effect.)
On Windows platform, syslog is accepted as a word and
is only useful along with the --syslog-target option
(the word has no effect otherwise).
• off, emer, err, warn, info, or dbg, to control the
log level. Messages of the given severity or higher
will be logged, and messages of lower severity will
be filtered out. off filters out all messages. See
ovs-appctl(8) for a definition of each log level.
Case is not significant within spec.
Regardless of the log levels set for file, logging to a file
will not take place unless --log-file is also specified (see
below).
For compatibility with older versions of OVS, any is
accepted as a word but has no effect.
-v
--verbose
Sets the maximum logging verbosity level, equivalent to
--verbose=dbg.
-vPATTERN:destination:pattern
--verbose=PATTERN:destination:pattern
Sets the log pattern for destination to pattern. Refer to
ovs-appctl(8) for a description of the valid syntax for
pattern.
-vFACILITY:facility
--verbose=FACILITY:facility
Sets the RFC5424 facility of the log message. facility can
be one of kern, user, mail, daemon, auth, syslog, lpr, news,
uucp, clock, ftp, ntp, audit, alert, clock2, local0, local1,
local2, local3, local4, local5, local6 or local7. If this
option is not specified, daemon is used as the default for
the local system syslog and local0 is used while sending a
message to the target provided via the --syslog-target
option.
--log-file[=file]
Enables logging to a file. If file is specified, then it is
used as the exact name for the log file. The default log
file name used if file is omitted is
/usr/local/var/log/ovn/program.log.
--syslog-target=host:port
Send syslog messages to UDP port on host, in addition to the
system syslog. The host must be a numerical IP address, not
a hostname.
--syslog-method=method
Specify method as how syslog messages should be sent to
syslog daemon. The following forms are supported:
• libc, to use the libc syslog() function. Downside of
using this options is that libc adds fixed prefix to
every message before it is actually sent to the
syslog daemon over /dev/log UNIX domain socket.
• unix:file, to use a UNIX domain socket directly. It
is possible to specify arbitrary message format with
this option. However, rsyslogd 8.9 and older versions
use hard coded parser function anyway that limits
UNIX domain socket use. If you want to use arbitrary
message format with older rsyslogd versions, then use
UDP socket to localhost IP address instead.
• udp:ip:port, to use a UDP socket. With this method it
is possible to use arbitrary message format also with
older rsyslogd. When sending syslog messages over UDP
socket extra precaution needs to be taken into
account, for example, syslog daemon needs to be
configured to listen on the specified UDP port,
accidental iptables rules could be interfering with
local syslog traffic and there are some security
considerations that apply to UDP sockets, but do not
apply to UNIX domain sockets.
• null, to discard all messages logged to syslog.
The default is taken from the OVS_SYSLOG_METHOD environment
variable; if it is unset, the default is libc.
PKI Options
PKI configuration is required in order to use SSL for the
connections to the Northbound and Southbound databases.
-p privkey.pem
--private-key=privkey.pem
Specifies a PEM file containing the private key used
as identity for outgoing SSL connections.
-c cert.pem
--certificate=cert.pem
Specifies a PEM file containing a certificate that
certifies the private key specified on -p or
--private-key to be trustworthy. The certificate must
be signed by the certificate authority (CA) that the
peer in SSL connections will use to verify it.
-C cacert.pem
--ca-cert=cacert.pem
Specifies a PEM file containing the CA certificate
for verifying certificates presented to this program
by SSL peers. (This may be the same certificate that
SSL peers use to verify the certificate specified on
-c or --certificate, or it may be a different one,
depending on the PKI design in use.)
-C none
--ca-cert=none
Disables verification of certificates presented by
SSL peers. This introduces a security risk, because
it means that certificates cannot be verified to be
those of known trusted hosts.
Other Options
--unixctl=socket
Sets the name of the control socket on which program
listens for runtime management commands (see RUNTIME
MANAGEMENT COMMANDS, below). If socket does not begin with
/, it is interpreted as relative to . If --unixctl is not
used at all, the default socket is /program.pid.ctl, where
pid is program’s process ID.
On Windows a local named pipe is used to listen for
runtime management commands. A file is created in the
absolute path as pointed by socket or if --unixctl is not
used at all, a file is created as program in the
configured OVS_RUNDIR directory. The file exists just to
mimic the behavior of a Unix domain socket.
Specifying none for socket disables the control socket
feature.
-h
--help
Prints a brief help message to the console.
-V
--version
Prints version information to the console.
ovs-appctl can send commands to a running ovn-northd process. The
currently supported commands are described below.
exit Causes ovn-northd to gracefully terminate.
pause Pauses ovn-northd. When it is paused, ovn-northd
receives changes from the Northbound and Southbound
database changes as usual, but it does not send any
updates. A paused ovn-northd also drops database
locks, which allows any other non-paused instance
of ovn-northd to take over.
resume Resumes the ovn-northd operation to process
Northbound and Southbound database contents and
generate logical flows. This will also instruct
ovn-northd to aspire for the lock on SB DB.
is-paused
Returns "true" if ovn-northd is currently paused,
"false" otherwise.
status Prints this server’s status. Status will be
"active" if ovn-northd has acquired OVSDB lock on
SB DB, "standby" if it has not or "paused" if this
instance is paused.
sb-cluster-state-reset
Reset southbound database cluster status when
databases are destroyed and rebuilt.
If all databases in a clustered southbound database
are removed from disk, then the stored index of all
databases will be reset to zero. This will cause
ovn-northd to be unable to read or write to the
southbound database, because it will always detect
the data as stale. In such a case, run this command
so that ovn-northd will reset its local index so
that it can interact with the southbound database
again.
nb-cluster-state-reset
Reset northbound database cluster status when
databases are destroyed and rebuilt.
This performs the same task as
sb-cluster-state-reset except for the northbound
database client.
set-n-threads N
Set the number of threads used for building logical
flows. When N is within [2-256], parallelization is
enabled. When N is 1 parallelization is disabled.
When N is less than 1 or more than 256, an error is
returned. If ovn-northd fails to start
parallelization (e.g. fails to setup semaphores,
parallelization is disabled and an error is
returned.
get-n-threads
Return the number of threads used for building
logical flows.
inc-engine/show-stats
Display ovn-northd engine counters. For each engine
node the following counters have been added:
• recompute
• compute
• abort
inc-engine/show-stats engine_node_name counter_name
Display the ovn-northd engine counter(s) for the
specified engine_node_name. counter_name is
optional and can be one of recompute, compute or
abort.
inc-engine/clear-stats
Reset ovn-northd engine counters.
You may run ovn-northd more than once in an OVN deployment. When
connected to a standalone or clustered DB setup, OVN will
automatically ensure that only one of them is active at a time.
If multiple instances of ovn-northd are running and the active
ovn-northd fails, one of the hot standby instances of ovn-northd
will automatically take over.
Active-Standby with multiple OVN DB servers
You may run multiple OVN DB servers in an OVN deployment with:
• OVN DB servers deployed in active/passive mode with
one active and multiple passive ovsdb-servers.
• ovn-northd also deployed on all these nodes, using
unix ctl sockets to connect to the local OVN DB
servers.
In such deployments, the ovn-northds on the passive nodes will
process the DB changes and compute logical flows to be thrown out
later, because write transactions are not allowed by the passive
ovsdb-servers. It results in unnecessary CPU usage.
With the help of runtime management command pause, you can pause
ovn-northd on these nodes. When a passive node becomes master,
you can use the runtime management command resume to resume the
ovn-northd to process the DB changes.
One of the main purposes of ovn-northd is to populate the
Logical_Flow table in the OVN_Southbound database. This section
describes how ovn-northd does this for switch and router logical
datapaths.
Logical Switch Datapaths
Ingress Table 0: Admission Control and Ingress Port Security check
Ingress table 0 contains these logical flows:
• Priority 100 flows to drop packets with VLAN tags
or multicast Ethernet source addresses.
• For each disabled logical port, a priority 100 flow
is added which matches on all packets and applies
the action REGBIT_PORT_SEC_DROP" = 1; next;" so
that the packets are dropped in the next stage.
• For each (enabled) vtep logical port, a priority 70
flow is added which matches on all packets and
applies the action next(pipeline=ingress,
table=S_SWITCH_IN_L3_LKUP) = 1; to skip most stages
of ingress pipeline and go directly to ingress L2
lookup table to determine the output port. Packets
from VTEP (RAMP) switch should not be subjected to
any ACL checks. Egress pipeline will do the ACL
checks.
• For each enabled logical port configured with qdisc
queue id in the options:qdisc_queue_id column of
Logical_Switch_Port, a priority 70 flow is added
which matches on all packets and applies the action
set_queue(id); REGBIT_PORT_SEC_DROP" =
check_in_port_sec(); next;".
• A priority 1 flow is added which matches on all
packets for all the logical ports and applies the
action REGBIT_PORT_SEC_DROP" = check_in_port_sec();
next; to evaluate the port security. The action
check_in_port_sec applies the port security rules
defined in the port_security column of
Logical_Switch_Port table.
Ingress Table 1: Ingress Port Security - Apply
For each logical switch port P of type router connected to a gw
router a priority-120 flow that matches ’recirculated’ icmp{4,6}
error ’packet too big’ and eth.src == D && outport == P &&
flags.tunnel_rx == 1 where D is the peer logical router port RP
mac address, swaps inport and outport and applies the action
next.
For each logical switch port P of type router connected to a
distributed router a priority-120 flow that matches
’recirculated’ icmp{4,6} error ’packet too big’ and eth.dst == D
&& flags.tunnel_rx == 1 where D is the peer logical router port
RP mac address, swaps inport and outport and applies the action
next(pipeline=S_SWITCH_IN_L2_LKUP).
For each logical switch port P a priority-110 flow that matches
’recirculated’ icmp{4,6} error ’packet too big’ and eth.src == D
&& outport == P && !is_chassis_resident("P") && flags.tunnel_rx
== 1
where D is the logical switch port mac address, swaps inport and
outport and applies the action next.
This table adds a priority-105 flow that matches ’recirculated’
icmp{4,6} error ’packet too big’ to drop the packet.
This table drops the packets if the port security check failed in
the previous stage i.e the register bit REGBIT_PORT_SEC_DROP is
set to 1.
Ingress table 1 contains these logical flows:
• A priority-50 fallback flow that drops the packet
if the register bit REGBIT_PORT_SEC_DROP is set to
1.
• One priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 2: Lookup MAC address learning table
This table looks up the MAC learning table of the logical switch
datapath to check if the port-mac pair is present or not. MAC is
learnt for logical switch VIF ports whose port security is
disabled and ’unknown’ address setn as well as for localnet ports
with option localnet_learn_fdb. A localnet port entry does not
overwrite a VIF port entry.
• For each such VIF logical port p whose port
security is disabled and ’unknown’ address set
following flow is added.
• Priority 100 flow with the match inport == p
and action reg0[11] = lookup_fdb(inport,
eth.src); next;
• For each such localnet logical port p following
flow is added.
• Priority 100 flow with the match inport == p
and action flags.localnet = 1; reg0[11] =
lookup_fdb(inport, eth.src); next;
• One priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 3: Learn MAC of ’unknown’ ports.
This table learns the MAC addresses seen on the VIF logical ports
whose port security is disabled and ’unknown’ address set as well
as on localnet ports with localnet_learn_fdb option set if the
lookup_fdb action returned false in the previous table. For
localnet ports (with flags.localnet = 1), lookup_fdb returns true
if (port, mac) is found or if a mac is found for a port of type
vif.
• For each such VIF logical port p whose port
security is disabled and ’unknown’ address set and
localnet port following flow is added.
• Priority 100 flow with the match inport == p
&& reg0[11] == 0 and action put_fdb(inport,
eth.src); next; which stores the port-mac in
the mac learning table of the logical switch
datapath and advances the packet to the next
table.
• One priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 4: from-lport Pre-ACLs
This table prepares flows for possible stateful ACL processing in
ingress table ACLs. It contains a priority-0 flow that simply
moves traffic to the next table. If stateful ACLs are used in the
logical datapath, a priority-100 flow is added that sets a hint
(with reg0[0] = 1; next;) for table Pre-stateful to send IP
packets to the connection tracker before eventually advancing to
ingress table ACLs. If special ports such as route ports or
localnet ports can’t use ct(), a priority-110 flow is added to
skip over stateful ACLs. This priority-110 flow is not addd for
router ports if the option enable_router_port_acl is set to true
in options:enable_router_port_acl column of Logical_Switch_Port.
Multicast, IPv6 Neighbor Discovery and MLD traffic also skips
stateful ACLs. For "allow-stateless" ACLs, a flow is added to
bypass setting the hint for connection tracker processing when
there are stateful ACLs or LB rules; REGBIT_ACL_STATELESS is set
for traffic matching stateless ACL flows.
This table also has a priority-110 flow with the match eth.dst ==
E for all logical switch datapaths to move traffic to the next
table. Where E is the service monitor mac defined in the
options:svc_monitor_mac column of NB_Global table.
Ingress Table 5: Pre-LB
This table prepares flows for possible stateful load balancing
processing in ingress table LB and Stateful. It contains a
priority-0 flow that simply moves traffic to the next table.
Moreover it contains two priority-110 flows to move multicast,
IPv6 Neighbor Discovery and MLD traffic to the next table. It
also contains two priority-110 flows to move stateless traffic,
i.e traffic for which REGBIT_ACL_STATELESS is set, to the next
table. If load balancing rules with virtual IP addresses (and
ports) are configured in OVN_Northbound database for a logical
switch datapath, a priority-100 flow is added with the match ip
to match on IP packets and sets the action reg0[2] = 1; next; to
act as a hint for table Pre-stateful to send IP packets to the
connection tracker for packet de-fragmentation (and to possibly
do DNAT for already established load balanced traffic) before
eventually advancing to ingress table Stateful. If
controller_event has been enabled and load balancing rules with
empty backends have been added in OVN_Northbound, a 130 flow is
added to trigger ovn-controller events whenever the chassis
receives a packet for that particular VIP. If event-elb meter has
been previously created, it will be associated to the empty_lb
logical flow
Prior to OVN 20.09 we were setting the reg0[0] = 1 only if the IP
destination matches the load balancer VIP. However this had few
issues cases where a logical switch doesn’t have any ACLs with
allow-related action. To understand the issue lets a take a TCP
load balancer - 10.0.0.10:80=10.0.0.3:80. If a logical port - p1
with IP - 10.0.0.5 opens a TCP connection with the VIP -
10.0.0.10, then the packet in the ingress pipeline of ’p1’ is
sent to the p1’s conntrack zone id and the packet is load
balanced to the backend - 10.0.0.3. For the reply packet from the
backend lport, it is not sent to the conntrack of backend lport’s
zone id. This is fine as long as the packet is valid. Suppose the
backend lport sends an invalid TCP packet (like incorrect
sequence number), the packet gets delivered to the lport ’p1’
without unDNATing the packet to the VIP - 10.0.0.10. And this
causes the connection to be reset by the lport p1’s VIF.
We can’t fix this issue by adding a logical flow to drop ct.inv
packets in the egress pipeline since it will drop all other
connections not destined to the load balancers. To fix this
issue, we send all the packets to the conntrack in the ingress
pipeline if a load balancer is configured. We can now add a lflow
to drop ct.inv packets.
This table also has priority-120 flows that punt all IGMP/MLD
packets to ovn-controller if the switch is an interconnect switch
with multicast snooping enabled.
This table also has a priority-110 flow with the match eth.dst ==
E for all logical switch datapaths to move traffic to the next
table. Where E is the service monitor mac defined in the
options:svc_monitor_mac column of NB_Global table.
This table also has a priority-110 flow with the match inport ==
I for all logical switch datapaths to move traffic to the next
table. Where I is the peer of a logical router port. This flow is
added to skip the connection tracking of packets which enter from
logical router datapath to logical switch datapath.
Ingress Table 6: Pre-stateful
This table prepares flows for all possible stateful processing in
next tables. It contains a priority-0 flow that simply moves
traffic to the next table.
• Priority-120 flows that send the packets to
connection tracker using ct_lb_mark; as the action
so that the already established traffic destined to
the load balancer VIP gets DNATted. These flows
match each VIPs IP and port. For IPv4 traffic the
flows also load the original destination IP and
transport port in registers reg1 and reg2. For IPv6
traffic the flows also load the original
destination IP and transport port in registers
xxreg1 and reg2.
• A priority-110 flow sends the packets that don’t
match the above flows to connection tracker based
on a hint provided by the previous tables (with a
match for reg0[2] == 1) by using the ct_lb_mark;
action.
• A priority-100 flow sends the packets to connection
tracker based on a hint provided by the previous
tables (with a match for reg0[0] == 1) by using the
ct_next; action.
Ingress Table 7: from-lport ACL hints
This table consists of logical flows that set hints (reg0 bits)
to be used in the next stage, in the ACL processing table, if
stateful ACLs or load balancers are configured. Multiple hints
can be set for the same packet. The possible hints are:
• reg0[7]: the packet might match an allow-related
ACL and might have to commit the connection to
conntrack.
• reg0[8]: the packet might match an allow-related
ACL but there will be no need to commit the
connection to conntrack because it already exists.
• reg0[9]: the packet might match a drop/reject.
• reg0[10]: the packet might match a drop/reject ACL
but the connection was previously allowed so it
might have to be committed again with ct_label=1/1.
The table contains the following flows:
• A priority-65535 flow to advance to the next table
if the logical switch has no ACLs configured,
otherwise a priority-0 flow to advance to the next
table.
• A priority-7 flow that matches on packets that
initiate a new session. This flow sets reg0[7] and
reg0[9] and then advances to the next table.
• A priority-6 flow that matches on packets that are
in the request direction of an already existing
session that has been marked as blocked. This flow
sets reg0[7] and reg0[9] and then advances to the
next table.
• A priority-5 flow that matches untracked packets.
This flow sets reg0[8] and reg0[9] and then
advances to the next table.
• A priority-4 flow that matches on packets that are
in the request direction of an already existing
session that has not been marked as blocked. This
flow sets reg0[8] and reg0[10] and then advances to
the next table.
• A priority-3 flow that matches on packets that are
in not part of established sessions. This flow sets
reg0[9] and then advances to the next table.
• A priority-2 flow that matches on packets that are
part of an established session that has been marked
as blocked. This flow sets reg0[9] and then
advances to the next table.
• A priority-1 flow that matches on packets that are
part of an established session that has not been
marked as blocked. This flow sets reg0[10] and then
advances to the next table.
Ingress table 8: from-lport ACL evaluation before LB
Logical flows in this table closely reproduce those in the ACL
table in the OVN_Northbound database for the from-lport direction
without the option apply-after-lb set or set to false. The
priority values from the ACL table have a limited range and have
1000 added to them to leave room for OVN default flows at both
higher and lower priorities.
• This table is responsible for evaluating ACLs, and
setting a register bit to indicate whether the ACL
decided to allow, drop, or reject the traffic. The
allow bit is reg8[16]. The drop bit is reg8[17].
All flows in this table will advance the packet to
the next table, where the bits from before are
evaluated to determine what to do with the packet.
Any flows in this table that intend for the packet
to pass will set reg8[16] to 1, even if an ACL with
an allow-type action was not matched. This lets the
next table know to allow the traffic to pass. These
bits will be referred to as the "allow", "drop",
and "reject" bits in the upcoming paragraphs.
• If the tier column has been configured on the ACL,
then OVN will also match the current tier counter
against the configured ACL tier. OVN keeps count of
the current tier in reg8[30..31].
• allow ACLs translate into logical flows that set
the allow bit to 1 and advance the packet to the
next table. If there are any stateful ACLs on this
datapath, then allow ACLs set the allow bit to one
and in addition perform ct_commit; (which acts as a
hint for future tables to commit the connection to
conntrack). In case the ACL has a label then reg3
is loaded with the label value and reg0[13] bit is
set to 1 (which acts as a hint for the next tables
to commit the label to conntrack).
• allow-related ACLs translate into logical flows
that set the allow bit and additionally have
ct_commit { ct_label=0/1; }; next; actions for new
connections and reg0[1] = 1; next; for existing
connections. In case the ACL has a label then reg3
is loaded with the label value and reg0[13] bit is
set to 1 (which acts as a hint for the next tables
to commit the label to conntrack).
• allow-stateless ACLs translate into logical flows
that set the allow bit and advance to the next
table.
• reject ACLs translate into logical flows with that
set the reject bit and advance to the next table.
• pass ACLs translate into logical flows that do not
set the allow, drop, or reject bit and advance to
the next table.
• Other ACLs set the drop bit and advance to the next
table for new or untracked connections. For known
connections, they set the drop bit, as well as
running the ct_commit { ct_label=1/1; }; action.
Setting ct_label marks a connection as one that was
previously allowed, but should no longer be allowed
due to a policy change.
This table contains a priority-65535 flow to set the allow bit
and advance to the next table if the logical switch has no ACLs
configured, otherwise a priority-0 flow to advance to the next
table is added. This flow does not set the allow bit, so that the
next table can decide whether to allow or drop the packet based
on the value of the options:default_acl_drop column of the
NB_Global table.
A priority-65532 flow is added that sets the allow bit for IPv6
Neighbor solicitation, Neighbor discover, Router solicitation,
Router advertisement and MLD packets regardless of other ACLs
defined.
If the logical datapath has a stateful ACL or a load balancer
with VIP configured, the following flows will also be added:
• If options:default_acl_drop column of NB_Global is
false or not set, a priority-1 flow that sets the
hint to commit IP traffic that is not part of
established sessions to the connection tracker
(with action reg0[1] = 1; next;). This is needed
for the default allow policy because, while the
initiator’s direction may not have any stateful
rules, the server’s may and then its return traffic
would not be known and marked as invalid.
• A priority-1 flow that sets the allow bit and sets
the hint to commit IP traffic to the connection
tracker (with action reg0[1] = 1; next;). This is
needed for the default allow policy because, while
the initiator’s direction may not have any stateful
rules, the server’s may and then its return traffic
would not be known and marked as invalid.
• A priority-65532 flow that sets the allow bit for
any traffic in the reply direction for a connection
that has been committed to the connection tracker
(i.e., established flows), as long as the committed
flow does not have ct_mark.blocked set. We only
handle traffic in the reply direction here because
we want all packets going in the request direction
to still go through the flows that implement the
currently defined policy based on ACLs. If a
connection is no longer allowed by policy,
ct_mark.blocked will get set and packets in the
reply direction will no longer be allowed, either.
This flow also clears the register bits reg0[9] and
reg0[10] and sets register bit reg0[17]. If ACL
logging and logging of related packets is enabled,
then a companion priority-65533 flow will be
installed that accomplishes the same thing but also
logs the traffic.
• A priority-65532 flow that sets the allow bit for
any traffic that is considered related to a
committed flow in the connection tracker (e.g., an
ICMP Port Unreachable from a non-listening UDP
port), as long as the committed flow does not have
ct_mark.blocked set. This flow also applies NAT to
the related traffic so that ICMP headers and the
inner packet have correct addresses. If ACL logging
and logging of related packets is enabled, then a
companion priority-65533 flow will be installed
that accomplishes the same thing but also logs the
traffic.
• A priority-65532 flow that sets the drop bit for
all traffic marked by the connection tracker as
invalid.
• A priority-65532 flow that sets the drop bit for
all traffic in the reply direction with
ct_mark.blocked set meaning that the connection
should no longer be allowed due to a policy change.
Packets in the request direction are skipped here
to let a newly created ACL re-allow this
connection.
If the logical datapath has any ACL or a load balancer with VIP
configured, the following flow will also be added:
• A priority 34000 logical flow is added for each
logical switch datapath with the match eth.dst = E
to allow the service monitor reply packet destined
to ovn-controller that sets the allow bit, where E
is the service monitor mac defined in the
options:svc_monitor_mac column of NB_Global table.
Ingress Table 9: from-lport ACL action
Logical flows in this table decide how to proceed based on the
values of the allow, drop, and reject bits that may have been set
in the previous table.
• If no ACLs are configured, then a priority 0 flow
is installed that matches everything and advances
to the next table.
• A priority 1000 flow is installed that will advance
the packet to the next table if the allow bit is
set.
• A priority 1000 flow is installed that will run the
drop; action if the drop bit is set.
• A priority 1000 flow is installed that will run the
tcp_reset { output <-> inport;
next(pipeline=egress,table=5);} action for TCP
connections,icmp4/icmp6 action for UDP connections,
and sctp_abort {output <-%gt; inport;
next(pipeline=egress,table=5);} action for SCTP
associations.
• If any ACLs have tiers configured on them, then
three priority 500 flows are installed. If the
current tier counter is 0, 1, or 2, then the
current tier counter is incremented by one and the
packet is sent back to the previous table for re-
evaluation.
Ingress Table 10: from-lport QoS Marking
Logical flows in this table closely reproduce those in the QoS
table with the action column set in the OVN_Northbound database
for the from-lport direction.
• For every qos_rules entry in a logical switch with
DSCP marking enabled, a flow will be added at the
priority mentioned in the QoS table.
• For every qos_rules entry in a logical switch with
packet marking enabled, a flow will be added at the
priority mentioned in the QoS table.
• One priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 11: from-lport QoS Meter
Logical flows in this table closely reproduce those in the QoS
table with the bandwidth column set in the OVN_Northbound
database for the from-lport direction.
• For every qos_rules entry in a logical switch with
metering enabled, a flow will be added at the
priority mentioned in the QoS table.
• One priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 12: Load balancing affinity check
Load balancing affinity check table contains the following
logical flows:
• For all the configured load balancing rules for a
switch in OVN_Northbound database where a positive
affinity timeout is specified in options column,
that includes a L4 port PORT of protocol P and IP
address VIP, a priority-100 flow is added. For IPv4
VIPs, the flow matches ct.new && ip && ip4.dst ==
VIP && P.dst == PORT. For IPv6 VIPs, the flow
matches ct.new && ip && ip6.dst == VIP&& P && P.dst
== PORT. The flow’s action is reg9[6] =
chk_lb_aff(); next;.
• A priority 0 flow is added which matches on all
packets and applies the action next;.
Ingress Table 13: LB
• For all the configured load balancing rules for a
switch in OVN_Northbound database where a positive
affinity timeout is specified in options column,
that includes a L4 port PORT of protocol P and IP
address VIP, a priority-150 flow is added. For IPv4
VIPs, the flow matches reg9[6] == 1 && ct.new && ip
&& ip4.dst == VIP && P.dst == PORT . For IPv6 VIPs,
the flow matches reg9[6] == 1 && ct.new && ip &&
ip6.dst == VIP && P && P.dst == PORT. The flow’s
action is ct_lb_mark(args), where args contains
comma separated IP addresses (and optional port
numbers) to load balance to. The address family of
the IP addresses of args is the same as the address
family of VIP.
• For all the configured load balancing rules for a
switch in OVN_Northbound database that includes a
L4 port PORT of protocol P and IP address VIP, a
priority-120 flow is added. For IPv4 VIPs , the
flow matches ct.new && ip && ip4.dst == VIP &&
P.dst == PORT. For IPv6 VIPs, the flow matches
ct.new && ip && ip6.dst == VIP && P && P.dst ==
PORT. The flow’s action is ct_lb_mark(args) , where
args contains comma separated IP addresses (and
optional port numbers) to load balance to. The
address family of the IP addresses of args is the
same as the address family of VIP. If health check
is enabled, then args will only contain those
endpoints whose service monitor status entry in
OVN_Southbound db is either online or empty. For
IPv4 traffic the flow also loads the original
destination IP and transport port in registers reg1
and reg2. For IPv6 traffic the flow also loads the
original destination IP and transport port in
registers xxreg1 and reg2. The above flow is
created even if the load balancer is attached to a
logical router connected to the current logical
switch and the install_ls_lb_from_router variable
in options is set to true.
• For all the configured load balancing rules for a
switch in OVN_Northbound database that includes
just an IP address VIP to match on, OVN adds a
priority-110 flow. For IPv4 VIPs, the flow matches
ct.new && ip && ip4.dst == VIP. For IPv6 VIPs, the
flow matches ct.new && ip && ip6.dst == VIP. The
action on this flow is ct_lb_mark(args), where args
contains comma separated IP addresses of the same
address family as VIP. For IPv4 traffic the flow
also loads the original destination IP and
transport port in registers reg1 and reg2. For IPv6
traffic the flow also loads the original
destination IP and transport port in registers
xxreg1 and reg2. The above flow is created even if
the load balancer is attached to a logical router
connected to the current logical switch and the
install_ls_lb_from_router variable in options is
set to true.
• If the load balancer is created with --reject
option and it has no active backends, a TCP reset
segment (for tcp) or an ICMP port unreachable
packet (for all other kind of traffic) will be sent
whenever an incoming packet is received for this
load-balancer. Please note using --reject option
will disable empty_lb SB controller event for this
load balancer.
Ingress Table 14: Load balancing affinity learn
Load balancing affinity learn table contains the following
logical flows:
• For all the configured load balancing rules for a
switch in OVN_Northbound database where a positive
affinity timeout T is specified in options column,
that includes a L4 port PORT of protocol P and IP
address VIP, a priority-100 flow is added. For IPv4
VIPs, the flow matches reg9[6] == 0 && ct.new && ip
&& ip4.dst == VIP && P.dst == PORT. For IPv6 VIPs,
the flow matches ct.new && ip && ip6.dst == VIP &&
P && P.dst == PORT . The flow’s action is
commit_lb_aff(vip = VIP:PORT, backend = backend ip:
backend port, proto = P, timeout = T); .
• A priority 0 flow is added which matches on all
packets and applies the action next;.
Ingress Table 15: Pre-Hairpin
• If the logical switch has load balancer(s)
configured, then a priority-100 flow is added with
the match ip && ct.trk to check if the packet needs
to be hairpinned (if after load balancing the
destination IP matches the source IP) or not by
executing the actions reg0[6] = chk_lb_hairpin();
and reg0[12] = chk_lb_hairpin_reply(); and advances
the packet to the next table.
• A priority-0 flow that simply moves traffic to the
next table.
Ingress Table 16: Nat-Hairpin
• If the logical switch has load balancer(s)
configured, then a priority-100 flow is added with
the match ip && ct.new && ct.trk && reg0[6] == 1
which hairpins the traffic by NATting source IP to
the load balancer VIP by executing the action
ct_snat_to_vip and advances the packet to the next
table.
• If the logical switch has load balancer(s)
configured, then a priority-100 flow is added with
the match ip && ct.est && ct.trk && reg0[6] == 1
which hairpins the traffic by NATting source IP to
the load balancer VIP by executing the action
ct_snat and advances the packet to the next table.
• If the logical switch has load balancer(s)
configured, then a priority-90 flow is added with
the match ip && reg0[12] == 1 which matches on the
replies of hairpinned traffic (i.e., destination IP
is VIP, source IP is the backend IP and source L4
port is backend port for L4 load balancers) and
executes ct_snat and advances the packet to the
next table.
• A priority-0 flow that simply moves traffic to the
next table.
Ingress Table 17: Hairpin
• If logical switch has attached logical switch port
of vtep type, then for each distributed gateway
router port RP attached to this logical switch and
has chassis redirect port cr-RP, a priority-2000
flow is added with the match .IP
reg0[14] == 1 && is_chassis_resident(cr-RP)
and action next;.
reg0[14] register bit is set in the ingress L2 port
security check table for traffic received from HW
VTEP (ramp) ports.
• If logical switch has attached logical switch port
of vtep type, then a priority-1000 flow that
matches on reg0[14] register bit for the traffic
received from HW VTEP (ramp) ports. This traffic is
passed to ingress table ls_in_l2_lkup.
• A priority-1 flow that hairpins traffic matched by
non-default flows in the Pre-Hairpin table.
Hairpinning is done at L2, Ethernet addresses are
swapped and the packets are looped back on the
input port.
• A priority-0 flow that simply moves traffic to the
next table.
Ingress table 18: from-lport ACL evaluation after LB
Logical flows in this table closely reproduce those in the ACL
eval table in the OVN_Northbound database for the from-lport
direction with the option apply-after-lb set to true. The
priority values from the ACL table have a limited range and have
1000 added to them to leave room for OVN default flows at both
higher and lower priorities. The flows in this table indicate the
ACL verdict by setting reg8[16] for allow-type ACLs, reg8[17] for
drop ACLs, and reg8[17] for reject ACLs, and then advancing the
packet to the next table. These will be reffered to as the allow
bit, drop bit, and reject bit throughout the documentation for
this table and the next one.
Like with ACLs that are evaluated before load balancers, if the
ACL is configured with a tier value, then the current tier
counter, supplied in reg8[30..31] is matched against the ACL’s
configured tier in addition to the ACL’s match.
• allow apply-after-lb ACLs translate into logical
flows that set the allow bit. If there are any
stateful ACLs (including both before-lb and after-
lb ACLs) on this datapath, then allow ACLs also run
ct_commit; next; (which acts as a hint for an
upcoming table to commit the connection to
conntrack). In case the ACL has a label then reg3
is loaded with the label value and reg0[13] bit is
set to 1 (which acts as a hint for the next tables
to commit the label to conntrack).
• allow-related apply-after-lb ACLs translate into
logical flows that set the allow bit and run the
ct_commit {ct_label=0/1; }; next; actions for new
connections and reg0[1] = 1; next; for existing
connections. In case the ACL has a label then reg3
is loaded with the label value and reg0[13] bit is
set to 1 (which acts as a hint for the next tables
to commit the label to conntrack).
• allow-stateless apply-after-lb ACLs translate into
logical flows that set the allow bit and advance to
the next table.
• reject apply-after-lb ACLs translate into logical
flows that set the reject bit and advance to the
next table.
• pass apply-after-lb ACLs translate into logical
flows that do not set the allow, drop, or reject
bit and advance to the next table.
• Other apply-after-lb ACLs set the drop bit for new
or untracked connections and ct_commit {
ct_label=1/1; } for known connections. Setting
ct_label marks a connection as one that was
previously allowed, but should no longer be allowed
due to a policy change.
• One priority-65532 flow matching packets with
reg0[17] set (either replies to existing sessions
or traffic related to existing sessions) and allows
these by setting the allow bit and advancing to the
next table.
• One priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 19: from-lport ACL action after LB
Logical flows in this table decide how to proceed based on the
values of the allow, drop, and reject bits that may have been set
in the previous table.
• If no ACLs are configured, then a priority 0 flow
is installed that matches everything and advances
to the next table.
• A priority 1000 flow is installed that will advance
the packet to the next table if the allow bit is
set.
• A priority 1000 flow is installed that will run the
drop; action if the drop bit is set.
• A priority 1000 flow is installed that will run the
tcp_reset { output <-> inport;
next(pipeline=egress,table=5);} action for TCP
connections,icmp4/icmp6 action for UDP connections,
and sctp_abort {output <-%gt; inport;
next(pipeline=egress,table=5);} action for SCTP
associations.
• If any ACLs have tiers configured on them, then
three priority 500 flows are installed. If the
current tier counter is 0, 1, or 2, then the
current tier counter is incremented by one and the
packet is sent back to the previous table for re-
evaluation.
Ingress Table 20: Stateful
• A priority 100 flow is added which commits the
packet to the conntrack and sets the most
significant 32-bits of ct_label with the reg3 value
based on the hint provided by previous tables (with
a match for reg0[1] == 1 && reg0[13] == 1). This is
used by the ACLs with label to commit the label
value to conntrack.
• For ACLs without label, a second priority-100 flow
commits packets to connection tracker using
ct_commit; next; action based on a hint provided by
the previous tables (with a match for reg0[1] == 1
&& reg0[13] == 0).
• A priority-0 flow that simply moves traffic to the
next table.
Ingress Table 21: ARP/ND responder
This table implements ARP/ND responder in a logical switch for
known IPs. The advantage of the ARP responder flow is to limit
ARP broadcasts by locally responding to ARP requests without the
need to send to other hypervisors. One common case is when the
inport is a logical port associated with a VIF and the broadcast
is responded to on the local hypervisor rather than broadcast
across the whole network and responded to by the destination VM.
This behavior is proxy ARP.
ARP requests arrive from VMs from a logical switch inport of type
default. For this case, the logical switch proxy ARP rules can be
for other VMs or logical router ports. Logical switch proxy ARP
rules may be programmed both for mac binding of IP addresses on
other logical switch VIF ports (which are of the default logical
switch port type, representing connectivity to VMs or
containers), and for mac binding of IP addresses on logical
switch router type ports, representing their logical router port
peers. In order to support proxy ARP for logical router ports, an
IP address must be configured on the logical switch router type
port, with the same value as the peer logical router port. The
configured MAC addresses must match as well. When a VM sends an
ARP request for a distributed logical router port and if the peer
router type port of the attached logical switch does not have an
IP address configured, the ARP request will be broadcast on the
logical switch. One of the copies of the ARP request will go
through the logical switch router type port to the logical router
datapath, where the logical router ARP responder will generate a
reply. The MAC binding of a distributed logical router, once
learned by an associated VM, is used for all that VM’s
communication needing routing. Hence, the action of a VM re-
arping for the mac binding of the logical router port should be
rare.
Logical switch ARP responder proxy ARP rules can also be hit when
receiving ARP requests externally on a L2 gateway port. In this
case, the hypervisor acting as an L2 gateway, responds to the ARP
request on behalf of a destination VM.
Note that ARP requests received from localnet logical inports can
either go directly to VMs, in which case the VM responds or can
hit an ARP responder for a logical router port if the packet is
used to resolve a logical router port next hop address. In either
case, logical switch ARP responder rules will not be hit. It
contains these logical flows:
• If packet was received from HW VTEP (ramp switch),
and this packet is ARP or Neighbor Solicitation,
such packet is passed to next table with max
proirity. ARP/ND requests from HW VTEP must be
handled in logical router ingress pipeline.
• If the logical switch has no router ports with
options:arp_proxy configured add a priority-100
flows to skip the ARP responder if inport is of
type localnet advances directly to the next table.
ARP requests sent to localnet ports can be received
by multiple hypervisors. Now, because the same mac
binding rules are downloaded to all hypervisors,
each of the multiple hypervisors will respond. This
will confuse L2 learning on the source of the ARP
requests. ARP requests received on an inport of
type router are not expected to hit any logical
switch ARP responder flows. However, no skip flows
are installed for these packets, as there would be
some additional flow cost for this and the value
appears limited.
• If inport V is of type virtual adds a priority-100
logical flows for each P configured in the
options:virtual-parents column with the match
inport == P && && ((arp.op == 1 && arp.spa == VIP && arp.tpa == VIP) || (arp.op == 2 && arp.spa == VIP))
inport == P && && ((nd_ns && ip6.dst == {VIP, NS_MULTICAST_ADDR} && nd.target == VIP) || (nd_na && nd.target == VIP))
and applies the action
bind_vport(V, inport);
and advances the packet to the next table.
Where VIP is the virtual ip configured in the
column options:virtual-ip and NS_MULTICAST_ADDR is
solicited-node multicast address corresponding to
the VIP.
• Priority-50 flows that match ARP requests to each
known IP address A of every logical switch port,
and respond with ARP replies directly with
corresponding Ethernet address E:
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
These flows are omitted for logical ports (other
than router ports or localport ports) that are down
(unless ignore_lsp_down is configured as true in
options column of NB_Global table of the Northbound
database), for logical ports of type virtual, for
logical ports with ’unknown’ address set, for
logical ports with the
options:disable_arp_nd_rsp=true and for logical
ports of a logical switch configured with
other_config:vlan-passthru=true.
The above ARP responder flows are added for the
list of IPv4 addresses if defined in
options:arp_proxy column of Logical_Switch_Port
table for logical switch ports of type router.
• Priority-50 flows that match IPv6 ND neighbor
solicitations to each known IP address A (and A’s
solicited node address) of every logical switch
port except of type router, and respond with
neighbor advertisements directly with corresponding
Ethernet address E:
nd_na {
eth.src = E;
ip6.src = A;
nd.target = A;
nd.tll = E;
outport = inport;
flags.loopback = 1;
output;
};
Priority-50 flows that match IPv6 ND neighbor
solicitations to each known IP address A (and A’s
solicited node address) of logical switch port of
type router, and respond with neighbor
advertisements directly with corresponding Ethernet
address E:
nd_na_router {
eth.src = E;
ip6.src = A;
nd.target = A;
nd.tll = E;
outport = inport;
flags.loopback = 1;
output;
};
These flows are omitted for logical ports (other
than router ports or localport ports) that are down
(unless ignore_lsp_down is configured as true in
options column of NB_Global table of the Northbound
database), for logical ports of type virtual and
for logical ports with ’unknown’ address set.
The above NDP responder flows are added for the
list of IPv6 addresses if defined in
options:arp_proxy column of Logical_Switch_Port
table for logical switch ports of type router.
• Priority-100 flows with match criteria like the ARP
and ND flows above, except that they only match
packets from the inport that owns the IP addresses
in question, with action next;. These flows prevent
OVN from replying to, for example, an ARP request
emitted by a VM for its own IP address. A VM only
makes this kind of request to attempt to detect a
duplicate IP address assignment, so sending a reply
will prevent the VM from accepting the IP address
that it owns.
In place of next;, it would be reasonable to use
drop; for the flows’ actions. If everything is
working as it is configured, then this would
produce equivalent results, since no host should
reply to the request. But ARPing for one’s own IP
address is intended to detect situations where the
network is not working as configured, so dropping
the request would frustrate that intent.
• For each SVC_MON_SRC_IP defined in the value of the
ip_port_mappings:ENDPOINT_IP column of
Load_Balancer table, priority-110 logical flow is
added with the match arp.tpa == SVC_MON_SRC_IP &&
&& arp.op == 1 and applies the action
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
where E is the service monitor source mac defined
in the options:svc_monitor_mac column in the
NB_Global table. This mac is used as the source mac
in the service monitor packets for the load
balancer endpoint IP health checks.
SVC_MON_SRC_IP is used as the source ip in the
service monitor IPv4 packets for the load balancer
endpoint IP health checks.
These flows are required if an ARP request is sent
for the IP SVC_MON_SRC_IP.
For IPv6 the similar flow is added with the
following action
nd_na {
eth.dst = eth.src;
eth.src = E;
ip6.src = A;
nd.target = A;
nd.tll = E;
outport = inport;
flags.loopback = 1;
output;
};
• For each VIP configured in the table
Forwarding_Group a priority-50 logical flow is
added with the match arp.tpa == vip && && arp.op ==
1
and applies the action
eth.dst = eth.src;
eth.src = E;
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = E;
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
where E is the forwarding group’s mac defined in
the vmac.
A is used as either the destination ip for load
balancing traffic to child ports or as nexthop to
hosts behind the child ports.
These flows are required to respond to an ARP
request if an ARP request is sent for the IP vip.
• One priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 22: DHCP option processing
This table adds the DHCPv4 options to a DHCPv4 packet from the
logical ports configured with IPv4 address(es) and DHCPv4
options, and similarly for DHCPv6 options. This table also adds
flows for the logical ports of type external.
• A priority-100 logical flow is added for these
logical ports which matches the IPv4 packet with
udp.src = 68 and udp.dst = 67 and applies the
action put_dhcp_opts and advances the packet to the
next table.
reg0[3] = put_dhcp_opts(offer_ip = ip, options...);
next;
For DHCPDISCOVER and DHCPREQUEST, this transforms
the packet into a DHCP reply, adds the DHCP offer
IP ip and options to the packet, and stores 1 into
reg0[3]. For other kinds of packets, it just stores
0 into reg0[3]. Either way, it continues to the
next table.
• A priority-100 logical flow is added for these
logical ports which matches the IPv6 packet with
udp.src = 546 and udp.dst = 547 and applies the
action put_dhcpv6_opts and advances the packet to
the next table.
reg0[3] = put_dhcpv6_opts(ia_addr = ip, options...);
next;
For DHCPv6 Solicit/Request/Confirm packets, this
transforms the packet into a DHCPv6
Advertise/Reply, adds the DHCPv6 offer IP ip and
options to the packet, and stores 1 into reg0[3].
For other kinds of packets, it just stores 0 into
reg0[3]. Either way, it continues to the next
table.
• A priority-0 flow that matches all packets to
advances to table 16.
Ingress Table 23: DHCP responses
This table implements DHCP responder for the DHCP replies
generated by the previous table.
• A priority 100 logical flow is added for the
logical ports configured with DHCPv4 options which
matches IPv4 packets with udp.src == 68 && udp.dst
== 67 && reg0[3] == 1 and responds back to the
inport after applying these actions. If reg0[3] is
set to 1, it means that the action put_dhcp_opts
was successful.
eth.dst = eth.src;
eth.src = E;
ip4.src = S;
udp.src = 67;
udp.dst = 68;
outport = P;
flags.loopback = 1;
output;
where E is the server MAC address and S is the
server IPv4 address defined in the DHCPv4 options.
Note that ip4.dst field is handled by
put_dhcp_opts.
(This terminates ingress packet processing; the
packet does not go to the next ingress table.)
• A priority 100 logical flow is added for the
logical ports configured with DHCPv6 options which
matches IPv6 packets with udp.src == 546 && udp.dst
== 547 && reg0[3] == 1 and responds back to the
inport after applying these actions. If reg0[3] is
set to 1, it means that the action put_dhcpv6_opts
was successful.
eth.dst = eth.src;
eth.src = E;
ip6.dst = A;
ip6.src = S;
udp.src = 547;
udp.dst = 546;
outport = P;
flags.loopback = 1;
output;
where E is the server MAC address and S is the
server IPv6 LLA address generated from the
server_id defined in the DHCPv6 options and A is
the IPv6 address defined in the logical port’s
addresses column.
(This terminates packet processing; the packet does
not go on the next ingress table.)
• A priority-0 flow that matches all packets to
advances to table 17.
Ingress Table 24 DNS Lookup
This table looks up and resolves the DNS names to the
corresponding configured IP address(es).
• A priority-100 logical flow for each logical switch
datapath if it is configured with DNS records,
which matches the IPv4 and IPv6 packets with
udp.dst = 53 and applies the action dns_lookup and
advances the packet to the next table.
reg0[4] = dns_lookup(); next;
For valid DNS packets, this transforms the packet
into a DNS reply if the DNS name can be resolved,
and stores 1 into reg0[4]. For failed DNS
resolution or other kinds of packets, it just
stores 0 into reg0[4]. Either way, it continues to
the next table.
Ingress Table 25 DNS Responses
This table implements DNS responder for the DNS replies generated
by the previous table.
• A priority-100 logical flow for each logical switch
datapath if it is configured with DNS records,
which matches the IPv4 and IPv6 packets with
udp.dst = 53 && reg0[4] == 1 and responds back to
the inport after applying these actions. If reg0[4]
is set to 1, it means that the action dns_lookup
was successful.
eth.dst <-> eth.src;
ip4.src <-> ip4.dst;
udp.dst = udp.src;
udp.src = 53;
outport = P;
flags.loopback = 1;
output;
(This terminates ingress packet processing; the
packet does not go to the next ingress table.)
Ingress table 26 External ports
Traffic from the external logical ports enter the ingress
datapath pipeline via the localnet port. This table adds the
below logical flows to handle the traffic from these ports.
• A priority-100 flow is added for each external
logical port which doesn’t reside on a chassis to
drop the ARP/IPv6 NS request to the router IP(s)
(of the logical switch) which matches on the inport
of the external logical port and the valid eth.src
address(es) of the external logical port.
This flow guarantees that the ARP/NS request to the
router IP address from the external ports is
responded by only the chassis which has claimed
these external ports. All the other chassis, drops
these packets.
A priority-100 flow is added for each external
logical port which doesn’t reside on a chassis to
drop any packet destined to the router mac - with
the match inport == external && eth.src == E &&
eth.dst == R && !is_chassis_resident("external")
where E is the external port mac and R is the
router port mac.
• A priority-0 flow that matches all packets to
advances to table 20.
Ingress Table 27 Destination Lookup
This table implements switching behavior. It contains these
logical flows:
• A priority-110 flow with the match eth.src == E for
all logical switch datapaths and applies the action
handle_svc_check(inport). Where E is the service
monitor mac defined in the options:svc_monitor_mac
column of NB_Global table.
• A priority-100 flow that punts all IGMP/MLD packets
to ovn-controller if multicast snooping is enabled
on the logical switch.
• A priority-100 flow that forwards all DHCP
broadcast packets coming from VIFs to the logical
router port’s MAC when DHCP relay is enabled on the
logical switch.
• Priority-90 flows for transit switches that forward
registered IP multicast traffic to their
corresponding multicast group , which ovn-northd
creates based on learnt IGMP_Group entries.
• Priority-90 flows for non-transit switches that
forward registered IP multicast traffic to their
corresponding multicast group, which ovn-northd
creates based on learnt IGMP_Group entries. The
flows also forward packets to the MC_MROUTER_FLOOD
multicast group, which ovn-nortdh populates with
all the logical ports that are connected to logical
routers with options:mcast_relay=’true’.
• A priority-85 flow that forwards all IP multicast
traffic destined to 224.0.0.X to the MC_FLOOD_L2
multicast group, which ovn-northd populates with
all non-router logical ports.
• A priority-85 flow that forwards all IP multicast
traffic destined to reserved multicast IPv6
addresses (RFC 4291, 2.7.1, e.g., Solicited-Node
multicast) to the MC_FLOOD multicast group, which
ovn-northd populates with all enabled logical
ports.
• A priority-80 flow that forwards all unregistered
IP multicast traffic to the MC_STATIC multicast
group, which ovn-northd populates with all the
logical ports that have options
:mcast_flood=’true’. The flow also forwards
unregistered IP multicast traffic to the
MC_MROUTER_FLOOD multicast group, which ovn-northd
populates with all the logical ports connected to
logical routers that have options
:mcast_relay=’true’.
• A priority-80 flow that drops all unregistered IP
multicast traffic if other_config
:mcast_snoop=’true’ and other_config
:mcast_flood_unregistered=’false’ and the switch is
not connected to a logical router that has options
:mcast_relay=’true’ and the switch doesn’t have any
logical port with options :mcast_flood=’true’.
• Priority-80 flows for each IP address/VIP/NAT
address owned by a router port connected to the
switch. These flows match ARP requests and ND
packets for the specific IP addresses. Matched
packets are forwarded only to the router that owns
the IP address and to the MC_FLOOD_L2 multicast
group which contains all non-router logical ports.
• Priority-75 flows for each port connected to a
logical router matching self originated ARP
request/RARP request/ND packets. These packets are
flooded to the MC_FLOOD_L2 which contains all non-
router logical ports.
• A priority-72 flow that outputs all ARP requests
and ND packets with an Ethernet broadcast or
multicast eth.dst to the MC_FLOOD_L2 multicast
group if
other_config:broadcast-arps-to-all-routers=true.
• A priority-70 flow that outputs all packets with an
Ethernet broadcast or multicast eth.dst to the
MC_FLOOD multicast group.
• One priority-50 flow that matches each known
Ethernet address against eth.dst. Action of this
flow outputs the packet to the single associated
output port if it is enabled. drop; action is
applied if LSP is disabled. If the logical switch
port of type VIF has the option
options:pkt_clone_type is set to the value
mc_unknown, then the packet is also forwarded to
the MC_UNKNOWN multicast group.
The above flow is not added if the logical switch
port is of type VIF, has unknown as one of its
address and has the option options:force_fdb_lookup
set to true.
For the Ethernet address on a logical switch port
of type router, when that logical switch port’s
addresses column is set to router and the connected
logical router port has a gateway chassis:
• The flow for the connected logical router
port’s Ethernet address is only programmed
on the gateway chassis.
• If the logical router has rules specified in
nat with external_mac, then those addresses
are also used to populate the switch’s
destination lookup on the chassis where
logical_port is resident.
For the Ethernet address on a logical switch port
of type router, when that logical switch port’s
addresses column is set to router and the connected
logical router port specifies a
reside-on-redirect-chassis and the logical router
to which the connected logical router port belongs
to has a distributed gateway LRP:
• The flow for the connected logical router
port’s Ethernet address is only programmed
on the gateway chassis.
For each forwarding group configured on the logical
switch datapath, a priority-50 flow that matches on
eth.dst == VIP
with an action of fwd_group(childports=args ),
where args contains comma separated logical switch
child ports to load balance to. If liveness is
enabled, then action also includes liveness=true.
• One priority-0 fallback flow that matches all
packets with the action outport = get_fdb(eth.dst);
next;. The action get_fdb gets the port for the
eth.dst in the MAC learning table of the logical
switch datapath. If there is no entry for eth.dst
in the MAC learning table, then it stores none in
the outport.
Ingress Table 28 Destination unknown
This table handles the packets whose destination was not found or
and looked up in the MAC learning table of the logical switch
datapath. It contains the following flows.
• Priority 50 flow with the match outport == P is
added for each disabled Logical Switch Port P. This
flow has action drop;.
• If the logical switch has logical ports with
’unknown’ addresses set, then the below logical
flow is added
• Priority 50 flow with the match outport ==
"none" then outputs them to the MC_UNKNOWN
multicast group, which ovn-northd populates
with all enabled logical ports that accept
unknown destination packets. As a small
optimization, if no logical ports accept
unknown destination packets, ovn-northd
omits this multicast group and logical flow.
If the logical switch has no logical ports with
’unknown’ address set, then the below logical flow
is added
• Priority 50 flow with the match outport ==
none and drops the packets.
• One priority-0 fallback flow that outputs the
packet to the egress stage with the outport learnt
from get_fdb action.
Egress Table 0: to-lport Pre-ACLs
This is similar to ingress table Pre-ACLs except for to-lport
traffic.
This table also has a priority-110 flow with the match eth.src ==
E for all logical switch datapaths to move traffic to the next
table. Where E is the service monitor mac defined in the
options:svc_monitor_mac column of NB_Global table.
This table also has a priority-110 flow with the match outport ==
I for all logical switch datapaths to move traffic to the next
table. Where I is the peer of a logical router port. This flow is
added to skip the connection tracking of packets which will be
entering logical router datapath from logical switch datapath for
routing.
Egress Table 1: Pre-LB
This table is similar to ingress table Pre-LB. It contains a
priority-0 flow that simply moves traffic to the next table.
Moreover it contains two priority-110 flows to move multicast,
IPv6 Neighbor Discovery and MLD traffic to the next table. If any
load balancing rules exist for the datapath, a priority-100 flow
is added with a match of ip and action of reg0[2] = 1; next; to
act as a hint for table Pre-stateful to send IP packets to the
connection tracker for packet de-fragmentation and possibly DNAT
the destination VIP to one of the selected backend for already
committed load balanced traffic.
This table also has a priority-110 flow with the match eth.src ==
E for all logical switch datapaths to move traffic to the next
table. Where E is the service monitor mac defined in the
options:svc_monitor_mac column of NB_Global table.
This table also has a priority-110 flow with the match outport ==
I for all logical switch datapaths to move traffic to the next
table, and, if there are no stateful_acl, clear the ct_state.
Where I is the peer of a logical router port. This flow is added
to skip the connection tracking of packets which will be entering
logical router datapath from logical switch datapath for routing.
Egress Table 2: Pre-stateful
This is similar to ingress table Pre-stateful. This table adds
the below 3 logical flows.
• A Priority-120 flow that send the packets to
connection tracker using ct_lb_mark; as the action
so that the already established traffic gets
unDNATted from the backend IP to the load balancer
VIP based on a hint provided by the previous tables
with a match for reg0[2] == 1. If the packet was
not DNATted earlier, then ct_lb_mark functions like
ct_next.
• A priority-100 flow sends the packets to connection
tracker based on a hint provided by the previous
tables (with a match for reg0[0] == 1) by using the
ct_next; action.
• A priority-0 flow that matches all packets to
advance to the next table.
Egress Table 3: from-lport ACL hints
This is similar to ingress table ACL hints.
Egress Table 4: to-lport ACL evaluation
This is similar to ingress table ACL eval except for to-lport
ACLs. As a reminder, these flows use the following register bits
to indicate their verdicts. Allow-type ACLs set reg8[16], drop
ACLs set reg8[17], and reject ACLs set reg8[18].
Also like with ingress ACLs, egress ACLs can have a configured
tier. If a tier is configured, then the current tier counter is
evaluated against the ACL’s configured tier in addition to the
ACL’s match. The current tier counter is stored in reg8[30..31].
Similar to ingress table, a priority-65532 flow is added to allow
IPv6 Neighbor solicitation, Neighbor discover, Router
solicitation, Router advertisement and MLD packets regardless of
other ACLs defined.
In addition, the following flows are added.
• A priority 34000 logical flow is added for each
logical port which has DHCPv4 options defined to
allow the DHCPv4 reply packet and which has DHCPv6
options defined to allow the DHCPv6 reply packet
from the Ingress Table 18: DHCP responses. This is
indicated by setting the allow bit.
• A priority 34000 logical flow is added for each
logical switch datapath configured with DNS records
with the match udp.dst = 53 to allow the DNS reply
packet from the Ingress Table 20: DNS responses.
This is indicated by setting the allow bit.
• A priority 34000 logical flow is added for each
logical switch datapath with the match eth.src = E
to allow the service monitor request packet
generated by ovn-controller with the action next,
where E is the service monitor mac defined in the
options:svc_monitor_mac column of NB_Global table.
This is indicated by setting the allow bit.
Egress Table 5: to-lport ACL action
This is similar to ingress table ACL action.
Egress Table 6: to-lport QoS Marking
This is similar to ingress table QoS marking except they apply to
to-lport QoS rules.
Egress Table 7: to-lport QoS Meter
This is similar to ingress table QoS meter except they apply to
to-lport QoS rules.
Egress Table 8: Stateful
This is similar to ingress table Stateful except that there are
no rules added for load balancing new connections.
Egress Table 9: Egress Port Security - check
This is similar to the port security logic in table Ingress Port
Security check except that action check_out_port_sec is used to
check the port security rules. This table adds the below logical
flows.
• A priority 100 flow which matches on the multicast
traffic and applies the action
REGBIT_PORT_SEC_DROP" = 0; next;" to skip the out
port security checks.
• A priority 0 logical flow is added which matches on
all the packets and applies the action
REGBIT_PORT_SEC_DROP" = check_out_port_sec();
next;". The action check_out_port_sec applies the
port security rules based on the addresses defined
in the port_security column of Logical_Switch_Port
table before delivering the packet to the outport.
Egress Table 10: Egress Port Security - Apply
This is similar to the ingress port security logic in ingress
table A Ingress Port Security - Apply. This table drops the
packets if the port security check failed in the previous stage
i.e the register bit REGBIT_PORT_SEC_DROP is set to 1.
The following flows are added.
• For each port configured with egress qos in the
options:qdisc_queue_id column of
Logical_Switch_Port, running a localnet port on the
same logical switch, a priority 110 flow is added
which matches on the localnet outport and on the
port inport and applies the action set_queue(id);
output;".
• For each localnet port configured with egress qos
in the options:qdisc_queue_id column of
Logical_Switch_Port, a priority 100 flow is added
which matches on the localnet outport and applies
the action set_queue(id); output;".
Please remember to mark the corresponding physical
interface with ovn-egress-iface set to true in
external_ids.
• A priority-50 flow that drops the packet if the
register bit REGBIT_PORT_SEC_DROP is set to 1.
• A priority-0 flow that outputs the packet to the
outport.
Logical Router Datapaths
Logical router datapaths will only exist for Logical_Router rows
in the OVN_Northbound database that do not have enabled set to
false
Ingress Table 0: L2 Admission Control
This table drops packets that the router shouldn’t see at all
based on their Ethernet headers. It contains the following flows:
• Priority-100 flows to drop packets with VLAN tags
or multicast Ethernet source addresses.
• For each enabled router port P with Ethernet
address E, a priority-50 flow that matches inport
== P && (eth.mcast || eth.dst == E), stores the
router port ethernet address and advances to next
table, with action xreg0[0..47]=E; next;.
For the gateway port on a distributed logical
router (where one of the logical router ports
specifies a gateway chassis), the above flow
matching eth.dst == E is only programmed on the
gateway port instance on the gateway chassis. If
LRP’s logical switch has attached LSP of vtep type,
the is_chassis_resident() part is not added to
lflow to allow traffic originated from logical
switch to reach LR services (LBs, NAT).
For each gateway port GW on a distributed logical
router a priority-120 flow that matches
’recirculated’ icmp{4,6} error ’packet too big’ and
eth.dst == D && !is_chassis_resident( cr-GW) where
D is the gateway port mac address and cr-GW is the
chassis resident port of GW, swap inport and
outport and stores GW as inport.
This table adds a priority-105 flow that matches
’recirculated’ icmp{4,6} error ’packet too big’ to
drop the packet.
For a distributed logical router or for gateway
router where the port is configured with
options:gateway_mtu the action of the above flow is
modified adding check_pkt_larger in order to mark
the packet setting REGBIT_PKT_LARGER if the size is
greater than the MTU. If the port is also
configured with options:gateway_mtu_bypass then
another flow is added, with priority-55, to bypass
the check_pkt_larger flow. This is useful for
traffic that normally doesn’t need to be fragmented
and for which check_pkt_larger, which might not be
offloadable, is not really needed. One such example
is TCP traffic.
• For each dnat_and_snat NAT rule on a distributed
router that specifies an external Ethernet address
E, a priority-50 flow that matches inport == GW &&
eth.dst == E, where GW is the logical router
distributed gateway port corresponding to the NAT
rule (specified or inferred), with action
xreg0[0..47]=E; next;.
This flow is only programmed on the gateway port
instance on the chassis where the logical_port
specified in the NAT rule resides.
• A priority-0 logical flow that matches all packets
not already handled (match 1) and drops them
(action drop;).
Other packets are implicitly dropped.
Ingress Table 1: Neighbor lookup
For ARP and IPv6 Neighbor Discovery packets, this table looks
into the MAC_Binding records to determine if OVN needs to learn
the mac bindings. Following flows are added:
• For each router port P that owns IP address A,
which belongs to subnet S with prefix length L, if
the option always_learn_from_arp_request is true
for this router, a priority-100 flow is added which
matches inport == P && arp.spa == S/L && arp.op ==
1 (ARP request) with the following actions:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
next;
If the option always_learn_from_arp_request is
false, the following two flows are added.
A priority-110 flow is added which matches inport
== P && arp.spa == S/L && arp.tpa == A && arp.op ==
1 (ARP request) with the following actions:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
reg9[3] = 1;
next;
A priority-100 flow is added which matches inport
== P && arp.spa == S/L && arp.op == 1 (ARP request)
with the following actions:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
reg9[3] = lookup_arp_ip(inport, arp.spa);
next;
If the logical router port P is a distributed
gateway router port, additional match
is_chassis_resident(cr-P) is added for all these
flows.
• A priority-100 flow which matches on ARP reply
packets and applies the actions if the option
always_learn_from_arp_request is true:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
next;
If the option always_learn_from_arp_request is
false, the above actions will be:
reg9[2] = lookup_arp(inport, arp.spa, arp.sha);
reg9[3] = 1;
next;
• A priority-100 flow which matches on IPv6 Neighbor
Discovery advertisement packet and applies the
actions if the option always_learn_from_arp_request
is true:
reg9[2] = lookup_nd(inport, nd.target, nd.tll);
next;
If the option always_learn_from_arp_request is
false, the above actions will be:
reg9[2] = lookup_nd(inport, nd.target, nd.tll);
reg9[3] = 1;
next;
• A priority-100 flow which matches on IPv6 Neighbor
Discovery solicitation packet and applies the
actions if the option always_learn_from_arp_request
is true:
reg9[2] = lookup_nd(inport, ip6.src, nd.sll);
next;
If the option always_learn_from_arp_request is
false, the above actions will be:
reg9[2] = lookup_nd(inport, ip6.src, nd.sll);
reg9[3] = lookup_nd_ip(inport, ip6.src);
next;
• A priority-0 fallback flow that matches all packets
and applies the action reg9[2] = 1; next; advancing
the packet to the next table.
Ingress Table 2: Neighbor learning
This table adds flows to learn the mac bindings from the ARP and
IPv6 Neighbor Solicitation/Advertisement packets if it is needed
according to the lookup results from the previous stage.
reg9[2] will be 1 if the lookup_arp/lookup_nd in the previous
table was successful or skipped, meaning no need to learn mac
binding from the packet.
reg9[3] will be 1 if the lookup_arp_ip/lookup_nd_ip in the
previous table was successful or skipped, meaning it is ok to
learn mac binding from the packet (if reg9[2] is 0).
• A priority-100 flow with the match reg9[2] == 1 ||
reg9[3] == 0 and advances the packet to the next
table as there is no need to learn the neighbor.
• A priority-95 flow with the match nd_ns && (ip6.src
== 0 || nd.sll == 0) and applies the action next;
• A priority-90 flow with the match arp and applies
the action put_arp(inport, arp.spa, arp.sha); next;
• A priority-95 flow with the match nd_na && nd.tll
== 0 and applies the action put_nd(inport,
nd.target, eth.src); next;
• A priority-90 flow with the match nd_na and applies
the action put_nd(inport, nd.target, nd.tll); next;
• A priority-90 flow with the match nd_ns and applies
the action put_nd(inport, ip6.src, nd.sll); next;
• A priority-0 logical flow that matches all packets
not already handled (match 1) and drops them
(action drop;).
Ingress Table 3: IP Input
This table is the core of the logical router datapath
functionality. It contains the following flows to implement very
basic IP host functionality.
• For each dnat_and_snat NAT rule on a distributed
logical routers or gateway routers with gateway
port configured with options:gateway_mtu to a valid
integer value M, a priority-160 flow with the match
inport == LRP && REGBIT_PKT_LARGER &&
REGBIT_EGRESS_LOOPBACK == 0, where LRP is the
logical router port and applies the following
action for ipv4 and ipv6 respectively:
icmp4_error {
icmp4.type = 3; /* Destination Unreachable. */
icmp4.code = 4; /* Frag Needed and DF was Set. */
icmp4.frag_mtu = M;
eth.dst = eth.src;
eth.src = E;
ip4.dst = ip4.src;
ip4.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER 0;
outport = LRP;
flags.loopback = 1;
output;
};
icmp6_error {
icmp6.type = 2;
icmp6.code = 0;
icmp6.frag_mtu = M;
eth.dst = eth.src;
eth.src = E;
ip6.dst = ip6.src;
ip6.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER 0;
outport = LRP;
flags.loopback = 1;
output;
};
where E and I are the NAT rule external mac and IP
respectively.
• For distributed logical routers or gateway routers
with gateway port configured with
options:gateway_mtu to a valid integer value, a
priority-150 flow with the match inport == LRP &&
REGBIT_PKT_LARGER && REGBIT_EGRESS_LOOPBACK == 0,
where LRP is the logical router port and applies
the following action for ipv4 and ipv6
respectively:
icmp4_error {
icmp4.type = 3; /* Destination Unreachable. */
icmp4.code = 4; /* Frag Needed and DF was Set. */
icmp4.frag_mtu = M;
eth.dst = E;
ip4.dst = ip4.src;
ip4.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER 0;
next(pipeline=ingress, table=0);
};
icmp6_error {
icmp6.type = 2;
icmp6.code = 0;
icmp6.frag_mtu = M;
eth.dst = E;
ip6.dst = ip6.src;
ip6.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER 0;
next(pipeline=ingress, table=0);
};
• For each NAT entry of a distributed logical router
(with distributed gateway router port(s)) of type
snat, a priority-120 flow with the match inport ==
P && ip4.src == A advances the packet to the next
pipeline, where P is the distributed logical router
port corresponding to the NAT entry (specified or
inferred) and A is the external_ip set in the NAT
entry. If A is an IPv6 address, then ip6.src is
used for the match.
The above flow is required to handle the routing of
the East/west NAT traffic.
• For each BFD port the two following priority-110
flows are added to manage BFD traffic:
• if ip4.src or ip6.src is any IP address
owned by the router port and udp.dst == 3784
, the packet is advanced to the next
pipeline stage.
• if ip4.dst or ip6.dst is any IP address
owned by the router port and udp.dst == 3784
, the handle_bfd_msg action is executed.
• For each logical router port configured with DHCP
relay the following priority-110 flows are added to
manage the DHCP relay traffic:
• if inport is lrp and ip4.src == 0.0.0.0
and ip4.dst == 255.255.255.255 and ip4.frag
== 0 and udp.src == 68 and udp.dst == 67,
the dhcp_relay_req_chk
action is executed.
reg9[7] = dhcp_relay_req_chk(lrp_ip,
dhcp_server_ip);next
if action is successful then, GIADDR in the
dhcp header is updated with lrp ip and
stores 1 into reg9[7] else stores 0 into
reg9[7].
• if ip4.src is DHCP server ip and ip4.dst
is lrp IP and udp.src == 67 and udp.dst ==
67, the packet is advanced to the next
pipeline stage.
• L3 admission control: Priority-120 flows allows
IGMP and MLD packets if the router has logical
ports that have options :mcast_flood=’true’.
• L3 admission control: A priority-100 flow drops
packets that match any of the following:
• ip4.src[28..31] == 0xe (multicast source)
• ip4.src == 255.255.255.255 (broadcast
source)
• ip4.src == 127.0.0.0/8 || ip4.dst ==
127.0.0.0/8 (localhost source or
destination)
• ip4.src == 0.0.0.0/8 || ip4.dst == 0.0.0.0/8
(zero network source or destination)
• ip4.src or ip6.src is any IP address owned
by the router, unless the packet was
recirculated due to egress loopback as
indicated by REGBIT_EGRESS_LOOPBACK.
• ip4.src is the broadcast address of any IP
network known to the router.
• A priority-100 flow parses DHCPv6 replies from IPv6
prefix delegation routers (udp.src == 547 &&
udp.dst == 546). The handle_dhcpv6_reply is used to
send IPv6 prefix delegation messages to the
delegation router.
• ICMP echo reply. These flows reply to ICMP echo
requests received for the router’s IP address. Let
A be an IP address owned by a router port. Then,
for each A that is an IPv4 address, a priority-90
flow matches on ip4.dst == A and icmp4.type == 8 &&
icmp4.code == 0 (ICMP echo request). For each A
that is an IPv6 address, a priority-90 flow matches
on ip6.dst == A and icmp6.type == 128 && icmp6.code
== 0 (ICMPv6 echo request). The port of the router
that receives the echo request does not matter.
Also, the ip.ttl of the echo request packet is not
checked, so it complies with RFC 1812, section
4.2.2.9. Flows for ICMPv4 echo requests use the
following actions:
ip4.dst <-> ip4.src;
ip.ttl = 255;
icmp4.type = 0;
flags.loopback = 1;
next;
Flows for ICMPv6 echo requests use the following
actions:
ip6.dst <-> ip6.src;
ip.ttl = 255;
icmp6.type = 129;
flags.loopback = 1;
next;
• Reply to ARP requests.
These flows reply to ARP requests for the router’s
own IP address. The ARP requests are handled only
if the requestor’s IP belongs to the same subnets
of the logical router port. For each router port P
that owns IP address A, which belongs to subnet S
with prefix length L, and Ethernet address E, a
priority-90 flow matches inport == P && arp.spa ==
S/L && arp.op == 1 && arp.tpa == A (ARP request)
with the following actions:
eth.dst = eth.src;
eth.src = xreg0[0..47];
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = xreg0[0..47];
arp.tpa = arp.spa;
arp.spa = A;
outport = inport;
flags.loopback = 1;
output;
For the gateway port on a distributed logical
router (where one of the logical router ports
specifies a gateway chassis), the above flows are
only programmed on the gateway port instance on the
gateway chassis. This behavior avoids generation of
multiple ARP responses from different chassis, and
allows upstream MAC learning to point to the
gateway chassis.
For the logical router port with the option
reside-on-redirect-chassis set (which is
centralized), the above flows are only programmed
on the gateway port instance on the gateway chassis
(if the logical router has a distributed gateway
port). This behavior avoids generation of multiple
ARP responses from different chassis, and allows
upstream MAC learning to point to the gateway
chassis.
• Reply to IPv6 Neighbor Solicitations. These flows
reply to Neighbor Solicitation requests for the
router’s own IPv6 address and populate the logical
router’s mac binding table.
For each router port P that owns IPv6 address A,
solicited node address S, and Ethernet address E, a
priority-90 flow matches inport == P && nd_ns &&
ip6.dst == {A, E} && nd.target == A with the
following actions:
nd_na_router {
eth.src = xreg0[0..47];
ip6.src = A;
nd.target = A;
nd.tll = xreg0[0..47];
outport = inport;
flags.loopback = 1;
output;
};
For the gateway port on a distributed logical
router (where one of the logical router ports
specifies a gateway chassis), the above flows
replying to IPv6 Neighbor Solicitations are only
programmed on the gateway port instance on the
gateway chassis. This behavior avoids generation of
multiple replies from different chassis, and allows
upstream MAC learning to point to the gateway
chassis.
• These flows reply to ARP requests or IPv6 neighbor
solicitation for the virtual IP addresses
configured in the router for NAT (both DNAT and
SNAT) or load balancing.
IPv4: For a configured NAT (both DNAT and SNAT) IP
address or a load balancer IPv4 VIP A, for each
router port P with Ethernet address E, a
priority-90 flow matches arp.op == 1 && arp.tpa ==
A (ARP request) with the following actions:
eth.dst = eth.src;
eth.src = xreg0[0..47];
arp.op = 2; /* ARP reply. */
arp.tha = arp.sha;
arp.sha = xreg0[0..47];
arp.tpa <-> arp.spa;
outport = inport;
flags.loopback = 1;
output;
IPv4: For a configured load balancer IPv4 VIP, a
similar flow is added with the additional match
inport == P if the VIP is reachable from any
logical router port of the logical router.
If the router port P is a distributed gateway
router port, then the is_chassis_resident(P) is
also added in the match condition for the load
balancer IPv4 VIP A.
IPv6: For a configured NAT (both DNAT and SNAT) IP
address or a load balancer IPv6 VIP A (if the VIP
is reachable from any logical router port of the
logical router), solicited node address S, for each
router port P with Ethernet address E, a
priority-90 flow matches inport == P && nd_ns &&
ip6.dst == {A, S} && nd.target == A with the
following actions:
eth.dst = eth.src;
nd_na {
eth.src = xreg0[0..47];
nd.tll = xreg0[0..47];
ip6.src = A;
nd.target = A;
outport = inport;
flags.loopback = 1;
output;
}
If the router port P is a distributed gateway
router port, then the is_chassis_resident(P) is
also added in the match condition for the load
balancer IPv6 VIP A.
For the gateway port on a distributed logical
router with NAT (where one of the logical router
ports specifies a gateway chassis):
• If the corresponding NAT rule cannot be
handled in a distributed manner, then a
priority-92 flow is programmed on the
gateway port instance on the gateway
chassis. A priority-91 drop flow is
programmed on the other chassis when ARP
requests/NS packets are received on the
gateway port. This behavior avoids
generation of multiple ARP responses from
different chassis, and allows upstream MAC
learning to point to the gateway chassis.
• If the corresponding NAT rule can be handled
in a distributed manner, then this flow is
only programmed on the gateway port instance
where the logical_port specified in the NAT
rule resides.
Some of the actions are different for this
case, using the external_mac specified in
the NAT rule rather than the gateway port’s
Ethernet address E:
eth.src = external_mac;
arp.sha = external_mac;
or in the case of IPv6 neighbor solicition:
eth.src = external_mac;
nd.tll = external_mac;
This behavior avoids generation of multiple
ARP responses from different chassis, and
allows upstream MAC learning to point to the
correct chassis.
• Priority-85 flows which drops the ARP and IPv6
Neighbor Discovery packets.
• A priority-84 flow explicitly allows IPv6 multicast
traffic that is supposed to reach the router
pipeline (i.e., router solicitation and router
advertisement packets).
• A priority-83 flow explicitly drops IPv6 multicast
traffic that is destined to reserved multicast
groups.
• A priority-82 flow allows IP multicast traffic if
options:mcast_relay=’true’, otherwise drops it.
• UDP port unreachable. Priority-80 flows generate
ICMP port unreachable messages in reply to UDP
datagrams directed to the router’s IP address,
except in the special case of gateways, which
accept traffic directed to a router IP for load
balancing and NAT purposes.
These flows should not match IP fragments with
nonzero offset.
• TCP reset. Priority-80 flows generate TCP reset
messages in reply to TCP datagrams directed to the
router’s IP address, except in the special case of
gateways, which accept traffic directed to a router
IP for load balancing and NAT purposes.
These flows should not match IP fragments with
nonzero offset.
• Protocol or address unreachable. Priority-70 flows
generate ICMP protocol or address unreachable
messages for IPv4 and IPv6 respectively in reply to
packets directed to the router’s IP address on IP
protocols other than UDP, TCP, and ICMP, except in
the special case of gateways, which accept traffic
directed to a router IP for load balancing
purposes.
These flows should not match IP fragments with
nonzero offset.
• Drop other IP traffic to this router. These flows
drop any other traffic destined to an IP address of
this router that is not already handled by one of
the flows above, which amounts to ICMP (other than
echo requests) and fragments with nonzero offsets.
For each IP address A owned by the router, a
priority-60 flow matches ip4.dst == A or ip6.dst ==
A and drops the traffic. An exception is made and
the above flow is not added if the router port’s
own IP address is used to SNAT packets passing
through that router or if it is used as a load
balancer VIP.
The flows above handle all of the traffic that might be directed
to the router itself. The following flows (with lower priorities)
handle the remaining traffic, potentially for forwarding:
• Drop Ethernet local broadcast. A priority-50 flow
with match eth.bcast drops traffic destined to the
local Ethernet broadcast address. By definition
this traffic should not be forwarded.
• Avoid ICMP time exceeded for multicast. A
priority-32 flow with match ip.ttl == {0, 1} &&
!ip.later_frag && (ip4.mcast || ip6.mcast) and
actions drop; drops multicast packets whose TTL has
expired without sending ICMP time exceeded.
• ICMP time exceeded. For each router port P, whose
IP address is A, a priority-31 flow with match
inport == P && ip.ttl == {0, 1} && !ip.later_frag
matches packets whose TTL has expired, with the
following actions to send an ICMP time exceeded
reply for IPv4 and IPv6 respectively:
icmp4 {
icmp4.type = 11; /* Time exceeded. */
icmp4.code = 0; /* TTL exceeded in transit. */
ip4.dst = ip4.src;
ip4.src = A;
ip.ttl = 254;
next;
};
icmp6 {
icmp6.type = 3; /* Time exceeded. */
icmp6.code = 0; /* TTL exceeded in transit. */
ip6.dst = ip6.src;
ip6.src = A;
ip.ttl = 254;
next;
};
• TTL discard. A priority-30 flow with match ip.ttl
== {0, 1} and actions drop; drops other packets
whose TTL has expired, that should not receive a
ICMP error reply (i.e. fragments with nonzero
offset).
• Next table. A priority-0 flows match all packets
that aren’t already handled and uses actions next;
to feed them to the next table.
Ingress Table 4: DHCP Relay Request
This stage process the DHCP request packets on which
dhcp_relay_req_chk action is applied in the IP input stage.
• A priority-100 logical flow is added for each
logical router port configured with DHCP relay that
matches inport is lrp and ip4.src == 0.0.0.0 and
ip4.dst == 255.255.255.255 and udp.src == 68
and udp.dst == 67 and reg9[7] == 1 and applies
following actions. If reg9[7] is set to 1 then,
dhcp_relay_req_chk action was successful.
ip4.src=lrp ip;
ip4.dst=dhcp server ip;
udp.src = 67;
next;
• A priority-1 logical flow is added for each logical
router port configured with DHCP relay that matches
inport is lrp and ip4.src == 0.0.0.0 and ip4.dst ==
255.255.255.255 and udp.src == 68
and udp.dst == 67 and reg9[7] == 0 and drops the
packet. If reg9[7] is set to 0 then,
dhcp_relay_req_chk action was unsuccessful.
• A priority-0 flow that matches all packets to
advance to the next table.
Ingress Table 5: UNSNAT
This is for already established connections’ reverse traffic.
i.e., SNAT has already been done in egress pipeline and now the
packet has entered the ingress pipeline as part of a reply. It is
unSNATted here.
Ingress Table 5: UNSNAT on Gateway and Distributed Routers
• If the Router (Gateway or Distributed) is
configured with load balancers, then below lflows
are added:
For each IPv4 address A defined as load balancer
VIP with the protocol P (and the protocol port T if
defined) is also present as an external_ip in the
NAT table, a priority-120 logical flow is added
with the match ip4 && ip4.dst == A && P with the
action next; to advance the packet to the next
table. If the load balancer has protocol port B
defined, then the match also has P.dst == B.
The above flows are also added for IPv6 load
balancers.
Ingress Table 5: UNSNAT on Gateway Routers
• If the Gateway router has been configured to force
SNAT any previously DNATted packets to B, a
priority-110 flow matches ip && ip4.dst == B or ip
&& ip6.dst == B with an action ct_snat; .
If the Gateway router is configured with
lb_force_snat_ip=router_ip then for every logical
router port P attached to the Gateway router with
the router ip B, a priority-110 flow is added with
the match inport == P && ip4.dst == B or inport ==
P && ip6.dst == B with an action ct_snat; .
If the Gateway router has been configured to force
SNAT any previously load-balanced packets to B, a
priority-100 flow matches ip && ip4.dst == B or ip
&& ip6.dst == B with an action ct_snat; .
For each NAT configuration in the OVN Northbound
database, that asks to change the source IP address
of a packet from A to B, a priority-90 flow matches
ip && ip4.dst == B or ip && ip6.dst == B with an
action ct_snat; . If the NAT rule is of type
dnat_and_snat and has stateless=true in the
options, then the action would be next;.
A priority-0 logical flow with match 1 has actions
next;.
Ingress Table 5: UNSNAT on Distributed Routers
• For each configuration in the OVN Northbound
database, that asks to change the source IP address
of a packet from A to B, two priority-100 flows are
added.
If the NAT rule cannot be handled in a distributed
manner, then the below priority-100 flows are only
programmed on the gateway chassis.
• The first flow matches ip && ip4.dst == B &&
inport == GW
or ip && ip6.dst == B && inport == GW where
GW is the distributed gateway port
corresponding to the NAT rule (specified or
inferred), with an action ct_snat; to unSNAT
in the common zone. If the NAT rule is of
type dnat_and_snat and has stateless=true in
the options, then the action would be next;.
If the NAT entry is of type snat, then there
is an additional match
is_chassis_resident(cr-GW)
where cr-GW is the chassis resident port of
GW.
A priority-0 logical flow with match 1 has actions
next;.
Ingress Table 6: DEFRAG
This is to send packets to connection tracker for tracking and
defragmentation. It contains a priority-0 flow that simply moves
traffic to the next table.
For all load balancing rules that are configured in
OVN_Northbound database for a Gateway router, a priority-100 flow
is added for each configured virtual IP address VIP. For IPv4
VIPs the flow matches ip && ip4.dst == VIP. For IPv6 VIPs, the
flow matches ip && ip6.dst == VIP. The flow applies the action
ct_dnat; to send IP packets to the connection tracker for packet
de-fragmentation and to dnat the destination IP for the committed
connection before sending it to the next table.
If ECMP routes with symmetric reply are configured in the
OVN_Northbound database for a gateway router, a priority-100 flow
is added for each router port on which symmetric replies are
configured. The matching logic for these ports essentially
reverses the configured logic of the ECMP route. So for instance,
a route with a destination routing policy will instead match if
the source IP address matches the static route’s prefix. The flow
uses the actions chk_ecmp_nh_mac(); ct_next or chk_ecmp_nh();
ct_next to send IP packets to table 76 or to table 77 in order to
check if source info are already stored by OVN and then to the
connection tracker for packet de-fragmentation and tracking
before sending it to the next table.
If load balancing rules are configured in OVN_Northbound database
for a Gateway router, a priority 50 flow that matches icmp ||
icmp6 with an action of ct_dnat;, this allows potentially related
ICMP traffic to pass through CT.
Ingress Table 7: Load balancing affinity check
Load balancing affinity check table contains the following
logical flows:
• For all the configured load balancing rules for a
logical router where a positive affinity timeout is
specified in options column, that includes a L4
port PORT of protocol P and IPv4 or IPv6 address
VIP, a priority-100 flow that matches on ct.new &&
ip && ip.dst == VIP && P && P.dst == PORT (xxreg0
== VIP
in the IPv6 case) with an action of reg0 = ip.dst;
reg9[16..31] = P.dst; reg9[6] = chk_lb_aff(); next;
(xxreg0 == ip6.dst in the IPv6 case)
• A priority 0 flow is added which matches on all
packets and applies the action next;.
Ingress Table 8: DNAT
Packets enter the pipeline with destination IP address that needs
to be DNATted from a virtual IP address to a real IP address.
Packets in the reverse direction needs to be unDNATed.
Ingress Table 8: Load balancing DNAT rules
Following load balancing DNAT flows are added for Gateway router
or Router with gateway port. These flows are programmed only on
the gateway chassis. These flows do not get programmed for load
balancers with IPv6 VIPs.
• For all the configured load balancing rules for a
logical router where a positive affinity timeout is
specified in options column, that includes a L4
port PORT of protocol P and IPv4 or IPv6 address
VIP, a priority-150 flow that matches on reg9[6] ==
1 && ct.new && ip && ip.dst == VIP && P && P.dst ==
PORT with an action of ct_lb_mark(args) , where
args contains comma separated IP addresses (and
optional port numbers) to load balance to. The
address family of the IP addresses of args is the
same as the address family of VIP.
• If controller_event has been enabled for all the
configured load balancing rules for a Gateway
router or Router with gateway port in
OVN_Northbound database that does not have
configured backends, a priority-130 flow is added
to trigger ovn-controller events whenever the
chassis receives a packet for that particular VIP.
If event-elb meter has been previously created, it
will be associated to the empty_lb logical flow
• For all the configured load balancing rules for a
Gateway router or Router with gateway port in
OVN_Northbound database that includes a L4 port
PORT of protocol P and IPv4 or IPv6 address VIP, a
priority-120 flow that matches on ct.new && !ct.rel
&& ip && ip.dst == VIP && P && P.dst ==
PORT with an action of ct_lb_mark(args), where
args contains comma separated IPv4 or IPv6
addresses (and optional port numbers) to load
balance to. If the router is configured to force
SNAT any load-balanced packets, the above action
will be replaced by flags.force_snat_for_lb = 1;
ct_lb_mark(args; force_snat);. If the load
balancing rule is configured with skip_snat set to
true, the above action will be replaced by
flags.skip_snat_for_lb = 1; ct_lb_mark(args;
skip_snat);. If health check is enabled, then args
will only contain those endpoints whose service
monitor status entry in OVN_Southbound db is either
online or empty.
• For all the configured load balancing rules for a
router in OVN_Northbound database that includes
just an IP address VIP to match on, a priority-110
flow that matches on ct.new && !ct.rel && ip4 &&
ip.dst == VIP with an action of ct_lb_mark(args),
where args contains comma separated IPv4 or IPv6
addresses. If the router is configured to force
SNAT any load-balanced packets, the above action
will be replaced by flags.force_snat_for_lb = 1;
ct_lb_mark(args; force_snat);. If the load
balancing rule is configured with skip_snat set to
true, the above action will be replaced by
flags.skip_snat_for_lb = 1; ct_lb_mark(args;
skip_snat);.
The previous table lr_in_defrag sets the register
reg0 (or xxreg0 for IPv6) and does ct_dnat. Hence
for established traffic, this table just advances
the packet to the next stage.
• If the load balancer is created with --reject
option and it has no active backends, a TCP reset
segment (for tcp) or an ICMP port unreachable
packet (for all other kind of traffic) will be sent
whenever an incoming packet is received for this
load-balancer. Please note using --reject option
will disable empty_lb SB controller event for this
load balancer.
• For the related traffic, a priority 50 flow that
matches ct.rel && !ct.est && !ct.new with an
action of ct_commit_nat;, if the router has load
balancer assigned to it. Along with two priority 70
flows that match skip_snat and force_snat flags,
setting the flags.force_snat_for_lb = 1 or
flags.skip_snat_for_lb = 1 accordingly.
• For the established traffic, a priority 50 flow
that matches ct.est && !ct.rel && !ct.new &&
ct_mark.natted with an action of next;, if the
router has load balancer assigned to it. Along with
two priority 70 flows that match skip_snat and
force_snat flags, setting the
flags.force_snat_for_lb = 1 or
flags.skip_snat_for_lb = 1 accordingly.
Ingress Table 8: DNAT on Gateway Routers
• For each configuration in the OVN Northbound
database, that asks to change the destination IP
address of a packet from A to B, a priority-100
flow matches ip && ip4.dst == A or ip && ip6.dst ==
A with an action flags.loopback = 1; ct_dnat(B);.
If the Gateway router is configured to force SNAT
any DNATed packet, the above action will be
replaced by flags.force_snat_for_dnat = 1;
flags.loopback = 1; ct_dnat(B);. If the NAT rule is
of type dnat_and_snat and has stateless=true in the
options, then the action would be ip4/6.dst= (B).
If the NAT rule has allowed_ext_ips configured,
then there is an additional match ip4.src ==
allowed_ext_ips . Similarly, for IPV6, match would
be ip6.src == allowed_ext_ips.
If the NAT rule has exempted_ext_ips set, then
there is an additional flow configured at priority
101. The flow matches if source ip is an
exempted_ext_ip and the action is next; . This flow
is used to bypass the ct_dnat action for a packet
originating from exempted_ext_ips.
• A priority-0 logical flow with match 1 has actions
next;.
Ingress Table 8: DNAT on Distributed Routers
On distributed routers, the DNAT table only handles packets with
destination IP address that needs to be DNATted from a virtual IP
address to a real IP address. The unDNAT processing in the
reverse direction is handled in a separate table in the egress
pipeline.
• For each configuration in the OVN Northbound
database, that asks to change the destination IP
address of a packet from A to B, a priority-100
flow matches ip && ip4.dst == B && inport == GW,
where GW is the logical router gateway port
corresponding to the NAT rule (specified or
inferred), with an action ct_dnat(B);. The match
will include ip6.dst == B in the IPv6 case. If the
NAT rule is of type dnat_and_snat and has
stateless=true in the options, then the action
would be ip4/6.dst=(B).
If the NAT rule cannot be handled in a distributed
manner, then the priority-100 flow above is only
programmed on the gateway chassis.
If the NAT rule has allowed_ext_ips configured,
then there is an additional match ip4.src ==
allowed_ext_ips . Similarly, for IPV6, match would
be ip6.src == allowed_ext_ips.
If the NAT rule has exempted_ext_ips set, then
there is an additional flow configured at priority
101. The flow matches if source ip is an
exempted_ext_ip and the action is next; . This flow
is used to bypass the ct_dnat action for a packet
originating from exempted_ext_ips.
A priority-0 logical flow with match 1 has actions
next;.
Ingress Table 9: Load balancing affinity learn
Load balancing affinity learn table contains the following
logical flows:
• For all the configured load balancing rules for a
logical router where a positive affinity timeout T
is specified in options
column, that includes a L4 port PORT of protocol P
and IPv4 or IPv6 address VIP, a priority-100 flow
that matches on reg9[6] == 0 && ct.new && ip &&
reg0 == VIP && P && reg9[16..31] == PORT (xxreg0
== VIP in the IPv6 case) with an action of
commit_lb_aff(vip = VIP:PORT, backend = backend ip:
backend port, proto = P, timeout = T);.
• A priority 0 flow is added which matches on all
packets and applies the action next;.
Ingress Table 10: ECMP symmetric reply processing
• If ECMP routes with symmetric reply are configured
in the OVN_Northbound database for a gateway
router, a priority-100 flow is added for each
router port on which symmetric replies are
configured. The matching logic for these ports
essentially reverses the configured logic of the
ECMP route. So for instance, a route with a
destination routing policy will instead match if
the source IP address matches the static route’s
prefix. The flow uses the action ct_commit {
ct_label.ecmp_reply_eth = eth.src;" "
ct_mark.ecmp_reply_port = K;}; commit_ecmp_nh();
next;
to commit the connection and storing eth.src and
the ECMP reply port binding tunnel key K in the
ct_label and the traffic pattern to table 76 or 77.
Ingress Table 11: IPv6 ND RA option processing
• A priority-50 logical flow is added for each
logical router port configured with IPv6 ND RA
options which matches IPv6 ND Router Solicitation
packet and applies the action put_nd_ra_opts and
advances the packet to the next table.
reg0[5] = put_nd_ra_opts(options);next;
For a valid IPv6 ND RS packet, this transforms the
packet into an IPv6 ND RA reply and sets the RA
options to the packet and stores 1 into reg0[5].
For other kinds of packets, it just stores 0 into
reg0[5]. Either way, it continues to the next
table.
• A priority-0 logical flow with match 1 has actions
next;.
Ingress Table 12: IPv6 ND RA responder
This table implements IPv6 ND RA responder for the IPv6 ND RA
replies generated by the previous table.
• A priority-50 logical flow is added for each
logical router port configured with IPv6 ND RA
options which matches IPv6 ND RA packets and
reg0[5] == 1 and responds back to the inport after
applying these actions. If reg0[5] is set to 1, it
means that the action put_nd_ra_opts was
successful.
eth.dst = eth.src;
eth.src = E;
ip6.dst = ip6.src;
ip6.src = I;
outport = P;
flags.loopback = 1;
output;
where E is the MAC address and I is the IPv6 link
local address of the logical router port.
(This terminates packet processing in ingress
pipeline; the packet does not go to the next
ingress table.)
• A priority-0 logical flow with match 1 has actions
next;.
Ingress Table 13: IP Routing Pre
If a packet arrived at this table from Logical Router Port P
which has options:route_table value set, a logical flow with
match inport == "P" with priority 100 and action setting unique-
generated per-datapath 32-bit value (non-zero) in OVS register 7.
This register’s value is checked in next table. If packet didn’t
match any configured inport (<main> route table), register 7
value is set to 0.
This table contains the following logical flows:
• Priority-100 flow with match inport == "LRP_NAME"
value and action, which set route table identifier
in reg7.
A priority-0 logical flow with match 1 has actions
reg7 = 0; next;.
Ingress Table 14: IP Routing
A packet that arrives at this table is an IP packet that should
be routed to the address in ip4.dst or ip6.dst. This table
implements IP routing, setting reg0 (or xxreg0 for IPv6) to the
next-hop IP address (leaving ip4.dst or ip6.dst, the packet’s
final destination, unchanged) and advances to the next table for
ARP resolution. It also sets reg1 (or xxreg1) to the IP address
owned by the selected router port (ingress table ARP Request will
generate an ARP request, if needed, with reg0 as the target
protocol address and reg1 as the source protocol address).
For ECMP routes, i.e. multiple static routes with same policy and
prefix but different nexthops, the above actions are deferred to
next table. This table, instead, is responsible for determine the
ECMP group id and select a member id within the group based on
5-tuple hashing. It stores group id in reg8[0..15] and member id
in reg8[16..31]. This step is skipped with a priority-10300 rule
if the traffic going out the ECMP route is reply traffic, and the
ECMP route was configured to use symmetric replies. Instead, the
stored values in conntrack is used to choose the destination. The
ct_label.ecmp_reply_eth tells the destination MAC address to
which the packet should be sent. The ct_mark.ecmp_reply_port
tells the logical router port on which the packet should be sent.
These values saved to the conntrack fields when the initial
ingress traffic is received over the ECMP route and committed to
conntrack. If REGBIT_KNOWN_ECMP_NH is set, the priority-10300
flows in this stage set the outport, while the eth.dst is set by
flows at the ARP/ND Resolution stage.
This table contains the following logical flows:
• Priority-10550 flow that drops IPv6 Router
Solicitation/Advertisement packets that were not
processed in previous tables.
• Priority-10550 flows that drop IGMP and MLD packets
with source MAC address owned by the router. These
are used to prevent looping statically forwarded
IGMP and MLD packets for which TTL is not
decremented (it is always 1).
• Priority-10500 flows that match IP multicast
traffic destined to groups registered on any of the
attached switches and sets outport to the
associated multicast group that will eventually
flood the traffic to all interested attached
logical switches. The flows also decrement TTL.
• Priority-10460 flows that match IGMP and MLD
control packets, set outport to the MC_STATIC
multicast group, which ovn-northd populates with
the logical ports that have options
:mcast_flood=’true’. If no router ports are
configured to flood multicast traffic the packets
are dropped.
• Priority-10450 flow that matches unregistered IP
multicast traffic decrements TTL and sets outport
to the MC_STATIC multicast group, which ovn-northd
populates with the logical ports that have options
:mcast_flood=’true’. If no router ports are
configured to flood multicast traffic the packets
are dropped.
• IPv4 routing table. For each route to IPv4 network
N with netmask M, on router port P with IP address
A and Ethernet address E, a logical flow with match
ip4.dst == N/M, whose priority is the number of
1-bits in M, has the following actions:
ip.ttl--;
reg8[0..15] = 0;
reg0 = G;
reg1 = A;
eth.src = E;
outport = P;
flags.loopback = 1;
next;
(Ingress table 1 already verified that ip.ttl--;
will not yield a TTL exceeded error.)
If the route has a gateway, G is the gateway IP
address. Instead, if the route is from a configured
static route, G is the next hop IP address. Else it
is ip4.dst.
• IPv6 routing table. For each route to IPv6 network
N with netmask M, on router port P with IP address
A and Ethernet address E, a logical flow with match
in CIDR notation ip6.dst == N/M, whose priority is
the integer value of M, has the following actions:
ip.ttl--;
reg8[0..15] = 0;
xxreg0 = G;
xxreg1 = A;
eth.src = E;
outport = inport;
flags.loopback = 1;
next;
(Ingress table 1 already verified that ip.ttl--;
will not yield a TTL exceeded error.)
If the route has a gateway, G is the gateway IP
address. Instead, if the route is from a configured
static route, G is the next hop IP address. Else it
is ip6.dst.
If the address A is in the link-local scope, the
route will be limited to sending on the ingress
port.
For each static route the reg7 == id && is prefixed
in logical flow match portion. For routes with
route_table value set a unique non-zero id is used.
For routes within <main> route table (no route
table set), this id value is 0.
For each connected route (route to the LRP’s subnet
CIDR) the logical flow match portion has no reg7 ==
id && prefix to have route to LRP’s subnets in all
routing tables.
• For ECMP routes, they are grouped by policy and
prefix. An unique id (non-zero) is assigned to each
group, and each member is also assigned an unique
id (non-zero) within each group.
For each IPv4/IPv6 ECMP group with group id GID and
member ids MID1, MID2, ..., a logical flow with
match in CIDR notation ip4.dst == N/M, or ip6.dst
== N/M, whose priority is the integer value of M,
has the following actions:
ip.ttl--;
flags.loopback = 1;
reg8[0..15] = GID;
select(reg8[16..31], MID1, MID2, ...);
• A priority-0 logical flow that matches all packets
not already handled (match 1) and drops them
(action drop;).
Ingress Table 15: IP_ROUTING_ECMP
This table implements the second part of IP routing for ECMP
routes following the previous table. If a packet matched a ECMP
group in the previous table, this table matches the group id and
member id stored from the previous table, setting reg0 (or xxreg0
for IPv6) to the next-hop IP address (leaving ip4.dst or ip6.dst,
the packet’s final destination, unchanged) and advances to the
next table for ARP resolution. It also sets reg1 (or xxreg1) to
the IP address owned by the selected router port (ingress table
ARP Request will generate an ARP request, if needed, with reg0 as
the target protocol address and reg1 as the source protocol
address).
This processing is skipped for reply traffic being sent out of an
ECMP route if the route was configured to use symmetric replies.
This table contains the following logical flows:
• A priority-150 flow that matches reg8[0..15] == 0
with action next; directly bypasses packets of non-
ECMP routes.
• For each member with ID MID in each ECMP group with
ID GID, a priority-100 flow with match reg8[0..15]
== GID && reg8[16..31] == MID has following
actions:
[xx]reg0 = G;
[xx]reg1 = A;
eth.src = E;
outport = P;
• A priority-0 logical flow that matches all packets
not already handled (match 1) and drops them
(action drop;).
Ingress Table 16: Router policies
This table adds flows for the logical router policies configured
on the logical router. Please see the OVN_Northbound database
Logical_Router_Policy table documentation in ovn-nb for supported
actions.
• For each router policy configured on the logical
router, a logical flow is added with specified
priority, match and actions.
• If the policy action is reroute with 2 or more
nexthops defined, then the logical flow is added
with the following actions:
reg8[0..15] = GID;
reg8[16..31] = select(1,..n);
where GID is the ECMP group id generated by
ovn-northd for this policy and n is the number of
nexthops. select action selects one of the nexthop
member id, stores it in the register reg8[16..31]
and advances the packet to the next stage.
• If the policy action is reroute with just one
nexhop, then the logical flow is added with the
following actions:
[xx]reg0 = H;
eth.src = E;
outport = P;
reg8[0..15] = 0;
flags.loopback = 1;
next;
where H is the nexthop defined in the router
policy, E is the ethernet address of the logical
router port from which the nexthop is reachable and
P is the logical router port from which the nexthop
is reachable.
• If a router policy has the option pkt_mark=m set
and if the action is not drop, then the action also
includes pkt.mark = m to mark the packet with the
marker m.
Ingress Table 17: ECMP handling for router policies
This table handles the ECMP for the router policies configured
with multiple nexthops.
• A priority-150 flow is added to advance the packet
to the next stage if the ECMP group id register
reg8[0..15] is 0.
• For each ECMP reroute router policy with multiple
nexthops, a priority-100 flow is added for each
nexthop H with the match reg8[0..15] == GID &&
reg8[16..31] == M where GID is the router policy
group id generated by ovn-northd and M is the
member id of the nexthop H generated by ovn-northd.
The following actions are added to the flow:
[xx]reg0 = H;
eth.src = E;
outport = P
"flags.loopback = 1; "
"next;"
where H is the nexthop defined in the router
policy, E is the ethernet address of the logical
router port from which the nexthop is reachable and
P is the logical router port from which the nexthop
is reachable.
• A priority-0 logical flow that matches all packets
not already handled (match 1) and drops them
(action drop;).
Ingress Table 18: DHCP Relay Response Check
This stage process the DHCP response packets coming from the DHCP
server.
• A priority 100 logical flow is added for each
logical router port configured with DHCP relay that
matches ip4.src is DHCP server ip and ip4.dst is
lrp IP and ip4.frag == 0 and udp.src == 67 and
udp.dst == 67 and applies dhcp_relay_resp_chk
action. Original destination ip is stored in reg2.
reg9[8] = dhcp_relay_resp_chk(lrp_ip,
dhcp_server_ip);next
if action is successful then, dest mac and dest IP
addresses are updated in the packet and stores 1
into reg9[8] else stores 0 into reg9[8].
• A priority-0 flow that matches all packets to
advance to the next table.
Ingress Table 19: DHCP Relay Response
This stage process the DHCP response packets on which
dhcp_relay_resp_chk action is applied in the previous stage.
• A priority 100 logical flow is added for each
logical router port configured with DHCP relay that
matches ip4.src is DHCP server ip and reg2 is lrp
IP and udp.src == 67 and udp.dst == 67 and reg9[8]
== 1 and applies following actions. If reg9[8] is
set to 1 then, dhcp_relay_resp_chk was successful.
ip4.src = lrp ip;
udp.dst = 68;
outport = lrp port;
output;
• A priority 1 logical flow is added for the logical
router port on which DHCP relay is enabled that
matches ip4.src is DHCP server ip and reg2 is lrp
IP and udp.src == 67 and udp.dst == 67 and reg9[8]
== 0 and drops the packet. If reg9[8] is set to 0
then, dhcp_relay_resp_chk was unsuccessful.
• A priority-0 flow that matches all packets to
advance to the next table.
Ingress Table 20: ARP/ND Resolution
Any packet that reaches this table is an IP packet whose next-hop
IPv4 address is in reg0 or IPv6 address is in xxreg0. (ip4.dst or
ip6.dst contains the final destination.) This table resolves the
IP address in reg0 (or xxreg0) into an output port in outport and
an Ethernet address in eth.dst, using the following flows:
• A priority-500 flow that matches IP multicast
traffic that was allowed in the routing pipeline.
For this kind of traffic the outport was already
set so the flow just advances to the next table.
• Priority-200 flows that match ECMP reply traffic
for the routes configured to use symmetric replies,
with actions push(xxreg1); xxreg1 = ct_label;
eth.dst = xxreg1[32..79]; pop(xxreg1); next;.
xxreg1 is used here to avoid masked access to
ct_label, to make the flow HW-offloading friendly.
• Static MAC bindings. MAC bindings can be known
statically based on data in the OVN_Northbound
database. For router ports connected to logical
switches, MAC bindings can be known statically from
the addresses column in the Logical_Switch_Port
table. (Note: the flow is not installed for IPs of
logical switch ports of type virtual, and dynamic
MAC binding is used for those IPs instead, so that
virtual parent failover does not depend on
ovn-northd, to achieve better failover
performance.) For router ports connected to other
logical routers, MAC bindings can be known
statically from the mac and networks column in the
Logical_Router_Port table. (Note: the flow is NOT
installed for the IP addresses that belong to a
neighbor logical router port if the current router
has the options:dynamic_neigh_routers set to true)
For each IPv4 address A whose host is known to have
Ethernet address E on router port P, a priority-100
flow with match outport === P && reg0 == A has
actions eth.dst = E; next;.
For each IPv6 address A whose host is known to have
Ethernet address E on router port P, a priority-100
flow with match outport === P && xxreg0 == A has
actions eth.dst = E; next;.
For each logical router port with an IPv4 address A
and a mac address of E that is reachable via a
different logical router port P, a priority-100
flow with match outport === P && reg0 == A has
actions eth.dst = E; next;.
For each logical router port with an IPv6 address A
and a mac address of E that is reachable via a
different logical router port P, a priority-100
flow with match outport === P && xxreg0 == A has
actions eth.dst = E; next;.
• Static MAC bindings from NAT entries. MAC bindings
can also be known for the entries in the NAT table.
Below flows are programmed for distributed logical
routers i.e with a distributed router port.
For each row in the NAT table with IPv4 address A
in the external_ip column of NAT table, below two
flows are programmed:
A priority-100 flow with the match outport == P &&
reg0 == A has actions eth.dst = E; next;, where P
is the distributed logical router port, E is the
Ethernet address if set in the external_mac column
of NAT table for of type dnat_and_snat, otherwise
the Ethernet address of the distributed logical
router port. Note that if the external_ip is not
within a subnet on the owning logical router, then
OVN will only create ARP resolution flows if the
options:add_route is set to true. Otherwise, no ARP
resolution flows will be added.
Corresponding to the above flow, a priority-150
flow with the match inport == P && outport == P &&
ip4.dst == A has actions drop; to exclude packets
that have gone through DNAT/unSNAT stage but failed
to convert the destination, to avoid loop.
For IPv6 NAT entries, same flows are added, but
using the register xxreg0 and field ip6 for the
match.
• If the router datapath runs a port with
redirect-type set to bridged, for each distributed
NAT rule with IP A in the logical_ip column and
logical port P in the logical_port column of NAT
table, a priority-90 flow with the match outport ==
Q && ip.src === A && is_chassis_resident(P), where
Q is the distributed logical router port and action
get_arp(outport, reg0); next; for IPv4 and
get_nd(outport, xxreg0); next; for IPv6.
• Traffic with IP destination an address owned by the
router should be dropped. Such traffic is normally
dropped in ingress table IP Input except for IPs
that are also shared with SNAT rules. However, if
there was no unSNAT operation that happened
successfully until this point in the pipeline and
the destination IP of the packet is still a router
owned IP, the packets can be safely dropped.
A priority-2 logical flow with match ip4.dst = {..}
matches on traffic destined to router owned IPv4
addresses which are also SNAT IPs. This flow has
action drop;.
A priority-2 logical flow with match ip6.dst = {..}
matches on traffic destined to router owned IPv6
addresses which are also SNAT IPs. This flow has
action drop;.
A priority-0 logical that flow matches all packets
not already handled (match 1) and drops them
(action drop;).
• Dynamic MAC bindings. These flows resolve MAC-to-IP
bindings that have become known dynamically through
ARP or neighbor discovery. (The ingress table ARP
Request will issue an ARP or neighbor solicitation
request for cases where the binding is not yet
known.)
A priority-0 logical flow with match ip4 has
actions get_arp(outport, reg0); next;.
A priority-0 logical flow with match ip6 has
actions get_nd(outport, xxreg0); next;.
• For a distributed gateway LRP with redirect-type
set to bridged, a priority-50 flow will match
outport == "ROUTER_PORT" and !is_chassis_resident
("cr-ROUTER_PORT") has actions eth.dst = E; next;,
where E is the ethernet address of the logical
router port.
Ingress Table 21: Check packet length
For distributed logical routers or gateway routers with gateway
port configured with options:gateway_mtu to a valid integer
value, this table adds a priority-50 logical flow with the match
outport == GW_PORT where GW_PORT is the gateway router port and
applies the action check_pkt_larger and advances the packet to
the next table.
REGBIT_PKT_LARGER = check_pkt_larger(L); next;
where L is the packet length to check for. If the packet is
larger than L, it stores 1 in the register bit REGBIT_PKT_LARGER.
The value of L is taken from options:gateway_mtu column of
Logical_Router_Port row.
If the port is also configured with options:gateway_mtu_bypass
then another flow is added, with priority-55, to bypass the
check_pkt_larger flow.
This table adds one priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 22: Handle larger packets
For distributed logical routers or gateway routers with gateway
port configured with options:gateway_mtu to a valid integer
value, this table adds the following priority-150 logical flow
for each logical router port with the match inport == LRP &&
outport == GW_PORT && REGBIT_PKT_LARGER &&
!REGBIT_EGRESS_LOOPBACK, where LRP is the logical router port and
GW_PORT is the gateway port and applies the following action for
ipv4 and ipv6 respectively:
icmp4 {
icmp4.type = 3; /* Destination Unreachable. */
icmp4.code = 4; /* Frag Needed and DF was Set. */
icmp4.frag_mtu = M;
eth.dst = E;
ip4.dst = ip4.src;
ip4.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER = 0;
next(pipeline=ingress, table=0);
};
icmp6 {
icmp6.type = 2;
icmp6.code = 0;
icmp6.frag_mtu = M;
eth.dst = E;
ip6.dst = ip6.src;
ip6.src = I;
ip.ttl = 255;
REGBIT_EGRESS_LOOPBACK = 1;
REGBIT_PKT_LARGER = 0;
next(pipeline=ingress, table=0);
};
• Where M is the (fragment MTU - 58) whose value is
taken from options:gateway_mtu column of
Logical_Router_Port row.
• E is the Ethernet address of the logical router
port.
• I is the IPv4/IPv6 address of the logical router
port.
This table adds one priority-0 fallback flow that matches all
packets and advances to the next table.
Ingress Table 23: Gateway Redirect
For distributed logical routers where one or more of the logical
router ports specifies a gateway chassis, this table redirects
certain packets to the distributed gateway port instances on the
gateway chassises. This table has the following flows:
• For all the configured load balancing rules that
include an IPv4 address VIP, and a list of IPv4
backend addresses B0, B1 .. Bn defined for the VIP
a priority-200 flow is added that matches ip4 &&
(ip4.src == B0 || ip4.src == B1 || ... || ip4.src
== Bn) with an action outport = CR; next; where CR
is the chassisredirect port representing the
instance of the logical router distributed gateway
port on the gateway chassis. If the backend IPv4
address Bx is also configured with L4 port PORT of
protocol P, then the match also includes P.src ==
PORT. Similar flows are added for IPv6.
• For each NAT rule in the OVN Northbound database
that can be handled in a distributed manner, a
priority-100 logical flow with match ip4.src == B
&& outport == GW && is_chassis_resident(P), where
GW is the distributed gateway port specified in the
NAT rule and P is the NAT logical port. IP traffic
matching the above rule will be managed locally
setting reg1 to C and eth.src to D, where C is NAT
external ip and D is NAT external mac.
• For each dnat_and_snat NAT rule with stateless=true
and allowed_ext_ips configured, a priority-75 flow
is programmed with match ip4.dst == B and action
outport = CR; next; where B is the NAT rule
external IP and CR is the chassisredirect port
representing the instance of the logical router
distributed gateway port on the gateway chassis.
Moreover a priority-70 flow is programmed with same
match and action drop;. For each dnat_and_snat NAT
rule with stateless=true and exempted_ext_ips
configured, a priority-75 flow is programmed with
match ip4.dst == B and action drop; where B is the
NAT rule external IP. A similar flow is added for
IPv6 traffic.
• For each NAT rule in the OVN Northbound database
that can be handled in a distributed manner, a
priority-80 logical flow with drop action if the
NAT logical port is a virtual port not claimed by
any chassis yet.
• A priority-50 logical flow with match outport == GW
has actions outport = CR; next;, where GW is the
logical router distributed gateway port and CR is
the chassisredirect port representing the instance
of the logical router distributed gateway port on
the gateway chassis.
• A priority-0 logical flow with match 1 has actions
next;.
Ingress Table 24: ARP Request
In the common case where the Ethernet destination has been
resolved, this table outputs the packet. Otherwise, it composes
and sends an ARP or IPv6 Neighbor Solicitation request. It holds
the following flows:
• Unknown MAC address. A priority-100 flow for IPv4
packets with match eth.dst == 00:00:00:00:00:00 has
the following actions:
arp {
eth.dst = ff:ff:ff:ff:ff:ff;
arp.spa = reg1;
arp.tpa = reg0;
arp.op = 1; /* ARP request. */
output;
};
Unknown MAC address. For each IPv6 static route
associated with the router with the nexthop IP: G,
a priority-200 flow for IPv6 packets with match
eth.dst == 00:00:00:00:00:00 && xxreg0 == G with
the following actions is added:
nd_ns {
eth.dst = E;
ip6.dst = I
nd.target = G;
output;
};
Where E is the multicast mac derived from the
Gateway IP, I is the solicited-node multicast
address corresponding to the target address G.
Unknown MAC address. A priority-100 flow for IPv6
packets with match eth.dst == 00:00:00:00:00:00 has
the following actions:
nd_ns {
nd.target = xxreg0;
output;
};
(Ingress table IP Routing initialized reg1 with the
IP address owned by outport and (xx)reg0 with the
next-hop IP address)
The IP packet that triggers the ARP/IPv6 NS request
is dropped.
• Known MAC address. A priority-0 flow with match 1
has actions output;.
Egress Table 0: Check DNAT local
This table checks if the packet needs to be DNATed in the router
ingress table lr_in_dnat after it is SNATed and looped back to
the ingress pipeline. This check is done only for routers
configured with distributed gateway ports and NAT entries. This
check is done so that SNAT and DNAT is done in different zones
instead of a common zone.
• A priority-0 logical flow with match 1 has actions
REGBIT_DST_NAT_IP_LOCAL = 0; next;.
Egress Table 1: UNDNAT
This is for already established connections’ reverse traffic.
i.e., DNAT has already been done in ingress pipeline and now the
packet has entered the egress pipeline as part of a reply. This
traffic is unDNATed here.
• A priority-0 logical flow with match 1 has actions
next;.
Egress Table 1: UNDNAT on Gateway Routers
• For IPv6 Neighbor Discovery or Router
Solicitation/Advertisement traffic, a priority-100
flow with action next;.
• For all IP packets, a priority-50 flow with an
action flags.loopback = 1; ct_dnat;.
Egress Table 1: UNDNAT on Distributed Routers
• For all the configured load balancing rules for a
router with gateway port in OVN_Northbound database
that includes an IPv4 address VIP, for every
backend IPv4 address B defined for the VIP a
priority-120 flow is programmed on gateway chassis
that matches ip && ip4.src == B && outport == GW,
where GW is the logical router gateway port with an
action ct_dnat;. If the backend IPv4 address B is
also configured with L4 port PORT of protocol P,
then the match also includes P.src == PORT. These
flows are not added for load balancers with IPv6
VIPs.
If the router is configured to force SNAT any load-
balanced packets, above action will be replaced by
flags.force_snat_for_lb = 1; ct_dnat;.
• For each configuration in the OVN Northbound
database that asks to change the destination IP
address of a packet from an IP address of A to B, a
priority-100 flow matches ip && ip4.src == B &&
outport == GW, where GW is the logical router
gateway port, with an action ct_dnat;. If the NAT
rule is of type dnat_and_snat and has
stateless=true in the options, then the action
would be next;.
If the NAT rule cannot be handled in a distributed
manner, then the priority-100 flow above is only
programmed on the gateway chassis with the action
ct_dnat.
If the NAT rule can be handled in a distributed
manner, then there is an additional action eth.src
= EA;, where EA is the ethernet address associated
with the IP address A in the NAT rule. This allows
upstream MAC learning to point to the correct
chassis.
Egress Table 2: Post UNDNAT
• A priority-70 logical flow is added that initiates
CT state for traffic that is configured to be
SNATed on Distributed routers. This allows the next
table, lr_out_snat, to effectively match on various
CT states.
• A priority-50 logical flow is added that commits
any untracked flows from the previous table
lr_out_undnat for Gateway routers. This flow
matches on ct.new && ip with action ct_commit { } ;
next; .
• A priority-0 logical flow with match 1 has actions
next;.
Egress Table 3: SNAT
Packets that are configured to be SNATed get their source IP
address changed based on the configuration in the OVN Northbound
database.
• A priority-120 flow to advance the IPv6 Neighbor
solicitation packet to next table to skip SNAT. In
the case where ovn-controller injects an IPv6
Neighbor Solicitation packet (for nd_ns action) we
don’t want the packet to go through conntrack.
Egress Table 3: SNAT on Gateway Routers
• If the Gateway router in the OVN Northbound
database has been configured to force SNAT a packet
(that has been previously DNATted) to B, a
priority-100 flow matches flags.force_snat_for_dnat
== 1 && ip with an action ct_snat(B);.
• If a load balancer configured to skip snat has been
applied to the Gateway router pipeline, a
priority-120 flow matches flags.skip_snat_for_lb ==
1 && ip with an action next;.
• If the Gateway router in the OVN Northbound
database has been configured to force SNAT a packet
(that has been previously load-balanced) using
router IP (i.e options:lb_force_snat_ip=router_ip),
then for each logical router port P attached to the
Gateway router, a priority-110 flow matches
flags.force_snat_for_lb == 1 && outport == P
with an action ct_snat(R); where R is the IP
configured on the router port. If R is an IPv4
address then the match will also include ip4 and if
it is an IPv6 address, then the match will also
include ip6.
If the logical router port P is configured with
multiple IPv4 and multiple IPv6 addresses, only the
first IPv4 and first IPv6 address is considered.
• If the Gateway router in the OVN Northbound
database has been configured to force SNAT a packet
(that has been previously load-balanced) to B, a
priority-100 flow matches flags.force_snat_for_lb
== 1 && ip with an action ct_snat(B);.
• For each configuration in the OVN Northbound
database, that asks to change the source IP address
of a packet from an IP address of A or to change
the source IP address of a packet that belongs to
network A to B, a flow matches ip && ip4.src == A
&& (!ct.trk || !ct.rpl) with an action ct_snat(B);.
The priority of the flow is calculated based on the
mask of A, with matches having larger masks getting
higher priorities. If the NAT rule is of type
dnat_and_snat and has stateless=true in the
options, then the action would be ip4/6.src= (B).
• If the NAT rule has allowed_ext_ips configured,
then there is an additional match ip4.dst ==
allowed_ext_ips . Similarly, for IPV6, match would
be ip6.dst == allowed_ext_ips.
• If the NAT rule has exempted_ext_ips set, then
there is an additional flow configured at the
priority + 1 of corresponding NAT rule. The flow
matches if destination ip is an exempted_ext_ip and
the action is next; . This flow is used to bypass
the ct_snat action for a packet which is destinted
to exempted_ext_ips.
• A priority-0 logical flow with match 1 has actions
next;.
Egress Table 3: SNAT on Distributed Routers
• For each configuration in the OVN Northbound
database, that asks to change the source IP address
of a packet from an IP address of A or to change
the source IP address of a packet that belongs to
network A to B, two flows are added. The priority P
of these flows are calculated based on the mask of
A, with matches having larger masks getting higher
priorities.
If the NAT rule cannot be handled in a distributed
manner, then the below flows are only programmed on
the gateway chassis increasing flow priority by 128
in order to be run first.
• The first flow is added with the calculated
priority P and match ip && ip4.src == A &&
outport == GW, where GW is the logical
router gateway port, with an action
ct_snat(B); to SNATed in the common zone. If
the NAT rule is of type dnat_and_snat and
has stateless=true in the options, then the
action would be ip4/6.src=(B).
If the NAT rule can be handled in a distributed
manner, then there is an additional action (for
both the flows) eth.src = EA;, where EA is the
ethernet address associated with the IP address A
in the NAT rule. This allows upstream MAC learning
to point to the correct chassis.
If the NAT rule has allowed_ext_ips configured,
then there is an additional match ip4.dst ==
allowed_ext_ips . Similarly, for IPV6, match would
be ip6.dst == allowed_ext_ips.
If the NAT rule has exempted_ext_ips set, then
there is an additional flow configured at the
priority P + 2 of corresponding NAT rule. The flow
matches if destination ip is an exempted_ext_ip and
the action is next; . This flow is used to bypass
the ct_snat action for a flow which is destinted to
exempted_ext_ips.
• An additional flow is added for traffic that goes
in opposite direction (i.e. it enters a network
with configured SNAT). Where the flow above matched
on ip4.src == A && outport == GW, this flow matches
on ip4.dst == A && inport == GW. A CT state is
initiated for this traffic so that the following
table, lr_out_post_snat, can identify whether the
traffic flow was initiated from the internal or
external network.
• A priority-0 logical flow with match 1 has actions
next;.
Egress Table 4: Post SNAT
Packets reaching this table are processed according to the flows
below:
• Traffic that goes directly into a network
configured with SNAT on Distributed routers, and
was initiated from an external network (i.e. it
matches ct.new), is committed to the SNAT CT zone.
This ensures that replies returning from the SNATed
network do not have their source address
translated. For details about match rules and
priority see section "Egress Table 3: SNAT on
Distributed Routers".
• A priority-0 logical flow that matches all packets
not already handled (match 1) and action next;.
Egress Table 5: Egress Loopback
For distributed logical routers where one of the logical router
ports specifies a gateway chassis.
While UNDNAT and SNAT processing have already occurred by this
point, this traffic needs to be forced through egress loopback on
this distributed gateway port instance, in order for UNSNAT and
DNAT processing to be applied, and also for IP routing and ARP
resolution after all of the NAT processing, so that the packet
can be forwarded to the destination.
This table has the following flows:
• For each NAT rule in the OVN Northbound database on
a distributed router, a priority-100 logical flow
with match ip4.dst == E && outport == GW &&
is_chassis_resident(P), where E is the external IP
address specified in the NAT rule, GW is the
distributed gateway port corresponding to the NAT
rule (specified or inferred). For dnat_and_snat NAT
rule, P is the logical port specified in the NAT
rule. If logical_port column of NAT table is NOT
set, then P is the chassisredirect port of GW with
the following actions:
clone {
ct_clear;
inport = outport;
outport = "";
flags = 0;
flags.loopback = 1;
reg0 = 0;
reg1 = 0;
...
reg9 = 0;
REGBIT_EGRESS_LOOPBACK = 1;
next(pipeline=ingress, table=0);
};
flags.loopback is set since in_port is unchanged
and the packet may return back to that port after
NAT processing. REGBIT_EGRESS_LOOPBACK is set to
indicate that egress loopback has occurred, in
order to skip the source IP address check against
the router address.
• A priority-0 logical flow with match 1 has actions
next;.
Egress Table 6: Delivery
Packets that reach this table are ready for delivery. It
contains:
• Priority-110 logical flows that match IP multicast
packets on each enabled logical router port and
modify the Ethernet source address of the packets
to the Ethernet address of the port and then
execute action output;.
• Priority-100 logical flows that match packets on
each enabled logical router port, with action
output;.
• A priority-0 logical flow that matches all packets
not already handled (match 1) and drops them
(action drop;).
As described in the previous section, there are several places
where ovn-northd might decided to drop a packet by explicitly
creating a Logical_Flow with the drop; action.
When debug drop-sampling has been cofigured in the OVN Northbound
database, the ovn-northd will replace all the drop; actions with
a sample(priority=65535, collector_set=id, obs_domain=obs_id,
obs_point=@cookie) action, where:
• id is the value the debug_drop_collector_set option
configured in the OVN Northbound.
• obs_id has it’s 8 most significant bits equal to
the value of the debug_drop_domain_id option in the
OVN Northbound and it’s 24 least significant bits
equal to the datapath’s tunnel key.
This page is part of the Open Virtual Network (Daemons for Open
vSwitch that translate virtual network configurations into
OpenFlow) project. Information about the project can be found at
⟨https://www.ovn.org/⟩. If you have a bug report for this manual
page, send it to bugs@openvswitch.org. This page was obtained
from the project's upstream Git repository
⟨https://github.com/ovn-org/ovn⟩ on 2024-06-14. (At that time,
the date of the most recent commit that was found in the
repository was 2024-06-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
OVN 24.03.90 ovn-northd ovn-northd(8)
Pages that refer to this page: ovn-sb(5), ovn-architecture(7)
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