ovn-trace(8) — Linux manual page


ovn-trace(8)                 Open vSwitch Manual                ovn-trace(8)

NAME         top

       ovn-trace - Open Virtual Network logical network tracing utility

SYNOPSIS         top

       ovn-trace [options] datapath microflow

       ovn-trace [options] --detach

DESCRIPTION         top

       This utility simulates packet forwarding within an OVN logical
       network. It can be used to run through ``what-if’’ scenarios: if a
       packet originates at a logical port, what will happen to it and where
       will it ultimately end up? Users already familiar with the Open
       vSwitch ofproto/trace command described in ovs-vswitch(8) will find
       ovn-trace to be a similar tool for logical networks.

       ovn-trace works by reading the Logical_Flow and other tables from the
       OVN southbound database (see ovn-sb(5)). It simulates a packet’s path
       through logical networks by repeatedly looking it up in the logical
       flow table, following the entire tree of possibilities.

       ovn-trace simulates only the OVN logical network. It does not
       simulate the physical elements on which the logical network is
       layered. This means that, for example, it is unimportant how VMs are
       distributed among hypervisors, or whether their hypervisors are
       functioning and reachable, so ovn-trace will yield the same results
       regardless. There is one important exception: ovn-northd, the daemon
       that generates the logical flows that ovn-trace simulates, treats
       logical ports differently based on whether they are up or down. Thus,
       if you see surprising results, ensure that the ports involved in a
       simulation are up.

       The simplest way to use ovn-trace is to provide datapath and
       microflow arguments on the command line. In this case, it simulates
       the behavior of a single packet and exits. For an alternate usage
       model, see Daemon Mode below.

       The datapath argument specifies the name of a logical datapath.
       Acceptable names are the name from the northbound Logical_Switch or
       Logical_Router table, the UUID of a record from one of those tables,
       or the UUID of a record from the southbound Datapath_Binding table.

       The microflow argument describes the packet whose forwarding is to be
       simulated, in the syntax of an OVN logical expression, as described
       in ovn-sb(5), to express constraints. The parser understands
       prerequisites; for example, if the expression refers to ip4.src,
       there is no need to explicitly state ip4 or eth.type == 0x800.

       For reasonable L2 behavior, the microflow should include at least
       inport and eth.dst, plus eth.src if port security is enabled. For

           inport == "lp11" && eth.src == 00:01:02:03:04:05 && eth.dst == ff:ff:ff:ff:ff:ff

       For reasonable L3 behavior, microflow should also include ip4.src and
       ip4.dst (or ip6.src and ip6.dst) and ip.ttl. For example:

           inport == "lp111" && eth.src == f0:00:00:00:01:11 && eth.dst == 00:00:00:00:ff:11
           && ip4.src == && ip4.dst == && ip.ttl == 64

       Here’s an ARP microflow example:

           inport == "lp123"
           && eth.dst == ff:ff:ff:ff:ff:ff && eth.src == f0:00:00:00:01:11
           && arp.op == 1 && arp.sha == f0:00:00:00:01:11 && arp.spa ==
           && arp.tha == ff:ff:ff:ff:ff:ff && arp.tpa ==

       ovn-trace will reject erroneous microflow expressions, which beyond
       syntax errors fall into two categories. First, they can be ambiguous.
       For example, tcp.src == 80 is ambiguous because it does not state
       IPv4 or IPv6 as the Ethernet type. ip4 && tcp.src > 1024 is also
       ambiguous because it does not constrain bits of tcp.src to particular
       values. Second, they can be contradictory, e.g. ip4 && ip6.

OUTPUT         top

       ovn-trace supports the three different forms of output, each
       described in a separate section below. Regardless of the selected
       output format, ovn-trace starts the output with a line that shows the
       microflow being traced in OpenFlow syntax.

   Detailed Output
       The detailed form of output is also the default form. This form
       groups output into sections headed up by the ingress or egress
       pipeline being traversed. Each pipeline lists each table that was
       visited (by number and name), the ovn-northd source file and line
       number of the code that added the flow, the match expression and
       priority of the logical flow that was matched, and the actions that
       were executed.

       The execution of OVN logical actions naturally forms a ``control
       stack’’ that resembles that of a program in conventional programming
       languages such as C or Java. Because the next action that calls into
       another logical flow table for a lookup is a recursive construct, OVN
       ``programs’’ in practice tend to form deep control stacks that,
       displayed in the obvious way using additional indentation for each
       level, quickly use up the horizontal space on all but the widest
       displays. To make detailed output more readable, without loss of
       generality, ovn-trace omits indentation for ``tail recursion,’’ that
       is, when next is the last action in a logical flow, it does not
       indent details of the next table lookup more deeply. Output still
       uses indentation when it is needed for clarity.

       OVN ``programs’’ traces also tend to encounter long strings of
       logical flows with match expression 1 (which matches every packet)
       and the single action next;. These are uninteresting and merely
       clutter output, so ovn-trace omits them entirely even from detailed

       The following excerpt from detailed ovn-trace output shows a section
       for a packet traversing the ingress pipeline of logical datapath ls1
       with ingress logical port lp111. The packet matches a logical flow in
       table 0 (aka ls_in_port_sec_l2) with priority 50 and executes
       next(1); to pass to table 1. Tables 1 through 11 are trivial and
       omitted. In table 12 (aka ls_in_l2_lkup), the packet matches a flow
       with priority 50 based on its Ethernet destination address and the
       flow’s actions output the packet to the lrp11-attachement logical

           ingress(dp="ls1", inport="lp111")
           0. ls_in_port_sec_l2: inport == "lp111", priority 50
           12. ls_in_l2_lkup: eth.dst == 00:00:00:00:ff:11, priority 50
           outport = "lrp11-attachment";

   Summary Output
       Summary output includes the logical pipelines visited by a packet and
       the logical actions executed on it. Compared to the detailed output,
       however, it removes details of tables and logical flows traversed by
       a packet. It uses a format closer to that of a programming language
       and does not attempt to avoid indentation. The summary output
       equivalent to the above detailed output fragment is:

           ingress(dp="ls1", inport="lp111") {
           outport = "lrp11-attachment";

   Minimal Output
       Minimal output includes only actions that modify packet data (not
       including OVN registers or metadata such as outport) and output
       actions that actually deliver a packet to a logical port (excluding
       patch ports). The operands of actions that modify packet data are
       displayed reduced to constants, e.g. ip4.dst = reg0; might be show as
       ip4.dst =; if that was the value actually loaded. This
       yields output even simpler than the summary format. (Users familiar
       with Open vSwitch may recognize this as similar in spirit to the
       datapath actions listed at the bottom of ofproto/trace output.)

       The minimal output format reflects the externally seen behavior of
       the logical networks more than it does the implementation. This makes
       this output format the most suitable for use in regression tests,
       because it is least likely to change when logical flow tables are
       rearranged without semantic change.


       Some OVN logical actions use or update state that is not available in
       the southbound database. ovn-trace handles these actions as described

                     By default ovn-trace treats flows as ``tracked’’ and
                     ``established.’’ See the description of the --ct option
                     for a way to override this behavior.

              ct_dnat (without an argument)
                     Forks the pipeline. In one fork, advances to the next
                     table as if next; were executed. The packet is not
                     changed, on the assumption that no NAT state was
                     available. In the other fork, the pipeline continues
                     without change after the ct_dnat action.

              ct_snat (without an argument)
                     This action distinguishes between gateway routers and
                     distributed routers. A gateway router is defined as a
                     logical datapath that contains an l3gateway port; any
                     other logical datapath is a distributed router. On a
                     gateway router, ct_snat; is treated as a no-op. On a
                     distributed router, it is treated the same way as

                   Forks the pipeline. In one fork, sets ip4.dst (or
                   ip4.src) to ip and ct.dnat (or ct.snat) to 1 and advances
                   to the next table as if next; were executed. In the other
                   fork, the pipeline continues without change after the
                   ct_dnat (or ct_snat) action.

                   Forks the pipeline. In one fork, sets ip4.dst (or
                   ip6.dst) to one of the load-balancer addresses and the
                   destination port to its associated port, if any, and sets
                   ct.dnat to 1. With one or more arguments, gives
                   preference to the address specified on --lb-dst, if any;
                   without arguments, uses the address and port specified on
                   --lb-dst. In the other fork, the pipeline continues
                   without change after the ct_lb action.

                   These actions are treated as no-ops.

DAEMON MODE         top

       If ovn-trace is invoked with the --detach option (see Daemon Options,
       below), it runs in the background as a daemon and accepts commands
       from ovs-appctl (or another JSON-RPC client) indefinitely. The
       currently supported commands are described below.

              trace [options] datapath microflow
                     Traces microflow through datapath and replies with the
                     results of the trace. Accepts the options described
                     under Trace Options below.

              exit   Causes ovn-trace to gracefully terminate.

OPTIONS         top

   Trace Options
            These options control the form and level of detail in ovn-trace
            output. If more than one of these options is specified, all of
            the selected forms are output, in the order listed above, each
            headed by a banner line. If none of these options is given,
            --detailed is the default. See Output, above, for a description
            of each kind of output.

            Selects all three forms of output.

            Makes ovn-trace attempt to obtain and display the OpenFlow flows
            that correspond to each OVN logical flow. To do so, ovn-trace
            connects to remote (by default,
            unix:/usr/local/var/run/openvswitch/br-int.mgmt) over OpenFlow
            and retrieves the flows. If remote is specified, it must be an
            active OpenFlow connection method described in ovsdb(7).

            To make the best use of the output, it is important to
            understand the relationship between logical flows and OpenFlow
            flows. ovn-architecture(7), under Architectural Physical Life
            Cycle of a Packet, describes this relationship. Keep in mind the
            following points:

            ·      ovn-trace currently shows all the OpenFlow flows to which
                   a logical flow corresponds, even though an actual packet
                   ordinarily matches only one of these.

            ·      Some logical flows can map to the Open vSwitch
                   ``conjunctive match’’ extension (see ovs-fields(7)).
                   Currently ovn-trace cannot display the flows with
                   conjunction actions that effectively produce the conj_id

            ·      Some logical flows may not be represented in the OpenFlow
                   tables on a given hypervisor, if they could not be used
                   on that hypervisor.

            ·      Some OpenFlow flows do not correspond to logical flows,
                   such as OpenFlow flows that map between physical and
                   logical ports. These flows will never show up in a trace.

            ·      When ovn-trace omits uninteresting logical flows from
                   output, it does not look up the corresponding OpenFlow

            This option sets the ct_state flags that a ct_next logical
            action will report. The flags must be a comma- or space-
            separated list of the following connection tracking flags:

            ·      trk: Include to indicate connection tracking has taken
                   place. (This bit is set automatically even if not listed
                   in flags.

            ·      new: Include to indicate a new flow.

            ·      est: Include to indicate an established flow.

            ·      rel: Include to indicate a related flow.

            ·      rpl: Include to indicate a reply flow.

            ·      inv: Include to indicate a connection entry in a bad

            ·      dnat: Include to indicate a packet whose destination IP
                   address has been changed.

            ·      snat: Include to indicate a packet whose source IP
                   address has been changed.

            The ct_next action is used to implement the OVN distributed
            firewall. For testing, useful flag combinations include:

            ·      trk,new: A packet in a flow in either direction through a
                   firewall that has not yet been committed (with

            ·      trk,est: A packet in an established flow going out
                   through a firewall.

            ·      trk,rpl: A packet coming in through a firewall in reply
                   to an established flow.

            ·      trk,inv: An invalid packet in either direction.

            A packet might pass through the connection tracker twice in one
            trip through OVN: once following egress from a VM as it passes
            outward through a firewall, and once preceding ingress to a
            second VM as it passes inward through a firewall. Use multiple
            --ct options to specify the flags for multiple ct_next actions.

            When --ct is unspecified, or when there are fewer --ct options
            than ct_next actions, the flags default to trk,est.

            Sets the IP from VIP pool to use as destination of the packet.
            --lb-dst is not available in daemon mode.

            When cloud management systems such as OpenStack are layered on
            top of OVN, they often use long, human-unfriendly names for
            ports and datapaths, for example, ones that include entire
            UUIDs. They do usually include friendlier names, but the long,
            hard-to-read names are the ones that appear in matches and
            actions. By default, or with --friendly-names, ovn-trace
            substitutes these friendlier names for the long names in its
            output. Use --no-friendly-names to disable this behavior; this
            option might be useful, for example, if a program is going to
            parse ovn-trace output.

   Daemon Options
              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 /usr/local/var/run/openvswitch.

              If --pidfile is not specified, no pidfile is created.

              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.

              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.

              Creates an additional process to monitor this program. If it
              dies due to a signal that indicates a programming error
              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.

              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

              This option has no effect when --detach is not specified.

              By default this daemon will try to self-confine itself to work
              with files under well-known directories whitelisted 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.

              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
            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

            For compatibility with older versions of OVS, any is accepted as
            a word but has no effect.

            Sets the maximum logging verbosity level, equivalent to

            Sets the log pattern for destination to pattern. Refer to
            ovs-appctl(8) for a description of the valid syntax for pattern.

            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.

            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

            Send syslog messages to UDP port on host, in addition to the
            system syslog. The host must be a numerical IP address, not a

            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 to use SSL for the connection to the
       database (and the switch, if --ovs is specified).

              -p privkey.pem
                   Specifies a PEM file containing the private key used as
                   identity for outgoing SSL connections.

              -c 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
                   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
                   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
       --db database
              The OVSDB database remote to contact. If the OVN_SB_DB
              environment variable is set, its value is used as the default.
              Otherwise, the default is
              unix:/usr/local/var/run/openvswitch/db.sock, but this default
              is unlikely to be useful outside of single-machine OVN test

                   Prints a brief help message to the console.

                   Prints version information to the console.

COLOPHON         top

       This page is part of the Open vSwitch (a distributed virtual
       multilayer switch) project.  Information about the project can be
       found at ⟨http://openvswitch.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/openvswitch/ovs.git⟩ on 2020-08-13.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-08-12.)  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

Open vSwitch 2.11.90              ovn-trace                     ovn-trace(8)

Pages that refer to this page: ovn-detrace(1)ovn-sbctl(8)