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NAME | SYNOPSIS | DESCRIPTION | EBTABLES COMMAND LINE ARGUMENTS | FILES | MAILINGLISTS | BUGS | SEE ALSO | COLOPHON |
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EBTABLES(8) System Manager's Manual EBTABLES(8)
ebtables — Ethernet bridge frame table administration (nft-based)
ebtables [-t table ] -[ACDI] chain rule specification [match
extensions] [watcher extensions] target
ebtables [-t table ] -P chain ACCEPT | DROP | RETURN
ebtables [-t table ] -F [chain]
ebtables [-t table ] -Z [chain]
ebtables [-t table ] -L [-Z] [chain] [ [--Ln] | [--Lx] ] [--Lc]
[--Lmac2]
ebtables [-t table ] -N chain [-P ACCEPT | DROP | RETURN]
ebtables [-t table ] -X [chain]
ebtables [-t table ] -E old-chain-name new-chain-name
ebtables [-t table ] --init-table
ebtables is an application program used to set up and maintain the
tables of rules (inside the Linux kernel) that inspect Ethernet
frames. It is analogous to the iptables application, but less
complicated, due to the fact that the Ethernet protocol is much
simpler than the IP protocol.
CHAINS
There are three ebtables tables with built-in chains in the Linux
kernel. These tables are used to divide functionality into
different sets of rules. Each set of rules is called a chain.
Each chain is an ordered list of rules that can match Ethernet
frames. If a rule matches an Ethernet frame, then a processing
specification tells what to do with that matching frame. The
processing specification is called a 'target'. However, if the
frame does not match the current rule in the chain, then the next
rule in the chain is examined and so forth. The user can create
new (user-defined) chains that can be used as the 'target' of a
rule. User-defined chains are very useful to get better
performance over the linear traversal of the rules and are also
essential for structuring the filtering rules into well-organized
and maintainable sets of rules.
TARGETS
A firewall rule specifies criteria for an Ethernet frame and a
frame processing specification called a target. When a frame
matches a rule, then the next action performed by the kernel is
specified by the target. The target can be one of these values:
ACCEPT, DROP, CONTINUE, RETURN, an 'extension' (see below) or a
jump to a user-defined chain.
ACCEPT means to let the frame through. DROP means the frame has
to be dropped. In the BROUTING chain however, the ACCEPT and DROP
target have different meanings (see the info provided for the -t
option). CONTINUE means the next rule has to be checked. This can
be handy, f.e., to know how many frames pass a certain point in
the chain, to log those frames or to apply multiple targets on a
frame. RETURN means stop traversing this chain and resume at the
next rule in the previous (calling) chain. For the extension
targets please refer to the TARGET EXTENSIONS section of this man
page.
TABLES
As stated earlier, the table names are filter, nat and broute. Of
these tables, the filter table is the default table that the
command operates on. If you are working with a table other than
filter, you will need to provide the -t argument. Moreover, the
-t argument must be the first argument on the ebtables command
line, if used.
-t, --table
filter is the default table and contains three built-in
chains: INPUT (for frames destined for the bridge itself,
on the level of the MAC destination address), OUTPUT (for
locally-generated or (b)routed frames) and FORWARD (for
frames being forwarded by the bridge).
nat is mostly used to change the mac addresses and contains
three built-in chains: PREROUTING (for altering frames as
soon as they come in), OUTPUT (for altering locally
generated or (b)routed frames before they are bridged) and
POSTROUTING (for altering frames as they are about to go
out). A small note on the naming of chains PREROUTING and
POSTROUTING: it would be more accurate to call them
PREFORWARDING and POSTFORWARDING, but for all those who
come from the iptables world to ebtables it is easier to
have the same names. Note that you can change the name (-E)
if you don't like the default.
broute is used to make a brouter, it has one built-in
chain: BROUTING. The targets DROP and ACCEPT have a
special meaning in the broute table (these names are used
for compatibility reasons with ebtables-legacy). DROP
actually means the frame has to be routed, while ACCEPT
means the frame has to be bridged. The BROUTING chain is
traversed very early. Normally those frames would be
bridged, but you can decide otherwise here.
After the initial ebtables '-t table' command line argument, the
remaining arguments can be divided into several groups. These
groups are commands, miscellaneous commands, rule specifications,
match extensions, watcher extensions and target extensions.
COMMANDS
The ebtables command arguments specify the actions to perform on
the table defined with the -t argument. If you do not use the -t
argument to name a table, the commands apply to the default filter
table. Only one command may be used on the command line at a
time, except when the commands -L and -Z are combined or the
commands -N and -P are combined.
-A, --append
Append a rule to the end of the selected chain.
-D, --delete
Delete the specified rule or rules from the selected chain.
There are two ways to use this command. The first is by
specifying an interval of rule numbers to delete (directly
after -D). Syntax: start_nr[:end_nr] (use -L --Ln to list
the rules with their rule number). When end_nr is omitted,
all rules starting from start_nr are deleted. Using
negative numbers is allowed, for more details about using
negative numbers, see the -I command. The second usage is
by specifying the complete rule as it would have been
specified when it was added. Only the first encountered
rule that is the same as this specified rule, in other
words the matching rule with the lowest (positive) rule
number, is deleted.
-C, --change-counters
Change the counters of the specified rule or rules from the
selected chain. There are two ways to use this command. The
first is by specifying an interval of rule numbers to do
the changes on (directly after -C). Syntax:
start_nr[:end_nr] (use -L --Ln to list the rules with their
rule number). The details are the same as for the -D
command. The second usage is by specifying the complete
rule as it would have been specified when it was added.
Only the counters of the first encountered rule that is the
same as this specified rule, in other words the matching
rule with the lowest (positive) rule number, are changed.
In the first usage, the counters are specified directly
after the interval specification, in the second usage
directly after -C. First the packet counter is specified,
then the byte counter. If the specified counters start with
a '+', the counter values are added to the respective
current counter values. If the specified counters start
with a '-', the counter values are decreased from the
respective current counter values. No bounds checking is
done. If the counters don't start with '+' or '-', the
current counters are changed to the specified counters.
-I, --insert
Insert the specified rule into the selected chain at the
specified rule number. If the rule number is not specified,
the rule is added at the head of the chain. If the current
number of rules equals N, then the specified number can be
between -N and N+1. For a positive number i, it holds that
i and i-N-1 specify the same place in the chain where the
rule should be inserted. The rule number 0 specifies the
place past the last rule in the chain and using this number
is therefore equivalent to using the -A command. Rule
numbers structly smaller than 0 can be useful when more
than one rule needs to be inserted in a chain.
-P, --policy
Set the policy for the chain to the given target. The
policy can be ACCEPT, DROP or RETURN.
-F, --flush
Flush the selected chain. If no chain is selected, then
every chain will be flushed. Flushing a chain does not
change the policy of the chain, however.
-Z, --zero
Set the counters of the selected chain to zero. If no chain
is selected, all the counters are set to zero. The -Z
command can be used in conjunction with the -L command.
When both the -Z and -L commands are used together in this
way, the rule counters are printed on the screen before
they are set to zero.
-L, --list
List all rules in the selected chain. If no chain is
selected, all chains are listed.
The following options change the output of the -L command.
--Ln
Places the rule number in front of every rule. This option
is incompatible with the --Lx option.
--Lc
Shows the counters at the end of each rule displayed by the
-L command. Both a frame counter (pcnt) and a byte counter
(bcnt) are displayed. The frame counter shows how many
frames have matched the specific rule, the byte counter
shows the sum of the frame sizes of these matching frames.
Using this option in combination with the --Lx option
causes the counters to be written out in the '-c <pcnt>
<bcnt>' option format.
--Lx
Changes the output so that it produces a set of ebtables
commands that construct the contents of the chain, when
specified. If no chain is specified, ebtables commands to
construct the contents of the table are given, including
commands for creating the user-defined chains (if any).
You can use this set of commands in an ebtables boot or
reload script. For example the output could be used at
system startup. The --Lx option is incompatible with the
--Ln listing option. Using the --Lx option together with
the --Lc option will cause the counters to be written out
in the '-c <pcnt> <bcnt>' option format.
--Lmac2
Shows all MAC addresses with the same length, adding
leading zeroes if necessary. The default representation
omits leading zeroes in the addresses.
-N, --new-chain
Create a new user-defined chain with the given name. The
number of user-defined chains is limited only by the number
of possible chain names. A user-defined chain name has a
maximum length of 31 characters. The standard policy of the
user-defined chain is ACCEPT. The policy of the new chain
can be initialized to a different standard target by using
the -P command together with the -N command. In this case,
the chain name does not have to be specified for the -P
command.
-X, --delete-chain
Delete the specified user-defined chain. There must be no
remaining references (jumps) to the specified chain,
otherwise ebtables will refuse to delete it. If no chain is
specified, all user-defined chains that aren't referenced
will be removed.
-E, --rename-chain
Rename the specified chain to a new name. Besides renaming
a user-defined chain, you can rename a standard chain to a
name that suits your taste. For example, if you like
PREFORWARDING more than PREROUTING, then you can use the -E
command to rename the PREROUTING chain. If you do rename
one of the standard ebtables chain names, please be sure to
mention this fact should you post a question on the
ebtables mailing lists. It would be wise to use the
standard name in your post. Renaming a standard ebtables
chain in this fashion has no effect on the structure or
functioning of the ebtables kernel table.
--init-table
Replace the current table data by the initial table data.
MISCELLANEOUS COMMANDS
-v, --verbose
Verbose mode. For appending, insertion, deletion and
replacement, this causes detailed information on the rule
or rules to be printed. -v may be specified multiple times
to possibly emit more detailed debug statements.
-V, --version
Show the version of the ebtables userspace program.
-h, --help [list of module names]
Give a brief description of the command syntax. Here you
can also specify names of extensions and ebtables will try
to write help about those extensions. E.g. ebtables -h
snat log ip arp. Specify list_extensions to list all
extensions supported by the userspace utility.
-j, --jump target
The target of the rule. This is one of the following
values: ACCEPT, DROP, CONTINUE, RETURN, a target extension
(see TARGET EXTENSIONS) or a user-defined chain name.
-M, --modprobe program
When talking to the kernel, use this program to try to
automatically load missing kernel modules.
--concurrent
This would use a file lock to support concurrent scripts
updating the ebtables kernel tables. It is not needed with
ebtables-nft though and thus ignored.
RULE SPECIFICATIONS
The following command line arguments make up a rule specification
(as used in the add and delete commands). A "!" option before the
specification inverts the test for that specification. Apart from
these standard rule specifications there are some other command
line arguments of interest. See both the MATCH EXTENSIONS and the
WATCHER EXTENSIONS below.
[!] -p, --protocol protocol
The protocol that was responsible for creating the frame.
This can be a hexadecimal number, above 0x0600, a name
(e.g. ARP ) or LENGTH. The protocol field of the Ethernet
frame can be used to denote the length of the header
(802.2/802.3 networks). When the value of that field is
below or equals 0x0600, the value equals the size of the
header and shouldn't be used as a protocol number. Instead,
all frames where the protocol field is used as the length
field are assumed to be of the same 'protocol'. The
protocol name used in ebtables for these frames is LENGTH.
The file /etc/ethertypes can be used to show readable
characters instead of hexadecimal numbers for the
protocols. For example, 0x0800 will be represented by IPV4.
The use of this file is not case sensitive. See that file
for more information. The flag --proto is an alias for this
option.
[!] -i, --in-interface name
The interface (bridge port) via which a frame is received
(this option is useful in the INPUT, FORWARD, PREROUTING
and BROUTING chains). If the interface name ends with '+',
then any interface name that begins with this name
(disregarding '+') will match. The flag --in-if is an
alias for this option.
[!] --logical-in name
The (logical) bridge interface via which a frame is
received (this option is useful in the INPUT, FORWARD,
PREROUTING and BROUTING chains). If the interface name
ends with '+', then any interface name that begins with
this name (disregarding '+') will match.
[!] -o, --out-interface name
The interface (bridge port) via which a frame is going to
be sent (this option is useful in the OUTPUT, FORWARD and
POSTROUTING chains). If the interface name ends with '+',
then any interface name that begins with this name
(disregarding '+') will match. The flag --out-if is an
alias for this option.
[!] --logical-out name
The (logical) bridge interface via which a frame is going
to be sent (this option is useful in the OUTPUT, FORWARD
and POSTROUTING chains). If the interface name ends with
'+', then any interface name that begins with this name
(disregarding '+') will match.
[!] -s, --source address[/mask]
The source MAC address. Both mask and address are written
as 6 hexadecimal numbers separated by colons. Alternatively
one can specify Unicast, Multicast, Broadcast or BGA
(Bridge Group Address):
Unicast=00:00:00:00:00:00/01:00:00:00:00:00,
Multicast=01:00:00:00:00:00/01:00:00:00:00:00,
Broadcast=ff:ff:ff:ff:ff:ff/ff:ff:ff:ff:ff:ff or
BGA=01:80:c2:00:00:00/ff:ff:ff:ff:ff:ff. Note that a
broadcast address will also match the multicast
specification. The flag --src is an alias for this option.
[!] -d, --destination address[/mask]
The destination MAC address. See -s (above) for more
details on MAC addresses. The flag --dst is an alias for
this option.
-c, --set-counter pcnt bcnt
If used with -A or -I, then the packet and byte counters of
the new rule will be set to pcnt, resp. bcnt. If used with
the -C or -D commands, only rules with a packet and byte
count equal to pcnt, resp. bcnt will match.
MATCH EXTENSIONS
Ebtables extensions are dynamically loaded into the userspace
tool, there is therefore no need to explicitly load them with a -m
option like is done in iptables. These extensions deal with
functionality supported by kernel modules supplemental to the core
ebtables code.
802_3
Specify 802.3 DSAP/SSAP fields or SNAP type. The protocol must be
specified as LENGTH (see the option -p above).
[!] --802_3-sap sap
DSAP and SSAP are two one byte 802.3 fields. The bytes are
always equal, so only one byte (hexadecimal) is needed as
an argument.
[!] --802_3-type type
If the 802.3 DSAP and SSAP values are 0xaa then the SNAP
type field must be consulted to determine the payload
protocol. This is a two byte (hexadecimal) argument. Only
802.3 frames with DSAP/SSAP 0xaa are checked for type.
among
Match a MAC address or MAC/IP address pair versus a list of MAC
addresses and MAC/IP address pairs. A list entry has the
following format: xx:xx:xx:xx:xx:xx[=ip.ip.ip.ip][,]. Multiple
list entries are separated by a comma, specifying an IP address
corresponding to the MAC address is optional. Multiple MAC/IP
address pairs with the same MAC address but different IP address
(and vice versa) can be specified. If the MAC address doesn't
match any entry from the list, the frame doesn't match the rule
(unless "!" was used).
[!] --among-dst list
Compare the MAC destination to the given list. If the
Ethernet frame has type IPv4 or ARP, then comparison with
MAC/IP destination address pairs from the list is possible.
[!] --among-src list
Compare the MAC source to the given list. If the Ethernet
frame has type IPv4 or ARP, then comparison with MAC/IP
source address pairs from the list is possible.
[!] --among-dst-file file
Same as --among-dst but the list is read in from the
specified file.
[!] --among-src-file file
Same as --among-src but the list is read in from the
specified file.
arp
Specify (R)ARP fields. The protocol must be specified as ARP or
RARP.
[!] --arp-opcode opcode
The (R)ARP opcode (decimal or a string, for more details
see ebtables -h arp).
[!] --arp-htype hardware-type
The hardware type, this can be a decimal or the string
Ethernet (which sets type to 1). Most (R)ARP packets have
Eternet as hardware type.
[!] --arp-ptype protocol-type
The protocol type for which the (r)arp is used (hexadecimal
or the string IPv4, denoting 0x0800). Most (R)ARP packets
have protocol type IPv4.
[!] --arp-ip-src address[/mask]
The (R)ARP IP source address specification.
[!] --arp-ip-dst address[/mask]
The (R)ARP IP destination address specification.
[!] --arp-mac-src address[/mask]
The (R)ARP MAC source address specification.
[!] --arp-mac-dst address[/mask]
The (R)ARP MAC destination address specification.
[!] --arp-gratuitous
Checks for ARP gratuitous packets: checks equality of IPv4
source address and IPv4 destination address inside the ARP
header.
ip
Specify IPv4 fields. The protocol must be specified as IPv4.
[!] --ip-source address[/mask]
The source IP address. The flag --ip-src is an alias for
this option.
[!] --ip-destination address[/mask]
The destination IP address. The flag --ip-dst is an alias
for this option.
[!] --ip-tos tos
The IP type of service, in hexadecimal numbers. IPv4.
[!] --ip-protocol protocol
The IP protocol. The flag --ip-proto is an alias for this
option.
[!] --ip-source-port port1[:port2]
The source port or port range for the IP protocols 6 (TCP),
17 (UDP), 33 (DCCP) or 132 (SCTP). The --ip-protocol option
must be specified as TCP, UDP, DCCP or SCTP. If port1 is
omitted, 0:port2 is used; if port2 is omitted but a colon
is specified, port1:65535 is used. The flag --ip-sport is
an alias for this option.
[!] --ip-destination-port port1[:port2]
The destination port or port range for ip protocols 6
(TCP), 17 (UDP), 33 (DCCP) or 132 (SCTP). The --ip-protocol
option must be specified as TCP, UDP, DCCP or SCTP. If
port1 is omitted, 0:port2 is used; if port2 is omitted but
a colon is specified, port1:65535 is used. The flag --ip-
dport is an alias for this option.
ip6
Specify IPv6 fields. The protocol must be specified as IPv6.
[!] --ip6-source address[/mask]
The source IPv6 address. The flag --ip6-src is an alias
for this option.
[!] --ip6-destination address[/mask]
The destination IPv6 address. The flag --ip6-dst is an
alias for this option.
[!] --ip6-tclass tclass
The IPv6 traffic class, in hexadecimal numbers.
[!] --ip6-protocol protocol
The IP protocol. The flag --ip6-proto is an alias for this
option.
[!] --ip6-source-port port1[:port2]
The source port or port range for the IPv6 protocols 6
(TCP), 17 (UDP), 33 (DCCP) or 132 (SCTP). The
--ip6-protocol option must be specified as TCP, UDP, DCCP
or SCTP. If port1 is omitted, 0:port2 is used; if port2 is
omitted but a colon is specified, port1:65535 is used. The
flag --ip6-sport is an alias for this option.
[!] --ip6-destination-port port1[:port2]
The destination port or port range for IPv6 protocols 6
(TCP), 17 (UDP), 33 (DCCP) or 132 (SCTP). The
--ip6-protocol option must be specified as TCP, UDP, DCCP
or SCTP. If port1 is omitted, 0:port2 is used; if port2 is
omitted but a colon is specified, port1:65535 is used. The
flag --ip6-dport is an alias for this option.
[!] --ip6-icmp-type {type[:type]/code[:code]|typename}
Specify ipv6-icmp type and code to match. Ranges for both
type and code are supported. Type and code are separated by
a slash. Valid numbers for type and range are 0 to 255. To
match a single type including all valid codes, symbolic
names can be used instead of numbers. The list of known
type names is shown by the command
ebtables --help ip6
This option is only valid for --ip6-prococol ipv6-icmp.
limit
This module matches at a limited rate using a token bucket filter.
A rule using this extension will match until this limit is
reached. It can be used with the --log watcher to give limited
logging, for example. Its use is the same as the limit match of
iptables.
--limit [value]
Maximum average matching rate: specified as a number, with
an optional /second, /minute, /hour, or /day suffix; the
default is 3/hour.
--limit-burst [number]
Maximum initial number of packets to match: this number
gets recharged by one every time the limit specified above
is not reached, up to this number; the default is 5.
mark_m
[!] --mark [value][/mask]
Matches frames with the given unsigned mark value. If a
value and mask are specified, the logical AND of the mark
value of the frame and the user-specified mask is taken
before comparing it with the user-specified mark value.
When only a mark value is specified, the packet only
matches when the mark value of the frame equals the user-
specified mark value. If only a mask is specified, the
logical AND of the mark value of the frame and the user-
specified mask is taken and the frame matches when the
result of this logical AND is non-zero. Only specifying a
mask is useful to match multiple mark values.
pkttype
[!] --pkttype-type type
Matches on the Ethernet "class" of the frame, which is
determined by the generic networking code. Possible values:
broadcast (MAC destination is the broadcast address),
multicast (MAC destination is a multicast address), host
(MAC destination is the receiving network device), or
otherhost (none of the above).
stp
Specify stp BPDU (bridge protocol data unit) fields. The
destination address (-d) must be specified as the bridge group
address (BGA). For all options for which a range of values can be
specified, it holds that if the lower bound is omitted (but the
colon is not), then the lowest possible lower bound for that
option is used, while if the upper bound is omitted (but the colon
again is not), the highest possible upper bound for that option is
used.
[!] --stp-type type
The BPDU type (0–255), recognized non-numerical types are
config, denoting a configuration BPDU (=0), and tcn,
denothing a topology change notification BPDU (=128).
[!] --stp-flags flag
The BPDU flag (0–255), recognized non-numerical flags are
topology-change, denoting the topology change flag (=1),
and topology-change-ack, denoting the topology change
acknowledgement flag (=128).
[!] --stp-root-prio [prio][:prio]
The root priority (0–65535) range.
[!] --stp-root-addr [address][/mask]
The root mac address, see the option -s for more details.
[!] --stp-root-cost [cost][:cost]
The root path cost (0–4294967295) range.
[!] --stp-sender-prio [prio][:prio]
The BPDU's sender priority (0–65535) range.
[!] --stp-sender-addr [address][/mask]
The BPDU's sender mac address, see the option -s for more
details.
[!] --stp-port [port][:port]
The port identifier (0–65535) range.
[!] --stp-msg-age [age][:age]
The message age timer (0–65535) range.
[!] --stp-max-age [age][:age]
The max age timer (0–65535) range.
[!] --stp-hello-time [time][:time]
The hello time timer (0–65535) range.
[!] --stp-forward-delay [delay][:delay]
The forward delay timer (0–65535) range.
vlan
Specify 802.1Q Tag Control Information fields. The protocol must
be specified as 802_1Q (0x8100).
[!] --vlan-id id
The VLAN identifier field (VID). Decimal number from 0 to
4095.
[!] --vlan-prio prio
The user priority field, a decimal number from 0 to 7. The
VID should be set to 0 ("null VID") or unspecified (in the
latter case the VID is deliberately set to 0).
[!] --vlan-encap type
The encapsulated Ethernet frame type/length. Specified as
a hexadecimal number from 0x0000 to 0xFFFF or as a symbolic
name from /etc/ethertypes.
WATCHER EXTENSIONS
Watchers only look at frames passing by, they don't modify them
nor decide to accept the frames or not. These watchers only see
the frame if the frame matches the rule, and they see it before
the target is executed.
log
The log watcher writes descriptive data about a frame to the
syslog.
--log
Log with the default logging options: log-level= info, log-
prefix="", no ip logging, no arp logging.
--log-level level
Defines the logging level. For the possible values, see
ebtables -h log. The default level is info.
--log-prefix text
Defines the prefix text to be printed at the beginning of
the line with the logging information.
--log-ip
Will log the ip information when a frame made by the ip
protocol matches the rule. The default is no ip information
logging.
--log-ip6
Will log the ipv6 information when a frame made by the ipv6
protocol matches the rule. The default is no ipv6
information logging.
--log-arp
Will log the (r)arp information when a frame made by the
(r)arp protocols matches the rule. The default is no (r)arp
information logging.
nflog
The nflog watcher passes the packet to the loaded logging backend
in order to log the packet. This is usually used in combination
with nfnetlink_log as logging backend, which will multicast the
packet through a netlink socket to the specified multicast group.
One or more userspace processes may subscribe to the group to
receive the packets.
--nflog
Log with the default logging options
--nflog-group nlgroup
The netlink group (1–2^32-1) to which packets are (only
applicable for nfnetlink_log). The default value is 1.
--nflog-prefix prefix
A prefix string to include in the log message, up to 30
characters long, useful for distinguishing messages in the
logs.
--nflog-range size
The number of bytes to be copied to userspace (only
applicable for nfnetlink_log). nfnetlink_log instances may
specify their own range, this option overrides it.
--nflog-threshold size
Number of packets to queue inside the kernel before sending
them to userspace (only applicable for nfnetlink_log).
Higher values result in less overhead per packet, but
increase delay until the packets reach userspace. The
default value is 1.
ulog
The ulog watcher passes the packet to a userspace logging daemon
using netlink multicast sockets. This differs from the log watcher
in the sense that the complete packet is sent to userspace instead
of a descriptive text and that netlink multicast sockets are used
instead of the syslog. This watcher enables parsing of packets
with userspace programs, the physical bridge in and out ports are
also included in the netlink messages. The ulog watcher module
accepts 2 parameters when the module is loaded into the kernel
(e.g. with modprobe): nlbufsiz specifies how big the buffer for
each netlink multicast group is. If you say nlbufsiz=8192, for
example, up to eight kB of packets will get accumulated in the
kernel until they are sent to userspace. It is not possible to
allocate more than 128kB. Please also keep in mind that this
buffer size is allocated for each nlgroup you are using, so the
total kernel memory usage increases by that factor. The default is
4096. flushtimeout specifies after how many hundredths of a
second the queue should be flushed, even if it is not full yet.
The default is 10 (one tenth of a second).
--ulog
Use the default settings: ulog-prefix="", ulog-nlgroup=1,
ulog-cprange=4096, ulog-qthreshold=1.
--ulog-prefix text
Defines the prefix included with the packets sent to
userspace.
--ulog-nlgroup group
Defines which netlink group number to use (a number from 1
to 32). Make sure the netlink group numbers used for the
iptables ULOG target differ from those used for the
ebtables ulog watcher. The default group number is 1.
--ulog-cprange range
Defines the maximum copy range to userspace, for packets
matching the rule. The default range is 0, which means the
maximum copy range is given by nlbufsiz. A maximum copy
range larger than 128*1024 is meaningless as the packets
sent to userspace have an upper size limit of 128*1024.
--ulog-qthreshold threshold
Queue at most threshold number of packets before sending
them to userspace with a netlink socket. Note that packets
can be sent to userspace before the queue is full, this
happens when the ulog kernel timer goes off (the frequency
of this timer depends on flushtimeout).
TARGET EXTENSIONS
arpreply
The arpreply target can be used in the PREROUTING chain of the nat
table. If this target sees an ARP request it will automatically
reply with an ARP reply. The used MAC address for the reply can be
specified. The protocol must be specified as ARP. When the ARP
message is not an ARP request or when the ARP request isn't for an
IP address on an Ethernet network, it is ignored by this target
(CONTINUE). When the ARP request is malformed, it is dropped
(DROP).
--arpreply-mac address
Specifies the MAC address to reply with: the Ethernet
source MAC and the ARP payload source MAC will be filled in
with this address.
--arpreply-target target
Specifies the standard target. After sending the ARP reply,
the rule still has to give a standard target so ebtables
knows what to do with the ARP request. The default target
is DROP.
dnat
The dnat target can only be used in the PREROUTING and OUTPUT
chains of the nat table. It specifies that the destination MAC
address has to be changed.
--to-destination address
Change the destination MAC address to the specified
address. The flag --to-dst is an alias for this option.
--dnat-target target
Specifies the standard target. After doing the dnat, the
rule still has to give a standard target so ebtables knows
what to do with the dnated frame. The default target is
ACCEPT. Making it CONTINUE could let you use multiple
target extensions on the same frame. Making it DROP only
makes sense in the BROUTING chain but using the redirect
target is more logical there. RETURN is also allowed. Note
that using RETURN in a base chain is not allowed (for
obvious reasons).
mark
The mark target can be used in every chain of every table. It is
possible to use the marking of a frame/packet in both ebtables and
iptables, if the bridge-nf code is compiled into the kernel. Both
put the marking at the same place. This allows for a form of
communication between ebtables and iptables.
--mark-set value
Mark the frame with the specified non-negative value.
--mark-or value
Or the frame with the specified non-negative value.
--mark-and value
And the frame with the specified non-negative value.
--mark-xor value
Xor the frame with the specified non-negative value.
--mark-target target
Specifies the standard target. After marking the frame, the
rule still has to give a standard target so ebtables knows
what to do. The default target is ACCEPT. Making it
CONTINUE can let you do other things with the frame in
subsequent rules of the chain.
redirect
The redirect target will change the MAC target address to that of
the bridge device the frame arrived on. This target can only be
used in the PREROUTING chain of the nat table. The MAC address of
the bridge is used as destination address."
--redirect-target target
Specifies the standard target. After doing the MAC
redirect, the rule still has to give a standard target so
ebtables knows what to do. The default target is ACCEPT.
Making it CONTINUE could let you use multiple target
extensions on the same frame. Making it DROP in the
BROUTING chain will let the frames be routed. RETURN is
also allowed. Note that using RETURN in a base chain is not
allowed.
snat
The snat target can only be used in the POSTROUTING chain of the
nat table. It specifies that the source MAC address has to be
changed.
--to-source address
Changes the source MAC address to the specified address.
The flag --to-src is an alias for this option.
--snat-target target
Specifies the standard target. After doing the snat, the
rule still has to give a standard target so ebtables knows
what to do. The default target is ACCEPT. Making it
CONTINUE could let you use multiple target extensions on
the same frame. Making it DROP doesn't make sense, but you
could do that too. RETURN is also allowed. Note that using
RETURN in a base chain is not allowed.
--snat-arp
Also change the hardware source address inside the arp
header if the packet is an arp message and the hardware
address length in the arp header is 6 bytes.
/etc/ethertypes
See http://netfilter.org/mailinglists.html
The version of ebtables this man page ships with does not support
the string match. Further, support for atomic-options (--atomic-
file, --atomic-init, --atomic-save, --atomic-commit) has not been
implemented, although ebtables-save and ebtables-restore might
replace them entirely given the inherent atomicity of nftables.
Finally, this list is probably not complete.
xtables-nft(8), iptables(8), ip(8)
See https://wiki.nftables.org
This page is part of the iptables (administer and maintain packet
filter rules) project. Information about the project can be found
at ⟨http://www.netfilter.org/⟩. If you have a bug report for this
manual page, see ⟨http://bugzilla.netfilter.org/⟩. This page was
obtained from the project's upstream Git repository
⟨git://git.netfilter.org/iptables⟩ on 2025-02-02. (At that time,
the date of the most recent commit that was found in the
repository was 2025-01-28.) 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
December 2011 EBTABLES(8)
Pages that refer to this page: arptables-nft(8), xtables-nft(8), xtables-translate(8)
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