EBTABLES(8) System Manager's Manual EBTABLES(8)
NAME
ebtables - Ethernet bridge frame table administration (nft-based)
SYNOPSIS
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 [-t table ] [--atomic-file file] --atomic-commit
ebtables [-t table ] [--atomic-file file] --atomic-init
ebtables [-t table ] [--atomic-file file] --atomic-save
DESCRIPTION
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 pro‐
tocol is much simpler than the IP protocol.
CHAINS
There are two 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 Ether‐
net 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. 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, there are two ebtables tables in the Linux kernel. The table names are filter and nat. Of these two ta‐
bles, the filter table is the default table that the command operates on. If you are working with the filter table, then
you can drop the '-t filter' argument to the ebtables command. However, you will need to provide the -t argument for nat
table. 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.
EBTABLES COMMAND LINE ARGUMENTS
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 ex‐
tensions.
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 com‐
mand line at a time, except when the commands -L and -Z are combined, the commands -N and -P are combined, or when --atomic-
file is used.
-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 nega‐
tive 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 com‐
mand. 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 op‐
tion 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, other‐
wise 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.
--atomic-init
Copy the kernel's initial data of the table to the specified file. This can be used as the first action, after which
rules are added to the file. The file can be specified using the --atomic-file command or through the EBTA‐
BLES_ATOMIC_FILE environment variable.
--atomic-save
Copy the kernel's current data of the table to the specified file. This can be used as the first action, after which
rules are added to the file. The file can be specified using the --atomic-file command or through the EBTA‐
BLES_ATOMIC_FILE environment variable.
--atomic-commit
Replace the kernel table data with the data contained in the specified file. This is a useful command that allows you
to load all your rules of a certain table into the kernel at once, saving the kernel a lot of precious time and al‐
lowing atomic updates of the tables. The file which contains the table data is constructed by using either the
--atomic-init or the --atomic-save command to generate a starting file. After that, using the --atomic-file command
when constructing rules or setting the EBTABLES_ATOMIC_FILE environment variable allows you to extend the file and
build the complete table before committing it to the kernel. This command can be very useful in boot scripts to popu‐
late the ebtables tables in a fast way.
MISCELLANOUS COMMANDS
-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 exten‐
sions 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.
--atomic-file file
Let the command operate on the specified file. The data of the table to operate on will be extracted from the file
and the result of the operation will be saved back into the file. If specified, this option should come before the
command specification. An alternative that should be preferred, is setting the EBTABLES_ATOMIC_FILE environment vari‐
able.
-M, --modprobe program
When talking to the kernel, use this program to try to automatically load missing kernel modules.
--concurrent
Use a file lock to support concurrent scripts updating the ebtables kernel tables.
RULE SPECIFICATIONS
The following command line arguments make up a rule specification (as used in the add and delete commands). A "!" option be‐
fore 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 (disre‐
garding '+') 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 (dis‐
regarding '+') 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 (disre‐
garding '+') 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, Broad‐
cast=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 proto‐
col. 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 ad‐
dress 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 pack‐
ets 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 op‐
tion 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 op‐
tion 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, sym‐
bolic 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 ad‐
dress (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, de‐
nothing 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 sym‐
bolic 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 loggin 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 infor‐
mation 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 combi‐
nation with nfnetlink_log as logging backend, which will multicast the packet through a netlink socket to the specified mul‐
ticast 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 spec‐
ify 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 allo‐
cated 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 auto‐
matically 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 tar‐
get 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 ebta‐
bles 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 RE‐
TURN 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 ad‐
dress length in the arp header is 6 bytes.
FILES
/etc/ethertypes
ENVIRONMENT VARIABLES
EBTABLES_ATOMIC_FILE
MAILINGLISTS
See http://netfilter.org/mailinglists.html
BUGS
The version of ebtables this man page ships with does not support the broute table. Also there is no support for string
match. And finally, this list is probably not complete.
SEE ALSO
xtables-nft(8), iptables(8), ip(8)
See https://wiki.nftables.org
December 2011 EBTABLES(8)