man
8 ebtables
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 exten-
sions] [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
DESCRIPTION
This tool is deprecated in Red Hat Enterprise Linux. It is maintenance
only and will not receive new features. New setups should use nft(8).
Existing setups should migrate to nft(8) when possible. See
<https://red.ht/nft_your_tables> for details.
ebtables is an application program used to set up and maintain the ta-
bles 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 pro-
tocol.
CHAINS
There are three ebtables tables with built-in chains in the Linux ker-
nel. These tables are used to divide functionality into different sets
of rules. Each set of rules is called a chain. Each chain is an or-
dered 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 'tar-
get' of a rule. User-defined chains are very useful to get better per-
formance over the linear traversal of the rules and are also essential
for structuring the filtering rules into well-organized and maintain-
able 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 tar-
get. 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.
EBTABLES COMMAND LINE ARGUMENTS
After the initial ebtables '-t table' command line argument, the re-
maining arguments can be divided into several groups. These groups are
commands, miscellaneous commands, rule specifications, match exten-
sions, 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 specify-
ing 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 com-
mand. The second usage is by specifying the complete rule as it
would have been specified when it was added. Only the first en-
countered 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 se-
lected 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 speci-
fied 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 cur-
rent counters are changed to the specified counters.
-I, --insert
Insert the specified rule into the selected chain at the speci-
fied 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 pol-
icy 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 com-
bination 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 com-
mands 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 com-
mands in an ebtables boot or reload script. For example the
output could be used at system startup. The --Lx option is in-
compatible 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 ze-
roes if necessary. The default representation omits leading ze-
roes 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 dif-
ferent 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 re-
maining 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 ebta-
bles 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 ebta-
bles 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.
MISCELLANOUS COMMANDS
-v, --verbose
Verbose mode. For appending, insertion, deletion and replace-
ment, 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: AC-
CEPT, DROP, CONTINUE, RETURN, a target extension (see TARGET EX-
TENSIONS) or a user-defined chain name.
-M, --modprobe program
When talking to the kernel, use this program to try to automati-
cally load missing kernel modules.
--concurrent
Use a file lock to support concurrent scripts updating the ebta-
bles kernel tables.
RULE SPECIFICATIONS
The following command line arguments make up a rule specification (as
used in the add and delete commands). A "!" option before the specifi-
cation inverts the test for that specification. Apart from these stan-
dard rule specifications there are some other command line arguments of
interest. See both the MATCH EXTENSIONS and the WATCHER EXTENSIONS be-
low.
-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 proto-
col 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 POSTROUT-
ING chains). If the interface name ends with '+', then any in-
terface 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 POSTROUT-
ING chains). If the interface name ends with '+', then any in-
terface 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 Ad-
dress):
Unicast=00:00:00:00:00:00/01:00:00:00:00:00, Multi-
cast=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 al-
ways equal, so only one byte (hexadecimal) is needed as an argu-
ment.
--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 ad-
dresses and MAC/IP address pairs. A list entry has the following for-
mat: xx:xx:xx:xx:xx:xx[=ip.ip.ip.ip][,]. Multiple list entries are sep-
arated 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 destina-
tion 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 op-
tion.
--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 op-
tion.
--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 omit-
ted, 0:port2 is used; if port2 is omitted but a colon is speci-
fied, 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 sin-
gle 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 exam-
ple. 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 deter-
mined by the generic networking code. Possible values: broadcast
(MAC destination is the broadcast address), multicast (MAC des-
tination 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 con-
fig, 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 topol-
ogy-change, denoting the topology change flag (=1), and topol-
ogy-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 de-
tails.
--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 de-
cide 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 exe-
cuted.
log
The log watcher writes descriptive data about a frame to the syslog.
--log
Log with the default loggin options: log-level= info, log-pre-
fix="", 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 pro-
tocol matches the rule. The default is no ipv6 information log-
ging.
--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 appli-
cable for nfnetlink_log). The default value is 1.
--nflog-prefix prefix
A prefix string to include in the log message, up to 30 charac-
ters 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 de-
scriptive 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 match-
ing 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 ta-
ble. 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 Eth-
ernet 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 ad-
dress.
--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. RE-
TURN 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 possi-
ble 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. RE-
TURN 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 al-
lowed.
--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.
FILES
/etc/ethertypes
MAILINGLISTS
See http://netfilter.org/mailinglists.html
BUGS
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 imple-
mented, although ebtables-save and ebtables-restore might replace them
entirely given the inherent atomicity of nftables. Finally, this list
is probably not complete.
SEE ALSO
xtables-nft(8), iptables(8), ip(8), nft(8)
See https://wiki.nftables.org
December 2011 EBTABLES(8)