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EBTABLES(8) System Manager's Manual EBTABLES(8)
NAME
ebtables (v2.0.10-4) - Ethernet bridge frame table administration
SYNOPSIS
ebtables [-t table ] -[ACDI] chain rule specification [match extensions] [watcher exten-
sions] 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 applica-
tion, 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 'tar-
get' 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 specifica-
tion 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, there are three ebtables tables in the Linux kernel. The table names
are filter, nat and broute. Of these three tables, 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 the other two tables. Moreover, the -t argument must be the first argu-
ment 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), OUT-
PUT (for locally-generated or (b)routed frames) and FORWARD (for frames being for-
warded 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
instead of more descriptive names to keep the implementation generic). DROP actu-
ally means the frame has to be routed, while ACCEPT means the frame has to be
bridged. The BROUTING chain is traversed very early. However, it is only traversed
by frames entering on a bridge port that is in forwarding state. Normally those
frames would be bridged, but you can decide otherwise here. The redirect target is
very handy here.
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 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, 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 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 com-
mands to construct the contents of the table are given, including commands for cre-
ating 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 ebta-
bles mailing lists. It would be wise to use the standard name in your post. Renam-
ing 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 spec-
ified using the --atomic-file command or through the EBTABLES_ATOMIC_FILE environ-
ment 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 spec-
ified using the --atomic-file command or through the EBTABLES_ATOMIC_FILE environ-
ment 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 allowing 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 set-
ting 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 populate 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. ebta-
bles -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, CON-
TINUE, 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 specifica-
tion. An alternative that should be preferred, is setting the EBTABLES_ATOMIC_FILE
environment variable.
-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 before the specification inverts the test for that specifi-
cation. 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 net-
works). 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 hexa-
decimal 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, 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 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 con-
sulted to determine the payload protocol. This is a two byte (hexadecimal) argu-
ment. 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 pos-
sible.
--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 sup-
ported. 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 speci-
fied, 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 omit-
ted (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 con-
figuration 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 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 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 mes-
sage 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 pay-
load 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 BROUTING chain of the broute table and the PRE-
ROUTING 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 mark-
ing 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 commu-
nication 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. Mak-
ing 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 BROUTING chain of the broute table
and the PREROUTING chain of the nat table. In the BROUTING chain, the MAC address of the
bridge port is used as destination address, in the PREROUTING chain, the MAC address of
the bridge is used.
--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.
FILES
/etc/ethertypes /run/ebtables.lock
ENVIRONMENT VARIABLES
EBTABLES_ATOMIC_FILE
MAILINGLISTS
See http://netfilter.org/mailinglists.html
SEE ALSO
iptables(8), brctl(8), ifconfig(8), route(8)
See http://ebtables.sf.net
December 2011 EBTABLES(8)
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