ebtables.8

.TH EBTABLES 8  "15 March 2003"
.\"
.\" Man page written by Bart De Schuymer <bdschuym@pandora.be>
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.SH NAME
ebtables (v.2.0) \- Ethernet bridge frame table administration
.SH SYNOPSIS
.BR "ebtables [-t table] -[ADI] " "chain rule-specification [match-extensions] [watcher-extensions] TARGET"
.br
.BR "ebtables [-t table] -P " "chain " "ACCEPT | DROP | RETURN"
.br
.BR "ebtables [-t table] -F [" "chain" "]"
.br
.BR "ebtables [-t table] -Z [" "chain" "]"
.br
.BR "ebtables [-t table] -L [-Z] [" chain "] [ [" --Ln "] [" --Lc "] ] " | " [" --Lx "]"
.br
.BR "ebtables [-t table] -[NX] " chain
.br
.BR "ebtables [-t table] -E " "old-chain-name new-chain-name"
.br
.BR "ebtables [-t table] --init-table"
.br
.BR "ebtables [-t table] [--atomic-file file] --atomic-commit
.br
.BR "ebtables [-t table] [--atomic-file file] --atomic-init"
.br
.BR "ebtables [-t table] [--atomic-file file] --atomic-save"
.br
.SH DESCRIPTION
.B ebtables
is a user space tool, it is used to set up and maintain the
tables of Ethernet frame rules in the Linux kernel. These rules inspect
the Ethernet frames which they see.
.B ebtables
is analogous to the
.B iptables
user space tool, but
.B ebtables
is less complicated.

.SS CHAINS
There are three Ethernet frame tables with built-in chains in the
Linux kernel. The kernel 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 which can be used as the 'target' of a rule.

.SS 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:
.IR ACCEPT ,
.IR DROP ,
.IR CONTINUE ,
.IR RETURN ,
an 'extension' (see below) or a user-defined chain.
.PP
.I ACCEPT
means to let the frame through.
.I DROP
means the frame has to be dropped.
.I CONTINUE
means the next rule has to be checked. This can be handy to know how many
frames pass a certain point in the chain or to log those frames.
.I RETURN
means stop traversing this chain and resume at the next rule in the
previous (calling) chain.
For the extension targets please see the
.B "TARGET EXTENSIONS"
section of this man page.
.SS TABLES
As stated earlier, there are three Ethernet frame tables in the Linux
kernel.  The tables are
.BR filter ", " nat " and " broute .
Of these three tables,
the filter table is the default table that the
.B ebtables
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.  The -t argument must be the
first argument on the ebtables command line, if used. 
.TP
.B "-t, --table"
.br
.BR filter ,
is the default table and contains three built-in chains:
.B INPUT 
(for frames destined for the bridge itself), 
.B OUTPUT 
(for locally-generated frames) and
.B FORWARD 
(for frames being bridged).
.br
.br
.BR nat ,
is used to change the mac addresses and contains three built-in chains:
.B PREROUTING 
(for altering frames as soon as they come in), 
.B OUTPUT 
(for altering locally generated frames before they are bridged) and 
.B POSTROUTING
(for altering frames as they are about to go out). A small note on the naming
of chains POSTROUTING and PREROUTING: it would be more accurate to call them
PREFORWARDING and POSTFORWARDING, but for all those who come from the
.BR iptables " world to " ebtables
it is easier to have the same names.
.br
.br
.BR broute ,
is used to make a brouter, it has one built-in chain:
.BR BROUTING .
The targets
.BR DROP " and " ACCEPT
have special meaning in the broute table.
.B DROP
actually means the frame has to be routed, while
.B ACCEPT
means the frame has to be bridged. The
.B BROUTING
chain is traversed very early. It is only traversed by frames entering on
a bridge enslaved NIC that is in forwarding state. Normally those frames
would be bridged, but you can decide otherwise here. The
.B redirect
target is very handy here.
.SH EBTABLES COMMAND LINE ARGUMENTS
After the initial ebtables -t, table command line argument, the remaining
arguments can be divided into several different groups.  These groups
are commands, miscellaneous commands, rule-specifications, match-extensions,
and watcher-extensions.
.SS 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.
With the exception of both the
.B "-Z"
and
.B "--atomic-file"
commands, only one command may be used on the command line at a time.
.TP
.B "-A, --append"
Append a rule to the end of the selected chain.
.TP
.B "-D, --delete"
Delete the specified rule from the selected chain. There are two ways to
use this command. The first is by specifying an interval of rule numbers
to delete, syntax: start_nr[:end_nr]. 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.
.TP
.B "-I, --insert"
Insert the specified rule into the selected chain at the specified rule number.
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 number 0 specifies
the place past the last rule in the chain and using this number is therefore
equivalent with using the -A command.
.TP
.B "-P, --policy"
Set the policy for the chain to the given target. The policy can be
.BR ACCEPT ", " DROP " or " RETURN .
.TP
.B "-F, --flush"
Flush the selected chain. If no chain is selected, then every chain will be
flushed. Flushing the chain does not change the policy of the
chain, however.
.TP
.B "-Z, --zero"
Set the counters of the selected chain to zero. If no chain is selected, all the counters
are set to zero. The
.B "-Z"
command can be used in conjunction with the 
.B "-L"
command.
When both the
.B "-Z"
and
.B "-L"
commands are used together in this way, the rule counters are printed on the screen
before they are set to zero.
.TP
.B "-L, --list"
List all rules in the selected chain. If no chain is selected, all chains
are listed.
.br
The following three options change the output of the
.B "-L"
list command:
.br
.B "--Ln"
.br
Places the rule number in front of every rule.
.br
.B "--Lc"
.br
Shows the counters at the end of each rule displayed by the
.B "-L"
command. Both a frame counter (pcnt) and a byte counter (bcnt) are displayed.
.br
.B "--Lx"
.br
The output of the 
.B "--Lx"
option may be used to create a set of
.B ebtables
commands.  You may use this set of commands in an
.B ebtables
boot or reload
script.  For example the output could be used at system startup.
The 
.B "--Lx"
option is incompatible with both of the other
.B "--Ln"
and
.B "--Lc"
chain listing options, 
.B "-L."
All necessary
.B ebtables
commands for making the current list of
user-defined chains in the kernel and any commands issued by the user to
rename the standard
.B ebtables
chains will be listed, when no chain name is
supplied for the
.B "-L"
command while using the
.B "-Lx"
option.
.TP
.B "-N, --new-chain"
Create a new user-defined chain with the given name. The number of
user-defined chains is unlimited. A user-defined chain name has maximum
length of 31 characters.
.TP
.B "-X, --delete-chain"
Delete the specified user-defined chain. There must be no remaining references
to the to be deleted chain.  Otherwise,
.B ebtables
will complain if there are.
.TP
.B "-E, --rename-chain"
Rename the specified chain to a new name.  Besides renaming a user-defined
chain, you may rename a standard chain name to a name that suits your
taste. For example, if you like PREBRIDGING more than PREROUTING,
then you can use the -E command to rename the PREROUTING chain. If you do
rename one of the standard
.B ebtables
chain names, please be sure to mention
this fact should you post a question on the
.B ebtables
mailing lists.
It would be wise to use the standard name in your post. Renaming a standard
.B ebtables
chain in this fashion has no effect on the structure or function
of the
.B ebtables
kernel table.
.TP
.B "--init-table"
Replace the current table data by the initial table data.
.TP
.B "--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
.B --atomic-file
command or through the
.IR EBTABLES_ATOMIC_FILE " environment variable."
.TP
.B "--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
.B --atomic-file
command or through the
.IR EBTABLES_ATOMIC_FILE " environment variable."
.TP
.B "--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
.B "--atomic-init"
or the
.B "--atomic-save"
command to generate a starting file. After that, using the
.B "--atomic-file"
command when constructing rules or setting the
.IR EBTABLES_ATOMIC_FILE " environment variable"
allows you to extend the file and build the complete table before
committing it to the kernel.
.TP
.B "--atomic-file -Z"
The counters stored in a file with, say,
.B "--atomic-init"
can be optionally zeroed by supplying the
.B "-Z"
command. You may also zero the counters by setting the
.IR EBTABLES_ATOMIC_FILE " environment variable."

.SS MISCELLANOUS COMMANDS
.TP
.B "-V, --version"
Show the version of the ebtables userspace program.
.TP
.B "-h, --help"
Give a brief description of the command syntax. Here you can also specify
names of extensions and
.B ebtables
will try to write help about those extensions. E.g. ebtables -h snat log ip arp.
Specify
.I list_extensions
to list all extensions supported by the userspace
utility.
.TP
.BR "-j, --jump " "\fItarget\fP"
The target of the rule. This is one of the following values:
.BR ACCEPT ,
.BR DROP ,
.BR CONTINUE ,
.BR RETURN ,
a target extension (see
.BR "TARGET EXTENSIONS" ")"
or a user-defined chain name.
.TP
.B --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
.IR EBTABLES_ATOMIC_FILE " environment variable."
.TP
.B -M, --modprobe program
When talking to the kernel, use this program to try to automatically load
missing kernel modules.

.SS
RULE-SPECIFICATIONS
The following command line arguments make up a rule specification (as used 
in the add and delete commands). A "!" option before the specification 
inverts the test for that specification. Apart from these standard rule 
specifications there are some other command line arguments of interest.
See both the 
.BR "MATCH-EXTENSIONS" 
and the
.BR "WATCHER-EXTENSION(S)" 
below.
.TP
.BR "-p, --protocol " "[!] \fIprotocol\fP"
The protocol that was responsible for creating the frame. This can be a
hexadecimal number, above 
.IR 0x0600 ,
a name (e.g.
.I ARP
) or
.BR 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)
.IR 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
.B ebtables
for these frames is
.BR LENGTH .
.br
The file
.B /etc/ethertypes
can be used to show readable
characters instead of hexadecimal numbers for the protocols. For example,
.I 0x0800
will be represented by 
.IR IPV4 .
The use of this file is not case sensitive. 
See that file for more information. The flag 
.B --proto
is an alias for this option.
.TP 
.BR "-i, --in-interface " "[!] \fIname\fP"
The interface via which a frame is received (for the
.BR INPUT ,
.BR FORWARD ,
.BR PREROUTING " and " BROUTING
chains). The flag
.B --in-if
is an alias for this option.
.TP
.BR "--logical-in " "[!] \fIname\fP"
The (logical) bridge interface via which a frame is received (for the
.BR INPUT ,
.BR FORWARD ,
.BR PREROUTING " and " BROUTING
chains).
.TP
.BR "-o, --out-interface " "[!] \fIname\fP"
The interface via which a frame is going to be sent (for the
.BR OUTPUT ,
.B FORWARD
and
.B POSTROUTING
chains). The flag
.B --out-if
is an alias for this option.
.TP
.BR "--logical-out " "[!] \fIname\fP"
The (logical) bridge interface via which a frame is going to be sent (for
the
.BR OUTPUT ,
.B FORWARD
and
.B POSTROUTING
chains).
.TP
.BR "-s, --source " "[!] \fIaddress\fP[/\fImask\fP]"
The source mac address. Both mask and address are written as 6 hexadecimal
numbers separated by colons. Alternatively one can specify Unicast,
Multicast or Broadcast.
.br
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 and
Broadcast=ff:ff:ff:ff:ff:ff/ff:ff:ff:ff:ff:ff. Note that a broadcast
address will also match the multicast specification. The flag
.B --src
is an alias for this option.
.TP
.BR "-d, --destination " "[!] \fIaddress\fP[/\fImask\fP]"
The destination mac address. See -s (above) for more details. The flag
.B --dst
is an alias for this option.

.SS MATCH-EXTENSIONS
.B ebtables
extensions are precompiled into the userspace tool. So there is no need
to explicitly load them with a -m option like in
.BR iptables .
However, these
extensions deal with functionality supported by supplemental kernel modules.
.SS arp
Specify arp fields. These will only work if the protocol equals
.BR ARP " or " RARP .
.TP
.BR "--arp-opcode " "[!] \fIopcode\fP"
The (r)arp opcode (decimal or a string, for more details see
.BR "ebtables -h arp" ).
.TP
.BR "--arp-htype " "[!] \fIhardware type\fP"
The hardware type, this can be a decimal or the string "Ethernet". This
is normally Ethernet (value 1).
.TP
.BR "--arp-ptype " "[!] \fIprotocol type\fP"
The protocol type for which the (r)arp is used (hexadecimal or the string "IPv4").
This is normally IPv4 (0x0800).
.TP
.BR "--arp-ip-src " "[!] \fIaddress\fP[/\fImask\fP]"
The ARP IP source address specification.
.TP
.BR "--arp-ip-dst " "[!] \fIaddress\fP[/\fImask\fP]"
The ARP IP destination address specification.
.SS ip
Specify ip fields. These will only work if the protocol equals
.BR IPv4 .
.TP
.BR "--ip-source " "[!] \fIaddress\fP[/\fImask\fP]"
The source ip address.
The flag
.B --ip-src
is an alias for this option.
.TP
.BR "--ip-destination " "[!] \fIaddress\fP[/\fImask\fP]"
The destination ip address.
The flag
.B --ip-dst
is an alias for this option.
.TP
.BR "--ip-tos " "[!] \fItos\fP"
The ip type of service, in hexadecimal numbers.
.BR IPv4 .
.TP
.BR "--ip-protocol " "[!] \fIprotocol\fP"
The ip protocol.
The flag
.B --ip-proto
is an alias for this option.
.TP
.BR "--ip-source-port " "[!] \fIport\fP[:\fIport\fP]"
The source port or port range for the ip protocols 6 (TCP) and 17
(UDP). If the first port is omitted, "0" is assumed; if the last
is omitted, "65535" is assumed. The flag
.B --ip-sport
is an alias for this option.
.TP
.BR "--ip-destination-port " "[!] \fIport\fP[:\fIport\fP]"
The destination port or port range for ip protocols 6 (TCP) and
17 (UDP). The flag
.B --ip-dport
is an alias for this option.
.SS mark_m
.TP
.BR "--mark " "[!] [\fIvalue\fP][/\fImask\fP]"
Matches frames with the given unsigned mark value. If a mark value and
mask is 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. If only a mask is specified (start with '/') the logical AND
of the mark value of the frame and the user-specified mark is taken and
the result is compared with zero.
.SS vlan
Specify 802.1Q Tag Control Information fields.
The protocol rule specification (frame type) should be set to
.BR 802_1Q " (0x8100)."
.TP
.BR "--vlan-id " "[!] \fIid\fP"
The VLAN identifier field (VID). Decimal number from 0 to 4095.
.TP
.BR "--vlan-prio " "[!] \fIprio\fP"
The user_priority field. Decimal number from 0 to 7.
The VID should be set to 0 ("null VID") or unspecified
(for this case the VID is deliberately set to 0).
.TP
.BR "--vlan-encap " "[!] \fItype\fP"
The encapsulated Ethernet frame type/length.
Specified as hexadecimal
number from 0x0000 to 0xFFFF or as a symbolic name
from
.BR /etc/ethertypes .

.SS WATCHER-EXTENSION(S)
Watchers are things that only look at frames passing by. These watchers only
see the frame if the frame matches the rule.
.SS log
The fact that the log module is a watcher lets us log stuff while giving a target
by choice. Note that the log module therefore is not a target.
.TP
.B "--log"
.br
Use this if you won't specify any other log options, so if you want to use the default
settings: log-prefix="", no arp logging, no ip logging, log-level=info.
.TP
.B --log-level "\fIlevel\fP"
.br
defines the logging level. For the possible values: ebtables -h log.
The default level is 
.IR info .
.TP
.BR --log-prefix " \fItext\fP"
.br
defines the prefix to be printed before the logging information.
.TP
.B --log-ip 
.br
will log the ip information when a frame made by the ip protocol matches 
the rule. The default is no ip information logging.
.TP
.B --log-arp
.br
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.
.SS TARGET EXTENSIONS
.SS
.B dnat
The
.B dnat
target can only be used in the
.BR BROUTING " chain of the " broute " table and the "
.BR PREROUTING " and " OUTPUT " chains of the " nat " table."
It specifies that the destination mac address has to be changed.
.TP
.BR "--to-destination " "\fIaddress\fP"
.br
The flag
.B --to-dst
is an alias for this option.
.TP
.BR "--dnat-target " "\fItarget\fP"
.br
Specifies the standard target. After doing the dnat, the rule still has to
give a standard target so
.B 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 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.
.SS
.B mark
The mark target can be used in every chain of every table. It is possible
to use the marking of a frame/packet in both ebtables and iptables,
if the br-nf code is compiled into the kernel. Both put the marking at the
same place. So, you can consider this fact as a feature, or as something to
watch out for.
.TP
.BR "--set-mark " "\fIvalue\fP"
.br
Mark the frame with the specified unsigned value.
.TP
.BR "--mark-target " "\fItarget\fP"
.br
Specifies the standard target. After marking the frame, the rule
still has to give a standard target so
.B ebtables
knows what to do.
The default target is ACCEPT. Making it CONTINUE can let you do other
things with the frame in other rules of the chain.
.SS
.B redirect
The
.B 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
.BR BROUTING " chain of the " broute " table and the "
.BR PREROUTING " chain of the " nat " table."
.TP
.BR "--redirect-target " "\fItarget\fP"
.br
Specifies the standard target. After doing the MAC redirect, the rule
still has to give a standard target so
.B 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.
.SS
.B snat
The
.B snat
target can only be used in the
.BR POSTROUTING " chain of the " nat " table."
It specifies that the source mac address has to be changed.
.TP
.BR "--to-source " "\fIaddress\fP"
.br
The flag
.B --to-src
is an alias for this option.
.TP
.BR "--snat-target " "\fItarget\fP"
.br
Specifies the standard target. After doing the snat, the rule still has 
to give a standard target so
.B 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.
.br
.SH FILES
.I /etc/ethertypes
.SH ENVIRONMENT VARIABLES
.I EBTABLES_ATOMIC_FILE
.SH BUGS
This won't work on an architecture with a user32/kernel64 situation like the Sparc64.
.SH MAILINGLISTS
.I ebtables-user@lists.sourceforge.net
.br
.I ebtables-devel@lists.sourceforge.net
.SH SEE ALSO
.BR iptables "(8), " brctl "(8), " ifconfig "(8), " route (8)