Ubuntu Manpage: arptables - ARP table administration (legacy)

NAME

       arptables - ARP table administration (legacy)

SYNOPSIS

       arptables [-t table] -[AD] chain rule-specification [options]
       arptables [-t table] -[RI] chain rulenum rule-specification [options]
       arptables [-t table] -D chain rulenum [options]
       arptables [-t table] -[LFZ] [chain] [options]
       arptables [-t table] -[NX] chain
       arptables [-t table] -E old-chain-name new-chain-name
       arptables [-t table] -P chain target [options]

LEGACY

       This  tool  uses  the  old xtables/setsockopt framework, and is a legacy version of arptables. That means
       that a new, more modern tool exists with the same functionality using the nf_tables framework and you are
       encouraged to migrate now.  The new binaries (formerly  known  as  -compat)  uses  the  same  syntax  and
       semantics than this legacy one.

       You  can  still  use  this legacy tool. You should probably get some specific information from your Linux
       distribution or vendor.  More docs are available at https://wiki.nftables.org

DESCRIPTION

arptables is a user space tool, it is used to set up and maintain the tables of ARP rules in the Linux
kernel. These rules inspect the ARP frames which they see. arptables is analogous to the iptables user
space tool, but arptables is less complicated.

CHAINS
The kernel table is 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 ARP frames. If a rule matches an
ARP 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.

TARGETS
A firewall rule specifies criteria for an ARP 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
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 to know how many frames pass a certain point in the chain or to
log those frames. RETURN means stop traversing this chain and resume at the next rule in the previous
(calling) chain. For the extension targets please see the TARGET EXTENSIONS section of this man page.

TABLES
There is only one ARP table in the Linux kernel. The table is filter. You can drop the '-t filter'
argument to the arptables command. The -t argument must be the first argument on the arptables command
line, if used.

-t, --table
filter, is the only table and contains two (Linux kernels 2.4.X) or three (Linux kernels 2.6.0 and
later) built-in chains: INPUT (for frames destined for the host), OUTPUT (for locally-generated
frames) and FORWARD (for frames being forwarded by the bridge code). The FORWARD chain doesn't
exist in Linux 2.4.X kernels.

ARPTABLES COMMAND LINE ARGUMENTS

After the initial arptables 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.

COMMANDS
The arptables 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 the -Z command, only one command may be used on the command line at a time.

-A, --append
Append a rule to the end of the selected chain.

-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.

-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.

-R, --replace
Replaces 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 1 and N. i specifies the place
in the chain where the rule should be replaced.

-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 the
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.

-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.

-X, --delete-chain
Delete the specified user-defined chain. There must be no remaining references to the specified
chain, otherwise arptables 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 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 arptables chain names, please be sure to mention this fact should you post a
question on the arptables mailing lists. It would be wise to use the standard name in your post.
Renaming a standard arptables chain in this fashion has no effect on the structure or function of
the arptables kernel table.

MISCELLANEOUS COMMANDS
-V, --version
Show the version of the arptables userspace program.

-h, --help
Give a brief description of the command syntax.

-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.

-c, --set-counters PKTS BYTES
This enables the administrator to initialize the packet and byte counters of a rule (during
INSERT, APPEND, REPLACE operations).

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.

-s, --source-ip [!] address[/mask]
The Source IP specification.

-d, --destination-ip [!] address[/mask]
The Destination IP specification.

--source-mac [!] address[/mask]
The source mac address. Both mask and address are written as 6 hexadecimal numbers separated by
colons.

--destination-mac [!] address[/mask]
The destination mac address. Both mask and address are written as 6 hexadecimal numbers separated
by colons.

-i, --in-interface [!] name
The interface via which a frame is received (for the INPUT and FORWARD chains). The flag --in-if
is an alias for this option.

-o, --out-interface [!] name
The interface via which a frame is going to be sent (for the OUTPUT and FORWARD chains). The flag
--out-if is an alias for this option.

-l, --h-length length[/mask]
The hardware length (nr of bytes)

--opcode code[/mask]
The operation code (2 bytes). Available values are: 1=Request 2=Reply 3=Request_Reverse
4=Reply_Reverse 5=DRARP_Request 6=DRARP_Reply 7=DRARP_Error 8=InARP_Request 9=ARP_NAK.

--h-type type[/mask]
The hardware type (2 bytes, hexadecimal). Available values are: 1=Ethernet.

--proto-type type[/mask]
The protocol type (2 bytes). Available values are: 0x800=IPv4.

TARGET-EXTENSIONS
arptables extensions are precompiled into the userspace tool. So there is no need to explicitly load them
with a -m option like in iptables. However, these extensions deal with functionality supported by
supplemental kernel modules.

mangle
--mangle-ip-s IP address
Mangles Source IP Address to given value.

--mangle-ip-d IP address
Mangles Destination IP Address to given value.

--mangle-mac-s MAC address
Mangles Source MAC Address to given value.

--mangle-mac-d MAC address
Mangles Destination MAC Address to given value.

--mangle-target target
Target of ARP mangle operation (DROP, CONTINUE or ACCEPT -- default is ACCEPT).

CLASSIFY
This module allows you to set the skb->priority value (and thus clas- sify the packet into a specific
CBQ class).

--set-class major:minor

Set the major and minor class value. The values are always interpreted as hexadecimal even
if no 0x prefix is given.

MARK
This module allows you to set the skb->mark value (and thus classify the packet by the mark in u32)

--set-mark mark
Set the mark value. The values are always interpreted as hexadecimal even if no 0x prefix is
given

--and-mark mark
Binary AND the mark with bits.

--or-mark mark
Binary OR the mark with bits.

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