ARPTABLES(8) System Manager's Manual ARPTABLES(8)
NAME
arptables — ARP table administration (nft-based)
SYNOPSIS
arptables [-t table] {-A|-D} chain rule-specification [options...]
arptables [-t table] -I chain [rulenum] rule-specification
arptables [-t table] -R chain rulenum rule-specification
arptables [-t table] -D chain rulenum
arptables [-t table] {-F|-L|-Z} [chain [rulenum]] [options...]
arptables [-t table] -N chain
arptables [-t table] -X [chain]
arptables [-t table] -P chain policy
arptables [-t table] -E old-chain-name new-chain-name
rule-specification := [matches...] [target]
match := -m matchname [per-match-options]
target := -j targetname [per-target-options]
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 process-
ing 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 tar-
gets 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 built-in chains: INPUT
(for frames destined for the host) and OUTPUT (for locally-gener-
ated frames).
ARPTABLES COMMAND LINE ARGUMENTS
After the initial arptables command line argument, the remaining argu-
ments 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 nega-
tive numbers is allowed, for more details about using negative
numbers, see the -I command. The second usage is by specifying
the complete rule as it would have been specified when it was
added.
-I, --insert
Insert the specified rule into the selected chain at the speci-
fied 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 speci-
fied 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 remain-
ing 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 arpta-
bles 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 arpta-
bles 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: AC-
CEPT, DROP, CONTINUE, RETURN, a target extension (see TARGET EX-
TENSIONS) 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 specifica-
tion inverts the test for that specification. Apart from these standard
rule specifications there are some other command line arguments of in-
terest.
-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
chain). 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 OUT-
PUT chain). 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 supple-
mental 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 — de-
fault is ACCEPT).
CLASSIFY
This module allows you to set the skb->priority value (and thus classify
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 hexa-
decimal 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.
NOTES
In this nft-based version of arptables, support for FORWARD chain has
not been implemented. Since ARP packets are "forwarded" only by Linux
bridges, the same may be achieved using FORWARD chain in ebtables.
MAILINGLISTS
See http://netfilter.org/mailinglists.html
SEE ALSO
xtables-nft(8), iptables(8), ebtables(8), ip(8)
See https://wiki.nftables.org
March 2019 ARPTABLES(8)
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