|
NAME | SYNOPSIS | DESCRIPTION | TARGETS | TABLES | OPTIONS | MATCH AND TARGET EXTENSIONS | DIAGNOSTICS | BUGS | COMPATIBILITY WITH IPCHAINS | SEE ALSO | AUTHORS | VERSION | COLOPHON |
|
IPTABLES(8) iptables 1.6.1 IPTABLES(8)
iptables/ip6tables — administration tool for IPv4/IPv6 packet filter‐
ing and NAT
iptables [-t table] {-A|-C|-D} chain rule-specification
ip6tables [-t table] {-A|-C|-D} chain rule-specification
iptables [-t table] -I chain [rulenum] rule-specification
iptables [-t table] -R chain rulenum rule-specification
iptables [-t table] -D chain rulenum
iptables [-t table] -S [chain [rulenum]]
iptables [-t table] {-F|-L|-Z} [chain [rulenum]] [options...]
iptables [-t table] -N chain
iptables [-t table] -X [chain]
iptables [-t table] -P chain target
iptables [-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]
Iptables and ip6tables are used to set up, maintain, and inspect the
tables of IPv4 and IPv6 packet filter rules in the Linux kernel.
Several different tables may be defined. Each table contains a
number of built-in chains and may also contain user-defined chains.
Each chain is a list of rules which can match a set of packets. Each
rule specifies what to do with a packet that matches. This is called
a `target', which may be a jump to a user-defined chain in the same
table.
A firewall rule specifies criteria for a packet and a target. If the
packet does not match, the next rule in the chain is examined; if it
does match, then the next rule is specified by the value of the
target, which can be the name of a user-defined chain, one of the
targets described in iptables-extensions(8), or one of the special
values ACCEPT, DROP or RETURN.
ACCEPT means to let the packet through. DROP means to drop the
packet on the floor. RETURN means stop traversing this chain and
resume at the next rule in the previous (calling) chain. If the end
of a built-in chain is reached or a rule in a built-in chain with
target RETURN is matched, the target specified by the chain policy
determines the fate of the packet.
There are currently five independent tables (which tables are present
at any time depends on the kernel configuration options and which
modules are present).
-t, --table table
This option specifies the packet matching table which the
command should operate on. If the kernel is configured with
automatic module loading, an attempt will be made to load the
appropriate module for that table if it is not already there.
The tables are as follows:
filter:
This is the default table (if no -t option is passed). It
contains the built-in chains INPUT (for packets destined
to local sockets), FORWARD (for packets being routed
through the box), and OUTPUT (for locally-generated
packets).
nat:
This table is consulted when a packet that creates a new
connection is encountered. It consists of four built-ins:
PREROUTING (for altering packets as soon as they come in),
INPUT (for altering packets destined for local sockets),
OUTPUT (for altering locally-generated packets before
routing), and POSTROUTING (for altering packets as they
are about to go out). IPv6 NAT support is available since
kernel 3.7.
mangle:
This table is used for specialized packet alteration.
Until kernel 2.4.17 it had two built-in chains: PREROUTING
(for altering incoming packets before routing) and OUTPUT
(for altering locally-generated packets before routing).
Since kernel 2.4.18, three other built-in chains are also
supported: INPUT (for packets coming into the box itself),
FORWARD (for altering packets being routed through the
box), and POSTROUTING (for altering packets as they are
about to go out).
raw:
This table is used mainly for configuring exemptions from
connection tracking in combination with the NOTRACK
target. It registers at the netfilter hooks with higher
priority and is thus called before ip_conntrack, or any
other IP tables. It provides the following built-in
chains: PREROUTING (for packets arriving via any network
interface) OUTPUT (for packets generated by local
processes)
security:
This table is used for Mandatory Access Control (MAC)
networking rules, such as those enabled by the SECMARK and
CONNSECMARK targets. Mandatory Access Control is
implemented by Linux Security Modules such as SELinux.
The security table is called after the filter table,
allowing any Discretionary Access Control (DAC) rules in
the filter table to take effect before MAC rules. This
table provides the following built-in chains: INPUT (for
packets coming into the box itself), OUTPUT (for altering
locally-generated packets before routing), and FORWARD
(for altering packets being routed through the box).
The options that are recognized by iptables and ip6tables can be
divided into several different groups.
COMMANDS
These options specify the desired action to perform. Only one of them
can be specified on the command line unless otherwise stated below.
For long versions of the command and option names, you need to use
only enough letters to ensure that iptables can differentiate it from
all other options.
-A, --append chain rule-specification
Append one or more rules to the end of the selected chain.
When the source and/or destination names resolve to more than
one address, a rule will be added for each possible address
combination.
-C, --check chain rule-specification
Check whether a rule matching the specification does exist in
the selected chain. This command uses the same logic as -D to
find a matching entry, but does not alter the existing
iptables configuration and uses its exit code to indicate
success or failure.
-D, --delete chain rule-specification
-D, --delete chain rulenum
Delete one or more rules from the selected chain. There are
two versions of this command: the rule can be specified as a
number in the chain (starting at 1 for the first rule) or a
rule to match.
-I, --insert chain [rulenum] rule-specification
Insert one or more rules in the selected chain as the given
rule number. So, if the rule number is 1, the rule or rules
are inserted at the head of the chain. This is also the
default if no rule number is specified.
-R, --replace chain rulenum rule-specification
Replace a rule in the selected chain. If the source and/or
destination names resolve to multiple addresses, the command
will fail. Rules are numbered starting at 1.
-L, --list [chain]
List all rules in the selected chain. If no chain is
selected, all chains are listed. Like every other iptables
command, it applies to the specified table (filter is the
default), so NAT rules get listed by
iptables -t nat -n -L
Please note that it is often used with the -n option, in order
to avoid long reverse DNS lookups. It is legal to specify the
-Z (zero) option as well, in which case the chain(s) will be
atomically listed and zeroed. The exact output is affected by
the other arguments given. The exact rules are suppressed
until you use
iptables -L -v
or iptables-save(8).
-S, --list-rules [chain]
Print all rules in the selected chain. If no chain is
selected, all chains are printed like iptables-save. Like
every other iptables command, it applies to the specified
table (filter is the default).
-F, --flush [chain]
Flush the selected chain (all the chains in the table if none
is given). This is equivalent to deleting all the rules one
by one.
-Z, --zero [chain [rulenum]]
Zero the packet and byte counters in all chains, or only the
given chain, or only the given rule in a chain. It is legal to
specify the -L, --list (list) option as well, to see the
counters immediately before they are cleared. (See above.)
-N, --new-chain chain
Create a new user-defined chain by the given name. There must
be no target of that name already.
-X, --delete-chain [chain]
Delete the optional user-defined chain specified. There must
be no references to the chain. If there are, you must delete
or replace the referring rules before the chain can be
deleted. The chain must be empty, i.e. not contain any rules.
If no argument is given, it will attempt to delete every non-
builtin chain in the table.
-P, --policy chain target
Set the policy for the built-in (non-user-defined) chain to
the given target. The policy target must be either ACCEPT or
DROP.
-E, --rename-chain old-chain new-chain
Rename the user specified chain to the user supplied name.
This is cosmetic, and has no effect on the structure of the
table.
-h Help. Give a (currently very brief) description of the
command syntax.
PARAMETERS
The following parameters make up a rule specification (as used in the
add, delete, insert, replace and append commands).
-4, --ipv4
This option has no effect in iptables and iptables-restore.
If a rule using the -4 option is inserted with (and only with)
ip6tables-restore, it will be silently ignored. Any other uses
will throw an error. This option allows to put both IPv4 and
IPv6 rules in a single rule file for use with both iptables-
restore and ip6tables-restore.
-6, --ipv6
If a rule using the -6 option is inserted with (and only with)
iptables-restore, it will be silently ignored. Any other uses
will throw an error. This option allows to put both IPv4 and
IPv6 rules in a single rule file for use with both iptables-
restore and ip6tables-restore. This option has no effect in
ip6tables and ip6tables-restore.
[!] -p, --protocol protocol
The protocol of the rule or of the packet to check. The
specified protocol can be one of tcp, udp, udplite, icmp,
icmpv6,esp, ah, sctp, mh or the special keyword "all", or it
can be a numeric value, representing one of these protocols or
a different one. A protocol name from /etc/protocols is also
allowed. A "!" argument before the protocol inverts the test.
The number zero is equivalent to all. "all" will match with
all protocols and is taken as default when this option is
omitted. Note that, in ip6tables, IPv6 extension headers
except esp are not allowed. esp and ipv6-nonext can be used
with Kernel version 2.6.11 or later. The number zero is
equivalent to all, which means that you cannot test the
protocol field for the value 0 directly. To match on a HBH
header, even if it were the last, you cannot use -p 0, but
always need -m hbh.
[!] -s, --source address[/mask][,...]
Source specification. Address can be either a network name, a
hostname, a network IP address (with /mask), or a plain IP
address. Hostnames will be resolved once only, before the rule
is submitted to the kernel. Please note that specifying any
name to be resolved with a remote query such as DNS is a
really bad idea. The mask can be either an ipv4 network mask
(for iptables) or a plain number, specifying the number of 1's
at the left side of the network mask. Thus, an iptables mask
of 24 is equivalent to 255.255.255.0. A "!" argument before
the address specification inverts the sense of the address.
The flag --src is an alias for this option. Multiple
addresses can be specified, but this will expand to multiple
rules (when adding with -A), or will cause multiple rules to
be deleted (with -D).
[!] -d, --destination address[/mask][,...]
Destination specification. See the description of the -s
(source) flag for a detailed description of the syntax. The
flag --dst is an alias for this option.
-m, --match match
Specifies a match to use, that is, an extension module that
tests for a specific property. The set of matches make up the
condition under which a target is invoked. Matches are
evaluated first to last as specified on the command line and
work in short-circuit fashion, i.e. if one extension yields
false, evaluation will stop.
-j, --jump target
This specifies the target of the rule; i.e., what to do if the
packet matches it. The target can be a user-defined chain
(other than the one this rule is in), one of the special
builtin targets which decide the fate of the packet
immediately, or an extension (see EXTENSIONS below). If this
option is omitted in a rule (and -g is not used), then
matching the rule will have no effect on the packet's fate,
but the counters on the rule will be incremented.
-g, --goto chain
This specifies that the processing should continue in a user
specified chain. Unlike the --jump option return will not
continue processing in this chain but instead in the chain
that called us via --jump.
[!] -i, --in-interface name
Name of an interface via which a packet was received (only for
packets entering the INPUT, FORWARD and PREROUTING chains).
When the "!" argument is used before the interface name, the
sense is inverted. If the interface name ends in a "+", then
any interface which begins with this name will match. If this
option is omitted, any interface name will match.
[!] -o, --out-interface name
Name of an interface via which a packet is going to be sent
(for packets entering the FORWARD, OUTPUT and POSTROUTING
chains). When the "!" argument is used before the interface
name, the sense is inverted. If the interface name ends in a
"+", then any interface which begins with this name will
match. If this option is omitted, any interface name will
match.
[!] -f, --fragment
This means that the rule only refers to second and further
IPv4 fragments of fragmented packets. Since there is no way
to tell the source or destination ports of such a packet (or
ICMP type), such a packet will not match any rules which
specify them. When the "!" argument precedes the "-f" flag,
the rule will only match head fragments, or unfragmented
packets. This option is IPv4 specific, it is not available in
ip6tables.
-c, --set-counters packets bytes
This enables the administrator to initialize the packet and
byte counters of a rule (during INSERT, APPEND, REPLACE
operations).
OTHER OPTIONS
The following additional options can be specified:
-v, --verbose
Verbose output. This option makes the list command show the
interface name, the rule options (if any), and the TOS masks.
The packet and byte counters are also listed, with the suffix
'K', 'M' or 'G' for 1000, 1,000,000 and 1,000,000,000
multipliers respectively (but see the -x flag to change this).
For appending, insertion, deletion and replacement, 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.
-w, --wait [seconds]
Wait for the xtables lock. To prevent multiple instances of
the program from running concurrently, an attempt will be made
to obtain an exclusive lock at launch. By default, the
program will exit if the lock cannot be obtained. This option
will make the program wait (indefinitely or for optional
seconds) until the exclusive lock can be obtained.
-W, --wait-interval microseconds
Interval to wait per each iteration. When running latency
sensitive applications, waiting for the xtables lock for
extended durations may not be acceptable. This option will
make each iteration take the amount of time specified. The
default interval is 1 second. This option only works with -w.
-n, --numeric
Numeric output. IP addresses and port numbers will be printed
in numeric format. By default, the program will try to
display them as host names, network names, or services
(whenever applicable).
-x, --exact
Expand numbers. Display the exact value of the packet and
byte counters, instead of only the rounded number in K's
(multiples of 1000) M's (multiples of 1000K) or G's (multiples
of 1000M). This option is only relevant for the -L command.
--line-numbers
When listing rules, add line numbers to the beginning of each
rule, corresponding to that rule's position in the chain.
--modprobe=command
When adding or inserting rules into a chain, use command to
load any necessary modules (targets, match extensions, etc).
iptables can use extended packet matching and target modules. A list
of these is available in the iptables-extensions(8) manpage.
Various error messages are printed to standard error. The exit code
is 0 for correct functioning. Errors which appear to be caused by
invalid or abused command line parameters cause an exit code of 2,
and other errors cause an exit code of 1.
Bugs? What's this? ;-) Well, you might want to have a look at
http://bugzilla.netfilter.org/
This iptables is very similar to ipchains by Rusty Russell. The main
difference is that the chains INPUT and OUTPUT are only traversed for
packets coming into the local host and originating from the local
host respectively. Hence every packet only passes through one of the
three chains (except loopback traffic, which involves both INPUT and
OUTPUT chains); previously a forwarded packet would pass through all
three.
The other main difference is that -i refers to the input interface;
-o refers to the output interface, and both are available for packets
entering the FORWARD chain.
The various forms of NAT have been separated out; iptables is a pure
packet filter when using the default `filter' table, with optional
extension modules. This should simplify much of the previous
confusion over the combination of IP masquerading and packet
filtering seen previously. So the following options are handled
differently:
-j MASQ
-M -S
-M -L
There are several other changes in iptables.
iptables-apply(8), iptables-save(8), iptables-restore(8),
iptables-extensions(8),
The packet-filtering-HOWTO details iptables usage for packet
filtering, the NAT-HOWTO details NAT, the netfilter-extensions-HOWTO
details the extensions that are not in the standard distribution, and
the netfilter-hacking-HOWTO details the netfilter internals.
See http://www.netfilter.org/ .
Rusty Russell originally wrote iptables, in early consultation with
Michael Neuling.
Marc Boucher made Rusty abandon ipnatctl by lobbying for a generic
packet selection framework in iptables, then wrote the mangle table,
the owner match, the mark stuff, and ran around doing cool stuff
everywhere.
James Morris wrote the TOS target, and tos match.
Jozsef Kadlecsik wrote the REJECT target.
Harald Welte wrote the ULOG and NFQUEUE target, the new libiptc, as
well as the TTL, DSCP, ECN matches and targets.
The Netfilter Core Team is: Jozsef Kadlecsik, Patrick McHardy, Pablo
Neira Ayuso, Eric Leblond and Florian Westphal. Emeritus Core Team
members are: Marc Boucher, Martin Josefsson, Yasuyuki Kozakai, James
Morris, Harald Welte and Rusty Russell.
Man page originally written by Herve Eychenne <rv@wallfire.org>.
This manual page applies to iptables/ip6tables 1.6.1.
This page is part of the iptables (administer and maintain packet
filter rules) project. Information about the project can be found at
⟨http://www.netfilter.org/⟩. If you have a bug report for this man‐
ual page, see ⟨http://bugzilla.netfilter.org/⟩. This page was
obtained from the project's upstream Git repository
⟨http://bugzilla.netfilter.org/⟩ on 2018-02-02. (At that time, the
date of the most recent commit that was found in the repository was
2018-01-31.) If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-to-
date source for the page, or you have corrections or improvements to
the information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
iptables 1.6.1 IPTABLES(8)
Pages that refer to this page: iptables-xml(1), proc(5), systemd.socket(5), network_namespaces(7), brctl(8), flowtop(8), ifconfig(8), iptables-apply(8), iptables-restore(8), iptables-save(8), mountd(8), netstat(8), ovs-ctl(8), statd(8), tc-bpf(8), tc-fw(8), tc-mqprio(8)
|
HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
|
|