iptables

IPTABLES(8)                     iptables 1.8.3                     IPTABLES(8)



NAME
       iptables/ip6tables — administration tool for IPv4/IPv6 packet filtering
       and NAT

SYNOPSIS
       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]

DESCRIPTION
       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.

TARGETS
       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.

TABLES
       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).

OPTIONS
       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).

MATCH AND TARGET EXTENSIONS
       iptables can use extended packet matching and target modules.  A list
       of these is available in the iptables-extensions(8) manpage.

DIAGNOSTICS
       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
       Bugs?  What's this? ;-) Well, you might want to have a look at
       http://bugzilla.netfilter.org/

COMPATIBILITY WITH IPCHAINS
       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.

SEE ALSO
       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/.

AUTHORS
       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, Pablo Neira Ayuso, Eric
       Leblond, Florian Westphal and  Arturo Borrero Gonzalez.  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>.

VERSION
       This manual page applies to iptables/ip6tables 1.8.3.



iptables 1.8.3                                                     IPTABLES(8)