iptables

IPTABLES(8)                      iptables 1.8.6                      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 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 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).


LOCK FILE
       iptables uses the /run/xtables.lock file to take an exclusive lock at
       launch.

       The XTABLES_LOCKFILE environment variable can be used to override the
       default setting.


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 1.8.6.



iptables 1.8.6                                                       IPTABLES(8)