iptables

IPTABLES(8)                     iptables 1.6.1                     IPTABLES(8)

NAME
       iptables/ip6tables  -- administration tool for IPv4/IPv6 packet filter-
       ing 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.  Sev-
       eral 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 ta-
       ble.

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 mod-
       ules are present).

       -t, --table table
              This option specifies the packet matching table which  the  com-
              mand  should operate on.  If the kernel is configured with auto-
              matic module loading, an attempt will be made to load the appro-
              priate 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  rout-
                  ing),  and  POSTROUTING  (for  altering  packets as they are
                  about to go out).  IPv6 NAT support is available since  ker-
                  nel 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 sup-
                  ported: INPUT (for packets coming into the box itself), FOR-
                  WARD  (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) net-
                  working rules, such as those  enabled  by  the  SECMARK  and
                  CONNSECMARK  targets.   Mandatory  Access  Control is imple-
                  mented by Linux Security Modules such as SELinux.  The secu-
                  rity  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 combina-
              tion.

       -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 des-
              tination 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 ipt-
              ables  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  coun-
              ters 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 speci-
              fied 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  differ-
              ent  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 ipt-
              ables) 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  speci-
              fied,  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, eval-
              uation 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 con-
              tinue 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 multipli-
              ers 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 sen-
              sitive 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  inter-
              val 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 appli-
              cable).

       -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  pre-
       viously.  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),   ipta-
       bles-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  netfil-
       ter-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 every-
       where.

       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 mem-
       bers are: Marc Boucher, Martin Josefsson, Yasuyuki Kozakai, James  Mor-
       ris, Harald Welte and Rusty Russell.

       Man page originally written by Herve Eychenne <rv@wallfire.org>.

VERSION
       This manual page applies to iptables/ip6tables 1.6.1.

iptables 1.6.1                                                     IPTABLES(8)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2021 Hurricane Electric. All Rights Reserved.