Provided by: iptables_1.8.9-2ubuntu2_amd64 bug

NAME

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

SYNOPSIS

       iptables [-t table] {-A|-C|-D|-V} chain rule-specification

       ip6tables [-t table] {-A|-C|-D|-V} 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  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 delete all empty chains in the table. Empty builtin chains can  only
              be deleted with iptables-nft.

       -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: Specified twice, iptables-legacy will  dump  table  info
              and entries in libiptc, iptables-nft dumps rules in netlink (VM code) presentation.
              Specified three times, iptables-nft will also dump any  netlink  messages  sent  to
              kernel.

       -V, --version
              Show program version and the kernel API used.

       -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.

       -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/ iptables will exit immediately with an error code of 111 if
       it finds that it was called as a setuid-to-root program.  iptables cannot be  used  safely
       in  this  manner  because  it trusts the shared libraries (matches, targets) loaded at run
       time, the search path can be set using environment variables.

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 1.8.9.