Provided by: iptables_1.6.1-2ubuntu3_amd64 bug

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).

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, Patrick McHardy, Pablo Neira Ayuso, Eric
       Leblond and Florian Westphal.  Emeritus  Core  Team  members  are:  Marc  Boucher,  Martin
       Josefsson, Yasuyuki Kozakai, James Morris, Harald Welte and Rusty Russell.

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

VERSION

       This manual page applies to iptables/ip6tables 1.6.1.