iptables

IPTABLES(8)                     iptables 1.6.0                     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 three built-ins:
                  PREROUTING (for altering packets as soon as they  come  in),
                  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

       -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.

       -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 1.6.0.

iptables 1.6.0                                                     IPTABLES(8)
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