man > iptables(8)

IPTABLES(8)                                iptables 1.8.10                               IPTABLES(8)

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  ta‐
       ble 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-de‐
       fined 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  encoun‐
                  tered.  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  al‐
                  tering  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) and 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 differ‐
       ent 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 pos‐
              sible 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 ex‐
              isting 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 com‐
              mand: 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 spec‐
              ified 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  ig‐
              nored. 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 ip6ta‐
              bles, 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, be‐
              fore  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 prop‐
              erty.  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  exten‐
              sion  (see  MATCH  AND  TARGET 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
              with  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 in‐
              terface 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 in‐
              terface 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 in‐
              terface  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  in‐
              terface name will match.

       [!] -f, --fragment
              This  means  that  the  rule only refers to second and further IPv4 fragments of frag‐
              mented 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 ip6ta‐
              bles.

       -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 re‐
              spectively (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, ipta‐
              bles-nft dumps rules in netlink (VM code) presentation.  Specified three times,  ipta‐
              bles-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  de‐
              fault,  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  ser‐
              vices (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 func‐
       tioning.  Errors which appear to be caused by invalid or abused command line parameters cause
       an exit code of 2. Errors which indicate an incompatibility between  kernel  and  user  space
       cause an exit code of 3. Errors which indicate a resource problem, such as a busy lock, fail‐
       ing  memory  allocation or error messages from kernel cause an exit code of 4. Finally, other
       errors cause an exit code of 1.

BUGS
       Bugs?  What's this? ;-) Well, you might want  to  have  a  look  at  https://bugzilla.netfil‐
       ter.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 origi‐
       nating 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); previ‐
       ously 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 avoid much of the
       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 dis‐
       tribution, and the netfilter-hacking-HOWTO details the netfilter internals.
       See https://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 do‐
       ing 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 West‐
       phal 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 AT wallfire.org>.

VERSION
       This manual page applies to iptables/ip6tables 1.8.10.

iptables 1.8.10                                                                          IPTABLES(8)