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IPTABLES(8)                                                                                     iptables 1.8.9                                                                                    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 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 appropri‐
              ate 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 Se‐
                  curity 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 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 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  nu‐
              meric  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  al‐
              lowed.   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 di‐
              rectly. 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 sub‐
              mitted 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  specifica‐
              tion  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 tar‐
              gets 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 in‐
              formation 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 en‐
              tries 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  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).

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, Ya‐
       suyuki 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.

iptables 1.8.9                                                                                                                                                                                    IPTABLES(8)</nowiki>