NAME | SYNOPSIS | DESCRIPTION | TARGETS | TABLES | OPTIONS | MATCH AND TARGET EXTENSIONS | DIAGNOSTICS | BUGS | COMPATIBILITY WITH IPCHAINS | SEE ALSO | AUTHORS | VERSION | COLOPHON

IPTABLES(8)                    iptables 1.6.2                    IPTABLES(8)

NAME         top

       iptables/ip6tables — administration tool for IPv4/IPv6 packet filter‐
       ing and NAT

SYNOPSIS         top

       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         top

       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         top

       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         top

       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         top

       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 to put both 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 to put both 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         top

       iptables can use extended packet matching and target modules.  A list
       of these is available in the iptables-extensions(8) manpage.

DIAGNOSTICS         top

       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         top

       Bugs?  What's this? ;-) Well, you might want to have a look at
       http://bugzilla.netfilter.org/

COMPATIBILITY WITH IPCHAINS         top

       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         top

       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         top

       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         top

       This manual page applies to iptables/ip6tables 1.6.2.

COLOPHON         top

       This page is part of the iptables (administer and maintain packet
       filter rules) project.  Information about the project can be found at
       ⟨http://www.netfilter.org/⟩.  If you have a bug report for this man‐
       ual page, see ⟨http://bugzilla.netfilter.org/⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨http://bugzilla.netfilter.org/⟩ on 2018-04-30.  (At that time, the
       date of the most recent commit that was found in the repository was
       2018-04-29.)  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-to-
       date source for the page, or you have corrections or improvements to
       the information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

iptables 1.6.2                                                   IPTABLES(8)

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