NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | AUTHOR | COLOPHON

IP-RULE(8)                          Linux                         IP-RULE(8)

NAME         top

       ip-rule - routing policy database management

SYNOPSIS         top

       ip [ OPTIONS ] rule { COMMAND | help }

       ip rule [ list [ SELECTOR ]]

       ip rule { add | del } SELECTOR ACTION

       ip rule { flush | save | restore }

       SELECTOR := [ not ] [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [
               fwmark FWMARK[/MASK] ] [ iif STRING ] [ oif STRING ] [ pref
               NUMBER ] [ l3mdev ]

       ACTION := [ table TABLE_ID ] [ nat ADDRESS ] [ realms
               [SRCREALM/]DSTREALM ] [ goto NUMBER ] SUPPRESSOR

       SUPPRESSOR := [ suppress_prefixlength NUMBER ] [ suppress_ifgroup
               GROUP ]

       TABLE_ID := [ local | main | default | NUMBER ]

DESCRIPTION         top

       ip rule manipulates rules in the routing policy database control the
       route selection algorithm.

       Classic routing algorithms used in the Internet make routing
       decisions based only on the destination address of packets (and in
       theory, but not in practice, on the TOS field).

       In some circumstances we want to route packets differently depending
       not only on destination addresses, but also on other packet fields:
       source address, IP protocol, transport protocol ports or even packet
       payload.  This task is called 'policy routing'.

       To solve this task, the conventional destination based routing table,
       ordered according to the longest match rule, is replaced with a
       'routing policy database' (or RPDB), which selects routes by
       executing some set of rules.

       Each policy routing rule consists of a selector and an action
       predicate.  The RPDB is scanned in order of decreasing priority (note
       that lower number means higher priority, see the description of
       PREFERENCE below). The selector of each rule is applied to {source
       address, destination address, incoming interface, tos, fwmark} and,
       if the selector matches the packet, the action is performed. The
       action predicate may return with success.  In this case, it will
       either give a route or failure indication and the RPDB lookup is
       terminated. Otherwise, the RPDB program continues with the next rule.

       Semantically, the natural action is to select the nexthop and the
       output device.

       At startup time the kernel configures the default RPDB consisting of
       three rules:

       1.     Priority: 0, Selector: match anything, Action: lookup routing
              table local (ID 255).  The local table is a special routing
              table containing high priority control routes for local and
              broadcast addresses.

       2.     Priority: 32766, Selector: match anything, Action: lookup
              routing table main (ID 254).  The main table is the normal
              routing table containing all non-policy routes. This rule may
              be deleted and/or overridden with other ones by the
              administrator.

       3.     Priority: 32767, Selector: match anything, Action: lookup
              routing table default (ID 253).  The default table is empty.
              It is reserved for some post-processing if no previous default
              rules selected the packet.  This rule may also be deleted.

       Each RPDB entry has additional attributes. F.e. each rule has a
       pointer to some routing table. NAT and masquerading rules have an
       attribute to select new IP address to translate/masquerade. Besides
       that, rules have some optional attributes, which routes have, namely
       realms.  These values do not override those contained in the routing
       tables. They are only used if the route did not select any
       attributes.

       The RPDB may contain rules of the following types:

              unicast - the rule prescribes to return the route found in the
              routing table referenced by the rule.

              blackhole - the rule prescribes to silently drop the packet.

              unreachable - the rule prescribes to generate a 'Network is
              unreachable' error.

              prohibit - the rule prescribes to generate 'Communication is
              administratively prohibited' error.

              nat - the rule prescribes to translate the source address of
              the IP packet into some other value.

       ip rule add - insert a new rule

       ip rule delete - delete a rule

              type TYPE (default)
                     the type of this rule. The list of valid types was
                     given in the previous subsection.

              from PREFIX
                     select the source prefix to match.

              to PREFIX
                     select the destination prefix to match.

              iif NAME
                     select the incoming device to match. If the interface
                     is loopback, the rule only matches packets originating
                     from this host. This means that you may create separate
                     routing tables for forwarded and local packets and,
                     hence, completely segregate them.

              oif NAME
                     select the outgoing device to match. The outgoing
                     interface is only available for packets originating
                     from local sockets that are bound to a device.

              tos TOS

              dsfield TOS
                     select the TOS value to match.

              fwmark MARK
                     select the fwmark value to match.

              priority PREFERENCE
                     the priority of this rule.  PREFERENCE is an unsigned
                     integer value, higher number means lower priority, and
                     rules get processed in order of increasing number. Each
                     rule should have an explicitly set unique priority
                     value.  The options preference and order are synonyms
                     with priority.

              table TABLEID
                     the routing table identifier to lookup if the rule
                     selector matches.  It is also possible to use lookup
                     instead of table.

              suppress_prefixlength NUMBER
                     reject routing decisions that have a prefix length of
                     NUMBER or less.

              suppress_ifgroup GROUP
                     reject routing decisions that use a device belonging to
                     the interface group GROUP.

              realms FROM/TO
                     Realms to select if the rule matched and the routing
                     table lookup succeeded. Realm TO is only used if the
                     route did not select any realm.

              nat ADDRESS
                     The base of the IP address block to translate (for
                     source addresses).  The ADDRESS may be either the start
                     of the block of NAT addresses (selected by NAT routes)
                     or a local host address (or even zero).  In the last
                     case the router does not translate the packets, but
                     masquerades them to this address.  Using map-to instead
                     of nat means the same thing.

                     Warning: Changes to the RPDB made with these commands
                     do not become active immediately. It is assumed that
                     after a script finishes a batch of updates, it flushes
                     the routing cache with ip route flush cache.

       ip rule flush - also dumps all the deleted rules.
              This command has no arguments.

       ip rule show - list rules
              This command has no arguments.  The options list or lst are
              synonyms with show.

       ip rule save
              save rules table information to stdout
              This command behaves like ip rule show except that the output
              is raw data suitable for passing to ip rule restore.

       ip rule restore
              restore rules table information from stdin
              This command expects to read a data stream as returned from ip
              rule save.  It will attempt to restore the rules table
              information exactly as it was at the time of the save. Any
              rules already in the table are left unchanged, and duplicates
              are not ignored.

SEE ALSO         top

       ip(8)

AUTHOR         top

       Original Manpage by Michail Litvak <mci@owl.openwall.com>

COLOPHON         top

       This page is part of the iproute2 (utilities for controlling TCP/IP
       networking and traffic) project.  Information about the project can
       be found at 
       ⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
       If you have a bug report for this manual page, send it to
       netdev@vger.kernel.org, shemminger@osdl.org.  This page was obtained
       from the project's upstream Git repository 
       ⟨git://git.kernel.org/pub/scm/linux/kernel/git/shemminger/iproute2.git⟩
       on 2017-07-05.  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

iproute2                         20 Dec 2011                      IP-RULE(8)

Pages that refer to this page: ip(8)