Provided by: iproute2_4.3.0-1ubuntu3_i386 bug

NAME

       ip-rule - routing policy database management

SYNOPSIS

       ip [ OPTIONS ] rule  { COMMAND | help }

       ip rule  [ list | add | del | flush | save ] SELECTOR ACTION

       ip rule  restore

       SELECTOR := [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ fwmark
               FWMARK[/MASK] ] [ iif STRING ] [ oif STRING ] [ pref NUMBER ]

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

       SUPPRESSOR := [ suppress_prefixlength NUMBER ] [ suppress_ifgroup GROUP
               ]

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

DESCRIPTION

       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. 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.

              Rule 0 is special. It cannot be deleted or overridden.

       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. 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

       ip(8)

AUTHOR

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