ip-rule man page on ElementaryOS

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

NAME
       ip-rule - routing policy database management

SYNOPSIS
       ip [ OPTIONS ] rule  { COMMAND | help }

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

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

       ACTION := [ table TABLE_ID ] [ nat ADDRESS ] [ prohibit | reject |
	       unreachable ] [ 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 'rout‐
       ing policy database' (or RPDB), which selects routes by executing some
       set of rules.

       Each policy routing rule consists of a selector and an action predi‐
       cate.  The RPDB is scanned in order of decreasing priority. The selec‐
       tor 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 indica‐
       tion 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 out‐
       put 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 ta‐
	      ble containing high priority control routes for local and broad‐
	      cast addresses.

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

       2.     Priority: 32766, Selector: match anything, Action: lookup rout‐
	      ing 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 rout‐
	      ing 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 rout‐
		     ing tables for forwarded and local packets and, hence,
		     completely segregate them.

	      oif NAME
		     select the outgoing device to match.  The outgoing inter‐
		     face 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 pref‐
		     erence and order are synonyms with priority.

	      table TABLEID
		     the routing table identifier to lookup if the rule selec‐
		     tor 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 ta‐
		     ble 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 syn‐
	      onyms with show.

SEE ALSO
       ip(8)

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

iproute2			  20 Dec 2011			    IP-RULE(8)
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