IP-RULE(8) Linux IP-RULE(8)
NAME
ip-rule - routing policy database management
SYNOPSIS
ip [ OPTIONS ] rule { COMMAND | help }
ip rule [ list ]
ip rule { add | del } SELECTOR ACTION
ip rule { flush }
SELECTOR := [ not ] [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ fwmark FWMARK[/MASK] ] [ iif STRING ] [ oif
STRING ] [ pref NUMBER ]
ACTION := [ table TABLE_ID ] [ nat ADDRESS ] [ realms [SRCREALM/]DSTREALM ] [ goto NUMBER ]
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.
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 origi‐
nating 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.
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.
SEE ALSO
ip(8)
AUTHOR
Original Manpage by Michail Litvak <[email protected]>
iproute2 20 Dec 2011 IP-RULE(8)
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