IP-RULE

Section: Linux (8)
Updated: 20 Dec 2011
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NAME

i-rule - routing policy database management  

SYNOPSIS

ip [ OPTIONS ] rule { COMMAND | help }

ip rule [ show [ SELECTOR ]]

ip rule { add | del } SELECTOR ACTION

ip rule { flush | save | restore }

SELECTOR := [ not ] [ from PREFIX ] [ to PREFIX ] [ tos TOS ] [ dscp DSCP[/MASK] ] [ fwmark FWMARK[/MASK] ] [ iif STRING ] [ oif STRING ] [ priority PREFERENCE ] [ l3mdev ] [ uidrange NUMBER-NUMBER ] [ ipproto PROTOCOL ] [ sport [ NUMBER[/MASK] | NUMBER-NUMBER ] ] [ dport [ NUMBER[/MASK] | NUMBER-NUMBER ] ] [ tun_id TUN_ID ] [ flowlabel FLOWLABEL[/MASK] ]

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

SUPPRESSOR := [ suppress_prefixlength NUMBER ] [ suppress_ifgroup GROUP ]

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

 

DESCRIPTION

ip rule manipulates rules in the routing policy database that controls 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 a 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 no-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 pos-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 returns the route found in the routing table referenced by the rule.

blackhole - the rule causes a silent drop the packet.

unreachable - the rule generates a 'Network is unreachable' error.

prohibit - the rule generates 'Communication is administratively prohibited' error.

nat - the rule translates 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 separate 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.

dscp DSCP[/MASK]

select the DSCP value to match with an optional mask. DSCP values can be written either directly as numeric values (valid values are -63), or using symbolic names specified in /usr/share/iproute2/rt_dsfield or /etc/iproute2/rt_dsfield (has precedence if exists). However, note that the file specifies full -bit dsfield values, whereas ip rule will only use the higher six bits. ip rule show will similarly format DSCP values as symbolic names if possible. The command line option -N turns the show translation off.

fwmark MARK

select the fwmark value to match.

uidrange NUMBE-NUMBER

select the uid value to match.

ipproto PROTOCOL

select the ip protocol value to match.

sport NUMBER[/MASK] | NUMBE-NUMBER

select the source port value to match with an optional mask. Supports port range.

dport NUMBER[/MASK] | NUMBE-NUMBER

select the destination port value to match with an optional mask. Supports port range.

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.

protocol PROTO

the routing protocol who installed the rule in question. As an example when zebra installs a rule it would get RTPROT_ZEBRA as the installing protocol.

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 ma-to instead of nat means the same thing.

flowlabel FLOWLABEL[/MASK]

select the IPv6 flow label to match with an optional mask.

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.

protocol PROTO

Select the originating protocol.

ip rule show- list rules

This command has no arguments. The options list or lst are synonyms with show.

ip rule save

protocol PROTO

Select the originating protocol.

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>

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Index

NAME

SYNOPSIS

DESCRIPTION

SEE ALSO

AUTHOR