ip-rule(8) - phpMan

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

NAME
ip-rule - routing policy database management

SYNOPSIS
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 ] [ uidrange NUMBER-NUMBER ]
[ ipproto PROTOCOL ] [ sport [ NUMBER | NUMBER-NUMBER ] ] [ dport [ NUMBER | NUM-
BER-NUMBER ] ] [ tun_id TUN_ID ]

ACTION := [ table TABLE_ID ] [ protocol PROTO ] [ nat ADDRESS ] [ realms [SR-
CREALM/]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 control the route selection algo-
rithm.

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 destina-
tion 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 se-
lects 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 ad-
dress, 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 termi-
nated. 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 trans-
late/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 refer-
enced 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 pro-
hibited' 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 avail-
able 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.

uidrange NUMBER-NUMBER
select the uid value to match.

ipproto PROTOCOL
select the ip protocol value to match.

sport NUMBER | NUMBER-NUMBER
select the source port value to match. supports port range.

dport NUMBER | NUMBER-NUMBER
select the destination port value to match. 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 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.

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 ig-
nored.