iprule 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 actionpredicate. 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 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 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.
ipruleadd-insertanewruleipruledelete-deletearuletypeTYPE(default)
the type of this rule. The list of valid types was given in the previous subsection.
fromPREFIX
select the source prefix to match.
toPREFIX
select the destination prefix to match.
iifNAME
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.
oifNAME
select the outgoing device to match. The outgoing interface is only available for packets
originating from local sockets that are bound to a device.
tosTOSdsfieldTOS
select the TOS value to match.
dscpDSCP
select the DSCP value to match. DSCP values can be written either directly as numeric
values (valid values are 0-63), 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 8-bit dsfield values, whereas iprule will only
use the higher six bits. ipruleshow will similarly format DSCP values as symbolic names
if possible. The command line option -N turns the show translation off.
fwmarkMARK
select the fwmark value to match.
uidrangeNUMBER-NUMBER
select the uid value to match.
ipprotoPROTOCOL
select the ip protocol value to match.
sportNUMBER|NUMBER-NUMBER
select the source port value to match. supports port range.
dportNUMBER|NUMBER-NUMBER
select the destination port value to match. supports port range.
priorityPREFERENCE
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.
tableTABLEID
the routing table identifier to lookup if the rule selector matches. It is also possible
to use lookup instead of table.
protocolPROTO
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_prefixlengthNUMBER
reject routing decisions that have a prefix length of NUMBER or less.
suppress_ifgroupGROUP
reject routing decisions that use a device belonging to the interface group GROUP.
realmsFROM/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.
natADDRESS
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.
flowlabelFLOWLABEL[/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 iprouteflushcache.
ipruleflush-alsodumpsallthedeletedrules.protocolPROTO
Select the originating protocol.
ipruleshow-listrules
This command has no arguments. The options list or lst are synonyms with show.
iprulesaveprotocolPROTO
Select the originating protocol.
save rules table information to stdout
This command behaves like ipruleshow except that the output is raw data suitable for passing to
iprulerestore.
iprulerestore
restore rules table information from stdin
This command expects to read a data stream as returned from iprulesave. 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.
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