import statements. The format of an import
statement varies depending on the source protocol.
restrict
preference preference
restrict is specified on the first line of a
statement), all routes from the specfied source will match that
statement. If any filters are specified, only routes that match the
specified filters will be imported. Put differently, if any filters
are specified, an all restrict ; is assumed at the end of
the list.
network [ exact | refines ]
network mask mask [exact | refines ]
network masklen number [ exact | refines ]
default
host host
import proto bgp | egp autonomoussystem autonomous_system
restrict ;
import proto bgp | egp autonomoussystem autonomous_system
[ preference preference ] {
route_filter [ restrict | ( preference preference ) ] ;
} ;
import proto bgp aspath aspath_regexp
origin any | ( [ igp ] [egp ] [ incomplete ] )
restrict ;
import proto bgp aspath aspath_regexp
origin any | ( [ igp ] [egp ] [ incomplete ] )
[ preference preference ] {
route_filter [ restrict | ( preference preference ) ] ;
} ;
EGP importation may be controlled by autonomous system.
BGP also supports controlling propagation by the use of an AS path
regular expressions, which are documented in the section on Matching AS paths.
Note that EGP and BGP versions 2 and 3 only support the propagation of
natural networks, so the host and
default route filters are meaningless. BGP version 4
supports the propagation of any destination along with a
contiguous network mask.
EGP and BGP both store any routes that were rejected implicitly by not
being metioned in a route filter, or explicitly with the
restrict keyword in the routing table with a negative
preference. A negative preference prevents a route from becoming
active, which prevents it from being installed in the forwarding
table, or exported to other protocols. This aleviates the need to
break and re-establish a session upon reconfiguration if importation
policy is changed.
import proto rip | hello | redirect
[ ( interface interface_list ) | (gateway gateway_list ) ]
restrict ;
import proto rip | hello | redirect
[ ( interface interface_list ) | (gateway gateway_list ) ]
[ preference preference ] {
route_filter [ restrict | ( preference preference ) ] ;
} ;
The importation of RIP, HELLO and Redirect routes may be controlled by
any of protocol, source interface and source gateway. If more than
one is specified, they are processed from most general (protocol) to
most specific (gateway). RIP and HELLO don't support the use of preference to choose between routes of the same protocol. That is left to the protocol metrics. These protocols do not save routes that were rejected since they have short update intervals.
import proto ospfase [ tag ospf_tag ] restrict ;
import proto ospfase [ tag ospf_tag ]
[ preference preference ] {
route_filter [ restrict | ( preference preference ) ] ;
} ;
Due to the nature of OSPF, only the importation of ASE routes may be
controlled. OSPF intra- and inter-area routes are always imported
into the gated routing table with a preference of 10.
If a tag is specified, the import clause will only apply to routes
with the specified tag.
It is only possible to restrict the importation of OSPF ASE routes when functioning as an AS border router. This is accomplished by specifying an export ospfase clause. Specification of an empty export clause may be used to restrict importation of ASEs when no ASEs are being exported.
Like the other interior protocols, preference can not be used to choose between OSPF ASE routes, that is done by the OSPF costs. Routes that are rejected by policy are stored in the table with a negative preference.