Importing routes from BGP and EGP
import proto bgp | egp autonomoussystem autonomous_system restrict ; import proto bgp | egp autonomoussystem autonomous_system [ preference preference ] { route_filter [ restrict | ( preference preference ) ] ; } ;EGP importation may be controlled by autonomous_system. BGP also supports controlling propagation by the use of 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.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 and BGP both store any routes that were rejected implicitly by not being mentioned 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 alleviates breaking and reestablishing a session upon reconfiguration if importation policy is changed.