Understanding BGP ORF
Outbound Route Filtering Capability for BGP-4 is prefix filtering that can occur between a customer edge (CE) router and a provider edge (PE) router that are exchanging IPv4 unicast BGP prefixes. With BGP ORF the downstream CE router dynamically tells the upstream PE router what routes to filter outbound. This means that the downstream CE router will only receive update messages about the prefixes that it wants. The big advantage of using BGP ORF is that the CE router not has to process al all routes that should be filtered out.
Configuring BGP ORF:
In the example bellow only the default route will received by the CE router. The filtering is done by BGP ORF on the PE router.
Example configuration BGP ORF:
PE router:
router bgp 100
neighbor 10.0.0.2 remote-as 200
!
address-family ipv4
neighbor 10.0.0.2 capability orf prefix-list receive
exit-address-family
PE router:
router bgp 200
neighbor 10.0.0.1 remote-as 100
!
address-family ipv4
neighbor 10.0.0.1 capability orf prefix-list send
neighbor 10.0.0.1 prefix-list AS_100_INBOUND in
exit-address-family
!
ip prefix-list INBOUND seq 10 permit 0.0.0.0/0
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