BGP prefix-based outbound route filtering uses the BGP ORF send and receive capabilities to minimize the number of BGP updates
that are sent between BGP peers. Configuring BGP ORF can help reduce the amount of system resources required for generating
and processing routing updates by filtering out unwanted routing updates at the source. For example, BGP ORF can be used to
reduce the amount of processing required on a router that is not accepting full routes from a service provider network.
The BGP prefix-based outbound route filtering is enabled through the advertisement of ORF capabilities to peer routers. The
advertisement of the ORF capability indicates that a BGP peer will accept a prefix list from a neighbor and apply the prefix
list to locally configured ORFs (if any exist). When this capability is enabled, the BGP speaker can install the inbound prefix
list filter to the remote peer as an outbound filter, which reduces unwanted routing updates.
The BGP prefix-based outbound route filtering can be configured with send or receive ORF capabilities. The local peer advertises
the ORF capability in send mode. The remote peer receives the ORF capability in receive mode and applies the filter as an
outbound policy. The local and remote peers exchange updates to maintain the ORF on each router. Updates are exchanged between
peer routers by address family depending on the ORF prefix list capability that is advertised. The remote peer starts sending
updates to the local peer after a route refresh has been requested with the
prefix-filter command or after an ORF prefix list with immediate status is processed. The BGP peer will continue to apply the inbound prefix
list to received updates after the local peer pushes the inbound prefix list to the remote peer.