Appendix C. BGP Outbound Route Filter (ORF)

Outbound Route Filter (ORF) is a new BGP functionality used to minimize the number of BGP updates sent to a neighbor. This appendix provides information on BGP ORF as it relates to IOS versions 12.0ST and 12.1.

The idea is to push the locally-configured BGP prefix filter to the remote peer so that the remote peer applies this received filter as yet another outbound filter. This results in two benefits:

  • The number of prefixes that are sent are reduced and thus leads to a lesser number of BGP updates.

  • Less work for the local router which previously used to process all those extra updates. This might mean less transient memory consumption and less attribute and cache creation.

This appendix covers the ORF. The inbound prefix list can be pushed down to the peer acting as its outbound policy.

ORF is defined as a new capability, IOS uses 130 as its code value. The new capability reflects the latest draft which lists all the ORF-types supported as send, receive or both. This means that there is a compatibility issue between routers running these two capabilities. The old knob is accepted only as receive capability.

The local-peer that advertises support for BGP ORF in send-mode will push its inbound prefix list only if it receives the receive-mode BGP ORF capability from the remote-peer. The remote-peer however will wait before sending the first update until it receives a ROUTE-REFRESH request or BGP ORF with IMMEDIATE from the peer. Note that this is done for each address-family (AF) for updates exchanged between the peers depending on the BGP ORF capability advertised.

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