BGP-4 Protocol Specification and Functionality

RFC 1771 defines the current Border Gateway Protocol 4 (BGP-4) implementation. BGP relies on a reliable transport mechanism to establish its connection and for exchanging information between BGP peers. BGP uses TCP port 179 for this purpose and benefits from the TCP protocol to offer reliable communication between BGP speakers . RFC 1771 describes in detail the requirements of BGP neighbor relationships, BGP update format, error notifications, and handling of special cases.

Proper BGP functionality requires proper configuration on the routers and correct implementation of the protocol per RFC 1771.

The sections that follow address these aspects of BGP:

• Neighbor relationships (peering)

• Advertising routes and the concept of synchronization

• Receiving routes

• Best- path calculation

• Policy control through the following:

  - Use of BGP attributes (LOCAL_PREF, AS_PATH, MULTI_EXIT_DISC (MED), ORIGIN, NEXT_HOP)

  - Use of route maps in policy control

  - Use of filter lists in policy control

  - Use of distribute lists in policy control

  - Use of communities in policy control

  - Use of prefix list

  - Use of outbound route-filtering (ORF) capability in policy control

  - Aggregation in BGP

• Scaling IBGP in large networks

• Route reflectors

• Confederations