Cabletron Systems SmartSwitch manual BGP Peering Session Example

Chapter 10: BGP Configuration Guide

•BGP Multi-Exit Discriminator (MED) attribute

•EBGP aggregation

•Route reflection

BGP Peering Session Example

The router process used for a specific BGP peering session is known as a BGP speaker. A single router can have several BGP speakers. Successful BGP peering depends on the establishment of a neighbor relationship between BGP speakers. The first step in creating a BGP neighbor relationship is the establishment of a TCP connection (using TCP port 179) between peers.

A BGP Open message can then be sent between peers across the TCP connection to establish various BGP variables (BGP Version, AS number (ASN), hold time, BGP identifier, and optional parameters). Upon successful completion of the BGP Open negotiations, BGP Update messages containing the BGP routing table can be sent between peers.

BGP does not require a periodic refresh of the entire BGP routing table between peers. Only incremental routing changes are exchanged. Therefore, each BGP speaker is required to retain the entire BGP routing table of their peer for the duration of the peer’s connection.

BGP “keepalive” messages are sent between peers periodically to ensure that the peers stay connected. If one of the routers encounters a fatal error condition, a BGP notification message is sent to its BGP peer, and the TCP connection is closed.

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