3Com 10014299 manual Configuring BGP

450CHAPTER 30: CONFIGURING BGP

The BGP system runs on a specific router as a high layer protocol. At system startup, the whole BGP routing table is transmitted for the exchange of routing information. Later on, only an update message is transmitted for updating the routing table. In the system, keep-alive messages are received and transmitted to check whether the connection between routers is normal.

The router transmitting the BGP message is called the BGP speaker. It receives and generates new routing information from time to time and advertises to other BGP speakers. When a BGP speaker receives a new route advertisement from other ASs, if this route is better than the existing route, or if there is no acceptable route currently, the BGP speaker broadcasts this route to all other BGP speakers in the AS. BGP speakers are peers to each other and several related peers form a peer group.

	BGP runs on the router in two modes:
	■	IBGP (Internal BGP)
	■	EBGP (External BGP)
	IBGP is run when routers in an autonomous system exchange network reachable
	information. When routers of different ASs exchange network reachable
	information, they use EBGP.
	The BGP protocol system is driven by messages that can be divided into 4
	categories:
	■ Open message. This is the first transmitted message after the connection is
		created. It is used to create a connection between BGP peers
	■ Update message is the most important message in BGP system, and is used to
		switch routing information among the peers. Update message consists of three
		parts: unreachable route, path attributes and Network Layer Reachability
		Information (NLRI).
	■ Notification message notifies errors.
	■ Keep-alive message is used to check the validity of the connection.
Configuring BGP	A BGP configuration includes tasks described in the following sections:
	■	Enabling BGP
	■ Configuring Networks for BGP Distribution
	■	Configuring Peers

A BGP advanced configuration includes:

■Setting the MED for the AS

■Allow Comparing Path MED

■Configuring the Local Preference

■Configuring BGP Timers

■Configuring a BGP Peer Group

■Creating Aggregate Addresses

■Configure BGP Route Reflector