Border Gateway Protocol
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
Alcatel-Lucent
BGP OVERVIEW
BGP is an inter-Autonomous System routing protocol. The primary function for a
BGP speaking system is to exchange network reachability information (NLRI) with
other BGP systems. This network reachability information includes information on
the list of Autonomous Systems (ASs). This is sufficient to construct a graph of AS
connectivity from which routing loops may be pruned and some policy decisions at
the AS level may be enforced. The Alcatel-Lucent implementation of BGP
supports BGP-4 specified in RFC 1771.
Each BGP update message consists of a list of NLRI and a set of Path Attributes
shared amongst them. Common path-attributes are AS_PATH, NEXT-HOP, etc.
BGP uses locally configured policies for route-selection among the different
updates.
BGP neighbors form a TCP connection between one another. They exchange
messages to open and confirm the connection parameters. The initial data flow is
the entire BGP routing table. Incremental updates are sent as the routing tables
change. BGP does not require periodic refresh of the entire BGP routing table,
therefore a BGP speaker must retain the current version of the entire BGP routing
tables from all of its peers for the duration of the connection. Keepalive messages
are sent periodically to ensure the liveness of the connection. Notification
messages are sent in response to errors or special conditions.
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