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BGP Network Layer Reachability Information (NLRI)

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The Network Layer Reachability Information (NLRI) is exchanged between BGP routers using UPDATE messages. An NLRI is composed of a LENGTH and a PREFIX. The length is a network mask in CIDR notation (eg. /25) specifying the number of network bits, and the prefix is the Network address for that subnet.

The NLRI is unique to BGP version 4 and allows BGP to carry supernetting information, as well as perform aggregation.

The NLRI would look something like one of these:

     /25, 204.149.16.128
     /23, 206.134.32
     /8, 10

Only one NLRI is included in an UPDATE Message, though there may be multiple AS-paths and AS-path attributes.

 

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