NLRI

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.