Chapter 2 Advanced Routing for FortiOS 5.0 : Border Gateway Protocol (BGP) : BGP background and concepts : Parts and terminology of BGP : Network Layer Reachability Information (NLRI)
  
Network Layer Reachability Information (NLRI)
Network Layer Reachability Information (NLRI) is unique to BGP-4. It is sent as part of the update messages sent between BGP routers, and contains information necessary to supernet, or aggregate route, information. The NLRI includes the length and prefix that when combined are the address of the aggregated routes referred to.
There is only one NLRI entry per BGP update message.