BGP NLRI

• Network Layer Reachability Information
  • Network Statement
    • MUST BE EXACT MATCH!
  • Redistribute Statement
    • Won’t include OSPF E1/2 by default.
  • Aggregate Address Statement
    • Requires one subnet in BGP Table first.
    • BGP inject-map
      • opposite of aggregation.

BGP Network Statement:

• Originates prefixes with ORIGIN of IGP (i)
• Requires exact match in the routing table
  • can be learned via IGP.
• No mask keyword assumes classful.
• Sets weight to 32768

BGP Redistribute Statement:

• Originates prefixes with ORIGIN INCOMPLETE (?)
• Originates classful summary if auto-summary is enabled.
• Auto copies IGP metric to BGP MED.
• Won’t include OSPF External by default.
  • redistribute ospf <id> match internal external
• Sets weight to 32768.

BGP Redistribute Internal:

• By default, only external BGP routes are redistributed into IGP with redistribution.
• ‘bgp redistribute internal’ lets internal BGP routes to be redistributed into IGP.
• Can result in a routing loop if not careful.

BGP Conditional Advertisement:

• Advertises prefix matched in advertise-map.
  • If prefix matched in non-exist map does not exist
  • If prefix matched in exist-map does exist.
• Typically used to track failure of a transit link.
  • Advertise to backup provider, only if primary provider is down.

BGP Conditional Route Injection:

• Originates subnets from aggregate for purpose of longest match traffic engineering.
• ‘bgp inject-map inject-map exist-map exist-map <copy attributes>
  • Inject map
    • subnet to be advertised
    • set ip address prefix-list<list>
  • Exist Map
    • Aggregate to be originated from
    • Match ip address prefix-list <list>
    • match ip route-source prefix-list <list>