BGP Series 9: BGP Rules for advertising of routes, Next-Hop Reachability with iBGP

• BGP Rules for advertising of routes:

• • BGP will only advertise the best route in any BGP table and will not include all the other routes for the same prefix.

  • • BGP has lots of tie-breakers that will help bgp to always choose a single route as the best route when lots of routes exist for the same prefix.

BGP Series 8: eBGP vs iBGP route, Using BGP for Outbound Routing, iBGP BGP Table Entries and Next-Hop issues with iBGP

• eBGP vs iBGP route:

• • If we learn a route via external neighbor (eBGP), the administrative distance is 20
  • If we learn a route via iBGP, the administrative distance is 200

BGP Series 7: Injecting Routes into BGP- network, redistribution, route summarization

Injecting Routes into BGP:

• 3 Primary ways to inject routes into BGP:

• • Using the BGP ‘network’ command
  • Using redistribution
  • By using route summarization

BGP Series 6: BGP AS-Path Attribute

BGP AS-Path Attribute:

• This attribute is used to decide the best-path for a certain prefix.

• By default, if a bgp router gets two or more updates for the same prefix, then, it will decide at the best path by simply looking at the AS-path attribute...ie. which of these routes went through the fewest number of AS and whichever route had the lowest number (quantity, not value) of AS-path, that is the best route

BGP Series 5: BGP Neighbor States, Message Types, BGP Table and Verification Commands

BGP Neighbor States:

• Idle: bgp process is not even active. Could be due to bgp being administratively shut (or) no route to neighbor in routing table [most likely]
• Connect: [very rarely seen] bgp is waiting for tcp connection to be completed