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Forum Replies

  1. Thanx a lot Rene … Excellent explanation … It was so systematic … to the point … and U made it so easy to understand … Great work

  2. Rafa,
    What you are seeing is the effect of the backdoor command. The backdoor command changes the BGP administrative distance of the selected route from 20 to 200. 200 is chosen because that AD is worse than any IGP’s AD. This way, BGP will be used as a last resort if either static or other IGP routing mechanisms become unavailable.

  3. Why would someone run OSPF between 2 different AS? Could you please provide me with practical scenarios? Because I don’t understand that when there is BGP to run between AS then why is that OSPF being used.


  4. Hello Ravi

    There are many situations in which it would be beneficial for you to run an IGP such as OSPF between AS’s. These include:

    1. Allowing multiple routing protocols to inject routes into the routing table provides backup routing capabilities if a routing protocol fails
    2. In order for BGP to function, and in order for it to be able to share routing between neighbours, the neighbours themselves must be reachable to each other. In order to achieve this, an IGP is often used.

    I hope this has been helpful!


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