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Notable Replies

  1. Rene,

    Great lesson however, I do have a question about prepending AS in ISP-1 because we don't want other ISPs to learn about is that correct?

    64984:0 is a number we get from ISP? It varies from ISP to ISP?
    If we need to add another loopback or network we can use the same community on the customer side which is 64984:0 or do we need something else?

    Please clarify.

  2. Hello Hamood,

    Usually Prepending AS is used to make the path less preferable over other. In the case of this example Rene was just trying to show that using community is much easier to set attributes and refine the way you want the prefixes to be advertised.

    @Rene now i also have a question, i have notice that on customer you had use the SEND COMMUNITY command but on the ISP1 to ISP2 u didn't, is that a reason for that to not happen? Since you said that the router doesn't send the community automatically.

    Waiting patiently for your reply.


  3. mark1 says:


    Is the prefix list defined on the Customer router in the example correct? I had to change it to to get it to work in my testing.



  4. Hi Mark,

    It depends on your loopback interface. In my case, I had a /32 on the loopback which was advertised in BGP:

    Customer#show running-config | section bgp
    router bgp 10
     no synchronization
     bgp log-neighbor-changes
     network mask
  5. Hi Rene,

    very nice introduction to BGP communities. However, I've a little improvement: A hint that communities were only forwarded from second router to a third one if send-community is activated on that neighborhood were be helpful.


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