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  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. Hi Hamood,

    Like Mauro explained below, AS path prepending is used to make the path less preferable. BGP uses AS path length in its selection for the best path.

    The community values are defined by an ISP, there are no fixed values or anything. Basically it’s just a “tag”, if you tag your prefixes with a certain value then the ISP will do something with it…prepend it’s AS path, set the local preference, etc.


  3. Hi Rene,

    Now I have a problem that makes me want to pull my hairs out. We’re a global company that has 5 different branches in 3 different countries. The current situation is every branch has its own private AS# and we use eBGP to connect all the branches. We have all the devices run OSPF and IBGP inside of each branch. As I said before, we have 5 different branches in 3 different countries, which means actually 3 branches we’ll need to use the same ISP. In order to help with the understanding, please refer to the diagram attached. let’s see 65521 R3 is running static route to go to ISP A. For 65524, I want the traffic to go through ISP A by adding a static route on R3. This will need us to redistribute the static route to EB GP for R8 to know it, right? As we redistribute the static route to the BGP, all the router in 65523 will know the road to ISP A. However, same traffic sometimes will also initiate on 65523, which I don’t want them to go ISP A, I want them to go ISP B. Which means i don’t want any redistributed static route to affect anything for R4 and R5, is there any easy way to achieve this?

    It will be highly appreciated if you can help me with it.

  4. Hello,

    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.



  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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