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Forum Replies

  1. 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.

    Rene

  2. 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

    ... Continue reading in our forum

  3. Hello,

    Is the prefix list defined on the Customer router in the example correct? I had to change it to 10.10.10.0/24 to get it to work in my testing.

    Thanks

    Mark

  4. 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.

    Br,
    Sebastian

  5. Hello Staut

    You make a good point, and this is an opportunity for clarification.

    The Internet community is actually a Cisco defined community. It is kind of like a “catch all” that defines “normal” behaviour in the event that no other communities are defined. So in a sense, it is the “default” community that allows all prefixes to be advertised. Where the other three say “don’t advertise such and such” the Internet community says “advertise everything!”

    I hope this has been helpful!

    Laz

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