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Forum Replies

  1. Shannon,
    This is a good question, and there is a lot going on behind the scene to answer it. As you know, AllowAS-In and AS-Override are both essentially tricks that can be used to deal with what would normally be considered a BGP looped route (since the ASN number will appear in the AS Path).

    The important consideration is whether the BGP “loop” route will actually be filtered on the PE side or the CE side. AllowAS-In assumes the filtering is being done on the CE side, but in reality, most PEs would have already filtered the route before it got to the CE.


    ... Continue reading in our forum

  2. Hi Rene,
    Thanks for your nice article !
    Is AS Override only support on MPLS environment ??


  3. Hi Rene,

    Thanks for the Great explanation. I was wondering how does MPLS work & configured between different autonomous systems. Like when there are more than 2 Service providers involved. I checked in google but couldn’t find any article in simple terms… Could you please help ?

    Thank you

  4. Just being picky :smile: , I believe that “If you take a closer look, you can see that AS number 1 has been replaced with AS number 234.” should be replaced with “If you take a closer look, you can see that AS number 12 has been replaced with AS number 234.” Also the picture and interfaces from Configurations files are not the same (in this lesson and also the previous one).

    A question would be why the PE routers are not configured as BGP neighbors with P router? I guess the MPLS VPN does the trick (haven’t read the MPLS lessons yet).

    You make great lessons and comments! Thank you all,

  5. Hi Stefanita,

    Thanks for letting me know about this error, I just fixed it.

    About your question, it’s indeed MPLS VPN that does the trick. The P routers only do label switching, they only need to know how to reach the PE routers. The PE routers require iBGP to exchange VPN routes. If you haven’t seen it before, take a look at this explanation:


    That should help :slight_smile:


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