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Forum Replies

  1. Hi Rene,

    So I’ve learned so far that BGP Allow_AS_IN and BPG Override achieve a similar outcome when confronted with using same ASes for MPLS VPN customer sites that use eBGP for the last mile, but from different end points: CE vs PE. So my question is, is there an advantage/disadvantage using one over another? Or in what context would one method be preferred over another?



  2. 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

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


  4. Hi Zaman,

    It is a BGP feature so it’s not only for MPLS. MPLS VPN however is one of those situations where this can be useful.


  5. 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

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