Server Fault is a question and answer site for system and network administrators. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I'm learning about MPLS. I have two sites in my scenario using eBGP for PE-CE communication, and both using the same ASN (deliberately as I want to know about SOO) and I cannot advertise a route from one site into the other due to the AS Path containing the local AS.

I know I can use as-override and that's all fine. What I don't understand is how the site of origin extended community attribute works with this, though. Questions I have are:

  1. Do I have to enable as-override as well as declaring SOO?
  2. I think SOO is set at the PE router rather than CE?
  3. Is route filtering based on SOO an automatic process or do I have to do it explicitly with an inbound route-map? If so, where? CE or PE?


I think I get it now. The SOO isn't about allowing a prefix to be advertised back into another part of the same AS (i.e. site 1 --> site 2), but is about preventing the prefix being advertised back into the same site (in the case of multiple links to to the upstream provider). So in light of this I would expect that I do have to use as-override regardless. Is this correct?

My question about filtering based on SOO still stands, though.

share|improve this question

BGP Site-of-Origin (SoO) is used to prevent looping in the following set-up.

1) Customer sites connected to the MPLS/VPN provider use a single AS (thus needing as-override configured). 2) A customer site (usually the hub or other important location) has multiple connections to the provider.

The SoO filtering is automatic once SoO is configured. No BGP filtering is needed.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.