Orhan Ergun 2 Comments

Is Inter-AS MPLS VPNs commonly deployed ? In real-life deployment which Inter-AS MPLS VPN Option is most common ? What are the use cases of Inter-AS MPLS VPNs ? This is not a theory post , I will share practical information with you.

 

For those who want to learn the details of Inter-AS MPLS VPNs, I wrote an article on Inter-AS Option A , Option B , Option C and Option AB earlier, you should take a look at those.

 

For those who know the different deployment options of Inter-AS MPLS VPNs, you can skip those posts and continue to read this post.

 

In fact, Inter-AS MPLS VPNs are more common than you imagine.

 

You might think that it is only deployed between the companies to support the common/dual-homed customers but this is not the use case.

 

I have seen and involved, so many Inter-AS MPLS VPN deployments and more and more what I see is, companies which have an operation in more than one country, they separate IGP and BGP.

 

They use separate IGP and BGP domains per country and to offer MPLS VPN service to customers which have a location in more than one country, these Service Provider create an Inter-AS MPLS VPNs.

 

So, in their network, they use different AS number per country and connect the countries by using one of the Inter-AS MPLS VPN design options.

 

When you research Inter-AS MPLS VPN options, you commonly see that Inter-AS MPLS VPN Option C is the most scalable option and many people recommend , Option C to be used between the ASes which belong the same business due to security concerns. Only if different ASes (Autonomous Systems) belong to same business, same company.

 

This is not the common case in real life deployment.

 

Even the companies which have an operation in many countries, deploy either Inter-AS Option A or B.

 

I would say Option A is most commonly deployed, due to its simplicity.

 

One of these companies is looking to stop this design and have flat network.

 

Which mean, instead of having separate IGP and BGP domains, they want to convert their design to single IGP and single BGP AS.

 

They don’t have so much routers per country. Configuring and managing so many entry for the Inter-AS customers is just cumbersome for them.

 

Also, when they have flat network design, they know that they will have better control on their network. Traffic engineering will be easier.

 

They could have a problem with the IGP scalability, but as I said above, they don’t have so many routers in IGP.

 

I mentioned earlier that, I have a customer who has 200 routers in OSPF domain and they don’t have a problem with their OSPF deployment. Careful readers will remember the important OSPF feature which that company deployed to support 200 routers in a OSPF domain.. What was that ? Share your answer in the comment box below.

 

 

— 2 Comments —

  1. I believe the feature is prefix-suppression 🙂 I do also like it.

    But actually I only know Cisco implementation of “prefix-suppression” as a direct CLI command.
    Almost similar behavior can be achieved in IS-IS protocol with “advertise passive-only” in some manner.

    Do other vendors have this feature as well? or it could be only applied using additional policies telling the routing process to export only particular prefixes?

    Also I don’t remember such feature in open-source implementations.

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