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MPLS in the SDN Era by Krzysztof Grzegorz Szarkowicz, Antonio Sanchez Monge

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Chapter 9. Inter-Domain MPLS Services

Inter-domain MPLS services is such a vast topic that it could fill a book on its own. This chapter focuses on an inter-domain type (Inter-AS) and a service type (IP VPN). Although this is just one piece of the entire picture, it is enough to get an idea of the challenges and techniques that are typically seen in inter-domain MPLS services.

But, before diving into Inter-AS IP VPN, let’s get an overview of what the different inter-domain MPLS services are and how they can be classified.

Inter-Domain Architectures

Given two domains, D1 and D2, there are two ways to design the border:

Inter-AS
Each domain is a different AS: D1 = AS1, D2 = AS2. The border is composed of two devices, each belonging to a single domain. These are AS Border Routers (ASBRs). One ASBR belongs to D1 and the other one belongs to D2. They both peer with each other through a neutral inter-domain link.
Inter-area
Each IGP area is one domain: D1 = Area X, D2 = Area Y. One single device is enough to instantiate the border. Such a border device is typically called a Border Node (BN) or Area Border Router (ABR). It has some interfaces in D1 and other interfaces in D2. Actually, it can also connect to D3, D4, and so on.
Note

Two ASs are connected through a link with one device at each end, whereas two areas are connected through a network device.

This chapter focuses on Inter-AS. Chapter 16 and Chapter 17 also feature inter-area scenarios.

In classic networking, an AS and ...

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