Designing and Implementing AToM-Based Layer 2 VPNs

Any Transport over MPLS (AToM) allows the transport of Layer 2 protocols and connections over a Multiprotocol Label Switching (MPLS) backbone network. Transport over the MPLS backbone network is provided by encapsulating frames, cells, or Service Data Units (SDU), and transmitting them over a pseudowire.

If you have read Chapter 2, "Designing and Deploying L2TPv3-Based Layer 2 VPNs (L2VPN)," and you are thinking that all of this seems rather familiar, then you would be rightAToM pseudowires do a similar job to L2TPv3 pseudowires. The major difference is that L2TPv3 can transport Layer 2 protocols and connections over an IP backbone network, whereas AToM transports Layer 2 protocols and connections over an MPLS network.

Figure 3-1 illustrates the transport of Layer 2 protocols and connections over AToM pseudowires.

Figure 3-1. Transport of Layer 2 Protocols and Connections over AToM Pseudowires

In Figure 3-1, ATM traffic is transported over an AToM pseudowire between VectorIT.LA.ATM.Switch and VectorIT.SJ.ATM.Switch; PPP traffic is transported over an AToM pseudowire between mjlnet.Los.Angeles.CE and mjlnet. Seattle.CE; and Ethernet traffic is transported over an AToM pseudowire between cisco.Seattle.CE and cisco.San.Jose.CE.

This chapter describes the design and implementation of AToM-based, pseudowire-based L2VPNs. But before looking at design and implementation, it is important to understand AToM pseudowire operation.