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# Layer 2 Services over MPLS Overview

Many Internet service providers offer multiple services such as Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet, High-Speed Data Link Control (HDLC), and IP to their customers, but are consolidating to a single, packet-based, optical network from several service-specific legacy layer 2 networks. Although legacy layer 2 network links are disappearing from the Internet service provider’s network, the legacy layer 2 network links and services to customers must remain.

Layer 2 services over IP/MPLS enable service providers to emulate the legacy layer 2 network links and services over their IP/MPLS-based network. Layer 2 services over MPLS are especially desirable because MPLS provides features such as traffic engineering and fast reroute. These MPLS features can be used to emulate certain layer 2 service characteristics. From the perspective of the customer edge (CE) devices, all that exists is the layer 2 circuit, even though the circuit actually exists over the service provider’s MPLS network.

The JUNOSe software currently support the following layer 2 services over MPLS:

- ATM with ATM Adaptation Layer 5 (AAL5) encapsulation
- ATM with virtual channel connection (VCC) cell relay encapsulation
- Ethernet (Fast Ethernet, Gigabit Ethernet, 10-Gigabit Ethernet, bridged Ethernet, bridged Ethernet/VLAN, Ethernet/VLAN)

  | Note: For the purposes of configuring layer 2 services over MPLS, Ethernet interfaces and bridged Ethernet interfaces function identically, as do Ethernet/VLAN interfaces and bridged Ethernet/VLAN interfaces. For simplicity, the term Ethernet in this chapter refers to both Ethernet interfaces and bridged Ethernet interfaces, and the term Ethernet/VLAN interfaces refers to both Ethernet/VLAN interfaces and bridged Ethernet/VLAN interfaces.

- Frame Relay
- HDLC

Figure 114 illustrates layer 2 services being supported over an Internet service provider’s MPLS network. Customers using Frame Relay, ATM, or other legacy layer 2 connections to E-series routers are unaware that MPLS tunneling is used.

Figure 114: Layer 2 Services over a Provider’s MPLS Network

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