What is a Layer 2 MPLS VPN and why to use it?
Layer 2 VPNs are a type of Virtual Private Network (VPN) that uses MPLS labels to transport data. The communication occurs between routers that are known as Provider Edge routers (PEs), as they sit on the edge of the provider's network, next to the customer's network. Internet providers who have an existing Layer 2 network may choose to use these VPNs instead of the other common MPLS VPN, Layer 3. Layer 2 VPNs uses the Label Distribution Protocol (LDP) to communicate between PE routers and established a virtual circuit providing the customer one or more private point-to-point connection.
In the example below we will configure three MPLS service provider routers (PEs), two routers for customer 1 (CE), and two additional routers for Customer 2 (CE). The service provider MPLS network will run a basic OSPF configuration and all customer routers will simply use static routers to point to their other sites. Both customer 1 and customer 2 must be provisioned a private virtual circuit to facilitate a direct point-to-point connection. Using CDP both customer routers should appear directly connected.
Verify the configuration
Now that the configuration is finished lets verify our neighbors and routes. Using the show cdp neighbors, show mpls forwarding-table, and show mpls l2transport vc # commands you can verify the MPLS deployment. Use the ping command to verify connectivity from PC1 to PC2 from PC3 to PC4. In Customer 1 Site 1 issue the show cdp neighbors command to verify CE-R2 appears directly connected.
Use the show mpls forwarding-table to verify the virtual circuits on PE-R1, PE-R2, and PE-R3. Using the show mpls l2transport vc 101 and show mpls l2transport vc 102 commands you can verify the local interface participating in the virtual circuit and the destination where the virtual circuit is terminated. You can repeat on the other provider routers to verify the virtual configuration end to end.
