Configuring Egress Protection Service Mirroring for BGP Signaled Layer 2 Services

Figure 1 shows a simplified topology of the use case that explains this feature.

Figure 1: Egress Protection LSP Configured from Router PE1 to Router PE2

CE1 is multihomed to PE1 and PE2. There are two paths connecting CE1 and CE2. The working path is CE2-PE3-P-PE1-CE1, via pseudowire PW21. The protecting path is CE2-PE3-P-PE2-CE1, via pseudowire PW22 Traffic is flowing through the working path under normal circumstances. When the end-to-end OAM between CE1 and CE2 detects failure on the working path, traffic will be switched from the working path to the protecting path. The end-to-end failure detection and recovery relies on control plane hence should be relatively slow. To achieve faster protection, local repair mechanisms similar to those used by MPLS fast reroute should be used. In Figure 1 above, if link or node failed in the core network (like link failure on P-PE1, P-PE3, or node failure on P), the MPLS fast reroute will happen on the transport LSPs between PE1 and PE3. The failure could be locally repaired within tens of milliseconds. However, if link or node failure happens at the edge (like link failure on PE3-CE2 or node failure on PE3), there is no local repair currently so we have to rely on the CE1-CE2 end-to-end protection to repair the failure.

• Device CE2—Traffic origin

• Router PE3—Ingress PE router

• Router PE1— (Primary) Egress PE router

• Router PE2—Protector PE router

• Device CE1—Traffic destination

When the link between CE1– PE1 goes downs, PE1 will briefly redirect that traffic towards CE1, to PE2. PE2 forwards it to CE1 until ingress router PE3 recalculates to forward the traffic to PE2.

Initially the traffic direction was; CE2 – PE3 – P – PE1 – CE1.

When the link between CE1– PE1 goes down, the traffic will be; CE2 – PE3 – P – PE1 – PE2 –CE1. PE3 then recalculates the path; CE2 – PE3 – P – PE2 – CE1.