4. Advanced functions

4.1 Pseudowire resilience

Without extension, VPLS provides pseudowire resilience only through the underlying routing protocol (IGP). When connectivity between VPLS PE routers fails, then an alternative path is found by the routing protocol, the tunnel IGP converges and then client connectivity is regained via this new path. However, this natural method does not protect all elements of the VPLS network, as PE routers and attachment circuits are not protected.

Pseudowire redundancy ensures that the CE router can always maintain connectivity even if one element fails. This is achieved by defining the redundant pseudowire. This secondary pseudowire is configured and established in advance, but is inactive. It becomes active as soon as the primary fails. It is the...