Mar 12, 2013

Layer 2 VPNs Cisco IOS MPLS Virtual Private LAN Service

The signaling requirements of VPLS:

The virtual circuit setup uses the same LDP signaling mechanism defined for point-to-point services. Using a directed LDP session, each provider edge advertises a virtual circuit label mapping that is used as part of the label stack imposed on the Ethernet frames by the ingress provider edge during packet forwarding.

The reachability information distributed in a VPLS

Cisco VPLS does not require the exchange of reachability (MAC addresses) information via a signaling protocol. This information is learned from the data plane using standard address learning, aging, and filtering mechanisms defined for Ethernet bridging. However, the LDP signaling used for setting up and tearing down the virtual circuits can be used to indicate to a remote provider edge that some or all MAC addresses learned over a virtual circuit need to be withdrawn from the VSI. This mechanism provides a convergence optimization over the normal address aging that would eventually flush the invalid addresses.

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