R-VPLS specific ARP cache behavior

In typical routing behavior, the system uses the IP route table to select the egress interface, and then at the egress forwarding engine, an ARP entry is used to forward the packet to the appropriate Ethernet MAC. With R-VPLS, the egress IP interface may be represented by a multiple egress forwarding engine (wherever the VPLS service virtual ports exist).

To optimize routing performance, the ingress forwarding engine processing has been augmented to perform an ingress ARP lookup to resolve which VPLS MAC address the IP frame must be routed toward. This MAC address may be currently known or unknown within the VPLS FDB. If the MAC is unknown, the packet is flooded by the ingress forwarding engine to all egress forwarding engines where the VPLS service exists. When the MAC is known on a virtual port, the ingress forwarding engine forwards the packet to the correct egress forwarding engine. Table: Ingress routed to VPLS next-hop behavior describes how the ARP cache and MAC FDB entry states interact at ingress and Table: Egress R-VPLS next-hop behavior describes the corresponding egress behavior.