In typical routing behavior, the system uses the IP route table to select the egress interface, an ARP entry is used forward the packet to the appropriate Ethernet MAC. With routed VPLS, the egress IP interface may be represented by multiple egress (VPLS service SAPs).
The following table describes how the ARP cache and MAC FIB entry states interact.
| ARP cache entry | MAC FIB entry | Routing or system behavior |
|---|---|---|
ARP Cache Miss (No Entry) |
Known or Unknown |
Triggers a request to control plane ARP processing module, to send out an ARP request, out of all the SAPs. (also known as virtual ports) of the VPLS instance. |
ARP Cache Hit |
Known |
Forward to specific VPLS virtual port or SAP. |
Unknown |
This behavior cannot happen typically in 7210 SAS, as and when a L2 entry is removed from the FDB, the matching MAC address is also removed from the ARP cache. |