The definition of interface tags in Advanced Routing and Forwarding (ARF) facilitates the use of virtual routers, which only use a part of the overall routing table. The interface tag for a packet received from another local router is set according to the following procedure:
- If there is only one ARF network on a LAN interface/VLAN pair, this is selected automatically.
- If there are multiple ARF networks on a LAN descriptor / VLAN pair, then a check is made to see if the source address of the packet is local to one of the ARF networks. If so, this network is then selected.
- If not, a reverse ARP lookup is performed for the source MAC address, which determines the address of the next hop to the source address. If the address can be resolved, then a check is made to see whether it is local to one of the ARF networks. If so, this network is then selected.
- If the address cannot be resolved, then the first ARF network of the LAN interface / VLAN pair is selected.
- The selected ARF network determines the interface tag to be used.
