The most important protocol when dealing with virtual routers is ARP (Address Resolution Protocol), which provides the ability to match logical addresses such as IP addresses to hardware addresses such as MAC addresses. The use of virtual and physical IP and MAC addresses means that the router's reaction to ARP requests is of great importance:
- An ARP request to the virtual router's address may only be answered when the R&S®NC router is the master. This request must be answered with the corresponding virtual MAC address. All other requests must be ignored.
- ARP requests that list a virtual router's address as the sender address must be ignored.
- When using proxy ARP, an ARP request must be checked in order to determine if a virtual router is associated with the remote site through which the requested address can be reached. If so, then the request may only be answered when the R&S®NC router is the master. This also applies to virtual remote sites (i.e. PPTP or VPN) when they use a remote site that is associated with a virtual router as a physical connection.
- ARP requests sent by the R&S®NC router itself are always sent with the real sender address, as long as this is not the address of a virtual router. In this event, the virtual MAC address must be entered in the ARP request.
