ICMP Router Discovery

Windows 2000 can perform router discovery as specified in RFC 1256. Router discovery provides an improved method of configuring and detecting default gateways. Instead of using manually- or DHCP-configured default gateways, hosts can dynamically discover routers on their subnet. If the primary router fails or the network administrators change router preferences, hosts can automatically switch to a backup router. When a host that supports router discovery initializes, it joins the all-systems IP multicast group (224.0.0.1), and then listens for the router advertisements that routers send to that group. Hosts can also send router-solicitation messages to the all-routers IP multicast address (224.0.0.2) when an interface initializes to avoid any delay in being configured. Windows 2000 sends a maximum of three solicitations at intervals of approximately 600 milliseconds. The use of router discovery is controlled by the PerformRouterDiscovery and SolicitationAddressBCast registry parameters, and it defaults to DHCP controlled in Windows 2000. Setting SolicitationAddressBCast to 1 causes router solicitations to be broadcast, instead of multicast, as described in the RFC.