Internet Control Message Protocol (ICMP) router discovery is the use of ICMP messages to discover the default gateway on a network segment when a default gateway is not manually configured or assigned by using DHCP. ICMP router discovery consists of two ICMP messages: the router solicitation and the router advertisement. A router solicitation is sent by a host to discover the routers on the network. A router advertisement is sent by a router in response to a router solicitation, and is sent periodically to notify hosts on the network that the router is still available. ICMP router discovery is enabled by default on TCP/IP for Windows 2000 hosts.
You can configure a Windows 2000 Server computer running the Routing and Remote Access service to support ICMP router discovery as a router.
ICMP router discovery is described in RFC 1256, "ICMP Router Discovery Messages."