Background

Before a host can send packets to another network, it must know the IP address of at least one router on the local subnet. The host can obtain this information either through manual configuration, or from routing protocol packets sent by routers on the local subnet.

Both methods have disadvantages. The first method requires the administrator to manually configure and maintain router address information on hosts, and cannot track dynamic changes. The second method requires hosts to recognize various routing protocols, and will fail to work if no routing protocol runs on the local subnet.

IRDP was introduced to solve the problem. IRDP uses two new types of ICMP messages to allow hosts to discover neighboring routers. IRDP adapts to dynamic changes, requires less manual configuration, and does not rely on any routing protocols.