Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 273
Neighbor Discovery

A DVMRP router can and does discover neighbor DVMRP routers through a process known as Neighbor Discovery using the probe packet. When a DVMRP router is initialized, it transmits these discovery packets to inform other DVMRP routers that it is operational. These messages are sent periodically (every 10 seconds) to the All DVMRP Routers multicast address. Each of the messages should contain the list of neighbor DVMRP routers that it knows about on that interface. Other routers on other interfaces are not included in this listing; this is local only. Routers should see their IP addresses in their neighbors’ messages.

The probe packets allow other DVMRP routers to discover each other and to also detect when a neighbor router no longer exists. If a DVMRP router does not detect this message from a neighbor within 35 seconds, it considers that neighbor to be down.

Contained in this message is a listing of all other DVMRP neighbor routers that the router knows about. If a router does not receive any Probe messages, it considers the subnet to be a leaf network only.

Neighbor Discovery