Distance vector routing protocols share updates between neighbors. Neighbors are routers that share a link and are configured to use the same routing protocol. The router is only aware of the network addresses of its own interfaces and the remote network addresses it can reach through its neighbors. Routers using distance vector routing are not aware of the network topology.
Some distance vector routing protocols send periodic updates. For example, RIP sends a periodic update to all of its neighbors every 30 seconds. RIP does this even if the topology has not changed; it continues to send updates. RIPv1 reaches all of its neighbors by sending updates to the all-hosts IPv4 address of 255.255.255.255, a broadcast.
The broadcasting of periodic updates is inefficient because the updates consume bandwidth and consume network device CPU resources. Every network device has to process a broadcast message. RIPv2 and EIGRP, instead, use multicast addresses so that only neighbors that need updates will receive them. EIGRP can also send a unicast message to only the affected neighbor. Additionally, EIGRP will only send an update when needed, instead of periodically.
As shown in the figure, the two modern IPv4 distance vector routing protocols are RIPv2 and EIGRP. RIPv1 and IGRP are listed only for historical accuracy.