Most routing protocols fall into one of two classes: distance vector or link state. The basics of distance
vector routing protocols are examined here; the next section covers link state routing protocols. Distance
vector algorithms are based on the work done of R. E. Bellman,[1] L. R. Ford, and D. R. Fulkerson[2] and
for this reason occasionally are referred to as Bellman-Ford or Ford-Fulkerson algorithms.
[1] R. E. Bellman. Dynamic Programming. Princeton, New Jersey: Princeton University Press; 1957.
[2] L. R. Ford Jr. and D. R. Fulkerson. Flows in Networks. Princeton, New Jersey: Princeton University Press; 1962.
The name distance vector is derived from the fact that routes are advertised as vectors of (distance,
direction), where distance is defined in terms of a metric and direction is defined in terms of the next-hop
router. For example, "Destination A is a distance of 5 hops away, in the direction of next-hop router X."
As that statement implies, each router learns routes from its neighboring routers' perspectives and then
advertises the routes from its own perspective. Because each router depends on its neighbors for
information, which the neighbors in turn may have learned from their neighbors, and so on, distance
vector routing is sometimes facetiously referred to as "routing by rumor."
Distance vector routing protocols include the following:
Routing Information Protocol (RIP) for IP
Xerox Networking System's XNS RIP
Novell's IPX RIP
Cisco's Internet Gateway Routing Protocol (IGRP)
DEC's DNA Phase IV
AppleTalk's Routing Table Maintenance Protocol (RTMP)