The first routing protocols produced were distance vector routing protocols, and are occasionally referred to as Bellman-Ford or Ford-Fulkerson routing protocols, based on the work of R.E. Bellman, L.R. Ford, and D.R. Fulkerson. These protocols are simpler than linkstate protocols. In distance vector routing protocols, distance vector routes are advertised as vectors of distance and direction. The distance metric is usually router hop count. The direction is the next-hop router to forward the packet to. The hop count is usually limited to 15 hops in distance vector routing protocols, an important scaling limitation.
Distance vector algorithms call for each router to send all or some portion of its routing table only to its neighbors. The router builds a new table and sends it to its neighbors, and so on. The table is sent in a periodic fashion. The following is a list of distance-vector routing protocols (including non-IP routing protocols):
• IP Routing Information Protocol (RIP)
• Cisco's Interior Gateway Routing Protocol (IGRP)
• IPX Routing Information Protocol (IPX RIP)
• AppleTalk Router Table Maintenance Protocol (RTMP)
• Xerox's XNS Routing Information Protocol (XNS RIP)
Another protocol, Enhanced Interior Gateway Routing Protocol, is considered a hybrid routing protocol. This is a distance vector that acts as a link-state routing protocol.
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