• Distance vector protocol is an old Internet routing protocol.computers network image by Orlando Florin Rosu from Fotolia.com
  
  When messages (or parts of messages) are passed along by Internet routers, they almost always use one of two protocols: distance vector protocol or link state protocol. Distance vector protocol is the oldest and most reliable of these protocols, but it is not always the best choice for fast routing.
  
  

Distance Vector Protocol

• Distance vector protocol is one of the oldest protocols for deciding on which path a message leaves a router on the way to its destination. The process is handled by Routing Information Protocol (RIP) which is part of Information Protocol (IP) which, along with Transfer Control Protocol (TCP), form the original Internet protocol TCP/IP. RIP uses two pieces of information to decide on a path: the distance and the vector. The distance is the number of routers between the current router and the target router. The target router is the router that services the machine that the message is addressed to. The vector is a pointer to the target---there are usually several of these (one for each path from the current node to the target node). Each router periodically passes its routing table to each of its neighbors---this provides the distance and vector information. The protocol uses just this information to make path decisions.
  
  

Advantages

• The major advantages of distance vector protocol are that it is simple and that is is an old, well-established technology that is almost universally available. Because it is simple, distance vector protocol means simple hardware. You can buy a cheaper router because all routers implement distance vector protocol. If you are building an Application Specific Integrated Circuit (ASIC) such as a phone, you can have simpler digital logic circuitry and less of it. Because distance vector protocol is part of RIP, there is no incompatibility with any Internet device.
  
  

Disadvantages

• Distance vector protocol does not always find the best path. Suppose, for example, one path has five nodes (distance = 5) but the path is very high speed and not busy at all----and another path has only two nodes but is very low speed and unreliable, sometimes requiring retransmissions. Assuming that the vector includes both paths, the distance vector protocol will always choose the 2 node path although it may be a lot slower. Because of this, a newer style routing protocol called "link state protocol" was invented. Link site protocol uses a much more complicated algorithm based on information like how busy a channel is, what its transmission rate is and how reliable the connection is at the present time.