Purpose of Routing Protocol Routing protocols can be described as a set of guidelines that are used by routers to resolve the best path to which it should forward packets destined for a remote network. The routing algorithms determine the specific route that is the best choice for the packet to be forwarded to. Every router holds a carnal knowledge of any networks that are attached to them directly and understand which interfaces connect them to these networks and their associated costs. Routing protocols allow routers to have the ability to share information with other routers that run that same protocol; advertising routes thru a series of broadcasts are one method used to accomplish this task. These protocols have the ability to dynamically update their routing tables based on information received from other devices in the network. Some routing protocol simply share their own routing tables with adjacent nodes till all nodes have a common understanding of the best routing costs to all attached networks. Other routing protocols have a much more complex methodology of propagating their information in the form of a distributed database that each router holds a working copy of. When a change is executed or occurs, the change is distributed to all nodes in the system and their local routing tables are updated to reflect the change. These methods are how routers gain their knowledge of the topology that is in the network. (Doyle, J. 2001)
Distance-vector Routing Protocol
Distance vector routing protocols are simple protocols that are typically used in packet switching network. These protocols use the Bellman-Ford algorithm, Ford–Fulkerson algorithm, or DUAL FSM algorithms to decide on the best path to which a routing device should advance a packet destined for another network. These decisions are based on calculations of distance and direction to an adjacent network with the least cost and shortest distance between the nodes. Distance vector typically uses a cost associated with every link to determine the best path for forwarding packets; this cost is normally referred to as the “hop” count. (linfo 2005) When a path has less cost associated with it, it is determined to be the best path to a destination network. Information is propagated in the form of broadcasts containing either a portion or a router’s entire routing table as the payload. Distance vector protocols are usually best when used in smaller networks because of the ease at which they are setup and configured and how quickly they converge in smaller networks.
Advantages and Disadvantages of Distance-vector Protocols
The downside of distance vector protocols is that they typically do not scale well in larger networks and have a much greater convergence time factor than protocols of a different nature. Another less attractive side effect of distance vector protocols are the fact that most distance vector protocols send their entire routing table instead of incremental updates every 30 seconds to every active interface. This causes an increased amount of traffic on the network and also causes associated routers to consume much more resources than with a link state protocols in larger network scenarios. One of the other issues with distance vector is the routing by rumor effect of receiving information from neighboring routers or second hand information. (Heshamtecom 2011)If a route is lost from an associated router on the network then all routers who’s routing table still show that network as being an available path with a valid hop count, will continue to advertise this path as valid. If the router who has lost this path does not advertise the loss of this link fast enough, it is conceptually possible for it to receive a route for that lost network from an adjacent neighbors update. If this happens then a network loop is created when the router who lost the network, receives a routing…