IGNOU BCA 4th sem Solved Assignment - Explain the working of Distance Vector Routing using an example. Also, discuss the Count to Infinity Problem

Explain the working of Distance Vector Routing using an example. Also, discuss the Count to Infinity Problem

Ans

Distance Vector means that Routers are advertised as vector of distance and direction. 'Direction' is represented by next hop address and exit interface, whereas 'Distance' uses metrics such as hop count.

Routers using distance vector protocol do not have knowledge of the entire path to a destination. Instead DV uses two methods:

1.      Direction in which or interface to which a packet should be forwarded.

2.      Distance from its destination.

In Distance Vector routing, routers update their record based on these events:

·         When routers are started

·         When routers have changes to their routing tables

·         On a periodic basis

Advantages of Distance Vector routing:

·         It is simpler to configure than Link State

·         It is simpler to maintain than Link State

Disadvantages of Distance Vector routing:

·         It is slower to converge than Link State

·         It is at risk from the count-to-infinity problem

·         It creates more traffic than Link State since a hop count change must be propagated to all routers and processed on each router. Hop count updates take place on a periodic basis, even if there are no changes in the network topology, so bandwidth-wasting broadcasts still occur.

·         For larger networks, Distance Vector routing results in larger routing tables than Link State since each router must know about all other routers. This can also lead to congestion on WAN links. RIP announces host or default routes by default.

The count-to-infinity problem happens when a router is unableto reach an adjoining network. A second router, 1 hop away from the first router, thinks that the unreachable network is 2 hops away. Meanwhile, the first router then updates its records to say it is 3 hops away from the unreachable network based on the fact it is 1 hop from the second router, which says it is 2 hops from the unreachable network. The routers continue incrementing their hop count until the maximum (15), "infinity", is reached.

There are three methods of preventing this problem: Split Horizon, Split Horizon with Poison Reverse, and Triggered updates.