1. Consider the following network of routers (A, B, C and D) in which the numbers above each link indicate the relative routing cost of that link.
2. Assume a distance vector routing algorithm has been deployed in this network (Bellman-Ford algorithm without split horizon or poison reverse method). Starting from an initial blank state (empty routing table), each node sends its routing tables to its neighbours periodically each T seconds. 
3.  
4. How many update periods (excluding the initial point) does it take until the routing protocol converges? Show the content of the routing table at each node (next hop and total cost for all destinations) at each update period until the final convergence. Show the final routing table at each node.
5.  Now suppose some time after the convergence in part (a), the link A - D is upgraded to higher speed so that the cost of this link is now 3.  Starting from the routing tables you calculated in step (a), show how the routing tables change toward a new state. Show all steps and calculate how long does it take until the routing tables converge.
6. Some time after the upgrade in part (b), the link B-C fails.  Starting from the routing tables you calculated in step (b), show how the routing tables change toward a new state Show all steps and calculate how long does it take until the routing tables converge. Is there a difference in convergence time between case (b) and (c)? Comment on your results.
7.  
8. Hint: Use the following format for the routing tables: (Node A as example):

  

2 B 2 5 6 1 D