You submitted this homework on Sun 23 Feb :12 PM PST. You got a score of 5.00 out of 5.00.

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1 Feedback Homework 5 Help You submitted this homework on Sun 23 Feb :12 PM PST. You got a score of 5.00 out of Question 1 Consider the network given. Distance vector routing is used, and the following vectors have just come in to router C: from B: (6, 0, 8, 12, 6, 2); from D: (4, 12, 6, 0, 9, 10); and from E: (1, 6, 3, 9, 0, 4). (A routing vector gives the costs of the paths from a given node to every other node in the system in alphabetical order of their names. For example, the routing vector from B indicates that its distance to A is 6, its distance to B is 0, and so on.) The cost of the links from C to B, D, and E, are 4, 3, and 5, respectively. After C updates its routing table, what is C s next hop on its route towards A, and what is the cost of the computed route? 3 Next hop is D, cost is 6 Next hop is E, cost is Forwarding to E(1+5) is better than B(6+4) or D(4+3) Next hop is D, cost is 1/5

2 7 6 Next hop is B, cost is A node updates its distance to a target node by identifying the neighbor that provides it the best route to the target. The cost of the route is the sum of the advertised distance from its neighbor and the cost of its link to the neighbor. Question 2 Consider a network with 60 routers in which every router is connected to five other routers. Assume that costs (to other destination/self) are recorded as 8-bit numbers, and distance vectors are exchanged thrice a. What is the total bandwidth consumed by the distance vector updates coming out of a node/router? (Note that you need to count only the traffic coming out of it and not the traffic going into it.) 300 per 7200 per 900 per Size of each DV update = 60 * (8 bits) = 60 Number of DV updates sent every = 3 * 5 Hence, total bandwidth = 60*3*5 = 900 per = 7200 bits per 180 per 2/5

3 Each update carries costs for every router in the network (including itself). The number of neighbors and frequency of exchanges determines the number of updates per. Question 3 Consider a network with 50 routers in which every router is connected to four other routers. Assume that link state packets have the following format: number of neighbors connected to a node (represented using 8 bits), and for each neighbor, the identity of the neighbor (represented using 8 bits) and the cost of the link to the neighbor (also represented by 8 bits). What is the size of a single link state packet? We suggest that you draw the link state packet. Your Answer Score Explanation Size of link state update in bytes = 1 (to denote number of neighbours) + number of neighbors * 2 (cost and ID of neighbour) = 1 + 4*2 = 9 bytes 72 The format of the link state packet described in the question determines the size of the link state packet when configured for the specific network. 3/5

4 Question 4 Consider the given network. How many ECMP routes exist from D to A and what is the cost of these routes? 3 routes of cost 3 D->C->B->A D->F->E->A D->F->B->A 2 routes of cost 3 4 routes of cost 3 3 routes of cost 4 ECMP routes are equal cost routes through the network. Try to find all possible ways in which you can route from the source to the destination that matches the cost of the shortest path between them. Question 5 A router has computed the following paths: 4/5

5 packets to prefix /24 are sent through line 1 packets to /24 through line 2 packets to /24 through line 2 packets to /24 through line 1 Which one of the following is NOT a valid routing table configuration given these paths? Route to /22 through line 2, route to /24 through line 1, and route to /24 through line 1 Route to /22 through line 1, route to /23 through line /23 is not a valid prefix Route to /22 through line 1, route to /24 through line 2, and route to /24 through line 2 Route to /23 through line 1, route to /24 through line 2, route to /23 through line 2, route to /24 through line 1 Check whether the aggregated routing entries send packets through the appropriate line for each of the target addresses. 5/5