a3-sol - Solution to CSE 489/589Homework Assignment 3...

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Solution to CSE 489/589Homework Assignment 3 Prepared by Hung Q. Ngo * Problem 1. Consider the graph in Figure 1. Assume the routing tables contain only two fields: the destination and the next node router. Using Dijkstra’s algorithm , compute the routing table at node F . Show work by using the table of iterations of the algorithm as we did in class. No points will be given if you only give the final shortest path tree and/or the routing table. Figure 1: Network of routers for this question Iteration The Set T Node A Node B Node C Node D Node E Node F 0 Nil, Nil, Nil, Nil, Nil, Nil, 0 1 F F, 2 F,3 2 F,A A,12 A,4 3 F,A,D D,6 D,11 4 F,A,D,E E,10 5 F,A,D,E,B B,9 6 F,A,D,E,B,C Draw your tree here Your routing table for node F here Two branches: F–D–B–C, F–A–E Destination Next Router A A B D C D D D E A * Please let me know of any mistake/typo ASAP. 1
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Problem 2. Consider the network in Figure 2. Suppose the routing tables’s entries for destination F Figure 2: Network of routers for this question at time 0 are shown below. Also assume that all routers are perfectly synchronized so that they all send updates at the same time slot. (The table below shows the table states at time 0 .) Compute the routing table entries for destination F as the Distance Vector protocol is run over time, until no further changes are possible for any table. Time entry at F entry at A entry at B entry at C entry at D entry at E 0 ( 0 , NULL) ( , NULL) ( , NULL) ( , NULL) ( , NULL) ( , NULL) 1 3, F 1, F 2 2, B 5, A 9, A 3 4, A 7, C 10, D 4 6, C 8, D 5 7, D 6 7 8 9 10 The semantic of an entry is: (cost, next-hop). (The table might have more rows than needed.) Problem 3. (a) Consider a subnet with prefix 202.84.208/21, give an example of one IP address (of the form xxx.xxx.xxx.xxx) that can be assigned to this network (b) Suppose an ISP owns a block of addresses of the form 202.84.208/21, and suppose it wants to create 4 equal-sized subnets from this block, what are the prefixes (of the form a.b.c.d/x) for the four subnets? Solution. (a) The network address and mask in binary are 11001010.1010100.11010000.00000000 (net address) 11111111.1111111.11111000.00000000 (mask) A valid address is basically any address that starts with the same first 21 bits as the network address above. For instance, 2
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11001010.1010100.11010000.00000001
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This note was uploaded on 12/03/2010 for the course CS 489 taught by Professor Hungngo during the Fall '10 term at SUNY Buffalo.

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a3-sol - Solution to CSE 489/589Homework Assignment 3...

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