CNT 4704: Computer Communication Networks

Fall 2010

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Homework 3

(assigned 10/21; due: 10/28, submitted via webcourse, late submission: Oct. 31th with 15 points off)

1.  Consider a datagram network using 32- bit host addresses. Suppose a router has four links, numbered 0 through 3, and packets are to be forwarded to the link interfaces as follows:
Destination Address Range                                Link Interface
11100000 00000000 00000000 00000000           
through                                                                  0
11100000 00111111 11111111 11111111

11100000 01000000 00000000 00000000
through                                                                  1
11100000 01000000 11111111 11111111

11100000 01000001 00000000 00000000
through                                                                 2
11100001 01111111 11111111 11111111

otherwise                                                              3

a). Provide a forwarding table that has four entries, uses longest prefix match-ing, and forwards packets to the correct link interfaces.
b). Describe how your forwarding table determines the appropriate link inter-face for datagrams with destination addresses:
11001000 10010001 01010001 01010101
11100001 01000000 11000011 00111100
11100001 10000000 00010001 01110111

2. Consider a router that interconnects three subnets: Subnet 1, Subnet 2, and Subnet 3. Suppose all of the interfaces in each of these three subnets are required to have the prefix 223.1.17/24. Also suppose that Subnet 1 is required to support up to 63 interfaces, Subnet 2 is to support up to 95 inter-faces, and Subnet 3 is to support up to 16 interfaces. Provide three network addresses ( of the form a.b.c.d/x) that satisfy these constraints.

3. You need to show how the algorithm works by computing a table similar to the table shown in Page 23 in Chapter4-part2.ppt.

4. Distance Vector Routing: Consider the network shown below, and assume that each node initially knows the costs to each of its neighbors. Assume all nodes receive their neighbors' update message at the same time and update their own distance table at the same time (similar to the example shown in Page 32,33 in Chapter4-part2.ppt). Show the distance table update procedure in the similar way as Page 33 in Chapter4-part2.ppt.

5. What are the three major routing protocols used in Internet? Give their full name and their acronym. Which protocol is mainly based on link-sate algorithm? Which protocol is mainly based on distance vector algorithm?