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the link connecting Host A to the Internet by R bps. Suppose that the process in Host A is capable of sending data into its TCP socket at a rate S bps, where S = 10*R. Further suppose that the TCP receive buffer is large enough to hold the entire file, and the send buffer can hold only one percent of the file. What would prevent the process in Host A from continuously passing data to its TCP socket at rate S bps? TCP flow control? TCP congestion control? Or something else? Elaborate.
Chapter 4
1. What is the difference between routing and forwarding?
2. What are the two most important network-layer functions in a datagram network? What are
the three most important network-layer functions in a virtual-circuit network? 3. Do the routers in both datagram networks and virtual-circuit networks use forwarding tables?
If so, describe the forwarding tables for both classes of networks. 4. Describe how packet loss can occur at input ports. Describe how packet loss at input ports
can be eliminated (without using infinite buffers). 5. Describe how packet loss can occur at output ports.
6. What is HOL blocking? Does it occur in input ports or output ports? 7. What is the 32-bit binary equivalent of the IP address 223.1.3.27?
8. Do routers have IP addresses? If so, how many?
9. Is it necessary that every autonomous system use the same intra-AS routing algorithm? Why or why not?
10. Consider Figure 4.35. Starting with the original table in D, suppose that D receives from A
the following advertisement:
Will the table in D change? If so how?
11. Why are different inter-AS and intra-AS protocols used in the Internet?
12. Consider a datagram network using 32-bit host addresses. Suppose a router has five links,
numbered 0 through 4, and packets are to be forwarded to the link interfaces as follows:
Destination Address Range Link Interface
11100000 00000000 00000000 00000000
Through 0 11100000 00000000 11111111 11111111
11100000 00000001 00000000 00000000
Through 1 11100000 00000001 11111111 11111111
11100000 00000010 00000000 00000000
Through 2
11100000 11111111 11111111 11111111
11100001 00000000 00000000 00000000
Through 3
11100001 11111111 11111111 11111111
Otherwise 4
a. Provide a forwarding table that has four entries, uses longest prefix matching, and forwards packets to the correct link interfaces.
b. Describe how your forwarding table determines the appropriate link interface for datagrams with destination addresses:
11001000 10010001 01010001 01010101 11100000 10101101 11000011 00111100
11100001 10000000 00010001 01110111
13. Consider a datagram network using 4 bit host addresses. Suppose a router uses longest prefix
matching and has the following forwarding table: Prefix Match 00 01 10 11 Interface 0 1 2 3 For each of the four interfaces, give the associated range of destination host addresses and the number of addresses in the range. （14、15、16可选讲）
14. 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
220.2.240/120. Also suppose that Subnet 1 is required to support up to 2000 interfaces, and Subnets 2 and 3 are each required to support up to 1000 interfaces. Provide three network addresses (of the form a.b.c.d/x) that satisfy these constraints.
15. Consider a subnet with prefix 101.101.101.64/26. Give an example of one IP address (of form
xxx.xxx.xxx.xxx) that can be assigned to this network. Suppose an ISP owns the block of
addresses of the form 101.101.128/17. Suppose it wants to create four subnets from this block, with each block having the same number of IP addresses. What are the prefixes (of form a.b.c.d/x) for the four subnets?
16. Consider the topology shown in Figure 4.17. Denote the three subnets with hosts (starting
clockwise at l2:fi)) as Networks A, B, and C. Denote the subnets without hosts as Networks D, E, and F.
a. Assign network addresses to each of these six subnets, with the following constraints: All addresses must be allocated from214.97.254/23; Subnet A should have enough addresses to support 250 interfaces; Subnet B should have enough addresses to support 120 interfaces; and Subnet C should have enough addresses to support 120 interfaces. Of course, subnets D, E and F should each be able to support two interfaces. For each subnet, the assignment should take the form a.b.c.d/x or a.b.c.d/x - e.f.g.h/y.
b. Using your answer to part (a), provide the forwarding tables (using longest prefix matching) for each of the three routers.
17. Consider sending a 4,000-byte datagram into a link that has an MTU of 400 bytes. Suppose
the original datagram is stamped with the identification number 422-How many fragments are generated? What are their characteristics?
Consider the following network. With the indicated link costs, use Dijkstra's shortest-path algorithm to compute the shortest path from r to all network nodes. Show how the algorithm works by computing a table similar to Table 4.3.
18. Consider the network shown below, and assume that each node initially knows the costs to
each of its neighbors. Consider the distance-vector algorithm and show the distance table entries at node z.
19. Consider the network fragment shown below. -r has only two attached neighbors, w and y. w
has a minimum-cost path to destination u (not shown) of 5,and y has a minimum-cost path to u of 6. The complete paths from w and y to z (and between w and y) are not shown. All link costs in the network have strictly positive integer values.