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Homework 2 Answers

Jeffrey Absher

xxx-xx-xxxx

7. (10 pts) Ex. 70 in Chapter 3.
What are the four connecting devices? Describe their functions, rank them according to their complexity and give the OSI layer on which they operate
Layer1 – repeater – takes a degraded/attenuated input and repeats it “clean” for output.
Layer2 – Bridge – keeps lists of devices (MAC addresses) present on each interface, and repeats frames on the appropriate interface if it hears them on a different interface. This allows a network to be partitioned and increase the data rate of shared media.
Layer3.-.Router.-. Maintains tables of destinations and “next hops,” Listens for packets destined for remote networks and forwards them to the appropriate network for most efficient delivery.
Layer4 & above – Gateway – converts protocols (TCP/IP to AppleTalk etc.)

8. Refer to the figure on p.25 of Unit 2. Assume that the port connected to LAN A is port X and the one connected to LAN B is port Y. Further assume that the forwarding table is currently empty. The following sequence of transmissions occur:

· Station 4 transmits a frame to station 10

· Station 5 transmits a frame to station 10

· Station 20 transmits a frame to station 5

· Station 5 transmits a frame to station 4

a. (10 pts) For each transmission, list the port(s) on which the frame will be transmitted by the bridge.

b. (10 pts) Show the contents (without showing the timeout values) of the final table.

Station 4 xmits to 10, Bridge will flood & retransmit on port Y, table is

X	Y
Station 4

Station 5 xmits to 10, Bridge will flood and retransmit on port Y, table is

X	Y
Station 5
Station 4

Station 20 xmits to 5, Bridge retransmit on port X, table is

X	Y
Station 5	Station 20
Station 4

Station 5 xmits to 4, Bridge will not retransmit, table is

X	Y
Station 5	Station 20
Station 4

9. (20 pts) Ex. 32, 34, 35, 39 in Chapter 4.
32. A host with IP address 128.23.67.3 sends a message to a host with IP address 193.45.23.7. Does the message travel thru any router?
Yes Class B to C
34. A host with IP address 128.23.67.3 sends a message to a host with IP address 128.45.23.7. Does the message travel thru any router?
Yes Class B to B outside of subnet
35. A host with IP address 128.23.67.3 sends a message to a host with IP address 128.23.23.7. Does the message travel thru any router?
Probably No, Class B to B inside same subnet.
39. A host with IP address 9.11.67.3 sends a message to a host with IP address 9.34.2.7. Does the message travel thru any router?
No, Class a to A inside same subnet.

10. (20 pts) Ex. 48. 50, 54, 55 in Chapter 4.
48. A router is connected to network 108.0.0.0. It sends a direct broadcast packet to all hosts in this network. What are the source and destination IP addresses used in this packet?
S.The router’s IP (probably 108.0.0.1)
D.108.255.255.255
50. A host with IP address 108.67.18.70 sends a limited broadcast packet to all hosts in the same network. What are the source and destination IP addresses used in this packet?”
S.108.67.28.70
D.255.255.255.255
54. A host with IP address 185.42.56.88 wants to use loopback testing. What are the source and destination addresses?
S.185.42.56.88
D.127.0.0.1
55. A host with IP address 218.34.13.89 wants to use loopback testing. What are the source and destination addresses?
S.218.34.13.89
D.127.0.0.1

11. (15 pts) Ex. 59, 60, 61 in Chapter 4.
59.A host in class A which does not know its IP address wants to send a message to a bootstrap server to find its address. What are the source and destination addresses?
S.0.0.0.0
D.255.255.255.255
60.A host in class B which does not know its IP address wants to send a message to a bootstrap server to find its address. What are the source and destination addresses?
S.0.0.0.0
D.255.255.255.255
61.A host in class C which does not know its IP address wants to send a message to a bootstrap server to find its address. What are the source and destination addresses?
S.0.0.0.0
D.255.255.255.255

12. (5 pts) Ex. 19 in Chapter 5.
The IP address of a host on a class C network is 198.123.46.237. Four subnets are allowed for this network. What is the subnet mask? Assume a contiguous address space.
255.255.255.192

13. (20 pts) Ex. 32 and 33 in Chapter 5.

14. (20 pts) Ex. 36 and 37 in Chapter 5.

15. (20 pts) Ex. 44 in Chapter 5.

16. (10 pts) Ex. 54 and 55 in Chapter 5.

17. (20 pts) Ex. 21, 23, 26 and 29 in Chapter 6.
21.Using Table 6.1 determine the next-hop address if router R1 receives a packet destined for 111.45.32.16?
The next hop is 111.45.32.16 and it will go out interface m0.
23. Using Table 6.1 determine the next-hop address if router R1 receives a packet destined for 194.17.21.45?
The next hop is 111.20.18.14 and it will go out interface m0.
26. Using Table 6.1 determine the next-hop address if router R1 receives a packet destined for 193.14.5.196?
The next hop is 193.14.5.196 and it will go out interface m1.
29. Using Table 6.1 determine the next-hop address if router R1 receives a packet destined for 189.73.43.23?
The next hop is 111.30.31.18 and it will go out interface m0.

18. (20 pts) Ex. 33 in Chapter 6.
Show the routing table for R5 in figure 6.9.

Mask	Dest	NxtHop	F	R.C.	U.	I.
255.255.255.0	194.17.21.0	-	U	0	0	M1
255.255.255.0	192.16.7.0	-	U	0	0	M0
0.0.0.0	0.0.0.0	192.16.7.5	U	0	0	M0

19. (10 pts) Ex. 28 in Chapter 7.

20. (10 pts) Ex. 32 and 34 in Chapter 7.

21. (20 pts) Ex. 39 in Chapter 7.

22. (20 pts)

a. The transport layer has 1500 bytes (entire TCP segment) to be transmitted over a network, using the IP protocol, that supports a maximum packet size of 1024 bytes (headers + data). Assuming a minimum IP header size, derive the following fields in each of the datagram headers:identification (you can make up a number for this), total length, fragment offset, and more fragments flag.

Packet #1

ID:1796

Total Length:1020

MoreFrags:1

Frag Offset:0
Packet #2

ID:1796

Total Length:520

MoreFrags:0

Frag Offset:125

Now the first fragment in part (a) go through a network that supports a maximum packet size of 256 bytes, while the remaining fragment(s) go to another network that supports a maximum packet size of 512 bytes. Derive the various fields in the fragments.
Packet #1a

ID:1796

Total Length:252

MoreFrags:1

Frag Offset:0

Packet #1b

ID:1796

Total Length:252

MoreFrags:1

Frag Offset:29
Packet #1c

ID:1796

Total Length:252

MoreFrags:1

Frag Offset:58
Packet #1d

ID:1796

Total Length:252

MoreFrags:1

Frag Offset:87
Packet #1e

ID:1796

Total Length:92

MoreFrags:1

Frag Offset:116

Packet #2a

ID:1796

Total Length:508

MoreFrags:1

Frag Offset:125
Packet #2b

ID:1796

Total Length:32

MoreFrags:0

Frag Offset:186