Link Layer Switching

Part 1 – Link Layer Switching (7 pts)

Consider the LAN below consisting of 10 computers connected by two self-learning Ethernet switches.

At t=0 the switch table entries for both switches are empty. At t = 1, 2, 3, and 4, a source ends to a destination as shown below, and the destination replies immediately (well before the next time step).

Assume that the following connections occur:

t=1: K -> A    (K has sent a frame to A and A has responded to K)
t=2: L -> H    (L has sent a frame to H and H has responded to L)
t=3: D -> E    (D has sent a frame to E and E has responded to D)
t=4: F -> D    (F has sent a frame to D and D has responded to F)

Provide the content of the switching tables below after all the connections occurred.

Important note about grading: assuming that the sum of entries in both switches is N, each correct entry will be graded as +(5/N) and each false entry will be graded –(5/N). Therefore, do not provide any entry that should not be there and that will make you lose points.

Switch 1

Switch 2

Part 2 – IP Network Architecture (9 pts)

An organization has acquired the IP address 193.178.0.0 and wants to build a network as described in Fig. 1.

Fig.1: Network architecture.

• What is the default subnet mask of the IP address purchased by the organization?

• How many different IP subnets you count in this network architecture?

• What is the subnet mask you will use in this network to fit this organization’s network while maximizing the number of hosts in the different subnets? Explain your method.

• What is the subnet mask you will use in this network if the organization wants to have only 12 hosts only in each of the subnets? Explain your method.

• With the subnet masks found in questions 3 and 4, do you notice any lost addresses the organization will never use, which means the organization will never be able to allocate to hosts?

If yes, indicate where and how many addresses are lost in the two cases.

Part 2 – IP Fragmentation (9 pts)

When they are routed to their destinations, the indicated packets below arrive on an interface I1 of a router and the routing table of this latter indicates that it should forward them (if necessary) through its interface I2, which would deliver out the packets on a network with an MTU of 425 bytes.

Specify the processing that each of these packets will undergo and its result at the output of the interface I2. Indicate the header of each packet when necessary.

IP packet header.