This question is based on the two figures shown below. One figure shows the topology of the network, and the other figure shows the assigned IP address and MAC address. If we replace the router between subnets 1 and 2 with a switch S1, and label the router between subnets 2 and 3 as R1.

a) Consider sending an IP datagram from Host E to Host F. Will Host E ask router R1 to help forward the datagram? In the Ethernet frame containing the IP datagram, what are the source and destination IP and MAC addresses?

b) Suppose E would like to send an IP datagram to B, and assume that Es ARP cache does not contain Bs MAC address. Will E perform an ARP query to find Bs MAC address? In the Ethernet frame (containing the IP datagram destined to B) that is delivered to router R1, what are the source and destination IP and MAC addresses?

c) Suppose Host A would like to send an IP datagram to Host B, and neither As ARP cache contains Bs MAC address nor does Bs ARP cache contain As MAC address. Further suppose that the switch S1s forwarding table contains entries for Host B and router R1 only. Thus, A will broadcast an ARP request message. What actions will switch S1 perform once it receives the ARP request message? Will router R1 also receive this ARP request message? If so, will R1 forward the message to Subnet 3? Once Host B receives this ARP request message, it will send back to Host A an ARP response message. But will it send an ARP query message to ask for As MAC address? Why? What will switch S1 do once it receives an ARP response message from Host B?

d) Suppose now that the router between subnets 2 and 3 is replaced by a switch. Answer questions (a)(b) in the previous problem in this new context.

Subnet 1 Subnet 22 Subnet 3