Consider the following network: A ------- R1 -------- R2 ------ B. Host A IP Add
ID: 3709468 • Letter: C
Question
Consider the following network: A ------- R1 -------- R2 ------ B.
Host A IP Address: 192.168.1.10
Host A MAC Address of its interface: 00-11-22-33-44-55
Router R1 IP address of left interface: 192.168.1.1
Router R1 MAC Address of left interface: aa-bb-cc-dd-ee-ff
Host B IP address: 10.1.1.1
Host B MAC Address of its interface: 22-33-44-55-66-77
Host A sends an IP datagram to Host B. The datagram is encapsulated inside an Ethernet frame and sent to router R1. What source MAC address and destination MAC address will A put in the header of the Ethernet frame? What source IP address and destination IP address will A put in the header of the IP datagram?
Explanation / Answer
network: A ------- R1 -------- R2 ------ B.
Host A IP Address: 192.168.1.10
Host A MAC Address of its interface: 00-11-22-33-44-55
Router R1 IP address of left interface: 192.168.1.1
Router R1 MAC Address of left interface: aa-bb-cc-dd-ee-ff
Host B IP address: 10.1.1.1
Host B MAC Address of its interface: 22-33-44-55-66-77
Host A sends an IP datagram to Host B. The datagram is encapsulated inside an Ethernet frame and sent to router R1. As the Host B is not inside the network of the host A, so host A will generate a arp request for its default gateway. The default gateway will reply with its MAC address. So the host A will fill the source IP as its IP i.e. 192.168.1.10 and destination IP as IP of B i.e. 10.1.1.1 and Source MAC as its MAC i.e. 00-11-22-33-44-55 and Destination MAC as aa-bb-cc-dd-ee-ff (Router's MAC). The router will take care of forwarding the packet in the appropriate route. Before forwarding the packet to the other network(router R2), R1 will replace the L2 header with its MAC on right interface(Which is connected to R2) as source MAC and destination MAC as the left interface MAC of R2. The MAC of left interface of R2 would have been learned by R1 using arp by then. Then as Host B is inside the network of R2, it will forward the packet directly after changing the sources and destination MAC as R1 did.