Play detective: After monitoring IP traffic on a 15-node Ethernet LAN for 10 min
ID: 3594369 • Letter: P
Question
Play detective: After monitoring IP traffic on a 15-node Ethernet LAN for 10 minutes one evening, someone notices that all frames from node A to node B carry IP packets that have destination IP addresses matching B’s IP address. However, all frames from node B to node A carry IP packets with destination IP addresses NOT matching A’s IP address. Nodes A and B are connected to the same switch, and both appear to accept those frames without incidents. Why would node A behave this way? Explain (Hint: there is nothing abnormal here, so don’t go on a wild goose chase).
Explanation / Answer
On the same switch,
1.Node A determines it needs to talk to an IP(Node B's IP).
2.Node A sends an ARP request asking the IP which is matching to someone(Node B)
3.The switch broadcasts Node A's ARP request.
4.Node B sees the ARP request, knows that he has the IP Node A is looking for, and sends an ARP response that includes his MAC address to Node A.
5.Node A now has Node B's MAC address, and will send a frame with Node B's MAC address as the source and Node A's MAC as the destination, which the switch will pass along.
6.Future communication between Node A and Node B will be through the switch via MAC addresses.