Question

LAN adapter A H B 2 6 C (router) E D Figure 2: LAN network diagram IL Question 4 (a) Consider the LAN in Figure 2 i. How many subnets can you find? Write down the labels (letters) of the hosts in each subnet i. What is the physical topology of the subnet(s)? i. How does the switch know A is reachable via interface 1, B reach- able via interface 2 and so on (Use a simple example to briefly explain your answer)?

Answer 1

i. When an IP network is divided into smaller sub-networks, subnets are obtained.There are two subnets in the LAN in Figure 2. One comprises of hosts A, B, D, E and F and the other comprises of G, H, I and J.

ii. The physical topology of both the networks is star topology. Each host in the subnet is directly connected to a switch using a LAN adapter. This is indicative of star topology where each host is connected to a central hub (switch or a central host) using a point-to-point connection.

iii. A switch maintains a MAC (Media Access Control) table or CAM (Content Addressable Memory) table which maps the MAC address of each host with the interface it is connected on. For example, If the router C receives a packet, first the destination IP address is translated to destination MAC address using Address Resolution Protocol (ARP). Then the switch references the MAC table to find the relevant interface to reach the destination host.