Your senior network engineer tells you to configure the DHCP server to lease the last 100 usable IP addresses in subnet 12.5.4.0/23. Which of the following IP addresses could be leased as a result of your new configuration?
12.5.5.200 is the correct answer. To answer this question, you need to find the range of addresses in the subnet, which typically then means you need to calculate the subnet ID and subnet broadcast address. With a subnet ID/mask of 12.5.4.0/23, the mask converts to 255.255.254.0.
The subnet mask is 255.255.254.0, so the network ID multiplier is 256 – 254 = 2.
The possible subnet IDs are 12.5.0.0, 12.5.2.0, 12.5.4.0, 12.5.6.0, 12.5.8.0, 12.5.10.0 and so on. In this case, the network 12.5.4.0 is the winner.
The IP address range of the network is 12.5.4.0 – 12.5.5.255 (the next address 12.5.6.0 is the next subnet ID)
The broadcast address is the last address of the network so, the broadcast address is 12.5.5.255. The usable addresses of that network are 12.5.4.1 – 12.5.5.254 we exclude the network ID (12.5.4.0) and the broadcast address (12.5.5.255).
Now you need to find the last 100 usable addresses to configure the DHCP. The range of the last 100 usable IP addresses is 12.5.5.155 – 12.5.5.254
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