Recently, I thought to write on “why we cannot use first or last IP address in a subnet?”. In fact, I expended my previous network of 192.168.10.0/24 to 192.168.8.0/22. Previously, I used IP subnet 192.168.10.0/24 with IP range 192.168.10.0 to 192.168.10.255 in the network. Now, IP subnet 192.168.8.0/22 with IP range 192.168.8.0 to 192.168.11.255 where 1022 usable IP Addresses are available to use.
Now, the question is that why we cannot use these in a subnet? Of course, the answer is very much straight forward but let me creates some awareness on this.
Network Address:
Indeed, the network address is the first IP address of the subnet. Here, we used /22 subnet starting with 192.168.8.0 but you may have any other IP starting with any subnet mask. Thus, 192.168.8.0 IP address is called network IP Address in our scenario.
Scenario: Network Address
For example, you own very small network where you are using 192.168.10.192/28 subnetting. Here, your network address will 192.168.10.192 instead of 192.168.0.
Broadcast Address:
Now, Simplest definition of Broadcast address is that last or highest IP address of your subnet is called broadcast Address. Earlier, we used /22 subnet where IP address starts from 192.168.8.0. Now, if you calculate 192.168.8.0/22 with online IP Subnet Calculator, you can view 192.168.11.255 as broadcast address. Then, we conclude that highest IP address is called broadcast address. Broadcast address is used to broadcast anything in a network instead of a single host.
Scenario: Broadcast Address
Of course, with example mentioned in network address scenario, let’s expand it here too. 192.168.10.192/28 will give us 192.168.10.207 as broadcast address.
First or Last IP Address in a Subnet
Now, we have better understanding about the network address and broadcast address. Thus, First IP will always be used to identify the network. Secondly, the last IP address will be broadcast address to reach all hosts in a network.
Now, if you are a Windows user, open the command prompt and type netstat -r to see the IP routing table as image below.
Finally, in the image above, you can see three highlighted lines. Now, just remember that the first and last address in any network or subnet can’t be assigned to any individual host.
