Some organizations may need even more subnets. For example, a small ISP that requires 2000 subnets for its clients. Each client will need an abundance of space in the host portion to create their own subnets.
The network address 10.0.0.0 has a default subnet mask of 255.0.0.0 or /8 prefix. This means there are 24 host bits available to borrow toward subnetting with /8 prefix length address. Therefore, the small ISP will subnet the 10.0.0.0/8 network. To create subnets we must borrow bits from the host portion of the IP address. Starting from the left to the right with the first available host bit, we will borrow a single bit at a time until we reach the number of bits necessary to create 2000 subnets. As shown in in the table in table in figure 1, we need to borrow 11 bits to create 2048 subnets. Specifically, we need to borrow the 8 bits in the second octet and 3 extra bits from the third octet. Figure 2 display the resulting subnet mask for all sub-network convert from (255.0.0.0 – 11111111.00000000.00000000.00000000) to (255.255.224.0 – 11111111.11111111.11100000.00000000) or a /19 prefix.
The resulting subnets of borrowing 11 bits creating subnets from 10.0.0.0 /19 to 10.255.224.0 /19. Each sub-network containing 8190 hosts. The Sub-network starting from 0 to 2047 (2048 total sub-networks).So how can we find the address range of any sub-network.? There are several ways to find the address range of any sub-network. Here we will find the address range for any sub-network using the sub-network number. There are five steps to find the address ranges for any sub-network which is following
- Convert the number of the network into binary.
- Place the binary digits into borrowed bits positions.
- For the first usable IP address, all bits will be 0, except the most right bit which should be 1.
- For the last usable IP address, all bits will be 1’s except the rightmost bit, which should be 0.
- All bits should be changed to 1 in the host portion of the broadcast address.
Examples of finding the network range for any subnetwork
Example-1 – fined the address range for network number 300.
Example-2 – fined the address range for network number 1035.
Example-3 – fined the address range for network number 1975.
Example-4 – fined the address range for network number 2047