Having treated how to subnet class B and Class C addresses, I did mention that class A was next in line. Starting from class C,
then to class B was a deliberate move since it is easier to understand C simply because it has less host bits (8) than the rest. With class A you have a total of 24 host bits to manipulate. In this demonstration, I will share with us how to subnet class A addresses with three examples. The examples have been carefully selected to address issues students face when subnetting class A addresses. Lets get going.
0-27; usable is 1-26. What this means is that if the values in the first octet of an IP fall between 0 and 127, then that IP is a class A address, although you can only use from 1 to 126.
that the given IP and subnetmask will produce
per subnet generated in (i) above
table, list the subnets, first, last and broadcast IPs in each subnet.
where x equals the number of bits borrowed. If the default subnetmask for class
A is /8 which is 255.0.0.0 and we are given /10 in this question, it therefore
means we borrowed 2 bits. Substituting 2 into the formula, we have 2^2=4. We
have 4 subnets.
subnets=2^y-2, where y equals the number of off bits. To get our off bit is
simple. 32-10=22. IPv4 is a 32-bit address but we are give /10 in this
question, therefore, we simply subtract 10 from 32 to get 22. Now substituting 22 into
the formula, we get 2^22-2=4,194,302. we will have 4,194,302 per each of the
four subnets.
to be able to list out subnets. Block size is 256-192=64. Because the subnet
bit falls in the second octet, we will list our subnets with the change
happening in the second octet.
|
Subnets
|
10.0.0.0
|
10.64.0.0
|
10.128.0.0
|
10.192.0.0
|
|
First IP
|
10.0.0.1
|
10.64.0.1
|
10.128.0.1
|
10.192.0.1
|
|
Last IP
|
10.63.255.254
|
10.127.255.254
|
10.191.255.254
|
10.255.255.254
|
|
Broadcast
|
10.63.255.255
|
10.127.255.255
|
10.191.255.255
|
10.255.255.255
|
(ii) The number of hosts per subnet generated in (i) above
(iii) With the aid of a table, list the subnets, first, last and broadcast IPs in each subnet./17=255.255.128.0
Answers:
(i) Number of subnets=2^9=512
(ii) Number of hosts per subnet=2^15-2=32,766
(iii)
First eight, using the last three octet( that 0.0.0 instead of 10.0.0.0, just because of space)
| subnets | 0.0.0 | 0.128.0 | 1.0.0 | 1.128.0 | 2.0.0 | 2.128.0 | 3.0.0 | 3.128.0 |
| First IP | 0.0.1 | 0.128.1 | 1.0.1 | 1.128.1 | 2.0.1 | 2.128.1 | 3.0.1 | 3.128.1 |
| Last IP | 0.127.254 | 0.255.254 | 1.127.254 | 1.255.254 | 2.127.254 | 2.255.254 | 3.127.254 | 3.255.254 |
| Broadcast | 0.127.255 | 0.255.255 | 1.127.255 | 1.255.255 | 2.127.255 | 2.255.2555 | 3.127.255 | 3.255.255 |
Last eight, using the last three octets (0.0.0 instead of 10.0.0.0, just because of space)
| Subnet | 252.0.0 | 252.128.0 | 253.0.0 | 253.128.0 | 254.0.0 | 254.128.0 | 255.0.0 | 255.128.0 |
| First IP | 252.0.1 | 252.128.1 | 253.0.1 | 253.128.1 | 25454.0.1 | 254.128.1 | 255.0.1 | 255.128.1 |
| Last IP | 252.127.254 | 252.255.254 | 253.127.254 | 253.255.254 | 254.127.254 | 254.255.254 | 255.127.254 | 255.255.254 |
| BC | 252.127.255 | 252.255.255 | 253.127.255 | 253.255.255 | 254.127.255 | 254.255.2555 | 255.127.255 | 255.255.255 |
(ii) The number of hosts per subnet generated in (i) above
(iii) With the aid of a table, list the subnets, first, last and broadcast IPs in each subnet./24=255.255.255.0
Answers:
(i) Number of subnets=2^16=65,536
(ii) Number of hosts=2^8-2=254
(iii) Our valid subnets, hosts and broadcasts are as given in the tables below:
First eight subnets, using the last three octets:
| Subnet | 0.0.0 | 0.1.0 | 0.2.0 | 0.3.0 | 0.4.0 | 0.5.0 | 0.6.0 | 0.7.0 |
| First IP | 0.0.1 | 0.1.1 | 0.2.1 | 0.3.1 | 0.4.1 | 0.5.1 | 0.6.1 | 0.7.1 |
| Last IP | 0.0.254 | 0.1.254 | 0.2.254 | 0.3.254 | 0.4.254 | 0.5.254 | 0.6.254 | 0.7.254 |
| BC | 0.0.255 | 0.1.255 | 0.2.255 | 0.3.255 | 0.4.255 | 0.5.255 | 0.6.255 | 0.7.255 |
Last eight subnets, using the last three octets:
| Sub | 255.248.0 | 255.249.0 | 255.250.0 | 255.251.0 | 255.252.0 | 255.253.0 | 255.254.0 | 255.255.0 |
| First IP | 255.248.1 | 255.249.1 | 255.250.1 | 255.251.1 | 255.252.1 | 255.253.1 | 255.254.1 | 255.255.1 |
| Last IP | 255.248.254 | 255.249.254 | 255.250.254 | 255.251.254 | 255.252.254 | 255.253.254 | 255.254.254 | 255.255.254 |
| BC | 255.248.255 | 255.249.255 | 255.250.255 | 255.251.255 | 255.252.255 | 255.253.255 | 255.254.255 | 255.255.255 |
All questions regarding this should be dropped in the comment box. Thank you.