I am currently preparing for my CCNA exam and am almost done with it. I will be taking it in few days time but this one subnetting problem has been nailing me constantly.
If i have an ip address 10.0.0.0/20, then will the subnets range from 10.0.0.0 to 10.0.240.0 or 10.0.0.0 to 10.255.240.0?
Another example: if the ip address is 10.0.0.0/26, will the subnets range from 10.0.0.0 to 10.0.0.192 or from 10.0.0.0 to 10.255.255.192?
I know how to calculate the host bits, subnet bits, # of hosts and subnets n all related stuff but still i cant figure out the solution to above mentioned problem.
Please give appropriate guidance.
If you have the network 10.0.0.0/20, this means that the first 20 bits define the netowrk/subnet, leaving 12 bits for host addressing.
So for this network your subnet mask is 255.255.240.0. So the octet of the mask in which subnetting is taking place is the 3rd octet.
Therefore your subnet spans the range 10.0.0.0 to 10.0.15.255
If you have the entire 10.0 range, then you could have 16 subnets, each with 4094 usable IP addresses. Each subnet number would be 16 higher then the previous one (in the third octet).
10.0.0.0 - 10.0.15.255
10.0.16.0 - 10.0.31.255
10.0.32.0 - 10.0.47.255
10.0.48.0 - 10.0.63.255
10.0.240.0 - 10.0.255.255
In example 2 you have a network 10.0.0.0.26. This means that the first 26 bits define the network/subnet, leaving 6 bits for host addressing.
So in this example your netmask is 255.255.255.192. So the octet in which subneting is taking place is the last octet.
Therefore in this example your subnet range is 10.0.0.0 to 10.0.0.63.
Again if you had the entire 10.0.0.x range you would have 4 subnets, each with 62 available host IP addresses. Each subnet number would be 64 higher then the previous subnet (in the last octet)
10.0.0.0 - 10.0.0.63
10.0.0.64 - 10.0.0.127
10.0.0.128 - 10.0.0.191
10.0.0.192 - 10.0.0.255
HTH and does not cause even more confusion so close to your exam.