How to subnet an IP address?

[thecomptguy]

First of all sorry if this question is very easy. I am a new student in networking, so I am still learning the basics. I have a problem that I have been working on for a while, but can't figure what I am doing wrong. I have been given an address "172.16.128.0/19". I want to divide this address into two equal subnets, but can't figure out how:

This is what I have done:

           128  64 32  16| 8   4   2   1

172.16.x    x    x    x   | x   x   x   x.0 

                                    2   4   8  16

                                    1    0   0   0

I have drawn my line for /19, and assigned 1 to subnet 2 and 0s to those that are not subnet 2. I can't figure out how to find a IP address for first network and second network.  

[Georg Pauwen · Accepted solution]

Hello,

to get two subnets out of the 172.16.128.0/19 range, you need to change the mask to 17. This would give you the two subnets below:

Network: 172.16.0.0/17
Broadcast: 172.16.127.255
HostMin: 172.16.0.1
HostMax: 172.16.127.254
Hosts/Net: 32766

Network: 172.16.128.0/17
Broadcast: 172.16.255.255
HostMin: 172.16.128.1
HostMax: 172.16.255.254
Hosts/Net: 32766

If you change the mask to 20, this would give you 16 usable networks, the first two ones would be:

Network: 172.16.128.0/20
Broadcast: 172.16.143.255
HostMin: 172.16.128.1
HostMax: 172.16.143.254
Hosts/Net: 4094

Network: 172.16.144.0/20
Broadcast: 172.16.159.255
HostMin: 172.16.144.1
HostMax: 172.16.159.254
Hosts/Net: 4094

[Joseph W. Doherty]

Georg, your two /20s are correct, but why the need to go to a /17?

[Georg Pauwen]

Joseph,

this looks like some sort of exam question to me to be honest. With the /17 mask, you would get exactly two subnets. The /20 mask would leave another 14 unused subnets. I don't know which of the two the OP was looking for...

[George Stefanick]

So many folks have their own way of doing subnetting. Having learned all the ways long and short I highly recommend Lazaro Diaz.