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How to subnet an IP address?

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.  

Everyone's tags (1)
1 ACCEPTED SOLUTION

Accepted Solutions
VIP Purple

Hello,

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

4 REPLIES
VIP Purple

Hello,

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

Super Bronze

Georg, your two /20s are

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

VIP Purple

Joseph,

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...

So many folks have their own

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

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
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