Subnetting Question

If IP address 172.16.0.0 is given, what combination of addresses and masks will be valid to create subnets?

172.16.160.0 /20 and 172.16.168.0 /20
172.16.32.0 /19 and 172.16.64.128 /25
172.16.192.0 /18 and 172.16.224.0 /19
172.16.128.0 /18 and 172.16.128.192 /26

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Comments

david_r

1) /20 Magic number = 16; Network = 172.16.160.0 - 172.16.175.255. 168 isn't divisible by 16.

2) /19 Magic number =32; Network = 172.16.32.0 - 172.16.64.0. /25 magic number is 128; 128 is divisible by 128. Network = 172.16.64.128-255

3) /18 Magic number is 64; 192 is divisible by 64. Network = 172.16.192.0 - 172.16.223.255. /19 Magic number is 32. 224 is divisible by 32. Network = 172.16.224.0 - 172.16.255.255.

4) /18 Magic number is 64. 128 is divisible by 64. Network = 172.16.128.0 - 172.16.191.255. /26 Magic number is 64. 192 is divisible by 64. Network - 172.16.128.192-255

Aaron.Stones

Thanks for your answer, however I am not sure how to interpret it.

Is any of given combinations more appropriate than others?

Thanks for your patience.

david_r

Aaron,
Are there 4 choices? If so, 2,3 and 4 are valid. They don't overlap and the network numbers given are the starting points of the subnets. IOW, they are valid subnets. As to appropriatness, there'd have to be alot more info to determine that.

Or is the question asking, of all 8 of these, which work together? If so, I gave you the complete range for each subnet. If two overlap they aren't "appropriate."

Or maybe you don't understand my process?

172.16.160.0/20 = 172.16.160.0 - 172.16.175.255. That's 4096 hosts.
172.16.168.0/20 does not exist as a network. 172.16.168.0 is a host address in the above range.

172.16.32.0/19 = 172.16.32.0 - 172.16.64.0.
172.16.64.128/25 = 172.16.64.128-255

172.16.192.0/18 = 172.16.192.0 - 172.16.223.255.
172.16.224.0/19 = 172.16.224.0 - 172.16.255.255.

172.16.128.0/18 = 172.16.128.0 - 172.16.191.255.
172.16.128.192/26 = 172.16.128.192-255

edit: removed "...overlap (like 172.16.192.0/19 and 172.16.128.192/24)" as it is just plain wrong. Sorry about that.

elvant

david_r wrote:

172.16.32.0/19 = 172.16.32.0 - 172.16.64.0.

should it be 172.16.32.0 - 172.16.63.255

:
correct me if not

david_r

You are absolutely right