How to tell which IP is valid only based on the given subnet mask

Question

I'm looking for a way to tell which IP is valid only based on the given subnet mask.

For example : given the subnet mask : 255.255.255.240, is 195.206.108.25 a valid IP? Why?

The subnet mask is only useful if you also have the network prefix. — Oliver Charlesworth, Oct 20 '14 at 07:24
@OliverCharlesworth Actually this is a question I'm facing : http://pik.vn/2014d8df73e2-3e8b-4d2a-abe9-606bad30d266.jpeg , maybe I misunderstood the question — f855a864, Oct 20 '14 at 07:27
@t.thielemans: It's possible to answer the question "Given mask `M` and network `N`, is IP `v` valid?" But if `N` is not given, then the answer is always "yes" (other than for reserved IP addresses). — Oliver Charlesworth, Oct 28 '14 at 13:57

CustomX · Accepted Answer · 2014-10-28T12:25:50.257

IP: 195.206.108.25

MASK: 255.255.255.240 (/28)

     255.255.255.255
  -  255.255.255.240
---------------------
       0.  0.  0. 15

Network: 195.206.108.0/28
Usable hosts: 195.206.108.1-195.206.108.14
Broadcast: 195.206.108.15

Network: 195.206.108.16/28
Usable hosts: 195.206.108.17-195.206.108.30
Broadcast: 195.206.108.31

So 195.206.108.25 is a valid IP address of the 195.206.108.16/28 network. (correct me if I'm wrong)

How to tell which IP is valid only based on the given subnet mask

1 Answers1