I am new to networking. I was wondering if it is possible to subnet an IP from my ISP multiple times with different netmasks.

For example, if I was given the IP block Can I subnet this to something like and use it for one department and then subnet that same IP block a second time to something like and used it for another department?

  • Both answers (so far) are correct because your examples overlap. While you can't have a and a, you could have (for example) a and a
    – YLearn
    Commented Feb 24, 2018 at 6:10
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Commented Apr 1, 2018 at 21:24

2 Answers 2


No, IP addresses need to be unique (like telephone numbers). You can subnet your /16 network into 64 /22 subnets.


Yes, you can subnet it any way you like, but if you want to advertise the subnets, you cannot advertise any network prefix longer than /24. That doesn't mean you can't subnet and use it as you like and only advertise the summary.

You could have something like:

  • One /17 (
  • One /18 (
  • Two /19 ( and

or any combination that adds up to the full /16.

Since the RIRs have run out of IPv4 addresses to assign to ISPs, getting a prefix as small as /16 will be pretty expensive.

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