I have the following subnets:

How can I combine all these subnets to form one single subnet so that the first usable address in the subnet is and the last usable one is

  • I've been trying to formulate an answer but I cant get it readable enough. But remember that netmasks are in fact binary and need to be of base 2. This means a subnet must be of size 1/2^n of the original adress space and the number if IPs in a subnet always is 2^m. You are asking for a 111 adress subnet but 111 is not base 2. (2^7 = 128) – Peter Jul 9 '15 at 10:16
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    This looks suspiciously like homework – Ron Trunk Jul 9 '15 at 11:28
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  • Hi. I am not in school. I am a Network Professional and CCNP certified. I can understand your point of view that this may seem as ridiculously simple question. However this was a need of one of my customers. Currently he has servers in / 28 subnet and wants to enlarge the subnet by using addresses starting from I told him this was not possible but he is totally convinced that this is possible. So I thought probably I am missing something really fundamental and so I posted this here. And if this is a "Networking" forum I don't understand why such questions are a problem !? – Thorsten Dahl Jul 10 '15 at 11:37
  • Additional Sidenote - The crazy customer also wants me to consult Cisco about subnetting ! Any ideas how to handle such people ? – Thorsten Dahl Jul 10 '15 at 11:38

The lowest ip is, and the highest is (from

The smallest subnet (bigest mask) to cover both is

When you sub-dived the subnet, by increasing the mask to /25 you get two subnets, not one can covers all the subnets in the question. (Range (Range

The ranges you provided is not continuous, and the answer covers them all and the network in between and at the start and end of the ranges.

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