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TCP/IP addressing

Greetings all,

I have a quick question, simple, but quick. A few of us here at work are having a little disagreement as to what and what you can not use when it comes to addresses when subnetting. We do know that in the host portion of the address ranges, you need to take 2 away 2^2-2. The issue comes up when we are talking about the bits that have been borrowed to make subnets. Can you use the first range and the last range, for example, with a /27 can you have the subnet address address and the first address or would the first subnet be and the first address If I remember correctly, I have indeed used the .0 subnet address and .1 as the first host on my test network when I did use subnetting.

If anyone can help maybe clear this up that knows for sure if you can or can not do this it would help greatly.


  • Other Network Infrastructure Subjects

Re: TCP/IP addressing

It is not recommended to use subnet 0 or the all ones subnet, but you can. You just have to be careful there isn't a problem with your routing scheme and/or routing protocols. To use subnet 0 use the IOS command ip subnet-zero. More info here:

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