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How does IPv4 Subnetting Work?

I thought I understood this but I am momentarily confused. Here is an example:

Are all IPv4 addresses from to in the private range, regardless of subnet mask / routing prefix?

According to this page, the CIDR prefix is not routed on the public internet. My understanding is this means that all IP addresses from to are private, if you are using a subnet mask of prefix of 16.

I thought that means if your subnet mask is prefix is 24, you are no longer covered in the private range, because you are not on the same subnet when using a prefix of 24 instead of 16.

Is this correct? If this is not correct, can someone explain how the addressing using prefix 24 still covers prefix 16? I know there is a lot of info on the net about subnetting; if there is somewhere that answers this specific question please point me to it.

Edit: is it that a smaller routing prefix would not guarantee the IP to be in the same range, but a larger routing prefix would?

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marked as duplicate by Skyhawk, Michael Hampton, Chris S Nov 7 '12 at 2:25

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

by the way, if you use chrome, there's a really handy chrome app called "subnet calculator" that helps with a lot of these issues. – Sirex Nov 6 '12 at 23:28
up vote 8 down vote accepted

Think of the /16 and /24's as a notation for how large a network is. A /24 is ~255 times smaller than a /16, but that does not mean it's not in the same range of addresses.

so yes, is private, so is, as both are subsets of

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Yes, that is correct.

Maybe the wikipedia article should be improved with if you are using a subnet mask of prefix of 16 OR SMALLER.

Though I am not sure smaller is clear in this context. Smaller value? Smaller net? Smaller host part. Maybe 192.168/Foo where foo is 16 or larger. (Damm. Clear documentation is hard.)

If one source is confusing then I like to consult another source as reference. Serverfault has one such source at

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I think in this case, "smaller" means towards 0 on a number line. – taz Nov 6 '12 at 23:36
I had to think about it. When I have to do that with a sentence I wrote myself then I am not writing the clearest explanation (or documentation) ever. My habit is to mark such things and revise them after a break. (Or add graphics. Sometimes a picture actually is worth a thousand words.) – Hennes Nov 6 '12 at 23:42

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