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Possible Duplicate:
How does Subnetting Work?

Amazon's elastic compute tool (among others) requires the ip block format for their command:

ec2-authorize websrv -P tcp -p 80 -s 205.192.0.0/16

I may be doing this wrong, but as far as I can tell I need to use the block format even for a single IP address. 1) So, how would I do that for this IP?

71.75.232.132

Several years ago I took a CCNA class, and I remember going over IPs and subnets, masks, broadcast addresses, class a/b/c networks, etc. However a lot seems to have changed since then - for example I don't think you can tell what "class" a network is in just by looking at it anymore - sometimes they could be multiple classes.

2) Anyhow, my second question is where do I go to get a refresher on all these things?

3) Or should I just be using ipcalc or an online calculator to do it all for me - and if so, which one?

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marked as duplicate by Mark Henderson Nov 22 '11 at 2:07

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2 Answers 2

up vote 1 down vote accepted

1) For the single IP, you can say "71.75.232.132/32".

2) and 3) You can google for CIDR. You will see the wikipedia page on CIDR, which should have something about subnetting to refresh your memor, and should have a calculator pretty high up in search results.

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I use the following in a pinch...

http://subnetmask.info/

http://www.skullbox.net/subnetcalculator.php

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