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# Blocking an IP or IPs.

Posted on 2002-06-06
Medium Priority
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I was given an IP of 213.248.112.0/24 to block on our firewall. What exactly does the /24 mean at the end. Should I block 213.248.112.1 to 213.248.112.24?
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Question by:scully12
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Accepted Solution

scott_renton earned 400 total points
ID: 7059355
The /24 is a common method for denoting the subnet mask used with a particular network block.  In order to translate this into a X.X.X.X format, simply start countint the number of bits from LEFT to RIGHT, up to 24.  So in your case, its:

1 1 1 1 1 1 1 1  = 8 bits = 255

If you multiply those 8 bits by three, you get 24, so the subnet mask is:

255.255.255.0 <- 8 bits.8 bits. 8 bits

As for your firewall, you should put in the network number (the address ending with .0), and the 255.255.255.0 as the subnet mask.  On some systems, the firewall OS will autopmatically change the notation for you.
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Author Comment

ID: 7059647
Thanks for the quick response.
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