Re: What is "/24" in front of the IP number?

["Steven M. Bellovin" <smb () research att com>]

In message <20001031124400.3739.qmail () web1502 mail yahoo com>, =?iso-8859-1?q?F
abio=20Losnak?= writes:
> Nowadays I'm working with firewall linux, and I'm
> configuring one in a client organization. I found in
> the script who apply the rules of the firewall
> (IPCHAINS) the follow lines:
>
> INT0="eth0"
> IP0="192.168.1.125/24"
> NET0="192.168.1.0"
>
> What is "/24" in the IP number?

The /24 is the "prefix length" -- the number of leading bits that 
identify a network.  A traditional class C is a /24, since it has 24 
bits of network number and 8 bits of host number within the network.  
Similarly, class A nets are /8s, and class Bs are /16s.  But that 
distinction is obsolete, and network numbers are no longer constrained 
to byte boundaries.

                --Steve Bellovin



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