Mailing List SIMS@mail.stalker.com Message #14780
From: Lewis Butler <lbutler@covisp.net>
Subject: Re: (OT) Interpreting CIDR network info
Date: Thu, 30 Sep 2004 13:29:54 -0600
To: SIMS Discussions <SIMS@mail.stalker.com>
X-Mailer: Apple Mail (2.619)
On 29 Sep 2004, at 11:08, NetHead wrote:
For example, 218.175.0.0/16... how do I interpret that? I have read some
of the RFC's on CIDR notation, but it still boggles my mind. Would that
mean that they own the entire range from 218.175.0.0-218.175.254.254?

Exactly right.

Is there an easy way to read CIDR? or a tool that will do the conversion?

There are a bazillion pages on google that will calculate CIDRs and netmasks for you.  It is pretty easy to do yourself.

218.175.0.0 is

11011010.10101111.00000000.00000000

/16 is

11111111.11111111.00000000.00000000 (first 16 bits are ON)

this means that anything in the address that is masked (has a 1 in the netmask) does not change, so the range is

11011010.10101111.00000000.00000000-11011010.10101111.11111111.111111111

if their address range was, say, /18 then the range would be:

11011010.10101111.00000000.00000000-11011010.10101111.00111111.11111111  (218.175.0.0-218.175.63.255


if the address was a /24 then the range would be:

11011010.10101111.00000000.00000000-11011010.10101111.00000000.11111111 (218.175.0.0-218.175.0.255)

/8 is a Class A address, /16 is a Class B, and /24 is a Class C.  A Class C, of course, has 256 IPs in it.  A class B has 256^2 IPs (65536) and a class A has 256^3 IPs in it (16,777,216).  The entire IP address range contains 256^4 IPs (about 4.3 billion addresses).

--
"Let's get back to syntax of procmail and forget the syntax of fools." - Don

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