format for IP address ranges?

[Peter Murray]

It is supplied in many ways, and most of them are based on the old 
notion of IP address range "classes" (e.g. the "Class A", "Class B", 
and "Class C", etc., blocks).  We now live in a world of "classless" IP 
addressing (isn't it wonderful to have a classless society), so it can 
be argued that IP address ranges should be sent in CIDR notation.

Webopedia has an article (<http://www.webopedia.com/TERM/C/CIDR.html>) 
on the topic, and there is also a good, but technical, discussion of 
the history and reasoning behind CIDR at:

  <http://public.pacbell.net/dedicated/cidr.html>

Part of that document says:

    Classless Inter-Domain Routing (CIDR) is a replacement for the old
    process of assigning Class A, B and C addresses with a generalized
    network "prefix". Instead of being limited to network identifiers
    (or "prefixes") of 8, 16 or 24 bits, CIDR currently uses prefixes
    anywhere from 13 to 27 bits. Thus, blocks of addresses can be
    assigned to networks as small as 32 hosts or to those with over
    500,000 hosts. This allows for address assignments that much more
    closely fit an organization's specific needs.

    A CIDR address includes the standard 32-bit IP address and also
    information on how many bits are used for the network prefix. For
    example, in the CIDR address 206.13.01.48/25, the "/25" indicates
    the first 25 bits are used to identify the unique network leaving
    the remaining bits to identify the specific host.

Our law school has four of what one would have called "Class C" 
addresses (137.99.233.*, 137.99.234.*, 137.99.235.* and 137.99.236.*, 
in the old notation).  That is all represented as:

  137.99.233.0/22

The great thing about that notation is one can copy it and paste it 
into the Apache access directive lines and it will be properly 
understood.  I don't know how many vendors support CIDR notation, but 
(IMHO) they should.


Peter

--On Monday, July 2, 2001 10:16 PM -0700 Eric Hellman <eric at openly.com> 
wrote:

> This is probably an easy question, but when a library supplies IP
> address ranges to an information provider for the purposes of IP
> address authentication, is there a standard or semi-standard format
> for this information? I imagine this might be pretty simple for an
> academic institution, but rather complicated for a corporate library
> or a consortium.


--
Peter Murray, Computer Services Librarian              W: 860-570-5233
University of Connecticut Law School             Hartford, Connecticut