v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space

Owen DeLong owen at delong.com
Thu Feb 5 18:38:08 UTC 2009

On Feb 5, 2009, at 8:24 AM, Roger Marquis wrote:

>>> * NAT disadvantage #3: RFC1918 was created because people were  
>>> afraid of
>>> running out of addresses. (in 1992?)
>> Yes. One of my colleague, who participated in development of RFC  
>> 1918 confirmed it.
> Your colleague was wrong.  I was one of several engineers who handed  
> out
> "private" addresses back before RFC1918 even though we could get  
> "public"

You are wrong....

Quoting from RFC 1597 (a precursor which was obsoleted by RFC 1918):

2. Motivation

    With the proliferation of TCP/IP technology worldwide, including
    outside the Internet itself, an increasing number of non-connected
    enterprises use this technology and its addressing capabilities for
    sole intra-enterprise communications, without any intention to ever
    directly connect to other enterprises or the Internet itself.

    The current practice is to assign globally unique addresses to all
    hosts that use TCP/IP.  There is a growing concern that the finite  
    address space might become exhausted.  Therefore, the guidelines for
    assigning IP address space have been tightened in recent years [1].
    These rules are often more conservative than enterprises would like,
    in order to implement and operate their networks.

Note the specific reference in the second paragraph to address space  


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