> I looked around a bit, and found only this reference in RFC 1812:
> 
>     IP addresses are not permitted to have the value 0 or -1 for the
>     <Host-number> or <Network-prefix> fields except in the special cases
>     listed above.  This implies that each of these fields will be at
>     least two bits long.
> 
> The "special classes listed above" are all zeros, and all zeros
> only for the network portion of the address;  both are to be used
> for configuring addresses.
> 
> I'd love to hear if there are more recent RFCs describing this;
> it certainly seems like it'd be nice to be able to use those extra
> addresses.

There are two issues here.  One is would anything bad happen if host-0
on a network were to be used as a unicast host address.  The other is,
would the RFC police drag us away from out keyboards in the dead of
the night.

Unless I'm overlooking something, the only danger is that some old
4.1BSD or SunOS machine on the same net would get confused and assume
its a broadcast.  (Fix: load netbsd 1.4 on the SunOS machine. ;-))

As far as I see host-0 is much in the same category as subnet-0 which
the router-rfc mumbles the following about:
 
   DISCUSSION
      Previous versions of this document also noted that subnet numbers
      must be neither 0 nor -1, and must be at least two bits in length.
      In a CIDR world, the subnet number is clearly an extension of the
      network prefix and cannot be interpreted without the remainder of
      the prefix.  This restriction of subnet numbers is therefore
      meaningless in view of CIDR and may be safely ignored.

I especially like the part "and may be safely ignored".  As far as I
can tell the same can be said for the host-0 restrictions.  Host-0 is
after all in someone's private CIDR block.  Who on the greater
internet is going to be any of the wiser about what one's internal
network netmasks look like?  Its the private business of the hosts on
that ethernet and as long as they all play by the same scorecard it
should work out just fine.

Aren't RFC's supposed to be done after the code is working?  Lets just
do it and then write about it. ;-)

-wolfgang
-- 
Wolfgang Rupprecht    <wolfgang@wsrcc.com>     http://www.wsrcc.com/wolfgang/
DGPS signals via the Internet  http://www.wsrcc.com/wolfgang/gps/dgps-ip.html