I would like to amplify Howard's comments below and doubly 
stress two words in his one line explanation, 
namely "controlled" and "violation".  

In terms of **Internet Gateways** (read routers) this is an 
acceptable practice for what the RFC describes in its 
title, "Using 31-Bit Prefixes on IPv4 Point-to-Point Links".

In my humble opinion, that is the **ONLY** place where this 
should be used.  A case in point is this:

3.1. "Requirements for Internet Hosts -- Communication Layers" 
[RFC1122]

   Section 3.2.1.3 (e) is replaced with:

      (e)  { , , -1 }

         Directed broadcast to the specified subnet.  It MUST 
NOT be used as a source address, except when the originator is 
one of the endpoints of a point-to-point link with a 31-bit 
mask.

Anybody want to take any bets as to how well that will work on 
your standard Winthing?  I already tried it, and it is very 
unhappy (to put it mildly).  This goes back to a previous post 
and a previous discussion we had about IP subnet zero and the 
subtle differences spelled out on RFC 1122 and RFC 1812.  I 
submit then, as I do now, that RFC 1122 does still remain in 
force and describe the intended behavior of Internet hosts (non-
Gateways/routers).  Personally, I would not have recommended 
the change listed in the paragraph above, since it clearly has 
very little relevance (how many Internet hosts sit on a local 
area network with a point to point connection?)

If what I said was not clear enough, heed these words - test 
this out wherever you think you may want to implement it, and 
make sure it works for everything you need to do.

I can't wait to shed the legacy baggage of IPv4.

v/r,

Paul Werner


> >I read the RFC, so I guess it can be used.  My bad.
> >
> >AM I correct in saying that one interface will be assigned 
the all zero
> >subnet as it's IP and the other will be assigned the 
broadcast IP
> address
> >for that subnet?
> >
> >Steve
> 
> 
> Yes. It's a controlled violation of that addressing rule.

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