Subject: LL10 Add warnings to applicability statement

From: Stuart Cheshire <[email-masked]>
Date: Fri, 14 Feb 2003 23:24:24 -0800

Keith Moore wrote:

>> The whole rationale behind IPv4LL is that effectively *ALL*
>> application protocols can function usefully with link-local
>> addresses on a single isolated link.
>
>This may be the rationale, but it's simply not the case.  There
>are apps that, for a variety of reasons, need to have external
>connectivity even if all of the participants in the session are
>all on the local link.

This looks like an oxymoron -- if the application needs external 
connectivity, then at least *one* of the participants must be external 
(i.e. not on the local link).

However, regardless of this, the point remains that I still believe that 
with a small group of hosts connected to an Ethernet hub, IPv4LL enables 
any application to work at least as well as it could work with with *any* 
kind of addressing. Some applications may still fail by virtue of lack of 
necessary connectivity, but that lack of necessary connectivity would 
exist no matter how addresses were assigned.

I feel that this IPv4LL document is being subjected to demands that it 
contain an absolutely unprecedented amount of self-critical pejorative 
language suggesting that it is a worthless technology that is little use 
for anything.

The fact is that if you have an isolated LAN, then you don't have 
external connectivity. You can assign manual addresses, but you won't 
have external connectivity. You can set up a DHCP server, but you still 
won't have external connectivity. If you don't take any such action to 
configure an address somehow, then you won't have any IP connectivity at 
all, not even to hosts that are physically reachable. Having 
self-configuring self-assigned addresses means that hosts can at least 
communicate with the other hosts which which it is *possible* to 
communicate.

If anyone can come up with a real application (or list of applications) 
that DO NOT work with a small group of hosts connected to an Ethernet hub 
using IPv4LL addresses, but DO work with a small group of hosts connected 
to an Ethernet hub using manually-assigned (or DHCP) addresses, then I 
would support mentioning these specific applications in the document.

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer, Inc.
 * www.stuartcheshire.org