Subject: RE: "unique enough" generation

From: "Christian Huitema" <[email-masked]>
Date: Thu, 21 Nov 2002 14:00:59 -0800

> I'm assuming that for the intents and purposes of replacing
> "local" site-locals, "nearly unique" site-locals would be enough.

Not quite. You should get the slides of Rob Austein presentation to the
working group. We must really separate two issues, reachability and
ambiguity. It is very easy to ensure that a block of address is not
reachable -- any firewall can do that. But just because an address is
unreachable does not mean that they could just as well be ambiguous,
because these ambiguous addresses end up leaking in various places: DNS
records, source of ICMP packets, next hop in BGP messages, "received"
headers in mail or "via" headers in SIP, etc. In short, buggy addresses
appear at places where they should not. Ambiguity causes problem,
because you can never debug these problems.

I realize that we have a tension between two requirements, uniqueness
which imposes some form of registration, and "free use" which imply
making up the addresses locally and virtually guaranteeing possible
collisions. Maybe we have to embrace the dilemma, and allow for several
types of identifiers, some guaranteed unique and some quasi random. But
you must definitely provide unique numbers to those who are ready to
wait for registration.

-- Christian Huitema

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From: Pekka Savola <[email-masked]>
Date: Fri, 22 Nov 2002 00:21:46 +0200 (EET)

On Thu, 21 Nov 2002, Christian Huitema wrote:
> Not quite. 

Depends on what you want.  (Perhaps we should try to formulate these 
better first, but it's more interesting to just pop up some solutions :-).

I believe these will allow for all the cases site-locals were used in 
"limited" cases in the meeting, probably even those in "moderate" on the 
side.

[...]
> because you can never debug these problems.

I'm not sure what you mean exactly.  Suppose someone's fec0:1234:5678::1
leaks to the global DNS somehow.  Someone else has fec0:abcd:deff::1
configured in their site.  When you configure your sites prefix length as
e.g.  /48 but still have a null-route (and filters) for fec0::/10, there
should be no problems with connections at all -- they don't work as they 
shouldn't.

> types of identifiers, some guaranteed unique and some quasi random. 
...
> But

Which kind of users would require this kind of complete, guaranteed 
uniqueness?

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords