Subject: Re: I-D ACTION:draft-palet-v6ops-tun-auto-disc-00.txt

From: Brian E Carpenter <[email-masked]>
Date: Wed, 21 Apr 2004 08:44:31 +0200

A couple of points..

In section 3 (possible solutions) I am surprised that you don't include
SLP. That is the IETF's discovery protocol, after all, and should be
discussed. Why can't we use SLP to find tunnel servers?

Section 4 puzzles me. My understanding is that anycast is best
if used in single-shot mode: send an anycast UDP packet, pick one of
the replies, and then use unicast to establish a session with the host 
that sent that reply. You won't use the anycast address again after
that initial discovery packet. It's the same as the initial broadcast
in DHCP or the initial multicast in SLP. 

Admittedly, that's not the model in RFC 3068 (Anycast for 6to4). But 6to4
is a special case, since there is no tunnel negotiation.

   Brian

> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-palet-v6ops-tun-auto-disc-00.txt

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From: Pekka Savola <[email-masked]>
Date: Wed, 21 Apr 2004 11:10:21 +0300 (EEST)

> is a special case, since there is no tunnel negotiation.

Shared-unicast DNS root servers and other load-balanced services also 
use the similar technique as 6to4.

I.e., when you just use one address, it's closest to you whereever you 
roam in the network where there are multiple anycasting servers.

Obviously, this only works if you don't need to store state in the
anycast server, or if it's OK to lose the state if the routing changes
or you move.

There doesn't have to be stored state if the IPv4 address is embedded
completely or encoded in a reversible fashion in the IPv6 address.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

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From: Brian E Carpenter <[email-masked]>
Date: Wed, 21 Apr 2004 10:47:16 +0200

> completely or encoded in a reversible fashion in the IPv6 address.

Which isn't the case in configured tunnels, hence my puzzlement at why
we would do it this way.

   Brian

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From: Pekka Savola <[email-masked]>
Date: Wed, 21 Apr 2004 12:31:17 +0300 (EEST)

> Pekka Savola wrote:
[...]
> Which isn't the case in configured tunnels, hence my puzzlement at why

I general, exactly; this would have problems.

In specific, there has been discussion of different tunnel server
models (e.g., see Alains requirements document).  It could be very
simple to figure out a solution which would give a user an IPv6 /128
address which would embed the topographical v4 address (similar but
simpler compared to e.g. what one could do with ISATAP).