Subject: RE: threats ID

From: "Christian Huitema" <[email-masked]>
Date: Fri, 23 Jan 2004 09:35:42 -0800

> > However, TCP is not IP, which is the point of my presentation
> > at Vienna.
> We can hardly disagree. But TCP is not SCTP, UDP, DCCP or ICMP either.
> The systems level argument for a layer 3.5 solution is that it can
cover
> all cases, including ones we have not invented yet.

The flip side of that argument is that different transport layers have
different ways of coping with multiple paths between two nodes.
Currently, TCP does not; SCTP has an integrated support for multi-path;
UDP is a pass-through layer and leaves multi-path handling to the
application; and ICMP just does not care. If multi-path support becomes
important, the transports will evolve, and develop different algorithms
that fit different usage model. It is not hard to see how transports
could use per path RTT measurements and congestion windows to arbitrage
between load balancing, resiliency, and re-sequencing. By imposing a
"3.5" layer, you make an early decision to forestall this evolution.

-- Christian Huitema

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From: Iljitsch van Beijnum <[email-masked]>
Date: Fri, 23 Jan 2004 19:01:56 +0100

On 23-jan-04, at 18:35, Christian Huitema wrote:

> It is not hard to see how transports

There are two main aspects to this problem: finding addresses and 
binding them to a session, and switching between the addresses that are 
available for a session. I agree that transport protocols are in the 
best position to do the latter, so we should make sure they are allowed 
to do so by any new mechanisms we create. At the same time, we can 
provide a simple mechanism for this that allows unmodified transport 
protocols to work over multiple addresses.

But finding and binding addresses is something that has many 
repercussions that fall outside the competence of transport protocols 
and that would benefit from being implemented just once rather than 
separately for each transport protocol.

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From: Masataka Ohta <[email-masked]>
Date: Sat, 24 Jan 2004 08:31:53 +0900

Christian;

>>The systems level argument for a layer 3.5 solution is that it can cover

To deny such a sweeping argument of Brian, a counter example is
just enough.

> application;

Thus, UDP is a counter example.

NAT can not properly handle UDP.

							Masataka Ohta

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From: Eliot Lear <[email-masked]>
Date: Fri, 23 Jan 2004 16:02:42 -0800

> NAT can not properly handle UDP.

Name service queries have worked PROPERLY with NAT since day 1. 
Similarly, NTP will work perfectly fine for client services.  This is 
demonstrated by the fact that Apple Computer actually specifies a 
default of time.apple.com as a time server (brave souls).  Not that this 
is an advertisement for NAT, mind you.  There are lots of things with it 
that break, like your sweeping statement.

What's really too bad is that when you make such sweeping statements you 
lose credibility, and that would be just fine with me except that every 
now and again you actually say something that advances the discussion.

Eliot

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From: Masataka Ohta <[email-masked]>
Date: Sat, 24 Jan 2004 11:57:49 +0900

Eliot Lear;

> Name service queries have worked PROPERLY with NAT since day 1. Similarly, NTP will work perfectly fine for client services.

That some application over UDP works over NAT does not deny
that UDP is a counter example.

> like your sweeping statement.

Your misunderstanding is that you thought a counter example
must be sweeping.

However, an example, by definition, is merely required to
be an example.

                            Masataka Ohta