Re: [tae] New draft: announcing the supported transports via DNS

Caitlin Bestler <cait@asomi.com> Fri, 18 September 2009 23:50 UTC

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From: Caitlin Bestler <cait@asomi.com>
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Date: Fri, 18 Sep 2009 16:50:53 -0700
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To: Dan Wing <dwing@cisco.com>
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Cc: tae@ietf.org, 'Bryan Ford' <bryan.ford@yale.edu>, 'Joe Touch' <touch@ISI.EDU>
Subject: Re: [tae] New draft: announcing the supported transports via DNS
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On Sep 18, 2009, at 3:55 PM, Dan Wing wrote:

>
>
> I have seen ideas on this mailing list for how to do in-band with  
> TCP (using
> TCP options).  I haven't seen any ideas for how to do in-band with  
> UDP;
> perhaps because nobody cares about evolving UDP, or perhaps because  
> there
> isn't an in-band solution for UDP (I expect it's the latter).
>
>

There is no simple solution for UDP because all possible UDP datagrams  
are
already legal. You cannot define a new meaning for a set of UDP  
datagrams
when those binary images are already legal to to transmit.

The closest you could come is having a reserved port number for the UDP
negotiation. Theoretically, your remote peer had no basis to send to  
that
port number anyway so can't really be upset that you have attached a
special meaning to all messages arriving on that port.

But such a solution would have the negative side-effect of cluttering up
UDP NATP tables in middle-boxes that don't know the special meaning
of the newly reserved port number.

--
Caitlin Bestler
cait@asomi.com
http://www.asomi.com/CaitlinBestlerResume.html