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Re: [Spud] discovery

Michael Welzl <michawe@ifi.uio.no> Thu, 19 March 2015 23:21 UTC

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From: Michael Welzl <michawe@ifi.uio.no>
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Cc: Aaron Falk <aaron.falk@gmail.com>, "spud@ietf.org" <spud@ietf.org>
Subject: Re: [Spud] discovery
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> On 19. mar. 2015, at 17.18, Brian Trammell <ietf@trammell.ch> wrote:
> 
> hi Aaron,
> 
>> On 19 Mar 2015, at 11:48, Aaron Falk <aaron.falk@gmail.com> wrote:
>> 
>> The draft
> 
> ... where "the draft" is draft-hildebrand-spud-prototype ...
> 
>> doesn't say much about how one efficiently determines whether the other end is SPUD-capable so that an application can know whether it can use it.
> 
> No, it doesn't.
> 
>> Has anyone given thought to this?
> 
> Yes, I have...
> 
> I think for the most part that this question is (1) very important but (2) mostly orthogonal to that we're trying to answer in spud-prototype.
> 
> Initially, I would expect that discovery works the same way that it does for any other user of the transport layer: you either have a URL, or a name and a port, or some information from your application-layer protocol's discovery service, which includes "uses x-over-SPUD" in its semantics.
> 
> Dynamically discovering a SPUD endpoint might make sense if a server port / URL schema is assigned to a service over X or a service over x-over-SPUD. In this case, the magic number we've selected makes SPUD server probing by the client possible: a SPUD packet is neither valid UTF-8, UTF-16, UTF-32, ASN.1 BER or DER, DTLS, NTP, DNS, DHCP, TFTP, or Bittorrent. This is not an exhaustive list, but we haven't found a protocol over UDP that is likely to consider d8 00 00 d8 as the first four bytes anything other than an error.

- but that won't tell you if SPUD actually does work across the path...


> Maybe we should mention this in the draft, but I think it's the *next* problem to solve.

to me, this has a "famous last words" feel to it...

Cheers,
Michael

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