Subject: Re: Requirements for Service Discovery

From: Stuart Cheshire <[email-masked]>
Date: Wed, 7 Aug 2002 15:44:10 -0700

>You just root the SLP DAs within the DNS, so that you can  reach the
>SLP DAs for a given domain. This is described in the following draft:
>
>draft-zhao-slp-remote-da-discovery-03.txt

Forgive me if I laugh, but let me quote from the introduction of that 
document:

1. Introduction

   DNS SRV [2] provides a convenient way for a UA
   to discover the SLP service

Isn't that what I've been arguing all along? DNS SRV (as described in 
NIAS) provides a convenient way to discover any service.

If you need to use DNS SRV to discover the service discovery server, why 
not just skip the middleman and use DNS SRV to discover the service 
you're actually looking for?

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer
 * Chairman, IETF ZEROCONF
 * www.stuartcheshire.org

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From: Mark Thompson <[email-masked]>
Date: Thu, 8 Aug 2002 09:47:23 +0100

> you're actually looking for?

I think I agree in principle, but disagree with choice of implementation:

NIAS promotes abuse of the TXT RR, which has been accepted
(abused?) by many as having no semantic definition and therefore used
in non-standard ways across many installations. 

If you're lucky then at least people might adopt style similar to that
suggested in experimental RFC1464 (i.e. lots of 'IN TXT "attr=val"'
entries for a single domain name), but then we're back to the game of
"which ontology for attribute names does this definition belong to?"

Just because an RR exists and its use accepted as being
non-standardised doesn't mean that a later standard can come along and
blat all over everyone else's (legitimate) use of the RR.

*blush* - we abuse it by tieing registrar/warranty information
etc. against domain names - stuff that isn't sensitive and therefore no
problem if its public, but stuff for which there is no schema or ontology
defining a syntax of use and no more convenient location to store it.

Without creating yet another RR for service attributes within the DNS
(and I'm not suggesting this!), I don't see how NIAS can reliably scale
across sites.

Maybe I've missed this being covered in an earlier thread. If so, shout
at me and direct me to the nearest archive. Thanks ;-)

Mark/

--
equator÷ irc .. .- -- university of southampton, uk

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From: Erik Guttman <[email-masked]>
Date: Thu, 8 Aug 2002 13:07:27 +0200 (CEST)

> NIAS) provides a convenient way to discover any service.

It provides a way to discover some services with various limitations.
 
> you're actually looking for?

Finding the service discovery service allows you to send complex
queries.  We are at loggerheads here, Stuart.  Some argue for the
utility of complex queries, others argue against their importance.
I suggest we discontinue this largely esthetic debate.

Erik