Subject: Re: Relationship DNS-SD and SLP

From: Stuart Cheshire <[email-masked]>
Date: Tue, 30 Jul 2002 21:15:11 -0700

>I wonder why Zeroconf uses DNS-SD and not SLP. Especially as older MacOS X 
>versions already supported SLP, and now Rendezvous adds DNS-SD. Does SLP 
>have any disadvantages that prevent it from being used for Zeroconf?

This question has been asked many times. To attempt to answer it, I wrote:

<http://files.dns-sd.org/draft-cheshire-dnsext-nbp.txt>

>Thanks, this is what I was looking for. Its arguments did not
>convince me though.

I will try to answer your questions. Please remember when reading these 
answers that Apple has millions of customers still using AppleTalk. They 
like AppleTalk. If we want to get rid of AppleTalk, we need to replace it 
with something at least as good. Hence it needs to meet the requirements 
I outlined. Arguing that you disagree with the requirements does not 
help. If AppleTalk did it and the customers value it, then Apple needs to 
meet that requirement in any replacement.

>1. If a user-friendly name for a SLP SA is needed, you can put it
>into an attribute
>2. You can append those attributes to the URL if
>you need to display them to the user (for example
>"service:printer:http://169.254.17.202;(name=Epson Stylus 900n)")

This does not satisfy:

2.1 Name-to-Address Mapping
2.7 "Name Space Management -or- Name Conflict Detection".

If you're really suggesting displaying that URL to the user, then it also 
does not satisfy:

2.5 User-Friendly Names

>3. If you need a persistent identifier for a SA or device and the
>host name or IP is not persistent, you can put an identifier in an
>attribute (for example a large random number or a ethernet
>hardware address).

This does not satisfy:

2.8 Late Binding

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

---

From: Erik Guttman <[email-masked]>
Date: Wed, 31 Jul 2002 11:33:36 +0200 (CEST)

> 2.1 Name-to-Address Mapping

Sure it does.  Search for the printer which has the name attribute
equal to the name of the printer you are seeking.   Get its address.

> 2.7 "Name Space Management -or- Name Conflict Detection".

Sure it does.  Search for the printer which has the name X.  If a
printer replies, do not use the name X.  If you want to find out
*immediately* if a printer is advertising itself with the name X, use
RFC 3082, Notification and Subscription for SLP.

> If you're really suggesting displaying that URL to the user, then it also 

No, you can display a user friendly name attribute or even a binary
image attribute icon, etc. in a human interface.
 
> >attribute (for example a large random number or a ethernet

I don't remember what this refers to, sorry.

Erik