Subject: Multicast DNS clarification needed

From: "Nicolae, Dan" <[email-masked]>
Date: Tue, 15 Aug 2000 19:12:46 -0400

First of all, before commenting over the MDNS drafts draft it would be good
to know if draft-aboba-dnsext-mdns-01.txt and Bill Manning's draft, both
with similar names, are being seen as competing specifications or they are
supposed to coexist.

I am assuming here that, despite the identical name, the two drafts
complement each other and commenting on one involves keeping the other in
mind.

I remember seeing remark about the practical impossibility to have two
separate processes listening on the same IP port but different IP addresses
(unicast and multicast). I am not sure how true that is, but if it is, it is
important to consider it when talking about three mechanisms (DNS and two
MDNS) that plan to share the same port (53).

This issue was mentioned in the SSDP draft (now defunct). Here is the
relevant paragraph:
 " 8.3.2.    Why does SSDP need to use a port other than 80? 
 
   The result is that if we used port 80 on the SSDP multicast scope 
   then we would require that the SSDP software also grab port 80 for 
   the local machine. This would mean that SSDP could only be 
   implemented on machines which either didn't have HTTP servers or 
   whose HTTP servers had been enhanced to support SSDP. 
    
   We felt this was a unnecessary restriction. Therefore we are 
   choosing to use a port other than 80 on the SSDP multicast channel. "

Assuming that all three DNS protocols may have to be implemented in a single
process, and the DNS server behavior is dependent on what IP address a DNS
packet is received from (unicast or the two multicast groups), I see
potential implementation problems.

I hope some sockets gurus will pick this one up and validate it for various
flavors of OSes and sockets.

Then we'll know if the two drafts can be treated separately or all three
(add standard DNS) must be judged together from a single process
perspective.

Thanks,
/dan

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From: Randy Bush <[email-masked]>
Date: Tue, 15 Aug 2000 17:44:04 -0700

it is possibly relevant that the iesg asked the dnsext wg for help with the
link local autoconf issue.

randy

---

From: [email-masked]
Date: Wed, 16 Aug 2000 17:16:23 +0900

>MDNS) that plan to share the same port (53).

	I'm not sure if it is at all relevant to the topic...

	We (KAME team, www.kame.net) have fairly stable aboba-mDNS
	implementation, based on 00 draft.  Our implementation works as
	a tiny DNS server daemon.  application programs will contact the
	mDNS daemon using unicast UDP, and the mDNS server daemon relays it
	to link-local multicast on the wire, and that would reach the
	adjacent node.  We only have single daemon listening to UDP port 53
	(which is mDNS daemon).

	if it is necessary for mDNS daemon to contact normal unicast DNS
	servers, it can also relay traffic to normal DNS servers using
	unicast UDP.

	application programs
	libc resolver
	  | unicast UDP port 53
	  v				unicast
	mDNS daemon -----------------------------> normal DNS servers
	  | multicast, UDP port 53
	  v
	mDNS daemon on adjacent node

	as aboba-mDNS is a zeroconf solution, I do not really expect to run
	aboba-mDNS daemon on the same machine as we run normal DNS server.

	i'm not sure if the above example is relevant to manning-mDNS at all.

itojun