Subject: RE: Stateless DNS discovery draft

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Wed, 17 Apr 2002 11:52:52 +0200

> > 
  > > Ok, I should say that the functionality I'd like to see is the
  > > ability to discover a DNS without relying on functional entities
  > > other than the DNS. (not necessarily the entire node, but 
  > the server
  > > itself, I think the term server is very clear and does 
  > not imply an
  > > entire node).
  > 
  > Sorry, but it really is not clear enough to sift fact from confusion
  > in some of the comments that people (not necessarily you) have made.
  > 
  > Ok, a "server" isn't a whole node, good.  But is it a 
  > process, or the
  > entity listening to a particular well-known port, or a collection of
  > subroutines that perform a particular set of conceptual functions?
  > 
  > If, say, a single process is listening to both port 53 and 
  > to port 67,
  > is that one server or two?

=> Eh, I would say 2, but if it's the same piece
of code, then who cares!

  > 
  > > The point of the work is to limit the effects of third party node
  > > failures on discovering the DNS. I.e. When I'm running a network
  > > with a million user devices in it, I can either spend 
  > money to make
  > > sure that my DHCP server is super reliable or, make sure that, at
  > > least the very basic functions of the server, are done 
  > e2e. That is,
  > > between the end host and the DNS.
  > 
  > So if the DHCP server role and the DNS server role were being
  > performed by the same "server", this would not be a problem.  Right?

=> OK, but my question is below.

  > > Exactly, but propagating information across routers is _the_ issue
  > > here. People were not comfortable with relying on 
  > multicast routing.
  > > Also having an additional function in every router (relay 
  > agent) to
  > > simply repackage this single packet didn't seem like a good
  > > investment.  Hence the chosen 'transport' mechanism in the
  > > draft. The content could well look identical to a DHCP 
  > message, but
  > > the issue is how to send this packet across the network.
  > 

  > 
  > Well, entities performing the server role of DHCP only answer Inform
  > requests when (they think) they have something useful to say.  The
  > specific mechanism by which multiple entities could act in the DHCP
  > server role on a single node 

=> But it doesn't have to be a single node. There maybe
multiple nodes, that what I don't understand. 

The rest of the discussion above is simply saying 
don't use the DNS request to discover the DNS, 
send a DHCP message first and get more. But what
happens if you have more than one server pretending
to be a DHCP server? Does the RA send the request
to a multicast address and filter the replies? 

Hesham
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From: Rob Austein <[email-masked]>
Date: Wed, 17 Apr 2002 14:13:11 -0400

At Wed, 17 Apr 2002 11:52:52 +0200, Hesham Soliman wrote:
> 
>> Well, entities performing the server role of DHCP only answer
>> Inform requests when (they think) they have something useful to
>> say.  The specific mechanism by which multiple entities could act
>> in the DHCP server role on a single node
> 
> But it doesn't have to be a single node. There maybe multiple nodes,
> that what I don't understand.

I don't think I understand what it is that you don't understand. :)

If a node that supports a DNS server choses to do so by somehow
inserting its address into a DHCP server on another node, that's ok,
but it's not necessary, and some people are concerned about that
approach because of fate sharing issues, so it'd probably be better
for each node that offers DNS service to answer the appropriate DHCP
Information Request messages for itself.

The point, however, is that the client doesn't care either way.

> The rest of the discussion above is simply saying don't use the DNS
> request to discover the DNS, send a DHCP message first and get
> more. But what happens if you have more than one server pretending
> to be a DHCP server? Does the RA send the request to a multicast
> address and filter the replies?

No "pretending" involved.  DHCP allows multiple servers, DHCP clients
cope, and DHCP relay agents just relay.
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