Subject: Re: summary/conclusion of discussion on mdns-00

From: Robert Elz <[email-masked]>
Date: Wed, 23 May 2001 18:29:42 +0700

Date:        Wed, 23 May 2001 12:33:47 +0200 (MEST)
    From:        Erik Guttman <[email-masked]>
    Message-ID:  <[email-masked]>

  | The only problem with this suggestion I see is that there're many DHCP 
  | servers which don't support this option

Of course, as there are also many which don't support the currently
not yet defined search list option.   No big difference there.
If we wanted something which works with current DHCP servers, then
something like the "magic address in the DNS server list option"
would be needed - but that really is pretty ugly.

  | A *better* outcome would be to allow mDNS in configured networks.

Sure, I have no problem with that.

kre

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---

From: Erik Guttman <[email-masked]>
Date: Wed, 23 May 2001 12:33:47 +0200 (MEST)

> I'd prefer to have to do the config to get that to happen.
> 
>   | There may be operational reasons, in some cases, to disable mDNS.  
>   | I want to distinguish this mode from other modes - such as a host 
>   | being configured to use certain DNS servers or being configured 
>   | to use a particular set of domains in its search list. 
> 
> Sure, I'd prefer that too.   I actually believe that a new DHCP option
> is the right way to go, rather than trying to overload an existing one
> with a new meaning.   
<snip>
> But I think that option should enable mDNS (as should most probably not
> getting any DNS "server" list from DHCP at all - that's essentially 
> returning the net to "no DNS configured" state).  Without the option, 
> and assuming that the DNS is configured, I'd leave mDNS off.

A DHCP option to turn on mDNS explicitely makes good sense.  

The only problem with this suggestion I see is that there're many DHCP 
servers which don't support this option - so enabling mDNS in configured 
networks could require DHCP server upgrades.  But following your very
reasonable principal, this is not so bad:

   > I'd just prefer that my net not just start behaving differently 
   > because I didn't change something.

>   | Isn't that an implementation decision?  Any value we specify in 
>   | seconds to wait or adaptive timeout based on RTT will in some 
>   | cases not be enough.  The real question is one of policy - is 
>   | mDNS allowed or disallowed?
> 
> Yes.   But another policy question for a network might be "what constitutes
> failure".   
<snip>
> Another reason for simply using a new DHCP option to config mDNS, all of
> this data could be included in it.

I think this is a great idea.

> You said "Please see my argument below" for why you believe that mDNS should
> default to on, even in a configured net - but I didn't ever find the
> argument in the message (or nothing more than "one could not use mDNS"
> which is just a fact, and a desireable outcome...)

Sorry I wasn't clear.  Consider:  The common configured case is to receive
DHCP DNS server configuration.  This configuration may not provide the
location of any *currently* available DNS back end resolvers (which may be
down, or so slow in responding the resolver considers it to be down).  If
this (same) DNS server configuration disables mDNS, one cannot use it in
precisely the situation where it would be valuable - as a last resort.  

Harald's suggestion allows mDNS in only unconfigured networks.  This
certainly achieves your desire that 'my net not just start behaving
differently because I didn't change something.'  A *better* outcome
would be to allow mDNS in configured networks.  OK, not by default, 
but by configuration.   Let's pursue the DHCP mDNS-Enable option.

Erik

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From: Bernard Aboba <[email-masked]>
Date: Wed, 23 May 2001 10:34:00 -0700 (PDT)

>   | A *better* outcome would be to allow mDNS in configured networks.

That's already allowed. There's nothing in the drafts that says that mDNS
is only for zero config networks.