Re: TR : Stepping back on the DNS discovery discussion

[Tim Chown <tjc@ecs.soton.ac.uk>]

On Wed, Jul 16, 2003 at 02:31:14PM +0200, BELOEIL Luc FTRD/DMI/CAE wrote:
> 
> As DNS is a critical service between "applications world" and "IP layer world", we might be careful on consequences. From application point of view, we might ask in the future to extende that solution to other type of services (NTP, ...). In that way, RA-based solution might not be the good solution, because I do think that RA must not be extended to any sort of service discovery. Any idea about that?

So where do you draw the boundary between "network device autoconfiguration" 
and "service discovery".   For IPv4, you (manually or via DHCP) configure
IPv4 address, netmask, gateway and DNS resolver(s) as the "basic" four 
components to be able to get up and running.   In IPv6, when using stateless 
autoconfiguration, the RA mechanism takes care of the first three (because 
the stateless mechanism implies the /64 "netmask"), but the DNS resolver 
address(es) cannot be learnt (although I believe WinXP implements the 
well-known site local discovery method).

So an interesting question is what we mean by "stateless autoconfiguration".
I think this term is causing some of the religion in the discussion :)   It 
seems that probably mean "autoconfiguration without servers (i.e. DHCPv6)",
since there would have to be state (pre-configuration) in the router (the 
prefix configuration).   The RA camp seems to want the routers to be able to
issue DNS resolver information, not a separate full-blown DHCPv6 server.

But it's not that clear cut as, for example, my home DSL router includes
a DHCP server (as well my DNS server and print server and other stuff).
The functionality is combined, all in a very cheap (<100 Euro) commodity box.

So are we really concerned as to whether we need a separate DHCPv6 server on
our network (and the overhead of that in ad-hoc networks), or that we would 
like a router to be able to provide DNS resolver information on link (such that
we can plumb networks without needing a separate DHCPv6 box)?   If the latter, 
then does it matter if the router does that via RA piggybacks or DHCPv6 Lite?
What is the real difference in implementation cost?

Of course the mode of operation is also an interesting issue, but it's possible
for DHCPv6(Lite) to have an unsolicited response mode added, if that is felt
to be important.

Something has to configure the prefix information to the router, likewise
the DNS information has to be configured.  I don't think we've discusse that
much, but distributing the DNS resolver information to multiple routers rather
than one (or a small number of) DHCPv6 servers may require more thought.  But
in my home network, it'll all be in my DSL router :)

Tim
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