Re: TR : Stepping back on the DNS discovery discussion

[Jaehoon Jeong <jaehoon_paul@yahoo.com>]

In this DNSOP meeting, RA-based DNS discovery has been
being discussed in comparison with DHCP-based DNS
discovery. As it seems that this discussion is related
to IPv6 wg, I send this issue in CC to IPv6 wg for
listening to IPv6 members' liberal opinions and
comments.

> 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).
>

For consistent and time-saving autoconfiguration, I
think, we need to adopt one of two alternatives in
sequence (stateless and stateful approaches). In IPv4
domain, DHCP is enough for the autoconfiguration. But,
in IPv6, we introduced stateless autoconfiguration.
Like Tim's opinion, DNS information is missing in the
current IPv6 stateless autoconfiguration. Of course,
DHCPv6 is a good solution. However, in order to get
only DNS information, it is so limited direction for
all kinds of IPv6 networks, such as home network,
HMIPv6, NEMO and MANET connected to the Internet, to
adopt only DHCPv6-based DNS discovery. 
IMHO, RA-based DNS discovery is a really really good
companion with DHCP approach, not enemy or competitor.

> 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?
>

I think no great difference.
 
> 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.
>
 
Just in order to announce DNS information, isn't to
run  DHCPv6(Lite) overactive? RA-piggyback
announcement of DNS information with prefix
information is efficient in the respect of the amount
of announced traffic.

> 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, 

Right, let's discuss further.

> but distributing the DNS resolver information
> to multiple routers rather
> than one (or a small number of) DHCPv6 servers may
> require more thought.  

In current Cisco router, we configure the addresses of
recursive DNS servers for its own name resolution.
Therefore, the DNS servers' addresses have already
been configured. We only have to use the information
so as to announce DNS information through RA message.
How about?

/Jaehoon Paul

> But
> in my home network, it'll all be in my DSL router :)
> 
> Tim
>
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