Re: DNS discovery

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 12-nov-03, at 11:14, Alain Durand wrote:

>>> My proposal is to adopt both RA-approach and DHCP-lite
>>> as in the case of Prefix Delegation.
>>> Could those who insist only on DHCP-lite hum for the coexistence of 
>>> these two mechanisms?

>> 	if you propose coexistence you need to provide details on how to
>> 	use those two, like:
>> 	- try A then B
>> 	- try A if condition X, try B if condition !X
>> 	- whatever
>> 	otherwise implementors will get highly confused.

Reading RFC 2462 will clear that confusion right up. There is an 
explicit bit in router advertisements that tells hosts whether they 
should use a stateful mechanism (sorry, this is what it's called, 
replace with "DHCPv6lite" in the next version) to discover additional 
configuration information. If this bit is set then the only reason for 
the existence of DNS RA options would be for the benefit of hosts that 
don't implement DHCP, so it would make sense for hosts that do 
implement DHCP to ignore the option in this case.

Another approach would be to simply take all the DNS addresses that can 
be found and validate this list by doing a test query or use RTT 
measurements to select the best one.

(I have a box with a long since forgotten implementation of IP(v4) + 
PPP that allows the use of DHCP to gather additional configuration 
information. This implementation also allows DNS servers to be probed 
before they are installed in the list of resolvers. All of this works 
very well.)

> And so will network admin that will now have potentially two places to 
> look after to maintain the correct information. This is bad.

This is exactly why requiring the use of some form of DHCP by making 
this the only way DNS addresses can be found is a bad idea. Hosts are 
already required to implement Stateless Autoconfiguration (again, I 
didn't come up with the name) so in this case there are two things that 
can go wrong: RAs and DHCP. If DNS discovery is integrated in RA we 
have fate sharing.

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