DHCP, Dynamic DNS, and IPv6

[David W. Hankins]

On Sat, Aug 30, 2008 at 09:27:42AM +0100, Simon Hobson wrote:
> 1) The RFC says that the IP6 DHCP server cannot simply ignore all IP4 stuff 
> in the DNS.

The RFC actually is extremely permissive, documenting an algorithm and
then admitting that there are "many possible permutations of working
update algorithms, of which the following is only an example."

Our sources right now key on DHCID matches where the name is already
in use.  It all works out of DDNS update PREREQ semantics, which makes
it all lightweight and easily atomic (very limited race conditions,
although we don't do it right now, you eliminate them by just running
in a loop for (n) times).

Since both the v4 and v6 side uses DHCID's, and they mismatch, and
there is no PREREQ to say "if no DHCID RR exists of type ___", you
have to perform a recursive query and look inside the DHCIDs.  This
puts us into potential cache implications and oh my.

But there's probably something doable in here somewhere.  There are
at least easy workarounds (give the v4 and v6 clients different
names in server-side config logic).

> 2) And the IP6 DHCP isn't compatible with existing IP4 clients in it's 
> handling of IP4 DNS unless you does 'special' things with the IP4 clients.
>
> 3) These 'special things' aren't supported on the IP4 clients - and 
> probably NEVER will be on some of them with closed source.

As the clients develop DHCPv6 capabilities, it gets fairly likely they
will support transmitting a DUID.  It is not terribly hard or onerus.

But is is an unknown.


By the by, I just remembered we actually recently added a flag to
disable conflict detection.  It actually deletes the DHCID RR's.
This was long enough ago I don't remember it all very clearly.

-- 
Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
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-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins