Subject: Re: DNAME (was: Re: I-D ACTION:draft-ietf-dnsext-ipv6-addresses-00.txt)

From: Johan Ihren <[email-masked]>
Date: 04 Oct 2001 11:48:31 +0200

Paul A Vixie <[email-masked]> writes:

Paul,

I am fairly sure that you and I are misunderstanding each other
here. I'll try to make my point somewhat clearer...

> and you think an AAAA/PTR tree will have fewer redelegation points
> than an A6/DNAME tree?  why?

No, no, no, no.

> please answer on-list, i can't post there right now.

I make no claims whatsoever about the number of delegation points in
the tree. For the sake of discussion I like to assume that there are
exactly the same number of delegations regardless of the metod used
for delegation. Also, I only talk about the reverse tree here, and
usage of DNAME in it. The AAAA vs A6 issue is completely orthogonal to
this.

My point is that regardless of how many delegations there are below
the point of a prefix change, these delgations

* with DNAME will survive, since only the DNAMEs at the apex has
  to be changed (a maximum of sixteen given nibbles).

* with traditional NS delegations the entire subtree will break apart,
  since the names of every single down-tree old delegation point will
  change.

A very contrived example: let's say that 192.in-addr.arpa gets changed
to 193.in-addr.arpa (yes, I said it was contrived...):

With DNAME: change

1.192.in-addr.arpa.       DNAME   ip6.isp1.net.
2.192.in-addr.arpa.       DNAME   ip6.isp2.net.
...

into 

1.193.in-addr.arpa.       DNAME   ip6.isp1.net.
2.193.in-addr.arpa.       DNAME   ip6.isp2.net.
...

and we're done.

Without DNAME: recursively update every single delegation point in the
set

*.*.192.in-addr.arpa.       NS      ...
...

For 192.in-addr.arpa this is roughly 2000+ delegation points as far as
I know, but that's only because 192 is unusually clean. And because
the v6 nibbles have a much deeper hierarchy I guess that it is not
unreasonable to expect more delegations in the v6 reverse trees.

My claim is that an hierarchy with thousands of delegation points will
not simply reconstruct itself if you break it apart from above unless
there is a *really* driving force for it, and then they will still be
rather unpleased about all the extra work.

Regards,

Johan Ihren
Autonomica

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