Re: [dnsext] draft-li-dnsext-ipv4-ipv6 -- a more versatile proposal

[Stuart Cheshire <cheshire@apple.com>]

On 6 Nov 2009, at 13:35, Paul Vixie wrote:

> the way to handle this is to include
> AAAA as additional data in A responses, and include A as additional  
> data
> in AAAA responses.


I agree. FWIW, this is exactly what we do in Multicast DNS:

<http://tools.ietf.org/id/draft-cheshire-dnsext-multicastdns.txt>

8.2 Responding to Address Queries

   In Multicast DNS, whenever a Responder places an IPv4 or IPv6  
address
   record (rrtype "A" or "AAAA") into a response packet, it SHOULD also
   place the corresponding other address type into the additional
   section, if there is space in the packet.

In addition, if there isn't a record of one or other type, we indicate  
this using an NSEC record.

This is for cases like where an SRV response has an A record in the  
additional section but no AAAA. Including the NSEC asserting the  
nonexistence of AAAA records saves us having to do another round-trip  
to get the no-answer-no-error response telling us that the name has no  
AAAA records.

   In the event that a device has only IPv4 addresses but no IPv6
   addresses, or vice versa, then the appropriate NSEC record SHOULD
   be placed into the additional section, so that queriers can know
   with certainty that the device has no addresses of that kind.

Stuart Cheshire <cheshire@apple.com>
* Wizard Without Portfolio, Apple Inc.
* Internet Architecture Board
* www.stuartcheshire.org