Re: [BEHAVE] I-D Action: draft-wing-behave-dhcpv6-reconfigure-00.txt

[Prashanth Patil <[e-mail]>]

Hi Brian, 
The idea behind the proposal is to provision a means by which traffic is
sent using IPv4 and not through the IPv6/IPv4 translator. The advantage
being that if NAT44 and NAT64 are deployed on the same network, it is
preferable to use NAT44 over NAT64 because of scale, performance and
application incompatibility issues (e.g., FTP) [RFC6384].
A "normal" DNS server does not have DNS64 capability. The IPv4-mapped
address for this "normal" server ensures that it can be reached only by
IPv4š. So if a host is IPv4-only, it will send a DNS query to the "normal"
server just to get the A records. If the host is dual-stack it will also
send a DNS query to the "normal" server to get both A and AAAA records. If
the destination address is an IPv4 address,  dual-stack host just gets A
records but not synthesized AAAA records. So this technique will ensure that
IPv4 is preferred over the IPv6/IPv4 translator prefix and also gives native
IPv6 higher precedence than IPv4.
If the host happens to be IPv6 only, then it cannot reach the "normal"
server because it has IPv4-mapped prefix as explained previously. So IPv6
only host can only reach DNS64 server. So this host will send the DNS query
to DNS64 to get AAAA records. Based on the destination address the host will
get IPv4-embedded IPv6 address or just the global IPv6 address.

šNote: From RFC 6052
³When presented with the IPv4-mapped prefix, current versions of Windows and
Mac OS generate IPv4 packets, but will not send IPv6 packets.²

-Prashanth 

On 22/10/11 6:20 AM, Brian E Carpenter wrote:
> I have a basic question. Why does this draft define a 'normal'
> DNS server as one having an IPv4-mapped IPv6 address?
> 
> That seems like a completely *abnormal* DNS server for a dual
> stack host. A dual stack host should normally have a DNS server
> with a regular IPv6 address that will return both A and AAAA
> records if they exist. Normally the server will be dual stacked
> anyway, and will return exactly the same response whether the
> query arrives via v4 or v6.
> 
> A DNS server which only has an IPv4 address will also return
> A and AAAA records if they exist, so there is absolutely no
> difference as far as the dual stack host is concerned anyway.
> So what is the point in using the IPv4-mapped address?
> 
> Regards 
>     Brian 
> 
> On 2011-10-18 11:17, [e-mail] wrote:
>> A New Internet-Draft is available from the on-line Internet-Drafts
>> directories. 
>> 
>>     Title           : DHCPv6 Dynamic Re-Configuration
>>     Author(s)       : Dan Wing
>>                            Tirumaleswar Reddy
>>                            Prashanth Patil
>>     Filename        : draft-wing-behave-dhcpv6-reconfigure-00.txt
>>     Pages           : 10
>>     Date            : 2011-10-17
>> 
>>     Some networks are expected to support IPv4-only, dual-stack, and
>>     IPV6-only hosts at the same time.  This makes prioritizing the DNS
>>     servers for hosts tricky due to a heterogeneous mix of protocol
>>     stacks causing optimal behavior to occur only when the host stack re-
>>     initializes.  The networks infrastructure is usually well equipped to
>>     be aware of single/dual-stack nature of hosts.  This specification
>>     extends DHCPv6 so that the DHCPv6 Relay Agent can dynamically
>>     influence the priority of DNS servers provided to the host, so that
>>     the host can use the optimal DNS server for resolution.
>> 
>> 
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-wing-behave-dhcpv6-reconfigure-00.t
>> xt 
>> 
>> Internet-Drafts are also available by anonymous FTP at:
>> ftp://ftp.ietf.org/internet-drafts/
>> 
>> This Internet-Draft can be retrieved at:
>> ftp://ftp.ietf.org/internet-drafts/draft-wing-behave-dhcpv6-reconfigure-00.tx
>> t 
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