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RE: A few ipv6 questions

2010-12-17 17:34:06

-----Original Message-----
From: owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org 
[mailto:owner-ietf-smtp(_at_)mail(_dot_)imc(_dot_)org] On Behalf Of 
Sent: Friday, December 17, 2010 9:26 AM
To: SM
Cc: John R Levine; IETF SMTP list
Subject: Re: A few ipv6 questions

A dual stack client would favor the IPv6 address and try to connect
to it first.

Nope, not necessarily. In some cases it is entirely reasonable for a dual 
client to try IPv4 before IPv6. Or use some other criteria to decide which
addresses to try.

For simplicity one might try them in the order returned by the resolver, for 
example: Walk through the answer section and, if A, use AF_INET; if AAAA, use 

Right. This approach also makes sense in some load-balancing scenarios.
(Although it may be true today, there's no reason to assume that in the long
run the type of address has anything to do with service quality.)

I'll also add that this is exactly the sort of situation where standards that
try to say too much will end up giving bad advice and end up looking really


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