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Re: A few ipv6 questions

2010-12-17 01:13:01

On 17 dec 2010, at 06.52, John R Levine wrote:

3a. Let's say I have these DNS records:

baz.example MX 10 mail1.baz.example
baz.example MX 20 mail2.baz.example
mail1.baz.example A
mail1.baz.example AAAA a:b::c:d
mail2.baz.example A
mail2.baz.example AAAA b:c::d:e

3b. Let's say I have these DNS records:

baz.example MX 10 mail1a.baz.example
baz.example MX 10 mail1b.baz.example
baz.example MX 20 mail2a.baz.example
baz.example MX 20 mail2b.baz.example
mail1a.baz.example A
mail1b.baz.example AAAA a:b::c:d
mail2a.baz.example A
mail2b.baz.example AAAA b:c::d:e

In both of these examples, a v4 client tries, then

In both of these examples, a v6 client tries a:b::c:d, then b:c::d:e

A dual stack client tries and a:b::c:d in either order, then 
and b:c::d:e in either order.

Does this all look right?

I would say 3a is the only safe way of setting up DNS, but I am also a person 
that do not like multiple MX records as I think non-deliverable mail should be 
queued on the sender side.

Because of this, I think one should strongly recommend 3a as "the correct 
setup", possibly without the secondary MX.

If you do anything else (including 3b) the outcome might be random -- although 
I hope 3b is what in reality happens, and not that a single stack client give 
up when it tries one of the two MX that do not have connectivity with the 
version of the IP protocol it uses.


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