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Re: A few ipv6 questions

2010-12-17 02:11:34

Hi John,
At 21:52 16-12-10, John R Levine wrote:
I think the answers to these questions are obvious, but they're not obviously obvious, so:

1.  Let's say I have these DNS records:

foo.example AAAA a:b::c:d
foo.example MX 10 mail.foo.example
mail.foo.example A 1.2.3.4

Then a client would try to contact 1.2.3.4, and give up if it can't. A v6 only client can't send mail to foo.example. No client should try to send mail to a:b::c:d.

Yes.

2. Let's say I have these DNS records:

bar.example A 1.2.3.4
bar.example MX 10 mail.bar.example
mail.bar.example AAAA a:b::c:d

A client would try to connect to a:b::c:d, and give up if it can't. A v4 only client can't send mail to bar.example. No client should try to send mail to 1.2.3.4.

Yes.

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 1.2.3.4
mail1.baz.example AAAA a:b::c:d
mail2.baz.example A 2.3.4.5
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 1.2.3.4
mail1b.baz.example AAAA a:b::c:d
mail2a.baz.example A 2.3.4.5
mail2b.baz.example AAAA b:c::d:e

In both of these examples, a v4 client tries 1.2.3.4, then 2.3.4.5.

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

Yes.

A dual stack client tries 1.2.3.4 and a:b::c:d in either order, then 2.3.4.5 and b:c::d:e in either order.

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

Regards,
-sm
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