Gmail MX over IPv6

Gert Doering gert at
Thu Jun 21 09:16:27 CEST 2012


On Thu, Jun 21, 2012 at 02:28:31AM -0400, Mansoor Nathani wrote:
> Since Gmail has enabled AAAA records for some of its MX hosts, my IPv4 only
> machine gets the Gmail IPv6 address and attempts to deliver email. Its only
> when the timeout has been reached will it try the IPv4 address.
> I am curious if anyone else is experiencing this or perhaps I need to do
> something on the CentOS 6 box to disable IPv6 till the time when it has
> native IPv6 capability.
> Jun 21 02:14:47 onion postfix/cleanup[1494]: 435AD1A110A:
> message-id=<20120621061447.435AD1A110A at host.domain>
> Jun 21 02:14:47 onion postfix/qmgr[1348]: 435AD1A110A:
> from=<user at host.domain>, size=448, nrcpt=1 (queue active)
> Jun 21 02:15:09 onion postfix/smtp[1497]: connect to
>[2001:4860:b007::1b]:25: Connection timed out

The more interesting question, actually, is why it actually has to wait
for IPv6 to time-out if your machine is IPv4-only - it should immediately
fail for IPv6, and then try IPv4.

What does "ip -6 route" show on your machine?

I'd guess that your machine thinks it *does* have IPv6, because a friendly
Windows box in the neighbourhood announced a 2002 prefix...

*Broken* IPv6 is what causes these problems, "no IPv6" is handled just fine
(but then, for outgoing mail sent by a MTA, 30 seconds delay do not *really*
cause harm)

Gert Doering
        -- NetMaster
have you enabled IPv6 on something today...?

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