Re: Broken IPv6 / IPv4 configuration, or Gmail brokenness?
On Mon, 23 Jan 2023 18:32:41 +0000 (GMT)
Tim Woodall <debianuser@woodall.me.uk> wrote:
> On Sun, 22 Jan 2023, Celejar wrote:
>
> > On Sun, 22 Jan 2023 16:28:55 -0500
> > Dan Ritter <dsr@randomstring.org> wrote:
> >
> >> Celejar wrote:
> >>> Hello,
> >>>
> >>> My Debian Sid system, including its networking system, has been
> >>> working fine for a while. Recently, Gmail has not been working properly
> >>> on the system: sending (via SMTP with SSL) times out, and receiving
> >>> (via POP3 and IMAP) takes abnormally long. Today I finally made some
> >>> efforts to understand what's going on. Here's what I know /
> >>> understand / have been able to establish:
> >>>
> >>> 1) My ISP provides me with only IPv4, not IPv6.
> >>>
> >>> 2) Trying to send email through Gmail using "smtp.gmail.com", via
> >>> Sylpheed and Swaks, times out without getting anywhere. For example:
> >>>
> >>> $ swaks -t celejar@gmail.com -s smtp.gmail.com:587 -tls -a LOGIN
> >>> Username: celejar
> >>> Password: ********
> >>> === Trying smtp.gmail.com:587...
> >>> *** Error connecting to smtp.gmail.com:587:
> >>> *** IO::Socket::INET6: connect: timeout
> >>>
> >> Your system expects to be able to use IPv4 and IPv6. Google
> >> handles both. Your ISP does not. DNS returns both IPv4 A records
> >> and IPv6 AAAA records for smtp.gmail.com.
> >>
> >> In this particular case, you should change your system
> >> preference to IPv4 first.
> >>
> >
> > Shouldn't this be included somewhere prominently in the Debian
> > documentation, in the form of a Big Fat Warning that the standard
> > dual-stack condiguration used by Debian can cause serious breakage if
> > one's ISP doesn't support IPv6? (I'd be happy to add a warning to, say,
> > https://wiki.debian.org/DebianIPv6, if I thought I understood the
> > issues well enough to get it right.)
> >
> I think, although I'm not 100% sure as I now have fully working IPv6
> everywhere, that your problem might be that something is providing a
> default route.
>
> If the box trying to connect to gmail knows there's no route then it
> will use IPv4. If it thinks there's a route it will use it.
>
> At a guess, your router is sending out RA messages that say the router
> is a default route and then dropping packets when you actually try to
> send.
>
> radvdump will let you see who is broadcasting advertisements.
Thank you - the plot thickens. I tried radvdump, and I was indeed
receiving IPv6 advertisements. I inspected my router (an OpenWrt box)
more carefully, and lo and behold, the router *thinks* that it has IPv6
connectivity: it reports that it has configured its WAN interface via
DHCPv6, that it has an IPv6 prefix delegation (a /56), and that it has
accordingly handed out an IPv6 address via DHCPv6 to my Debian system
(which indeed shows having its network interface configured with that
address). The problem is that IPv6 is not actually working at all:
ping6 to IPv6 hosts, even from the router itself, get no response, and
traceroute to IPv6 hosts show replies from only the first two hops, and
just asterisks afterward.
My ISP is notoriously cagey about the details of its (slow and
incremental) IPv6 rollout. I suppose I can try customer service, but in
the meantime, I just don't know whether I have a misconfiguration on the
router, or whether the ISP is not actually providing working IPv6.
--
Celejar
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