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Having some connection problems with my website, i found out that my server has a bigger problem. I installed it, with ubuntu 14.04. It is a cloud machine bought from a specific isp (ovh) but entirely configured by me, os included: i have full access to it. Since yesterday, i receive messages of connection timeout on sites like google so i tried 

 telnet google.it 80

It replies:

 Trying 2a00:1450:4007:80e::2003...
 Trying 216.58.208.227... 
 Connected to google.it.
 Escape character is '^]'.

But the second line gets printed after nearly a minute. It is extremely slow. And seemed to me strange even that the second line gets printed. So i did

 telnet 216.58.208.227 80

and the reply was immediate and fine.

Now, this means a dns problem, i guess. How can i investigate to know the real source for the issue, for sure? Considering the server stopped suddenly to work (till yesterday all was working fine) and that i leaved it untouched, can i say for certain that is my isp fault or it can be something went wrong on my machine, due to an external attack, for example?

Sasha Grievus
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1 Answers1

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This indicates an issue with the IPv6 address configuration.

Normally, if IPv6 is not configured at all, then IPv6 addresses aren't tried when you're trying to connect to any other host.

However, if IPv6 is, in fact, configured, but is configured incorrectly, then the problems as you describe will appear.

Solution:

You either have to disable IPv6 at all (make sure it is not configured at all), or make sure that if it is configured, then the configuration is applied correctly.

cnst
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  • How to disable it (and make sure it not configured at all)? I'm using Apache. I changed the Listen 80 to Listen 0.0.0.0:80 (idem for 443) but i doesn't seems to change anything – Sasha Grievus Oct 01 '15 at 08:03
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    This is not related to Apache at all, don't change Apache here, it is configurable through `ifconfig` and friends. – cnst Oct 01 '15 at 08:06
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    did it! thank you very much. I struggled an entire day to solve this. I disabled ipv6 adding these lines net.ipv6.conf.all.disable_ipv6 = 1 net.ipv6.conf.default.disable_ipv6 = 1 net.ipv6.conf.lo.disable_ipv6 = 1 to /etc/sysctl.conf and restarting it (sudo sysctl -p). You can add it to your answer. Maybe it will help someone. – Sasha Grievus Oct 01 '15 at 08:17
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    @SashaGrievus, whist it is fixing the problem short-term for you, it would probably be a better idea to raise this issue with OVH (sounds like they might have messed up the IPv6 configuration of your server or maybe even their whole network or subnet); it was just a couple of days ago that we've had the news of another milestone in the shortage of IPv4 address space (ARIN ran out), so, getting familiar with IPv6 sooner rather than later is quite advisable – cnst Oct 01 '15 at 08:23
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    Yes, i did it yesterday, already. I hope they will solve the problem as soon as they can. Interesting news! Thank you again. – Sasha Grievus Oct 01 '15 at 08:47