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I have a fresh install of Ubuntu 16.04.1 LTS (I don't think this matters, but I did apt install ubuntu-gnome-desktop after the initial install) and I have inexplicable problems with DNS resolution and after piles of searching I haven't seen this exact problem described anywhere. After the OS boots, resumes, or changes network, DNS resolution does work, but only for simple commands like ping and nslookup. Most other services like curl, ssh, and web browsers like chrome or firefox fail entirely (that is, time out without successfully resolving the host name). Here's an example.

Ping and nslookup both work:

root@myhostname:/etc/avahi# nslookup github.com
Server:     8.8.8.8
Address:    8.8.8.8#53
Non-authoritative answer:
Name:   github.com
Address: 192.30.253.112
Name:   github.com
Address: 192.30.253.113
root@myhostname:/etc/avahi# ping github.com
PING github.com (192.30.253.112) 56(84) bytes of data.
64 bytes from 192.30.253.112: icmp_seq=1 ttl=55 time=21.5 ms
64 bytes from 192.30.253.112: icmp_seq=2 ttl=55 time=28.0 ms
^C
--- github.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1000ms
rtt min/avg/max/mdev = 21.527/24.797/28.068/3.274 ms

But if I curl immediately after it fails:

root@myhostname:/etc/avahi# curl github.com
curl: (6) Could not resolve host: github.com

I've disabled dnsmasq in NetworkManager. I've tried disabling IPV6. I've tried various changes I've read online regarding avahi settings. All to no avail. One poster went so far as to say "systemd is a mess, you're best off to just reinstall until you get it working".

Here's the kicker, though. Some time later if I leave it alone, it does start to work. Maybe 5-15 minutes later everything magically works. Does anybody have any idea how to resolve this? Thank you.

Michael Litherland
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  • Welcome to askubuntu! Could you please [edit] your post to tell us what "fail entirely" means? Any error messages the might help us help you! Thank you. – Elder Geek Feb 27 '17 at 17:29
  • Thank you. I edited for some clarity. There are no other errors that I can find anywhere in dmesg or system logs related to the DNS failures. – Michael Litherland Feb 27 '17 at 19:00
  • Intermittent failures are the most difficult to troubleshoot. This sounds like a problem in the application layer. I would thinnk of a misconfigured firewall, however, that doesn't seem to explain the magically works after x minutes part. Perhaps someone else can chime in. Meanwhile you might find this or that Or perhaps this one helpful – Elder Geek Feb 28 '17 at 15:39
  • Thanks for the links; I will look through them. I appreciate the help. – Michael Litherland Feb 28 '17 at 15:44
  • Is this a desktop or a laptop? – Elder Geek Feb 28 '17 at 16:01
  • It's a new Dell XPS 13 9360. So it moves frequently between APs, sleeps, etc.; all things that trigger the issue. Dell actually recommends using a newer kernel than 16.04 ships with, so I might end up biting the bullet and switching to 16.10. – Michael Litherland Feb 28 '17 at 17:51
  • Please [edit] the triggers into your post. You might also include information from the wireless script here to help us help you! – Elder Geek Feb 28 '17 at 17:58

1 Answers1

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Edit:

After trying to cajole the Killer 1535 into working reliably for months I gave up, bought an Intel 7265NGW, which is a drop in replacement and works perfectly. There are guides online to replacing the Wifi adapter in this machine and the Intel part is available on various online sources for less than 20 USD. Well worth getting rid of that headache.

Previous comment:

Apparently the drivers for Killer 1535 Wifi card were causing my problems with intermittent odd behavior like I described above. Dell recommends running the very latest kernels with this machine, so I opted to switch to Gnome Ubuntu 16.10 and I haven't had any problems whatsoever since then. There are ways of upgrading the kernel for the LTS releases, but I try not to deviate too much from a base install in case of running into other problems that are hard to diagnose. Thanks to anybody who may have taken a look at my problem, and especially @Elder Geek for the hints.

Michael Litherland
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