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16.04 wifi was operating normally until the home router was overhauled today. Wifi service was restored and the OSX / IOS wifi devices are running well. The 16.04 wifi is able to ping the gateway:

 $ ping -c 3 192.168.8.1

however replacing the gateway ip with yahoo.com returns:

 $ ping -c 3 192.168.8.1
 ping: unknown host yahoo.com

yahoo.com resolved to 72.30.35.9 and pinging 72.30.35.9 was successful: this leads me to believe there is a DNS failure. Router provides DHCP service

Interesting observations:

  • The OSX box does not suffer said DNS failures.
  • 16.04 wifi works perfectly with cellular wifi hotspot

Question

What tests can be performed to confirm the problem and determine corrective action?

UPDATES

DNS-based Filtering was turned off in the router and the problem is now resolved.

Per Stephen Boston:

$ cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.1.1

Per Stephen Boston:

ls -l /etc/resolv.conf
lrwxrwxrwx 1 root root 29 Nov 13  2018 /etc/resolv.conf -> ../run/resolvconf/resolv.conf

Flushing DNS Cache did not resolve issue:

$ sudo /etc/init.d/networking restart
[sudo] password for user: 
[ ok ] Restarting networking (via systemctl): networking.service.
gatorback
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  • Is the router also your DHCP server? Or is your Ubuntu system on a static (LAN) IP address? – user535733 Jan 07 '20 at 02:55
  • Oh, and on 16.04, take a look at some of these almost similar problems: https://askubuntu.com/questions/368435 . I recall needing to fix DNS in 16.04. – user535733 Jan 07 '20 at 02:59
  • @user535733 Which of the answers to your link do you suggest? – gatorback Jan 07 '20 at 03:34
  • Check your /var/log/syslog for name-resolution errors. My own problem (long ago) generated huge logfiles, which made it easy to spot and diagnose. – user535733 Jan 07 '20 at 03:36
  • @user535733 Please see OP: "Updates". 16.04 wifi DNS seems to work with smartphone hotspot: maybe this is a clue? – gatorback Jan 07 '20 at 03:40
  • Since your Ubuntu system networking works properly with the phone access point, seems like you have conclusively demonstrated that your Ubuntu system is properly configured and not a likely culprit. Time to take another look at your router, especially the IP address range that it issues and the DNS servers that it knows about. – user535733 Jan 07 '20 at 03:43
  • try cat /etc/resolv.conf and ls -l /etc/resolv.conf – Stephen Boston Jan 07 '20 at 04:34
  • @StephenBoston Results from your suggestion are posted in OP under UPDATES. Looking forward to your interpretation of the results – gatorback Jan 07 '20 at 04:39
  • Okay. For a try: delete the link to resolv.conf and recreate it using two lines: nameserver 1.1.1.1 and nameserver 1.0.0.1. If your name lookups then work we know something new. You can easily recreate the link so that's okay. – Stephen Boston Jan 07 '20 at 09:42

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