DNS issues - How to debug?

Question

Im using Ubuntu 16.04. I have some issues regarding DNS resolving. It only happens at my home network. However, my other wifi devices work fine. After startup, DNS resolving doesn't work for about 5/10 minutes. Then it starts working. Pinging to addresses like 8.8.8.8 work fine, but ping to hostnames doesn't (so I guess DNS issue).

My /etc/resolv.conf doesn't change before and after the issue, it keeps the same. I added "nameserver 8.8.8.8" but no change. It has 3 nameservers (2 of them got by DHCP).

On other networks my system works ok, DNS works from the beginning. Chrome status bar says "Resolving host..." and then timeouts. Any tips so I can debug while the issue is present?

Regards from Argentina.

Solution

Check if you have

dns=dnsmasq

in /etc/NetworkManager/NetworkManager.conf. If you do, try commenting it out and restart network-manager:

sudo service network-manager restart

Also check that /etc/resolv.conf is a symlink to /run/resolvconf/resolv.conf

Comments

[Gansheim]

I would change your primary nameserver to use Google's DNS to see if that improves name resolution when you startup. If it does then at least you've narrowed down the issue to those nameservers that are set via DHCP.

[Leonardo Giordano]

Not sure how to do it. My /etc/resolv.conf has the 2 nameservers got by DHCP first, and then 8.8.8.8. My network configuration is "Automatic DHCP", and added 8.8.8.8 in Aditional DNS servers (I translated from spanish, don't know how exactly it appears in english system). By the way, if I reboot my system it starts working. The issue usually appears after suspend/resume.