[PLUG] Ubuntu 16.04 fails to update DNS IP from DHCP server

[Amey Abhyankar]

Hello,

Recently I observed, couple of Ubuntu 16.04 workstations are getting
valid IP address from DHCP server but fails to update DNS IP.
I checked /var/log/kern.log but that isn't showing any interesting
error regarding networking part.

My DHCP server is hosted on Cisco SG300-28 28-Port switch.
Everything seems ok at switch side as other Ubuntu,Macbook & Windows
OS users are not facing this issue in same VLAN/network.

For now as a work around I am modifying /run/resolvconf/resolv.conf
and adding 8.8.8.8 DNS.
But again, if the user reboots respective Ubuntu 16.04 workstation,
that change are overwritten by system.

Anybody knows permanent fix for this issue? Thanks.
I did Google and got plenty of results but none of them are working so
far for me.

Regards,
Amey.

[Arun Khan]

Post by Amey Abhyankar
Hello,
Recently I observed, couple of Ubuntu 16.04 workstations are getting
valid IP address from DHCP server but fails to update DNS IP.
I checked /var/log/kern.log but that isn't showing any interesting
error regarding networking part.

What is the content of /etc/resolv.conf (soft link file) after boot?
IIRC package 'resolvconf' is part of the Ubuntu base install.
It's possible to configure resolvconf to write specific DNS servers
[a]. I think there are other methods to tell resolvconf to pick up
DNS servers from the DHCP server via Network Manager settings.

[a] https://unix.stackexchange.com/questions/128220/how-do-i-set-my-dns-when-resolv-conf-is-being-overwritten

-- Arun Khan

[Amey Abhyankar]

Post by Arun Khan

Post by Amey Abhyankar
Hello,
Recently I observed, couple of Ubuntu 16.04 workstations are getting
valid IP address from DHCP server but fails to update DNS IP.
I checked /var/log/kern.log but that isn't showing any interesting
error regarding networking part.

What is the content of /etc/resolv.conf (soft link file) after boot?

Will give a check shortly.
In my Ubuntu 16.04 workstation [with no DNS issue], /etc/resolv.conf output =

------------------------------------------------------------------------------------------------------
# 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 8.8.8.8
------------------------------------------------------------------------------------------------------

The other Ubuntu 16.04 workstations with DNS problem has = nameserver
127.0.1.1 value in /run/resolvconf/resolv.conf

Post by Arun Khan
IIRC package 'resolvconf' is part of the Ubuntu base install.
It's possible to configure resolvconf to write specific DNS servers
[a]. I think there are other methods to tell resolvconf to pick up
DNS servers from the DHCP server via Network Manager settings.
[a] https://unix.stackexchange.com/questions/128220/how-do-i-set-my-dns-when-resolv-conf-is-being-overwritten
-- Arun Khan
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