#745103 network-manager: NM doesn't remove VPN dns from resolv.conf when VPN connection is closed

Package:
network-manager
Source:
network-manager
Description:
network management framework (daemon and userspace tools)
Submitter:
Mike Hommey
Date:
2024-04-04 10:39:03 UTC
Severity:
important
#745103#5
Date:
2014-04-17 23:51:57 UTC
From:
To:
Dear Maintainer,

Steps to reproduce:
- Look at /etc/resolv.conf
- Setup a VPN connection when the other end pushes DNS configuration
- Connect to that VPN.
- Look at /etc/resolv.conf getting the VPN DNS added
- Disconnect from VPN
- Look at /etc/resolv.conf *not* being updated (or, if you're lucky, just have the entries reordered, but that doesn't happen a lot)

The outcome is that every connection from thereafter is slow because the first thing libc does is to query the VPN DNS since it's first, which, since you're not connected anymore, doesn't answer.

A cursory look at the code suggests this is a problem on network-manager's end, not on the particular VPN plugin's end, but fwiw, i'm using the n-m-openvpn plugin.

Mike
#745103#10
Date:
2015-12-28 21:32:47 UTC
From:
To:
I can confirm this with NM 1.0.8-1 in current testing.
#745103#15
Date:
2024-04-03 11:42:35 UTC
From:
To:
I can confirm that something like this is still happening with
network-manager 1.46.0-1 (Debian testing machine), when using
network-manager-strongswan: before switching on the VPN,
/etc/resolv.conf reads:

nameserver 192.168.0.1
nameserver 0.0.0.0

then with the VPN on, it becomes

# Generated by NetworkManager
nameserver <VPN nameserver redacted>
nameserver <VPN nameserver redacted>

but after the VPN is switched off, it collapses to just one line:

# Generated by NetworkManager

making DNS lookups impossible.  Manually reverting /etc/resolv.conf to
its original state restores normal networking.

Best wishes,

   Julian
#745103#20
Date:
2024-04-03 13:41:17 UTC
From:
To:
Am 03.04.24 um 13:42 schrieb Julian Gilbey:

If that is really /etc/resolv.conf verbatim, it means it was not created
by NetworkManager. Which somehow suggests you use another network
management tool besides NetworkManager.
A mix and match is not a good idea and as far as I'm concerned,
unsupportable.
#745103#25
Date:
2024-04-04 05:21:26 UTC
From:
To:
Hi Michael,

Ah, you've probably just solved my problem - thank you!  I had no idea
that there was another network management tool involved.  A quick look
suggests that it's ifupdown, so I'll try removing that and see what
happens.

Best wishes,

   Julian
#745103#30
Date:
2024-04-04 08:28:08 UTC
From:
To:
Am 04.04.24 um 07:21 schrieb Julian Gilbey:

Don't forget to remove the configuration from /etc/network/interfaces
(or completely remove that file) after uninstalling ifupdown.

Michael
#745103#35
Date:
2024-04-04 10:37:12 UTC
From:
To:
Thanks; I figured that out after a while ;-)

And I'm pleased to say it's all working well now.

Best wishes,

   Julian