IPv6 nameservers not removed from /etc/resolv.conf when switching to a IPv4 network

[Matija Grabnar]

I installed rdnssd on a laptop which I mostly use in two places. At one place, I have dual stack network, with dual stack DNS servers, in the other place, the network is IPv4 only.

When I go to the first place, rdnssd correctly receives the advertised DNS (IPv6) servers and places them in /etc/resolv.conf. Everything works.

However, when I go to the second network, the IPv6 addresses for the DNS servers remain in /etc/resolv.conf, and that means networking mostly doesn't work, since most DNS queries are sent to the two IPv6 addresses which are now "Network unreachable".

When switching to a IPv4 only network (or an IPv6 network which doesn't advertise IPv6 addresses for it's DNS via RDNSS), the IPv6 addresses of the DNS should be removed from /etc/resolv.conf

lsb_release -rd
Description: Ubuntu 14.04.4 LTS
Release: 14.04

apt-cache policy rdnssd
rdnssd:
  Installed: 1.0.1-1ubuntu1
  Candidate: 1.0.1-1ubuntu1
  Version table:
 *** 1.0.1-1ubuntu1 0
        500 http://ftp.arnes.si/pub/mirrors/ubuntu/ trusty/universe amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: rdnssd 1.0.1-1ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-58.64~14.04.1-generic 3.19.8-ckt16
Uname: Linux 3.19.0-58-generic x86_64
NonfreeKernelModules: nvidia wl
ApportVersion: 2.14.1-0ubuntu3.19
Architecture: amd64
CurrentDesktop: Unity
Date: Mon May 9 09:16:48 2016
InstallationDate: Installed on 2015-11-28 (162 days ago)
InstallationMedia: Ubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
SourcePackage: ndisc6
UpgradeStatus: No upgrade log present (probably fresh install)

[Rémi Denis-Courmont (rdenis)]

rdnssd simply tracks the kernel notion's of what are the RDNSS at a time. The kernel did not send expiration for the entries when you left the network, hence the entries are considered still valid.

What you want is an integrated IPv4/IPv6 connection manager, like e.. network-manager. This is way out of scope of rdnssd.