Bug 1214443

Hi,

if a host is configured with IPv4 nameservers in its /etc/resolv.conf, these entries are applied to the containers /etc/resolv.conf as expected:

```
host # grep ^name /etc/resolv.conf
nameserver 10.160.0.1
host # docker run --rm -it opensuse/leap:latest
364728f6206a:/ # grep ^name /etc/resolv.conf
nameserver 10.160.0.1
```

However, if the host is configured with IPv6 nameservers, Docker applies Google nameservers instead:

```
host # grep ^name /etc/resolv.conf
nameserver 2a07:de40:b205:7:10:144:53:53
nameserver 2a07:de40:b205:7:10:144:53:54
host # docker run --rm -it opensuse/leap:latest
08de5e58e3bb:/ # grep ^name /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4
```

The upstream documentation (https://docs.docker.com/network/#dns-services) suggests that this is a fallback mechanism, however the IPv6 nameservers configured on the host are perfectly operational, and even resolve external/internet queries:

```
host # dig @2a07:de40:b205:7:10:144:53:53 opensuse.org +short
195.135.221.140
host # dig @2a07:de40:b205:7:10:144:53:53 opensuse.org +short AAAA
2001:67c:2178:8::16
host # dig @2a07:de40:b205:7:10:144:53:54 opensuse.org +short
195.135.221.140
host # dig @2a07:de40:b205:7:10:144:53:54 opensuse.org +short AAAA
2001:67c:2178:8::16
```

The Docker installation is a stock one without any configuration changes:

```
host # grep PRETTY /etc/os-release
PRETTY_NAME="SUSE Linux Enterprise Server 15 SP5"
host # zypper se -ivx docker

S  | Name   | Type    | Version                | Arch   | Repository
---+--------+---------+------------------------+--------+-----------------------------
i+ | docker | package | 23.0.6_ce-150000.178.1 | x86_64 | SLE-Module-Containers-Update
```

Best,
Georg