Description of problem:

It seams that the "hosts: resolve" entry in /etc/nsswitch.conf doesn't work on Fedora 34. It works on Fedora 33.


Version-Release number of selected component (if applicable):
systemd-248-2.fc34.x86_64
glibc-2.33-8.fc34.x86_64


How reproducible:
Always.

Steps to Reproduce:
1. Create or change the file /etc/nsswitch.conf,
   so that the line that starts with "hosts:" contain only
hosts:      resolve [!UNAVAIL=return]
   It should not contain other entries,
   because we want to test the result / answer of systemd-resolved.
2. Chech that systemd-resolved is running and correctly configured.
   Run "resolvectl status" to see the active configuration.
3. Choose a host which is running and you know the dns name and the ip address.
   It should be reachable by "ping".
4. Test that resolvectl can resolve this dns name and this ip address.
   Example:
     resolvectl query pinghost.example.com
     resolvectl query 192.0.2.6
5. Run "ping" to this host.
     ping pinghost.example.com
6. Change the hosts entry in /etc/nsswitch.conf and append " dns".
7. Repeat step 5.


Actual results:

Step 5:
ping doesn't know the dns name of the host
(it cannot resolve it (from the ip address?)):

PING pinghost.example.com (192.0.2.6) 56(84) bytes of data.
64 Bytes von 192.0.2.6 (192.0.2.6): icmp_seq=1 ttl=64 Zeit=0.627 ms

Step7:
ping works as expected and prints the dns name and the ip address.



Expected results:

Step 5:
ping prints the dns name and the ip address:

PING pinghost.example.com (192.0.2.6) 56(84) bytes of data.
64 Bytes von pinghost.example.com (192.0.2.6): icmp_seq=1 ttl=64 Zeit=0.627 ms

Step7:
ping works as expected and prints the dns name and the ip address.


Additional info:

The behavior is problematic when programs does an dns / ip address check from dns name to ip address and back from ip address to dns name.