After moving host interface to the secondary OVS bridge the host lost DNS config

[jianjuns]

Describe the bug
In a secondary network test by @meibensteiner, after the node's primary interface is moved to the secondary OVS bridge, the node lost its DNS config in /etc/resolv.conf.

cat /etc/resolv.conf
# Generated by NetworkManager 

It may be an interoperability issue with NetworkManager.

To Reproduce

• cloud-init with the most straight forward settings for formatting and networking
• networking via ipv4 DHCP, no proxy or anything alike
• Basic RKE2 without CNI
• Install Antrea (configured node's primary interface for secondary network OVS bridge)

Versions:
It happened in cluster with both Ubuntu 24.04 and Debian 12 nodes.

[meibensteiner]

This issue is probably caused by systemd-resolved. Adding a static dns server in /etc/systemd/resolved.conf fixes it.

[Resolve]
DNS=192.168.1.254

[luolanzone]

Hi @meibensteiner , thanks for the update, systemd-resolved will update /etc/resolv.conf whenever there is a change in network configuration, DNS settings, or when the service is restarted or reloaded. You can try to run chattr +i /etc/resolv.conf command to make the file immutable to avoid the file being modified again.

@jianjuns Looks like the issue is not directly with Antrea secondary network feature but systemd-resolved, considering there are several processes can modify the file, I feel it may not be easy to check from Antrea side, any suggestion for next step?

[jianjuns]

But do we know why systemd removed the DNS config? We need to understand if that is because of OVS (e.g. systemd/network manager do not recognize interfaces on the OVS even we keep the original host interface names).

[luolanzone]

Sure, I can check if this can be reproduced locally first.

[luolanzone]

No chance to take a look at this recently, assigning this to @hongliangl to move forward.