Supervisor Control Plane Management floating IP address is not persisting due to extra Ipv6 DNS in network config

Products

• vSphere with Tanzu

Issue/Introduction

 All 3 CPVMs are showing this repeated eth0 interface setting change. (and ending up in a systemd-networkd restart loop)

/var/log/update-controller/sync.log

2024-12-24T19:53:58.56Z INFO network_setting: Network setting changed for if eth0
2024-12-24T19:53:58.56Z DEBUG network_setting: curr if network = eth0, network={'Address': 'x.x.x.x/x', 'Gateway': 'x.x.x.x', 'DNS': 'x.x.x.x x.x.x.x x:x:x:x:x:x:x:x x:x:x:x:x:x:x:x x:x:x:x:x:x:x:x', 'Domains': 'domain.com', 'NTP': 'ntp.com'}, dhcp={}, desired if network = eth0, network={'Address': 'x.x.x.x/x', 'Gateway': 'x.x.x.x', 'DNS': 'x.x.x.x x.x.x.x', 'Domains': 'domain.com', 'NTP': 'ntp.com'}, dhcp={}
2024-12-24T19:53:58.66Z DEBUG network_setting: Ensured DHCP=ipv6 not present in eth0's network file
2024-12-24T19:53:58.478Z DEBUG network_setting: Restarted resolved and networkd.

Environment

vSphere 7.x

vSphere 8.x

Cause

An extra DNS (IPv6) server ending up in the eth0 settings that is causing update-controller to repeatedly think it needs to resync the interface settings.

Resolution

- SSH into one of the CPVMs
- cd to /etc/systemd/network/
- Backup the 10-eth0.network file somewhere in /root (_not_ in the systemd directory to be safe)
- Open the 10-eth0.network file for editing
- Add the following line in the [Network] section.

IPv6AcceptRA=no

alternate way to update the network file

echo "IPv6AcceptRA = no" >> /etc/systemd/network/10-eth0.network && systemctl restart systemd-networkd

- Restart networkd using `systemctl restart systemd-networkd` (this might already be happening every 10 seconds)

- Check/tail the output of /var/log/update-controller/sync.log on the node to see if it still logging 'Network setting changed for if eth0' with recent timestamps

- Check if the update-controller sync loop is stabilizing (no longer repeating every 10s)

- Repeat on the other two and verify if the system stabilizes.