VMs and LXC cannot be adressed by DNS after reboot / migration, IP still works

[maxim.webster]

Hi,

I am facing an issue that might be related to Proxmox, but also to my UniFi network equipment.

I have a 3-node-cluster (pve-manager/9.0.11/3bf5476b8a4699e2 (running kernel: 6.14.11-4-pve)) running several VMs and LXC, using HA/replication for failover. The clients use DHCP to get an IPv4 address from my UniFi Controller (Dream Machine Pro). Also - the DNS is located on the controller (built-in). Whenever I reboot a guest or it get's migrated to another node, it cannot be contacted from a client using it's FQDN or host name for several minutes. However, since the IP address assigned via DHCP stays the same, it can be contacted by IP anytime. Also, networking on the guest works.

Did anybody face the same issue and may provide a hint where to look? The behaviour is not only anoying, but contradicts the purpose of "high availability".

Additional info:

• the cluster nodes have fixed IPs from a dedicated VLAN 10. The CIDR is 192.168.10.0/24
• the clients use DHCP for dynamic IPs from another VLAN 20. The CIDR is 192.168.20.0/24

Sample network configuration of one cluster node

auto lo
iface lo inet loopback

iface enp2s0 inet manual

auto vmbr0
iface vmbr0 inet static
        address 192.168.10.3/24
        gateway 192.168.10.1
        bridge-ports enp2s0
        bridge-stp off
        bridge-fd 0
        bridge-vlan-aware yes
        bridge-vids 2-4094

Sample configuration of one VM

name: gary
net0: virtio=BC:24:11:0D:E3:BE,bridge=vmbr0,firewall=1,tag=20

UniFi port config for cluster node ports





Settings for VLAN 20 ("HOME")