I run a lot of VMs for development on my network, and all of a sudden one day they stop getting DHCP addresses. Trying many things later, updating and rebooting, even with or without changing configurations not only do they fail getting DHCP addresses but even with a static configuration they cant contact the router. This happened suddenly.
It doesnt matter which proxmox server i use, or if i use virtualbox on my laptop or how i connect things up to the router VMs cant contact the router. I can see their mac addresses and i can do an ARP ping from the router but its impossible for VMs to contact the router for internet . If i set up another router on the network for them and double NAT it works but not at 100% as container image pulls always fail on name resolution regardless of the ip set. Currently my kubernetes network is set up with a dual NIC but it turns out that causes them to fail in the new network configuration rather than having a single virtual NIC to internet and LAN.
i did not change any firewall settings or any settings on the network. On static configuration all devices can communicate fine. Networking is fine for all clients and hardware but not for VMs (proxmox and host OS has internet like normal but not the VMs anywhere on the network with any setting without going through some middle router on the network).