Can You Prevent NIC Reset During ISO/Install Start in Proxmox?

Can you prevent NIC reset during ISO/install start in Proxmox? Yes. The fix is to set the bridge to disable MAC learning and add a kernel module option. It’s not a bug, it’s how the bridge handles the new MAC from the install media.

Why the NIC resets

When you boot a VM from an ISO to install an OS, the virtual NIC gets a new MAC address. The Linux bridge on the Proxmox host sees this new MAC and flushes its forwarding table. That’s the reset. It drops the link for a second or two, and if you’re doing a network install, it can kill the connection.

The fix

You need to tell the bridge to stop learning MAC addresses on that port. Edit the network config on the Proxmox host:

nano /etc/network/interfaces

Find the bridge for your VM network, usually vmbr0. Add bridge-learning off and bridge-unicast-flood off to the bridge stanza:

auto vmbr0
iface vmbr0 inet static
    address 192.168.1.10/24
    gateway 192.168.1.1
    bridge-ports eno1
    bridge-stp off
    bridge-fd 0
    bridge-learning off
    bridge-unicast-flood off

Then restart networking:

systemctl restart networking

That stops the bridge from flushing the table when the VM’s MAC changes. No more reset.

If that doesn’t do it

Some NIC drivers also reset on link state change. You can disable that with a module option. For e1000e, add this to /etc/modprobe.d/e1000e.conf:

options e1000e SmartPowerDownEnable=0

For igb, it’s options igb IntMode=0. Reboot or reload the module.

My take

This is a stupid default. The bridge shouldn’t flush on a new MAC from a port that’s already up. But at least the fix is two lines. If you’re doing a lot of installs, just add those bridge options to every bridge and forget about it. Check the NIC firmware and ASPM fix if you still see resets after this.