Technical Tip: Interface mapping for FortiGate VM on Proxmox

Description

This article explains how network interfaces defined in Proxmox are mapped to FortiGate VM interfaces and how incorrect ordering may impact connectivity.

Scope

FortiGate, Proxmox VE.

Solution

In Proxmox, network interfaces are assigned in a specific order when attached to the virtual machine. This order defines how interfaces are mapped inside the FortiGate VM.

The FortiGate assigns interfaces (port1, port2, etc.) based on the order in which virtual NICs are detected during boot.

If the interface order is changed on the Proxmox side (for example, by adding or removing NICs), the mapping inside the FortiGate VM may also change.

To ensure correct interface mapping:

• Verify the interface order in Proxmox before deploying or restoring configurations.

• Ensure that interfaces are added in the expected sequence.

• If needed, remove and re-add interfaces in the correct order.
  
  

The interface order can also be adjusted directly from the Proxmox CLI by modifying the VM configuration file:

/etc/pve/qemu-server/<vmid>.conf

Before:

net0: virtio=AA:BB:CC:00:00:01,bridge=vmbr0
net1: virtio=AA:BB:CC:00:00:02,bridge=vmbr1

After:

net0: virtio=AA:BB:CC:00:00:02,bridge=vmbr1
net1: virtio=AA:BB:CC:00:00:01,bridge=vmbr0

After updating the configuration, start the VM again.