Mellanox Linux Kernel Bug

Mellanox Linux Kernel Bug

A “fix” was made to the Mellanox driver some time around Linux version 6.5, which has a bug that makes it so 802.1q VLAN tagging doesn’t work unless the driver is put into promiscuous mode.

See a discussion around this in a Proxmox Forum topic: Mellanox ConnectX-4 LX and brigde-vlan-aware on Proxmox 8.0.1

To work around this problem you want to either of the following.

1. Run a kernel older than 6.5 (our recommended path for performance/security).
2. Setup the NIC in promiscuous mode. This is not ideal as it can have a performance and security impact, so proceed with caution.

link set enp1s0f0np0 promisc on

This command is not persistent across reboots, so you will want to add it to a startup script. Example with ‘netplan’ style configs:

auto vmbr0
iface vmbr0 inet manual
  # [...]
  post-up ip link set enp1s0f0np0 promisc on

We will update this KB as we discover more.