Troubleshooting Tip: Slow download speed when FortiGate VM is deployed on ProxMox

Some Dedicated Servers equipped with Broadcom BCM57502 NICs may experience really slow download speeds inside VMs or containers running on Proxmox VE (Virtual Environment). To resolve this the generic-receive-offload on the actual interface of the server, where Proxmox bridges, must be disabled

How to disable and make the change permanent:

SSH to the server and list all PCI devices with this command:

lspci -nnd ::200

For example:

If the PCI ID is [14e4:1752], the server is affected.

List the network interfaces with:

ip -brief link show

For example:

To find which interface corresponds to the Broadcom controller, run the following:

ethtool -i eno1

For example:

Now that the interface is identified, the 'generic-receive-offload' parameter needs to be disabled.

To check if 'generic-receive-offload' is enabled and disable it, use these commands:

ethtool --show-offload eno1 | grep generic-receive-offload

ethtool --offload eno1 generic-receive-offload off

Finally, to make the change permanent, the /etc/network/interfaces file needs to be modified and the network service needs a restart:

Service restart: