The Mellanox %%ConnectX%%-4 / %%ConnectX%%-5 drivers are not automatically loaded by the installer. To perform a network install using a %%ConnectX%% NIC the driver must be loaded manually.

During install, escape (ESC) to the loader prompt when you see the Welcome to %%FreeBSD%% Beastie menu and load the kernel and the following modules for Mellanox %%ConnectX%%-4/5 Ethernet support:

<code>
load boot/kernel/kernel
load boot/kernel/mlx.ko

load boot/kernel/mlx5.ko
load boot/kernel/mlx5en.ko
</code>

If this method fails for some reason, during install excape to a shell before network configuration and run, "kldload mlx5en.ko".

After install, add the following line to /etc/rc.conf to load the
modules automatically after mounting local disks:

kld_list="mlx mlxfw mlx5 mlx5en"

Please refer to the man page for further details or options:

https://www.freebsd.org/cgi/man.cgi?query=mlx5en