The required kernel module is not included in the base system. However you will find the needed modules as source-code, which you can compile and install manually. The required modules are: mlx4 and mlxen.
#tested with 'FreeBSD 11.0-Release-p7' #download the actual source-code files svn checkout https://svn.freebsd.org/base/releng/11.0 /usr/local/src/ #or update them only, if you have downloaded the files in the past svn update /usr/local/src #compile and install the mellanox base module 'mlx4' cd /usr/src/sys/modules/mlx4 make make install #compile and install the mellanox ethernet module 'mlxen' cd /usr/src/sys/modules/mlxen make make install #load both compiled modules into kernel kldload mlx4 kldload mlxen #check, if your card is found dmesg ifcontrol -a #configure and activate the new interface ifconfig mlxen0 192.168.0.1 netmask 255.255.255.0 up