fastnetmon-ng/docs/BUILDING_FREEBSD_KERNEL_FOR_NETMAP.md

Installing netmap in FreeBSD

Try to build kernel module for current kernel:

cd /usr/src/sys/modules/netmap
make 
make install
kldload netmap

But you could hit this bug:

KLD netmap.ko: depends on kernel - not available or version mismatch
linker_load_file: Unsupported file type

Enable netmap startup on server load:

echo 'netmap_load="YES"' >> /boot/loader.conf

And should rebuild kernel manually.

Install SVN:

pkg install devel/subversion

Download base repository for FreeBSD 10 stable (replace 10 by your FreeBSD version): svn checkput https://svn0.ru.freebsd.org/base/stable/10 /usr/src

Build and install new kernel:

cd /usr/src/sys/amd64/conf
cp GENERIC KERNELWITHNETMAP
cd /usr/src
make buildkernel KERNCONF=KERNELWITHNETMAP
make installkernel KERNCONF=KERNELWITHNETMAP