IPFilter Tuning on FreeBSD

If you're running ipfilter and ipnat on a fairly busy network, you may have to tune ipfilter to accomodate more than the default 30,000 NAT routings. These settings in your rc.conf should allow you to operate comfortably on a GigE network.

ipfilter_flags=”-D -T ipf_nattable_sz=34487, ipf_nattable_max=600011, fr_tcpidletimeout=7200, fr_tcphalfclosed=300, fr_statemax=21529, fr_statesize=30757 -E”

Keep in mind: Some of the tunings need to be prime numbers or you’ll get a lot of bad NATs (viewed using the command ipnat -s). Here’s a list of prime numbers up to 999,983.

After reboot, or after reloading ipfilter, you can check to make sure it's working by checking the list of ipfilter settings:

ipf -T list

Alternatively, if you didn’t want to tune ipfilter using rc.conf, you could remake ipfilter specifying the LARGE_NAT option:

make clean
make -DLARGE_NAT depend
make install

This increases a lot of the default settings, but might be overkill unless you know you really need it.

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