need description of IPFILTER sysctl's

[fbsd_user]

Here is the list of ipfilter sysctl's in FreeBSD.
Looking for documentation on their meanings.

net.inet.ipf.fr_flags: 1073741824
net.inet.ipf.fr_pass: 513
net.inet.ipf.fr_active: 0
net.inet.ipf.fr_tcpidletimeout: 864000
net.inet.ipf.fr_tcpclosewait: 480
net.inet.ipf.fr_tcplastack: 480
net.inet.ipf.fr_tcptimeout: 480
net.inet.ipf.fr_tcpclosed: 120
net.inet.ipf.fr_tcphalfclosed: 14400
net.inet.ipf.fr_udptimeout: 240
net.inet.ipf.fr_udpacktimeout: 24
net.inet.ipf.fr_icmptimeout: 120
net.inet.ipf.fr_icmpacktimeout: 12
net.inet.ipf.fr_defnatage: 1200
net.inet.ipf.fr_ipfrttl: 120
net.inet.ipf.ipl_unreach: 13
net.inet.ipf.fr_running: 1
net.inet.ipf.fr_authsize: 32
net.inet.ipf.fr_authused: 0
net.inet.ipf.fr_defaultauthage: 600
net.inet.ipf.fr_chksrc: 0
net.inet.ipf.ippr_ftp_pasvonly: 0
net.inet.ipf.fr_minttl: 3
net.inet.ipf.fr_minttllog: 1