IPFW(4)                FreeBSD Kernel Interfaces Manual                IPFW(4)

NAME
     ipfw - IP packet filter and traffic accounting

SYNOPSIS
     To compile the driver into the kernel, place the following option in the
     kernel configuration file:

           options IPFIREWALL

     Other related kernel options which may also be useful are:

           options IPFIREWALL_DEFAULT_TO_ACCEPT
           options IPDIVERT
           options IPFIREWALL_NAT
           options IPFIREWALL_NAT64
           options IPFIREWALL_NPTV6
           options IPFIREWALL_PMOD
           options IPFIREWALL_VERBOSE
           options IPFIREWALL_VERBOSE_LIMIT=100
           options LIBALIAS

     To load the driver as a module at boot time, add the following line into
     the loader.conf(5) file:

           ipfw_load="YES"

DESCRIPTION
     The ipfw system facility allows filtering, redirecting, and other
     operations on IP packets travelling through network interfaces.

     The default behavior of ipfw is to block all incoming and outgoing
     traffic.  This behavior can be modified, to allow all traffic through the
     ipfw firewall by default, by enabling the IPFIREWALL_DEFAULT_TO_ACCEPT
     kernel option.  This option may be useful when configuring ipfw for the
     first time.  If the default ipfw behavior is to allow everything, it is
     easier to cope with firewall-tuning mistakes which may accidentally block
     all traffic.

     When using natd(8) in conjunction with ipfw as NAT facility, the kernel
     option IPDIVERT enables diverting packets to natd(8) for translation.

     When using the in-kernel NAT facility of ipfw, the kernel option
     IPFIREWALL_NAT enables basic libalias(3) functionality in the kernel.

     When using any of the IPv4 to IPv6 transition mechanisms in ipfw, the
     kernel option IPFIREWALL_NAT64 enables all of these NAT64 methods in the
     kernel.

     When using the IPv6 network prefix translation facility of ipfw, the
     kernel option IPFIREWALL_NPTV6 enables this functionality in the kernel.

     When using the packet modification facility of ipfw, the kernel option
     IPFIREWALL_PMOD enables this functionality in the kernel.

     To enable logging of packets passing through ipfw, enable the
     IPFIREWALL_VERBOSE kernel option.  The IPFIREWALL_VERBOSE_LIMIT option
     will prevent syslogd(8) from flooding system logs or causing local Denial
     of Service.  This option may be set to the number of packets which will
     be logged on a per-entry basis before the entry is rate-limited.

     When using the in-kernel NAT facility of ipfw, the kernel option LIBALIAS
     enables full libalias(3) functionality in the kernel.  Full functionality
     refers to included support for ftp, bbt, skinny, irc, pptp and smedia
     packets, which are missing in the basic libalias(3) functionality
     accomplished with the IPFIREWALL_NAT kernel option.

     The user interface for ipfw is implemented by the ipfw(8) utility, so
     please refer to the ipfw(8) man page for a complete description of the
     ipfw capabilities and how to use it.

SEE ALSO
     setsockopt(2), divert(4), ip(4), ip6(4), ipfw(8), libalias(3), natd(8),
     sysctl(8), syslogd(8), pfil(9)

FreeBSD 13.1-RELEASE-p6         August 19, 2020        FreeBSD 13.1-RELEASE-p6