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