Provided by:
freebsd-manpages_6.2-1_all 
NAME
ipfw - IP packet filter and traffic accounting
SYNOPSIS
To compile ipfw into the kernel, place the following option in the kernel
configuration file:
options IPFIREWALL
Other kernel options related to ipfw which may also be useful are:
options IPFIREWALL_DEFAULT_TO_ACCEPT
options IPFIREWALL_FORWARD
options IPFIREWALL_VERBOSE
options IPFIREWALL_VERBOSE_LIMIT=100
To load ipfw 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 opera‐
tions on IP packets travelling through network interfaces.
The default behavior of ipfw is to block all incoming and outgoing traf‐
fic. 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.
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.
Policy routing and transparent forwarding features of ipfw can be enabled
by IPFIREWALL_FORWARD kernel option.
The user interface for ipfw is implemented by the ipfw(8) utility, so
please refer to the ipfw(8) manpage for a complete description of the
ipfw capabilities and how to use it.
setsockopt(2), divert(4), ip(4), ipfw(8), sysctl(8), syslogd(8), pfil(9)