.\"
.\" $FreeBSD: src/share/man/man4/ipfirewall.4,v 1.33.10.1.6.1 2010/12/21 17:09:25 kensmith Exp $
.\"
.Dd September 1, 2006
.Dt IPFW 4
.Os
.Sh NAME
.Nm ipfw
.Nd IP packet filter and traffic accounting
.Sh SYNOPSIS
To compile
.Ns Nm
into the kernel, place the following option in the kernel configuration
file:
.Bd -ragged -offset indent
.Cd "options IPFIREWALL"
.Ed
.Pp
Other kernel options related to
.Ns Nm
which may also be useful are:
.Bd -ragged -offset indent
.Cd "options IPFIREWALL_DEFAULT_TO_ACCEPT"
.Cd "options IPFIREWALL_FORWARD"
.Cd "options IPFIREWALL_VERBOSE"
.Cd "options IPFIREWALL_VERBOSE_LIMIT=100"
.Ed
.Pp
To load
.Ns Nm
as a module at boot time, add the following line into the
.Xr loader.conf 5
file:
.Bd -literal -offset indent
ipfw_load="YES"
.Ed
.Sh DESCRIPTION
The
.Nm
system facility allows filtering,
redirecting, and other operations on
.Tn IP
packets travelling through
network interfaces.
.Pp
The default behavior of
.Nm
is to block all incoming and outgoing traffic.
This behavior can be modified, to allow all traffic through the
.Nm
firewall by default, by enabling the
.Dv IPFIREWALL_DEFAULT_TO_ACCEPT
kernel option.
This option may be useful when configuring
.Nm
for the first time.
If the default
.Nm
behavior is to allow everything, it is easier to cope with
firewall-tuning mistakes which may accidentally block all traffic.
.Pp
To enable logging of packets passing through
.Nm ,
enable the
.Dv IPFIREWALL_VERBOSE
kernel option.
The
.Dv IPFIREWALL_VERBOSE_LIMIT
option will prevent
.Xr 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.
.Pp
Policy routing and transparent forwarding features of
.Nm
can be enabled by
.Dv IPFIREWALL_FORWARD
kernel option.
.Pp
The user interface for
.Nm
is implemented by the
.Xr ipfw 8
utility, so please refer to the
.Xr ipfw 8
manpage for a complete description of the
.Nm
capabilities and how to use it.
.Sh SEE ALSO
.Xr setsockopt 2 ,
.Xr divert 4 ,
.Xr ip 4 ,
.Xr ipfw 8 ,
.Xr sysctl 8 ,
.Xr syslogd 8 ,
.Xr pfil 9