.\"
.\" $FreeBSD$
.\"
.Dd June 22, 1997
.Dt IPFIREWALL 4
.Os
.Sh NAME
.Nm ipfirewall
.Nd IP packet filter and traffic accounting
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/queue.h>
.Fd #include <netinet/in.h>
.Fd #include <netinet/ip_fw.h>
.Ft int
.Fn setsockopt raw_socket IPPROTO_IP "ipfw option" "struct ipfw" size
.Sh DESCRIPTION
Ipfirewall (alias ipfw) is a system facility which allows filtering,
redirecting, and other operations on IP packets travelling through
system interfaces.
Packets are matched by applying an ordered list
of pattern rules against each packet until a match is found, at
which point the corresponding action is taken.
Rules are numbered
from 1 to 65534; multiple rules may share the same number.
.Pp
There is one rule that always exists, rule number 65535.
This rule
normally causes all packets to be dropped.
Hence, any packet which does not
match a lower numbered rule will be dropped.  However, a kernel compile
time option
.Dv IPFIREWALL_DEFAULT_TO_ACCEPT
allows the administrator to change this fixed rule to permit everything.
.Pp
The value passed to 
.Fn setsockopt
is a struct ip_fw describing the rule (see below).
In some cases
(such as
.Dv IP_FW_DEL ) ,
only the rule number is significant.
.Ss Commands
The following socket options are used to manage the rule list:
.Bl -tag -width "IP_FW_FLUSH"
.It Dv IP_FW_ADD
inserts the rule into the rule list
.It Dv IP_FW_DEL
deletes all rules having the matching rule number
.It Dv IP_FW_GET
returns the (first) rule having the matching rule number
.It Dv IP_FW_ZERO
zeros the statistics associated with all rules having the
matching rule number.
If the rule number is zero, all rules are zeroed.
.It Dv IP_FW_FLUSH
removes all rules (except 65535).
.El
.Pp
When the kernel security level is greater than 2, only
.Dv IP_FW_GET
is allowed.
.Ss Rule Structure
Rules are described by the structures in ip_fw.h.
.Ss Rule Actions
Each rule has an action described by the IP_FW_F_COMMAND bits in the
flags word:
.Bl -tag -width "IP_FW_F_DIVERT"
.It Dv IP_FW_F_DENY
Drop packet and stop processing.
.It Dv IP_FW_F_REJECT
drop packet; send rejection via ICMP or TCP and stop processing.
.It Dv IP_FW_F_ACCEPT
accept packet and stop processing.
.It Dv IP_FW_F_COUNT
increment counters; continue matching
.It Dv IP_FW_F_DIVERT
divert packet to a
.Xr divert 4
socket and stop processing.
.It Dv IP_FW_F_TEE
Send a copy of this packet to a
.Xr divert 4
socket and continue processing the original packet at the next rule.
.It Dv IP_FW_F_SKIPTO
skip to rule number
.Va fu_skipto_rule
At this time the target rule number must be greater than the active rule number.
.It Dv IP_FW_F_PIPE
The packet is marked for the use of
.Xr dummynet 4 ,
and processing stopped.
.It Dv IP_FW_F_QUEUE
The packet is marked for the use of
.Xr dummynet 4 ,
and processing stopped.
.It Dv IP_FW_F_FWD
The packet is accepted but the destination is hijacked. (see
.Xr ipfw 8 )
.El
.Pp
In the case of
.Dv IP_FW_F_REJECT ,
if the
.Va fu_reject_code
is a number
from 0 to 255, then an ICMP unreachable packet is sent back to the
original packet's source IP address, with the corresponding code.
Otherwise, the value must be 256 and the protocol
.Dv IPPROTO_TCP ,
in which case a TCP reset packet is sent instead.
.Pp
With
.Dv IP_FW_F_SKIPTO ,
all succeeding rules having rule number less
than
.Va fu_skipto_rule
are skipped.
.Ss Kernel Options
Options in the kernel configuration file:
.Bl -tag -width "options IPFIREWALL_VERBOSE_LIMIT"
.It Cd options IPFIREWALL
enable
.Nm
.It Cd options IPFIREWALL_VERBOSE
enable firewall logging
.It Cd options IPFIREWALL_VERBOSE_LIMIT
limit firewall logging
.It Cd options IPDIVERT
enable
.Xr divert 4
sockets
.El
.Pp
When packets match a rule with the
.Dv IP_FW_F_PRN
bit set, and if
.Dv IPFIREWALL_VERBOSE
has been enabled,
a message is written to
.Pa /dev/klog
with the
.Dv LOG_SECURITY
facility
(see
.Xr syslog 3 )
for further logging by
.Xr syslogd 8 ;
.Dv IPFIREWALL_VERBOSE_LIMIT
limits the maximum number of times each
rule can cause a log message.
These variables are also
available via the
.Xr sysctl 3
interface.
.Sh RETURN VALUES
The
.Fn setsockopt
function returns 0 on success.
Otherwise, -1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn setsockopt
function will fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The IP option field was improperly formed;
an option field was shorter than the minimum value
or longer than the option buffer provided.
.It Bq Er EINVAL
A structural error in ip_fw structure occurred
(n_src_p+n_dst_p too big, ports set for ALL/ICMP protocols etc.).
.It Bq Er EINVAL
An invalid rule number was used.
.El
.Sh SEE ALSO
.Xr setsockopt 2 ,
.Xr divert 4 ,
.Xr ip 4 ,
.Xr ipfw 8 ,
.Xr sysctl 8 ,
.Xr syslogd 8
.Sh BUGS
This man page still needs work.
.Sh HISTORY
The ipfw facility was initially written as package to BSDI
by
.An Daniel Boulet
.Aq danny@BouletFermat.ab.ca .
It has been heavily modified and ported to
.Fx
by
.An Ugen J.S. Antsilevich
.Aq ugen@NetVision.net.il .
.Pp
Several enhancements added by
.An Archie Cobbs
.Aq archie@FreeBSD.org .