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IPFW(8)			    System Manager's Manual		       IPFW(8)

     ipfw -- controlling utility for IP	firewall

     ipfw [-q] file
     ipfw [-f |	-q] flush
     ipfw [-q] zero [number ...]
     ipfw delete number	...
     ipfw [-aftN] list [number ...]
     ipfw [-ftN] show [number ...]
     ipfw [-q] add [number] action [log] proto from src	to dst
	  [via name | ipno] [options]

     If	used as	shown in the first synopsis line, the file will	be read	line
     by	line and applied as arguments to the ipfw command.

     The ipfw code works by going through the rule-list	for each packet, until
     a match is	found.	All rules have two associated counters,	a packet count
     and a byte	count.	These counters are updated when	a packet matches the

     The rules are ordered by a	``line-number''	from 1 to 65534	that is	used
     to	order and delete rules.	Rules are tried	in increasing order, and the
     first rule	that matches a packet applies.	Multiple rules may share the
     same number and apply in the order	in which they were added.

     If	a rule is added	without	a number, it is	numbered 100 higher than the
     previous rule. If the highest defined rule	number is greater than 65434,
     new rules are appended to the last	rule.

     The delete	operation deletes the first rule with number number, if	any.

     The list command prints out the current rule set.

     The show command is equivalent to `ipfw -a	list'.

     The zero operation	zeroes the counters associated with rule number

     The flush operation removes all rules.

     Any command beginning with	a '#', or being	all blank, is ignored.

     One rule is always	present:

		       65535 deny all from any to any

     This rule is the default policy, i.e., don't allow	anything at all.  Your
     job in setting up rules is	to modify this policy to match your needs.

     The following options are available:

     -a	   While listing, show counter values.	See also ``show'' command.

     -f	   Don't ask for confirmation for commands that	can cause problems if
	   misused (ie;	flush).	 Note, if there	is no tty associated with the
	   process, this is implied.

     -q	   While adding, zeroing or flushing, be quiet about actions (implies
	   -f).	This is	useful for adjusting rules by executing	multiple ipfw
	   commands in a script	(e.g. sh /etc/rc.firewall), or by processing a
	   file	of many	ipfw rules, across a remote login session.  If a flush
	   is performed	in normal (verbose) mode, it prints a message.
	   Because all rules are flushed, the message cannot be	delivered to
	   the login session, the login	session	is closed and the remainder of
	   the ruleset is not processed.  Access to the	console	is required to

     -t	   While listing, show last match timestamp.

     -N	   Try to resolve addresses and	service	names in output.


	 allow		   Allow packets that match rule.  The search termi-
			   nates. Aliases are pass, permit, and	accept.

	 deny		   Discard packets that	match this rule.  The search
			   terminates.	Drop is	an alias for deny.

	 reject		   (Deprecated.) Discard packets that match this rule,
			   and try to send an ICMP host	unreachable notice.
			   The search terminates.

	 unreach code	   Discard packets that	match this rule, and try to
			   send	an ICMP	unreachable notice with	code code,
			   where code is a number from zero to 255, or one of
			   these aliases: net, host, protocol, port, needfrag,
			   srcfail, net-unknown, host-unknown, isolated,
			   net-prohib, host-prohib, tosnet, toshost,
			   filter-prohib, host-precedence, or
			   precedence-cutoff.  The search terminates.

	 reset		   TCP packets only. Discard packets that match	this
			   rule, and try to send a TCP reset (RST) notice.
			   The search terminates.

	 count		   Update counters for all packets that	match rule.
			   The search continues	with the next rule.

	 divert	port	   Divert packets that match this rule to the
			   divert(4) socket bound to port port.	 The search

	 tee port	   Send	a copy of packets matching this	rule to	the
			   divert(4) socket bound to port port.	 The search
			   continues with the next rule.

	 skipto	number	   Skip	all subsequent rules numbered less than
			   number.  The	search continues with the first	rule
			   numbered number or higher.

     If	a packet matches more than one divert and/or tee rule, all but the
     last are ignored.

     If	the kernel was compiled	with IPFIREWALL_VERBOSE, then when a packet
     matches a rule with the ``log'' keyword a message will be printed on the
     console.  If the kernel was compiled with the IPFIREWALL_VERBOSE_LIMIT
     option, then logging will cease after the number of packets specified by
     the option	are received for that particular chain entry.  Logging may
     then be re-enabled	by clearing the	packet counter for that	entry.

     Console logging and the log limit are adjustable dynamically through the
     sysctl(8) interface.


	 ip		   All packets match. The alias	all has	the same

	 tcp		   Only	TCP packets match.

	 udp		   Only	UDP packets match.

	 icmp		   Only	ICMP packets match.

	 _number|name_	   Only	packets	for the	specified protocol matches
			   (see	/etc/protocols for a complete list).

     src and dst:

	 _address/mask_	[ports]

     The _address/mask_	may be specified as:

	 ipno		   An ipnumber of the form  Only this exact
			   ip number match the rule.

	 ipno/bits	   An ipnumber with a mask width of the	form	In this	case all ip numbers from to	will match.

	 ipno:mask	   An ipnumber with a mask width of the	form  In this case	all ip numbers
			   from	to will match.

     The sense of the match can	be inverted by preceding an address with the
     ``not'' modifier, causing all other addresses to be matched instead. This
     does not affect the selection of port numbers.

     With the TCP and UDP protocols, optional ports may	be specified as:


     Service names (from /etc/services)	may be used instead of numeric port
     values.  A	range may only be specified as the first value,	and the	length
     of	the port list is limited to IP_FW_MAX_PORTS (as	defined	in
     /usr/src/sys/netinet/ip_fw.h) ports.

     Fragmented	packets	which have a non-zero offset (i.e. not the first frag-
     ment) will	never match a rule which has one or more port specifications.
     See the frag option for details on	matching fragmented packets.

     Rules can apply to	packets	when they are incoming,	or outgoing, or	both.
     The in keyword indicates the rule should only match incoming packets.
     The out keyword indicates the rule	should only match outgoing packets.

     To	match packets going through a certain interface, specify the interface
     using via:

	 via ifX	   Packet must be going	through	interface ifX.

	 via if*	   Packet must be going	through	interface ifX, where X
			   is any unit number.

	 via any	   Packet must be going	through	some interface.

	 via ipno	   Packet must be going	through	the interface having
			   IP address ipno.

     The via keyword causes the	interface to always be checked.	 If recv or
     xmit is used instead of via, then the only	receive	or transmit interface
     (respectively) is checked.	 By specifying both, it	is possible to match
     packets based on both receive and transmit	interface, e.g.:

	   ipfw	add 100	deny ip	from any to any	out recv ed0 xmit ed1

     The recv interface	can be tested on either	incoming or outgoing packets,
     while the xmit interface can only be tested on outgoing packets. So out
     is	required (and in invalid) whenever xmit	is used. Specifying via
     together with xmit	or recv	is invalid.

     A packet may not have a receive or	transmit interface: packets originat-
     ing from the local	host have no receive interface.	while packets destined
     for the local host	have no	transmit interface.

     Additional	options:

	 frag		   Matches if the packet is a fragment and this	is not
			   the first fragment of the datagram.	frag may not
			   be used in conjunction with either tcpflags or
			   TCP/UDP port	specifications.

	 in		   Matches if this packet was on the way in.

	 out		   Matches if this packet was on the way out.

	 ipoptions spec	   Matches if the IP header contains the comma sepa-
			   rated list of options specified in spec.  The sup-
			   ported IP options are: ssrr (strict source route),
			   lsrr	(loose source route), rr (record packet
			   route), and ts (timestamp).	The absence of a par-
			   ticular option may be denoted with a	``!''.

	 established	   Matches packets that	have the RST or	ACK bits set.
			   TCP packets only.

	 setup		   Matches packets that	have the SYN bit set but no
			   ACK bit.  TCP packets only.

	 tcpflags spec	   Matches if the TCP header contains the comma	sepa-
			   rated list of flags specified in spec.  The sup-
			   ported TCP flags are: fin, syn, rst,	psh, ack, and
			   urg.	 The absence of	a particular flag may be
			   denoted with	a ``!''.  A rule which contains	a
			   tcpflags specification can never match a fragmented
			   packet which	has a non-zero offset.	See the	frag
			   option for details on matching fragmented packets.

	 icmptypes types   Matches if the ICMP type is in the list types.  The
			   list	may be specified as any	combination of ranges
			   or individual types separated by commas.

     Here are some important points to consider	when designing your rules:

	 +o   Remember that you filter both packets going in and	out.  Most
	     connections need packets going in both directions.

	 +o   Remember to test very carefully.  It is a good idea to be near
	     the console when doing this.

	 +o   Don't forget the loopback interface.

     There is one kind of packet that the firewall will	always discard,	that
     is	an IP fragment with a fragment offset of one.  This is a valid packet,
     but it only has one use, to try to	circumvent firewalls.

     If	you are	logged in over a network, loading the LKM version of ipfw is
     probably not as straightforward as	you would think.  I recommend this
     command line:

		       modload /lkm/ipfw_mod.o && \
		       ipfw add	32000 allow all	from any to any

     Along the same lines, doing an

		       ipfw flush

     in	similar	surroundings is	also a bad idea.

     A divert socket bound to the specified port will receive all packets
     diverted to that port; see	divert(4).  If no socket is bound to the des-
     tination port, or if the kernel wasn't compiled with divert socket	sup-
     port, diverted packets are	dropped.

     This command adds an entry	which denies all tcp packets from to	the telnet port	of from being forwarded
     by	the host:

	   ipfw	add deny tcp from to 23

     This one disallows	any connection from the	entire hackers network to my

	   ipfw	addf deny all from to

     Here is a good usage of the list command to see accounting	records	and
     timestamp information:

	   ipfw	-at l

     or	in short form without timestamps:

	   ipfw	-a l

     This rule diverts all incoming packets from	to divert port

	   ipfw	divert 5000 all	from to any in

     ip(4), ipfirewall(4), divert(4), protocols(5), services(5), reboot(8),
     syslogd(8), sysctl(8)


     This program can put your computer	in rather unusable state. When using
     it	for the	first time, work on the	console	of the computer, and do	NOT do
     anything you don't	understand.

     When manipulating/adding chain entries, service and protocol names	are
     not accepted.

     Incoming packet fragments diverted	by divert are reassembled before
     delivery to the socket, whereas fragments diverted	via tee	are not.

     Port aliases containing dashes cannot be first in a list.

     Ugen J. S.	Antsilevich,
     Poul-Henning Kamp,
     Alex Nash,
     Archie Cobbs.
     Archie Cobbs.  API	based upon code	written	by
     Daniel Boulet for BSDI.

     Ipfw first	appeared in FreeBSD 2.0.

FreeBSD				 July 20, 1996			       FreeBSD


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