.Dd February 24, 1996 .Dt IPFW 8 SMM .Os FreeBSD .Sh NAME .Nm ipfw .Nd controlling utility for IP firewall .Sh SYNOPSIS .Nm ipfw .Ar file .Nm ipfw flush .Nm ipfw zero .Oo .Ar number .Oc .Nm ipfw delete .Ar number .Nm ipfw .Oo .Fl atN .Oc list .Nm ipfw add .Oo .Ar number .Oc .Ar action .Oo log .Oc .Ar proto from .Ar src to .Ar dst .Oo via .Ar name|ipno .Oc .Oo .Ar options .Oc .Sh DESCRIPTION If used as shown in the first synopsis line, the .Ar file will be read line by line and applied as arguments to the .Nm ipfw command. .Pp The ipfw code works by going through the rule-list for each packet, until a match is found. All rules have two counters associated with them, a packet count and a byte count. These counters are updated when a packet matches the rule. .Pp The rules are ordered by a ``line-number'' that is used to order and delete rules. If a rule is added without a number, it is put at the end, just before the terminal ``policy-rule'', and numbered 100 higher than the previous rule. .Pp One rule is always present: .Bd -literal -offset center 65535 deny all from any to any .Ed this rule is the default policy, ie. don't allow anything at all. Your job in setting up rules is to modify this policy to match your needs. .Pp The following options are available: .Bl -tag -width flag .It Fl a While listing, show counter values. This option is the only way to see accounting records. .It Fl t While listing, show last match timestamp. .It Fl N Try to resolve addresses and service names. .El .Pp .Ar action : .Bl -hang -offset flag -width 1234567890123456 .It Nm allow Allow packets that match rule. The search terminates. .It Nm pass Same as allow. .It Nm accept Same as allow. .It Nm count Update counters for all packets that match rule. The search continues with next rule. .It Nm deny Discard packets that match this rule. The search terminates. .It Nm reject Discard packets that match this rule, try to send ICMP notice. The search terminates. .El .Pp When a packet matches a rule with the .Nm log keyword, a message will be printed on the console. If the kernel was compiled with the .Nm IP_FIREWALL_VERBOSE_LIMIT option, then logging will cease after the number of packets specified by the option are recieved for that particular chain entry. Logging may then be re-enabled by clearing the packet counter for that entry. .Pp .Ar proto : .Bl -hang -offset flag -width 1234567890123456 .It Nm ip All packets match. .It Nm all All packets match. .It Nm tcp Only TCP packets match. .It Nm udp Only UDP packets match. .It Nm icmp Only ICMP packets match. .El .Pp .Ar src and .Ar dst : .Pp .Bl -hang -offset flag .It
[ports] .El .Pp The .Em
may be specified as: .Bl -hang -offset flag -width 1234567890123456 .It Ar ipno An ipnumber of the form 1.2.3.4. Only this exact ip number match the rule. .It Ar ipno/bits An ipnumber with a mask width of the form 1.2.3.4/24. In this case all ip numbers from 1.2.3.0 to 1.2.3.255 will match. .It Ar ipno:mask An ipnumber with a mask width of the form 1.2.3.4:255.255.240.0 In this case all ip numbers from 1.2.0.0 to 1.2.15.255 will match. .El .Pp With the TCP and UDP .Em protocols , an optional .Em port may be specified as: .Pp .Bl -hang -offset flag .It Ns {port|port-port} Ns Op ,port Ns Op ,... .El .Pp Service names (from .Pa /etc/services ) may not be used instead of a numeric port value. Also, note that a range may only be specified as the first value, and the port list is limited to .Nm IP_FW_MAX_PORTS (as defined in /usr/src/sys/netinet/ip_fw.h) ports. .Pp If ``via'' .Ar name is specified, only packets received via or on their way out of an interface matching .Ar name will match this rule. .Pp If ``via'' .Ar ipno is specified, only packets received via or on their way out of an interface having the address .Ar ipno will match this rule. .Pp .Ar options : .Bl -hang -offset flag -width 1234567890123456 .It frag Matches if the packet is a fragment and this is not the first fragment of the datagram. .It in Matches if this packet was on the way in. .It out Matches if this packet was on the way out. .It ipoptions Ar spec Matches if the IP header contains the comma separated list of options specified in .Ar spec . The supported IP options are: .Nm ssrr (strict source route), .Nm lsrr (loose source route), .Nm rr (record packet route), and .Nm ts (timestamp). The absence of a particular option may be denoted with a ``!''. .It established Matches packets that have the RST or ACK bits set. TCP packets only. .It setup Matches packets that have the SYN bit set but no ACK bit. TCP packets only. .It tcpflags Ar spec Matches if the TCP header contains the comma separated list of flags specified in .Ar spec . The supported TCP flags are: .Nm fin , .Nm syn , .Nm rst , .Nm psh , .Nm ack , and .Nm urg . The absence of a particular flag may be denoted with a ``!''. .It icmptypes Ar types Matches if the ICMP type is in the list .Ar types . The list may be specified as any combination of ranges or individual types separated by commas. .El .Sh CHECKLIST Here are some important points to consider when designing your rules: .Bl -bullet -hang -offset flag -width 1234567890123456 .It Remember that you filter both packets going in and out. Most connections need packets going in both directions. .It Remember to test very carefully. It is a good idea to be near the console when doing this. .It Don't forget the loopback interface. .It Don't filter .Nm all if you are also specifying a port. .El .Sh FINE POINTS 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. .Pp If you are logged in over a network, loading the LKM version of .Nm is probably not as straightforward as you would think. I recommend this command line: .Bd -literal -offset center modload /lkm/ipfw_mod.o && \e ipfw add 32000 allow all from any to any .Ed Along the same lines, doing an .Bd -literal -offset center ipfw flush .Ed in similar surroundings is also a bad idea. .Sh EXAMPLES This command adds an entry which denies all tcp packets from .Em hacker.evil.org to the telnet port of .Em wolf.tambov.su from being forwarded by the host: .Pp .Dl ipfw add deny tcp from hacker.evil.org to wolf.tambov.su 23 .Pp This one disallows any connection from the entire hackers network to my host: .Pp .Dl ipfw addf deny all from 123.45.67.0/24 to my.host.org .Pp Here is good usage of list command to see accounting records: .Pp .Dl ipfw -at l .Pp or in short form .Pp .Dl ipfw -a l .Pp .Sh SEE ALSO .Xr gethostbyname 3 , .Xr getservbyport 3 , .Xr ip 4 , .Xr ipfirewall 4 , .Xr ipaccounting 4 , .Xr reboot 8 , .Xr syslogd 8 .Sh BUGS .Pp .Em WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!! .Pp 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 .Em NOT do anything you don't understand. .Pp When manipulating/adding chain entries, service names are not accepted. .Sh HISTORY Initially this utility was written for BSDI by: .Pp .Dl Daniel Boulet .Pp The FreeBSD version is written completely by: .Pp .Dl Ugen J.S.Antsilevich .Pp This has all been extensively rearranged by Poul-Henning Kamp and Alex Nash.