Manual Pages  — IPFW

ipfw – User interface for firewall, traffic shaper, packet scheduler, in-kernel NAT.

SYNOPSIS FIREWALL CONFIGURATION SYSCTL SHORTCUTS LOOKUP TABLES DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER) IN-KERNEL NAT STATEFUL IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION STATELESS IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION XLAT464 CLAT IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION IPv6-to-IPv6 NETWORK PREFIX TRANSLATION INTERNAL DIAGNOSTICS LIST OF RULES AND PREPROCESSING DESCRIPTION COMMAND OPTIONS LIST OF RULES AND PREPROCESSING TRAFFIC SHAPER CONFIGURATION PACKET FLOW SYNTAX RULE FORMAT RULE ACTIONS RULE BODY RULE OPTIONS (MATCH PATTERNS) LOOKUP TABLES SETS OF RULES STATEFUL FIREWALL TRAFFIC SHAPER (DUMMYNET) CONFIGURATION PIPE, QUEUE AND SCHEDULER CONFIGURATION CHECKLIST FINE POINTS PACKET DIVERSION NETWORK ADDRESS TRANSLATION (NAT) REDIRECT AND LSNAT SUPPORT IN IPFW SCTP NAT SUPPORT IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Stateful translation XLAT464 CLAT translation IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6) LOADER TUNABLES SYSCTL VARIABLES INTERNAL DIAGNOSTICS EXAMPLES BASIC PACKET FILTERING SELECTIVE MIRRORING DYNAMIC RULES TRAFFIC SHAPING LOOKUP TABLES SETS OF RULES NAT, REDIRECT AND LSNAT CONFIGURING CODEL, PIE, FQ-CODEL and FQ-PIE AQM SEE ALSO HISTORY AUTHORS BUGS

ipfw [-cq] add rule
ipfw [-acdefnNStT] [ set N] { list | show} [rule | first-last ...]
ipfw [-f | -q] [ set N] flush
ipfw [-q] [ set N] { delete | zero | resetlog} [number ...]

ipfw set [ disable number ... ][ enable number ...]
ipfw set move [ rule] number to number
ipfw set swap number number
ipfw set show

ipfw enable { firewall | altq | one_pass | debug | verbose | dyn_keepalive}
ipfw disable { firewall | altq | one_pass | debug | verbose | dyn_keepalive}

ipfw [ set N ] table name create create-options
ipfw [ set N ] table {name | all} destroy
ipfw [ set N ] table name modify modify-options
ipfw [ set N ] table name swap name
ipfw [ set N ] table name add table-key [value]
ipfw [ set N ] table name add [table-key value ...]
ipfw [ set N ] table name atomic add [table-key value ...]
ipfw [ set N ] table name delete [table-key ...]
ipfw [ set N ] table name lookup addr
ipfw [ set N ] table name lock
ipfw [ set N ] table name unlock
ipfw [ set N ] table {name | all} list
ipfw [ set N ] table {name | all} info
ipfw [ set N ] table {name | all} detail
ipfw [ set N ] table {name | all} flush

dnctl { pipe | queue | sched} number config config-options
dnctl [-s [field]] { pipe | queue | sched} { delete | list | show} [number ...]

ipfw [-q] nat number config config-options
ipfw nat number show { config | log}

ipfw [ set N ] nat64lsn name create create-options
ipfw [ set N ] nat64lsn name config config-options
ipfw [ set N ] nat64lsn {name | all} { list | show} [ states]
ipfw [ set N ] nat64lsn {name | all} destroy
ipfw [ set N ] nat64lsn name stats [ reset]

ipfw [ set N ] nat64stl name create create-options
ipfw [ set N ] nat64stl name config config-options
ipfw [ set N ] nat64stl {name | all} { list | show}
ipfw [ set N ] nat64stl {name | all} destroy
ipfw [ set N ] nat64stl name stats [ reset]

ipfw [ set N ] nat64clat name create create-options
ipfw [ set N ] nat64clat name config config-options
ipfw [ set N ] nat64clat {name | all} { list | show}
ipfw [ set N ] nat64clat {name | all} destroy
ipfw [ set N ] nat64clat name stats [ reset]

ipfw [ set N ] nptv6 name create create-options
ipfw [ set N ] nptv6 {name | all} { list | show}
ipfw [ set N ] nptv6 {name | all} destroy
ipfw [ set N ] nptv6 name stats [ reset]

ipfw internal iflist
ipfw internal talist
ipfw internal vlist

ipfw [-cfnNqS] [ -p preproc [ preproc-flags ] ] pathname

The following general options are available when invoking ipfw:

-a
	Show counter values when listing rules. The show command implies this option.
-b
	Only show the action and the comment, not the body of a rule. Implies -c.
-c
	When entering or showing rules, print them in compact form, i.e., omitting the "ip from any to any" string when this does not carry any additional information.
-d
	When listing, show dynamic rules in addition to static ones.
-D
	When listing, show only dynamic states. When deleting, delete only dynamic states.
-f
	Run without prompting for confirmation for commands that can cause problems if misused, i.e., flush. If there is no tty associated with the process, this is implied. The delete command with this flag ignores possible errors, i.e., nonexistent rule number. And for batched commands execution continues with the next command.
-i
	When listing a table (see the LOOKUP TABLES section below for more information on lookup tables), format values as IP addresses. By default, values are shown as integers.
-n
	Only check syntax of the command strings, without actually passing them to the kernel.
-N
	Try to resolve addresses and service names in output.
-q
	Be quiet when executing the add, nat, zero, resetlog or flush commands; (implies -f). This is useful when updating rulesets by executing multiple ipfw commands in a script (e.g., ‘sh /etc/rc.firewall’), or by processing a file with many ipfw rules across a remote login session. It also stops a table add or delete from failing if the entry already exists or is not present. The reason why this option may be important is that for some of these actions, ipfw may print a message; if the action results in blocking the traffic to the remote client, the remote login session will be closed and the rest of the ruleset will not be processed. Access to the console would then be required to recover.
-S
	When listing rules, show the set each rule belongs to. If this flag is not specified, disabled rules will not be listed.
-s [field]
	When listing pipes, sort according to one of the four counters (total or current packets or bytes).
-t
	When listing, show last match timestamp converted with ctime().
-T
	When listing, show last match timestamp as seconds from the epoch. This form can be more convenient for postprocessing by scripts.

The dnctl pipe, queue and sched commands are used to configure the traffic shaper and packet scheduler. See the TRAFFIC SHAPER (DUMMYNET) CONFIGURATION Section below for details.

If the world and the kernel get out of sync the ipfw ABI may break, preventing you from being able to add any rules. This can adversely affect the booting process. You can use ipfw disable firewall to temporarily disable the firewall to regain access to the network, allowing you to fix the problem.

A packet is checked against the active ruleset in multiple places in the protocol stack, under control of several sysctl variables. These places and variables are shown below, and it is important to have this picture in mind in order to design a correct ruleset.

       ^    to upper layers    V
       |                       |
       +----------->-----------+
       ^                       V
 [ip(6)_input]           [ip(6)_output]     net.inet(6).ip(6).fw.enable=1
       |                       |
       ^                       V
 [ether_demux]        [ether_output_frame]  net.link.ether.ipfw=1
       |                       |
       +-->--[bdg_forward]-->--+            net.link.bridge.ipfw=1
       ^                       V
       |      to devices       |

The number of times the same packet goes through the firewall can vary between 0 and 4 depending on packet source and destination, and system configuration.

Note that as packets flow through the stack, headers can be stripped or added to it, and so they may or may not be available for inspection. E.g., incoming packets will include the MAC header when ipfw is invoked from ether_demux(), but the same packets will have the MAC header stripped off when ipfw is invoked from ip_input() or ip6_input().

Also note that each packet is always checked against the complete ruleset, irrespective of the place where the check occurs, or the source of the packet. If a rule contains some match patterns or actions which are not valid for the place of invocation (e.g.amp; trying to match a MAC header within ip_input or ip6_input ), the match pattern will not match, but a not operator in front of such patterns will cause the pattern to always match on those packets. It is thus the responsibility of the programmer, if necessary, to write a suitable ruleset to differentiate among the possible places. skipto rules can be useful here, as an example:

# packets from ether_demux or bdg_forward
ipfw add 10 skipto 1000 all from any to any layer2 in
# packets from ip_input
ipfw add 10 skipto 2000 all from any to any not layer2 in
# packets from ip_output
ipfw add 10 skipto 3000 all from any to any not layer2 out
# packets from ether_output_frame
ipfw add 10 skipto 4000 all from any to any layer2 out

(yes, at the moment there is no way to differentiate between ether_demux and bdg_forward).

Also note that only actions allow, deny, netgraph, ngtee and related to dummynet are processed for layer2 frames and all other actions act as if they were allow for such frames. Full set of actions is supported for IP packets without layer2 headers only. For example, divert action does not divert layer2 frames.

In general, each keyword or argument must be provided as a separate command line argument, with no leading or trailing spaces. Keywords are case-sensitive, whereas arguments may or may not be case-sensitive depending on their nature (e.g.amp; uid's are, hostnames are not).

Some arguments (e.g., port or address lists) are comma-separated lists of values. In this case, spaces after commas ',' are allowed to make the line more readable. You can also put the entire command (including flags) into a single argument. E.g., the following forms are equivalent:

ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8
ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8
ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"

The format of firewall rules is the following: [rule_number] [ set set_number] [ prob match_probability] action [ log [ logamount number]] [ altq queue] [ { tag | untag }number ] body

where the body of the rule specifies which information is used for filtering packets, among the following:

Layer2 header fields	When available
IPv4 and IPv6 Protocol	SCTP, TCP, UDP, ICMP, etc.
Source and dest. addresses and ports Direction
	See Section PACKET FLOW
Transmit and receive interface	By name or address
Misc. IP header fields	Version, type of service, datagram length, identification, fragmentation flags, Time To Live
IP options IPv6 Extension headers
	Fragmentation, Hop-by-Hop options, Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options.
IPv6 Flow-ID Misc. TCP header fields
	TCP flags (SYN, FIN, ACK, RST, etc.), sequence number, acknowledgment number, window
TCP options ICMP types
	for ICMP packets
ICMP6 types	for ICMP6 packets
User/group ID	When the packet can be associated with a local socket.
Divert status	Whether a packet came from a divert socket (e.g., natd(8)).
Fib annotation state	Whether a packet has been tagged for using a specific FIB (routing table) in future forwarding decisions.

Note that some of the above information, e.g.amp; source MAC or IP addresses and TCP/UDP ports, can be easily spoofed, so filtering on those fields alone might not guarantee the desired results.

rule_number
	Each rule is associated with a rule_number in the range 1..65535, with the latter reserved for the default rule. Rules are checked sequentially by rule number. Multiple rules can have the same number, in which case they are checked (and listed) according to the order in which they have been added. If a rule is entered without specifying a number, the kernel will assign one in such a way that the rule becomes the last one before the default rule. Automatic rule numbers are assigned by incrementing the last non-default rule number by the value of the sysctl variable net.inet.ip.fw.autoinc_step which defaults to 100. If this is not possible (e.g.amp; because we would go beyond the maximum allowed rule number), the number of the last non-default value is used instead.
set set_number
	Each rule is associated with a set_number in the range 0..31. Sets can be individually disabled and enabled, so this parameter is of fundamental importance for atomic ruleset manipulation. It can be also used to simplify deletion of groups of rules. If a rule is entered without specifying a set number, set 0 will be used. Set 31 is special in that it cannot be disabled, and rules in set 31 are not deleted by the ipfw command (but you can delete them with the ipfw command). Set 31 is also used for the default rule.
prob match_probability
	A match is only declared with the specified probability (floating point number between 0 and 1). This can be useful for a number of applications such as random packet drop or (in conjunction with dummynet) to simulate the effect of multiple paths leading to out-of-order packet delivery. Note: this condition is checked before any other condition, including ones such as keep-state or check-state which might have side effects.
log [ logamount number]
	Packets matching a rule with the log keyword will be made available for logging in two ways: if the sysctl variable net.inet.ip.fw.verbose is set to 0 (default), one can use bpf(4) attached to the ipfw0 pseudo interface. This pseudo interface can be created manually after a system boot by using the following command: # ifconfig ipfw0 create Or, automatically at boot time by adding the following line to the rc.conf(5) file: firewall_logif="YES" There is zero overhead when no bpf(4) is attached to the pseudo interface. If net.inet.ip.fw.verbose is set to 1, packets will be logged to syslogd(8) with a LOG_SECURITY facility up to a maximum of logamount packets. If no logamount is specified, the limit is taken from the sysctl variable net.inet.ip.fw.verbose_limit. In both cases, a value of 0 means unlimited logging. Once the limit is reached, logging can be re-enabled by clearing the logging counter or the packet counter for that entry, see the resetlog command. Note: logging is done after all other packet matching conditions have been successfully verified, and before performing the final action (accept, deny, etc.) on the packet.
tag number
	When a packet matches a rule with the tag keyword, the numeric tag for the given number in the range 1..65534 will be attached to the packet. The tag acts as an internal marker (it is not sent out over the wire) that can be used to identify these packets later on. This can be used, for example, to provide trust between interfaces and to start doing policy-based filtering. A packet can have multiple tags at the same time. Tags are "sticky", meaning once a tag is applied to a packet by a matching rule it exists until explicit removal. Tags are kept with the packet everywhere within the kernel, but are lost when packet leaves the kernel, for example, on transmitting packet out to the network or sending packet to a divert(4) socket. To check for previously applied tags, use the tagged rule option. To delete previously applied tag, use the untag keyword. Note: since tags are kept with the packet everywhere in kernelspace, they can be set and unset anywhere in the kernel network subsystem (using the mbuf_tags(9) facility), not only by means of the ipfw(4) tag and untag keywords. For example, there can be a specialized netgraph(4) node doing traffic analyzing and tagging for later inspecting in firewall.
untag number
	When a packet matches a rule with the untag keyword, the tag with the number number is searched among the tags attached to this packet and, if found, removed from it. Other tags bound to packet, if present, are left untouched.
altq queue
	When a packet matches a rule with the altq keyword, the ALTQ identifier for the given queue (see altq(4)) will be attached. Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, and not being rejected or going to divert sockets. Note that if there is insufficient memory at the time the packet is processed, it will not be tagged, so it is wise to make your ALTQ "default" queue policy account for this. If multiple altq rules match a single packet, only the first one adds the ALTQ classification tag. In doing so, traffic may be shaped by using count altq queue rules for classification early in the ruleset, then later applying the filtering decision. For example, check-state and keep-state rules may come later and provide the actual filtering decisions in addition to the fallback ALTQ tag. You must run pfctl(8) to set up the queues before IPFW will be able to look them up by name, and if the ALTQ disciplines are rearranged, the rules in containing the queue identifiers in the kernel will likely have gone stale and need to be reloaded. Stale queue identifiers will probably result in misclassification. All system ALTQ processing can be turned on or off via ipfw enable altq and ipfw disable altq. The usage of net.inet.ip.fw.one_pass is irrelevant to ALTQ traffic shaping, as the actual rule action is followed always after adding an ALTQ tag.

A rule can be associated with one of the following actions, which will be executed when the packet matches the body of the rule.

allow | accept | pass | permit
	Allow packets that match rule. The search terminates.
check-state [:flowname | :any]
	Checks the packet against the dynamic ruleset. If a match is found, execute the action associated with the rule which generated this dynamic rule, otherwise move to the next rule. Check-state rules do not have a body. If no check-state rule is found, the dynamic ruleset is checked at the first keep-state or limit rule. The :flowname is symbolic name assigned to dynamic rule by keep-state opcode. The special flowname :any can be used to ignore states flowname when matching. The :default keyword is special name used for compatibility with old rulesets.
count	Update counters for all packets that match rule. The search continues with the next rule.
deny | drop
	Discard packets that match this rule. The search terminates.
divert port
	Divert packets that match this rule to the divert(4) socket bound to port port. The search terminates.
fwd | forward ipaddr | tablearg[,port]
	Change the next-hop on matching packets to ipaddr, which can be an IP address or a host name. The next hop can also be supplied by the last table looked up for the packet by using the tablearg keyword instead of an explicit address. The search terminates if this rule matches. If ipaddr is a local address, then matching packets will be forwarded to port (or the port number in the packet if one is not specified in the rule) on the local machine. If ipaddr is not a local address, then the port number (if specified) is ignored, and the packet will be forwarded to the remote address, using the route as found in the local routing table for that IP. A fwd rule will not match layer2 packets (those received on ether_input, ether_output, or bridged). The fwd action does not change the contents of the packet at all. In particular, the destination address remains unmodified, so packets forwarded to another system will usually be rejected by that system unless there is a matching rule on that system to capture them. For packets forwarded locally, the local address of the socket will be set to the original destination address of the packet. This makes the netstat(1) entry look rather weird but is intended for use with transparent proxy servers.
nat nat_nr | global | tablearg
	Pass packet to a nat instance (for network address translation, address redirect, etc.): see the NETWORK ADDRESS TRANSLATION (NAT) Section for further information.
nat64lsn name
	Pass packet to a stateful NAT64 instance (for IPv6/IPv4 network address and protocol translation): see the IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Section for further information.
nat64stl name
	Pass packet to a stateless NAT64 instance (for IPv6/IPv4 network address and protocol translation): see the IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Section for further information.
nat64clat name
	Pass packet to a CLAT NAT64 instance (for client-side IPv6/IPv4 network address and protocol translation): see the IPv6/IPv4 NETWORK ADDRESS AND PROTOCOL TRANSLATION Section for further information.
nptv6 name
	Pass packet to a NPTv6 instance (for IPv6-to-IPv6 network prefix translation): see the IPv6-to-IPv6 NETWORK PREFIX TRANSLATION (NPTv6) Section for further information.
pipe pipe_nr
	Pass packet to a dummynet "pipe" (for bandwidth limitation, delay, etc.). See the TRAFFIC SHAPER (DUMMYNET) CONFIGURATION Section for further information. The search terminates; however, on exit from the pipe and if the sysctl(8) variable net.inet.ip.fw.one_pass is not set, the packet is passed again to the firewall code starting from the next rule.
queue queue_nr
	Pass packet to a dummynet "queue" (for bandwidth limitation using WF2Q+).
reject
	(Deprecated). Synonym for unreach host.
reset	Discard packets that match this rule, and if the packet is a TCP packet, try to send a TCP reset (RST) notice. The search terminates.
reset6
	Discard packets that match this rule, and if the packet is a TCP packet, try to send a TCP reset (RST) notice. The search terminates.
skipto number | tablearg
	Skip all subsequent rules numbered less than number. The search continues with the first rule numbered number or higher. It is possible to use the tablearg keyword with a skipto for a computed skipto. Skipto may work either in O(log(N)) or in O(1) depending on amount of memory and/or sysctl variables. See the SYSCTL VARIABLES section for more details.
call number | tablearg
	The current rule number is saved in the internal stack and ruleset processing continues with the first rule numbered number or higher. If later a rule with the return action is encountered, the processing returns to the first rule with number of this call rule plus one or higher (the same behaviour as with packets returning from divert(4) socket after a divert action). This could be used to make somewhat like an assembly language "subroutine" calls to rules with common checks for different interfaces, etc. Rule with any number could be called, not just forward jumps as with skipto. So, to prevent endless loops in case of mistakes, both call and return actions don't do any jumps and simply go to the next rule if memory cannot be allocated or stack overflowed/underflowed. Internally stack for rule numbers is implemented using mbuf_tags(9) facility and currently has size of 16 entries. As mbuf tags are lost when packet leaves the kernel, divert should not be used in subroutines to avoid endless loops and other undesired effects.
return
	Takes rule number saved to internal stack by the last call action and returns ruleset processing to the first rule with number greater than number of corresponding call rule. See description of the call action for more details. Note that return rules usually end a "subroutine" and thus are unconditional, but ipfw command-line utility currently requires every action except check-state to have body. While it is sometimes useful to return only on some packets, usually you want to print just "return" for readability. A workaround for this is to use new syntax and -c switch: # Add a rule without actual body ipfw add 2999 return via any # List rules without "from any to any" part ipfw -c list This cosmetic annoyance may be fixed in future releases.
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.
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 0 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.
unreach6 code
	Discard packets that match this rule, and try to send an ICMPv6 unreachable notice with code code, where code is a number from 0, 1, 3 or 4, or one of these aliases: no-route, admin-prohib, address or port. The search terminates.
netgraph cookie
	Divert packet into netgraph with given cookie. The search terminates. If packet is later returned from netgraph it is either accepted or continues with the next rule, depending on net.inet.ip.fw.one_pass sysctl variable.
ngtee cookie
	A copy of packet is diverted into netgraph, original packet continues with the next rule. See ng_ipfw(4) for more information on netgraph and ngtee actions.
setfib fibnum | tablearg
	The packet is tagged so as to use the FIB (routing table) fibnum in any subsequent forwarding decisions. In the current implementation, this is limited to the values 0 through 15, see setfib(2). Processing continues at the next rule. It is possible to use the tablearg keyword with setfib. If the tablearg value is not within the compiled range of fibs, the packet's fib is set to 0.
setdscp DSCP | number | tablearg
	Set specified DiffServ codepoint for an IPv4/IPv6 packet. Processing continues at the next rule. Supported values are: cs0 ( 000000), cs1 ( 001000), cs2 ( 010000), cs3 ( 011000), cs4 ( 100000), cs5 ( 101000), cs6 ( 110000), cs7 ( 111000), af11 ( 001010), af12 ( 001100), af13 ( 001110), af21 ( 010010), af22 ( 010100), af23 ( 010110), af31 ( 011010), af32 ( 011100), af33 ( 011110), af41 ( 100010), af42 ( 100100), af43 ( 100110), va ( 101100), ef ( 101110), be ( 000000). Additionally, DSCP value can be specified by number (0..63). It is also possible to use the tablearg keyword with setdscp. If the tablearg value is not within the 0..63 range, lower 6 bits of supplied value are used.
tcp-setmss mss
	Set the Maximum Segment Size (MSS) in the TCP segment to value mss. The kernel module ipfw_pmod should be loaded or kernel should have options IPFIREWALL_PMOD to be able use this action. This command does not change a packet if original MSS value is lower than specified value. Both TCP over IPv4 and over IPv6 are supported. Regardless of matched a packet or not by the tcp-setmss rule, the search continues with the next rule.
reass	Queue and reassemble IPv4 fragments. If the packet is not fragmented, counters are updated and processing continues with the next rule. If the packet is the last logical fragment, the packet is reassembled and, if net.inet.ip.fw.one_pass is set to 0, processing continues with the next rule. Otherwise, the packet is allowed to pass and the search terminates. If the packet is a fragment in the middle of a logical group of fragments, it is consumed and processing stops immediately. Fragment handling can be tuned via net.inet.ip.maxfragpackets and net.inet.ip.maxfragsperpacket which limit, respectively, the maximum number of processable fragments (default: 800) and the maximum number of fragments per packet (default: 16). NOTA BENE: since fragments do not contain port numbers, they should be avoided with the reass rule. Alternatively, direction-based (like in / out ) and source-based (like via ) match patterns can be used to select fragments. Usually a simple rule like: # reassemble incoming fragments ipfw add reass all from any to any in is all you need at the beginning of your ruleset.
abort	Discard packets that match this rule, and if the packet is an SCTP packet, try to send an SCTP packet containing an ABORT chunk. The search terminates.
abort6
	Discard packets that match this rule, and if the packet is an SCTP packet, try to send an SCTP packet containing an ABORT chunk. The search terminates.

The body of a rule contains zero or more patterns (such as specific source and destination addresses or ports, protocol options, incoming or outgoing interfaces, etc.) that the packet must match in order to be recognised. In general, the patterns are connected by (implicit) and operators -- i.e., all must match in order for the rule to match. Individual patterns can be prefixed by the not operator to reverse the result of the match, as in

    ipfw add 100 allow ip from not 1.2.3.4 to any

Additionally, sets of alternative match patterns ( or-blocks) can be constructed by putting the patterns in lists enclosed between parentheses ( ) or braces { }, and using the or operator as follows:

    ipfw add 100 allow ip from { x or not y or z } to any

Only one level of parentheses is allowed. Beware that most shells have special meanings for parentheses or braces, so it is advisable to put a backslash \ in front of them to prevent such interpretations.

The body of a rule must in general include a source and destination address specifier. The keyword any can be used in various places to specify that the content of a required field is irrelevant.

The rule body has the following format: [proto from src to dst] [options]

The first part (proto from src to dst) is for backward compatibility with earlier versions of FreeBSD . In modern FreeBSD any match pattern (including MAC headers, IP protocols, addresses and ports) can be specified in the options section.

Rule fields have the following meaning:

proto : protocol | { protocol or ... } protocol : [ not ]protocol-name | protocol-number
	An IP protocol specified by number or name (for a complete list see /etc/protocols), or one of the following keywords:
ip4 | ipv4
	Matches IPv4 packets.
ip6 | ipv6
	Matches IPv6 packets.
ip | all
	Matches any packet.

The ipv6 in proto option will be treated as inner protocol. And, the ipv4 is not available in proto option.

The { protocol or ... } format (an or-block) is provided for convenience only but its use is deprecated.

src and dst : { addr | { addr or ... } }[[ not ]ports]
	An address (or a list, see below) optionally followed by ports specifiers. The second format ( or-block with multiple addresses) is provided for convenience only and its use is discouraged.
addr : [ not ]{
	any | me | me6 | table(name[,value]) | addr-list | addr-set }
any	Matches any IP address.
me	Matches any IP address configured on an interface in the system.
me6	Matches any IPv6 address configured on an interface in the system. The address list is evaluated at the time the packet is analysed.
table(name[,value])
	Matches any IPv4 or IPv6 address for which an entry exists in the lookup table number. If an optional 32-bit unsigned value is also specified, an entry will match only if it has this value. See the LOOKUP TABLES section below for more information on lookup tables.

addr-list : ip-addr[,addr-list] ip-addr:
	A host or subnet address specified in one of the following ways:
numeric-ip | hostname
	Matches a single IPv4 address, specified as dotted-quad or a hostname. Hostnames are resolved at the time the rule is added to the firewall list.
addr/masklen
	Matches all addresses with base addr (specified as an IP address, a network number, or a hostname) and mask width of masklen bits. As an example, 1.2.3.4/25 or 1.2.3.0/25 will match all IP numbers from 1.2.3.0 to 1.2.3.127 .
addr:mask
	Matches all addresses with base addr (specified as an IP address, a network number, or a hostname) and the mask of mask, specified as a dotted quad. As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 1.*.3.*. This form is advised only for non-contiguous masks. It is better to resort to the addr/masklen format for contiguous masks, which is more compact and less error-prone.

addr-set : addr[/masklen ] {list } list : {num | num-num }[,list]
	Matches all addresses with base address addr (specified as an IP address, a network number, or a hostname) and whose last byte is in the list between braces { } . Note that there must be no spaces between braces and numbers (spaces after commas are allowed). Elements of the list can be specified as single entries or ranges. The masklen field is used to limit the size of the set of addresses, and can have any value between 24 and 32. If not specified, it will be assumed as 24. This format is particularly useful to handle sparse address sets within a single rule. Because the matching occurs using a bitmask, it takes constant time and dramatically reduces the complexity of rulesets. As an example, an address specified as 1.2.3.4/24{128,35-55,89} or 1.2.3.0/24{128,35-55,89} will match the following IP addresses: 1.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 .
addr6-list : ip6-addr[,addr6-list] ip6-addr:
	A host or subnet specified one of the following ways:
numeric-ip | hostname
	Matches a single IPv6 address as allowed by inet_pton(3) or a hostname. Hostnames are resolved at the time the rule is added to the firewall list.
addr/masklen
	Matches all IPv6 addresses with base addr (specified as allowed by inet_pton(3) or a hostname) and mask width of masklen bits.
addr/mask
	Matches all IPv6 addresses with base addr (specified as allowed by inet_pton(3) or a hostname) and the mask of mask, specified as allowed by inet_pton(3). As an example, fe::640:0:0/ffff::ffff:ffff:0:0 will match fe:*:*:*:0:640:*:*. This form is advised only for non-contiguous masks. It is better to resort to the addr/masklen format for contiguous masks, which is more compact and less error-prone.

No support for sets of IPv6 addresses is provided because IPv6 addresses are typically random past the initial prefix.

ports : {port | portamp;-port}[,ports]
	For protocols which support port numbers (such as SCTP, TCP and UDP), optional ports may be specified as one or more ports or port ranges, separated by commas but no spaces, and an optional not operator. The ‘amp;-’ notation specifies a range of ports (including boundaries). Service names (from /etc/services) may be used instead of numeric port values. The length of the port list is limited to 30 ports or ranges, though one can specify larger ranges by using an or-block in the options section of the rule. A backslash (‘\’) can be used to escape the dash (‘-’) character in a service name (from a shell, the backslash must be typed twice to avoid the shell itself interpreting it as an escape character).     ipfw add count tcp from any ftp\\-data-ftp to any Fragmented packets which have a non-zero offset (i.e., not the first fragment) will never match a rule which has one or more port specifications. See the frag option for details on matching fragmented packets.

Additional match patterns can be used within rules. Zero or more of these so-called options can be present in a rule, optionally prefixed by the not operand, and possibly grouped into or-blocks.

The following match patterns can be used (listed in alphabetical order):

// this is a comment.
	Inserts the specified text as a comment in the rule. Everything following // is considered as a comment and stored in the rule. You can have comment-only rules, which are listed as having a count action followed by the comment.
bridged
	Alias for layer2.
defer-immediate-action | defer-action
	A rule with this option will not perform normal action upon a match. This option is intended to be used with record-state or keep-state as the dynamic rule, created but ignored on match, will work as intended. Rules with both record-state and defer-immediate-action create a dynamic rule and continue with the next rule without actually performing the action part of this rule. When the rule is later activated via the state table, the action is performed as usual.
diverted
	Matches only packets generated by a divert socket.
diverted-loopback
	Matches only packets coming from a divert socket back into the IP stack input for delivery.
diverted-output
	Matches only packets going from a divert socket back outward to the IP stack output for delivery.
dst-ip ip-address
	Matches IPv4 packets whose destination IP is one of the address(es) specified as argument.
{ dst-ip6 | dst-ipv6 }ip6-address
	Matches IPv6 packets whose destination IP is one of the address(es) specified as argument.
dst-port ports
	Matches IP packets whose destination port is one of the port(s) specified as argument.
established
	Matches TCP packets that have the RST or ACK bits set.
ext6hdr header
	Matches IPv6 packets containing the extended header given by header. Supported headers are: Fragment, ( frag), Hop-to-hop options ( hopopt), any type of Routing Header ( route), Source routing Routing Header Type 0 ( rthdr0), Mobile IPv6 Routing Header Type 2 ( rthdr2), Destination options ( dstopt), IPSec authentication headers ( ah), and IPsec encapsulated security payload headers ( esp).
fib fibnum
	Matches a packet that has been tagged to use the given FIB (routing table) number.
flow table(name[,value])
	Search for the flow entry in lookup table name. If not found, the match fails. Otherwise, the match succeeds and tablearg is set to the value extracted from the table. This option can be useful to quickly dispatch traffic based on certain packet fields. See the LOOKUP TABLES section below for more information on lookup tables.
flow-id labels
	Matches IPv6 packets containing any of the flow labels given in labels. labels is a comma separated list of numeric flow labels.
dst-mac table(name[,value])
	Search for the destination MAC address entry in lookup table name. If not found, the match fails. Otherwise, the match succeeds and tablearg is set to the value extracted from the table.
src-mac table(name[,value])
	Search for the source MAC address entry in lookup table name. If not found, the match fails. Otherwise, the match succeeds and tablearg is set to the value extracted from the table.
frag spec
	Matches IPv4 packets whose ip_off field contains the comma separated list of IPv4 fragmentation options specified in spec. The recognized options are: df ( don't fragment), mf ( more fragments), rf ( reserved fragment bit) offset ( non-zero fragment offset). The absence of a particular options may be denoted with a ‘amp;!’. Empty list of options defaults to matching on non-zero fragment offset. Such rule would match all not the first fragment datagrams, both IPv4 and IPv6. This is a backward compatibility with older rulesets.
gid group
	Matches all TCP or UDP packets sent by or received for a group. A group may be specified by name or number.
jail jail
	Matches all TCP or UDP packets sent by or received for the jail whose ID or name is jail.
icmptypes types
	Matches ICMP packets whose ICMP type is in the list types. The list may be specified as any combination of individual types (numeric) separated by commas. Ranges are not allowed. The supported ICMP types are: echo reply ( 0), destination unreachable ( 3), source quench ( 4), redirect ( 5), echo request ( 8), router advertisement ( 9), router solicitation ( 10), time-to-live exceeded ( 11), IP header bad ( 12), timestamp request ( 13), timestamp reply ( 14), information request ( 15), information reply ( 16), address mask request ( 17) and address mask reply ( 18).
icmp6types types
	Matches ICMP6 packets whose ICMP6 type is in the list of types. The list may be specified as any combination of individual types (numeric) separated by commas. Ranges are not allowed.
in | out
	Matches incoming or outgoing packets, respectively. in and out are mutually exclusive (in fact, out is implemented as not in).
ipid id-list
	Matches IPv4 packets whose ip_id field has value included in id-list, which is either a single value or a list of values or ranges specified in the same way as ports.
iplen len-list
	Matches IP packets whose total length, including header and data, is in the set len-list, which is either a single value or a list of values or ranges specified in the same way as ports.
ipoptions spec
	Matches packets whose IPv4 header contains the comma separated list of options specified in spec. The supported IP options are: ssrr (strict source route), lsrr (loose source route), rr (record packet route) and ts (timestamp). The absence of a particular option may be denoted with a ‘amp;!’.
ipprecedence precedence
	Matches IPv4 packets whose precedence field is equal to precedence.
ipsec	Matches packets that have IPSEC history associated with them (i.e., the packet comes encapsulated in IPSEC, the kernel has IPSEC support, and can correctly decapsulate it). Note that specifying ipsec is different from specifying proto ipsec as the latter will only look at the specific IP protocol field, irrespective of IPSEC kernel support and the validity of the IPSEC data. Further note that this flag is silently ignored in kernels without IPSEC support. It does not affect rule processing when given and the rules are handled as if with no ipsec flag.
iptos spec
	Matches IPv4 packets whose tos field contains the comma separated list of service types specified in spec. The supported IP types of service are: lowdelay ( IPTOS_LOWDELAY), throughput ( IPTOS_THROUGHPUT), reliability ( IPTOS_RELIABILITY), mincost ( IPTOS_MINCOST), congestion ( IPTOS_ECN_CE). The absence of a particular type may be denoted with a ‘amp;!’.
dscp spec[,spec]
	Matches IPv4/IPv6 packets whose DS field value is contained in spec mask. Multiple values can be specified via the comma separated list. Value can be one of keywords used in setdscp action or exact number.
ipttl ttl-list
	Matches IPv4 packets whose time to live is included in ttl-list, which is either a single value or a list of values or ranges specified in the same way as ports.
ipversion ver
	Matches IP packets whose IP version field is ver.
keep-state [:flowname]
	Upon a match, the firewall will create a dynamic rule, whose default behaviour is to match bidirectional traffic between source and destination IP/port using the same protocol. The rule has a limited lifetime (controlled by a set of sysctl(8) variables), and the lifetime is refreshed every time a matching packet is found. The :flowname is used to assign additional to addresses, ports and protocol parameter to dynamic rule. It can be used for more accurate matching by check-state rule. The :default keyword is special name used for compatibility with old rulesets.
layer2
	Matches only layer2 packets, i.e., those passed to ipfw from ether_demux() and ether_output_frame().
limit { src-addr | src-port | dst-addr | dst-port }N [:flowname]
	The firewall will only allow N connections with the same set of parameters as specified in the rule. One or more of source and destination addresses and ports can be specified.
lookup { dst-ip | dst-port | dst-mac | src-ip | src-port | src-mac | uid | jail }name
	Search an entry in lookup table name that matches the field specified as argument. If not found, the match fails. Otherwise, the match succeeds and tablearg is set to the value extracted from the table. This option can be useful to quickly dispatch traffic based on certain packet fields. See the LOOKUP TABLES section below for more information on lookup tables.
{ MAC | mac } dst-mac src-mac
	Match packets with a given dst-mac and src-mac addresses, specified as the any keyword (matching any MAC address), or six groups of hex digits separated by colons, and optionally followed by a mask indicating the significant bits. The mask may be specified using either of the following methods: A slash (/) followed by the number of significant bits. For example, an address with 33 significant bits could be specified as:     MAC 10:20:30:40:50:60/33 any An ampersand (&) followed by a bitmask specified as six groups of hex digits separated by colons. For example, an address in which the last 16 bits are significant could be specified as:     MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any Note that the ampersand character has a special meaning in many shells and should generally be escaped. Note that the order of MAC addresses (destination first, source second) is the same as on the wire, but the opposite of the one used for IP addresses.
mac-type mac-type
	Matches packets whose Ethernet Type field corresponds to one of those specified as argument. mac-type is specified in the same way as port numbers (i.e., one or more comma-separated single values or ranges). You can use symbolic names for known values such as vlan, ipv4, ipv6. Values can be entered as decimal or hexadecimal (if prefixed by 0x), and they are always printed as hexadecimal (unless the -N option is used, in which case symbolic resolution will be attempted).
proto protocol
	Matches packets with the corresponding IP protocol.
record-state
	Upon a match, the firewall will create a dynamic rule as if keep-state was specified. However, this option doesn't imply an implicit check-state in contrast to keep-state.
recv | xmit | via {ifX | ifmask | table(name[,value ])| ipno | any}
	Matches packets received, transmitted or going through, respectively, the interface specified by exact name (ifX ), by device mask (ifmask ), by IP address, or through some interface. Interface name may be matched against ifmask with fnmatch(3) according to the rules used by the shell (f.e. tun*). See also the EXAMPLES section. Table name may be used to match interface by its kernel ifindex. See the LOOKUP TABLES section below for more information on lookup tables. The via keyword causes the interface to always be checked. If recv or xmit is used instead of via, then only the 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 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 is invalid) whenever xmit is used. A packet might not have a receive or transmit interface: packets originating from the local host have no receive interface, while packets destined for the local host have no transmit interface.
set-limit { src-addr | src-port | dst-addr | dst-port }N
	Works like limit but does not have an implicit check-state attached to it.
setup	Matches TCP packets that have the SYN bit set but no ACK bit. This is the short form of "tcpflags syn,!ack".
sockarg
	Matches packets that are associated to a local socket and for which the SO_USER_COOKIE socket option has been set to a non-zero value. As a side effect, the value of the option is made available as tablearg value, which in turn can be used as skipto or pipe number.
src-ip ip-address
	Matches IPv4 packets whose source IP is one of the address(es) specified as an argument.
src-ip6 ip6-address
	Matches IPv6 packets whose source IP is one of the address(es) specified as an argument.
src-port ports
	Matches IP packets whose source port is one of the port(s) specified as argument.
tagged tag-list
	Matches packets whose tags are included in tag-list, which is either a single value or a list of values or ranges specified in the same way as ports. Tags can be applied to the packet using tag rule action parameter (see it's description for details on tags).
tcpack ack
	TCP packets only. Match if the TCP header acknowledgment number field is set to ack.
tcpdatalen tcpdatalen-list
	Matches TCP packets whose length of TCP data is tcpdatalen-list, which is either a single value or a list of values or ranges specified in the same way as ports.
tcpflags spec
	TCP packets only. Match if the TCP header contains the comma separated list of flags specified in spec. The supported TCP flags are: fin, syn, rst, psh, ack and urg. The absence of a particular flag may be denoted with a ‘amp;!’. 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.
tcpmss tcpmss-list
	Matches TCP packets whose MSS (maximum segment size) value is set to tcpmss-list, which is either a single value or a list of values or ranges specified in the same way as ports.
tcpseq seq
	TCP packets only. Match if the TCP header sequence number field is set to seq.
tcpwin tcpwin-list
	Matches TCP packets whose header window field is set to tcpwin-list, which is either a single value or a list of values or ranges specified in the same way as ports.
tcpoptions spec
	TCP packets only. Match if the TCP header contains the comma separated list of options specified in spec. The supported TCP options are: mss (maximum segment size), window (tcp window advertisement), sack (selective ack), ts (rfc1323 timestamp) and cc (rfc1644 t/tcp connection count). The absence of a particular option may be denoted with a ‘amp;!’.
uid user
	Match all TCP or UDP packets sent by or received for a user. A user may be matched by name or identification number.
verrevpath
	For incoming packets, a routing table lookup is done on the packet's source address. If the interface on which the packet entered the system matches the outgoing interface for the route, the packet matches. If the interfaces do not match up, the packet does not match. All outgoing packets or packets with no incoming interface match. The name and functionality of the option is intentionally similar to the Cisco IOS command:     ip verify unicast reverse-path This option can be used to make anti-spoofing rules to reject all packets with source addresses not from this interface. See also the option antispoof.
versrcreach
	For incoming packets, a routing table lookup is done on the packet's source address. If a route to the source address exists, but not the default route or a blackhole/reject route, the packet matches. Otherwise, the packet does not match. All outgoing packets match. The name and functionality of the option is intentionally similar to the Cisco IOS command:     ip verify unicast source reachable-via any This option can be used to make anti-spoofing rules to reject all packets whose source address is unreachable.
antispoof
	For incoming packets, the packet's source address is checked if it belongs to a directly connected network. If the network is directly connected, then the interface the packet came on in is compared to the interface the network is connected to. When incoming interface and directly connected interface are not the same, the packet does not match. Otherwise, the packet does match. All outgoing packets match. This option can be used to make anti-spoofing rules to reject all packets that pretend to be from a directly connected network but do not come in through that interface. This option is similar to but more restricted than verrevpath because it engages only on packets with source addresses of directly connected networks instead of all source addresses.

Lookup tables are useful to handle large sparse sets of addresses or other search keys (e.g., ports, jail IDs, interface names). In the rest of this section we will use the term ``key''. Table name needs to match the following spec: table-name. Tables with the same name can be created in different sets. However, rule links to the tables in set by default. This behavior can be controlled by net.inet.ip.fw.tables_sets variable. See the SETS OF RULES section for more information. There may be up to 65535 different lookup tables.

The following table types are supported:

table-type : addr | iface | number | flow | mac table-key : addr[/masklen ]| iface-name | number | flow-spec flow-spec : flow-field[,flow-spec] flow-field : src-ip | proto | src-port | dst-ip | dst-port addr
	Matches IPv4 or IPv6 address. Each entry is represented by an addr[/masklen] and will match all addresses with base addr (specified as an IPv4/IPv6 address, or a hostname) and mask width of masklen bits. If masklen is not specified, it defaults to 32 for IPv4 and 128 for IPv6. When looking up an IP address in a table, the most specific entry will match.
iface	Matches interface names. Each entry is represented by string treated as interface name. Wildcards are not supported.
number
	Matches protocol ports, uids/gids or jail IDs. Each entry is represented by 32-bit unsigned integer. Ranges are not supported.
flow	Matches packet fields specified by flow type suboptions with table entries.
mac	Matches MAC address. Each entry is represented by an addr[/masklen] and will match all addresses with base addr and mask width of masklen bits. If masklen is not specified, it defaults to 48. When looking up an MAC address in a table, the most specific entry will match.

Tables require explicit creation via create before use.

The following creation options are supported:

create-options : create-option | create-options create-option : type table-type | valtype value-mask | algo algo-desc |
	limit number | locked | missing | or-flush
type	Table key type.
valtype
	Table value mask.
algo	Table algorithm to use (see below).
limit	Maximum number of items that may be inserted into table.
locked
	Restrict any table modifications.
missing
	Do not fail if table already exists and has exactly same options as new one.
or-flush
	Flush existing table with same name instead of returning error. Implies missing so existing table must be compatible with new one.

Some of these options may be modified later via modify keyword. The following options can be changed:

modify-options : modify-option | modify-options modify-option : limit number limit
	Alter maximum number of items that may be inserted into table.

Additionally, table can be locked or unlocked using lock or unlock commands.

Tables of the same type can be swapped with each other using swap name command. Swap may fail if tables limits are set and data exchange would result in limits hit. Operation is performed atomically.

One or more entries can be added to a table at once using add command. Addition of all items are performed atomically. By default, error in addition of one entry does not influence addition of other entries. However, non-zero error code is returned in that case. Special atomic keyword may be specified before add to indicate all-or-none add request.

One or more entries can be removed from a table at once using delete command. By default, error in removal of one entry does not influence removing of other entries. However, non-zero error code is returned in that case.

It may be possible to check what entry will be found on particular table-key using lookup table-key command. This functionality is optional and may be unsupported in some algorithms.

The following operations can be performed on one or all tables:

list	List all entries.
flush	Removes all entries.
info	Shows generic table information.
detail
	Shows generic table information and algo-specific data.

The following lookup algorithms are supported:

algo-desc : algo-name | algo-name algo-data algo-name : addr: radix | addr: hash | iface: array | number: array | flow: hash | mac: radix addr: radix
	Separate Radix trees for IPv4 and IPv6, the same way as the routing table (see route(4)). Default choice for addr type.
addr:hash
	Separate auto-growing hashes for IPv4 and IPv6. Accepts entries with the same mask length specified initially via addr:hash masks=/v4,/v6 algorithm creation options. Assume /32 and /128 masks by default. Search removes host bits (according to mask) from supplied address and checks resulting key in appropriate hash. Mostly optimized for /64 and byte-ranged IPv6 masks.
iface:array
	Array storing sorted indexes for entries which are presented in the system. Optimized for very fast lookup.
number:array
	Array storing sorted u32 numbers.
flow:hash
	Auto-growing hash storing flow entries. Search calculates hash on required packet fields and searches for matching entries in selected bucket.
mac: radix
	Radix tree for MAC address

The tablearg feature provides the ability to use a value, looked up in the table, as the argument for a rule action, action parameter or rule option. This can significantly reduce number of rules in some configurations. If two tables are used in a rule, the result of the second (destination) is used.

Each record may hold one or more values according to value-mask. This mask is set on table creation via valtype option. The following value types are supported:

value-mask : value-type[,value-mask] value-type : skipto | pipe | fib | nat | dscp | tag | divert |
	netgraph | limit | ipv4
skipto
	rule number to jump to.
pipe	Pipe number to use.
fib	fib number to match/set.
nat	nat number to jump to.
dscp	dscp value to match/set.
tag	tag number to match/set.
divert
	port number to divert traffic to.
netgraph
	hook number to move packet to.
limit	maximum number of connections.
ipv4	IPv4 nexthop to fwd packets to.
ipv6	IPv6 nexthop to fwd packets to.

The tablearg argument can be used with the following actions: nat, pipe, queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib, action parameters: tag, untag, rule options: limit, tagged.

When used with the skipto action, the user should be aware that the code will walk the ruleset up to a rule equal to, or past, the given number.

See the EXAMPLES Section for example usage of tables and the tablearg keyword.

Each rule or table belongs to one of 32 different sets , numbered 0 to 31. Set 31 is reserved for the default rule.

By default, rules or tables are put in set 0, unless you use the set N attribute when adding a new rule or table. Sets can be individually and atomically enabled or disabled, so this mechanism permits an easy way to store multiple configurations of the firewall and quickly (and atomically) switch between them.

By default, tables from set 0 are referenced when adding rule with table opcodes regardless of rule set. This behavior can be changed by setting net.inet.ip.fw.tables_sets variable to 1. Rule's set will then be used for table references.

The command to enable/disable sets is ipfw set [ disable number ... ][ enable number ...]

where multiple enable or disable sections can be specified. Command execution is atomic on all the sets specified in the command. By default, all sets are enabled.

When you disable a set, its rules behave as if they do not exist in the firewall configuration, with only one exception: dynamic rules created from a rule before it had been disabled will still be active until they expire. In order to delete dynamic rules you have to explicitly delete the parent rule which generated them.

The set number of rules can be changed with the command ipfw set move { rule rule-number | old-set} to new-set

Also, you can atomically swap two rulesets with the command ipfw set swap first-set second-set

See the EXAMPLES Section on some possible uses of sets of rules.

Stateful operation is a way for the firewall to dynamically create rules for specific flows when packets that match a given pattern are detected. Support for stateful operation comes through the check-state, keep-state, record-state, limit and set-limit options of rules.

Dynamic rules are created when a packet matches a keep-state, record-state, limit or set-limit rule, causing the creation of a dynamic rule which will match all and only packets with a given protocol between a src-ip/src-port dst-ip/dst-port pair of addresses ( src and dst are used here only to denote the initial match addresses, but they are completely equivalent afterwards). Rules created by keep-state option also have a :flowname taken from it. This name is used in matching together with addresses, ports and protocol. Dynamic rules will be checked at the first check-state, keep-state or limit occurrence, and the action performed upon a match will be the same as in the parent rule.

Note that no additional attributes other than protocol and IP addresses and ports and :flowname are checked on dynamic rules.

The typical use of dynamic rules is to keep a closed firewall configuration, but let the first TCP SYN packet from the inside network install a dynamic rule for the flow so that packets belonging to that session will be allowed through the firewall:

    ipfw add check-state :OUTBOUND

    ipfw add allow tcp from my-subnet to any setup keep-state :OUTBOUND

    ipfw add deny tcp from any to any

A similar approach can be used for UDP, where an UDP packet coming from the inside will install a dynamic rule to let the response through the firewall:

    ipfw add check-state :OUTBOUND

    ipfw add allow udp from my-subnet to any keep-state :OUTBOUND

    ipfw add deny udp from any to any

Dynamic rules expire after some time, which depends on the status of the flow and the setting of some sysctl variables. See Section SYSCTL VARIABLES for more details. For TCP sessions, dynamic rules can be instructed to periodically send keepalive packets to refresh the state of the rule when it is about to expire.

See Section EXAMPLES for more examples on how to use dynamic rules.

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

• Remember that you filter both packets going in and out. Most connections need packets going in both directions.
• Remember to test very carefully. It is a good idea to be near the console when doing this. If you cannot be near the console, use an auto-recovery script such as the one in /usr/share/examples/ipfw/change_rules.sh.
• Do not forget the loopback interface.

ipfw supports in-kernel IPv6/IPv4 network address and protocol translation. Stateful NAT64 translation allows IPv6-only clients to contact IPv4 servers using unicast TCP, UDP or ICMP protocols. One or more IPv4 addresses assigned to a stateful NAT64 translator are shared among several IPv6-only clients. When stateful NAT64 is used in conjunction with DNS64, no changes are usually required in the IPv6 client or the IPv4 server. The kernel module ipfw_nat64 should be loaded or kernel should have options IPFIREWALL_NAT64 to be able use stateful NAT64 translator.

Stateful NAT64 uses a bunch of memory for several types of objects. When IPv6 client initiates connection, NAT64 translator creates a host entry in the states table. Each host entry uses preallocated IPv4 alias entry. Each alias entry has a number of ports group entries allocated on demand. Ports group entries contains connection state entries. There are several options to control limits and lifetime for these objects.

NAT64 translator follows RFC7915 when does ICMPv6/ICMP translation, unsupported message types will be silently dropped. IPv6 needs several ICMPv6 message types to be explicitly allowed for correct operation. Make sure that ND6 neighbor solicitation (ICMPv6 type 135) and neighbor advertisement (ICMPv6 type 136) messages will not be handled by translation rules.

After translation NAT64 translator by default sends packets through corresponding netisr queue. Thus translator host should be configured as IPv4 and IPv6 router. Also this means, that a packet is handled by firewall twice. First time an original packet is handled and consumed by translator, and then it is handled again as translated packet. This behavior can be changed by sysctl variable net.inet.ip.fw.nat64_direct_output. Also translated packet can be tagged using tag rule action, and then matched by tagged opcode to avoid loops and extra overhead.

The stateful NAT64 configuration command is the following: nat64lsn name create create-options

The following parameters can be configured:

prefix4 ipv4_prefix/plen
	The IPv4 prefix with mask defines the pool of IPv4 addresses used as source address after translation. Stateful NAT64 module translates IPv6 source address of client to one IPv4 address from this pool. Note that incoming IPv4 packets that don't have corresponding state entry in the states table will be dropped by translator. Make sure that translation rules handle packets, destined to configured prefix.
prefix6 ipv6_prefix/length
	The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent IPv4 addresses. This IPv6 prefix should be configured in DNS64. The translator implementation follows RFC6052, that restricts the length of prefixes to one of following: 32, 40, 48, 56, 64, or 96. The Well-Known IPv6 Prefix 64:ff9b:: must be 96 bits long. The special ::/length prefix can be used to handle several IPv6 prefixes with one NAT64 instance. The NAT64 instance will determine a destination IPv4 address from prefix length.
states_chunks number
	The number of states chunks in single ports group. Each ports group by default can keep 64 state entries in single chunk. The above value affects the maximum number of states that can be associated with single IPv4 alias address and port. The value must be power of 2, and up to 128.
host_del_age seconds
	The number of seconds until the host entry for a IPv6 client will be deleted and all its resources will be released due to inactivity. Default value is 3600.
pg_del_age seconds
	The number of seconds until a ports group with unused state entries will be released. Default value is 900.
tcp_syn_age seconds
	The number of seconds while a state entry for TCP connection with only SYN sent will be kept. If TCP connection establishing will not be finished, state entry will be deleted. Default value is 10.
tcp_est_age seconds
	The number of seconds while a state entry for established TCP connection will be kept. Default value is 7200.
tcp_close_age seconds
	The number of seconds while a state entry for closed TCP connection will be kept. Keeping state entries for closed connections is needed, because IPv4 servers typically keep closed connections in a TIME_WAIT state for a several minutes. Since translator's IPv4 addresses are shared among all IPv6 clients, new connections from the same addresses and ports may be rejected by server, because these connections are still in a TIME_WAIT state. Keeping them in translator's state table protects from such rejects. Default value is 180.
udp_age seconds
	The number of seconds while translator keeps state entry in a waiting for reply to the sent UDP datagram. Default value is 120.
icmp_age seconds
	The number of seconds while translator keeps state entry in a waiting for reply to the sent ICMP message. Default value is 60.
log	Turn on logging of all handled packets via BPF through ipfwlog0 interface. ipfwlog0 is a pseudo interface and can be created after a boot manually with ifconfig command. Note that it has different purpose than ipfw0 interface. Translators sends to BPF an additional information with each packet. With tcpdump you are able to see each handled packet before and after translation.
-log	Turn off logging of all handled packets via BPF.
allow_private
	Turn on processing private IPv4 addresses. By default IPv6 packets with destinations mapped to private address ranges defined by RFC1918 are not processed.
-allow_private
	Turn off private address handling in nat64 instance.

To inspect a states table of stateful NAT64 the following command can be used: nat64lsn name show states

Stateless NAT64 translator doesn't use a states table for translation and converts IPv4 addresses to IPv6 and vice versa solely based on the mappings taken from configured lookup tables. Since a states table doesn't used by stateless translator, it can be configured to pass IPv4 clients to IPv6-only servers.

The stateless NAT64 configuration command is the following: nat64stl name create create-options

The following parameters can be configured:

prefix6 ipv6_prefix/length
	The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent IPv4 addresses. This IPv6 prefix should be configured in DNS64.
table4 table46
	The lookup table table46 contains mapping how IPv4 addresses should be translated to IPv6 addresses.
table6 table64
	The lookup table table64 contains mapping how IPv6 addresses should be translated to IPv4 addresses.
log	Turn on logging of all handled packets via BPF through ipfwlog0 interface.
-log	Turn off logging of all handled packets via BPF.
allow_private
	Turn on processing private IPv4 addresses. By default IPv6 packets with destinations mapped to private address ranges defined by RFC1918 are not processed.
-allow_private
	Turn off private address handling in nat64 instance.

Note that the behavior of stateless translator with respect to not matched packets differs from stateful translator. If corresponding addresses was not found in the lookup tables, the packet will not be dropped and the search continues.

XLAT464 CLAT NAT64 translator implements client-side stateless translation as defined in RFC6877 and is very similar to statless NAT64 translator explained above. Instead of lookup tables it uses one-to-one mapping between IPv4 and IPv6 addresses using configured prefixes. This mode can be used as a replacement of DNS64 service for applications that are not using it (e.g. VoIP) allowing them to access IPv4-only Internet over IPv6-only networks with help of remote NAT64 translator.

The CLAT NAT64 configuration command is the following: nat64clat name create create-options

The following parameters can be configured:

clat_prefix ipv6_prefix/length
	The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent source IPv4 addresses.
plat_prefix ipv6_prefix/length
	The IPv6 prefix defines IPv4-embedded IPv6 addresses used by translator to represent destination IPv4 addresses. This IPv6 prefix should be configured on a remote NAT64 translator.
log	Turn on logging of all handled packets via BPF through ipfwlog0 interface.
-log	Turn off logging of all handled packets via BPF.
allow_private
	Turn on processing private IPv4 addresses. By default nat64clat instance will not process IPv4 packets with destination address from private ranges as defined in RFC1918.
-allow_private
	Turn off private address handling in nat64clat instance.

Note that the behavior of CLAT translator with respect to not matched packets differs from stateful translator. If corresponding addresses were not matched against prefixes configured, the packet will not be dropped and the search continues.

ipfw supports in-kernel IPv6-to-IPv6 network prefix translation as described in RFC6296. The kernel module ipfw_nptv6 should be loaded or kernel should has options IPFIREWALL_NPTV6 to be able use NPTv6 translator.

The NPTv6 configuration command is the following: nptv6 name create create-options

The following parameters can be configured:

int_prefix ipv6_prefix
	IPv6 prefix used in internal network. NPTv6 module translates source address when it matches this prefix.
ext_prefix ipv6_prefix
	IPv6 prefix used in external network. NPTv6 module translates destination address when it matches this prefix.
ext_if nic
	The NPTv6 module will use first global IPv6 address from interface nic as external prefix. It can be useful when IPv6 prefix of external network is dynamically obtained. ext_prefix and ext_if options are mutually exclusive.
prefixlen length
	The length of specified IPv6 prefixes. It must be in range from 8 to 64.

Note that the prefix translation rules are silently ignored when IPv6 packet forwarding is disabled. To enable the packet forwarding, set the sysctl variable net.inet6.ip6.forwarding to 1.

To let the packet continue after being translated, set the sysctl variable net.inet.ip.fw.one_pass to 0.

There are some commands that may be useful to understand current state of certain subsystems inside kernel module. These commands provide debugging output which may change without notice.

Currently the following commands are available as internal sub-options:

iflist
	Lists all interface which are currently tracked by ipfw with their in-kernel status.
talist
	List all table lookup algorithms currently available.

There are far too many possible uses of ipfw so this Section will only give a small set of examples.

This command adds an entry which denies all tcp packets from cracker.evil.org to the telnet port of wolf.tambov.su from being forwarded by the host:

    ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet

This one disallows any connection from the entire cracker's network to my host:

    ipfw add deny ip from 123.45.67.0/24 to my.host.org

A first and efficient way to limit access (not using dynamic rules) is the use of the following rules:

    ipfw add allow tcp from any to any established

    ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup

    ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup

    ...

    ipfw add deny tcp from any to any

The first rule will be a quick match for normal TCP packets, but it will not match the initial SYN packet, which will be matched by the setup rules only for selected source/destination pairs. All other SYN packets will be rejected by the final deny rule.

If you administer one or more subnets, you can take advantage of the address sets and or-blocks and write extremely compact rulesets which selectively enable services to blocks of clients, as below:

    goodguys=q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }q

    badguys=q10.1.2.0/24{8,38,60}q

   

    ipfw add allow ip from ${goodguys} to any

    ipfw add deny ip from ${badguys} to any

    ... normal policies ...

Allow any transit packets coming from single vlan 10 and going out to vlans 100-1000:

    ipfw add 10 allow out recv vlan10 \

    { xmit vlan1000 or xmit qvlan[1-9]??q }

The verrevpath option could be used to do automated anti-spoofing by adding the following to the top of a ruleset:

    ipfw add deny ip from any to any not verrevpath in

This rule drops all incoming packets that appear to be coming to the system on the wrong interface. For example, a packet with a source address belonging to a host on a protected internal network would be dropped if it tried to enter the system from an external interface.

The antispoof option could be used to do similar but more restricted anti-spoofing by adding the following to the top of a ruleset:

    ipfw add deny ip from any to any not antispoof in

This rule drops all incoming packets that appear to be coming from another directly connected system but on the wrong interface. For example, a packet with a source address of 192.168.0.0/24, configured on fxp0, but coming in on fxp1 would be dropped.

The setdscp option could be used to (re)mark user traffic, by adding the following to the appropriate place in ruleset:

    ipfw add setdscp be ip from any to any dscp af11,af21

The following rules show some of the applications of ipfw and dummynet for simulations and the like.

This rule drops random incoming packets with a probability of 5%:

    ipfw add prob 0.05 deny ip from any to any in

A similar effect can be achieved making use of dummynet pipes:

    dnctl add pipe 10 ip from any to any

    dnctl pipe 10 config plr 0.05

We can use pipes to artificially limit bandwidth, e.g.amp; on a machine acting as a router, if we want to limit traffic from local clients on 192.168.2.0/24 we do:

    ipfw add pipe 1 ip from 192.168.2.0/24 to any out

    dnctl pipe 1 config bw 300Kbit/s queue 50KBytes

note that we use the out modifier so that the rule is not used twice. Remember in fact that ipfw rules are checked both on incoming and outgoing packets.

Should we want to simulate a bidirectional link with bandwidth limitations, the correct way is the following:

    ipfw add pipe 1 ip from any to any out

    ipfw add pipe 2 ip from any to any in

    dnctl pipe 1 config bw 64Kbit/s queue 10Kbytes

    dnctl pipe 2 config bw 64Kbit/s queue 10Kbytes

The above can be very useful, e.g.amp; if you want to see how your fancy Web page will look for a residential user who is connected only through a slow link. You should not use only one pipe for both directions, unless you want to simulate a half-duplex medium (e.g.amp; AppleTalk, Ethernet, IRDA). It is not necessary that both pipes have the same configuration, so we can also simulate asymmetric links.

Should we want to verify network performance with the RED queue management algorithm:

    ipfw add pipe 1 ip from any to any

    dnctl pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1

Another typical application of the traffic shaper is to introduce some delay in the communication. This can significantly affect applications which do a lot of Remote Procedure Calls, and where the round-trip-time of the connection often becomes a limiting factor much more than bandwidth:

    ipfw add pipe 1 ip from any to any out

    ipfw add pipe 2 ip from any to any in

    dnctl pipe 1 config delay 250ms bw 1Mbit/s

    dnctl pipe 2 config delay 250ms bw 1Mbit/s

Per-flow queueing can be useful for a variety of purposes. A very simple one is counting traffic:

    ipfw add pipe 1 tcp from any to any

    ipfw add pipe 1 udp from any to any

    ipfw add pipe 1 ip from any to any

    dnctl pipe 1 config mask all

The above set of rules will create queues (and collect statistics) for all traffic. Because the pipes have no limitations, the only effect is collecting statistics. Note that we need 3 rules, not just the last one, because when ipfw tries to match IP packets it will not consider ports, so we would not see connections on separate ports as different ones.

A more sophisticated example is limiting the outbound traffic on a net with per-host limits, rather than per-network limits:

    ipfw add pipe 1 ip from 192.168.2.0/24 to any out

    ipfw add pipe 2 ip from any to 192.168.2.0/24 in

    dnctl pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes

    dnctl pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes

In the following example, we need to create several traffic bandwidth classes and we need different hosts/networks to fall into different classes. We create one pipe for each class and configure them accordingly. Then we create a single table and fill it with IP subnets and addresses. For each subnet/host we set the argument equal to the number of the pipe that it should use. Then we classify traffic using a single rule:

    dnctl pipe 1 config bw 1000Kbyte/s

    dnctl pipe 4 config bw 4000Kbyte/s

    ...

    ipfw table T1 create type addr

    ipfw table T1 add 192.168.2.0/24 1

    ipfw table T1 add 192.168.0.0/27 4

    ipfw table T1 add 192.168.0.2 1

    ...

    ipfw add pipe tablearg ip from 'table(T1)' to any

Using the fwd action, the table entries may include hostnames and IP addresses.

    ipfw table T2 create type addr valtype ipv4

    ipfw table T2 add 192.168.2.0/24 10.23.2.1

    ipfw table T2 add 192.168.0.0/27 router1.dmz

    ...

    ipfw add 100 fwd tablearg ip from any to 'table(T2)'

In the following example per-interface firewall is created:

    ipfw table IN create type iface valtype skipto,fib

    ipfw table IN add vlan20 12000,12

    ipfw table IN add vlan30 13000,13

    ipfw table OUT create type iface valtype skipto

    ipfw table OUT add vlan20 22000

    ipfw table OUT add vlan30 23000

    ..

    ipfw add 100 setfib tablearg ip from any to any recv 'table(IN)' in

    ipfw add 200 skipto tablearg ip from any to any recv 'table(IN)' in

    ipfw add 300 skipto tablearg ip from any to any xmit 'table(OUT)' out

The following example illustrate usage of flow tables:

    ipfw table fl create type flow:src-ip,proto,dst-ip,dst-port

    ipfw table fl add 2a02:6b8:77::88,tcp,2a02:6b8:77::99,80 11

    ipfw table fl add 10.0.0.1,udp,10.0.0.2,53 12

    ..

    ipfw add 100 allow ip from any to any flow 'table(fl,11)' recv ix0

To add a set of rules atomically, e.g.amp; set 18:

    ipfw set disable 18

    ipfw add NN set 18 ... # repeat as needed

    ipfw set enable 18

To delete a set of rules atomically the command is simply:

    ipfw delete set 18

To test a ruleset and disable it and regain control if something goes wrong:

    ipfw set disable 18

    ipfw add NN set 18 ... # repeat as needed

    ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18

Here if everything goes well, you press control-C before the "sleep" terminates, and your ruleset will be left active. Otherwise, e.g.amp; if you cannot access your box, the ruleset will be disabled after the sleep terminates thus restoring the previous situation.

To show rules of the specific set:

    ipfw set 18 show

To show rules of the disabled set:

    ipfw -S set 18 show

To clear a specific rule counters of the specific set:

    ipfw set 18 zero NN

To delete a specific rule of the specific set:

    ipfw set 18 delete NN

First redirect all the traffic to nat instance 123:

    ipfw add nat 123 all from any to any

Then to configure nat instance 123 to alias all the outgoing traffic with ip 192.168.0.123, blocking all incoming connections, trying to keep same ports on both sides, clearing aliasing table on address change and keeping a log of traffic/link statistics:

    ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports

Or to change address of instance 123, aliasing table will be cleared (see reset option):

    ipfw nat 123 config ip 10.0.0.1

To see configuration of nat instance 123:

    ipfw nat 123 show config

To show logs of all the instances in range 111-999:

    ipfw nat 111-999 show

To see configurations of all instances:

    ipfw nat show config

Or a redirect rule with mixed modes could looks like:

ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66
                         redirect_port tcp 192.168.0.1:80 500
                         redirect_proto udp 192.168.1.43 192.168.1.1
                         redirect_addr 192.168.0.10,192.168.0.11
                                    10.0.0.100  # LSNAT
                         redirect_port tcp 192.168.0.1:80,192.168.0.10:22
                                    500         # LSNAT

or it could be split in:

ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66
ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500
ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1
ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12
                                         10.0.0.100
ipfw nat 5 config redirect_port tcp
                        192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500

Sometimes you may want to mix NAT and dynamic rules. It could be achieved with record-state and defer-action options. Problem is, you need to create dynamic rule before NAT and check it after NAT actions (or vice versa) to have consistent addresses and ports. Rule with keep-state option will trigger activation of existing dynamic state, and action of such rule will be performed as soon as rule is matched. In case of NAT and allow rule packet need to be passed to NAT, not allowed as soon is possible.

There is example of set of rules to achieve this. Bear in mind that this is example only and it is not very useful by itself.

On way out, after all checks place this rules:

    ipfw add allow record-state skip-action

    ipfw add nat 1

And on way in there should be something like this:

    ipfw add nat 1

    ipfw add check-state

Please note, that first rule on way out doesn't allow packet and doesn't execute existing dynamic rules. All it does, create new dynamic rule with allow action, if it is not created yet. Later, this dynamic rule is used on way in by check-state rule.

codel and pie AQM can be configured for dummynet pipe or queue.

To configure a pipe with codel AQM using default configuration for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:

    dnctl pipe 1 config bw 1mbits/s codel

    ipfw add 100 pipe 1 ip from 192.168.0.0/24 to any

To configure a queue with codel AQM using different configurations parameters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:

    dnctl pipe 1 config bw 1mbits/s

    dnctl queue 1 config pipe 1 codel target 8ms interval 160ms ecn

    ipfw add 100 queue 1 ip from 192.168.0.0/24 to any

To configure a pipe with pie AQM using default configuration for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:

    dnctl pipe 1 config bw 1mbits/s pie

    ipfw add 100 pipe 1 ip from 192.168.0.0/24 to any

To configure a queue with pie AQM using different configuration parameters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:

    dnctl pipe 1 config bw 1mbits/s

    dnctl queue 1 config pipe 1 pie target 20ms tupdate 30ms ecn

    ipfw add 100 queue 1 ip from 192.168.0.0/24 to any

fq_codel and fq_pie AQM can be configured for dummynet schedulers.

To configure fq_codel scheduler using different configurations parameters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:

    dnctl pipe 1 config bw 1mbits/s

    dnctl sched 1 config pipe 1 type fq_codel

    dnctl queue 1 config sched 1

    ipfw add 100 queue 1 ip from 192.168.0.0/24 to any

To change fq_codel default configuration for a sched such as disable ECN and change the target to 10ms, we do:

    dnctl sched 1 config pipe 1 type fq_codel target 10ms noecn

Similar to fq_codel, to configure fq_pie scheduler using different configurations parameters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:

    dnctl pipe 1 config bw 1mbits/s

    dnctl sched 1 config pipe 1 type fq_pie

    dnctl queue 1 config sched 1

    ipfw add 100 queue 1 ip from 192.168.0.0/24 to any

The configurations of fq_pie sched can be changed in a similar way as for fq_codel

The ipfw utility first appeared in FreeBSD 2.0 . dummynet was introduced in FreeBSD 2.2.8 . Stateful extensions were introduced in FreeBSD 4.0 . ipfw2 was introduced in Summer 2002.