IPFW(8)

NAME
ipfw - controlling utility for IP firewall and traffic shaper

SYNOPSIS
ipfw [-q] [ -p preproc [-D macro [=value]] [-U macro]] file
ipfw [-f | -q] flush
ipfw [-q] [number ...]
ipfw [-s [field]] [-aftN] [number ...]
ipfw [-q] add [number] rule-body
ipfw pipe number config pipe-config-options
ipfw pipe [number ...]
ipfw queue number config queue-config-options
ipfw queue [number ...]

DESCRIPTION
ipfw is the user interface for controlling the ipfirewall(4) and the dummynet(4) traffic shaper in FreeBSD.

Each incoming or outgoing packet is passed through the ipfw rules. If host is acting as a gateway, packets forwarded by the gateway are processed by ipfw twice. In case a host is acting as a bridge, packets forwarded by the bridge are processed by ipfw once.

A firewall configuration is made of a list of numbered rules, which is scanned for each packet until a match is found and the relevant action is performed. Depending on the action and certain system settings, packets can be reinjected into the firewall at the rule after the matching one for further processing. All rules apply to all interfaces, so it is responsibility of the system administrator to write the ruleset in such a way as to minimize the number of checks.

A configuration always includes a DEFAULT rule (numbered 65535) which cannot be modified by the programmer and always matches packets. The action associated with the default rule can be either deny or allow depending on how the kernel is configured.

If the ruleset includes one or more rules with the keep-state option, then ipfw assumes a stateful behaviour, i.e. upon a match will create dynamic rules matching the exact parameters (addresses and ports) of the matching packet.

These dynamic rules, which have a limited lifetime, are checked at the first occurrence of a check-state or keep-state rule, and are typically used to open the firewall on-demand to legitimate traffic only. See the RULE FORMAT and EXAMPLES sections below for more information on the stateful behaviour of ipfw.

All rules (including dynamic ones) have a few associated counters: a packet count, a byte count, a log count and a timestamp indicating the time of the last match. Counters can be displayed or reset with ipfw commands.

Rules can be added with the add command; deleted individually with the delete command, and globally with the flush command; displayed, optionally with the content of the counters, using the show and list commands. Finally, counters can be reset with the zero and resetlog commands.

The following options are available:

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

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

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

-t  While listing, show last match timestamp.

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

-s [field]
    While listing pipes, sort according to one of the four counters (total and current packets or bytes).

To ease configuration, rules can be put into a file which is processed using ipfw as shown in the first synopsis line. The file will be read line by line and applied as arguments to the ipfw utility.

Optionally, a preprocessor can be specified using -p preproc where file is to be piped through. Useful preprocessors include cpp(1) and m4(1). If preproc doesn't start with a slash (‘/’) as its first character, the usual PATH name search is performed. Care should be taken with this in environments where not all filesystems are mounted (yet) by the time ipfw is being run (e.g. when they are mounted over NFS). Once -p has been specified, optional -D and -U specifications can follow and will be passed on to the preprocessor. This allows for flexible configuration files (like conditionalizing them on the local hostname) and the use of macros to centralize frequently required arguments like IP addresses.

The ipfw pipe commands are used to configure the traffic shaper, as shown in the TRAFFIC SHAPER CONFIGURATION section below.

RULE FORMAT
The ipfw rule format is the following:

[prob match_probability] action [log [logamount number]] proto from src to dst [interface-spec] [options]

Each packet can be filtered based on the following information that is associated with it:

Transmit and receive interface
    (by name or address)
Direction
    (incoming or outgoing)
Source and destination IP address
    (possibly masked)
Protocol
    (TCP, UDP, ICMP, etc.)
Source and destination port
    (lists, ranges or masks)
TCP flags
IP fragment flag
IP options
ICMP types
User/group ID of the socket associated with the packet

Note that it may be dangerous to filter on the source IP address or source TCP/UDP port because either or both could easily be spoofed.

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(4)) to simulate the effect of multiple paths leading to out-of-order packet delivery.

action:

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

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

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

    unreach code
        Discard packets that match this rule, and try to send an ICMP unreachable notice with code code, where code is a number from 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.

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

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

    check-state
        Checks the packet against the dynamic ruleset. If a match is found then the search terminates, otherwise we move to the next rule. If no check-state rule is found, the dynamic ruleset is checked at the first keep-state rule.

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

    tee port
        Send a copy of packets matching this rule to the divert(4) socket bound to port port. The search terminates and the original packet is accepted ( but see section BUGS below).

    fwd ipaddr
        [,port] Change the next-hop on matching packets to ipaddr, which can be an IP address in dotted quad or a host name. If ipaddr is not a directly-reachable address, the route as found in the local routing table for that IP is used instead. If ipaddr is a local address, then on a packet entering the system from a remote host it will be diverted to port on the local machine, keeping the local address of the socket set to the original IP address the packet was destined for. This is intended for use with transparent proxy servers. If the IP is not a local address then the port number (if specified) is ignored and the rule only applies to packets leaving the system. This will also map addresses to local ports when packets are generated locally. The search terminates if this rule matches. If the port number is not given then the port number in the packet is used, so that a packet for an external machine port Y would be forwarded to local port Y. The kernel must have been compiled with the IPFIREWALL_FORWARD option.

    pipe pipe_nr
        Pass packet to a dummynet(4) “pipe” (for bandwidth limitation, delay, etc.). See the TRAFFIC SHAPER 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(4) “queue” (for bandwidth limitation using WF2Q).

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

log [logamount number]
    If the kernel was compiled with IPFIREWALL_VERBOSE, then when a packet matches a rule with the log keyword a message will be printed on the console. If the kernel was compiled with the IPFIREWALL_VERBOSE_LIMIT option, then by default logging will cease after the number of packets specified by the option are received for that particular chain entry, and net.inet.ip.fw.verbose_limit will be set to that number. However, if logamount number is used, that number will be the logging limit rather than net.inet.ip.fw.verbose_limit, where the value “0” removes the logging limit. Logging may then be re-enabled by clearing the logging counter or the packet counter for that entry.

    Console logging and the log limit are adjustable dynamically through the sysctl(8) interface in the MIB base of net.inet.ip.fw.

proto
    An IP protocol specified by number or name (for a complete list see /etc/protocols). The ip or all keywords mean any protocol will match.

src and dst:
    <address/mask> [ports]

    The <address/mask> may be specified as:

    ipno
        An IP number of the form 1.2.3.4. Only this exact IP number will match the rule.

    ipno/bits
        An IP number 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.

    ipno:mask
        An IP number with a mask 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.

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

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

    { port| port-port| port:mask }[,port[,...]]

    The ‘-’ notation specifies a range of ports (including boundaries).

    The ‘’: notation specifies a port and a mask, a match is declared if the port number in the packet matches the one in the rule, limited to the bits which are set in the mask.

    Service names (from /etc/services) may be used instead of numeric port values. A range may only be specified as the first value, and the length of the port list is limited to IP_FW_MAX_PORTS ports (as defined in /usr/src/sys/netinet/ip_fw.h). A backslash (‘\’) can be used to escape the dash (‘-’) character in a service name:

        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.

interface-spec
    Some combinations of the following specifiers are allowed:

    in  Only match incoming packets.

    out Only match outgoing packets.

    via ifX
        Packet must be going through interface ifX.

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

    via any
        Packet must be going through some interface.

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

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

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

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

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

options:

    keep-state [method]
        Upon a match, the firewall will create a dynamic rule, whose default behaviour is to matching 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 actual behaviour can be modified by specifying a different method, although at the moment only the default one is specified.

    bridged
        Matches only bridged packets. This can be useful for multicast or broadcast traffic, which would otherwise pass through the firewall twice: once during bridging, and a second time when the packet is delivered to the local stack.

        Apart from a small performance penalty, this would be a problem when using pipes because the same packet would be accounted for twice in terms of bandwidth, queue occupation, and also counters.

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

    ipoptions spec
        Match if the IP 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 ‘’!.

    tcpoptions spec
        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 ‘’!.

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

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

    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 ‘’!. A rule which contains a tcpflags specification can never match a fragmented packet which has a non-zero offset. See the frag option for details on matching fragmented packets.

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

    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.

    gid group
        Match all TCP or UDP packets sent by or received for a group. A group may be matched by name or identification number.

TRAFFIC SHAPER CONFIGURATION
The ipfw utility is also the user interface for the dummynet(4) traffic shaper. The shaper operates by dividing packets into flows according to a user-specified mask on different fields of the IP header. Packets belonging to the same flow are then passed to two different objects, named pipe or queue.

A pipe emulates a link with given bandwidth, propagation delay, queue size and packet loss rate. Packets transit through the pipe according to its parameters.

A queue is an abstraction used to implement the WF2Q+ policy. The queue associates to each flow a weight and a reference pipe. Then, all flows linked to the same pipe are scheduled at the rate fixed by the pipe according to the WF2Q+ policy.

The ipfw pipe configuration format is the following:

pipe number config [bw bandwidth | device] [delay ms-delay] [ queue] [plr loss-probability] [mask mask-specifier] [buckets hash-table-size] [ red | gred w_q/ min_th/ max_th/ max_p]

The ipfw queue configuration format is the following:

queue number config [pipe pipe_nr] [weight weight] [ queue] [plr loss-probability] [mask mask-specifier] [buckets hash-table-size] [ red | gred w_q/ min_th/ max_th/ max_p]

The following parameters can be configured for a pipe:

bw bandwidth | device
    Bandwidth, measured in [ K|M]{ bit/s|Byte/s }.

    A value of 0 (default) means unlimited bandwidth. The unit must follow immediately the number, as in

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

    If a device name is specified instead of a numeric value, then the transmit clock is supplied by the specified device. At the moment only the tun(4) device supports this functionality, for use in conjunction with ppp(8).

delay ms-delay
    Propagation delay, measured in milliseconds. The value is rounded to the next multiple of the clock tick (typically 10ms, but it is a good practice to run kernels with “options HZ=1000” to reduce the granularity to 1ms or less). Default value is 0, meaning no delay.

queue
    Queue size, in slots or KBytes. Default value is 50 slots, which is the typical queue size for Ethernet devices. Note that for slow speed links you should keep the queue size short or your traffic might be affected by a significant queueing delay. E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit or 20s of queue on a 30Kbit/s pipe. Even worse effect can result if you get packets from an interface with a much larger MTU, e.g. the loopback interface with its 16KB packets.

plr packet-loss-rate
    Packet loss rate. Argument packet-loss-rate is a floating-point number between 0 and 1, with 0 meaning no loss, 1 meaning 100% loss. The loss rate is internally represented on 31 bits.

mask mask-specifier
    The dummynet(4) lets you to create per-flow queues. A flow identifier is constructed by masking the IP addresses, ports and protocol types as specified in the pipe configuration. Packets with the same identifier after masking fall into the same queue. Available mask specifiers are a combination of the following: dst-ip mask, src-ip mask, dst-port mask, src-port mask, proto mask or all, where the latter means all bits in all fields are significant. When used within a pipe configuration, each flow is assigned a rate equal to the rate of the pipe. When used within a queue configuration, each flow is assigned a weight equal to the weight of the queue, and all flows insisting on the same pipe share bandwidth proportionally to their weight.

buckets hash-table-size
    Specifies the size of the hash table used for storing the various queues. Default value is 64 controlled by the sysctl(8) variable net.inet.ip.dummynet.hash_size, allowed range is 16 to 1024.

pipe pipe_nr
    Connects a queue to the specified pipe. Multiple queues (usually with different weights) can be connected to the same pipe, which specifies the aggregate rate for the set of queues.

weight weight
    Specifies the weight to be used for flows matching this queue. The weight must be in the range 1..100, and defaults to 1.

red | gred
    w_q/ min_th/ max_th/ max_p Make use of the RED queue management algorithm. w_q and max_p are floating point numbers between 0 and 1 (0 not included), while min_th and max_th are integer numbers specifying thresholds for queue management (thresholds are computed in bytes if the queue has been defined in bytes, in slots otherwise). The dummynet(4) also supports the gentle RED variant (gred). Three sysctl(8) variables can be used to control the RED behaviour:

    net.inet.ip.dummynet.red_lookup_depth
        specifies the accuracy in computing the average queue when the link is idle (defaults to 256, must be greater than zero)

    net.inet.ip.dummynet.red_avg_pkt_size
        specifies the expected average packet size (defaults to 512, must be greater than zero)

    net.inet.ip.dummynet.red_max_pkt_size
        specifies the expected maximum packet size, only used when queue thresholds are in bytes (defaults to 1500, must be greater than zero).

CHECKLIST
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.

•   Don't forget the loopback interface.

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.

If you are logged in over a network, loading the kld(4) version of ipfw is probably not as straightforward as you would think. I recommend the following command line:

    kldload /modules/ipfw.ko && \
    ipfw add 32000 allow ip from any to any

Along the same lines, doing an

    ipfw flush

in similar surroundings is also a bad idea.

The ipfw filter list may not be modified if the system security level is set to 3 or higher ( see init(8) for information on system security levels).

PACKET DIVERSION
A divert(4) socket bound to the specified port will receive all packets diverted to that port. If no socket is bound to the destination port, or if the kernel wasn't compiled with divert socket support, the packets are dropped.

SYSCTL VARIABLES
A set of sysctl(8) variables controls the behaviour of the firewall. These are shown below together with their default value and meaning:

net.inet.ip.fw.debug: 1
    Controls debugging messages produced by ipfw.

net.inet.ip.fw.one_pass: 1
    When set, permits only one pass through the firewall. Otherwise, after a pipe or divert action, the packet is reinjected in the firewall starting from the next rule.

net.inet.ip.fw.verbose: 1
    Enables verbose messages.

net.inet.ip.fw.enable: 1
    Enables the firewall. Setting this variable to 0 lets you run your machine without firewall even if compiled in.

net.inet.ip.fw.verbose_limit: 0
    Limits the number of messages produced by a verbose firewall.

net.inet.ip.fw.dyn_buckets: 256

net.inet.ip.fw.curr_dyn_buckets: 256
    The configured and current size of the hash table used to hold dynamic rules. This must be a power of 2. The table can only be resized when empty, so in order to resize it on the fly you will probably have to flush and reload the ruleset.

net.inet.ip.fw.dyn_count: 3
    Current number of dynamic rules (read-only).

net.inet.ip.fw.dyn_max: 1000
    Maximum number of dynamic rules. When you hit this limit, no more dynamic rules can be installed until old ones expire.

net.inet.ip.fw.dyn_ack_lifetime: 300

net.inet.ip.fw.dyn_syn_lifetime: 20

net.inet.ip.fw.dyn_fin_lifetime: 20

net.inet.ip.fw.dyn_rst_lifetime: 5

net.inet.ip.fw.dyn_short_lifetime: 30
    These variables control the lifetime, in seconds, of dynamic rules. Upon the initial SYN exchange the lifetime is kept short, then increased after both SYN have been seen, then decreased again during the final FIN exchange or when a RST

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 crackers 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.

In order to protect a site from flood attacks involving fake TCP packets, it is safer to use dynamic rules:

    ipfw add check-state
    ipfw add deny tcp from any to any established
    ipfw add allow tcp from my-net to any setup keep-state

This will let the firewall install dynamic rules only for those connection which start with a regular SYN packet coming from the inside of our network. Dynamic rules are checked when encountering the first check-state or keep-state rule. A check-state rule should be usually placed near the beginning of the ruleset to minimize the amount of work scanning the ruleset. Your mileage may vary.

BEWARE: stateful rules can be subject to denial-of-service attacks by a SYN-flood which opens a huge number of dynamic rules. The effects of such attacks can be partially limited by acting on a set of sysctl(8) variables which control the operation of the firewall.

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

    ipfw -at list

or in short form without timestamps:

    ipfw -a list

Next rule diverts all incoming packets from 192.168.2.0/24 to divert port 5000:

    ipfw divert 5000 ip from 192.168.2.0/24 to any in

The following rules show some of the applications of ipfw and dummynet(4) 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:

    ipfw add pipe 10 ip from any to any
    ipfw pipe 10 config plr 0.05

We can use pipes to artificially limit bandwidth, e.g. 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
    ipfw 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 like 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
    ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes
    ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes

The above can be very useful, e.g. if you want to see how your fancy Web page will look for a residential user which 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. AppleTalk, Ethernet, IRDA). It is not necessary that both pipes have the same configuration, so we can also simulate asymmetric links.

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

    ipfw add pipe 1 ip from any to any
    ipfw 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 affect a lot 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
    ipfw pipe 1 config delay 250ms bw 1Mbit/s
    ipfw 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
    ipfw 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
    ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes
    ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes

SEE ALSO
cpp(1), m4(1), bridge(4), divert(4), dummynet(4), ip(4), ipfirewall(4), protocols(5), services(5), init(8), kldload(8), reboot(8), sysctl(8), syslogd(8).

BUGS

The syntax has grown over the years and it is not very clean.

WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!

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

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

Incoming packet fragments diverted by divert or tee are reassembled before delivery to the socket.

Packets that match a tee rule should not be immediately accepted, but should continue going through the rule list. This may be fixed in a later version.

AUTHORS
Ugen J. S. Antsilevich, Poul-Henning Kamp, Alex Nash, Archie Cobbs, Luigi Rizzo.

API based upon code written by Daniel Boulet for BSDI.

Work on dummynet(4) traffic shaper supported by Akamba Corp.

HISTORY
The ipfw utility first appeared in FreeBSD 2.0. dummynet(4) was introduced in FreeBSD 2.2.8. Stateful extensions were introduced in FreeBSD 4.0.