IPFW(8) BSD System Manager's Manual IPFW(8)
NAME
ipfw -- IP firewall and traffic shaper control program
SYNOPSIS
ipfw [-cq] add rule
ipfw [-acdefnNStT] {list | show} [rule | first-last ...]
ipfw [-f | -q] flush
ipfw [-q] {delete | zero | resetlog} [set] [number ...]
ipfw enable {firewall | one_pass | debug | verbose | dyn_keepalive}
ipfw disable {firewall | one_pass | debug | verbose | dyn_keepalive}
ipfw set [disable number ...] [enable number ...]
ipfw set move [rule] number to number
ipfw set swap number number
ipfw set show
ipfw {pipe | queue} number config config-options
ipfw [-s [field]] {pipe | queue} {delete | list | show} [number ...]
ipfw [-cnNqS] [-p preproc [preproc-flags]] pathname
DESCRIPTION
The ipfw utility is the user interface for controlling the ipfw(4) firewall and the dummynet(4) traffic
shaper in FreeBSD.
An ipfw configuration, or ruleset, is made of a list of rules numbered from 1 to 65535. Packets are
passed to ipfw from a number of different places in the protocol stack (depending on the source and
destination of the packet, it is possible that ipfw is invoked multiple times on the same packet). The
packet passed to the firewall is compared against each of the rules in the firewall ruleset. When a
match is found, the action corresponding to the matching rule is performed.
Depending on the action and certain system settings, packets can be reinjected into the firewall at
some rule after the matching one for further processing.
An ipfw ruleset always includes a default rule (numbered 65535) which cannot be modified or deleted,
and matches all 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 or limit option, then ipfw assumes a
stateful behaviour, i.e. upon a match it 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, keep-state or limit rule, and are typically used to open the firewall on-demand to legiti-mate legitimate
mate traffic only. See the STATEFUL FIREWALL 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 or in groups with the delete command, and
globally (except those in set 31) 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.
Also, each rule belongs to one of 32 different sets , and there are ipfw commands to atomically manipu-late manipulate
late sets, such as enable, disable, swap sets, move all rules in a set to another one, delete all rules
in a set. These can be useful to install temporary configurations, or to test them. See Section SETS
OF RULES for more information on sets.
The following options are available:
-a While listing, show counter values. The show command just implies this option.
-c When entering or showing rules, print them in compact form, i.e. without the optional "ip from
any to any" string when this does not carry any additional information.
-d While listing, show dynamic rules in addition to static ones.
-e While listing, if the -d option was specified, also show expired dynamic rules.
-f Don't ask 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.
-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 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 ses-sion. session.
sion. If a flush is performed in normal (verbose) mode (with the default kernel configura-tion), configuration),
tion), it prints a message. Because all rules are flushed, the message might not be delivered
to the login session, causing the remote login session to be closed and the remainder of the
ruleset to not be processed. Access to the console would then be required to recover.
-S While listing rules, show the set each rule belongs to. If this flag is not specified, dis-abled disabled
abled rules will not be listed.
-s [field]
While listing pipes, sort according to one of the four counters (total or current packets or
bytes).
-t While listing, show last match timestamp (converted with ctime()).
-T While listing, show last match timestamp (as seconds from the epoch). This form can be more
convenient for postprocessing by scripts.
To ease configuration, rules can be put into a file which is processed using ipfw as shown in the last
synopsis line. An absolute pathname must be used. 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 pathname 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 environ-ments environments
ments where not all file systems are mounted (yet) by the time ipfw is being run (e.g. when they are
mounted over NFS). Once -p has been specified, any additional arguments as passed on to the preproces-sor preprocessor
sor for interpretation. 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 and queue commands are used to configure the traffic shaper, as shown in the TRAFFIC
SHAPER (DUMMYNET) CONFIGURATION Section below.
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 effect 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.
PACKET FLOW
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_input] [ip_output] net.inet.ip.fw.enable=1
| |
^ V
[ether_demux] [ether_output_frame] net.link.ether.ipfw=1
| |
+-->--[bdg_forward]-->--+ net.link.ether.bridge_ipfw=1
^ V
| to devices |
As can be noted from the above picture, 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().
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. trying to match a MAC header within ip_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).
SYNTAX
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-sen-sitive case-sensitive
sitive depending on their nature (e.g. uid's are, hostnames are not).
In ipfw2 you can introduce spaces after commas ',' 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"
RULE FORMAT
The format of ipfw rules is the following:
[rule_number] [set set_number] [prob match_probability]
action [log [logamount number]] body
where the body of the rule specifies which information is used for filtering packets, among the follow-ing: following:
ing:
Layer-2 header fields When available
IPv4 Protocol 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,
fragment flag (non-zero IP offset), Time To Live
IP options
Misc. TCP header fields TCP flags (SYN, FIN, ACK, RST, etc.), sequence number,
acknowledgment number, window
TCP options
ICMP types for ICMP packets
User/group ID When the packet can be associated with a local socket.
Note that some of the above information, e.g. source MAC or IP addresses and TCP/UDP ports, could eas-ily easily
ily be 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 num-bers numbers
bers 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.
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 dis-abled disabled
abled and enabled, so this parameter is of fundamental importance for atomic ruleset manipula-tion. manipulation.
tion. It can be also used to simplify deletion of groups of rules. If a rule is entered with-out without
out 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 flush command (but you can delete them with the ipfw delete set 31 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 conjunc-tion conjunction
tion with dummynet(4)) 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]
When a packet matches a rule with the log keyword, a message will be logged to syslogd(8) with
a LOG_SECURITY facility. The logging only occurs if the sysctl variable net.inet.ip.fw.verbose
is set to 1 (which is the default when the kernel is compiled with IPFIREWALL_VERBOSE ) and the
number of packets logged so far for that particular rule does not exceed the logamount parame-ter. parameter.
ter. 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 removes the logging limit.
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 veri-fied, verified,
fied, and before performing the final action (accept, deny, etc.) on the packet.
RULE ACTIONS
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
Checks the packet against the dynamic ruleset. If a match is found, execute the action associ-ated associated
ated 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.
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[,port]
Change the next-hop on matching packets to ipaddr, which can be an IP address in dotted quad
format or a host name. The search terminates if this rule matches.
If ipaddr is a local address, then matching packets will be forwarded to port (or the port num-ber number
ber 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 layer-2 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 destina-tion destination
tion 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 destina-tion destination
tion address of the packet. This makes the netstat(1) entry look rather weird but is intended
for use with transparent proxy servers.
pipe pipe_nr
Pass packet to a dummynet(4) ``pipe'' (for bandwidth limitation, delay, etc.). See the TRAFFIC
SHAPER (DUMMYNET) CONFIGURATION Section for further information. The search terminates; how-ever, however,
ever, 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+).
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.
skipto number
Skip all subsequent rules numbered less than number. The search continues with the first rule
numbered number or higher.
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).
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.
RULE BODY
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 pat-terns patterns
terns 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 parenthe-ses parentheses
ses or braces, so it is advisable to put a backslash \ in front of them to prevent such interpreta-tions. interpretations.
tions.
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 ipfw1. In ipfw2 any match
pattern (including MAC headers, IPv4 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 IPv4 protocol specified by number or name (for a complete list see /etc/protocols). The ip
or all keywords mean any protocol will match.
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 | addr-list | addr-set}
any matches any IP address.
me matches any IP address configured on an interface in the system. The address list is evaluated
at the time the packet is analysed.
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 a dotted quad or a hostname) and
mask width of masklen bits. As an example, 1.2.3.4/25 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 a dotted quad or a hostname) and the
mask of mask, specified as a dotted quad. As an example, 1.2.3.4/255.0.255.0 will
match 1.*.3.*. We suggest to use this form only for non-contiguous masks, and resort
to the addr/masklen format for contiguous masks, which is more compact and less error-prone. errorprone.
prone.
addr-set: addr[/masklen]{list}
list: {num | num-num}[,list]
Matches all addresses with base address addr (specified as a dotted quad 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 com-plexity complexity
plexity of rulesets.
As an example, an address specified as 1.2.3.4/24{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 .
ports: {port | port-port}[,ports]
For protocols which support port numbers (such as 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 `-' 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.
RULE OPTIONS (MATCH PATTERNS)
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
Matches only bridged packets.
dst-ip ip-address
Matches IP 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.
frag Matches packets that are fragments and not the first fragment of an IP datagram. Note that
these packets will not have the next protocol header (e.g. TCP, UDP) so options that look into
these headers cannot match.
gid group
Matches all TCP or UDP packets sent by or received for a group. A group may be specified by
name or number.
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).
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 IP 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 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 (time-stamp). (timestamp).
stamp). The absence of a particular option may be denoted with a `!'.
ipprecedence precedence
Matches IP packets whose precedence field is equal to precedence.
ipsec Matches packets that have IPSEC history associated with them (i.e. the packet comes encapsu-lated encapsulated
lated in IPSEC, the kernel has IPSEC support and IPSEC_FILTERGIF option, 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.
iptos spec
Matches IP 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_CE). The absence of a particular type may be
denoted with a `!'.
ipttl ttl-list
Matches IP 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
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.
layer2 Matches only layer2 packets, i.e. those passed to ipfw from ether_demux() and ether_out-put_frame(). ether_output_frame().
put_frame().
limit {src-addr | src-port | dst-addr | dst-port} N
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.
{ MAC | mac } dst-mac src-mac
Match packets with a given dst-mac and src-mac addresses, specified as the any keyword (match-ing (matching
ing any MAC address), or six groups of hex digits separated by colons, and optionally followed
by a mask indicating how many bits are significant, as in
MAC 10:20:30:40:50:60/33 any
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. Val-ues Values
ues 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 IPv4 protocol.
recv | xmit | via {ifX | if* | ipno | any}
Matches packets received, transmitted or going through, respectively, the interface specified
by exact name (ifX), by device name (if*), by IP address, or through some interface.
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 inter-face interface
face can only be tested on outgoing packets. So out is required (and in is invalid) whenever
xmit is used.
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 inter-face. interface.
face.
setup Matches TCP packets that have the SYN bit set but no ACK bit. This is the short form of
``tcpflags syn,!ack''.
src-ip ip-address
Matches IP packets whose source IP is one of the address(es) specified as argument.
src-port ports
Matches IP packets whose source port is one of the port(s) specified as argument.
tcpack ack
TCP packets only. Match if the TCP header acknowledgment number field is set to ack.
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.
tcpseq seq
TCP packets only. Match if the TCP header sequence number field is set to seq.
tcpwin win
TCP packets only. Match if the TCP header window field is set to win.
tcpoptions spec
TCP packets only. Match if the TCP header contains the comma separated list of options speci-fied specified
fied 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 `!'.
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 outgo-ing outgoing
ing 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.
SETS OF RULES
Each rule belongs to one of 32 different sets , numbered 0 to 31. Set 31 is reserved for the default
rule.
By default, rules are put in set 0, unless you use the set N attribute when entering a new rule. 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. 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 gen-erated generated
erated 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 FIREWALL
Stateful operation is a way for the firewall to dynamically create rules for specific flows when pack-ets packets
ets that match a given pattern are detected. Support for stateful operation comes through the
check-state, keep-state and limit options of rules.
Dynamic rules are created when a packet matches a keep-state or 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). 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 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
ipfw add allow tcp from my-subnet to any setup keep-state
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
ipfw add allow udp from my-subnet to any keep-state
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.
TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
ipfw is also the user interface for the dummynet(4) traffic shaper.
dummynet operates by first using the firewall to classify packets and divide them into flows, using any
match pattern that can be used in ipfw rules. Depending on local policies, a flow can contain packets
for a single TCP connection, or from/to a given host, or entire subnet, or a protocol type, etc.
Packets belonging to the same flow are then passed to either of two different objects, which implement
the traffic regulation:
pipe A pipe emulates a link with given bandwidth, propagation delay, queue size and packet loss
rate. Packets are queued in front of the pipe as they come out from the classifier, and
then transferred to the pipe according to the pipe's parameters.
queue A queue is an abstraction used to implement the WF2Q+ (Worst-case Fair Weighted Fair Queue-ing) Queueing)
ing) policy, which is an efficient variant of the WFQ policy.
The queue associates a weight and a reference pipe to each flow, and then all backlogged
(i.e., with packets queued) flows linked to the same pipe share the pipe's bandwidth pro-portionally proportionally
portionally to their weights. Note that weights are not priorities; a flow with a lower
weight is still guaranteed to get its fraction of the bandwidth even if a flow with a
higher weight is permanently backlogged.
In practice, pipes can be used to set hard limits to the bandwidth that a flow can use, whereas queues
can be used to determine how different flow share the available bandwidth.
The pipe and queue configuration commands are the following:
pipe number config pipe-configuration
queue number config queue-configuration
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 immediately follow the number,
as in
ipfw pipe 1 config bw 300Kbit/s
If a device name is specified instead of a numeric value, as in
ipfw pipe 1 config bw tun0
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.
The following parameters can be configured for a queue:
pipe pipe_nr
Connects a queue to the specified pipe. Multiple queues (with the same or 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.
Finally, the following parameters can be configured for both pipes and queues:
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
65536.
mask mask-specifier
Packets sent to a given pipe or queue by an ipfw rule can be further classified into multiple
flows, each of which is then sent to a different dynamic pipe or queue. A flow identifier is
constructed by masking the IP addresses, ports and protocol types as specified with the mask
options in the configuration of the pipe or queue. For each different flow identifier, a new
pipe or queue is created with the same parameters as the original object, and matching packets
are sent to it.
Thus, when dynamic pipes are used, each flow will get the same bandwidth as defined by the pipe,
whereas when dynamic queues are used, each flow will share the parent's pipe bandwidth evenly
with other flows generated by the same queue (note that other queues with different weights might
be connected to the same pipe).
Available mask specifiers are a combination of one or more 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.
noerror
When a packet is dropped by a dummynet queue or pipe, the error is normally reported to the
caller routine in the kernel, in the same way as it happens when a device queue fills up. Setting
this option reports the packet as successfully delivered, which can be needed for some experimen-tal experimental
tal setups where you want to simulate loss or congestion at a remote router.
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.
queue {slots | sizeKbytes}
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.
red | gred w_q/min_th/max_th/max_p
Make use of the RED (Random Early Detection) 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 num-bers numbers
bers 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:
oo Remember that you filter both packets going in and out. Most connections need packets going in
both directions.
oo 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.
oo Don't forget the loopback interface.
FINE POINTS
oo There are circumstances where fragmented datagrams are unconditionally dropped. TCP packets are
dropped if they do not contain at least 20 bytes of TCP header, UDP packets are dropped if they do
not contain a full 8 byte UDP header, and ICMP packets are dropped if they do not contain 4 bytes
of ICMP header, enough to specify the ICMP type, code, and checksum. These packets are simply
logged as ``pullup failed'' since there may not be enough good data in the packet to produce a
meaningful log entry.
oo Another type of packet is unconditionally dropped, a TCP packet with a fragment offset of one.
This is a valid packet, but it only has one use, to try to circumvent firewalls. When logging is
enabled, these packets are reported as being dropped by rule -1.
oo 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 ipfw && \
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.
oo 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 and associated modules ( dummynet,
bridge ). These are shown below together with their default value (but always check with the sysctl(8)
command what value is actually in use) and meaning:
net.inet.ip.dummynet.expire: 1
Lazily delete dynamic pipes/queue once they have no pending traffic. You can disable this by
setting the variable to 0, in which case the pipes/queues will only be deleted when the thresh-old threshold
old is reached.
net.inet.ip.dummynet.hash_size: 64
Default size of the hash table used for dynamic pipes/queues. This value is used when no
buckets option is specified when configuring a pipe/queue.
net.inet.ip.dummynet.max_chain_len: 16
Target value for the maximum number of pipes/queues in a hash bucket. The product
max_chain_len*hash_size is used to determine the threshold over which empty pipes/queues will
be expired even when net.inet.ip.dummynet.expire=0.
net.inet.ip.dummynet.red_lookup_depth: 256
net.inet.ip.dummynet.red_avg_pkt_size: 512
net.inet.ip.dummynet.red_max_pkt_size: 1500
Parameters used in the computations of the drop probability for the RED algorithm.
net.inet.ip.fw.autoinc_step: 100
Delta between rule numbers when auto-generating them. The value must be in the range 1..1000.
This variable is only present in ipfw2, the delta is hardwired to 100 in ipfw1.
net.inet.ip.fw.curr_dyn_buckets: net.inet.ip.fw.dyn_buckets
The current number of buckets in the hash table for dynamic rules (readonly).
net.inet.ip.fw.debug: 1
Controls debugging messages produced by ipfw.
net.inet.ip.fw.dyn_buckets: 256
The number of buckets in the hash table for dynamic rules. Must be a power of 2, up to 65536.
It only takes effect when all dynamic rules have expired, so you are advised to use a flush
command to make sure that the hash table is resized.
net.inet.ip.fw.dyn_count: 3
Current number of dynamic rules (read-only).
net.inet.ip.fw.dyn_keepalive: 1
Enables generation of keepalive packets for keep-state rules on TCP sessions. A keepalive is
generated to both sides of the connection every 5 seconds for the last 20 seconds of the life-time lifetime
time of the rule.
net.inet.ip.fw.dyn_max: 8192
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: 1
net.inet.ip.fw.dyn_rst_lifetime: 1
net.inet.ip.fw.dyn_udp_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 is received. Both dyn_fin_lifetime
and dyn_rst_lifetime must be strictly lower than 5 seconds, the period of repetition of
keepalives. The firewall enforces that.
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.one_pass: 1
When set, the packet exiting from the dummynet(4) pipe is not passed though the firewall again.
Otherwise, after a pipe action, the packet is reinjected into the firewall at the next rule.
net.inet.ip.fw.verbose: 1
Enables verbose messages.
net.inet.ip.fw.verbose_limit: 0
Limits the number of messages produced by a verbose firewall.
net.link.ether.ipfw: 0
Controls whether layer-2 packets are passed to ipfw. Default is no.
net.link.ether.bridge_ipfw: 0
Controls whether bridged packets are passed to ipfw. Default is no.
IPFW2 ENHANCEMENTS
This Section lists the features that have been introduced in ipfw2 which were not present in ipfw1. We
list them in order of the potential impact that they can have in writing your rulesets. You might want
to consider using these features in order to write your rulesets in a more efficient way.
Syntax and flags
ipfw1 does not support the -n flag (only test syntax), nor it allows spaces after commas or
supports all rule fields in a single argument.
Handling of non-IPv4 packets
ipfw1 will silently accept all non-IPv4 packets (which ipfw1 will only see when
net.link.ether.bridge_ipfw=1). ipfw2 will filter all packets (including non-IPv4 ones) accord-ing according
ing to the ruleset. To achieve the same behaviour as ipfw1 you can use the following as the
very first rule in your ruleset:
ipfw add 1 allow layer2 not mac-type ip
The layer2 option might seem redundant, but it is necessary -- packets passed to the firewall
from layer3 will not have a MAC header, so the mac-type ip pattern will always fail on them,
and the not operator will make this rule into a pass-all.
Addresses
ipfw1 does not supports address sets or lists of addresses.
Port specifications
ipfw1 only allows one port range when specifying TCP and UDP ports, and is limited to 10
entries instead of the 15 allowed by ipfw2. Also, in ipfw1 you can only specify ports when the
rule is requesting tcp or udp packets. With ipfw2 you can put port specifications in rules
matching all packets, and the match will be attempted only on those packets carrying protocols
which include port identifiers.
Finally, ipfw1 allowed the first port entry to be specified as port:mask where mask can be an
arbitrary 16-bit mask. This syntax is of questionable usefulness and it is not supported any-more anymore
more in ipfw2.
Or-blocks
ipfw1 does not support Or-blocks.
keepalives
ipfw1 does not generate keepalives for stateful sessions. As a consequence, it might cause
idle sessions to drop because the lifetime of the dynamic rules expires.
Sets of rules
ipfw1 does not implement sets of rules.
MAC header filtering and Layer-2 firewalling.
ipfw1 does not implement filtering on MAC header fields, nor is it invoked on packets from
ether_demux() and ether_output_frame(). The sysctl variable net.link.ether.ipfw has no effect
there.
Options
In ipfw1, the following options only accept a single value as an argument:
ipid, iplen, ipttl
The following options are not implemented by ipfw1:
dst-ip, dst-port, layer2, mac, mac-type, src-ip, src-port.
Additionally, the RELENG_4 version of ipfw1 does not implement the following options:
ipid, iplen, ipprecedence, iptos, ipttl, ipversion, tcpack, tcpseq, tcpwin.
Dummynet options
The following option for dummynet pipes/queues is not supported: noerror.
EXAMPLES
There are far too many possible uses of ipfw so this Section will only give a small set of examples.
BASIC PACKET FILTERING
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 ipfw2 syntax to specify address
sets and or-blocks and write extremely compact rulesets which selectively enable services to blocks of
clients, as below:
goodguys="{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }"
badguys="10.1.2.0/24{8,38,60}"
ipfw add allow ip from ${goodguys} to any
ipfw add deny ip from ${badguys} to any
... normal policies ...
The ipfw1 syntax would require a separate rule for each IP in the above example.
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 sytem 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.
DYNAMIC RULES
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 usually be placed near the beginning
of the ruleset to minimize the amount of work scanning the ruleset. Your mileage may vary.
To limit the number of connections a user can open you can use the following type of rules:
ipfw add allow tcp from my-net/24 to any setup limit src-addr 10
ipfw add allow tcp from any to me setup limit src-addr 4
The former (assuming it runs on a gateway) will allow each host on a /24 network to open at most 10 TCP
connections. The latter can be placed on a server to make sure that a single client does not use more
than 4 simultaneous connections.
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
which is equivalent to:
ipfw show
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
TRAFFIC SHAPING
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 want to simulate a bidirectional link with bandwidth limitations, the correct way is the fol-lowing: following:
lowing:
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 residen-tial residential
tial user who is connected only through a slow link. You should not use only one pipe for both direc-tions, directions,
tions, 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 want 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 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
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
SETS OF RULES
To add a set of rules atomically, e.g. 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. if you cannot access your box, the ruleset will be disabled after the
sleep terminates thus restoring the previous situation.
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 sometimes it might be confusing. Unfortunately, backward com-patibility compatibility
patibility prevents cleaning up mistakes made in the definition of the syntax.
!!! WARNING !!!
Misconfiguring the firewall can put your computer in an unusable state, possibly shutting down network
services and requiring console access to regain control of it.
Incoming packet fragments diverted by divert or tee are reassembled before delivery to the socket. The
action used on those packet is the one from the rule which matches the first fragment of the packet.
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.
Packets diverted to userland, and then reinserted by a userland process may lose various packet
attributes. The packet source interface name will be preserved if it is shorter than 8 bytes and the
userland process saves and reuses the sockaddr_in (as does natd(8)); otherwise, it may be lost. If a
packet is reinserted in this manner, later rules may be incorrectly applied, making the order of divert
rules in the rule sequence very important.
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. ipfw2 was introduced in Summer 2002.
Darwin August 13, 2002 Darwin
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