Name: IPFW
Section: Maintenance Commands (8)
BSD mandoc
FreeBSD
NAME
ipfw
- controlling utility for IP firewall and traffic shaper
SYNOPSIS
[-q
]
[-p preproc
[-D
macro [= value
]
]
[-U macro
]
]
pathname
[-f | q
]
flush
[-q
]
Es { }
En Cm zero | resetlog | delete
[number ...
]
[-s [field
]
]
[-aftN
]
Es { }
En Cm list | show
[number ...
]
[-q
]
add
[number
]
rule-body
pipe
number
config
pipe-config-options
pipe
Es { }
En Cm delete | list | show
[number ...
]
queue
number
config
queue-config-options
queue
Es { }
En Cm delete | list | show
[number ...
]
DESCRIPTION
is the user interface for controlling the
ipfirewall(4)
and the
dummynet(4)
traffic shaper in
Fx .
Each incoming or outgoing packet is passed through the
rules.
If host is acting as a gateway, packets forwarded by
the gateway are processed by
twice.
In case a host is acting as a bridge, packets forwarded by
the bridge are processed by
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
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
Sx RULE FORMAT
and
Sx EXAMPLES
sections below for more information on the stateful behaviour of
.
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
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
add ing
zero ing
resetlog ging
or
flush ing
be quiet about actions
Po implies
-f
Pc .
This is useful for adjusting rules by executing multiple
commands in a script
Po e.g.,
`sh/etc/rc.firewall'
Pc ,
or by processing a file of many
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
as shown in the first synopsis line.
An absolute
pathname
must be used.
The file
will be read line by line and applied as arguments to the
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 environments where not all
filesystems are mounted (yet) by the time
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
pipe
commands are used to configure the traffic shaper, as shown in the
Sx TRAFFIC SHAPER CONFIGURATION
section below.
RULE FORMAT
The
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
Po in conjunction with
dummynet(4)
Pc 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
Po but see section
Sx BUGS
below
Pc .
- fwd ipaddr Xo [, 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
Sx 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
logged to
syslogd(8)
with a
LOG_SECURITY
facility.
Note
by default, they are appended to the
/var/log/security
file (see
syslog.conf5).
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
-
any | me | [not
]
Aq Ar address Ns / Ns Ar mask
[ports
]
Specifying
any
makes the rule match any IP number.
Specifying
me
makes the rule match any IP number configured on an interface in the system.
This is a computationally semi-expensive check which should be used with care.
The
Aq Ar address Ns / Ns Ar 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:
Sm off
Eo {
port
port - port
port : mask
Ec } Op , Ar port Op , Ar ...
Sm on
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
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
pipe configuration format is the following:
pipe number config
[bw bandwidth | device
]
[delay ms-delay
]
[queue
Es { }
En Ar slots | size
]
[plr loss-probability
]
[mask mask-specifier
]
[buckets hash-table-size
]
[red | gred
Sm off
w_q / Xo min_th /
max_th /
max_p
Sm on
]
The
queue configuration format is the following:
queue number config
[pipe pipe_nr
]
[weight weight
]
[queue
Es { }
En Ar slots | size
]
[plr loss-probability
]
[mask mask-specifier
]
[buckets hash-table-size
]
[red | gred
Sm off
w_q / Xo min_th /
max_th /
max_p
Sm on
]
The following parameters can be configured for a pipe:
- bw bandwidth | device
-
Bandwidth, measured in
Sm off
[K | M
Eo {
]
bit/s | Byte/s
Ec } .
Sm on
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 Xo Es { }
-
En Ar slots | size Ns Cm Kbytes
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 Xo Sm off
-
w_q /
min_th /
max_th /
max_p
Sm on
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
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
.
- 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.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
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
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
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
An Ugen J. S. Antsilevich ,
An Poul-Henning Kamp ,
An Alex Nash ,
An Archie Cobbs ,
An Luigi Rizzo .
An -nosplit
API based upon code written by
An Daniel Boulet
for BSDI.
Work on
dummynet(4)
traffic shaper supported by Akamba Corp.
HISTORY
The
utility first appeared in
Fx 2.0 .
dummynet(4)
was introduced in
Fx 2.2.8 .
Stateful extensions were introduced in
Fx 4.0 .
Table of Contents
- Name
- Synopsis
- Description
- Rule format
- Traffic shaper configuration
- Checklist
- Fine points
- Packet diversion
- Sysctl variables
- Examples
- See also
- Bugs
- Authors
- History