Manual Pages for UNIX Darwin command on man ipfw

IPFW(8) BSD System Manager's Manual IPFW(8)

NAME

iippffww - IP firewall and traffic shaper control program

SYNOPSIS

iippffww [-ccqq] aadddd rule

iippffww [-aaccddeeffnnNNSSttTT] {lliisstt | sshhooww} [rule | first-last ...]

iippffww [-ff | -qq] fflluusshh

iippffww [-qq] {ddeelleettee | zzeerroo | rreesseettlloogg} [sseett] [number ...]

iippffww eennaabbllee {ffiirreewwaallll | oonneeppaassss | ddeebbuugg | vveerrbboossee | ddyynnkkeeeeppaalliivvee} iippffww ddiissaabbllee {ffiirreewwaallll | oonneeppaassss | ddeebbuugg | vveerrbboossee | ddyynnkkeeeeppaalliivvee} iippffww sseett [ddiissaabbllee number ...] [eennaabbllee number ...] iippffww sseett mmoovvee [rruullee] number ttoo number iippffww sseett sswwaapp number number iippffww sseett sshhooww

iippffww {ppiippee | qquueeuuee} number ccoonnffiigg config-options

iippffww [-ss [field]] {ppiippee | qquueeuuee} {ddeelleettee | lliisstt | sshhooww} [number ...]

iippffww [-ccnnNNqqSS] [-pp preproc [preproc-flags]] pathname

DESCRIPTION

The iippffww utility is the user interface for controlling the ipfw(4) fire-

wall and the dummynet(4) traffic shaper in FreeBSD.

NOTE: this manual page documents the newer version of iippffww introduced

in FreeBSD CURRENT in July 2002, also known as iippffww22. iippffww22 is a superset of the old firewall, iippffww11. The differences between the two are listed in Section IPFW2 ENHANCEMENTS, which you are encouraged to

read to revise older rulesets and possibly write them more effi-

ciently. See Section USING IPFW2 IN FreeBSD-STABLE for instructions

on how to run iippffww22 on FreeBSD STABLE. An iippffww configuration, or ruleset, is made of a list of rules numbered from 1 to 65535. Packets are passed to iippffww from a number of different places in the protocol stack (depending on the source and destination of the packet, it is possible that iippffww 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 rein-

jected into the firewall at some rule after the matching one for further processing. An iippffww ruleset always includes a default rule (numbered 65535) which

cannot be modified or deleted, and matches all packets. The action asso-

ciated with the default rule can be either ddeennyy or aallllooww depending on how the kernel is configured.

If the ruleset includes one or more rules with the kkeeeepp-ssttaattee or lliimmiitt

option, then iippffww 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 cchheecckk-ssttaattee, kkeeeepp-ssttaattee or lliimmiitt rule, and are typ-

ically used to open the firewall on-demand to legitimate traffic only.

See the STATEFUL FIREWALL and EXAMPLES Sections below for more informa-

tion on the stateful behaviour of iippffww. 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 iippffww commands. Rules can be added with the aadddd command; deleted individually or in groups with the ddeelleettee command, and globally (except those in set 31) with the fflluusshh command; displayed, optionally with the content of the counters, using the sshhooww and lliisstt commands. Finally, counters can be reset with the zzeerroo and rreesseettlloogg commands. Also, each rule belongs to one of 32 different sets , and there are iippffww commands to atomically manipulate 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:

-aa While listing, show counter values. The sshhooww command just

implies this option.

-cc 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.

-dd While listing, show dynamic rules in addition to static ones.

-ee While listing, if the -dd option was specified, also show expired

dynamic rules.

-ff Don't ask for confirmation for commands that can cause problems

if misused, i.e. fflluusshh. If there is no tty associated with the process, this is implied.

-nn Only check syntax of the command strings, without actually pass-

ing them to the kernel.

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

-qq While aadddding, zzeerrooing, rreesseettllooggging or fflluusshhing, be quiet about

actions (implies -ff). This is useful for adjusting rules by exe-

cuting multiple iippffww commands in a script (e.g., `sh /etc/rc.firewall'), or by processing a file of many iippffww rules across a remote login session. If a fflluusshh is performed in normal (verbose) mode (with the default kernel configuration), 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.

-SS While listing rules, show the set each rule belongs to. If this

flag is not specified, disabled rules will not be listed.

-ss [field]

While listing pipes, sort according to one of the four counters (total or current packets or bytes).

-tt While listing, show last match timestamp (converted with

ctime()).

-TT 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 iippffww 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 iippffww utility.

Optionally, a preprocessor can be specified using -pp 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 charac-

ter, the usual PATH name search is performed. Care should be taken with this in environments where not all file systems are mounted (yet) by the

time iippffww is being run (e.g. when they are mounted over NFS). Once -pp

has been specified, any additional arguments as passed on to the pre-

processor 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 iippffww ppiippee and qquueeuuee 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 iippffww ABI may break, pre-

venting you from being able to add any rules. This can adversely effect the booting process. You can use iippffww ddiissaabbllee ffiirreewwaallll to temporarily disable the firewall to regain access to the network, allowing you to fix the problem. PPAACCKKEETT FFLLOOWW 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 [ipinput] [ipoutput] net.inet.ip.fw.enable=1 | | ^ V

[etherdemux] [etheroutputframe] net.link.ether.ipfw=1

| |

+->-[bdgforward]->-+ net.link.ether.bridgeipfw=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 iippffww is invoked from eetthheerrddeemmuuxx(()), but the same packets will have the MAC header stripped off when iippffww is invoked from iippiinnppuutt(()).

Also note that each packet is always checked against the complete rule-

set, 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 iippiinnppuutt(()) ), the match pattern will not match, but a nnoott 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. sskkiippttoo rules can be useful here, as an example:

# packets from etherdemux or bdgforward

ipfw add 10 skipto 1000 all from any to any layer2 in

# packets from ipinput

ipfw add 10 skipto 2000 all from any to any not layer2 in

# packets from ipoutput

ipfw add 10 skipto 3000 all from any to any not layer2 out

# packets from etheroutputframe

ipfw add 10 skipto 4000 all from any to any layer2 out

(yes, at the moment there is no way to differentiate between etherdemux and bdgforward). SSYYNNTTAAXX

In general, each keyword or argument must be provided as a separate com-

mand line argument, with no leading or trailing spaces. Keywords are

case-sensitive, whereas arguments may or may not be case-sensitive

depending on their nature (e.g. uid's are, hostnames are not). In iippffww22 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"

RRUULLEE FFOORRMMAATT The format of iippffww rules is the following: [rulenumber] [sseett setnumber] [pprroobb matchprobability] action [lloogg [llooggaammoouunntt number]] body

where the body of the rule specifies which information is used for fil-

tering packets, among the following:

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, data-

gram length, identification,

fragment flag (non-zero IP off-

set), Time To Live IP options Misc. TCP header fields TCP flags (SYN, FIN, ACK, RST,

etc.), sequence number, acknowl-

edgment number, window TCP options ICMP types for ICMP packets

User/group ID When the packet can be associ-

ated with a local socket. Note that some of the above information, e.g. source MAC or IP addresses and TCP/UDP ports, could easily be spoofed, so filtering on those fields alone might not guarantee the desired results. rulenumber Each rule is associated with a rulenumber in the range 1..65535, with the latter reserved for the default rule. Rules are checked sequentially by rule number. Multiple rules can have the same number, in which case they are checked (and listed) according to the order in which they have been added. If a rule is entered without specifying a number, the kernel will assign one in such a way that the rule becomes the last one before the default rule.

Automatic rule numbers are assigned by incrementing the last non-

default rule number by the value of the sysctl variable net.inet.ip.fw.autoincstep 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. sseett setnumber Each rule is associated with a setnumber in the range 0..31. Sets can be individually disabled and enabled, so this parameter is of fundamental importance for atomic ruleset manipulation. It can be also used to simplify deletion of groups of rules. If a rule is entered without specifying a set number, set 0 will be used. Set 31 is special in that it cannot be disabled, and rules in set 31 are not deleted by the iippffww fflluusshh command (but you can delete them with the iippffww ddeelleettee sseett 3311 command). Set 31 is also used for the default rule. pprroobb matchprobability 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 lead-

ing 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. lloogg [llooggaammoouunntt number] When a packet matches a rule with the lloogg keyword, a message will

be logged to syslogd(8) with a LOGSECURITY facility. The log-

ging 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 IPFIREWALLVERBOSE ) and the number of packets logged so far for that particular rule does not exceed the llooggaammoouunntt parameter. If no llooggaammoouunntt is specified, the limit is taken from the sysctl variable net.inet.ip.fw.verboselimit. 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 rreesseettlloogg command. Note: logging is done after all other packet matching conditions have been successfully verified, and before performing the final action (accept, deny, etc.) on the packet. RRUULLEE AACCTTIIOONNSS A rule can be associated with one of the following actions, which will be executed when the packet matches the body of the rule. aallllooww | aacccceepptt | ppaassss | ppeerrmmiitt Allow packets that match rule. The search terminates.

cchheecckk-ssttaattee

Checks the packet against the dynamic ruleset. If a match is

found, execute the action associated with the rule which gener-

ated this dynamic rule, otherwise move to the next rule.

CChheecckk-ssttaattee rules do not have a body. If no cchheecckk-ssttaattee rule is

found, the dynamic ruleset is checked at the first kkeeeepp-ssttaattee or

lliimmiitt rule.

ccoouunntt Update counters for all packets that match rule. The search con-

tinues with the next rule. ddeennyy | ddrroopp Discard packets that match this rule. The search terminates. ddiivveerrtt port Divert packets that match this rule to the divert(4) socket bound to port port. The search terminates. ffwwdd | ffoorrwwaarrdd 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 for-

warded to port (or the port number in the packet if one is not specified in the rule) on the local machine.

If ipaddr is not a local address, then the port number (if speci-

fied) 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

etherinput, etheroutput, or bridged). The ffwwdd action does not change the contents of the packet at all. In particular, the destination address remains unmodified, so packets forwarded to another system will usually be rejected by that system unless there is a matching rule on that system to capture them. For packets forwarded locally, the local address of the socket will be set to the original destination address of the packet. This makes the netstat(1) entry look rather weird but is intended for use with transparent proxy servers. ppiippee pipenr 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; however, on exit from the pipe and if the sysctl(8) variable net.inet.ip.fw.onepass is not set, the packet is passed again to the firewall code starting from the next rule. qquueeuuee queuenr Pass packet to a dummynet(4) ``queue'' (for bandwidth limitation using WF2Q+). rreejjeecctt (Deprecated). Synonym for uunnrreeaacchh hhoosstt. rreesseett Discard packets that match this rule, and if the packet is a TCP

packet, try to send a TCP reset (RST) notice. The search termi-

nates. sskkiippttoo number Skip all subsequent rules numbered less than number. The search continues with the first rule numbered number or higher. tteeee 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).

uunnrreeaacchh 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: nneett, hhoosstt, pprroottooccooll, ppoorrtt,

nneeeeddffrraagg, ssrrccffaaiill, nneett-uunnkknnoowwnn, hhoosstt-uunnkknnoowwnn, iissoollaatteedd,

nneett-pprroohhiibb, hhoosstt-pprroohhiibb, ttoossnneett, ttoosshhoosstt, ffiilltteerr-pprroohhiibb,

hhoosstt-pprreecceeddeennccee or pprreecceeddeennccee-ccuuttooffff. The search terminates.

RRUULLEE BBOODDYY 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) aanndd

operators - i.e. all must match in order for the rule to match. Indi-

vidual patterns can be prefixed by the nnoott operator to reverse the result of the match, as in

ipfw add 100 allow ip from not 1.2.3.4 to any

Additionally, sets of alternative match patterns ( or-blocks ) can be

constructed by putting the patterns in lists enclosed between parentheses ( ) or braces { }, and using the oorr operator as follows:

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

Only one level of parentheses is allowed. Beware that most shells have special meanings for parentheses or braces, so it is advisable to put a backslash \ in front of them to prevent such interpretations. The body of a rule must in general include a source and destination address specifier. The keyword any can be used in various places to specify that the content of a required field is irrelevant. The rule body has the following format: [proto ffrroomm src ttoo dst] [options] The first part (proto from src to dst) is for backward compatibility with

iippffww11. In iippffww22 any match pattern (including MAC headers, IPv4 proto-

cols, addresses and ports) can be specified in the options section. Rule fields have the following meaning: proto: protocol | {{ protocol oorr ...... }}

protocol: [nnoott] protocol-name | protocol-number

An IPv4 protocol specified by number or name (for a complete list see /etc/protocols). The iipp or aallll keywords mean any protocol will match.

The {{ protocol oorr ...... }} format (an or-block) is provided for con-

venience only but its use is deprecated. src and dst: {aaddddrr | {{ addr oorr ...... }}} [[nnoott] 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: [nnoott] {aannyy | mmee | addr-list | addr-set}

aannyy matches any IP address. mmee 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 dot-

ted quad or a hostname) and mask width of mmaasskklleenn 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 dot-

ted 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 for-

mat for contiguous masks, which is more compact and less

error-prone.

addr-set: addr[/masklen]{{list}}

list: {num | num-num}[,list]

Matches all addresses with base address addr (specified as a dot-

ted 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 bit-

mask, it takes constant time and dramatically reduces the com-

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 ppoorrttss may be specified as one or more ports or port ranges, separated by commas but no spaces, and an optional nnoott

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 ooppttiioonnss 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 ffrraagg option for details on matching fragmented packets. RRUULLEE OOPPTTIIOONNSS ((MMAATTCCHH PPAATTTTEERRNNSS)) 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

nnoott operand, and possibly grouped into or-blocks.

The following match patterns can be used (listed in alphabetical order): //// tthhiiss iiss aa ccoommmmeenntt.. 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

ccoouunntt action followed by the comment. bbrriiddggeedd Matches only bridged packets.

ddsstt-iipp ip-address

Matches IP packets whose destination IP is one of the address(es) specified as argument.

ddsstt-ppoorrtt ports

Matches IP packets whose destination port is one of the port(s) specified as argument. eessttaabblliisshheedd Matches TCP packets that have the RST or ACK bits set. ffrraagg 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. ggiidd group Matches all TCP or UDP packets sent by or received for a group. A group may be specified by name or number. iiccmmppttyyppeess 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 sup-

ported ICMP types are: echo reply (00), destination unreachable (33), source quench (44), redirect (55), echo request (88), router advertisement (99), router

solicitation (1100), time-to-live exceeded (1111), IP header bad

(1122), timestamp request (1133), timestamp reply (1144), information request (1155), information reply (1166), address mask request (1177) and address mask reply (1188). iinn | oouutt Matches incoming or outgoing packets, respectively. iinn and oouutt are mutually exclusive (in fact, oouutt is implemented as nnoott iinn).

iippiidd id-list

Matches IP packets whose iippiidd 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.

iipplleenn 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. iippooppttiioonnss spec Matches packets whose IP header contains the comma separated list of options specified in spec. The supported IP options are: ssssrrrr (strict source route), llssrrrr (loose source route), rrrr (record packet route) and ttss (timestamp). The absence of a particular option may be denoted with a `!'. iipppprreecceeddeennccee precedence Matches IP packets whose precedence field is equal to precedence. iippsseecc Matches packets that have IPSEC history associated with them (i.e. the packet comes encapsulated in IPSEC, the kernel has IPSEC support and IPSECFILTERGIF option, and can correctly decapsulate it). Note that specifying iippsseecc is different from specifying pprroottoo 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. iippttooss spec Matches IP packets whose ttooss field contains the comma separated list of service types specified in spec. The supported IP types of service are: lloowwddeellaayy (IPTOSLOWDELAY), tthhrroouugghhppuutt (IPTOSTHROUGHPUT), rreelliiaabbiilliittyy (IPTOSRELIABILITY), mmiinnccoosstt (IPTOSMINCOST), ccoonnggeessttiioonn (IPTOSCE). The absence of a particular type may be denoted with a `!'.

iippttttll 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. iippvveerrssiioonn ver Matches IP packets whose IP version field is ver.

kkeeeepp-ssttaattee

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) vari-

ables), and the lifetime is refreshed every time a matching packet is found. llaayyeerr22 Matches only layer2 packets, i.e. those passed to iippffww from etherdemux() and etheroutputframe().

lliimmiitt {ssrrcc-aaddddrr | ssrrcc-ppoorrtt | ddsstt-aaddddrr | ddsstt-ppoorrtt} 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.

{{ MMAACC | mmaacc }} dst-mac src-mac

Match packets with a given dst-mac and src-mac addresses, speci-

fied as the aannyy keyword (matching 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.

mmaacc-ttyyppee 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 ppoorrtt nnuummbbeerrss (i.e. one or more comma-separated single val-

ues or ranges). You can use symbolic names for known values such

as vlan, ipv4, ipv6. Values can be entered as decimal or hexa-

decimal (if prefixed by 0x), and they are always printed as hexa-

decimal (unless the -NN option is used, in which case symbolic

resolution will be attempted). pprroottoo protocol Matches packets with the corresponding IPv4 protocol. rreeccvv | xxmmiitt | vviiaa {ifX | if** | ipno | any}

Matches packets received, transmitted or going through, respec-

tively, the interface specified by exact name (ifX), by device name (if*), by IP address, or through some interface. The vviiaa keyword causes the interface to always be checked. If rreeccvv or xxmmiitt is used instead of vviiaa, 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 rreeccvv interface can be tested on either incoming or outgoing packets, while the xxmmiitt interface can only be tested on outgoing packets. So oouutt is required (and iinn is invalid) whenever xxmmiitt 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 interface. sseettuupp Matches TCP packets that have the SYN bit set but no ACK bit. This is the short form of ``tcpflags syn,!ack''.

ssrrcc-iipp ip-address

Matches IP packets whose source IP is one of the address(es) specified as argument.

ssrrcc-ppoorrtt ports

Matches IP packets whose source port is one of the port(s) speci-

fied as argument. ttccppaacckk ack TCP packets only. Match if the TCP header acknowledgment number field is set to ack. ttccppffllaaggss spec TCP packets only. Match if the TCP header contains the comma separated list of flags specified in spec. The supported TCP flags are: ffiinn, ssyynn, rrsstt, ppsshh, aacckk and uurrgg. The absence of a particular flag may be denoted with a `!'. A rule which contains a ttccppffllaaggss specification can never match a fragmented packet which has a

non-zero offset. See the ffrraagg option for details on matching

fragmented packets. ttccppsseeqq seq TCP packets only. Match if the TCP header sequence number field is set to seq. ttccppwwiinn win TCP packets only. Match if the TCP header window field is set to win. ttccppooppttiioonnss spec TCP packets only. Match if the TCP header contains the comma separated list of options specified in spec. The supported TCP options are: mmssss (maximum segment size), wwiinnddooww (tcp window advertisement), ssaacckk (selective ack), ttss (rfc1323 timestamp) and cccc (rfc1644 t/tcp connection count). The absence of a particular option may be denoted with a `!'. uuiidd user Match all TCP or UDP packets sent by or received for a user. A user may be matched by name or identification number. vveerrrreevvppaatthh For incoming packets, a routing table lookup is done on the packet's source address. If the interface on which the packet entered the system matches the outgoing interface for the route, the packet matches. If the interfaces do not match up, the packet does not match. All outgoing packets or packets with no incoming interface match. The name and functionality of the option is intentionally similar to the Cisco IOS command:

ip verify unicast reverse-path

This option can be used to make anti-spoofing rules.

SSEETTSS OOFF RRUULLEESS 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 sseett NN attribute when entering a new rule. Sets can be individually and atomically

enabled or disabled, so this mechanism permits an easy way to store mul-

tiple configurations of the firewall and quickly (and atomically) switch between them. The command to enable/disable sets is iippffww sseett [ddiissaabbllee number ...] [eennaabbllee number ...]

where multiple eennaabbllee or ddiissaabbllee sections can be specified. Command exe-

cution is atomic on all the sets specified in the command. By default, all sets are enabled. When you disable a set, its rules behave as if they do not exist in the firewall configuration, with only one exception: dynamic rules created from a rule before it had been disabled will still be active until they expire. In order to delete dynamic rules you have to explicitly delete the parent rule which generated them. The set number of rules can be changed with the command

iippffww sseett mmoovvee {rruullee rule-number | old-set} ttoo new-set

Also, you can atomically swap two rulesets with the command

iippffww sseett sswwaapp first-set second-set

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

SSTTAATTEEFFUULL FFIIRREEWWAALLLL Stateful operation is a way for the firewall to dynamically create rules for specific flows when packets that match a given pattern are detected.

Support for stateful operation comes through the cchheecckk-ssttaattee, kkeeeepp-ssttaattee

and lliimmiitt options of rruulleess..

Dynamic rules are created when a packet matches a kkeeeepp-ssttaattee or lliimmiitt

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 cchheecckk-ssttaattee,,

kkeeeepp-ssttaattee or lliimmiitt 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 configura-

tion, 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 ssyyssccttll 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.

TTRRAAFFFFIICC SSHHAAPPEERR ((DDUUMMMMYYNNEETT)) CCOONNFFIIGGUURRAATTIIOONN iippffww is also the user interface for the dummynet(4) traffic shaper. dduummmmyynneett operates by first using the firewall to classify packets and divide them into flows, using any match pattern that can be used in iippffww 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 dif-

ferent 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 Queueing) policy, which is an effi-

cient 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 to their weights. Note that weights are not pri-

orities; 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:

ppiippee number ccoonnffiigg pipe-configuration

qquueeuuee number ccoonnffiigg queue-configuration

The following parameters can be configured for a pipe: bbww bandwidth | device Bandwidth, measured in [KK|MM]{bbiitt//ss|BByyttee//ss}. 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).

ddeellaayy 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: ppiippee pipenr 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. wweeiigghhtt 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:

bbuucckkeettss 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.hashsize, allowed range is 16 to 65536.

mmaasskk mask-specifier

Packets sent to a given pipe or queue by an iippffww rule can be fur-

ther classified into multiple flows, each of which is then sent to

a different dynamic pipe or queue. A flow identifier is con-

structed by masking the IP addresses, ports and protocol types as specified with the mmaasskk 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 match-

ing 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:

ddsstt-iipp mask, ssrrcc-iipp mask, ddsstt-ppoorrtt mask, ssrrcc-ppoorrtt mask, pprroottoo mask

or aallll, where the latter means all bits in all fields are significant. nnooeerrrroorr 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 experimental setups where you want to simulate loss or congestion at a remote router.

ppllrr 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. qquueeuuee {slots | sizeKKbbyytteess} Queue size, in slots or KKBByytteess. 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 inter-

face with its 16KB packets. rreedd | ggrreedd wq/minth/maxth/maxp

Make use of the RED (Random Early Detection) queue management algo-

rithm. wq and maxp are floating point numbers between 0 and 1 (0

not included), while minth and maxth are integer numbers specify-

ing 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.redlookupdepth 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.redavgpktsize specifies the expected average packet size (defaults to 512, must be greater than zero) net.inet.ip.dummynet.redmaxpktsize specifies the expected maximum packet size, only used when queue thresholds are in bytes (defaults to 1500, must be greater than zero). CCHHEECCKKLLIISSTT Here are some important points to consider when designing your rules:

++oo Remember that you filter both packets going iinn and oouutt. Most connec-

tions 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/changerules.sh.

++oo Don't forget the loopback interface. FFIINNEE PPOOIINNTTSS

++oo There are circumstances where fragmented datagrams are uncondition-

ally 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

iippffww is probably not as straightforward as you would think. I recom-

mend 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 iippffww 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). PPAACCKKEETT DDIIVVEERRSSIIOONN 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. SSYYSSCCTTLL VVAARRIIAABBLLEESS A set of sysctl(8) variables controls the behaviour of the firewall and associated modules ( dduummmmyynneett,, bbrriiddggee ). 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 traf-

fic. You can disable this by setting the variable to 0, in which case the pipes/queues will only be deleted when the threshold is reached. net.inet.ip.dummynet.hashsize: 64 Default size of the hash table used for dynamic pipes/queues.

This value is used when no bbuucckkeettss option is specified when con-

figuring a pipe/queue. net.inet.ip.dummynet.maxchainlen: 16 Target value for the maximum number of pipes/queues in a hash bucket. The product mmaaxxcchhaaiinnlleenn**hhaasshhssiizzee is used to determine the threshold over which empty pipes/queues will be expired even when nneett..iinneett..iipp..dduummmmyynneett..eexxppiirree==00. net.inet.ip.dummynet.redlookupdepth: 256 net.inet.ip.dummynet.redavgpktsize: 512 net.inet.ip.dummynet.redmaxpktsize: 1500 Parameters used in the computations of the drop probability for the RED algorithm. net.inet.ip.fw.autoincstep: 100

Delta between rule numbers when auto-generating them. The value

must be in the range 1..1000. This variable is only present in iippffww22, the delta is hardwired to 100 in iippffww11. net.inet.ip.fw.currdynbuckets: net.inet.ip.fw.dynbuckets The current number of buckets in the hash table for dynamic rules (readonly). net.inet.ip.fw.debug: 1 Controls debugging messages produced by iippffww. net.inet.ip.fw.dynbuckets: 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 fflluusshh command to make sure that the hash table is resized. net.inet.ip.fw.dyncount: 3

Current number of dynamic rules (read-only).

net.inet.ip.fw.dynkeepalive: 1

Enables generation of keepalive packets for kkeeeepp-ssttaattee rules on

TCP sessions. A keepalive is generated to both sides of the con-

nection every 5 seconds for the last 20 seconds of the lifetime of the rule. net.inet.ip.fw.dynmax: 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.dynacklifetime: 300 net.inet.ip.fw.dynsynlifetime: 20 net.inet.ip.fw.dynfinlifetime: 1 net.inet.ip.fw.dynrstlifetime: 1 net.inet.ip.fw.dynudplifetime: 5 net.inet.ip.fw.dynshortlifetime: 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 dynfinlifetime and dynrstlifetime must be strictly lower

than 5 seconds, the period of repetition of keepalives. The fire-

wall 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.onepass: 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.verboselimit: 0 Limits the number of messages produced by a verbose firewall.

net.link.ether.ipfw: 0

Controls whether layer-2 packets are passed to iippffww. Default is

no.

net.link.ether.bridgeipfw: 0

Controls whether bridged packets are passed to iippffww. Default is no.

UUSSIINNGG IIPPFFWW22 IINN FFrreeeeBBSSDD-SSTTAABBLLEE

iippffww22 is standard in FreeBSD CURRENT, whereas FreeBSD STABLE still uses iippffww11 unless the kernel is compiled with ooppttiioonnss IIPPFFWW22, and //ssbbiinn//iippffww

and //uussrr//lliibb//lliibbaalliiaass are recompiled with -DDIIPPFFWW22 and reinstalled (the

same effect can be achieved by adding IIPPFFWW22==TTRRUUEE to //eettcc//mmaakkee..ccoonnff before a buildworld). IIPPFFWW22 EENNHHAANNCCEEMMEENNTTSS This Section lists the features that have been introduced in iippffww22 which were not present in iippffww11. 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

iippffww11 does not support the -n flag (only test syntax), nor it

allows spaces after commas or supports all rule fields in a sin-

gle argument.

Handling of non-IPv4 packets

iippffww11 will silently accept all non-IPv4 packets (which iippffww11 will

only see when net.link.ether.bridgeipfw=1). iippffww22 will filter

all packets (including non-IPv4 ones) according to the ruleset.

To achieve the same behaviour as iippffww11 you can use the following as the very first rule in your ruleset:

ipfw add 1 allow layer2 not mac-type ip

The llaayyeerr22 option might seem redundant, but it is necessary -

packets passed to the firewall from layer3 will not have a MAC

header, so the mmaacc-ttyyppee iipp pattern will always fail on them, and

the nnoott operator will make this rule into a pass-all.

Addresses iippffww11 does not supports address sets or lists of addresses. Port specifications iippffww11 only allows one port range when specifying TCP and UDP ports, and is limited to 10 entries instead of the 15 allowed by iippffww22. Also, in iippffww11 you can only specify ports when the rule is requesting ttccpp or uuddpp packets. With iippffww22 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, iippffww11 allowed the first port entry to be specified as

port:mask where mask can be an arbitrary 16-bit mask. This syn-

tax is of questionable usefulness and it is not supported anymore in iippffww22.

Or-blocks

iippffww11 does not support Or-blocks.

keepalives iippffww11 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 iippffww11 does not implement sets of rules.

MAC header filtering and Layer-2 firewalling.

iippffww11 does not implement filtering on MAC header fields, nor is it invoked on packets from eetthheerrddeemmuuxx(()) and

eetthheerroouuttppuuttffrraammee(()).. The sysctl variable net.link.ether.ipfw has

no effect there. Options In iippffww11, the following options only accept a single value as an argument: iippiidd,, iipplleenn,, iippttttll The following options are not implemented by iippffww11:

ddsstt-iipp,, ddsstt-ppoorrtt,, llaayyeerr22,, mmaacc,, mmaacc-ttyyppee,, ssrrcc-iipp,, ssrrcc-ppoorrtt..

Additionally, the RELENG4 version of iippffww11 does not implement the following options: iippiidd,, iipplleenn,, iipppprreecceeddeennccee,, iippttooss,, iippttttll,, iippvveerrssiioonn,, ttccppaacckk,, ttccppsseeqq,, ttccppwwiinn. Dummynet options The following option for dduummmmyynneett pipes/queues is not supported: nnooeerrrroorr. EEXXAAMMPPLLEESS There are far too many possible uses of iippffww so this Section will only give a small set of examples. BBAASSIICC PPAACCKKEETT FFIILLTTEERRIINNGG This command adds an entry which denies all tcp packets from

cracker.evil.org to the telnet port of wolf.tambov.su from being for-

warded 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 sseettuupp rules only for selected source/destination pairs. All other SYN packets will be rejected by the final ddeennyy rule. If you administer one or more subnets, you can take advantage of the

iippffww22 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 iippffww11 syntax would require a separate rule for each IP in the above example.

The vveerrrreevvppaatthh 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. DDYYNNAAMMIICC RRUULLEESS 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 connec-

tion which start with a regular SYN packet coming from the inside of our network. Dynamic rules are checked when encountering the first

cchheecckk-ssttaattee or kkeeeepp-ssttaattee rule. A cchheecckk-ssttaattee 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 fol-

lowing 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 lliisstt 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

TTRRAAFFFFIICC SSHHAAPPIINNGG The following rules show some of the applications of iippffww 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 act-

ing 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 oouutt modifier so that the rule is not used twice.

Remember in fact that iippffww rules are checked both on incoming and outgo-

ing packets.

Should we want to simulate a bidirectional link with bandwidth limita-

tions, 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 who is connected only through a slow link. You should not use only one pipe for both directions, unless

you want to simulate a half-duplex medium (e.g. 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 manage-

ment 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 band-

width:

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 iippffww 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 SSEETTSS OOFF RRUULLEESS 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" ter-

minates, and your ruleset will be left active. Otherwise, e.g. if you

cannot access your box, the ruleset will be disabled after the sleep ter-

minates thus restoring the previous situation.

BUGS

The syntax has grown over the years and sometimes it might be confusing. Unfortunately, backward compatibility 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 ddiivveerrtt or tteeee 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 tteeee 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 sockaddrin (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 ddiivveerrtt 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 iippffww utility first appeared in FreeBSD 2.0. dummynet(4) was intro-

duced in FreeBSD 2.2.8. Stateful extensions were introduced in FreeBSD 4.0. iippffww22 was introduced in Summer 2002. Darwin August 13, 2002 Darwin