1.\" 2.\" $FreeBSD$ 3.\" 4.Dd August 13, 2005 5.Dt IPFW 8 6.Os 7.Sh NAME 8.Nm ipfw 9.Nd IP firewall and traffic shaper control program 10.Sh SYNOPSIS 11.Nm 12.Op Fl cq 13.Cm add 14.Ar rule 15.Nm 16.Op Fl acdefnNStT 17.Brq Cm list | show 18.Op Ar rule | first-last ... 19.Nm 20.Op Fl f | q 21.Cm flush 22.Nm 23.Op Fl q 24.Brq Cm delete | zero | resetlog 25.Op Cm set 26.Op Ar number ... 27.Nm 28.Cm enable 29.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 30.Nm 31.Cm disable 32.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 33.Pp 34.Nm 35.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 36.Nm 37.Cm set move 38.Op Cm rule 39.Ar number Cm to Ar number 40.Nm 41.Cm set swap Ar number number 42.Nm 43.Cm set show 44.Pp 45.Nm 46.Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value 47.Nm 48.Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen 49.Nm 50.Cm table Ar number Cm flush 51.Nm 52.Cm table Ar number Cm list 53.Pp 54.Nm 55.Brq Cm pipe | queue 56.Ar number 57.Cm config 58.Ar config-options 59.Nm 60.Op Fl s Op Ar field 61.Brq Cm pipe | queue 62.Brq Cm delete | list | show 63.Op Ar number ... 64.Pp 65.Nm 66.Op Fl cfnNqS 67.Oo 68.Fl p Ar preproc 69.Oo 70.Ar preproc-flags 71.Oc 72.Oc 73.Ar pathname 74.Sh DESCRIPTION 75The 76.Nm 77utility is the user interface for controlling the 78.Xr ipfw 4 79firewall and the 80.Xr dummynet 4 81traffic shaper in 82.Fx . 83.Pp 84An 85.Nm 86configuration, or 87.Em ruleset , 88is made of a list of 89.Em rules 90numbered from 1 to 65535. 91Packets are passed to 92.Nm 93from a number of different places in the protocol stack 94(depending on the source and destination of the packet, 95it is possible that 96.Nm 97is invoked multiple times on the same packet). 98The packet passed to the firewall is compared 99against each of the rules in the firewall 100.Em ruleset . 101When a match is found, the action corresponding to the 102matching rule is performed. 103.Pp 104Depending on the action and certain system settings, packets 105can be reinjected into the firewall at some rule after the 106matching one for further processing. 107.Pp 108An 109.Nm 110ruleset always includes a 111.Em default 112rule (numbered 65535) which cannot be modified or deleted, 113and matches all packets. 114The action associated with the 115.Em default 116rule can be either 117.Cm deny 118or 119.Cm allow 120depending on how the kernel is configured. 121.Pp 122If the ruleset includes one or more rules with the 123.Cm keep-state 124or 125.Cm limit 126option, then 127.Nm 128assumes a 129.Em stateful 130behaviour, i.e., upon a match it will create dynamic rules matching 131the exact parameters (addresses and ports) of the matching packet. 132.Pp 133These dynamic rules, which have a limited lifetime, are checked 134at the first occurrence of a 135.Cm check-state , 136.Cm keep-state 137or 138.Cm limit 139rule, and are typically used to open the firewall on-demand to 140legitimate traffic only. 141See the 142.Sx STATEFUL FIREWALL 143and 144.Sx EXAMPLES 145Sections below for more information on the stateful behaviour of 146.Nm . 147.Pp 148All rules (including dynamic ones) have a few associated counters: 149a packet count, a byte count, a log count and a timestamp 150indicating the time of the last match. 151Counters can be displayed or reset with 152.Nm 153commands. 154.Pp 155Rules can be added with the 156.Cm add 157command; deleted individually or in groups with the 158.Cm delete 159command, and globally (except those in set 31) with the 160.Cm flush 161command; displayed, optionally with the content of the 162counters, using the 163.Cm show 164and 165.Cm list 166commands. 167Finally, counters can be reset with the 168.Cm zero 169and 170.Cm resetlog 171commands. 172.Pp 173Also, each rule belongs to one of 32 different 174.Em sets 175, and there are 176.Nm 177commands to atomically manipulate sets, such as enable, 178disable, swap sets, move all rules in a set to another 179one, delete all rules in a set. 180These can be useful to 181install temporary configurations, or to test them. 182See Section 183.Sx SETS OF RULES 184for more information on 185.Em sets . 186.Pp 187The following options are available: 188.Bl -tag -width indent 189.It Fl a 190While listing, show counter values. 191The 192.Cm show 193command just implies this option. 194.It Fl b 195Only show the action and the comment, not the body of a rule. 196Implies 197.Fl c . 198.It Fl c 199When entering or showing rules, print them in compact form, 200i.e., without the optional "ip from any to any" string 201when this does not carry any additional information. 202.It Fl d 203While listing, show dynamic rules in addition to static ones. 204.It Fl e 205While listing, if the 206.Fl d 207option was specified, also show expired dynamic rules. 208.It Fl f 209Do not ask for confirmation for commands that can cause problems 210if misused, 211.No i.e. Cm flush . 212If there is no tty associated with the process, this is implied. 213.It Fl n 214Only check syntax of the command strings, without actually passing 215them to the kernel. 216.It Fl N 217Try to resolve addresses and service names in output. 218.It Fl q 219While 220.Cm add Ns ing , 221.Cm zero Ns ing , 222.Cm resetlog Ns ging 223or 224.Cm flush Ns ing , 225be quiet about actions 226(implies 227.Fl f ) . 228This is useful for adjusting rules by executing multiple 229.Nm 230commands in a script 231(e.g., 232.Ql sh\ /etc/rc.firewall ) , 233or by processing a file of many 234.Nm 235rules across a remote login session. 236If a 237.Cm flush 238is performed in normal (verbose) mode (with the default kernel 239configuration), it prints a message. 240Because all rules are flushed, the message might not be delivered 241to the login session, causing the remote login session to be closed 242and the remainder of the ruleset to not be processed. 243Access to the console would then be required to recover. 244.It Fl S 245While listing rules, show the 246.Em set 247each rule belongs to. 248If this flag is not specified, disabled rules will not be 249listed. 250.It Fl s Op Ar field 251While listing pipes, sort according to one of the four 252counters (total or current packets or bytes). 253.It Fl t 254While listing, show last match timestamp (converted with ctime()). 255.It Fl T 256While listing, show last match timestamp (as seconds from the epoch). 257This form can be more convenient for postprocessing by scripts. 258.El 259.Pp 260To ease configuration, rules can be put into a file which is 261processed using 262.Nm 263as shown in the last synopsis line. 264An absolute 265.Ar pathname 266must be used. 267The file will be read line by line and applied as arguments to the 268.Nm 269utility. 270.Pp 271Optionally, a preprocessor can be specified using 272.Fl p Ar preproc 273where 274.Ar pathname 275is to be piped through. 276Useful preprocessors include 277.Xr cpp 1 278and 279.Xr m4 1 . 280If 281.Ar preproc 282does not start with a slash 283.Pq Ql / 284as its first character, the usual 285.Ev PATH 286name search is performed. 287Care should be taken with this in environments where not all 288file systems are mounted (yet) by the time 289.Nm 290is being run (e.g.\& when they are mounted over NFS). 291Once 292.Fl p 293has been specified, any additional arguments as passed on to the preprocessor 294for interpretation. 295This allows for flexible configuration files (like conditionalizing 296them on the local hostname) and the use of macros to centralize 297frequently required arguments like IP addresses. 298.Pp 299The 300.Nm 301.Cm pipe 302and 303.Cm queue 304commands are used to configure the traffic shaper, as shown in the 305.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 306Section below. 307.Pp 308If the world and the kernel get out of sync the 309.Nm 310ABI may break, preventing you from being able to add any rules. 311This can 312adversely effect the booting process. 313You can use 314.Nm 315.Cm disable 316.Cm firewall 317to temporarily disable the firewall to regain access to the network, 318allowing you to fix the problem. 319.Sh PACKET FLOW 320A packet is checked against the active ruleset in multiple places 321in the protocol stack, under control of several sysctl variables. 322These places and variables are shown below, and it is important to 323have this picture in mind in order to design a correct ruleset. 324.Bd -literal -offset indent 325 ^ to upper layers V 326 | | 327 +----------->-----------+ 328 ^ V 329 [ip(6)_input] [ip(6)_output] net.inet.ip.fw.enable=1 330 | | 331 ^ V 332 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 333 | | 334 +-->--[bdg_forward]-->--+ net.link.ether.bridge_ipfw=1 335 ^ V 336 | to devices | 337.Ed 338.Pp 339As can be noted from the above picture, the number of 340times the same packet goes through the firewall can 341vary between 0 and 4 depending on packet source and 342destination, and system configuration. 343.Pp 344Note that as packets flow through the stack, headers can be 345stripped or added to it, and so they may or may not be available 346for inspection. 347E.g., incoming packets will include the MAC header when 348.Nm 349is invoked from 350.Cm ether_demux() , 351but the same packets will have the MAC header stripped off when 352.Nm 353is invoked from 354.Cm ip_input() 355or 356.Cm ip6_input() . 357.Pp 358Also note that each packet is always checked against the complete ruleset, 359irrespective of the place where the check occurs, or the source of the packet. 360If a rule contains some match patterns or actions which are not valid 361for the place of invocation (e.g.\& trying to match a MAC header within 362.Cm ip_input 363or 364.Cm ip6_input ), 365the match pattern will not match, but a 366.Cm not 367operator in front of such patterns 368.Em will 369cause the pattern to 370.Em always 371match on those packets. 372It is thus the responsibility of 373the programmer, if necessary, to write a suitable ruleset to 374differentiate among the possible places. 375.Cm skipto 376rules can be useful here, as an example: 377.Bd -literal -offset indent 378# packets from ether_demux or bdg_forward 379ipfw add 10 skipto 1000 all from any to any layer2 in 380# packets from ip_input 381ipfw add 10 skipto 2000 all from any to any not layer2 in 382# packets from ip_output 383ipfw add 10 skipto 3000 all from any to any not layer2 out 384# packets from ether_output_frame 385ipfw add 10 skipto 4000 all from any to any layer2 out 386.Ed 387.Pp 388(yes, at the moment there is no way to differentiate between 389ether_demux and bdg_forward). 390.Sh SYNTAX 391In general, each keyword or argument must be provided as 392a separate command line argument, with no leading or trailing 393spaces. 394Keywords are case-sensitive, whereas arguments may 395or may not be case-sensitive depending on their nature 396(e.g.\& uid's are, hostnames are not). 397.Pp 398In 399.Nm ipfw2 400you can introduce spaces after commas ',' to make 401the line more readable. 402You can also put the entire 403command (including flags) into a single argument. 404E.g., the following forms are equivalent: 405.Bd -literal -offset indent 406ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 407ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 408ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" 409.Ed 410.Sh RULE FORMAT 411The format of 412.Nm 413rules is the following: 414.Bd -ragged -offset indent 415.Op Ar rule_number 416.Op Cm set Ar set_number 417.Op Cm prob Ar match_probability 418.br 419.Ar " " action 420.Op Cm log Op Cm logamount Ar number 421.Op Cm altq Ar queue 422.Ar body 423.Ed 424.Pp 425where the body of the rule specifies which information is used 426for filtering packets, among the following: 427.Pp 428.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact 429.It Layer-2 header fields 430When available 431.It IPv4 and IPv6 Protocol 432TCP, UDP, ICMP, etc. 433.It Source and dest. addresses and ports 434.It Direction 435See Section 436.Sx PACKET FLOW 437.It Transmit and receive interface 438By name or address 439.It Misc. IP header fields 440Version, type of service, datagram length, identification, 441fragment flag (non-zero IP offset), 442Time To Live 443.It IP options 444.It IPv6 Extension headers 445Fragmentation, Hop-by-Hop options, 446source routing, IPSec options. 447.It IPv6 Flow-ID 448.It Misc. TCP header fields 449TCP flags (SYN, FIN, ACK, RST, etc.), 450sequence number, acknowledgment number, 451window 452.It TCP options 453.It ICMP types 454for ICMP packets 455.It ICMP6 types 456for ICMP6 packets 457.It User/group ID 458When the packet can be associated with a local socket. 459.It Divert status 460Whether a packet came from a divert socket (e.g., 461.Xr natd 8 ) . 462.El 463.Pp 464Note that some of the above information, e.g.\& source MAC or IP addresses and 465TCP/UDP ports, could easily be spoofed, so filtering on those fields 466alone might not guarantee the desired results. 467.Bl -tag -width indent 468.It Ar rule_number 469Each rule is associated with a 470.Ar rule_number 471in the range 1..65535, with the latter reserved for the 472.Em default 473rule. 474Rules are checked sequentially by rule number. 475Multiple rules can have the same number, in which case they are 476checked (and listed) according to the order in which they have 477been added. 478If a rule is entered without specifying a number, the kernel will 479assign one in such a way that the rule becomes the last one 480before the 481.Em default 482rule. 483Automatic rule numbers are assigned by incrementing the last 484non-default rule number by the value of the sysctl variable 485.Ar net.inet.ip.fw.autoinc_step 486which defaults to 100. 487If this is not possible (e.g.\& because we would go beyond the 488maximum allowed rule number), the number of the last 489non-default value is used instead. 490.It Cm set Ar set_number 491Each rule is associated with a 492.Ar set_number 493in the range 0..31. 494Sets can be individually disabled and enabled, so this parameter 495is of fundamental importance for atomic ruleset manipulation. 496It can be also used to simplify deletion of groups of rules. 497If a rule is entered without specifying a set number, 498set 0 will be used. 499.br 500Set 31 is special in that it cannot be disabled, 501and rules in set 31 are not deleted by the 502.Nm ipfw flush 503command (but you can delete them with the 504.Nm ipfw delete set 31 505command). 506Set 31 is also used for the 507.Em default 508rule. 509.It Cm prob Ar match_probability 510A match is only declared with the specified probability 511(floating point number between 0 and 1). 512This can be useful for a number of applications such as 513random packet drop or 514(in conjunction with 515.Xr dummynet 4 ) 516to simulate the effect of multiple paths leading to out-of-order 517packet delivery. 518.Pp 519Note: this condition is checked before any other condition, including 520ones such as keep-state or check-state which might have side effects. 521.It Cm log Op Cm logamount Ar number 522When a packet matches a rule with the 523.Cm log 524keyword, a message will be 525logged to 526.Xr syslogd 8 527with a 528.Dv LOG_SECURITY 529facility. 530The logging only occurs if the sysctl variable 531.Em net.inet.ip.fw.verbose 532is set to 1 533(which is the default when the kernel is compiled with 534.Dv IPFIREWALL_VERBOSE ) 535and the number of packets logged so far for that 536particular rule does not exceed the 537.Cm logamount 538parameter. 539If no 540.Cm logamount 541is specified, the limit is taken from the sysctl variable 542.Em net.inet.ip.fw.verbose_limit . 543In both cases, a value of 0 removes the logging limit. 544.Pp 545Once the limit is reached, logging can be re-enabled by 546clearing the logging counter or the packet counter for that entry, see the 547.Cm resetlog 548command. 549.Pp 550Note: logging is done after all other packet matching conditions 551have been successfully verified, and before performing the final 552action (accept, deny, etc.) on the packet. 553.It Cm altq Ar queue 554When a packet matches a rule with the 555.Cm altq 556keyword, the ALTQ identifier for the given 557.Ar queue 558(see 559.Xr altq 4 ) 560will be attached. 561Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, 562and not being rejected or going to divert sockets. 563Note that if there is insufficient memory at the time the packet is 564processed, it will not be tagged, so it is wise to make your ALTQ 565"default" queue policy account for this. 566If multiple 567.Cm altq 568rules match a single packet, only the first one adds the ALTQ classification 569tag. 570In doing so, traffic may be shaped by using 571.Cm count Cm altq Ar queue 572rules for classification early in the ruleset, then later applying 573the filtering decision. 574For example, 575.Cm check-state 576and 577.Cm keep-state 578rules may come later and provide the actual filtering decisions in 579addition to the fallback ALTQ tag. 580.Pp 581You must run 582.Xr pfctl 8 583to set up the queues before IPFW will be able to look them up by name, 584and if the ALTQ disciplines are rearranged, the rules in containing the 585queue identifiers in the kernel will likely have gone stale and need 586to be reloaded. 587Stale queue identifiers will probably result in misclassification. 588.Pp 589All system ALTQ processing can be turned on or off via 590.Nm 591.Cm enable Ar altq 592and 593.Nm 594.Cm disable Ar altq . 595The usage of 596.Em net.inet.ip.fw.one_pass 597is irrelevant to ALTQ traffic shaping, as the actual rule action is followed 598always after adding an ALTQ tag. 599.El 600.Ss RULE ACTIONS 601A rule can be associated with one of the following actions, which 602will be executed when the packet matches the body of the rule. 603.Bl -tag -width indent 604.It Cm allow | accept | pass | permit 605Allow packets that match rule. 606The search terminates. 607.It Cm check-state 608Checks the packet against the dynamic ruleset. 609If a match is found, execute the action associated with 610the rule which generated this dynamic rule, otherwise 611move to the next rule. 612.br 613.Cm Check-state 614rules do not have a body. 615If no 616.Cm check-state 617rule is found, the dynamic ruleset is checked at the first 618.Cm keep-state 619or 620.Cm limit 621rule. 622.It Cm count 623Update counters for all packets that match rule. 624The search continues with the next rule. 625.It Cm deny | drop 626Discard packets that match this rule. 627The search terminates. 628.It Cm divert Ar port 629Divert packets that match this rule to the 630.Xr divert 4 631socket bound to port 632.Ar port . 633The search terminates. 634.It Cm fwd | forward Ar ipaddr Ns Op , Ns Ar port 635Change the next-hop on matching packets to 636.Ar ipaddr , 637which can be an IP address or a host name. 638The search terminates if this rule matches. 639.Pp 640If 641.Ar ipaddr 642is a local address, then matching packets will be forwarded to 643.Ar port 644(or the port number in the packet if one is not specified in the rule) 645on the local machine. 646.br 647If 648.Ar ipaddr 649is not a local address, then the port number 650(if specified) is ignored, and the packet will be 651forwarded to the remote address, using the route as found in 652the local routing table for that IP. 653.br 654A 655.Ar fwd 656rule will not match layer-2 packets (those received 657on ether_input, ether_output, or bridged). 658.br 659The 660.Cm fwd 661action does not change the contents of the packet at all. 662In particular, the destination address remains unmodified, so 663packets forwarded to another system will usually be rejected by that system 664unless there is a matching rule on that system to capture them. 665For packets forwarded locally, 666the local address of the socket will be 667set to the original destination address of the packet. 668This makes the 669.Xr netstat 1 670entry look rather weird but is intended for 671use with transparent proxy servers. 672.Pp 673To enable 674.Cm fwd 675a custom kernel needs to be compiled with the option 676.Cd "options IPFIREWALL_FORWARD" . 677With the additional option 678.Cd "options IPFIREWALL_FORWARD_EXTENDED" 679all safeguards are removed and it also makes it possible to redirect 680packets destined to locally configured IP addresses. 681Please note that such rules apply to locally generated packets as 682well and great care is required to ensure proper behaviour for 683automatically generated packets like ICMP message size exceeded 684and others. 685.It Cm pipe Ar pipe_nr 686Pass packet to a 687.Xr dummynet 4 688.Dq pipe 689(for bandwidth limitation, delay, etc.). 690See the 691.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 692Section for further information. 693The search terminates; however, on exit from the pipe and if 694the 695.Xr sysctl 8 696variable 697.Em net.inet.ip.fw.one_pass 698is not set, the packet is passed again to the firewall code 699starting from the next rule. 700.It Cm queue Ar queue_nr 701Pass packet to a 702.Xr dummynet 4 703.Dq queue 704(for bandwidth limitation using WF2Q+). 705.It Cm reject 706(Deprecated). 707Synonym for 708.Cm unreach host . 709.It Cm reset 710Discard packets that match this rule, and if the 711packet is a TCP packet, try to send a TCP reset (RST) notice. 712The search terminates. 713.It Cm reset6 714Discard packets that match this rule, and if the 715packet is a TCP packet, try to send a TCP reset (RST) notice. 716The search terminates. 717.It Cm skipto Ar number 718Skip all subsequent rules numbered less than 719.Ar number . 720The search continues with the first rule numbered 721.Ar number 722or higher. 723.It Cm tee Ar port 724Send a copy of packets matching this rule to the 725.Xr divert 4 726socket bound to port 727.Ar port . 728The search continues with the next rule. 729.It Cm unreach Ar code 730Discard packets that match this rule, and try to send an ICMP 731unreachable notice with code 732.Ar code , 733where 734.Ar code 735is a number from 0 to 255, or one of these aliases: 736.Cm net , host , protocol , port , 737.Cm needfrag , srcfail , net-unknown , host-unknown , 738.Cm isolated , net-prohib , host-prohib , tosnet , 739.Cm toshost , filter-prohib , host-precedence 740or 741.Cm precedence-cutoff . 742The search terminates. 743.It Cm unreach6 Ar code 744Discard packets that match this rule, and try to send an ICMPv6 745unreachable notice with code 746.Ar code , 747where 748.Ar code 749is a number from 0, 1, 3 or 4, or one of these aliases: 750.Cm no-route, admin-prohib, address 751or 752.Cm port . 753The search terminates. 754.It Cm netgraph Ar cookie 755Divert packet into netgraph with given 756.Ar cookie . 757The search terminates. 758If packet is later returned from netgraph it is either 759accepted or continues with the next rule, depending on 760.Em net.inet.ip.fw.one_pass 761sysctl variable. 762.It Cm ngtee Ar cookie 763A copy of packet is diverted into netgraph, original 764packet is either accepted or continues with the next rule, depending on 765.Em net.inet.ip.fw.one_pass 766sysctl variable. 767See 768.Xr ng_ipfw 4 769for more information on 770.Cm netgraph 771and 772.Cm ngtee 773actions. 774.El 775.Ss RULE BODY 776The body of a rule contains zero or more patterns (such as 777specific source and destination addresses or ports, 778protocol options, incoming or outgoing interfaces, etc.) 779that the packet must match in order to be recognised. 780In general, the patterns are connected by (implicit) 781.Cm and 782operators -- i.e., all must match in order for the 783rule to match. 784Individual patterns can be prefixed by the 785.Cm not 786operator to reverse the result of the match, as in 787.Pp 788.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any" 789.Pp 790Additionally, sets of alternative match patterns 791.Pq Em or-blocks 792can be constructed by putting the patterns in 793lists enclosed between parentheses ( ) or braces { }, and 794using the 795.Cm or 796operator as follows: 797.Pp 798.Dl "ipfw add 100 allow ip from { x or not y or z } to any" 799.Pp 800Only one level of parentheses is allowed. 801Beware that most shells have special meanings for parentheses 802or braces, so it is advisable to put a backslash \\ in front of them 803to prevent such interpretations. 804.Pp 805The body of a rule must in general include a source and destination 806address specifier. 807The keyword 808.Ar any 809can be used in various places to specify that the content of 810a required field is irrelevant. 811.Pp 812The rule body has the following format: 813.Bd -ragged -offset indent 814.Op Ar proto Cm from Ar src Cm to Ar dst 815.Op Ar options 816.Ed 817.Pp 818The first part (proto from src to dst) is for backward 819compatibility with 820.Nm ipfw1 . 821In 822.Nm ipfw2 823any match pattern (including MAC headers, IP protocols, 824addresses and ports) can be specified in the 825.Ar options 826section. 827.Pp 828Rule fields have the following meaning: 829.Bl -tag -width indent 830.It Ar proto : protocol | Cm { Ar protocol Cm or ... } 831.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number 832An IP protocol specified by number or name 833(for a complete list see 834.Pa /etc/protocols ) , 835or one of the following keywords: 836.Bl -tag -width indent 837.It Cm ip4 | ipv4 838Matches IPv4 packets. 839.It Cm ip6 | ipv6 840Matches IPv6 packets. 841.It Cm ip | all 842Matches any packet. 843.El 844.Pp 845The 846.Cm { Ar protocol Cm or ... } 847format (an 848.Em or-block ) 849is provided for convenience only but its use is deprecated. 850.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports 851An address (or a list, see below) 852optionally followed by 853.Ar ports 854specifiers. 855.Pp 856The second format 857.Em ( or-block 858with multiple addresses) is provided for convenience only and 859its use is discouraged. 860.It Ar addr : Oo Cm not Oc Bro 861.Cm any | me | me6 862.Cm table Ns Pq Ar number Ns Op , Ns Ar value 863.Ar | addr-list | addr-set 864.Brc 865.It Cm any 866matches any IP address. 867.It Cm me 868matches any IP address configured on an interface in the system. 869.It Cm me6 870matches any IPv6 address configured on an interface in the system. 871The address list is evaluated at the time the packet is 872analysed. 873.It Cm table Ns Pq Ar number Ns Op , Ns Ar value 874Matches any IPv4 address for which an entry exists in the lookup table 875.Ar number . 876If an optional 32-bit unsigned 877.Ar value 878is also specified, an entry will match only if it has this value. 879See the 880.Sx LOOKUP TABLES 881section below for more information on lookup tables. 882.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list 883.It Ar ip-addr : 884A host or subnet address specified in one of the following ways: 885.Bl -tag -width indent 886.It Ar numeric-ip | hostname 887Matches a single IPv4 address, specified as dotted-quad or a hostname. 888Hostnames are resolved at the time the rule is added to the firewall list. 889.It Ar addr Ns / Ns Ar masklen 890Matches all addresses with base 891.Ar addr 892(specified as an IP address or a hostname) 893and mask width of 894.Cm masklen 895bits. 896As an example, 1.2.3.4/25 will match 897all IP numbers from 1.2.3.0 to 1.2.3.127 . 898.It Ar addr Ns : Ns Ar mask 899Matches all addresses with base 900.Ar addr 901(specified as an IP address or a hostname) 902and the mask of 903.Ar mask , 904specified as a dotted quad. 905As an example, 1.2.3.4:255.0.255.0 will match 9061.*.3.*. 907This form is advised only for non-contiguous 908masks. 909It is better to resort to the 910.Ar addr Ns / Ns Ar masklen 911format for contiguous masks, which is more compact and less 912error-prone. 913.El 914.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm } 915.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list 916Matches all addresses with base address 917.Ar addr 918(specified as an IP address or a hostname) 919and whose last byte is in the list between braces { } . 920Note that there must be no spaces between braces and 921numbers (spaces after commas are allowed). 922Elements of the list can be specified as single entries 923or ranges. 924The 925.Ar masklen 926field is used to limit the size of the set of addresses, 927and can have any value between 24 and 32. 928If not specified, 929it will be assumed as 24. 930.br 931This format is particularly useful to handle sparse address sets 932within a single rule. 933Because the matching occurs using a 934bitmask, it takes constant time and dramatically reduces 935the complexity of rulesets. 936.br 937As an example, an address specified as 1.2.3.4/24{128,35-55,89} 938will match the following IP addresses: 939.br 9401.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . 941.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list 942.It Ar ip6-addr : 943A host or subnet specified one of the following ways: 944.Pp 945.Bl -tag -width indent 946.It Ar numeric-ip | hostname 947Matches a single IPv6 address as allowed by 948.Xr inet_pton 3 949or a hostname. 950Hostnames are resolved at the time the rule is added to the firewall 951list. 952.It Ar addr Ns / Ns Ar masklen 953Matches all IPv6 addresses with base 954.Ar addr 955(specified as allowed by 956.Xr inet_pton 957or a hostname) 958and mask width of 959.Cm masklen 960bits. 961.El 962.Pp 963No support for sets of IPv6 addresses is provided because IPv6 addresses 964are typically random past the initial prefix. 965.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports 966For protocols which support port numbers (such as TCP and UDP), optional 967.Cm ports 968may be specified as one or more ports or port ranges, separated 969by commas but no spaces, and an optional 970.Cm not 971operator. 972The 973.Ql \&- 974notation specifies a range of ports (including boundaries). 975.Pp 976Service names (from 977.Pa /etc/services ) 978may be used instead of numeric port values. 979The length of the port list is limited to 30 ports or ranges, 980though one can specify larger ranges by using an 981.Em or-block 982in the 983.Cm options 984section of the rule. 985.Pp 986A backslash 987.Pq Ql \e 988can be used to escape the dash 989.Pq Ql - 990character in a service name (from a shell, the backslash must be 991typed twice to avoid the shell itself interpreting it as an escape 992character). 993.Pp 994.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any" 995.Pp 996Fragmented packets which have a non-zero offset (i.e., not the first 997fragment) will never match a rule which has one or more port 998specifications. 999See the 1000.Cm frag 1001option for details on matching fragmented packets. 1002.El 1003.Ss RULE OPTIONS (MATCH PATTERNS) 1004Additional match patterns can be used within 1005rules. 1006Zero or more of these so-called 1007.Em options 1008can be present in a rule, optionally prefixed by the 1009.Cm not 1010operand, and possibly grouped into 1011.Em or-blocks . 1012.Pp 1013The following match patterns can be used (listed in alphabetical order): 1014.Bl -tag -width indent 1015.It Cm // this is a comment. 1016Inserts the specified text as a comment in the rule. 1017Everything following // is considered as a comment and stored in the rule. 1018You can have comment-only rules, which are listed as having a 1019.Cm count 1020action followed by the comment. 1021.It Cm bridged 1022Alias for 1023.Cm layer2 . 1024.It Cm diverted 1025Matches only packets generated by a divert socket. 1026.It Cm diverted-loopback 1027Matches only packets coming from a divert socket back into the IP stack 1028input for delivery. 1029.It Cm diverted-output 1030Matches only packets going from a divert socket back outward to the IP 1031stack output for delivery. 1032.It Cm dst-ip Ar ip-address 1033Matches IPv4 packets whose destination IP is one of the address(es) 1034specified as argument. 1035.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address 1036Matches IPv6 packets whose destination IP is one of the address(es) 1037specified as argument. 1038.It Cm dst-port Ar ports 1039Matches IP packets whose destination port is one of the port(s) 1040specified as argument. 1041.It Cm established 1042Matches TCP packets that have the RST or ACK bits set. 1043.It Cm ext6hdr Ar header 1044Matches IPv6 packets containing the extended header given by 1045.Ar header . 1046Supported headers are: 1047.Pp 1048Fragment, 1049.Pq Cm frag , 1050Hop-to-hop options 1051.Pq Cm hopopt , 1052Source routing 1053.Pq Cm route , 1054Destination options 1055.Pq Cm dstopt , 1056IPSec authentication headers 1057.Pq Cm ah , 1058and IPSec encapsulated security payload headers 1059.Pq Cm esp . 1060.It Cm flow-id Ar labels 1061Matches IPv6 packets containing any of the flow labels given in 1062.Ar labels . 1063.Ar labels 1064is a comma seperate list of numeric flow labels. 1065.It Cm frag 1066Matches packets that are fragments and not the first 1067fragment of an IP datagram. 1068Note that these packets will not have 1069the next protocol header (e.g.\& TCP, UDP) so options that look into 1070these headers cannot match. 1071.It Cm gid Ar group 1072Matches all TCP or UDP packets sent by or received for a 1073.Ar group . 1074A 1075.Ar group 1076may be specified by name or number. 1077.It Cm jail Ar prisonID 1078Matches all TCP or UDP packets sent by or received for the 1079jail whos prison ID is 1080.Ar prisonID . 1081.It Cm icmptypes Ar types 1082Matches ICMP packets whose ICMP type is in the list 1083.Ar types . 1084The list may be specified as any combination of 1085individual types (numeric) separated by commas. 1086.Em Ranges are not allowed. 1087The supported ICMP types are: 1088.Pp 1089echo reply 1090.Pq Cm 0 , 1091destination unreachable 1092.Pq Cm 3 , 1093source quench 1094.Pq Cm 4 , 1095redirect 1096.Pq Cm 5 , 1097echo request 1098.Pq Cm 8 , 1099router advertisement 1100.Pq Cm 9 , 1101router solicitation 1102.Pq Cm 10 , 1103time-to-live exceeded 1104.Pq Cm 11 , 1105IP header bad 1106.Pq Cm 12 , 1107timestamp request 1108.Pq Cm 13 , 1109timestamp reply 1110.Pq Cm 14 , 1111information request 1112.Pq Cm 15 , 1113information reply 1114.Pq Cm 16 , 1115address mask request 1116.Pq Cm 17 1117and address mask reply 1118.Pq Cm 18 . 1119.It Cm icmp6types Ar types 1120Matches ICMP6 packets whose ICMP6 type is in the list of 1121.Ar types . 1122The list may be specified as any combination of 1123individual types (numeric) separated by commas. 1124.Em Ranges are not allowed. 1125.It Cm in | out 1126Matches incoming or outgoing packets, respectively. 1127.Cm in 1128and 1129.Cm out 1130are mutually exclusive (in fact, 1131.Cm out 1132is implemented as 1133.Cm not in Ns No ). 1134.It Cm ipid Ar id-list 1135Matches IPv4 packets whose 1136.Cm ip_id 1137field has value included in 1138.Ar id-list , 1139which is either a single value or a list of values or ranges 1140specified in the same way as 1141.Ar ports . 1142.It Cm iplen Ar len-list 1143Matches IP packets whose total length, including header and data, is 1144in the set 1145.Ar len-list , 1146which is either a single value or a list of values or ranges 1147specified in the same way as 1148.Ar ports . 1149.It Cm ipoptions Ar spec 1150Matches packets whose IPv4 header contains the comma separated list of 1151options specified in 1152.Ar spec . 1153The supported IP options are: 1154.Pp 1155.Cm ssrr 1156(strict source route), 1157.Cm lsrr 1158(loose source route), 1159.Cm rr 1160(record packet route) and 1161.Cm ts 1162(timestamp). 1163The absence of a particular option may be denoted 1164with a 1165.Ql \&! . 1166.It Cm ipprecedence Ar precedence 1167Matches IPv4 packets whose precedence field is equal to 1168.Ar precedence . 1169.It Cm ipsec 1170Matches packets that have IPSEC history associated with them 1171(i.e., the packet comes encapsulated in IPSEC, the kernel 1172has IPSEC support and IPSEC_FILTERGIF option, and can correctly 1173decapsulate it). 1174.Pp 1175Note that specifying 1176.Cm ipsec 1177is different from specifying 1178.Cm proto Ar ipsec 1179as the latter will only look at the specific IP protocol field, 1180irrespective of IPSEC kernel support and the validity of the IPSEC data. 1181.Pp 1182Further note that this flag is silently ignored in kernels without 1183IPSEC support. 1184It does not affect rule processing when given and the 1185rules are handled as if with no 1186.Cm ipsec 1187flag. 1188.It Cm iptos Ar spec 1189Matches IPv4 packets whose 1190.Cm tos 1191field contains the comma separated list of 1192service types specified in 1193.Ar spec . 1194The supported IP types of service are: 1195.Pp 1196.Cm lowdelay 1197.Pq Dv IPTOS_LOWDELAY , 1198.Cm throughput 1199.Pq Dv IPTOS_THROUGHPUT , 1200.Cm reliability 1201.Pq Dv IPTOS_RELIABILITY , 1202.Cm mincost 1203.Pq Dv IPTOS_MINCOST , 1204.Cm congestion 1205.Pq Dv IPTOS_CE . 1206The absence of a particular type may be denoted 1207with a 1208.Ql \&! . 1209.It Cm ipttl Ar ttl-list 1210Matches IPv4 packets whose time to live is included in 1211.Ar ttl-list , 1212which is either a single value or a list of values or ranges 1213specified in the same way as 1214.Ar ports . 1215.It Cm ipversion Ar ver 1216Matches IP packets whose IP version field is 1217.Ar ver . 1218.It Cm keep-state 1219Upon a match, the firewall will create a dynamic rule, whose 1220default behaviour is to match bidirectional traffic between 1221source and destination IP/port using the same protocol. 1222The rule has a limited lifetime (controlled by a set of 1223.Xr sysctl 8 1224variables), and the lifetime is refreshed every time a matching 1225packet is found. 1226.It Cm layer2 1227Matches only layer2 packets, i.e., those passed to 1228.Nm 1229from ether_demux() and ether_output_frame(). 1230.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N 1231The firewall will only allow 1232.Ar N 1233connections with the same 1234set of parameters as specified in the rule. 1235One or more 1236of source and destination addresses and ports can be 1237specified. 1238Currently, 1239only IPv4 flows are supported. 1240.It Cm { MAC | mac } Ar dst-mac src-mac 1241Match packets with a given 1242.Ar dst-mac 1243and 1244.Ar src-mac 1245addresses, specified as the 1246.Cm any 1247keyword (matching any MAC address), or six groups of hex digits 1248separated by colons, 1249and optionally followed by a mask indicating the significant bits. 1250The mask may be specified using either of the following methods: 1251.Bl -enum -width indent 1252.It 1253A slash 1254.Pq / 1255followed by the number of significant bits. 1256For example, an address with 33 significant bits could be specified as: 1257.Pp 1258.Dl "MAC 10:20:30:40:50:60/33 any" 1259.Pp 1260.It 1261An ampersand 1262.Pq & 1263followed by a bitmask specified as six groups of hex digits separated 1264by colons. 1265For example, an address in which the last 16 bits are significant could 1266be specified as: 1267.Pp 1268.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any" 1269.Pp 1270Note that the ampersand character has a special meaning in many shells 1271and should generally be escaped. 1272.Pp 1273.El 1274Note that the order of MAC addresses (destination first, 1275source second) is 1276the same as on the wire, but the opposite of the one used for 1277IP addresses. 1278.It Cm mac-type Ar mac-type 1279Matches packets whose Ethernet Type field 1280corresponds to one of those specified as argument. 1281.Ar mac-type 1282is specified in the same way as 1283.Cm port numbers 1284(i.e., one or more comma-separated single values or ranges). 1285You can use symbolic names for known values such as 1286.Em vlan , ipv4, ipv6 . 1287Values can be entered as decimal or hexadecimal (if prefixed by 0x), 1288and they are always printed as hexadecimal (unless the 1289.Cm -N 1290option is used, in which case symbolic resolution will be attempted). 1291.It Cm proto Ar protocol 1292Matches packets with the corresponding IP protocol. 1293.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any 1294Matches packets received, transmitted or going through, 1295respectively, the interface specified by exact name 1296.Ns No ( Ar ifX Ns No ), 1297by device name 1298.Ns No ( Ar if Ns Ar * Ns No ), 1299by IP address, or through some interface. 1300.Pp 1301The 1302.Cm via 1303keyword causes the interface to always be checked. 1304If 1305.Cm recv 1306or 1307.Cm xmit 1308is used instead of 1309.Cm via , 1310then only the receive or transmit interface (respectively) 1311is checked. 1312By specifying both, it is possible to match packets based on 1313both receive and transmit interface, e.g.: 1314.Pp 1315.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1" 1316.Pp 1317The 1318.Cm recv 1319interface can be tested on either incoming or outgoing packets, 1320while the 1321.Cm xmit 1322interface can only be tested on outgoing packets. 1323So 1324.Cm out 1325is required (and 1326.Cm in 1327is invalid) whenever 1328.Cm xmit 1329is used. 1330.Pp 1331A packet may not have a receive or transmit interface: packets 1332originating from the local host have no receive interface, 1333while packets destined for the local host have no transmit 1334interface. 1335.It Cm setup 1336Matches TCP packets that have the SYN bit set but no ACK bit. 1337This is the short form of 1338.Dq Li tcpflags\ syn,!ack . 1339.It Cm src-ip Ar ip-address 1340Matches IPv4 packets whose source IP is one of the address(es) 1341specified as an argument. 1342.It Cm src-ip6 Ar ip6-address 1343Matches IPv6 packets whose source IP is one of the address(es) 1344specified as an argument. 1345.It Cm src-port Ar ports 1346Matches IP packets whose source port is one of the port(s) 1347specified as argument. 1348.It Cm tcpack Ar ack 1349TCP packets only. 1350Match if the TCP header acknowledgment number field is set to 1351.Ar ack . 1352.It Cm tcpdatalen Ar tcpdatalen-list 1353Matches TCP packets whose length of TCP data is 1354.Ar tcpdatalen-list , 1355which is either a single value or a list of values or ranges 1356specified in the same way as 1357.Ar ports . 1358.It Cm tcpflags Ar spec 1359TCP packets only. 1360Match if the TCP header contains the comma separated list of 1361flags specified in 1362.Ar spec . 1363The supported TCP flags are: 1364.Pp 1365.Cm fin , 1366.Cm syn , 1367.Cm rst , 1368.Cm psh , 1369.Cm ack 1370and 1371.Cm urg . 1372The absence of a particular flag may be denoted 1373with a 1374.Ql \&! . 1375A rule which contains a 1376.Cm tcpflags 1377specification can never match a fragmented packet which has 1378a non-zero offset. 1379See the 1380.Cm frag 1381option for details on matching fragmented packets. 1382.It Cm tcpseq Ar seq 1383TCP packets only. 1384Match if the TCP header sequence number field is set to 1385.Ar seq . 1386.It Cm tcpwin Ar win 1387TCP packets only. 1388Match if the TCP header window field is set to 1389.Ar win . 1390.It Cm tcpoptions Ar spec 1391TCP packets only. 1392Match if the TCP header contains the comma separated list of 1393options specified in 1394.Ar spec . 1395The supported TCP options are: 1396.Pp 1397.Cm mss 1398(maximum segment size), 1399.Cm window 1400(tcp window advertisement), 1401.Cm sack 1402(selective ack), 1403.Cm ts 1404(rfc1323 timestamp) and 1405.Cm cc 1406(rfc1644 t/tcp connection count). 1407The absence of a particular option may be denoted 1408with a 1409.Ql \&! . 1410.It Cm uid Ar user 1411Match all TCP or UDP packets sent by or received for a 1412.Ar user . 1413A 1414.Ar user 1415may be matched by name or identification number. 1416.It Cm verrevpath 1417For incoming packets, 1418a routing table lookup is done on the packet's source address. 1419If the interface on which the packet entered the system matches the 1420outgoing interface for the route, 1421the packet matches. 1422If the interfaces do not match up, 1423the packet does not match. 1424All outgoing packets or packets with no incoming interface match. 1425.Pp 1426The name and functionality of the option is intentionally similar to 1427the Cisco IOS command: 1428.Pp 1429.Dl ip verify unicast reverse-path 1430.Pp 1431This option can be used to make anti-spoofing rules to reject all 1432packets with source addresses not from this interface. 1433See also the option 1434.Cm antispoof . 1435.It Cm versrcreach 1436For incoming packets, 1437a routing table lookup is done on the packet's source address. 1438If a route to the source address exists, but not the default route 1439or a blackhole/reject route, the packet matches. 1440Otherwise, the packet does not match. 1441All outgoing packets match. 1442.Pp 1443The name and functionality of the option is intentionally similar to 1444the Cisco IOS command: 1445.Pp 1446.Dl ip verify unicast source reachable-via any 1447.Pp 1448This option can be used to make anti-spoofing rules to reject all 1449packets whose source address is unreachable. 1450.It Cm antispoof 1451For incoming packets, the packet's source address is checked if it 1452belongs to a directly connected network. 1453If the network is directly connected, then the interface the packet 1454came on in is compared to the interface the network is connected to. 1455When incoming interface and directly connected interface are not the 1456same, the packet does not match. 1457Otherwise, the packet does match. 1458All outgoing packets match. 1459.Pp 1460This option can be used to make anti-spoofing rules to reject all 1461packets that pretend to be from a directly connected network but do 1462not come in through that interface. 1463This option is similar to but more restricted than 1464.Cm verrevpath 1465because it engages only on packets with source addresses of directly 1466connected networks instead of all source addresses. 1467.El 1468.Sh LOOKUP TABLES 1469Lookup tables are useful to handle large sparse address sets, 1470typically from a hundred to several thousands of entries. 1471There may be up to 128 different lookup tables, numbered 0 to 127. 1472.Pp 1473Each entry is represented by an 1474.Ar addr Ns Op / Ns Ar masklen 1475and will match all addresses with base 1476.Ar addr 1477(specified as an IP address or a hostname) 1478and mask width of 1479.Ar masklen 1480bits. 1481If 1482.Ar masklen 1483is not specified, it defaults to 32. 1484When looking up an IP address in a table, the most specific 1485entry will match. 1486Associated with each entry is a 32-bit unsigned 1487.Ar value , 1488which can optionally be checked by a rule matching code. 1489When adding an entry, if 1490.Ar value 1491is not specified, it defaults to 0. 1492.Pp 1493An entry can be added to a table 1494.Pq Cm add , 1495removed from a table 1496.Pq Cm delete , 1497a table can be examined 1498.Pq Cm list 1499or flushed 1500.Pq Cm flush . 1501.Pp 1502Internally, each table is stored in a Radix tree, the same way as 1503the routing table (see 1504.Xr route 4 ) . 1505.Pp 1506Lookup tables currently support IPv4 addresses only. 1507.Sh SETS OF RULES 1508Each rule belongs to one of 32 different 1509.Em sets 1510, numbered 0 to 31. 1511Set 31 is reserved for the default rule. 1512.Pp 1513By default, rules are put in set 0, unless you use the 1514.Cm set N 1515attribute when entering a new rule. 1516Sets can be individually and atomically enabled or disabled, 1517so this mechanism permits an easy way to store multiple configurations 1518of the firewall and quickly (and atomically) switch between them. 1519The command to enable/disable sets is 1520.Bd -ragged -offset indent 1521.Nm 1522.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 1523.Ed 1524.Pp 1525where multiple 1526.Cm enable 1527or 1528.Cm disable 1529sections can be specified. 1530Command execution is atomic on all the sets specified in the command. 1531By default, all sets are enabled. 1532.Pp 1533When you disable a set, its rules behave as if they do not exist 1534in the firewall configuration, with only one exception: 1535.Bd -ragged -offset indent 1536dynamic rules created from a rule before it had been disabled 1537will still be active until they expire. 1538In order to delete 1539dynamic rules you have to explicitly delete the parent rule 1540which generated them. 1541.Ed 1542.Pp 1543The set number of rules can be changed with the command 1544.Bd -ragged -offset indent 1545.Nm 1546.Cm set move 1547.Brq Cm rule Ar rule-number | old-set 1548.Cm to Ar new-set 1549.Ed 1550.Pp 1551Also, you can atomically swap two rulesets with the command 1552.Bd -ragged -offset indent 1553.Nm 1554.Cm set swap Ar first-set second-set 1555.Ed 1556.Pp 1557See the 1558.Sx EXAMPLES 1559Section on some possible uses of sets of rules. 1560.Sh STATEFUL FIREWALL 1561Stateful operation is a way for the firewall to dynamically 1562create rules for specific flows when packets that 1563match a given pattern are detected. 1564Support for stateful 1565operation comes through the 1566.Cm check-state , keep-state 1567and 1568.Cm limit 1569options of 1570.Nm rules. 1571.Pp 1572Dynamic rules are created when a packet matches a 1573.Cm keep-state 1574or 1575.Cm limit 1576rule, causing the creation of a 1577.Em dynamic 1578rule which will match all and only packets with 1579a given 1580.Em protocol 1581between a 1582.Em src-ip/src-port dst-ip/dst-port 1583pair of addresses 1584.Em ( src 1585and 1586.Em dst 1587are used here only to denote the initial match addresses, but they 1588are completely equivalent afterwards). 1589Dynamic rules will be checked at the first 1590.Cm check-state, keep-state 1591or 1592.Cm limit 1593occurrence, and the action performed upon a match will be the same 1594as in the parent rule. 1595.Pp 1596Note that no additional attributes other than protocol and IP addresses 1597and ports are checked on dynamic rules. 1598.Pp 1599The typical use of dynamic rules is to keep a closed firewall configuration, 1600but let the first TCP SYN packet from the inside network install a 1601dynamic rule for the flow so that packets belonging to that session 1602will be allowed through the firewall: 1603.Pp 1604.Dl "ipfw add check-state" 1605.Dl "ipfw add allow tcp from my-subnet to any setup keep-state" 1606.Dl "ipfw add deny tcp from any to any" 1607.Pp 1608A similar approach can be used for UDP, where an UDP packet coming 1609from the inside will install a dynamic rule to let the response through 1610the firewall: 1611.Pp 1612.Dl "ipfw add check-state" 1613.Dl "ipfw add allow udp from my-subnet to any keep-state" 1614.Dl "ipfw add deny udp from any to any" 1615.Pp 1616Dynamic rules expire after some time, which depends on the status 1617of the flow and the setting of some 1618.Cm sysctl 1619variables. 1620See Section 1621.Sx SYSCTL VARIABLES 1622for more details. 1623For TCP sessions, dynamic rules can be instructed to periodically 1624send keepalive packets to refresh the state of the rule when it is 1625about to expire. 1626.Pp 1627See Section 1628.Sx EXAMPLES 1629for more examples on how to use dynamic rules. 1630.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 1631.Nm 1632is also the user interface for the 1633.Xr dummynet 4 1634traffic shaper. 1635.Pp 1636.Nm dummynet 1637operates by first using the firewall to classify packets and divide them into 1638.Em flows , 1639using any match pattern that can be used in 1640.Nm 1641rules. 1642Depending on local policies, a flow can contain packets for a single 1643TCP connection, or from/to a given host, or entire subnet, or a 1644protocol type, etc. 1645.Pp 1646Packets belonging to the same flow are then passed to either of two 1647different objects, which implement the traffic regulation: 1648.Bl -hang -offset XXXX 1649.It Em pipe 1650A pipe emulates a link with given bandwidth, propagation delay, 1651queue size and packet loss rate. 1652Packets are queued in front of the pipe as they come out from the classifier, 1653and then transferred to the pipe according to the pipe's parameters. 1654.Pp 1655.It Em queue 1656A queue 1657is an abstraction used to implement the WF2Q+ 1658(Worst-case Fair Weighted Fair Queueing) policy, which is 1659an efficient variant of the WFQ policy. 1660.br 1661The queue associates a 1662.Em weight 1663and a reference pipe to each flow, and then all backlogged (i.e., 1664with packets queued) flows linked to the same pipe share the pipe's 1665bandwidth proportionally to their weights. 1666Note that weights are not priorities; a flow with a lower weight 1667is still guaranteed to get its fraction of the bandwidth even if a 1668flow with a higher weight is permanently backlogged. 1669.Pp 1670.El 1671In practice, 1672.Em pipes 1673can be used to set hard limits to the bandwidth that a flow can use, whereas 1674.Em queues 1675can be used to determine how different flow share the available bandwidth. 1676.Pp 1677The 1678.Em pipe 1679and 1680.Em queue 1681configuration commands are the following: 1682.Bd -ragged -offset indent 1683.Cm pipe Ar number Cm config Ar pipe-configuration 1684.Pp 1685.Cm queue Ar number Cm config Ar queue-configuration 1686.Ed 1687.Pp 1688The following parameters can be configured for a pipe: 1689.Pp 1690.Bl -tag -width indent -compact 1691.It Cm bw Ar bandwidth | device 1692Bandwidth, measured in 1693.Sm off 1694.Op Cm K | M 1695.Brq Cm bit/s | Byte/s . 1696.Sm on 1697.Pp 1698A value of 0 (default) means unlimited bandwidth. 1699The unit must immediately follow the number, as in 1700.Pp 1701.Dl "ipfw pipe 1 config bw 300Kbit/s" 1702.Pp 1703If a device name is specified instead of a numeric value, as in 1704.Pp 1705.Dl "ipfw pipe 1 config bw tun0" 1706.Pp 1707then the transmit clock is supplied by the specified device. 1708At the moment only the 1709.Xr tun 4 1710device supports this 1711functionality, for use in conjunction with 1712.Xr ppp 8 . 1713.Pp 1714.It Cm delay Ar ms-delay 1715Propagation delay, measured in milliseconds. 1716The value is rounded to the next multiple of the clock tick 1717(typically 10ms, but it is a good practice to run kernels 1718with 1719.Dq "options HZ=1000" 1720to reduce 1721the granularity to 1ms or less). 1722Default value is 0, meaning no delay. 1723.El 1724.Pp 1725The following parameters can be configured for a queue: 1726.Pp 1727.Bl -tag -width indent -compact 1728.It Cm pipe Ar pipe_nr 1729Connects a queue to the specified pipe. 1730Multiple queues (with the same or different weights) can be connected to 1731the same pipe, which specifies the aggregate rate for the set of queues. 1732.Pp 1733.It Cm weight Ar weight 1734Specifies the weight to be used for flows matching this queue. 1735The weight must be in the range 1..100, and defaults to 1. 1736.El 1737.Pp 1738Finally, the following parameters can be configured for both 1739pipes and queues: 1740.Pp 1741.Bl -tag -width XXXX -compact 1742.Pp 1743.It Cm buckets Ar hash-table-size 1744Specifies the size of the hash table used for storing the 1745various queues. 1746Default value is 64 controlled by the 1747.Xr sysctl 8 1748variable 1749.Em net.inet.ip.dummynet.hash_size , 1750allowed range is 16 to 65536. 1751.Pp 1752.It Cm mask Ar mask-specifier 1753Packets sent to a given pipe or queue by an 1754.Nm 1755rule can be further classified into multiple flows, each of which is then 1756sent to a different 1757.Em dynamic 1758pipe or queue. 1759A flow identifier is constructed by masking the IP addresses, 1760ports and protocol types as specified with the 1761.Cm mask 1762options in the configuration of the pipe or queue. 1763For each different flow identifier, a new pipe or queue is created 1764with the same parameters as the original object, and matching packets 1765are sent to it. 1766.Pp 1767Thus, when 1768.Em dynamic pipes 1769are used, each flow will get the same bandwidth as defined by the pipe, 1770whereas when 1771.Em dynamic queues 1772are used, each flow will share the parent's pipe bandwidth evenly 1773with other flows generated by the same queue (note that other queues 1774with different weights might be connected to the same pipe). 1775.br 1776Available mask specifiers are a combination of one or more of the following: 1777.Pp 1778.Cm dst-ip Ar mask , 1779.Cm dst-ip6 Ar mask , 1780.Cm src-ip Ar mask , 1781.Cm src-ip6 Ar mask , 1782.Cm dst-port Ar mask , 1783.Cm src-port Ar mask , 1784.Cm flow-id Ar mask , 1785.Cm proto Ar mask 1786or 1787.Cm all , 1788.Pp 1789where the latter means all bits in all fields are significant. 1790.Pp 1791.It Cm noerror 1792When a packet is dropped by a dummynet queue or pipe, the error 1793is normally reported to the caller routine in the kernel, in the 1794same way as it happens when a device queue fills up. 1795Setting this 1796option reports the packet as successfully delivered, which can be 1797needed for some experimental setups where you want to simulate 1798loss or congestion at a remote router. 1799.Pp 1800.It Cm plr Ar packet-loss-rate 1801Packet loss rate. 1802Argument 1803.Ar packet-loss-rate 1804is a floating-point number between 0 and 1, with 0 meaning no 1805loss, 1 meaning 100% loss. 1806The loss rate is internally represented on 31 bits. 1807.Pp 1808.It Cm queue Brq Ar slots | size Ns Cm Kbytes 1809Queue size, in 1810.Ar slots 1811or 1812.Cm KBytes . 1813Default value is 50 slots, which 1814is the typical queue size for Ethernet devices. 1815Note that for slow speed links you should keep the queue 1816size short or your traffic might be affected by a significant 1817queueing delay. 1818E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit 1819or 20s of queue on a 30Kbit/s pipe. 1820Even worse effects can result if you get packets from an 1821interface with a much larger MTU, e.g.\& the loopback interface 1822with its 16KB packets. 1823.Pp 1824.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p 1825Make use of the RED (Random Early Detection) queue management algorithm. 1826.Ar w_q 1827and 1828.Ar max_p 1829are floating 1830point numbers between 0 and 1 (0 not included), while 1831.Ar min_th 1832and 1833.Ar max_th 1834are integer numbers specifying thresholds for queue management 1835(thresholds are computed in bytes if the queue has been defined 1836in bytes, in slots otherwise). 1837The 1838.Xr dummynet 4 1839also supports the gentle RED variant (gred). 1840Three 1841.Xr sysctl 8 1842variables can be used to control the RED behaviour: 1843.Bl -tag -width indent 1844.It Em net.inet.ip.dummynet.red_lookup_depth 1845specifies the accuracy in computing the average queue 1846when the link is idle (defaults to 256, must be greater than zero) 1847.It Em net.inet.ip.dummynet.red_avg_pkt_size 1848specifies the expected average packet size (defaults to 512, must be 1849greater than zero) 1850.It Em net.inet.ip.dummynet.red_max_pkt_size 1851specifies the expected maximum packet size, only used when queue 1852thresholds are in bytes (defaults to 1500, must be greater than zero). 1853.El 1854.El 1855.Pp 1856When used with IPv6 data, dummynet currently has several limitations. 1857First, debug.mpsafenet=0 must be set. 1858Second, the information necessicary to route link-local packets to an 1859interface is not avalable after processing by dummynet so those packets 1860are dropped in the output path. 1861Care should be taken to insure that link-local packets are not passed to 1862dummynet. 1863.Sh CHECKLIST 1864Here are some important points to consider when designing your 1865rules: 1866.Bl -bullet 1867.It 1868Remember that you filter both packets going 1869.Cm in 1870and 1871.Cm out . 1872Most connections need packets going in both directions. 1873.It 1874Remember to test very carefully. 1875It is a good idea to be near the console when doing this. 1876If you cannot be near the console, 1877use an auto-recovery script such as the one in 1878.Pa /usr/share/examples/ipfw/change_rules.sh . 1879.It 1880Do not forget the loopback interface. 1881.El 1882.Sh FINE POINTS 1883.Bl -bullet 1884.It 1885There are circumstances where fragmented datagrams are unconditionally 1886dropped. 1887TCP packets are dropped if they do not contain at least 20 bytes of 1888TCP header, UDP packets are dropped if they do not contain a full 8 1889byte UDP header, and ICMP packets are dropped if they do not contain 18904 bytes of ICMP header, enough to specify the ICMP type, code, and 1891checksum. 1892These packets are simply logged as 1893.Dq pullup failed 1894since there may not be enough good data in the packet to produce a 1895meaningful log entry. 1896.It 1897Another type of packet is unconditionally dropped, a TCP packet with a 1898fragment offset of one. 1899This is a valid packet, but it only has one use, to try 1900to circumvent firewalls. 1901When logging is enabled, these packets are 1902reported as being dropped by rule -1. 1903.It 1904If you are logged in over a network, loading the 1905.Xr kld 4 1906version of 1907.Nm 1908is probably not as straightforward as you would think. 1909I recommend the following command line: 1910.Bd -literal -offset indent 1911kldload ipfw && \e 1912ipfw add 32000 allow ip from any to any 1913.Ed 1914.Pp 1915Along the same lines, doing an 1916.Bd -literal -offset indent 1917ipfw flush 1918.Ed 1919.Pp 1920in similar surroundings is also a bad idea. 1921.It 1922The 1923.Nm 1924filter list may not be modified if the system security level 1925is set to 3 or higher 1926(see 1927.Xr init 8 1928for information on system security levels). 1929.El 1930.Sh PACKET DIVERSION 1931A 1932.Xr divert 4 1933socket bound to the specified port will receive all packets 1934diverted to that port. 1935If no socket is bound to the destination port, or if the divert module is 1936not loaded, or if the kernel was not compiled with divert socket support, 1937the packets are dropped. 1938.Sh SYSCTL VARIABLES 1939A set of 1940.Xr sysctl 8 1941variables controls the behaviour of the firewall and 1942associated modules 1943.Pq Nm dummynet , bridge . 1944These are shown below together with their default value 1945(but always check with the 1946.Xr sysctl 8 1947command what value is actually in use) and meaning: 1948.Bl -tag -width indent 1949.It Em net.inet.ip.dummynet.expire : No 1 1950Lazily delete dynamic pipes/queue once they have no pending traffic. 1951You can disable this by setting the variable to 0, in which case 1952the pipes/queues will only be deleted when the threshold is reached. 1953.It Em net.inet.ip.dummynet.hash_size : No 64 1954Default size of the hash table used for dynamic pipes/queues. 1955This value is used when no 1956.Cm buckets 1957option is specified when configuring a pipe/queue. 1958.It Em net.inet.ip.dummynet.max_chain_len : No 16 1959Target value for the maximum number of pipes/queues in a hash bucket. 1960The product 1961.Cm max_chain_len*hash_size 1962is used to determine the threshold over which empty pipes/queues 1963will be expired even when 1964.Cm net.inet.ip.dummynet.expire=0 . 1965.It Em net.inet.ip.dummynet.red_lookup_depth : No 256 1966.It Em net.inet.ip.dummynet.red_avg_pkt_size : No 512 1967.It Em net.inet.ip.dummynet.red_max_pkt_size : No 1500 1968Parameters used in the computations of the drop probability 1969for the RED algorithm. 1970.It Em net.inet.ip.fw.autoinc_step : No 100 1971Delta between rule numbers when auto-generating them. 1972The value must be in the range 1..1000. 1973This variable is only present in 1974.Nm ipfw2 , 1975the delta is hardwired to 100 in 1976.Nm ipfw1 . 1977.It Em net.inet.ip.fw.curr_dyn_buckets : Em net.inet.ip.fw.dyn_buckets 1978The current number of buckets in the hash table for dynamic rules 1979(readonly). 1980.It Em net.inet.ip.fw.debug : No 1 1981Controls debugging messages produced by 1982.Nm . 1983.It Em net.inet.ip.fw.dyn_buckets : No 256 1984The number of buckets in the hash table for dynamic rules. 1985Must be a power of 2, up to 65536. 1986It only takes effect when all dynamic rules have expired, so you 1987are advised to use a 1988.Cm flush 1989command to make sure that the hash table is resized. 1990.It Em net.inet.ip.fw.dyn_count : No 3 1991Current number of dynamic rules 1992(read-only). 1993.It Em net.inet.ip.fw.dyn_keepalive : No 1 1994Enables generation of keepalive packets for 1995.Cm keep-state 1996rules on TCP sessions. 1997A keepalive is generated to both 1998sides of the connection every 5 seconds for the last 20 1999seconds of the lifetime of the rule. 2000.It Em net.inet.ip.fw.dyn_max : No 8192 2001Maximum number of dynamic rules. 2002When you hit this limit, no more dynamic rules can be 2003installed until old ones expire. 2004.It Em net.inet.ip.fw.dyn_ack_lifetime : No 300 2005.It Em net.inet.ip.fw.dyn_syn_lifetime : No 20 2006.It Em net.inet.ip.fw.dyn_fin_lifetime : No 1 2007.It Em net.inet.ip.fw.dyn_rst_lifetime : No 1 2008.It Em net.inet.ip.fw.dyn_udp_lifetime : No 5 2009.It Em net.inet.ip.fw.dyn_short_lifetime : No 30 2010These variables control the lifetime, in seconds, of dynamic 2011rules. 2012Upon the initial SYN exchange the lifetime is kept short, 2013then increased after both SYN have been seen, then decreased 2014again during the final FIN exchange or when a RST is received. 2015Both 2016.Em dyn_fin_lifetime 2017and 2018.Em dyn_rst_lifetime 2019must be strictly lower than 5 seconds, the period of 2020repetition of keepalives. 2021The firewall enforces that. 2022.It Em net.inet.ip.fw.enable : No 1 2023Enables the firewall. 2024Setting this variable to 0 lets you run your machine without 2025firewall even if compiled in. 2026.It Em net.inet.ip.fw.one_pass : No 1 2027When set, the packet exiting from the 2028.Xr dummynet 4 2029pipe or from 2030.Xr ng_ipfw 4 2031node is not passed though the firewall again. 2032Otherwise, after an action, the packet is 2033reinjected into the firewall at the next rule. 2034.It Em net.inet.ip.fw.verbose : No 1 2035Enables verbose messages. 2036.It Em net.inet.ip.fw.verbose_limit : No 0 2037Limits the number of messages produced by a verbose firewall. 2038.It Em net.inet6.ip6.fw.deny_unknown_exthdrs : No 1 2039If enabled packets with unknown IPv6 Extension Headers will be denied. 2040.It Em net.link.ether.ipfw : No 0 2041Controls whether layer-2 packets are passed to 2042.Nm . 2043Default is no. 2044.It Em net.link.ether.bridge_ipfw : No 0 2045Controls whether bridged packets are passed to 2046.Nm . 2047Default is no. 2048.El 2049.Pp 2050.Sh IPFW2 ENHANCEMENTS 2051This Section lists the features that have been introduced in 2052.Nm ipfw2 2053which were not present in 2054.Nm ipfw1 . 2055They are listed in order of the potential impact that they can 2056have in writing your rulesets. 2057You might want to consider using these features in order to 2058write your rulesets in a more efficient way. 2059.Bl -tag -width indent 2060.It Syntax and flags 2061.Nm ipfw1 2062does not support the -n flag (only test syntax), 2063nor does it allow spaces after commas or support all 2064rule fields in a single argument. 2065.Nm ipfw1 2066does not allow the -f flag (force) in conjunction with 2067the -p flag (preprocessor). 2068.Nm ipfw1 2069does not support the -c (compact) flag. 2070.It Handling of non-IPv4 packets 2071.Nm ipfw1 2072will silently accept all non-IPv4 packets (which 2073.Nm ipfw1 2074will only see when 2075.Em net.link.ether.bridge_ipfw=1 ) . 2076.Nm ipfw2 2077will filter all packets (including non-IPv4 ones) according to the ruleset. 2078To achieve the same behaviour as 2079.Nm ipfw1 2080you can use the following as the very first rule in your ruleset: 2081.Pp 2082.Dl "ipfw add 1 allow layer2 not mac-type ip" 2083.Pp 2084The 2085.Cm layer2 2086option might seem redundant, but it is necessary -- packets 2087passed to the firewall from layer3 will not have a MAC header, 2088so the 2089.Cm mac-type ip 2090pattern will always fail on them, and the 2091.Cm not 2092operator will make this rule into a pass-all. 2093.It Addresses 2094.Nm ipfw1 2095does not support address sets or lists of addresses. 2096.Pp 2097.It Port specifications 2098.Nm ipfw1 2099only allows one port range when specifying TCP and UDP ports, and 2100is limited to 10 entries instead of the 30 allowed by 2101.Nm ipfw2 . 2102Also, in 2103.Nm ipfw1 2104you can only specify ports when the rule is requesting 2105.Cm tcp 2106or 2107.Cm udp 2108packets. 2109With 2110.Nm ipfw2 2111you can put port specifications in rules matching all packets, 2112and the match will be attempted only on those packets carrying 2113protocols which include port identifiers. 2114.Pp 2115Finally, 2116.Nm ipfw1 2117allowed the first port entry to be specified as 2118.Ar port:mask 2119where 2120.Ar mask 2121can be an arbitrary 16-bit mask. 2122This syntax is of questionable usefulness and it is not 2123supported anymore in 2124.Nm ipfw2 . 2125.It Or-blocks 2126.Nm ipfw1 2127does not support Or-blocks. 2128.It keepalives 2129.Nm ipfw1 2130does not generate keepalives for stateful sessions. 2131As a consequence, it might cause idle sessions to drop because 2132the lifetime of the dynamic rules expires. 2133.It Sets of rules 2134.Nm ipfw1 2135does not implement sets of rules. 2136.It MAC header filtering and Layer-2 firewalling. 2137.Nm ipfw1 2138does not implement filtering on MAC header fields, nor is it 2139invoked on packets from 2140.Cm ether_demux() 2141and 2142.Cm ether_output_frame(). 2143The sysctl variable 2144.Em net.link.ether.ipfw 2145has no effect there. 2146.It Options 2147In 2148.Nm ipfw1 , 2149the following options only accept a single value as an argument: 2150.Pp 2151.Cm ipid, iplen, ipttl 2152.Pp 2153The following options are not implemented by 2154.Nm ipfw1 : 2155.Pp 2156.Cm dst-ip, dst-port, layer2, mac, mac-type, src-ip, src-port. 2157.Pp 2158Additionally, the RELENG_4 version of 2159.Nm ipfw1 2160does not implement the following options: 2161.Pp 2162.Cm ipid, iplen, ipprecedence, iptos, ipttl, 2163.Cm ipversion, tcpack, tcpseq, tcpwin . 2164.It Dummynet options 2165The following option for 2166.Nm dummynet 2167pipes/queues is not supported: 2168.Cm noerror . 2169.It IPv6 Support 2170There was no IPv6 support in 2171.Nm ipfw1 . 2172.El 2173.Sh EXAMPLES 2174There are far too many possible uses of 2175.Nm 2176so this Section will only give a small set of examples. 2177.Pp 2178.Ss BASIC PACKET FILTERING 2179This command adds an entry which denies all tcp packets from 2180.Em cracker.evil.org 2181to the telnet port of 2182.Em wolf.tambov.su 2183from being forwarded by the host: 2184.Pp 2185.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet" 2186.Pp 2187This one disallows any connection from the entire cracker's 2188network to my host: 2189.Pp 2190.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org" 2191.Pp 2192A first and efficient way to limit access (not using dynamic rules) 2193is the use of the following rules: 2194.Pp 2195.Dl "ipfw add allow tcp from any to any established" 2196.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup" 2197.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup" 2198.Dl "..." 2199.Dl "ipfw add deny tcp from any to any" 2200.Pp 2201The first rule will be a quick match for normal TCP packets, 2202but it will not match the initial SYN packet, which will be 2203matched by the 2204.Cm setup 2205rules only for selected source/destination pairs. 2206All other SYN packets will be rejected by the final 2207.Cm deny 2208rule. 2209.Pp 2210If you administer one or more subnets, you can take advantage of the 2211.Nm ipfw2 2212syntax to specify address sets and or-blocks and write extremely 2213compact rulesets which selectively enable services to blocks 2214of clients, as below: 2215.Pp 2216.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q" 2217.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q" 2218.Dl "" 2219.Dl "ipfw add allow ip from ${goodguys} to any" 2220.Dl "ipfw add deny ip from ${badguys} to any" 2221.Dl "... normal policies ..." 2222.Pp 2223The 2224.Nm ipfw1 2225syntax would require a separate rule for each IP in the above 2226example. 2227.Pp 2228The 2229.Cm verrevpath 2230option could be used to do automated anti-spoofing by adding the 2231following to the top of a ruleset: 2232.Pp 2233.Dl "ipfw add deny ip from any to any not verrevpath in" 2234.Pp 2235This rule drops all incoming packets that appear to be coming to the 2236system on the wrong interface. 2237For example, a packet with a source 2238address belonging to a host on a protected internal network would be 2239dropped if it tried to enter the system from an external interface. 2240.Pp 2241The 2242.Cm antispoof 2243option could be used to do similar but more restricted anti-spoofing 2244by adding the following to the top of a ruleset: 2245.Pp 2246.Dl "ipfw add deny ip from any to any not antispoof in" 2247.Pp 2248This rule drops all incoming packets that appear to be coming from another 2249directly connected system but on the wrong interface. 2250For example, a packet with a source address of 2251.Li 192.168.0.0/24 2252, configured on 2253.Li fxp0 2254, but coming in on 2255.Li fxp1 2256would be dropped. 2257.Ss DYNAMIC RULES 2258In order to protect a site from flood attacks involving fake 2259TCP packets, it is safer to use dynamic rules: 2260.Pp 2261.Dl "ipfw add check-state" 2262.Dl "ipfw add deny tcp from any to any established" 2263.Dl "ipfw add allow tcp from my-net to any setup keep-state" 2264.Pp 2265This will let the firewall install dynamic rules only for 2266those connection which start with a regular SYN packet coming 2267from the inside of our network. 2268Dynamic rules are checked when encountering the first 2269.Cm check-state 2270or 2271.Cm keep-state 2272rule. 2273A 2274.Cm check-state 2275rule should usually be placed near the beginning of the 2276ruleset to minimize the amount of work scanning the ruleset. 2277Your mileage may vary. 2278.Pp 2279To limit the number of connections a user can open 2280you can use the following type of rules: 2281.Pp 2282.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10" 2283.Dl "ipfw add allow tcp from any to me setup limit src-addr 4" 2284.Pp 2285The former (assuming it runs on a gateway) will allow each host 2286on a /24 network to open at most 10 TCP connections. 2287The latter can be placed on a server to make sure that a single 2288client does not use more than 4 simultaneous connections. 2289.Pp 2290.Em BEWARE : 2291stateful rules can be subject to denial-of-service attacks 2292by a SYN-flood which opens a huge number of dynamic rules. 2293The effects of such attacks can be partially limited by 2294acting on a set of 2295.Xr sysctl 8 2296variables which control the operation of the firewall. 2297.Pp 2298Here is a good usage of the 2299.Cm list 2300command to see accounting records and timestamp information: 2301.Pp 2302.Dl ipfw -at list 2303.Pp 2304or in short form without timestamps: 2305.Pp 2306.Dl ipfw -a list 2307.Pp 2308which is equivalent to: 2309.Pp 2310.Dl ipfw show 2311.Pp 2312Next rule diverts all incoming packets from 192.168.2.0/24 2313to divert port 5000: 2314.Pp 2315.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in 2316.Pp 2317.Ss TRAFFIC SHAPING 2318The following rules show some of the applications of 2319.Nm 2320and 2321.Xr dummynet 4 2322for simulations and the like. 2323.Pp 2324This rule drops random incoming packets with a probability 2325of 5%: 2326.Pp 2327.Dl "ipfw add prob 0.05 deny ip from any to any in" 2328.Pp 2329A similar effect can be achieved making use of dummynet pipes: 2330.Pp 2331.Dl "ipfw add pipe 10 ip from any to any" 2332.Dl "ipfw pipe 10 config plr 0.05" 2333.Pp 2334We can use pipes to artificially limit bandwidth, e.g.\& on a 2335machine acting as a router, if we want to limit traffic from 2336local clients on 192.168.2.0/24 we do: 2337.Pp 2338.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2339.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes" 2340.Pp 2341note that we use the 2342.Cm out 2343modifier so that the rule is not used twice. 2344Remember in fact that 2345.Nm 2346rules are checked both on incoming and outgoing packets. 2347.Pp 2348Should we want to simulate a bidirectional link with bandwidth 2349limitations, the correct way is the following: 2350.Pp 2351.Dl "ipfw add pipe 1 ip from any to any out" 2352.Dl "ipfw add pipe 2 ip from any to any in" 2353.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes" 2354.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes" 2355.Pp 2356The above can be very useful, e.g.\& if you want to see how 2357your fancy Web page will look for a residential user who 2358is connected only through a slow link. 2359You should not use only one pipe for both directions, unless 2360you want to simulate a half-duplex medium (e.g.\& AppleTalk, 2361Ethernet, IRDA). 2362It is not necessary that both pipes have the same configuration, 2363so we can also simulate asymmetric links. 2364.Pp 2365Should we want to verify network performance with the RED queue 2366management algorithm: 2367.Pp 2368.Dl "ipfw add pipe 1 ip from any to any" 2369.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1" 2370.Pp 2371Another typical application of the traffic shaper is to 2372introduce some delay in the communication. 2373This can significantly affect applications which do a lot of Remote 2374Procedure Calls, and where the round-trip-time of the 2375connection often becomes a limiting factor much more than 2376bandwidth: 2377.Pp 2378.Dl "ipfw add pipe 1 ip from any to any out" 2379.Dl "ipfw add pipe 2 ip from any to any in" 2380.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s" 2381.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s" 2382.Pp 2383Per-flow queueing can be useful for a variety of purposes. 2384A very simple one is counting traffic: 2385.Pp 2386.Dl "ipfw add pipe 1 tcp from any to any" 2387.Dl "ipfw add pipe 1 udp from any to any" 2388.Dl "ipfw add pipe 1 ip from any to any" 2389.Dl "ipfw pipe 1 config mask all" 2390.Pp 2391The above set of rules will create queues (and collect 2392statistics) for all traffic. 2393Because the pipes have no limitations, the only effect is 2394collecting statistics. 2395Note that we need 3 rules, not just the last one, because 2396when 2397.Nm 2398tries to match IP packets it will not consider ports, so we 2399would not see connections on separate ports as different 2400ones. 2401.Pp 2402A more sophisticated example is limiting the outbound traffic 2403on a net with per-host limits, rather than per-network limits: 2404.Pp 2405.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2406.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in" 2407.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2408.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2409.Ss SETS OF RULES 2410To add a set of rules atomically, e.g.\& set 18: 2411.Pp 2412.Dl "ipfw set disable 18" 2413.Dl "ipfw add NN set 18 ... # repeat as needed" 2414.Dl "ipfw set enable 18" 2415.Pp 2416To delete a set of rules atomically the command is simply: 2417.Pp 2418.Dl "ipfw delete set 18" 2419.Pp 2420To test a ruleset and disable it and regain control if something goes wrong: 2421.Pp 2422.Dl "ipfw set disable 18" 2423.Dl "ipfw add NN set 18 ... # repeat as needed" 2424.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18" 2425.Pp 2426Here if everything goes well, you press control-C before the "sleep" 2427terminates, and your ruleset will be left active. 2428Otherwise, e.g.\& if 2429you cannot access your box, the ruleset will be disabled after 2430the sleep terminates thus restoring the previous situation. 2431.Sh SEE ALSO 2432.Xr cpp 1 , 2433.Xr m4 1 , 2434.Xr altq 4 , 2435.Xr bridge 4 , 2436.Xr divert 4 , 2437.Xr dummynet 4 , 2438.Xr ip 4 , 2439.Xr ipfirewall 4 , 2440.Xr ng_ipfw 4 , 2441.Xr protocols 5 , 2442.Xr services 5 , 2443.Xr init 8 , 2444.Xr kldload 8 , 2445.Xr reboot 8 , 2446.Xr sysctl 8 , 2447.Xr syslogd 8 2448.Sh HISTORY 2449The 2450.Nm 2451utility first appeared in 2452.Fx 2.0 . 2453.Xr dummynet 4 2454was introduced in 2455.Fx 2.2.8 . 2456Stateful extensions were introduced in 2457.Fx 4.0 . 2458.Nm ipfw2 2459was introduced in Summer 2002. 2460.Sh AUTHORS 2461.An Ugen J. S. Antsilevich , 2462.An Poul-Henning Kamp , 2463.An Alex Nash , 2464.An Archie Cobbs , 2465.An Luigi Rizzo . 2466.Pp 2467.An -nosplit 2468API based upon code written by 2469.An Daniel Boulet 2470for BSDI. 2471.Pp 2472Work on 2473.Xr dummynet 4 2474traffic shaper supported by Akamba Corp. 2475.Sh BUGS 2476Use of dummynet with IPv6 requires that debug.mpsafenet be set to 0. 2477.Pp 2478The syntax has grown over the years and sometimes it might be confusing. 2479Unfortunately, backward compatibility prevents cleaning up mistakes 2480made in the definition of the syntax. 2481.Pp 2482.Em !!! WARNING !!! 2483.Pp 2484Misconfiguring the firewall can put your computer in an unusable state, 2485possibly shutting down network services and requiring console access to 2486regain control of it. 2487.Pp 2488Incoming packet fragments diverted by 2489.Cm divert 2490are reassembled before delivery to the socket. 2491The action used on those packet is the one from the 2492rule which matches the first fragment of the packet. 2493.Pp 2494Packets diverted to userland, and then reinserted by a userland process 2495may lose various packet attributes. 2496The packet source interface name 2497will be preserved if it is shorter than 8 bytes and the userland process 2498saves and reuses the sockaddr_in 2499(as does 2500.Xr natd 8 ) ; 2501otherwise, it may be lost. 2502If a packet is reinserted in this manner, later rules may be incorrectly 2503applied, making the order of 2504.Cm divert 2505rules in the rule sequence very important. 2506.Pp 2507Dummynet drops all packets with IPv6 link-local addresses. 2508.Pp 2509Rules using 2510.Cm uid 2511or 2512.Cm gid 2513may not behave as expected. 2514In particular, incoming SYN packets may 2515have no uid or gid associated with them since they do not yet belong 2516to a TCP connection, and the uid/gid associated with a packet may not 2517be as expected if the associated process calls 2518.Xr setuid 2 2519or similar system calls. 2520