1.\" 2.\" $FreeBSD$ 3.\" 4.Dd October 25, 2012 5.Dt IPFW 8 6.Os 7.Sh NAME 8.Nm ipfw 9.Nd User interface for firewall, traffic shaper, packet scheduler, 10in-kernel NAT. 11.Sh SYNOPSIS 12.Ss FIREWALL CONFIGURATION 13.Nm 14.Op Fl cq 15.Cm add 16.Ar rule 17.Nm 18.Op Fl acdefnNStT 19.Op Cm set Ar N 20.Brq Cm list | show 21.Op Ar rule | first-last ... 22.Nm 23.Op Fl f | q 24.Op Cm set Ar N 25.Cm flush 26.Nm 27.Op Fl q 28.Op Cm set Ar N 29.Brq Cm delete | zero | resetlog 30.Op Ar number ... 31.Pp 32.Nm 33.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 34.Nm 35.Cm set move 36.Op Cm rule 37.Ar number Cm to Ar number 38.Nm 39.Cm set swap Ar number number 40.Nm 41.Cm set show 42.Ss SYSCTL SHORTCUTS 43.Nm 44.Cm enable 45.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 46.Nm 47.Cm disable 48.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 49.Ss LOOKUP TABLES 50.Nm 51.Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value 52.Nm 53.Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen 54.Nm 55.Cm table 56.Brq Ar number | all 57.Cm flush 58.Nm 59.Cm table 60.Brq Ar number | all 61.Cm list 62.Ss DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER) 63.Nm 64.Brq Cm pipe | queue | sched 65.Ar number 66.Cm config 67.Ar config-options 68.Nm 69.Op Fl s Op Ar field 70.Brq Cm pipe | queue | sched 71.Brq Cm delete | list | show 72.Op Ar number ... 73.Ss IN-KERNEL NAT 74.Nm 75.Op Fl q 76.Cm nat 77.Ar number 78.Cm config 79.Ar config-options 80.Pp 81.Nm 82.Op Fl cfnNqS 83.Oo 84.Fl p Ar preproc 85.Oo 86.Ar preproc-flags 87.Oc 88.Oc 89.Ar pathname 90.Sh DESCRIPTION 91The 92.Nm 93utility is the user interface for controlling the 94.Xr ipfw 4 95firewall, the 96.Xr dummynet 4 97traffic shaper/packet scheduler, and the 98in-kernel NAT services. 99.Pp 100A firewall configuration, or 101.Em ruleset , 102is made of a list of 103.Em rules 104numbered from 1 to 65535. 105Packets are passed to the firewall 106from a number of different places in the protocol stack 107(depending on the source and destination of the packet, 108it is possible for the firewall to be 109invoked multiple times on the same packet). 110The packet passed to the firewall is compared 111against each of the rules in the 112.Em ruleset , 113in rule-number order 114(multiple rules with the same number are permitted, in which case 115they are processed in order of insertion). 116When a match is found, the action corresponding to the 117matching rule is performed. 118.Pp 119Depending on the action and certain system settings, packets 120can be reinjected into the firewall at some rule after the 121matching one for further processing. 122.Pp 123A ruleset always includes a 124.Em default 125rule (numbered 65535) which cannot be modified or deleted, 126and matches all packets. 127The action associated with the 128.Em default 129rule can be either 130.Cm deny 131or 132.Cm allow 133depending on how the kernel is configured. 134.Pp 135If the ruleset includes one or more rules with the 136.Cm keep-state 137or 138.Cm limit 139option, 140the firewall will have a 141.Em stateful 142behaviour, i.e., upon a match it will create 143.Em dynamic rules , 144i.e., rules that match packets with the same 5-tuple 145(protocol, source and destination addresses and ports) 146as the packet which caused their creation. 147Dynamic rules, which have a limited lifetime, are checked 148at the first occurrence of a 149.Cm check-state , 150.Cm keep-state 151or 152.Cm limit 153rule, and are typically used to open the firewall on-demand to 154legitimate traffic only. 155See the 156.Sx STATEFUL FIREWALL 157and 158.Sx EXAMPLES 159Sections below for more information on the stateful behaviour of 160.Nm . 161.Pp 162All rules (including dynamic ones) have a few associated counters: 163a packet count, a byte count, a log count and a timestamp 164indicating the time of the last match. 165Counters can be displayed or reset with 166.Nm 167commands. 168.Pp 169Each rule belongs to one of 32 different 170.Em sets 171, and there are 172.Nm 173commands to atomically manipulate sets, such as enable, 174disable, swap sets, move all rules in a set to another 175one, delete all rules in a set. 176These can be useful to 177install temporary configurations, or to test them. 178See Section 179.Sx SETS OF RULES 180for more information on 181.Em sets . 182.Pp 183Rules can be added with the 184.Cm add 185command; deleted individually or in groups with the 186.Cm delete 187command, and globally (except those in set 31) with the 188.Cm flush 189command; displayed, optionally with the content of the 190counters, using the 191.Cm show 192and 193.Cm list 194commands. 195Finally, counters can be reset with the 196.Cm zero 197and 198.Cm resetlog 199commands. 200.Pp 201.Ss COMMAND OPTIONS 202The following general options are available when invoking 203.Nm : 204.Bl -tag -width indent 205.It Fl a 206Show counter values when listing rules. 207The 208.Cm show 209command implies this option. 210.It Fl b 211Only show the action and the comment, not the body of a rule. 212Implies 213.Fl c . 214.It Fl c 215When entering or showing rules, print them in compact form, 216i.e., omitting the "ip from any to any" string 217when this does not carry any additional information. 218.It Fl d 219When listing, show dynamic rules in addition to static ones. 220.It Fl e 221When listing and 222.Fl d 223is specified, also show expired dynamic rules. 224.It Fl f 225Do not ask for confirmation for commands that can cause problems 226if misused, i.e., 227.Cm flush . 228If there is no tty associated with the process, this is implied. 229.It Fl i 230When listing a table (see the 231.Sx LOOKUP TABLES 232section below for more information on lookup tables), format values 233as IP addresses. 234By default, values are shown as integers. 235.It Fl n 236Only check syntax of the command strings, without actually passing 237them to the kernel. 238.It Fl N 239Try to resolve addresses and service names in output. 240.It Fl q 241Be quiet when executing the 242.Cm add , 243.Cm nat , 244.Cm zero , 245.Cm resetlog 246or 247.Cm flush 248commands; 249(implies 250.Fl f ) . 251This is useful when updating rulesets by executing multiple 252.Nm 253commands in a script 254(e.g., 255.Ql sh\ /etc/rc.firewall ) , 256or by processing a file with many 257.Nm 258rules across a remote login session. 259It also stops a table add or delete 260from failing if the entry already exists or is not present. 261.Pp 262The reason why this option may be important is that 263for some of these actions, 264.Nm 265may print a message; if the action results in blocking the 266traffic to the remote client, 267the remote login session will be closed 268and the rest of the ruleset will not be processed. 269Access to the console would then be required to recover. 270.It Fl S 271When listing rules, show the 272.Em set 273each rule belongs to. 274If this flag is not specified, disabled rules will not be 275listed. 276.It Fl s Op Ar field 277When listing pipes, sort according to one of the four 278counters (total or current packets or bytes). 279.It Fl t 280When listing, show last match timestamp converted with ctime(). 281.It Fl T 282When listing, show last match timestamp as seconds from the epoch. 283This form can be more convenient for postprocessing by scripts. 284.El 285.Ss LIST OF RULES AND PREPROCESSING 286To ease configuration, rules can be put into a file which is 287processed using 288.Nm 289as shown in the last synopsis line. 290An absolute 291.Ar pathname 292must be used. 293The file will be read line by line and applied as arguments to the 294.Nm 295utility. 296.Pp 297Optionally, a preprocessor can be specified using 298.Fl p Ar preproc 299where 300.Ar pathname 301is to be piped through. 302Useful preprocessors include 303.Xr cpp 1 304and 305.Xr m4 1 . 306If 307.Ar preproc 308does not start with a slash 309.Pq Ql / 310as its first character, the usual 311.Ev PATH 312name search is performed. 313Care should be taken with this in environments where not all 314file systems are mounted (yet) by the time 315.Nm 316is being run (e.g.\& when they are mounted over NFS). 317Once 318.Fl p 319has been specified, any additional arguments are passed on to the preprocessor 320for interpretation. 321This allows for flexible configuration files (like conditionalizing 322them on the local hostname) and the use of macros to centralize 323frequently required arguments like IP addresses. 324.Ss TRAFFIC SHAPER CONFIGURATION 325The 326.Nm 327.Cm pipe , queue 328and 329.Cm sched 330commands are used to configure the traffic shaper and packet scheduler. 331See the 332.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 333Section below for details. 334.Pp 335If the world and the kernel get out of sync the 336.Nm 337ABI may break, preventing you from being able to add any rules. 338This can 339adversely effect the booting process. 340You can use 341.Nm 342.Cm disable 343.Cm firewall 344to temporarily disable the firewall to regain access to the network, 345allowing you to fix the problem. 346.Sh PACKET FLOW 347A packet is checked against the active ruleset in multiple places 348in the protocol stack, under control of several sysctl variables. 349These places and variables are shown below, and it is important to 350have this picture in mind in order to design a correct ruleset. 351.Bd -literal -offset indent 352 ^ to upper layers V 353 | | 354 +----------->-----------+ 355 ^ V 356 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1 357 | | 358 ^ V 359 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 360 | | 361 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1 362 ^ V 363 | to devices | 364.Ed 365.Pp 366The number of 367times the same packet goes through the firewall can 368vary between 0 and 4 depending on packet source and 369destination, and system configuration. 370.Pp 371Note that as packets flow through the stack, headers can be 372stripped or added to it, and so they may or may not be available 373for inspection. 374E.g., incoming packets will include the MAC header when 375.Nm 376is invoked from 377.Cm ether_demux() , 378but the same packets will have the MAC header stripped off when 379.Nm 380is invoked from 381.Cm ip_input() 382or 383.Cm ip6_input() . 384.Pp 385Also note that each packet is always checked against the complete ruleset, 386irrespective of the place where the check occurs, or the source of the packet. 387If a rule contains some match patterns or actions which are not valid 388for the place of invocation (e.g.\& trying to match a MAC header within 389.Cm ip_input 390or 391.Cm ip6_input ), 392the match pattern will not match, but a 393.Cm not 394operator in front of such patterns 395.Em will 396cause the pattern to 397.Em always 398match on those packets. 399It is thus the responsibility of 400the programmer, if necessary, to write a suitable ruleset to 401differentiate among the possible places. 402.Cm skipto 403rules can be useful here, as an example: 404.Bd -literal -offset indent 405# packets from ether_demux or bdg_forward 406ipfw add 10 skipto 1000 all from any to any layer2 in 407# packets from ip_input 408ipfw add 10 skipto 2000 all from any to any not layer2 in 409# packets from ip_output 410ipfw add 10 skipto 3000 all from any to any not layer2 out 411# packets from ether_output_frame 412ipfw add 10 skipto 4000 all from any to any layer2 out 413.Ed 414.Pp 415(yes, at the moment there is no way to differentiate between 416ether_demux and bdg_forward). 417.Sh SYNTAX 418In general, each keyword or argument must be provided as 419a separate command line argument, with no leading or trailing 420spaces. 421Keywords are case-sensitive, whereas arguments may 422or may not be case-sensitive depending on their nature 423(e.g.\& uid's are, hostnames are not). 424.Pp 425Some arguments (e.g., port or address lists) are comma-separated 426lists of values. 427In this case, spaces after commas ',' are allowed to make 428the line more readable. 429You can also put the entire 430command (including flags) into a single argument. 431E.g., the following forms are equivalent: 432.Bd -literal -offset indent 433ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 434ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 435ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" 436.Ed 437.Sh RULE FORMAT 438The format of firewall rules is the following: 439.Bd -ragged -offset indent 440.Bk -words 441.Op Ar rule_number 442.Op Cm set Ar set_number 443.Op Cm prob Ar match_probability 444.Ar action 445.Op Cm log Op Cm logamount Ar number 446.Op Cm altq Ar queue 447.Oo 448.Bro Cm tag | untag 449.Brc Ar number 450.Oc 451.Ar body 452.Ek 453.Ed 454.Pp 455where the body of the rule specifies which information is used 456for filtering packets, among the following: 457.Pp 458.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact 459.It Layer-2 header fields 460When available 461.It IPv4 and IPv6 Protocol 462TCP, UDP, ICMP, etc. 463.It Source and dest. addresses and ports 464.It Direction 465See Section 466.Sx PACKET FLOW 467.It Transmit and receive interface 468By name or address 469.It Misc. IP header fields 470Version, type of service, datagram length, identification, 471fragment flag (non-zero IP offset), 472Time To Live 473.It IP options 474.It IPv6 Extension headers 475Fragmentation, Hop-by-Hop options, 476Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options. 477.It IPv6 Flow-ID 478.It Misc. TCP header fields 479TCP flags (SYN, FIN, ACK, RST, etc.), 480sequence number, acknowledgment number, 481window 482.It TCP options 483.It ICMP types 484for ICMP packets 485.It ICMP6 types 486for ICMP6 packets 487.It User/group ID 488When the packet can be associated with a local socket. 489.It Divert status 490Whether a packet came from a divert socket (e.g., 491.Xr natd 8 ) . 492.It Fib annotation state 493Whether a packet has been tagged for using a specific FIB (routing table) 494in future forwarding decisions. 495.El 496.Pp 497Note that some of the above information, e.g.\& source MAC or IP addresses and 498TCP/UDP ports, can be easily spoofed, so filtering on those fields 499alone might not guarantee the desired results. 500.Bl -tag -width indent 501.It Ar rule_number 502Each rule is associated with a 503.Ar rule_number 504in the range 1..65535, with the latter reserved for the 505.Em default 506rule. 507Rules are checked sequentially by rule number. 508Multiple rules can have the same number, in which case they are 509checked (and listed) according to the order in which they have 510been added. 511If a rule is entered without specifying a number, the kernel will 512assign one in such a way that the rule becomes the last one 513before the 514.Em default 515rule. 516Automatic rule numbers are assigned by incrementing the last 517non-default rule number by the value of the sysctl variable 518.Ar net.inet.ip.fw.autoinc_step 519which defaults to 100. 520If this is not possible (e.g.\& because we would go beyond the 521maximum allowed rule number), the number of the last 522non-default value is used instead. 523.It Cm set Ar set_number 524Each rule is associated with a 525.Ar set_number 526in the range 0..31. 527Sets can be individually disabled and enabled, so this parameter 528is of fundamental importance for atomic ruleset manipulation. 529It can be also used to simplify deletion of groups of rules. 530If a rule is entered without specifying a set number, 531set 0 will be used. 532.br 533Set 31 is special in that it cannot be disabled, 534and rules in set 31 are not deleted by the 535.Nm ipfw flush 536command (but you can delete them with the 537.Nm ipfw delete set 31 538command). 539Set 31 is also used for the 540.Em default 541rule. 542.It Cm prob Ar match_probability 543A match is only declared with the specified probability 544(floating point number between 0 and 1). 545This can be useful for a number of applications such as 546random packet drop or 547(in conjunction with 548.Nm dummynet ) 549to simulate the effect of multiple paths leading to out-of-order 550packet delivery. 551.Pp 552Note: this condition is checked before any other condition, including 553ones such as keep-state or check-state which might have side effects. 554.It Cm log Op Cm logamount Ar number 555Packets matching a rule with the 556.Cm log 557keyword will be made available for logging in two ways: 558if the sysctl variable 559.Va net.inet.ip.fw.verbose 560is set to 0 (default), one can use 561.Xr bpf 4 562attached to the 563.Li ipfw0 564pseudo interface. 565This pseudo interface can be created after a boot 566manually by using the following command: 567.Bd -literal -offset indent 568# ifconfig ipfw0 create 569.Ed 570.Pp 571Or, automatically at boot time by adding the following 572line to the 573.Xr rc.conf 5 574file: 575.Bd -literal -offset indent 576firewall_logif="YES" 577.Ed 578.Pp 579There is no overhead if no 580.Xr bpf 4 581is attached to the pseudo interface. 582.Pp 583If 584.Va net.inet.ip.fw.verbose 585is set to 1, packets will be logged to 586.Xr syslogd 8 587with a 588.Dv LOG_SECURITY 589facility up to a maximum of 590.Cm logamount 591packets. 592If no 593.Cm logamount 594is specified, the limit is taken from the sysctl variable 595.Va net.inet.ip.fw.verbose_limit . 596In both cases, a value of 0 means unlimited logging. 597.Pp 598Once the limit is reached, logging can be re-enabled by 599clearing the logging counter or the packet counter for that entry, see the 600.Cm resetlog 601command. 602.Pp 603Note: logging is done after all other packet matching conditions 604have been successfully verified, and before performing the final 605action (accept, deny, etc.) on the packet. 606.It Cm tag Ar number 607When a packet matches a rule with the 608.Cm tag 609keyword, the numeric tag for the given 610.Ar number 611in the range 1..65534 will be attached to the packet. 612The tag acts as an internal marker (it is not sent out over 613the wire) that can be used to identify these packets later on. 614This can be used, for example, to provide trust between interfaces 615and to start doing policy-based filtering. 616A packet can have multiple tags at the same time. 617Tags are "sticky", meaning once a tag is applied to a packet by a 618matching rule it exists until explicit removal. 619Tags are kept with the packet everywhere within the kernel, but are 620lost when packet leaves the kernel, for example, on transmitting 621packet out to the network or sending packet to a 622.Xr divert 4 623socket. 624.Pp 625To check for previously applied tags, use the 626.Cm tagged 627rule option. 628To delete previously applied tag, use the 629.Cm untag 630keyword. 631.Pp 632Note: since tags are kept with the packet everywhere in kernelspace, 633they can be set and unset anywhere in the kernel network subsystem 634(using the 635.Xr mbuf_tags 9 636facility), not only by means of the 637.Xr ipfw 4 638.Cm tag 639and 640.Cm untag 641keywords. 642For example, there can be a specialized 643.Xr netgraph 4 644node doing traffic analyzing and tagging for later inspecting 645in firewall. 646.It Cm untag Ar number 647When a packet matches a rule with the 648.Cm untag 649keyword, the tag with the number 650.Ar number 651is searched among the tags attached to this packet and, 652if found, removed from it. 653Other tags bound to packet, if present, are left untouched. 654.It Cm altq Ar queue 655When a packet matches a rule with the 656.Cm altq 657keyword, the ALTQ identifier for the given 658.Ar queue 659(see 660.Xr altq 4 ) 661will be attached. 662Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, 663and not being rejected or going to divert sockets. 664Note that if there is insufficient memory at the time the packet is 665processed, it will not be tagged, so it is wise to make your ALTQ 666"default" queue policy account for this. 667If multiple 668.Cm altq 669rules match a single packet, only the first one adds the ALTQ classification 670tag. 671In doing so, traffic may be shaped by using 672.Cm count Cm altq Ar queue 673rules for classification early in the ruleset, then later applying 674the filtering decision. 675For example, 676.Cm check-state 677and 678.Cm keep-state 679rules may come later and provide the actual filtering decisions in 680addition to the fallback ALTQ tag. 681.Pp 682You must run 683.Xr pfctl 8 684to set up the queues before IPFW will be able to look them up by name, 685and if the ALTQ disciplines are rearranged, the rules in containing the 686queue identifiers in the kernel will likely have gone stale and need 687to be reloaded. 688Stale queue identifiers will probably result in misclassification. 689.Pp 690All system ALTQ processing can be turned on or off via 691.Nm 692.Cm enable Ar altq 693and 694.Nm 695.Cm disable Ar altq . 696The usage of 697.Va net.inet.ip.fw.one_pass 698is irrelevant to ALTQ traffic shaping, as the actual rule action is followed 699always after adding an ALTQ tag. 700.El 701.Ss RULE ACTIONS 702A rule can be associated with one of the following actions, which 703will be executed when the packet matches the body of the rule. 704.Bl -tag -width indent 705.It Cm allow | accept | pass | permit 706Allow packets that match rule. 707The search terminates. 708.It Cm check-state 709Checks the packet against the dynamic ruleset. 710If a match is found, execute the action associated with 711the rule which generated this dynamic rule, otherwise 712move to the next rule. 713.br 714.Cm Check-state 715rules do not have a body. 716If no 717.Cm check-state 718rule is found, the dynamic ruleset is checked at the first 719.Cm keep-state 720or 721.Cm limit 722rule. 723.It Cm count 724Update counters for all packets that match rule. 725The search continues with the next rule. 726.It Cm deny | drop 727Discard packets that match this rule. 728The search terminates. 729.It Cm divert Ar port 730Divert packets that match this rule to the 731.Xr divert 4 732socket bound to port 733.Ar port . 734The search terminates. 735.It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port 736Change the next-hop on matching packets to 737.Ar ipaddr , 738which can be an IP address or a host name. 739For IPv4, the next hop can also be supplied by the last table 740looked up for the packet by using the 741.Cm tablearg 742keyword instead of an explicit address. 743The search terminates if this rule matches. 744.Pp 745If 746.Ar ipaddr 747is a local address, then matching packets will be forwarded to 748.Ar port 749(or the port number in the packet if one is not specified in the rule) 750on the local machine. 751.br 752If 753.Ar ipaddr 754is not a local address, then the port number 755(if specified) is ignored, and the packet will be 756forwarded to the remote address, using the route as found in 757the local routing table for that IP. 758.br 759A 760.Ar fwd 761rule will not match layer-2 packets (those received 762on ether_input, ether_output, or bridged). 763.br 764The 765.Cm fwd 766action does not change the contents of the packet at all. 767In particular, the destination address remains unmodified, so 768packets forwarded to another system will usually be rejected by that system 769unless there is a matching rule on that system to capture them. 770For packets forwarded locally, 771the local address of the socket will be 772set to the original destination address of the packet. 773This makes the 774.Xr netstat 1 775entry look rather weird but is intended for 776use with transparent proxy servers. 777.It Cm nat Ar nat_nr | tablearg 778Pass packet to a 779nat instance 780(for network address translation, address redirect, etc.): 781see the 782.Sx NETWORK ADDRESS TRANSLATION (NAT) 783Section for further information. 784.It Cm pipe Ar pipe_nr 785Pass packet to a 786.Nm dummynet 787.Dq pipe 788(for bandwidth limitation, delay, etc.). 789See the 790.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 791Section for further information. 792The search terminates; however, on exit from the pipe and if 793the 794.Xr sysctl 8 795variable 796.Va net.inet.ip.fw.one_pass 797is not set, the packet is passed again to the firewall code 798starting from the next rule. 799.It Cm queue Ar queue_nr 800Pass packet to a 801.Nm dummynet 802.Dq queue 803(for bandwidth limitation using WF2Q+). 804.It Cm reject 805(Deprecated). 806Synonym for 807.Cm unreach host . 808.It Cm reset 809Discard packets that match this rule, and if the 810packet is a TCP packet, try to send a TCP reset (RST) notice. 811The search terminates. 812.It Cm reset6 813Discard packets that match this rule, and if the 814packet is a TCP packet, try to send a TCP reset (RST) notice. 815The search terminates. 816.It Cm skipto Ar number | tablearg 817Skip all subsequent rules numbered less than 818.Ar number . 819The search continues with the first rule numbered 820.Ar number 821or higher. 822It is possible to use the 823.Cm tablearg 824keyword with a skipto for a 825.Em computed 826skipto, but care should be used, as no destination caching 827is possible in this case so the rules are always walked to find it, 828starting from the 829.Cm skipto . 830.It Cm call Ar number | tablearg 831The current rule number is saved in the internal stack and 832ruleset processing continues with the first rule numbered 833.Ar number 834or higher. 835If later a rule with the 836.Cm return 837action is encountered, the processing returns to the first rule 838with number of this 839.Cm call 840rule plus one or higher 841(the same behaviour as with packets returning from 842.Xr divert 4 843socket after a 844.Cm divert 845action). 846This could be used to make somewhat like an assembly language 847.Dq subroutine 848calls to rules with common checks for different interfaces, etc. 849.Pp 850Rule with any number could be called, not just forward jumps as with 851.Cm skipto . 852So, to prevent endless loops in case of mistakes, both 853.Cm call 854and 855.Cm return 856actions don't do any jumps and simply go to the next rule if memory 857can't be allocated or stack overflowed/undeflowed. 858.Pp 859Internally stack for rule numbers is implemented using 860.Xr mbuf_tags 9 861facility and currently has size of 16 entries. 862As mbuf tags are lost when packet leaves the kernel, 863.Cm divert 864should not be used in subroutines to avoid endless loops 865and other undesired effects. 866.It Cm return 867Takes rule number saved to internal stack by the last 868.Cm call 869action and returns ruleset processing to the first rule 870with number greater than number of corresponding 871.Cm call 872rule. 873See description of the 874.Cm call 875action for more details. 876.Pp 877Note that 878.Cm return 879rules usually end a 880.Dq subroutine 881and thus are unconditional, but 882.Nm 883command-line utility currently requires every action except 884.Cm check-state 885to have body. 886While it is sometimes useful to return only on some packets, 887usually you want to print just 888.Dq return 889for readability. 890A workaround for this is to use new syntax and 891.Fl c 892switch: 893.Bd -literal -offset indent 894# Add a rule without actual body 895ipfw add 2999 return via any 896 897# List rules without "from any to any" part 898ipfw -c list 899.Ed 900.Pp 901This cosmetic annoyance may be fixed in future releases. 902.It Cm tee Ar port 903Send a copy of packets matching this rule to the 904.Xr divert 4 905socket bound to port 906.Ar port . 907The search continues with the next rule. 908.It Cm unreach Ar code 909Discard packets that match this rule, and try to send an ICMP 910unreachable notice with code 911.Ar code , 912where 913.Ar code 914is a number from 0 to 255, or one of these aliases: 915.Cm net , host , protocol , port , 916.Cm needfrag , srcfail , net-unknown , host-unknown , 917.Cm isolated , net-prohib , host-prohib , tosnet , 918.Cm toshost , filter-prohib , host-precedence 919or 920.Cm precedence-cutoff . 921The search terminates. 922.It Cm unreach6 Ar code 923Discard packets that match this rule, and try to send an ICMPv6 924unreachable notice with code 925.Ar code , 926where 927.Ar code 928is a number from 0, 1, 3 or 4, or one of these aliases: 929.Cm no-route, admin-prohib, address 930or 931.Cm port . 932The search terminates. 933.It Cm netgraph Ar cookie 934Divert packet into netgraph with given 935.Ar cookie . 936The search terminates. 937If packet is later returned from netgraph it is either 938accepted or continues with the next rule, depending on 939.Va net.inet.ip.fw.one_pass 940sysctl variable. 941.It Cm ngtee Ar cookie 942A copy of packet is diverted into netgraph, original 943packet continues with the next rule. 944See 945.Xr ng_ipfw 4 946for more information on 947.Cm netgraph 948and 949.Cm ngtee 950actions. 951.It Cm setfib Ar fibnum | tablearg 952The packet is tagged so as to use the FIB (routing table) 953.Ar fibnum 954in any subsequent forwarding decisions. 955In the current implementation, this is limited to the values 0 through 15, see 956.Xr setfib 2 . 957Processing continues at the next rule. 958It is possible to use the 959.Cm tablearg 960keyword with setfib. 961If the tablearg value is not within the compiled range of fibs, 962the packet's fib is set to 0. 963.It Cm reass 964Queue and reassemble IP fragments. 965If the packet is not fragmented, counters are updated and 966processing continues with the next rule. 967If the packet is the last logical fragment, the packet is reassembled and, if 968.Va net.inet.ip.fw.one_pass 969is set to 0, processing continues with the next rule. 970Otherwise, the packet is allowed to pass and the search terminates. 971If the packet is a fragment in the middle of a logical group of fragments, 972it is consumed and 973processing stops immediately. 974.Pp 975Fragment handling can be tuned via 976.Va net.inet.ip.maxfragpackets 977and 978.Va net.inet.ip.maxfragsperpacket 979which limit, respectively, the maximum number of processable 980fragments (default: 800) and 981the maximum number of fragments per packet (default: 16). 982.Pp 983NOTA BENE: since fragments do not contain port numbers, 984they should be avoided with the 985.Nm reass 986rule. 987Alternatively, direction-based (like 988.Nm in 989/ 990.Nm out 991) and source-based (like 992.Nm via 993) match patterns can be used to select fragments. 994.Pp 995Usually a simple rule like: 996.Bd -literal -offset indent 997# reassemble incoming fragments 998ipfw add reass all from any to any in 999.Ed 1000.Pp 1001is all you need at the beginning of your ruleset. 1002.El 1003.Ss RULE BODY 1004The body of a rule contains zero or more patterns (such as 1005specific source and destination addresses or ports, 1006protocol options, incoming or outgoing interfaces, etc.) 1007that the packet must match in order to be recognised. 1008In general, the patterns are connected by (implicit) 1009.Cm and 1010operators -- i.e., all must match in order for the 1011rule to match. 1012Individual patterns can be prefixed by the 1013.Cm not 1014operator to reverse the result of the match, as in 1015.Pp 1016.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any" 1017.Pp 1018Additionally, sets of alternative match patterns 1019.Pq Em or-blocks 1020can be constructed by putting the patterns in 1021lists enclosed between parentheses ( ) or braces { }, and 1022using the 1023.Cm or 1024operator as follows: 1025.Pp 1026.Dl "ipfw add 100 allow ip from { x or not y or z } to any" 1027.Pp 1028Only one level of parentheses is allowed. 1029Beware that most shells have special meanings for parentheses 1030or braces, so it is advisable to put a backslash \\ in front of them 1031to prevent such interpretations. 1032.Pp 1033The body of a rule must in general include a source and destination 1034address specifier. 1035The keyword 1036.Ar any 1037can be used in various places to specify that the content of 1038a required field is irrelevant. 1039.Pp 1040The rule body has the following format: 1041.Bd -ragged -offset indent 1042.Op Ar proto Cm from Ar src Cm to Ar dst 1043.Op Ar options 1044.Ed 1045.Pp 1046The first part (proto from src to dst) is for backward 1047compatibility with earlier versions of 1048.Fx . 1049In modern 1050.Fx 1051any match pattern (including MAC headers, IP protocols, 1052addresses and ports) can be specified in the 1053.Ar options 1054section. 1055.Pp 1056Rule fields have the following meaning: 1057.Bl -tag -width indent 1058.It Ar proto : protocol | Cm { Ar protocol Cm or ... } 1059.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number 1060An IP protocol specified by number or name 1061(for a complete list see 1062.Pa /etc/protocols ) , 1063or one of the following keywords: 1064.Bl -tag -width indent 1065.It Cm ip4 | ipv4 1066Matches IPv4 packets. 1067.It Cm ip6 | ipv6 1068Matches IPv6 packets. 1069.It Cm ip | all 1070Matches any packet. 1071.El 1072.Pp 1073The 1074.Cm ipv6 1075in 1076.Cm proto 1077option will be treated as inner protocol. 1078And, the 1079.Cm ipv4 1080is not available in 1081.Cm proto 1082option. 1083.Pp 1084The 1085.Cm { Ar protocol Cm or ... } 1086format (an 1087.Em or-block ) 1088is provided for convenience only but its use is deprecated. 1089.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports 1090An address (or a list, see below) 1091optionally followed by 1092.Ar ports 1093specifiers. 1094.Pp 1095The second format 1096.Em ( or-block 1097with multiple addresses) is provided for convenience only and 1098its use is discouraged. 1099.It Ar addr : Oo Cm not Oc Bro 1100.Cm any | me | me6 | 1101.Cm table Ns Pq Ar number Ns Op , Ns Ar value 1102.Ar | addr-list | addr-set 1103.Brc 1104.Bl -tag -width indent 1105.It Cm any 1106matches any IP address. 1107.It Cm me 1108matches any IP address configured on an interface in the system. 1109.It Cm me6 1110matches any IPv6 address configured on an interface in the system. 1111The address list is evaluated at the time the packet is 1112analysed. 1113.It Cm table Ns Pq Ar number Ns Op , Ns Ar value 1114Matches any IPv4 address for which an entry exists in the lookup table 1115.Ar number . 1116If an optional 32-bit unsigned 1117.Ar value 1118is also specified, an entry will match only if it has this value. 1119See the 1120.Sx LOOKUP TABLES 1121section below for more information on lookup tables. 1122.El 1123.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list 1124.It Ar ip-addr : 1125A host or subnet address specified in one of the following ways: 1126.Bl -tag -width indent 1127.It Ar numeric-ip | hostname 1128Matches a single IPv4 address, specified as dotted-quad or a hostname. 1129Hostnames are resolved at the time the rule is added to the firewall list. 1130.It Ar addr Ns / Ns Ar masklen 1131Matches all addresses with base 1132.Ar addr 1133(specified as an IP address, a network number, or a hostname) 1134and mask width of 1135.Cm masklen 1136bits. 1137As an example, 1.2.3.4/25 or 1.2.3.0/25 will match 1138all IP numbers from 1.2.3.0 to 1.2.3.127 . 1139.It Ar addr Ns : Ns Ar mask 1140Matches all addresses with base 1141.Ar addr 1142(specified as an IP address, a network number, or a hostname) 1143and the mask of 1144.Ar mask , 1145specified as a dotted quad. 1146As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 11471.*.3.*. 1148This form is advised only for non-contiguous 1149masks. 1150It is better to resort to the 1151.Ar addr Ns / Ns Ar masklen 1152format for contiguous masks, which is more compact and less 1153error-prone. 1154.El 1155.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm } 1156.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list 1157Matches all addresses with base address 1158.Ar addr 1159(specified as an IP address, a network number, or a hostname) 1160and whose last byte is in the list between braces { } . 1161Note that there must be no spaces between braces and 1162numbers (spaces after commas are allowed). 1163Elements of the list can be specified as single entries 1164or ranges. 1165The 1166.Ar masklen 1167field is used to limit the size of the set of addresses, 1168and can have any value between 24 and 32. 1169If not specified, 1170it will be assumed as 24. 1171.br 1172This format is particularly useful to handle sparse address sets 1173within a single rule. 1174Because the matching occurs using a 1175bitmask, it takes constant time and dramatically reduces 1176the complexity of rulesets. 1177.br 1178As an example, an address specified as 1.2.3.4/24{128,35-55,89} 1179or 1.2.3.0/24{128,35-55,89} 1180will match the following IP addresses: 1181.br 11821.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . 1183.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list 1184.It Ar ip6-addr : 1185A host or subnet specified one of the following ways: 1186.Bl -tag -width indent 1187.It Ar numeric-ip | hostname 1188Matches a single IPv6 address as allowed by 1189.Xr inet_pton 3 1190or a hostname. 1191Hostnames are resolved at the time the rule is added to the firewall 1192list. 1193.It Ar addr Ns / Ns Ar masklen 1194Matches all IPv6 addresses with base 1195.Ar addr 1196(specified as allowed by 1197.Xr inet_pton 1198or a hostname) 1199and mask width of 1200.Cm masklen 1201bits. 1202.El 1203.Pp 1204No support for sets of IPv6 addresses is provided because IPv6 addresses 1205are typically random past the initial prefix. 1206.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports 1207For protocols which support port numbers (such as TCP and UDP), optional 1208.Cm ports 1209may be specified as one or more ports or port ranges, separated 1210by commas but no spaces, and an optional 1211.Cm not 1212operator. 1213The 1214.Ql \&- 1215notation specifies a range of ports (including boundaries). 1216.Pp 1217Service names (from 1218.Pa /etc/services ) 1219may be used instead of numeric port values. 1220The length of the port list is limited to 30 ports or ranges, 1221though one can specify larger ranges by using an 1222.Em or-block 1223in the 1224.Cm options 1225section of the rule. 1226.Pp 1227A backslash 1228.Pq Ql \e 1229can be used to escape the dash 1230.Pq Ql - 1231character in a service name (from a shell, the backslash must be 1232typed twice to avoid the shell itself interpreting it as an escape 1233character). 1234.Pp 1235.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any" 1236.Pp 1237Fragmented packets which have a non-zero offset (i.e., not the first 1238fragment) will never match a rule which has one or more port 1239specifications. 1240See the 1241.Cm frag 1242option for details on matching fragmented packets. 1243.El 1244.Ss RULE OPTIONS (MATCH PATTERNS) 1245Additional match patterns can be used within 1246rules. 1247Zero or more of these so-called 1248.Em options 1249can be present in a rule, optionally prefixed by the 1250.Cm not 1251operand, and possibly grouped into 1252.Em or-blocks . 1253.Pp 1254The following match patterns can be used (listed in alphabetical order): 1255.Bl -tag -width indent 1256.It Cm // this is a comment. 1257Inserts the specified text as a comment in the rule. 1258Everything following // is considered as a comment and stored in the rule. 1259You can have comment-only rules, which are listed as having a 1260.Cm count 1261action followed by the comment. 1262.It Cm bridged 1263Alias for 1264.Cm layer2 . 1265.It Cm diverted 1266Matches only packets generated by a divert socket. 1267.It Cm diverted-loopback 1268Matches only packets coming from a divert socket back into the IP stack 1269input for delivery. 1270.It Cm diverted-output 1271Matches only packets going from a divert socket back outward to the IP 1272stack output for delivery. 1273.It Cm dst-ip Ar ip-address 1274Matches IPv4 packets whose destination IP is one of the address(es) 1275specified as argument. 1276.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address 1277Matches IPv6 packets whose destination IP is one of the address(es) 1278specified as argument. 1279.It Cm dst-port Ar ports 1280Matches IP packets whose destination port is one of the port(s) 1281specified as argument. 1282.It Cm established 1283Matches TCP packets that have the RST or ACK bits set. 1284.It Cm ext6hdr Ar header 1285Matches IPv6 packets containing the extended header given by 1286.Ar header . 1287Supported headers are: 1288.Pp 1289Fragment, 1290.Pq Cm frag , 1291Hop-to-hop options 1292.Pq Cm hopopt , 1293any type of Routing Header 1294.Pq Cm route , 1295Source routing Routing Header Type 0 1296.Pq Cm rthdr0 , 1297Mobile IPv6 Routing Header Type 2 1298.Pq Cm rthdr2 , 1299Destination options 1300.Pq Cm dstopt , 1301IPSec authentication headers 1302.Pq Cm ah , 1303and IPsec encapsulated security payload headers 1304.Pq Cm esp . 1305.It Cm fib Ar fibnum 1306Matches a packet that has been tagged to use 1307the given FIB (routing table) number. 1308.It Cm flow-id Ar labels 1309Matches IPv6 packets containing any of the flow labels given in 1310.Ar labels . 1311.Ar labels 1312is a comma separated list of numeric flow labels. 1313.It Cm frag 1314Matches packets that are fragments and not the first 1315fragment of an IP datagram. 1316Note that these packets will not have 1317the next protocol header (e.g.\& TCP, UDP) so options that look into 1318these headers cannot match. 1319.It Cm gid Ar group 1320Matches all TCP or UDP packets sent by or received for a 1321.Ar group . 1322A 1323.Ar group 1324may be specified by name or number. 1325.It Cm jail Ar prisonID 1326Matches all TCP or UDP packets sent by or received for the 1327jail whos prison ID is 1328.Ar prisonID . 1329.It Cm icmptypes Ar types 1330Matches ICMP packets whose ICMP type is in the list 1331.Ar types . 1332The list may be specified as any combination of 1333individual types (numeric) separated by commas. 1334.Em Ranges are not allowed . 1335The supported ICMP types are: 1336.Pp 1337echo reply 1338.Pq Cm 0 , 1339destination unreachable 1340.Pq Cm 3 , 1341source quench 1342.Pq Cm 4 , 1343redirect 1344.Pq Cm 5 , 1345echo request 1346.Pq Cm 8 , 1347router advertisement 1348.Pq Cm 9 , 1349router solicitation 1350.Pq Cm 10 , 1351time-to-live exceeded 1352.Pq Cm 11 , 1353IP header bad 1354.Pq Cm 12 , 1355timestamp request 1356.Pq Cm 13 , 1357timestamp reply 1358.Pq Cm 14 , 1359information request 1360.Pq Cm 15 , 1361information reply 1362.Pq Cm 16 , 1363address mask request 1364.Pq Cm 17 1365and address mask reply 1366.Pq Cm 18 . 1367.It Cm icmp6types Ar types 1368Matches ICMP6 packets whose ICMP6 type is in the list of 1369.Ar types . 1370The list may be specified as any combination of 1371individual types (numeric) separated by commas. 1372.Em Ranges are not allowed . 1373.It Cm in | out 1374Matches incoming or outgoing packets, respectively. 1375.Cm in 1376and 1377.Cm out 1378are mutually exclusive (in fact, 1379.Cm out 1380is implemented as 1381.Cm not in Ns No ). 1382.It Cm ipid Ar id-list 1383Matches IPv4 packets whose 1384.Cm ip_id 1385field has value included in 1386.Ar id-list , 1387which is either a single value or a list of values or ranges 1388specified in the same way as 1389.Ar ports . 1390.It Cm iplen Ar len-list 1391Matches IP packets whose total length, including header and data, is 1392in the set 1393.Ar len-list , 1394which is either a single value or a list of values or ranges 1395specified in the same way as 1396.Ar ports . 1397.It Cm ipoptions Ar spec 1398Matches packets whose IPv4 header contains the comma separated list of 1399options specified in 1400.Ar spec . 1401The supported IP options are: 1402.Pp 1403.Cm ssrr 1404(strict source route), 1405.Cm lsrr 1406(loose source route), 1407.Cm rr 1408(record packet route) and 1409.Cm ts 1410(timestamp). 1411The absence of a particular option may be denoted 1412with a 1413.Ql \&! . 1414.It Cm ipprecedence Ar precedence 1415Matches IPv4 packets whose precedence field is equal to 1416.Ar precedence . 1417.It Cm ipsec 1418Matches packets that have IPSEC history associated with them 1419(i.e., the packet comes encapsulated in IPSEC, the kernel 1420has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly 1421decapsulate it). 1422.Pp 1423Note that specifying 1424.Cm ipsec 1425is different from specifying 1426.Cm proto Ar ipsec 1427as the latter will only look at the specific IP protocol field, 1428irrespective of IPSEC kernel support and the validity of the IPSEC data. 1429.Pp 1430Further note that this flag is silently ignored in kernels without 1431IPSEC support. 1432It does not affect rule processing when given and the 1433rules are handled as if with no 1434.Cm ipsec 1435flag. 1436.It Cm iptos Ar spec 1437Matches IPv4 packets whose 1438.Cm tos 1439field contains the comma separated list of 1440service types specified in 1441.Ar spec . 1442The supported IP types of service are: 1443.Pp 1444.Cm lowdelay 1445.Pq Dv IPTOS_LOWDELAY , 1446.Cm throughput 1447.Pq Dv IPTOS_THROUGHPUT , 1448.Cm reliability 1449.Pq Dv IPTOS_RELIABILITY , 1450.Cm mincost 1451.Pq Dv IPTOS_MINCOST , 1452.Cm congestion 1453.Pq Dv IPTOS_ECN_CE . 1454The absence of a particular type may be denoted 1455with a 1456.Ql \&! . 1457.It Cm ipttl Ar ttl-list 1458Matches IPv4 packets whose time to live is included in 1459.Ar ttl-list , 1460which is either a single value or a list of values or ranges 1461specified in the same way as 1462.Ar ports . 1463.It Cm ipversion Ar ver 1464Matches IP packets whose IP version field is 1465.Ar ver . 1466.It Cm keep-state 1467Upon a match, the firewall will create a dynamic rule, whose 1468default behaviour is to match bidirectional traffic between 1469source and destination IP/port using the same protocol. 1470The rule has a limited lifetime (controlled by a set of 1471.Xr sysctl 8 1472variables), and the lifetime is refreshed every time a matching 1473packet is found. 1474.It Cm layer2 1475Matches only layer2 packets, i.e., those passed to 1476.Nm 1477from ether_demux() and ether_output_frame(). 1478.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N 1479The firewall will only allow 1480.Ar N 1481connections with the same 1482set of parameters as specified in the rule. 1483One or more 1484of source and destination addresses and ports can be 1485specified. 1486Currently, 1487only IPv4 flows are supported. 1488.It Cm lookup Bro Cm dst-ip | dst-port | src-ip | src-port | uid | jail Brc Ar N 1489Search an entry in lookup table 1490.Ar N 1491that matches the field specified as argument. 1492If not found, the match fails. 1493Otherwise, the match succeeds and 1494.Cm tablearg 1495is set to the value extracted from the table. 1496.Pp 1497This option can be useful to quickly dispatch traffic based on 1498certain packet fields. 1499See the 1500.Sx LOOKUP TABLES 1501section below for more information on lookup tables. 1502.It Cm { MAC | mac } Ar dst-mac src-mac 1503Match packets with a given 1504.Ar dst-mac 1505and 1506.Ar src-mac 1507addresses, specified as the 1508.Cm any 1509keyword (matching any MAC address), or six groups of hex digits 1510separated by colons, 1511and optionally followed by a mask indicating the significant bits. 1512The mask may be specified using either of the following methods: 1513.Bl -enum -width indent 1514.It 1515A slash 1516.Pq / 1517followed by the number of significant bits. 1518For example, an address with 33 significant bits could be specified as: 1519.Pp 1520.Dl "MAC 10:20:30:40:50:60/33 any" 1521.Pp 1522.It 1523An ampersand 1524.Pq & 1525followed by a bitmask specified as six groups of hex digits separated 1526by colons. 1527For example, an address in which the last 16 bits are significant could 1528be specified as: 1529.Pp 1530.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any" 1531.Pp 1532Note that the ampersand character has a special meaning in many shells 1533and should generally be escaped. 1534.Pp 1535.El 1536Note that the order of MAC addresses (destination first, 1537source second) is 1538the same as on the wire, but the opposite of the one used for 1539IP addresses. 1540.It Cm mac-type Ar mac-type 1541Matches packets whose Ethernet Type field 1542corresponds to one of those specified as argument. 1543.Ar mac-type 1544is specified in the same way as 1545.Cm port numbers 1546(i.e., one or more comma-separated single values or ranges). 1547You can use symbolic names for known values such as 1548.Em vlan , ipv4, ipv6 . 1549Values can be entered as decimal or hexadecimal (if prefixed by 0x), 1550and they are always printed as hexadecimal (unless the 1551.Cm -N 1552option is used, in which case symbolic resolution will be attempted). 1553.It Cm proto Ar protocol 1554Matches packets with the corresponding IP protocol. 1555.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar table Ns Pq Ar number Ns Op , Ns Ar value | Ar ipno | Ar any 1556Matches packets received, transmitted or going through, 1557respectively, the interface specified by exact name 1558.Po Ar ifX Pc , 1559by device name 1560.Po Ar if* Pc , 1561by IP address, or through some interface. 1562.Pp 1563The 1564.Cm via 1565keyword causes the interface to always be checked. 1566If 1567.Cm recv 1568or 1569.Cm xmit 1570is used instead of 1571.Cm via , 1572then only the receive or transmit interface (respectively) 1573is checked. 1574By specifying both, it is possible to match packets based on 1575both receive and transmit interface, e.g.: 1576.Pp 1577.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1" 1578.Pp 1579The 1580.Cm recv 1581interface can be tested on either incoming or outgoing packets, 1582while the 1583.Cm xmit 1584interface can only be tested on outgoing packets. 1585So 1586.Cm out 1587is required (and 1588.Cm in 1589is invalid) whenever 1590.Cm xmit 1591is used. 1592.Pp 1593A packet might not have a receive or transmit interface: packets 1594originating from the local host have no receive interface, 1595while packets destined for the local host have no transmit 1596interface. 1597.It Cm setup 1598Matches TCP packets that have the SYN bit set but no ACK bit. 1599This is the short form of 1600.Dq Li tcpflags\ syn,!ack . 1601.It Cm sockarg 1602Matches packets that are associated to a local socket and 1603for which the SO_USER_COOKIE socket option has been set 1604to a non-zero value. 1605As a side effect, the value of the 1606option is made available as 1607.Cm tablearg 1608value, which in turn can be used as 1609.Cm skipto 1610or 1611.Cm pipe 1612number. 1613.It Cm src-ip Ar ip-address 1614Matches IPv4 packets whose source IP is one of the address(es) 1615specified as an argument. 1616.It Cm src-ip6 Ar ip6-address 1617Matches IPv6 packets whose source IP is one of the address(es) 1618specified as an argument. 1619.It Cm src-port Ar ports 1620Matches IP packets whose source port is one of the port(s) 1621specified as argument. 1622.It Cm tagged Ar tag-list 1623Matches packets whose tags are included in 1624.Ar tag-list , 1625which is either a single value or a list of values or ranges 1626specified in the same way as 1627.Ar ports . 1628Tags can be applied to the packet using 1629.Cm tag 1630rule action parameter (see it's description for details on tags). 1631.It Cm tcpack Ar ack 1632TCP packets only. 1633Match if the TCP header acknowledgment number field is set to 1634.Ar ack . 1635.It Cm tcpdatalen Ar tcpdatalen-list 1636Matches TCP packets whose length of TCP data is 1637.Ar tcpdatalen-list , 1638which is either a single value or a list of values or ranges 1639specified in the same way as 1640.Ar ports . 1641.It Cm tcpflags Ar spec 1642TCP packets only. 1643Match if the TCP header contains the comma separated list of 1644flags specified in 1645.Ar spec . 1646The supported TCP flags are: 1647.Pp 1648.Cm fin , 1649.Cm syn , 1650.Cm rst , 1651.Cm psh , 1652.Cm ack 1653and 1654.Cm urg . 1655The absence of a particular flag may be denoted 1656with a 1657.Ql \&! . 1658A rule which contains a 1659.Cm tcpflags 1660specification can never match a fragmented packet which has 1661a non-zero offset. 1662See the 1663.Cm frag 1664option for details on matching fragmented packets. 1665.It Cm tcpseq Ar seq 1666TCP packets only. 1667Match if the TCP header sequence number field is set to 1668.Ar seq . 1669.It Cm tcpwin Ar tcpwin-list 1670Matches TCP packets whose header window field is set to 1671.Ar tcpwin-list , 1672which is either a single value or a list of values or ranges 1673specified in the same way as 1674.Ar ports . 1675.It Cm tcpoptions Ar spec 1676TCP packets only. 1677Match if the TCP header contains the comma separated list of 1678options specified in 1679.Ar spec . 1680The supported TCP options are: 1681.Pp 1682.Cm mss 1683(maximum segment size), 1684.Cm window 1685(tcp window advertisement), 1686.Cm sack 1687(selective ack), 1688.Cm ts 1689(rfc1323 timestamp) and 1690.Cm cc 1691(rfc1644 t/tcp connection count). 1692The absence of a particular option may be denoted 1693with a 1694.Ql \&! . 1695.It Cm uid Ar user 1696Match all TCP or UDP packets sent by or received for a 1697.Ar user . 1698A 1699.Ar user 1700may be matched by name or identification number. 1701.It Cm verrevpath 1702For incoming packets, 1703a routing table lookup is done on the packet's source address. 1704If the interface on which the packet entered the system matches the 1705outgoing interface for the route, 1706the packet matches. 1707If the interfaces do not match up, 1708the packet does not match. 1709All outgoing packets or packets with no incoming interface match. 1710.Pp 1711The name and functionality of the option is intentionally similar to 1712the Cisco IOS command: 1713.Pp 1714.Dl ip verify unicast reverse-path 1715.Pp 1716This option can be used to make anti-spoofing rules to reject all 1717packets with source addresses not from this interface. 1718See also the option 1719.Cm antispoof . 1720.It Cm versrcreach 1721For incoming packets, 1722a routing table lookup is done on the packet's source address. 1723If a route to the source address exists, but not the default route 1724or a blackhole/reject route, the packet matches. 1725Otherwise, the packet does not match. 1726All outgoing packets match. 1727.Pp 1728The name and functionality of the option is intentionally similar to 1729the Cisco IOS command: 1730.Pp 1731.Dl ip verify unicast source reachable-via any 1732.Pp 1733This option can be used to make anti-spoofing rules to reject all 1734packets whose source address is unreachable. 1735.It Cm antispoof 1736For incoming packets, the packet's source address is checked if it 1737belongs to a directly connected network. 1738If the network is directly connected, then the interface the packet 1739came on in is compared to the interface the network is connected to. 1740When incoming interface and directly connected interface are not the 1741same, the packet does not match. 1742Otherwise, the packet does match. 1743All outgoing packets match. 1744.Pp 1745This option can be used to make anti-spoofing rules to reject all 1746packets that pretend to be from a directly connected network but do 1747not come in through that interface. 1748This option is similar to but more restricted than 1749.Cm verrevpath 1750because it engages only on packets with source addresses of directly 1751connected networks instead of all source addresses. 1752.El 1753.Sh LOOKUP TABLES 1754Lookup tables are useful to handle large sparse sets of 1755addresses or other search keys (e.g., ports, jail IDs, interface names). 1756In the rest of this section we will use the term ``address''. 1757There may be up to 65535 different lookup tables, numbered 0 to 65534. 1758.Pp 1759Each entry is represented by an 1760.Ar addr Ns Op / Ns Ar masklen 1761and will match all addresses with base 1762.Ar addr 1763(specified as an IPv4/IPv6 address, a hostname or an unsigned integer) 1764and mask width of 1765.Ar masklen 1766bits. 1767If 1768.Ar masklen 1769is not specified, it defaults to 32 for IPv4 and 128 for IPv6. 1770When looking up an IP address in a table, the most specific 1771entry will match. 1772Associated with each entry is a 32-bit unsigned 1773.Ar value , 1774which can optionally be checked by a rule matching code. 1775When adding an entry, if 1776.Ar value 1777is not specified, it defaults to 0. 1778.Pp 1779An entry can be added to a table 1780.Pq Cm add , 1781or removed from a table 1782.Pq Cm delete . 1783A table can be examined 1784.Pq Cm list 1785or flushed 1786.Pq Cm flush . 1787.Pp 1788Internally, each table is stored in a Radix tree, the same way as 1789the routing table (see 1790.Xr route 4 ) . 1791.Pp 1792Lookup tables currently support only ports, jail IDs, IPv4/IPv6 addresses 1793and interface names. 1794Wildcards is not supported for interface names. 1795.Pp 1796The 1797.Cm tablearg 1798feature provides the ability to use a value, looked up in the table, as 1799the argument for a rule action, action parameter or rule option. 1800This can significantly reduce number of rules in some configurations. 1801If two tables are used in a rule, the result of the second (destination) 1802is used. 1803The 1804.Cm tablearg 1805argument can be used with the following actions: 1806.Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib, 1807action parameters: 1808.Cm tag, untag, 1809rule options: 1810.Cm limit, tagged. 1811.Pp 1812When used with 1813.Cm fwd 1814it is possible to supply table entries with values 1815that are in the form of IP addresses or hostnames. 1816See the 1817.Sx EXAMPLES 1818Section for example usage of tables and the tablearg keyword. 1819.Pp 1820When used with the 1821.Cm skipto 1822action, the user should be aware that the code will walk the ruleset 1823up to a rule equal to, or past, the given number, 1824and should therefore try keep the 1825ruleset compact between the skipto and the target rules. 1826.Sh SETS OF RULES 1827Each rule belongs to one of 32 different 1828.Em sets 1829, numbered 0 to 31. 1830Set 31 is reserved for the default rule. 1831.Pp 1832By default, rules are put in set 0, unless you use the 1833.Cm set N 1834attribute when entering a new rule. 1835Sets can be individually and atomically enabled or disabled, 1836so this mechanism permits an easy way to store multiple configurations 1837of the firewall and quickly (and atomically) switch between them. 1838The command to enable/disable sets is 1839.Bd -ragged -offset indent 1840.Nm 1841.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 1842.Ed 1843.Pp 1844where multiple 1845.Cm enable 1846or 1847.Cm disable 1848sections can be specified. 1849Command execution is atomic on all the sets specified in the command. 1850By default, all sets are enabled. 1851.Pp 1852When you disable a set, its rules behave as if they do not exist 1853in the firewall configuration, with only one exception: 1854.Bd -ragged -offset indent 1855dynamic rules created from a rule before it had been disabled 1856will still be active until they expire. 1857In order to delete 1858dynamic rules you have to explicitly delete the parent rule 1859which generated them. 1860.Ed 1861.Pp 1862The set number of rules can be changed with the command 1863.Bd -ragged -offset indent 1864.Nm 1865.Cm set move 1866.Brq Cm rule Ar rule-number | old-set 1867.Cm to Ar new-set 1868.Ed 1869.Pp 1870Also, you can atomically swap two rulesets with the command 1871.Bd -ragged -offset indent 1872.Nm 1873.Cm set swap Ar first-set second-set 1874.Ed 1875.Pp 1876See the 1877.Sx EXAMPLES 1878Section on some possible uses of sets of rules. 1879.Sh STATEFUL FIREWALL 1880Stateful operation is a way for the firewall to dynamically 1881create rules for specific flows when packets that 1882match a given pattern are detected. 1883Support for stateful 1884operation comes through the 1885.Cm check-state , keep-state 1886and 1887.Cm limit 1888options of 1889.Nm rules . 1890.Pp 1891Dynamic rules are created when a packet matches a 1892.Cm keep-state 1893or 1894.Cm limit 1895rule, causing the creation of a 1896.Em dynamic 1897rule which will match all and only packets with 1898a given 1899.Em protocol 1900between a 1901.Em src-ip/src-port dst-ip/dst-port 1902pair of addresses 1903.Em ( src 1904and 1905.Em dst 1906are used here only to denote the initial match addresses, but they 1907are completely equivalent afterwards). 1908Dynamic rules will be checked at the first 1909.Cm check-state, keep-state 1910or 1911.Cm limit 1912occurrence, and the action performed upon a match will be the same 1913as in the parent rule. 1914.Pp 1915Note that no additional attributes other than protocol and IP addresses 1916and ports are checked on dynamic rules. 1917.Pp 1918The typical use of dynamic rules is to keep a closed firewall configuration, 1919but let the first TCP SYN packet from the inside network install a 1920dynamic rule for the flow so that packets belonging to that session 1921will be allowed through the firewall: 1922.Pp 1923.Dl "ipfw add check-state" 1924.Dl "ipfw add allow tcp from my-subnet to any setup keep-state" 1925.Dl "ipfw add deny tcp from any to any" 1926.Pp 1927A similar approach can be used for UDP, where an UDP packet coming 1928from the inside will install a dynamic rule to let the response through 1929the firewall: 1930.Pp 1931.Dl "ipfw add check-state" 1932.Dl "ipfw add allow udp from my-subnet to any keep-state" 1933.Dl "ipfw add deny udp from any to any" 1934.Pp 1935Dynamic rules expire after some time, which depends on the status 1936of the flow and the setting of some 1937.Cm sysctl 1938variables. 1939See Section 1940.Sx SYSCTL VARIABLES 1941for more details. 1942For TCP sessions, dynamic rules can be instructed to periodically 1943send keepalive packets to refresh the state of the rule when it is 1944about to expire. 1945.Pp 1946See Section 1947.Sx EXAMPLES 1948for more examples on how to use dynamic rules. 1949.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 1950.Nm 1951is also the user interface for the 1952.Nm dummynet 1953traffic shaper, packet scheduler and network emulator, a subsystem that 1954can artificially queue, delay or drop packets 1955emulating the behaviour of certain network links 1956or queueing systems. 1957.Pp 1958.Nm dummynet 1959operates by first using the firewall to select packets 1960using any match pattern that can be used in 1961.Nm 1962rules. 1963Matching packets are then passed to either of two 1964different objects, which implement the traffic regulation: 1965.Bl -hang -offset XXXX 1966.It Em pipe 1967A 1968.Em pipe 1969emulates a 1970.Em link 1971with given bandwidth and propagation delay, 1972driven by a FIFO scheduler and a single queue with programmable 1973queue size and packet loss rate. 1974Packets are appended to the queue as they come out from 1975.Nm ipfw , 1976and then transferred in FIFO order to the link at the desired rate. 1977.It Em queue 1978A 1979.Em queue 1980is an abstraction used to implement packet scheduling 1981using one of several packet scheduling algorithms. 1982Packets sent to a 1983.Em queue 1984are first grouped into flows according to a mask on the 5-tuple. 1985Flows are then passed to the scheduler associated to the 1986.Em queue , 1987and each flow uses scheduling parameters (weight and others) 1988as configured in the 1989.Em queue 1990itself. 1991A scheduler in turn is connected to an emulated link, 1992and arbitrates the link's bandwidth among backlogged flows according to 1993weights and to the features of the scheduling algorithm in use. 1994.El 1995.Pp 1996In practice, 1997.Em pipes 1998can be used to set hard limits to the bandwidth that a flow can use, whereas 1999.Em queues 2000can be used to determine how different flows share the available bandwidth. 2001.Pp 2002A graphical representation of the binding of queues, 2003flows, schedulers and links is below. 2004.Bd -literal -offset indent 2005 (flow_mask|sched_mask) sched_mask 2006 +---------+ weight Wx +-------------+ 2007 | |->-[flow]-->--| |-+ 2008 -->--| QUEUE x | ... | | | 2009 | |->-[flow]-->--| SCHEDuler N | | 2010 +---------+ | | | 2011 ... | +--[LINK N]-->-- 2012 +---------+ weight Wy | | +--[LINK N]-->-- 2013 | |->-[flow]-->--| | | 2014 -->--| QUEUE y | ... | | | 2015 | |->-[flow]-->--| | | 2016 +---------+ +-------------+ | 2017 +-------------+ 2018.Ed 2019It is important to understand the role of the SCHED_MASK 2020and FLOW_MASK, which are configured through the commands 2021.Dl "ipfw sched N config mask SCHED_MASK ..." 2022and 2023.Dl "ipfw queue X config mask FLOW_MASK ..." . 2024.Pp 2025The SCHED_MASK is used to assign flows to one or more 2026scheduler instances, one for each 2027value of the packet's 5-tuple after applying SCHED_MASK. 2028As an example, using ``src-ip 0xffffff00'' creates one instance 2029for each /24 destination subnet. 2030.Pp 2031The FLOW_MASK, together with the SCHED_MASK, is used to split 2032packets into flows. 2033As an example, using 2034``src-ip 0x000000ff'' 2035together with the previous SCHED_MASK makes a flow for 2036each individual source address. 2037In turn, flows for each /24 2038subnet will be sent to the same scheduler instance. 2039.Pp 2040The above diagram holds even for the 2041.Em pipe 2042case, with the only restriction that a 2043.Em pipe 2044only supports a SCHED_MASK, and forces the use of a FIFO 2045scheduler (these are for backward compatibility reasons; 2046in fact, internally, a 2047.Nm dummynet's 2048pipe is implemented exactly as above). 2049.Pp 2050There are two modes of 2051.Nm dummynet 2052operation: 2053.Dq normal 2054and 2055.Dq fast . 2056The 2057.Dq normal 2058mode tries to emulate a real link: the 2059.Nm dummynet 2060scheduler ensures that the packet will not leave the pipe faster than it 2061would on the real link with a given bandwidth. 2062The 2063.Dq fast 2064mode allows certain packets to bypass the 2065.Nm dummynet 2066scheduler (if packet flow does not exceed pipe's bandwidth). 2067This is the reason why the 2068.Dq fast 2069mode requires less CPU cycles per packet (on average) and packet latency 2070can be significantly lower in comparison to a real link with the same 2071bandwidth. 2072The default mode is 2073.Dq normal . 2074The 2075.Dq fast 2076mode can be enabled by setting the 2077.Va net.inet.ip.dummynet.io_fast 2078.Xr sysctl 8 2079variable to a non-zero value. 2080.Pp 2081.Ss PIPE, QUEUE AND SCHEDULER CONFIGURATION 2082The 2083.Em pipe , 2084.Em queue 2085and 2086.Em scheduler 2087configuration commands are the following: 2088.Bd -ragged -offset indent 2089.Cm pipe Ar number Cm config Ar pipe-configuration 2090.Pp 2091.Cm queue Ar number Cm config Ar queue-configuration 2092.Pp 2093.Cm sched Ar number Cm config Ar sched-configuration 2094.Ed 2095.Pp 2096The following parameters can be configured for a pipe: 2097.Pp 2098.Bl -tag -width indent -compact 2099.It Cm bw Ar bandwidth | device 2100Bandwidth, measured in 2101.Sm off 2102.Op Cm K | M 2103.Brq Cm bit/s | Byte/s . 2104.Sm on 2105.Pp 2106A value of 0 (default) means unlimited bandwidth. 2107The unit must immediately follow the number, as in 2108.Pp 2109.Dl "ipfw pipe 1 config bw 300Kbit/s" 2110.Pp 2111If a device name is specified instead of a numeric value, as in 2112.Pp 2113.Dl "ipfw pipe 1 config bw tun0" 2114.Pp 2115then the transmit clock is supplied by the specified device. 2116At the moment only the 2117.Xr tun 4 2118device supports this 2119functionality, for use in conjunction with 2120.Xr ppp 8 . 2121.Pp 2122.It Cm delay Ar ms-delay 2123Propagation delay, measured in milliseconds. 2124The value is rounded to the next multiple of the clock tick 2125(typically 10ms, but it is a good practice to run kernels 2126with 2127.Dq "options HZ=1000" 2128to reduce 2129the granularity to 1ms or less). 2130The default value is 0, meaning no delay. 2131.Pp 2132.It Cm burst Ar size 2133If the data to be sent exceeds the pipe's bandwidth limit 2134(and the pipe was previously idle), up to 2135.Ar size 2136bytes of data are allowed to bypass the 2137.Nm dummynet 2138scheduler, and will be sent as fast as the physical link allows. 2139Any additional data will be transmitted at the rate specified 2140by the 2141.Nm pipe 2142bandwidth. 2143The burst size depends on how long the pipe has been idle; 2144the effective burst size is calculated as follows: 2145MAX( 2146.Ar size 2147, 2148.Nm bw 2149* pipe_idle_time). 2150.Pp 2151.It Cm profile Ar filename 2152A file specifying the additional overhead incurred in the transmission 2153of a packet on the link. 2154.Pp 2155Some link types introduce extra delays in the transmission 2156of a packet, e.g., because of MAC level framing, contention on 2157the use of the channel, MAC level retransmissions and so on. 2158From our point of view, the channel is effectively unavailable 2159for this extra time, which is constant or variable depending 2160on the link type. 2161Additionally, packets may be dropped after this 2162time (e.g., on a wireless link after too many retransmissions). 2163We can model the additional delay with an empirical curve 2164that represents its distribution. 2165.Bd -literal -offset indent 2166 cumulative probability 2167 1.0 ^ 2168 | 2169 L +-- loss-level x 2170 | ****** 2171 | * 2172 | ***** 2173 | * 2174 | ** 2175 | * 2176 +-------*-------------------> 2177 delay 2178.Ed 2179The empirical curve may have both vertical and horizontal lines. 2180Vertical lines represent constant delay for a range of 2181probabilities. 2182Horizontal lines correspond to a discontinuity in the delay 2183distribution: the pipe will use the largest delay for a 2184given probability. 2185.Pp 2186The file format is the following, with whitespace acting as 2187a separator and '#' indicating the beginning a comment: 2188.Bl -tag -width indent 2189.It Cm name Ar identifier 2190optional name (listed by "ipfw pipe show") 2191to identify the delay distribution; 2192.It Cm bw Ar value 2193the bandwidth used for the pipe. 2194If not specified here, it must be present 2195explicitly as a configuration parameter for the pipe; 2196.It Cm loss-level Ar L 2197the probability above which packets are lost. 2198(0.0 <= L <= 1.0, default 1.0 i.e., no loss); 2199.It Cm samples Ar N 2200the number of samples used in the internal 2201representation of the curve (2..1024; default 100); 2202.It Cm "delay prob" | "prob delay" 2203One of these two lines is mandatory and defines 2204the format of the following lines with data points. 2205.It Ar XXX Ar YYY 22062 or more lines representing points in the curve, 2207with either delay or probability first, according 2208to the chosen format. 2209The unit for delay is milliseconds. 2210Data points do not need to be sorted. 2211Also, the number of actual lines can be different 2212from the value of the "samples" parameter: 2213.Nm 2214utility will sort and interpolate 2215the curve as needed. 2216.El 2217.Pp 2218Example of a profile file: 2219.Bd -literal -offset indent 2220name bla_bla_bla 2221samples 100 2222loss-level 0.86 2223prob delay 22240 200 # minimum overhead is 200ms 22250.5 200 22260.5 300 22270.8 1000 22280.9 1300 22291 1300 2230#configuration file end 2231.Ed 2232.El 2233.Pp 2234The following parameters can be configured for a queue: 2235.Pp 2236.Bl -tag -width indent -compact 2237.It Cm pipe Ar pipe_nr 2238Connects a queue to the specified pipe. 2239Multiple queues (with the same or different weights) can be connected to 2240the same pipe, which specifies the aggregate rate for the set of queues. 2241.Pp 2242.It Cm weight Ar weight 2243Specifies the weight to be used for flows matching this queue. 2244The weight must be in the range 1..100, and defaults to 1. 2245.El 2246.Pp 2247The following case-insensitive parameters can be configured for a 2248scheduler: 2249.Pp 2250.Bl -tag -width indent -compact 2251.It Cm type Ar {fifo | wf2q+ | rr | qfq} 2252specifies the scheduling algorithm to use. 2253.Bl -tag -width indent -compact 2254.It Cm fifo 2255is just a FIFO scheduler (which means that all packets 2256are stored in the same queue as they arrive to the scheduler). 2257FIFO has O(1) per-packet time complexity, with very low 2258constants (estimate 60-80ns on a 2GHz desktop machine) 2259but gives no service guarantees. 2260.It Cm wf2q+ 2261implements the WF2Q+ algorithm, which is a Weighted Fair Queueing 2262algorithm which permits flows to share bandwidth according to 2263their weights. 2264Note that weights are not priorities; even a flow 2265with a minuscule weight will never starve. 2266WF2Q+ has O(log N) per-packet processing cost, where N is the number 2267of flows, and is the default algorithm used by previous versions 2268dummynet's queues. 2269.It Cm rr 2270implements the Deficit Round Robin algorithm, which has O(1) processing 2271costs (roughly, 100-150ns per packet) 2272and permits bandwidth allocation according to weights, but 2273with poor service guarantees. 2274.It Cm qfq 2275implements the QFQ algorithm, which is a very fast variant of 2276WF2Q+, with similar service guarantees and O(1) processing 2277costs (roughly, 200-250ns per packet). 2278.El 2279.El 2280.Pp 2281In addition to the type, all parameters allowed for a pipe can also 2282be specified for a scheduler. 2283.Pp 2284Finally, the following parameters can be configured for both 2285pipes and queues: 2286.Pp 2287.Bl -tag -width XXXX -compact 2288.It Cm buckets Ar hash-table-size 2289Specifies the size of the hash table used for storing the 2290various queues. 2291Default value is 64 controlled by the 2292.Xr sysctl 8 2293variable 2294.Va net.inet.ip.dummynet.hash_size , 2295allowed range is 16 to 65536. 2296.Pp 2297.It Cm mask Ar mask-specifier 2298Packets sent to a given pipe or queue by an 2299.Nm 2300rule can be further classified into multiple flows, each of which is then 2301sent to a different 2302.Em dynamic 2303pipe or queue. 2304A flow identifier is constructed by masking the IP addresses, 2305ports and protocol types as specified with the 2306.Cm mask 2307options in the configuration of the pipe or queue. 2308For each different flow identifier, a new pipe or queue is created 2309with the same parameters as the original object, and matching packets 2310are sent to it. 2311.Pp 2312Thus, when 2313.Em dynamic pipes 2314are used, each flow will get the same bandwidth as defined by the pipe, 2315whereas when 2316.Em dynamic queues 2317are used, each flow will share the parent's pipe bandwidth evenly 2318with other flows generated by the same queue (note that other queues 2319with different weights might be connected to the same pipe). 2320.br 2321Available mask specifiers are a combination of one or more of the following: 2322.Pp 2323.Cm dst-ip Ar mask , 2324.Cm dst-ip6 Ar mask , 2325.Cm src-ip Ar mask , 2326.Cm src-ip6 Ar mask , 2327.Cm dst-port Ar mask , 2328.Cm src-port Ar mask , 2329.Cm flow-id Ar mask , 2330.Cm proto Ar mask 2331or 2332.Cm all , 2333.Pp 2334where the latter means all bits in all fields are significant. 2335.Pp 2336.It Cm noerror 2337When a packet is dropped by a 2338.Nm dummynet 2339queue or pipe, the error 2340is normally reported to the caller routine in the kernel, in the 2341same way as it happens when a device queue fills up. 2342Setting this 2343option reports the packet as successfully delivered, which can be 2344needed for some experimental setups where you want to simulate 2345loss or congestion at a remote router. 2346.Pp 2347.It Cm plr Ar packet-loss-rate 2348Packet loss rate. 2349Argument 2350.Ar packet-loss-rate 2351is a floating-point number between 0 and 1, with 0 meaning no 2352loss, 1 meaning 100% loss. 2353The loss rate is internally represented on 31 bits. 2354.Pp 2355.It Cm queue Brq Ar slots | size Ns Cm Kbytes 2356Queue size, in 2357.Ar slots 2358or 2359.Cm KBytes . 2360Default value is 50 slots, which 2361is the typical queue size for Ethernet devices. 2362Note that for slow speed links you should keep the queue 2363size short or your traffic might be affected by a significant 2364queueing delay. 2365E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit 2366or 20s of queue on a 30Kbit/s pipe. 2367Even worse effects can result if you get packets from an 2368interface with a much larger MTU, e.g.\& the loopback interface 2369with its 16KB packets. 2370The 2371.Xr sysctl 8 2372variables 2373.Em net.inet.ip.dummynet.pipe_byte_limit 2374and 2375.Em net.inet.ip.dummynet.pipe_slot_limit 2376control the maximum lengths that can be specified. 2377.Pp 2378.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p 2379Make use of the RED (Random Early Detection) queue management algorithm. 2380.Ar w_q 2381and 2382.Ar max_p 2383are floating 2384point numbers between 0 and 1 (0 not included), while 2385.Ar min_th 2386and 2387.Ar max_th 2388are integer numbers specifying thresholds for queue management 2389(thresholds are computed in bytes if the queue has been defined 2390in bytes, in slots otherwise). 2391The 2392.Nm dummynet 2393also supports the gentle RED variant (gred). 2394Three 2395.Xr sysctl 8 2396variables can be used to control the RED behaviour: 2397.Bl -tag -width indent 2398.It Va net.inet.ip.dummynet.red_lookup_depth 2399specifies the accuracy in computing the average queue 2400when the link is idle (defaults to 256, must be greater than zero) 2401.It Va net.inet.ip.dummynet.red_avg_pkt_size 2402specifies the expected average packet size (defaults to 512, must be 2403greater than zero) 2404.It Va net.inet.ip.dummynet.red_max_pkt_size 2405specifies the expected maximum packet size, only used when queue 2406thresholds are in bytes (defaults to 1500, must be greater than zero). 2407.El 2408.El 2409.Pp 2410When used with IPv6 data, 2411.Nm dummynet 2412currently has several limitations. 2413Information necessary to route link-local packets to an 2414interface is not available after processing by 2415.Nm dummynet 2416so those packets are dropped in the output path. 2417Care should be taken to ensure that link-local packets are not passed to 2418.Nm dummynet . 2419.Sh CHECKLIST 2420Here are some important points to consider when designing your 2421rules: 2422.Bl -bullet 2423.It 2424Remember that you filter both packets going 2425.Cm in 2426and 2427.Cm out . 2428Most connections need packets going in both directions. 2429.It 2430Remember to test very carefully. 2431It is a good idea to be near the console when doing this. 2432If you cannot be near the console, 2433use an auto-recovery script such as the one in 2434.Pa /usr/share/examples/ipfw/change_rules.sh . 2435.It 2436Do not forget the loopback interface. 2437.El 2438.Sh FINE POINTS 2439.Bl -bullet 2440.It 2441There are circumstances where fragmented datagrams are unconditionally 2442dropped. 2443TCP packets are dropped if they do not contain at least 20 bytes of 2444TCP header, UDP packets are dropped if they do not contain a full 8 2445byte UDP header, and ICMP packets are dropped if they do not contain 24464 bytes of ICMP header, enough to specify the ICMP type, code, and 2447checksum. 2448These packets are simply logged as 2449.Dq pullup failed 2450since there may not be enough good data in the packet to produce a 2451meaningful log entry. 2452.It 2453Another type of packet is unconditionally dropped, a TCP packet with a 2454fragment offset of one. 2455This is a valid packet, but it only has one use, to try 2456to circumvent firewalls. 2457When logging is enabled, these packets are 2458reported as being dropped by rule -1. 2459.It 2460If you are logged in over a network, loading the 2461.Xr kld 4 2462version of 2463.Nm 2464is probably not as straightforward as you would think. 2465The following command line is recommended: 2466.Bd -literal -offset indent 2467kldload ipfw && \e 2468ipfw add 32000 allow ip from any to any 2469.Ed 2470.Pp 2471Along the same lines, doing an 2472.Bd -literal -offset indent 2473ipfw flush 2474.Ed 2475.Pp 2476in similar surroundings is also a bad idea. 2477.It 2478The 2479.Nm 2480filter list may not be modified if the system security level 2481is set to 3 or higher 2482(see 2483.Xr init 8 2484for information on system security levels). 2485.El 2486.Sh PACKET DIVERSION 2487A 2488.Xr divert 4 2489socket bound to the specified port will receive all packets 2490diverted to that port. 2491If no socket is bound to the destination port, or if the divert module is 2492not loaded, or if the kernel was not compiled with divert socket support, 2493the packets are dropped. 2494.Sh NETWORK ADDRESS TRANSLATION (NAT) 2495.Nm 2496support in-kernel NAT using the kernel version of 2497.Xr libalias 3 . 2498.Pp 2499The nat configuration command is the following: 2500.Bd -ragged -offset indent 2501.Bk -words 2502.Cm nat 2503.Ar nat_number 2504.Cm config 2505.Ar nat-configuration 2506.Ek 2507.Ed 2508.Pp 2509The following parameters can be configured: 2510.Bl -tag -width indent 2511.It Cm ip Ar ip_address 2512Define an ip address to use for aliasing. 2513.It Cm if Ar nic 2514Use ip address of NIC for aliasing, dynamically changing 2515it if NIC's ip address changes. 2516.It Cm log 2517Enable logging on this nat instance. 2518.It Cm deny_in 2519Deny any incoming connection from outside world. 2520.It Cm same_ports 2521Try to leave the alias port numbers unchanged from 2522the actual local port numbers. 2523.It Cm unreg_only 2524Traffic on the local network not originating from an 2525unregistered address spaces will be ignored. 2526.It Cm reset 2527Reset table of the packet aliasing engine on address change. 2528.It Cm reverse 2529Reverse the way libalias handles aliasing. 2530.It Cm proxy_only 2531Obey transparent proxy rules only, packet aliasing is not performed. 2532.It Cm skip_global 2533Skip instance in case of global state lookup (see below). 2534.El 2535.Pp 2536Some specials value can be supplied instead of 2537.Va nat_number: 2538.Bl -tag -width indent 2539.It Cm global 2540Looks up translation state in all configured nat instances. 2541If an entry is found, packet is aliased according to that entry. 2542If no entry was found in any of the instances, packet is passed unchanged, 2543and no new entry will be created. 2544See section 2545.Sx MULTIPLE INSTANCES 2546in 2547.Xr natd 8 2548for more information. 2549.It Cm tablearg 2550Uses argument supplied in lookup table. 2551See 2552.Sx LOOKUP TABLES 2553section below for more information on lookup tables. 2554.El 2555.Pp 2556To let the packet continue after being (de)aliased, set the sysctl variable 2557.Va net.inet.ip.fw.one_pass 2558to 0. 2559For more information about aliasing modes, refer to 2560.Xr libalias 3 . 2561See Section 2562.Sx EXAMPLES 2563for some examples about nat usage. 2564.Ss REDIRECT AND LSNAT SUPPORT IN IPFW 2565Redirect and LSNAT support follow closely the syntax used in 2566.Xr natd 8 . 2567See Section 2568.Sx EXAMPLES 2569for some examples on how to do redirect and lsnat. 2570.Ss SCTP NAT SUPPORT 2571SCTP nat can be configured in a similar manner to TCP through the 2572.Nm 2573command line tool. 2574The main difference is that 2575.Nm sctp nat 2576does not do port translation. 2577Since the local and global side ports will be the same, 2578there is no need to specify both. 2579Ports are redirected as follows: 2580.Bd -ragged -offset indent 2581.Bk -words 2582.Cm nat 2583.Ar nat_number 2584.Cm config if 2585.Ar nic 2586.Cm redirect_port sctp 2587.Ar ip_address [,addr_list] {[port | port-port] [,ports]} 2588.Ek 2589.Ed 2590.Pp 2591Most 2592.Nm sctp nat 2593configuration can be done in real-time through the 2594.Xr sysctl 8 2595interface. 2596All may be changed dynamically, though the hash_table size will only 2597change for new 2598.Nm nat 2599instances. 2600See 2601.Sx SYSCTL VARIABLES 2602for more info. 2603.Sh LOADER TUNABLES 2604Tunables can be set in 2605.Xr loader 8 2606prompt, 2607.Xr loader.conf 5 2608or 2609.Xr kenv 1 2610before ipfw module gets loaded. 2611.Bl -tag -width indent 2612.It Va net.inet.ip.fw.default_to_accept: No 0 2613Defines ipfw last rule behavior. 2614This value overrides 2615.Cd "options IPFW_DEFAULT_TO_(ACCEPT|DENY)" 2616from kernel configuration file. 2617.It Va net.inet.ip.fw.tables_max: No 128 2618Defines number of tables available in ipfw. 2619Number cannot exceed 65534. 2620.El 2621.Sh SYSCTL VARIABLES 2622A set of 2623.Xr sysctl 8 2624variables controls the behaviour of the firewall and 2625associated modules 2626.Pq Nm dummynet , bridge , sctp nat . 2627These are shown below together with their default value 2628(but always check with the 2629.Xr sysctl 8 2630command what value is actually in use) and meaning: 2631.Bl -tag -width indent 2632.It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0 2633Defines how the 2634.Nm nat 2635responds to receipt of global OOTB ASCONF-AddIP: 2636.Bl -tag -width indent 2637.It Cm 0 2638No response (unless a partially matching association exists - 2639ports and vtags match but global address does not) 2640.It Cm 1 2641.Nm nat 2642will accept and process all OOTB global AddIP messages. 2643.El 2644.Pp 2645Option 1 should never be selected as this forms a security risk. 2646An attacker can 2647establish multiple fake associations by sending AddIP messages. 2648.It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5 2649Defines the maximum number of chunks in an SCTP packet that will be 2650parsed for a 2651packet that matches an existing association. 2652This value is enforced to be greater or equal than 2653.Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit . 2654A high value is 2655a DoS risk yet setting too low a value may result in 2656important control chunks in 2657the packet not being located and parsed. 2658.It Va net.inet.ip.alias.sctp.error_on_ootb: No 1 2659Defines when the 2660.Nm nat 2661responds to any Out-of-the-Blue (OOTB) packets with ErrorM packets. 2662An OOTB packet is a packet that arrives with no existing association 2663registered in the 2664.Nm nat 2665and is not an INIT or ASCONF-AddIP packet: 2666.Bl -tag -width indent 2667.It Cm 0 2668ErrorM is never sent in response to OOTB packets. 2669.It Cm 1 2670ErrorM is only sent to OOTB packets received on the local side. 2671.It Cm 2 2672ErrorM is sent to the local side and on the global side ONLY if there is a 2673partial match (ports and vtags match but the source global IP does not). 2674This value is only useful if the 2675.Nm nat 2676is tracking global IP addresses. 2677.It Cm 3 2678ErrorM is sent in response to all OOTB packets on both 2679the local and global side 2680(DoS risk). 2681.El 2682.Pp 2683At the moment the default is 0, since the ErrorM packet is not yet 2684supported by most SCTP stacks. 2685When it is supported, and if not tracking 2686global addresses, we recommend setting this value to 1 to allow 2687multi-homed local hosts to function with the 2688.Nm nat . 2689To track global addresses, we recommend setting this value to 2 to 2690allow global hosts to be informed when they need to (re)send an 2691ASCONF-AddIP. 2692Value 3 should never be chosen (except for debugging) as the 2693.Nm nat 2694will respond to all OOTB global packets (a DoS risk). 2695.It Va net.inet.ip.alias.sctp.hashtable_size: No 2003 2696Size of hash tables used for 2697.Nm nat 2698lookups (100 < prime_number > 1000001). 2699This value sets the 2700.Nm hash table 2701size for any future created 2702.Nm nat 2703instance and therefore must be set prior to creating a 2704.Nm nat 2705instance. 2706The table sizes may be changed to suit specific needs. 2707If there will be few 2708concurrent associations, and memory is scarce, you may make these smaller. 2709If there will be many thousands (or millions) of concurrent associations, you 2710should make these larger. 2711A prime number is best for the table size. 2712The sysctl 2713update function will adjust your input value to the next highest prime number. 2714.It Va net.inet.ip.alias.sctp.holddown_time: No 0 2715Hold association in table for this many seconds after receiving a 2716SHUTDOWN-COMPLETE. 2717This allows endpoints to correct shutdown gracefully if a 2718shutdown_complete is lost and retransmissions are required. 2719.It Va net.inet.ip.alias.sctp.init_timer: No 15 2720Timeout value while waiting for (INIT-ACK|AddIP-ACK). 2721This value cannot be 0. 2722.It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2 2723Defines the maximum number of chunks in an SCTP packet that will be parsed when 2724no existing association exists that matches that packet. 2725Ideally this packet 2726will only be an INIT or ASCONF-AddIP packet. 2727A higher value may become a DoS 2728risk as malformed packets can consume processing resources. 2729.It Va net.inet.ip.alias.sctp.param_proc_limit: No 25 2730Defines the maximum number of parameters within a chunk that will be 2731parsed in a 2732packet. 2733As for other similar sysctl variables, larger values pose a DoS risk. 2734.It Va net.inet.ip.alias.sctp.log_level: No 0 2735Level of detail in the system log messages (0 \- minimal, 1 \- event, 27362 \- info, 3 \- detail, 4 \- debug, 5 \- max debug). 2737May be a good 2738option in high loss environments. 2739.It Va net.inet.ip.alias.sctp.shutdown_time: No 15 2740Timeout value while waiting for SHUTDOWN-COMPLETE. 2741This value cannot be 0. 2742.It Va net.inet.ip.alias.sctp.track_global_addresses: No 0 2743Enables/disables global IP address tracking within the 2744.Nm nat 2745and places an 2746upper limit on the number of addresses tracked for each association: 2747.Bl -tag -width indent 2748.It Cm 0 2749Global tracking is disabled 2750.It Cm >1 2751Enables tracking, the maximum number of addresses tracked for each 2752association is limited to this value 2753.El 2754.Pp 2755This variable is fully dynamic, the new value will be adopted for all newly 2756arriving associations, existing associations are treated 2757as they were previously. 2758Global tracking will decrease the number of collisions within the 2759.Nm nat 2760at a cost 2761of increased processing load, memory usage, complexity, and possible 2762.Nm nat 2763state 2764problems in complex networks with multiple 2765.Nm nats . 2766We recommend not tracking 2767global IP addresses, this will still result in a fully functional 2768.Nm nat . 2769.It Va net.inet.ip.alias.sctp.up_timer: No 300 2770Timeout value to keep an association up with no traffic. 2771This value cannot be 0. 2772.It Va net.inet.ip.dummynet.expire : No 1 2773Lazily delete dynamic pipes/queue once they have no pending traffic. 2774You can disable this by setting the variable to 0, in which case 2775the pipes/queues will only be deleted when the threshold is reached. 2776.It Va net.inet.ip.dummynet.hash_size : No 64 2777Default size of the hash table used for dynamic pipes/queues. 2778This value is used when no 2779.Cm buckets 2780option is specified when configuring a pipe/queue. 2781.It Va net.inet.ip.dummynet.io_fast : No 0 2782If set to a non-zero value, 2783the 2784.Dq fast 2785mode of 2786.Nm dummynet 2787operation (see above) is enabled. 2788.It Va net.inet.ip.dummynet.io_pkt 2789Number of packets passed to 2790.Nm dummynet . 2791.It Va net.inet.ip.dummynet.io_pkt_drop 2792Number of packets dropped by 2793.Nm dummynet . 2794.It Va net.inet.ip.dummynet.io_pkt_fast 2795Number of packets bypassed by the 2796.Nm dummynet 2797scheduler. 2798.It Va net.inet.ip.dummynet.max_chain_len : No 16 2799Target value for the maximum number of pipes/queues in a hash bucket. 2800The product 2801.Cm max_chain_len*hash_size 2802is used to determine the threshold over which empty pipes/queues 2803will be expired even when 2804.Cm net.inet.ip.dummynet.expire=0 . 2805.It Va net.inet.ip.dummynet.red_lookup_depth : No 256 2806.It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512 2807.It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500 2808Parameters used in the computations of the drop probability 2809for the RED algorithm. 2810.It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576 2811.It Va net.inet.ip.dummynet.pipe_slot_limit : No 100 2812The maximum queue size that can be specified in bytes or packets. 2813These limits prevent accidental exhaustion of resources such as mbufs. 2814If you raise these limits, 2815you should make sure the system is configured so that sufficient resources 2816are available. 2817.It Va net.inet.ip.fw.autoinc_step : No 100 2818Delta between rule numbers when auto-generating them. 2819The value must be in the range 1..1000. 2820.It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets 2821The current number of buckets in the hash table for dynamic rules 2822(readonly). 2823.It Va net.inet.ip.fw.debug : No 1 2824Controls debugging messages produced by 2825.Nm . 2826.It Va net.inet.ip.fw.default_rule : No 65535 2827The default rule number (read-only). 2828By the design of 2829.Nm , the default rule is the last one, so its number 2830can also serve as the highest number allowed for a rule. 2831.It Va net.inet.ip.fw.dyn_buckets : No 256 2832The number of buckets in the hash table for dynamic rules. 2833Must be a power of 2, up to 65536. 2834It only takes effect when all dynamic rules have expired, so you 2835are advised to use a 2836.Cm flush 2837command to make sure that the hash table is resized. 2838.It Va net.inet.ip.fw.dyn_count : No 3 2839Current number of dynamic rules 2840(read-only). 2841.It Va net.inet.ip.fw.dyn_keepalive : No 1 2842Enables generation of keepalive packets for 2843.Cm keep-state 2844rules on TCP sessions. 2845A keepalive is generated to both 2846sides of the connection every 5 seconds for the last 20 2847seconds of the lifetime of the rule. 2848.It Va net.inet.ip.fw.dyn_max : No 8192 2849Maximum number of dynamic rules. 2850When you hit this limit, no more dynamic rules can be 2851installed until old ones expire. 2852.It Va net.inet.ip.fw.dyn_ack_lifetime : No 300 2853.It Va net.inet.ip.fw.dyn_syn_lifetime : No 20 2854.It Va net.inet.ip.fw.dyn_fin_lifetime : No 1 2855.It Va net.inet.ip.fw.dyn_rst_lifetime : No 1 2856.It Va net.inet.ip.fw.dyn_udp_lifetime : No 5 2857.It Va net.inet.ip.fw.dyn_short_lifetime : No 30 2858These variables control the lifetime, in seconds, of dynamic 2859rules. 2860Upon the initial SYN exchange the lifetime is kept short, 2861then increased after both SYN have been seen, then decreased 2862again during the final FIN exchange or when a RST is received. 2863Both 2864.Em dyn_fin_lifetime 2865and 2866.Em dyn_rst_lifetime 2867must be strictly lower than 5 seconds, the period of 2868repetition of keepalives. 2869The firewall enforces that. 2870.It Va net.inet.ip.fw.enable : No 1 2871Enables the firewall. 2872Setting this variable to 0 lets you run your machine without 2873firewall even if compiled in. 2874.It Va net.inet6.ip6.fw.enable : No 1 2875provides the same functionality as above for the IPv6 case. 2876.It Va net.inet.ip.fw.one_pass : No 1 2877When set, the packet exiting from the 2878.Nm dummynet 2879pipe or from 2880.Xr ng_ipfw 4 2881node is not passed though the firewall again. 2882Otherwise, after an action, the packet is 2883reinjected into the firewall at the next rule. 2884.It Va net.inet.ip.fw.tables_max : No 128 2885Maximum number of tables. 2886.It Va net.inet.ip.fw.verbose : No 1 2887Enables verbose messages. 2888.It Va net.inet.ip.fw.verbose_limit : No 0 2889Limits the number of messages produced by a verbose firewall. 2890.It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1 2891If enabled packets with unknown IPv6 Extension Headers will be denied. 2892.It Va net.link.ether.ipfw : No 0 2893Controls whether layer-2 packets are passed to 2894.Nm . 2895Default is no. 2896.It Va net.link.bridge.ipfw : No 0 2897Controls whether bridged packets are passed to 2898.Nm . 2899Default is no. 2900.El 2901.Sh EXAMPLES 2902There are far too many possible uses of 2903.Nm 2904so this Section will only give a small set of examples. 2905.Pp 2906.Ss BASIC PACKET FILTERING 2907This command adds an entry which denies all tcp packets from 2908.Em cracker.evil.org 2909to the telnet port of 2910.Em wolf.tambov.su 2911from being forwarded by the host: 2912.Pp 2913.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet" 2914.Pp 2915This one disallows any connection from the entire cracker's 2916network to my host: 2917.Pp 2918.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org" 2919.Pp 2920A first and efficient way to limit access (not using dynamic rules) 2921is the use of the following rules: 2922.Pp 2923.Dl "ipfw add allow tcp from any to any established" 2924.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup" 2925.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup" 2926.Dl "..." 2927.Dl "ipfw add deny tcp from any to any" 2928.Pp 2929The first rule will be a quick match for normal TCP packets, 2930but it will not match the initial SYN packet, which will be 2931matched by the 2932.Cm setup 2933rules only for selected source/destination pairs. 2934All other SYN packets will be rejected by the final 2935.Cm deny 2936rule. 2937.Pp 2938If you administer one or more subnets, you can take advantage 2939of the address sets and or-blocks and write extremely 2940compact rulesets which selectively enable services to blocks 2941of clients, as below: 2942.Pp 2943.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q" 2944.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q" 2945.Dl "" 2946.Dl "ipfw add allow ip from ${goodguys} to any" 2947.Dl "ipfw add deny ip from ${badguys} to any" 2948.Dl "... normal policies ..." 2949.Pp 2950The 2951.Cm verrevpath 2952option could be used to do automated anti-spoofing by adding the 2953following to the top of a ruleset: 2954.Pp 2955.Dl "ipfw add deny ip from any to any not verrevpath in" 2956.Pp 2957This rule drops all incoming packets that appear to be coming to the 2958system on the wrong interface. 2959For example, a packet with a source 2960address belonging to a host on a protected internal network would be 2961dropped if it tried to enter the system from an external interface. 2962.Pp 2963The 2964.Cm antispoof 2965option could be used to do similar but more restricted anti-spoofing 2966by adding the following to the top of a ruleset: 2967.Pp 2968.Dl "ipfw add deny ip from any to any not antispoof in" 2969.Pp 2970This rule drops all incoming packets that appear to be coming from another 2971directly connected system but on the wrong interface. 2972For example, a packet with a source address of 2973.Li 192.168.0.0/24 , 2974configured on 2975.Li fxp0 , 2976but coming in on 2977.Li fxp1 2978would be dropped. 2979.Ss DYNAMIC RULES 2980In order to protect a site from flood attacks involving fake 2981TCP packets, it is safer to use dynamic rules: 2982.Pp 2983.Dl "ipfw add check-state" 2984.Dl "ipfw add deny tcp from any to any established" 2985.Dl "ipfw add allow tcp from my-net to any setup keep-state" 2986.Pp 2987This will let the firewall install dynamic rules only for 2988those connection which start with a regular SYN packet coming 2989from the inside of our network. 2990Dynamic rules are checked when encountering the first 2991occurrence of a 2992.Cm check-state , 2993.Cm keep-state 2994or 2995.Cm limit 2996rule. 2997A 2998.Cm check-state 2999rule should usually be placed near the beginning of the 3000ruleset to minimize the amount of work scanning the ruleset. 3001Your mileage may vary. 3002.Pp 3003To limit the number of connections a user can open 3004you can use the following type of rules: 3005.Pp 3006.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10" 3007.Dl "ipfw add allow tcp from any to me setup limit src-addr 4" 3008.Pp 3009The former (assuming it runs on a gateway) will allow each host 3010on a /24 network to open at most 10 TCP connections. 3011The latter can be placed on a server to make sure that a single 3012client does not use more than 4 simultaneous connections. 3013.Pp 3014.Em BEWARE : 3015stateful rules can be subject to denial-of-service attacks 3016by a SYN-flood which opens a huge number of dynamic rules. 3017The effects of such attacks can be partially limited by 3018acting on a set of 3019.Xr sysctl 8 3020variables which control the operation of the firewall. 3021.Pp 3022Here is a good usage of the 3023.Cm list 3024command to see accounting records and timestamp information: 3025.Pp 3026.Dl ipfw -at list 3027.Pp 3028or in short form without timestamps: 3029.Pp 3030.Dl ipfw -a list 3031.Pp 3032which is equivalent to: 3033.Pp 3034.Dl ipfw show 3035.Pp 3036Next rule diverts all incoming packets from 192.168.2.0/24 3037to divert port 5000: 3038.Pp 3039.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in 3040.Ss TRAFFIC SHAPING 3041The following rules show some of the applications of 3042.Nm 3043and 3044.Nm dummynet 3045for simulations and the like. 3046.Pp 3047This rule drops random incoming packets with a probability 3048of 5%: 3049.Pp 3050.Dl "ipfw add prob 0.05 deny ip from any to any in" 3051.Pp 3052A similar effect can be achieved making use of 3053.Nm dummynet 3054pipes: 3055.Pp 3056.Dl "ipfw add pipe 10 ip from any to any" 3057.Dl "ipfw pipe 10 config plr 0.05" 3058.Pp 3059We can use pipes to artificially limit bandwidth, e.g.\& on a 3060machine acting as a router, if we want to limit traffic from 3061local clients on 192.168.2.0/24 we do: 3062.Pp 3063.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 3064.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes" 3065.Pp 3066note that we use the 3067.Cm out 3068modifier so that the rule is not used twice. 3069Remember in fact that 3070.Nm 3071rules are checked both on incoming and outgoing packets. 3072.Pp 3073Should we want to simulate a bidirectional link with bandwidth 3074limitations, the correct way is the following: 3075.Pp 3076.Dl "ipfw add pipe 1 ip from any to any out" 3077.Dl "ipfw add pipe 2 ip from any to any in" 3078.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes" 3079.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes" 3080.Pp 3081The above can be very useful, e.g.\& if you want to see how 3082your fancy Web page will look for a residential user who 3083is connected only through a slow link. 3084You should not use only one pipe for both directions, unless 3085you want to simulate a half-duplex medium (e.g.\& AppleTalk, 3086Ethernet, IRDA). 3087It is not necessary that both pipes have the same configuration, 3088so we can also simulate asymmetric links. 3089.Pp 3090Should we want to verify network performance with the RED queue 3091management algorithm: 3092.Pp 3093.Dl "ipfw add pipe 1 ip from any to any" 3094.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1" 3095.Pp 3096Another typical application of the traffic shaper is to 3097introduce some delay in the communication. 3098This can significantly affect applications which do a lot of Remote 3099Procedure Calls, and where the round-trip-time of the 3100connection often becomes a limiting factor much more than 3101bandwidth: 3102.Pp 3103.Dl "ipfw add pipe 1 ip from any to any out" 3104.Dl "ipfw add pipe 2 ip from any to any in" 3105.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s" 3106.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s" 3107.Pp 3108Per-flow queueing can be useful for a variety of purposes. 3109A very simple one is counting traffic: 3110.Pp 3111.Dl "ipfw add pipe 1 tcp from any to any" 3112.Dl "ipfw add pipe 1 udp from any to any" 3113.Dl "ipfw add pipe 1 ip from any to any" 3114.Dl "ipfw pipe 1 config mask all" 3115.Pp 3116The above set of rules will create queues (and collect 3117statistics) for all traffic. 3118Because the pipes have no limitations, the only effect is 3119collecting statistics. 3120Note that we need 3 rules, not just the last one, because 3121when 3122.Nm 3123tries to match IP packets it will not consider ports, so we 3124would not see connections on separate ports as different 3125ones. 3126.Pp 3127A more sophisticated example is limiting the outbound traffic 3128on a net with per-host limits, rather than per-network limits: 3129.Pp 3130.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 3131.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in" 3132.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 3133.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 3134.Ss LOOKUP TABLES 3135In the following example, we need to create several traffic bandwidth 3136classes and we need different hosts/networks to fall into different classes. 3137We create one pipe for each class and configure them accordingly. 3138Then we create a single table and fill it with IP subnets and addresses. 3139For each subnet/host we set the argument equal to the number of the pipe 3140that it should use. 3141Then we classify traffic using a single rule: 3142.Pp 3143.Dl "ipfw pipe 1 config bw 1000Kbyte/s" 3144.Dl "ipfw pipe 4 config bw 4000Kbyte/s" 3145.Dl "..." 3146.Dl "ipfw table 1 add 192.168.2.0/24 1" 3147.Dl "ipfw table 1 add 192.168.0.0/27 4" 3148.Dl "ipfw table 1 add 192.168.0.2 1" 3149.Dl "..." 3150.Dl "ipfw add pipe tablearg ip from table(1) to any" 3151.Pp 3152Using the 3153.Cm fwd 3154action, the table entries may include hostnames and IP addresses. 3155.Pp 3156.Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1" 3157.Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz" 3158.Dl "..." 3159.Dl "ipfw add 100 fwd tablearg ip from any to table(1)" 3160.Pp 3161In the following example per-interface firewall is created: 3162.Pp 3163.Dl "ipfw table 10 add vlan20 12000" 3164.Dl "ipfw table 10 add vlan30 13000" 3165.Dl "ipfw table 20 add vlan20 22000" 3166.Dl "ipfw table 20 add vlan30 23000" 3167.Dl ".." 3168.Dl "ipfw add 100 ipfw skipto tablearg ip from any to any recv 'table(10)' in" 3169.Dl "ipfw add 200 ipfw skipto tablearg ip from any to any xmit 'table(10)' out" 3170.Ss SETS OF RULES 3171To add a set of rules atomically, e.g.\& set 18: 3172.Pp 3173.Dl "ipfw set disable 18" 3174.Dl "ipfw add NN set 18 ... # repeat as needed" 3175.Dl "ipfw set enable 18" 3176.Pp 3177To delete a set of rules atomically the command is simply: 3178.Pp 3179.Dl "ipfw delete set 18" 3180.Pp 3181To test a ruleset and disable it and regain control if something goes wrong: 3182.Pp 3183.Dl "ipfw set disable 18" 3184.Dl "ipfw add NN set 18 ... # repeat as needed" 3185.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18" 3186.Pp 3187Here if everything goes well, you press control-C before the "sleep" 3188terminates, and your ruleset will be left active. 3189Otherwise, e.g.\& if 3190you cannot access your box, the ruleset will be disabled after 3191the sleep terminates thus restoring the previous situation. 3192.Pp 3193To show rules of the specific set: 3194.Pp 3195.Dl "ipfw set 18 show" 3196.Pp 3197To show rules of the disabled set: 3198.Pp 3199.Dl "ipfw -S set 18 show" 3200.Pp 3201To clear a specific rule counters of the specific set: 3202.Pp 3203.Dl "ipfw set 18 zero NN" 3204.Pp 3205To delete a specific rule of the specific set: 3206.Pp 3207.Dl "ipfw set 18 delete NN" 3208.Ss NAT, REDIRECT AND LSNAT 3209First redirect all the traffic to nat instance 123: 3210.Pp 3211.Dl "ipfw add nat 123 all from any to any" 3212.Pp 3213Then to configure nat instance 123 to alias all the outgoing traffic with ip 3214192.168.0.123, blocking all incoming connections, trying to keep 3215same ports on both sides, clearing aliasing table on address change 3216and keeping a log of traffic/link statistics: 3217.Pp 3218.Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports" 3219.Pp 3220Or to change address of instance 123, aliasing table will be cleared (see 3221reset option): 3222.Pp 3223.Dl "ipfw nat 123 config ip 10.0.0.1" 3224.Pp 3225To see configuration of nat instance 123: 3226.Pp 3227.Dl "ipfw nat 123 show config" 3228.Pp 3229To show logs of all the instances in range 111-999: 3230.Pp 3231.Dl "ipfw nat 111-999 show" 3232.Pp 3233To see configurations of all instances: 3234.Pp 3235.Dl "ipfw nat show config" 3236.Pp 3237Or a redirect rule with mixed modes could looks like: 3238.Pp 3239.Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66" 3240.Dl " redirect_port tcp 192.168.0.1:80 500" 3241.Dl " redirect_proto udp 192.168.1.43 192.168.1.1" 3242.Dl " redirect_addr 192.168.0.10,192.168.0.11" 3243.Dl " 10.0.0.100 # LSNAT" 3244.Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22" 3245.Dl " 500 # LSNAT" 3246.Pp 3247or it could be split in: 3248.Pp 3249.Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66" 3250.Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500" 3251.Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1" 3252.Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12" 3253.Dl " 10.0.0.100" 3254.Dl "ipfw nat 5 config redirect_port tcp" 3255.Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500" 3256.Sh SEE ALSO 3257.Xr cpp 1 , 3258.Xr m4 1 , 3259.Xr altq 4 , 3260.Xr divert 4 , 3261.Xr dummynet 4 , 3262.Xr if_bridge 4 , 3263.Xr ip 4 , 3264.Xr ipfirewall 4 , 3265.Xr ng_ipfw 4 , 3266.Xr protocols 5 , 3267.Xr services 5 , 3268.Xr init 8 , 3269.Xr kldload 8 , 3270.Xr reboot 8 , 3271.Xr sysctl 8 , 3272.Xr syslogd 8 3273.Sh HISTORY 3274The 3275.Nm 3276utility first appeared in 3277.Fx 2.0 . 3278.Nm dummynet 3279was introduced in 3280.Fx 2.2.8 . 3281Stateful extensions were introduced in 3282.Fx 4.0 . 3283.Nm ipfw2 3284was introduced in Summer 2002. 3285.Sh AUTHORS 3286.An Ugen J. S. Antsilevich , 3287.An Poul-Henning Kamp , 3288.An Alex Nash , 3289.An Archie Cobbs , 3290.An Luigi Rizzo . 3291.Pp 3292.An -nosplit 3293API based upon code written by 3294.An Daniel Boulet 3295for BSDI. 3296.Pp 3297Dummynet has been introduced by Luigi Rizzo in 1997-1998. 3298.Pp 3299Some early work (1999-2000) on the 3300.Nm dummynet 3301traffic shaper supported by Akamba Corp. 3302.Pp 3303The ipfw core (ipfw2) has been completely redesigned and 3304reimplemented by Luigi Rizzo in summer 2002. 3305Further 3306actions and 3307options have been added by various developer over the years. 3308.Pp 3309.An -nosplit 3310In-kernel NAT support written by 3311.An Paolo Pisati Aq piso@FreeBSD.org 3312as part of a Summer of Code 2005 project. 3313.Pp 3314SCTP 3315.Nm nat 3316support has been developed by 3317.An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au . 3318The primary developers and maintainers are David Hayes and Jason But. 3319For further information visit: 3320.Aq http://www.caia.swin.edu.au/urp/SONATA 3321.Pp 3322Delay profiles have been developed by Alessandro Cerri and 3323Luigi Rizzo, supported by the 3324European Commission within Projects Onelab and Onelab2. 3325.Sh BUGS 3326The syntax has grown over the years and sometimes it might be confusing. 3327Unfortunately, backward compatibility prevents cleaning up mistakes 3328made in the definition of the syntax. 3329.Pp 3330.Em !!! WARNING !!! 3331.Pp 3332Misconfiguring the firewall can put your computer in an unusable state, 3333possibly shutting down network services and requiring console access to 3334regain control of it. 3335.Pp 3336Incoming packet fragments diverted by 3337.Cm divert 3338are reassembled before delivery to the socket. 3339The action used on those packet is the one from the 3340rule which matches the first fragment of the packet. 3341.Pp 3342Packets diverted to userland, and then reinserted by a userland process 3343may lose various packet attributes. 3344The packet source interface name 3345will be preserved if it is shorter than 8 bytes and the userland process 3346saves and reuses the sockaddr_in 3347(as does 3348.Xr natd 8 ) ; 3349otherwise, it may be lost. 3350If a packet is reinserted in this manner, later rules may be incorrectly 3351applied, making the order of 3352.Cm divert 3353rules in the rule sequence very important. 3354.Pp 3355Dummynet drops all packets with IPv6 link-local addresses. 3356.Pp 3357Rules using 3358.Cm uid 3359or 3360.Cm gid 3361may not behave as expected. 3362In particular, incoming SYN packets may 3363have no uid or gid associated with them since they do not yet belong 3364to a TCP connection, and the uid/gid associated with a packet may not 3365be as expected if the associated process calls 3366.Xr setuid 2 3367or similar system calls. 3368.Pp 3369Rule syntax is subject to the command line environment and some patterns 3370may need to be escaped with the backslash character 3371or quoted appropriately. 3372.Pp 3373Due to the architecture of 3374.Xr libalias 3 , 3375ipfw nat is not compatible with the TCP segmentation offloading (TSO). 3376Thus, to reliably nat your network traffic, please disable TSO 3377on your NICs using 3378.Xr ifconfig 8 . 3379.Pp 3380ICMP error messages are not implicitly matched by dynamic rules 3381for the respective conversations. 3382To avoid failures of network error detection and path MTU discovery, 3383ICMP error messages may need to be allowed explicitly through static 3384rules. 3385.Pp 3386Rules using 3387.Cm call 3388and 3389.Cm return 3390actions may lead to confusing behaviour if ruleset has mistakes, 3391and/or interaction with other subsystems (netgraph, dummynet, etc.) is used. 3392One possible case for this is packet leaving 3393.Nm 3394in subroutine on the input pass, while later on output encountering unpaired 3395.Cm return 3396first. 3397As the call stack is kept intact after input pass, packet will suddenly 3398return to the rule number used on input pass, not on output one. 3399Order of processing should be checked carefully to avoid such mistakes. 3400