1.\" 2.\" $FreeBSD$ 3.\" 4.Dd November 26, 2007 5.Dt IPFW 8 6.Os 7.Sh NAME 8.Nm ipfw 9.Nd IP firewall and traffic shaper control program 10.Sh SYNOPSIS 11.Nm 12.Op Fl cq 13.Cm add 14.Ar rule 15.Nm 16.Op Fl acdefnNStT 17.Op Cm set Ar N 18.Brq Cm list | show 19.Op Ar rule | first-last ... 20.Nm 21.Op Fl f | q 22.Op Cm set Ar N 23.Cm flush 24.Nm 25.Op Fl q 26.Op Cm set Ar N 27.Brq Cm delete | zero | resetlog 28.Op Ar number ... 29.Nm 30.Cm enable 31.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 32.Nm 33.Cm disable 34.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 35.Pp 36.Nm 37.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 38.Nm 39.Cm set move 40.Op Cm rule 41.Ar number Cm to Ar number 42.Nm 43.Cm set swap Ar number number 44.Nm 45.Cm set show 46.Pp 47.Nm 48.Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value 49.Nm 50.Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen 51.Nm 52.Cm table Ar number Cm flush 53.Nm 54.Cm table Ar number Cm list 55.Pp 56.Nm 57.Brq Cm pipe | queue 58.Ar number 59.Cm config 60.Ar config-options 61.Nm 62.Op Fl s Op Ar field 63.Brq Cm pipe | queue 64.Brq Cm delete | list | show 65.Op Ar number ... 66.Pp 67.Nm 68.Cm nat 69.Ar number 70.Cm config 71.Ar config-options 72.Pp 73.Nm 74.Op Fl cfnNqS 75.Oo 76.Fl p Ar preproc 77.Oo 78.Ar preproc-flags 79.Oc 80.Oc 81.Ar pathname 82.Sh DESCRIPTION 83The 84.Nm 85utility is the user interface for controlling the 86.Xr ipfw 4 87firewall and the 88.Xr dummynet 4 89traffic shaper in 90.Fx . 91.Pp 92An 93.Nm 94configuration, or 95.Em ruleset , 96is made of a list of 97.Em rules 98numbered from 1 to 65535. 99Packets are passed to 100.Nm 101from a number of different places in the protocol stack 102(depending on the source and destination of the packet, 103it is possible that 104.Nm 105is invoked multiple times on the same packet). 106The packet passed to the firewall is compared 107against each of the rules in the firewall 108.Em ruleset . 109When a match is found, the action corresponding to the 110matching rule is performed. 111.Pp 112Depending on the action and certain system settings, packets 113can be reinjected into the firewall at some rule after the 114matching one for further processing. 115.Pp 116An 117.Nm 118ruleset always includes a 119.Em default 120rule (numbered 65535) which cannot be modified or deleted, 121and matches all packets. 122The action associated with the 123.Em default 124rule can be either 125.Cm deny 126or 127.Cm allow 128depending on how the kernel is configured. 129.Pp 130If the ruleset includes one or more rules with the 131.Cm keep-state 132or 133.Cm limit 134option, then 135.Nm 136assumes a 137.Em stateful 138behaviour, i.e., upon a match it will create dynamic rules matching 139the exact parameters (addresses and ports) of the matching packet. 140.Pp 141These dynamic rules, which have a limited lifetime, are checked 142at the first occurrence of a 143.Cm check-state , 144.Cm keep-state 145or 146.Cm limit 147rule, and are typically used to open the firewall on-demand to 148legitimate traffic only. 149See the 150.Sx STATEFUL FIREWALL 151and 152.Sx EXAMPLES 153Sections below for more information on the stateful behaviour of 154.Nm . 155.Pp 156All rules (including dynamic ones) have a few associated counters: 157a packet count, a byte count, a log count and a timestamp 158indicating the time of the last match. 159Counters can be displayed or reset with 160.Nm 161commands. 162.Pp 163Rules can be added with the 164.Cm add 165command; deleted individually or in groups with the 166.Cm delete 167command, and globally (except those in set 31) with the 168.Cm flush 169command; displayed, optionally with the content of the 170counters, using the 171.Cm show 172and 173.Cm list 174commands. 175Finally, counters can be reset with the 176.Cm zero 177and 178.Cm resetlog 179commands. 180.Pp 181Also, each rule belongs to one of 32 different 182.Em sets 183, and there are 184.Nm 185commands to atomically manipulate sets, such as enable, 186disable, swap sets, move all rules in a set to another 187one, delete all rules in a set. 188These can be useful to 189install temporary configurations, or to test them. 190See Section 191.Sx SETS OF RULES 192for more information on 193.Em sets . 194.Pp 195The following options are available: 196.Bl -tag -width indent 197.It Fl a 198While listing, show counter values. 199The 200.Cm show 201command just implies this option. 202.It Fl b 203Only show the action and the comment, not the body of a rule. 204Implies 205.Fl c . 206.It Fl c 207When entering or showing rules, print them in compact form, 208i.e., without the optional "ip from any to any" string 209when this does not carry any additional information. 210.It Fl d 211While listing, show dynamic rules in addition to static ones. 212.It Fl e 213While listing, if the 214.Fl d 215option was specified, also show expired dynamic rules. 216.It Fl f 217Do not ask for confirmation for commands that can cause problems 218if misused, 219.No i.e. Cm flush . 220If there is no tty associated with the process, this is implied. 221.It Fl i 222While listing a table (see the 223.Sx LOOKUP TABLES 224section below for more information on lookup tables), format values 225as IP addresses. By default, values are shown as integers. 226.It Fl n 227Only check syntax of the command strings, without actually passing 228them to the kernel. 229.It Fl N 230Try to resolve addresses and service names in output. 231.It Fl q 232While 233.Cm add Ns ing , 234.Cm zero Ns ing , 235.Cm resetlog Ns ging 236or 237.Cm flush Ns ing , 238be quiet about actions 239(implies 240.Fl f ) . 241This is useful for adjusting rules by executing multiple 242.Nm 243commands in a script 244(e.g., 245.Ql sh\ /etc/rc.firewall ) , 246or by processing a file of many 247.Nm 248rules across a remote login session. 249It also stops a table add or delete 250from failing if the entry already exists or is not present. 251If a 252.Cm flush 253is performed in normal (verbose) mode (with the default kernel 254configuration), it prints a message. 255Because all rules are flushed, the message might not be delivered 256to the login session, causing the remote login session to be closed 257and the remainder of the ruleset to not be processed. 258Access to the console would then be required to recover. 259.It Fl S 260While listing rules, show the 261.Em set 262each rule belongs to. 263If this flag is not specified, disabled rules will not be 264listed. 265.It Fl s Op Ar field 266While listing pipes, sort according to one of the four 267counters (total or current packets or bytes). 268.It Fl t 269While listing, show last match timestamp (converted with ctime()). 270.It Fl T 271While listing, show last match timestamp (as seconds from the epoch). 272This form can be more convenient for postprocessing by scripts. 273.El 274.Pp 275To ease configuration, rules can be put into a file which is 276processed using 277.Nm 278as shown in the last synopsis line. 279An absolute 280.Ar pathname 281must be used. 282The file will be read line by line and applied as arguments to the 283.Nm 284utility. 285.Pp 286Optionally, a preprocessor can be specified using 287.Fl p Ar preproc 288where 289.Ar pathname 290is to be piped through. 291Useful preprocessors include 292.Xr cpp 1 293and 294.Xr m4 1 . 295If 296.Ar preproc 297does not start with a slash 298.Pq Ql / 299as its first character, the usual 300.Ev PATH 301name search is performed. 302Care should be taken with this in environments where not all 303file systems are mounted (yet) by the time 304.Nm 305is being run (e.g.\& when they are mounted over NFS). 306Once 307.Fl p 308has been specified, any additional arguments as passed on to the preprocessor 309for interpretation. 310This allows for flexible configuration files (like conditionalizing 311them on the local hostname) and the use of macros to centralize 312frequently required arguments like IP addresses. 313.Pp 314The 315.Nm 316.Cm pipe 317and 318.Cm queue 319commands are used to configure the traffic shaper, as shown in the 320.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 321Section below. 322.Pp 323If the world and the kernel get out of sync the 324.Nm 325ABI may break, preventing you from being able to add any rules. 326This can 327adversely effect the booting process. 328You can use 329.Nm 330.Cm disable 331.Cm firewall 332to temporarily disable the firewall to regain access to the network, 333allowing you to fix the problem. 334.Sh PACKET FLOW 335A packet is checked against the active ruleset in multiple places 336in the protocol stack, under control of several sysctl variables. 337These places and variables are shown below, and it is important to 338have this picture in mind in order to design a correct ruleset. 339.Bd -literal -offset indent 340 ^ to upper layers V 341 | | 342 +----------->-----------+ 343 ^ V 344 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1 345 | | 346 ^ V 347 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 348 | | 349 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1 350 ^ V 351 | to devices | 352.Ed 353.Pp 354As can be noted from the above picture, the number of 355times the same packet goes through the firewall can 356vary between 0 and 4 depending on packet source and 357destination, and system configuration. 358.Pp 359Note that as packets flow through the stack, headers can be 360stripped or added to it, and so they may or may not be available 361for inspection. 362E.g., incoming packets will include the MAC header when 363.Nm 364is invoked from 365.Cm ether_demux() , 366but the same packets will have the MAC header stripped off when 367.Nm 368is invoked from 369.Cm ip_input() 370or 371.Cm ip6_input() . 372.Pp 373Also note that each packet is always checked against the complete ruleset, 374irrespective of the place where the check occurs, or the source of the packet. 375If a rule contains some match patterns or actions which are not valid 376for the place of invocation (e.g.\& trying to match a MAC header within 377.Cm ip_input 378or 379.Cm ip6_input ), 380the match pattern will not match, but a 381.Cm not 382operator in front of such patterns 383.Em will 384cause the pattern to 385.Em always 386match on those packets. 387It is thus the responsibility of 388the programmer, if necessary, to write a suitable ruleset to 389differentiate among the possible places. 390.Cm skipto 391rules can be useful here, as an example: 392.Bd -literal -offset indent 393# packets from ether_demux or bdg_forward 394ipfw add 10 skipto 1000 all from any to any layer2 in 395# packets from ip_input 396ipfw add 10 skipto 2000 all from any to any not layer2 in 397# packets from ip_output 398ipfw add 10 skipto 3000 all from any to any not layer2 out 399# packets from ether_output_frame 400ipfw add 10 skipto 4000 all from any to any layer2 out 401.Ed 402.Pp 403(yes, at the moment there is no way to differentiate between 404ether_demux and bdg_forward). 405.Sh SYNTAX 406In general, each keyword or argument must be provided as 407a separate command line argument, with no leading or trailing 408spaces. 409Keywords are case-sensitive, whereas arguments may 410or may not be case-sensitive depending on their nature 411(e.g.\& uid's are, hostnames are not). 412.Pp 413In 414.Nm ipfw2 415you can introduce spaces after commas ',' to make 416the line more readable. 417You can also put the entire 418command (including flags) into a single argument. 419E.g., the following forms are equivalent: 420.Bd -literal -offset indent 421ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 422ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 423ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" 424.Ed 425.Sh RULE FORMAT 426The format of 427.Nm 428rules is the following: 429.Bd -ragged -offset indent 430.Bk -words 431.Op Ar rule_number 432.Op Cm set Ar set_number 433.Op Cm prob Ar match_probability 434.Ar action 435.Op Cm log Op Cm logamount Ar number 436.Op Cm altq Ar queue 437.Oo 438.Bro Cm tag | untag 439.Brc Ar number 440.Oc 441.Ar body 442.Ek 443.Ed 444.Pp 445where the body of the rule specifies which information is used 446for filtering packets, among the following: 447.Pp 448.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact 449.It Layer-2 header fields 450When available 451.It IPv4 and IPv6 Protocol 452TCP, UDP, ICMP, etc. 453.It Source and dest. addresses and ports 454.It Direction 455See Section 456.Sx PACKET FLOW 457.It Transmit and receive interface 458By name or address 459.It Misc. IP header fields 460Version, type of service, datagram length, identification, 461fragment flag (non-zero IP offset), 462Time To Live 463.It IP options 464.It IPv6 Extension headers 465Fragmentation, Hop-by-Hop options, 466Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options. 467.It IPv6 Flow-ID 468.It Misc. TCP header fields 469TCP flags (SYN, FIN, ACK, RST, etc.), 470sequence number, acknowledgment number, 471window 472.It TCP options 473.It ICMP types 474for ICMP packets 475.It ICMP6 types 476for ICMP6 packets 477.It User/group ID 478When the packet can be associated with a local socket. 479.It Divert status 480Whether a packet came from a divert socket (e.g., 481.Xr natd 8 ) . 482.El 483.Pp 484Note that some of the above information, e.g.\& source MAC or IP addresses and 485TCP/UDP ports, could easily be spoofed, so filtering on those fields 486alone might not guarantee the desired results. 487.Bl -tag -width indent 488.It Ar rule_number 489Each rule is associated with a 490.Ar rule_number 491in the range 1..65535, with the latter reserved for the 492.Em default 493rule. 494Rules are checked sequentially by rule number. 495Multiple rules can have the same number, in which case they are 496checked (and listed) according to the order in which they have 497been added. 498If a rule is entered without specifying a number, the kernel will 499assign one in such a way that the rule becomes the last one 500before the 501.Em default 502rule. 503Automatic rule numbers are assigned by incrementing the last 504non-default rule number by the value of the sysctl variable 505.Ar net.inet.ip.fw.autoinc_step 506which defaults to 100. 507If this is not possible (e.g.\& because we would go beyond the 508maximum allowed rule number), the number of the last 509non-default value is used instead. 510.It Cm set Ar set_number 511Each rule is associated with a 512.Ar set_number 513in the range 0..31. 514Sets can be individually disabled and enabled, so this parameter 515is of fundamental importance for atomic ruleset manipulation. 516It can be also used to simplify deletion of groups of rules. 517If a rule is entered without specifying a set number, 518set 0 will be used. 519.br 520Set 31 is special in that it cannot be disabled, 521and rules in set 31 are not deleted by the 522.Nm ipfw flush 523command (but you can delete them with the 524.Nm ipfw delete set 31 525command). 526Set 31 is also used for the 527.Em default 528rule. 529.It Cm prob Ar match_probability 530A match is only declared with the specified probability 531(floating point number between 0 and 1). 532This can be useful for a number of applications such as 533random packet drop or 534(in conjunction with 535.Nm dummynet ) 536to simulate the effect of multiple paths leading to out-of-order 537packet delivery. 538.Pp 539Note: this condition is checked before any other condition, including 540ones such as keep-state or check-state which might have side effects. 541.It Cm log Op Cm logamount Ar number 542When a packet matches a rule with the 543.Cm log 544keyword, a message will be 545logged to 546.Xr syslogd 8 547with a 548.Dv LOG_SECURITY 549facility. 550The logging only occurs if the sysctl variable 551.Va net.inet.ip.fw.verbose 552is set to 1 553(which is the default when the kernel is compiled with 554.Dv IPFIREWALL_VERBOSE ) 555and the number of packets logged so far for that 556particular rule does not exceed the 557.Cm logamount 558parameter. 559If no 560.Cm logamount 561is specified, the limit is taken from the sysctl variable 562.Va net.inet.ip.fw.verbose_limit . 563In both cases, a value of 0 removes the logging limit. 564.Pp 565Once the limit is reached, logging can be re-enabled by 566clearing the logging counter or the packet counter for that entry, see the 567.Cm resetlog 568command. 569.Pp 570Note: logging is done after all other packet matching conditions 571have been successfully verified, and before performing the final 572action (accept, deny, etc.) on the packet. 573.It Cm tag Ar number 574When a packet matches a rule with the 575.Cm tag 576keyword, the numeric tag for the given 577.Ar number 578in the range 1..65534 will be attached to the packet. 579The tag acts as an internal marker (it is not sent out over 580the wire) that can be used to identify these packets later on. 581This can be used, for example, to provide trust between interfaces 582and to start doing policy-based filtering. 583A packet can have mutiple tags at the same time. 584Tags are "sticky", meaning once a tag is applied to a packet by a 585matching rule it exists until explicit removal. 586Tags are kept with the packet everywhere within the kernel, but are 587lost when packet leaves the kernel, for example, on transmitting 588packet out to the network or sending packet to a 589.Xr divert 4 590socket. 591.Pp 592To check for previously applied tags, use the 593.Cm tagged 594rule option. 595To delete previously applied tag, use the 596.Cm untag 597keyword. 598.Pp 599Note: since tags are kept with the packet everywhere in kernelspace, 600they can be set and unset anywhere in kernel network subsystem 601(using 602.Xr mbuf_tags 9 603facility), not only by means of 604.Xr ipfw 4 605.Cm tag 606and 607.Cm untag 608keywords. 609For example, there can be a specialized 610.Xr netgraph 4 611node doing traffic analyzing and tagging for later inspecting 612in firewall. 613.It Cm untag Ar number 614When a packet matches a rule with the 615.Cm untag 616keyword, the tag with the number 617.Ar number 618is searched among the tags attached to this packet and, 619if found, removed from it. 620Other tags bound to packet, if present, are left untouched. 621.It Cm altq Ar queue 622When a packet matches a rule with the 623.Cm altq 624keyword, the ALTQ identifier for the given 625.Ar queue 626(see 627.Xr altq 4 ) 628will be attached. 629Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, 630and not being rejected or going to divert sockets. 631Note that if there is insufficient memory at the time the packet is 632processed, it will not be tagged, so it is wise to make your ALTQ 633"default" queue policy account for this. 634If multiple 635.Cm altq 636rules match a single packet, only the first one adds the ALTQ classification 637tag. 638In doing so, traffic may be shaped by using 639.Cm count Cm altq Ar queue 640rules for classification early in the ruleset, then later applying 641the filtering decision. 642For example, 643.Cm check-state 644and 645.Cm keep-state 646rules may come later and provide the actual filtering decisions in 647addition to the fallback ALTQ tag. 648.Pp 649You must run 650.Xr pfctl 8 651to set up the queues before IPFW will be able to look them up by name, 652and if the ALTQ disciplines are rearranged, the rules in containing the 653queue identifiers in the kernel will likely have gone stale and need 654to be reloaded. 655Stale queue identifiers will probably result in misclassification. 656.Pp 657All system ALTQ processing can be turned on or off via 658.Nm 659.Cm enable Ar altq 660and 661.Nm 662.Cm disable Ar altq . 663The usage of 664.Va net.inet.ip.fw.one_pass 665is irrelevant to ALTQ traffic shaping, as the actual rule action is followed 666always after adding an ALTQ tag. 667.El 668.Ss RULE ACTIONS 669A rule can be associated with one of the following actions, which 670will be executed when the packet matches the body of the rule. 671.Bl -tag -width indent 672.It Cm allow | accept | pass | permit 673Allow packets that match rule. 674The search terminates. 675.It Cm check-state 676Checks the packet against the dynamic ruleset. 677If a match is found, execute the action associated with 678the rule which generated this dynamic rule, otherwise 679move to the next rule. 680.br 681.Cm Check-state 682rules do not have a body. 683If no 684.Cm check-state 685rule is found, the dynamic ruleset is checked at the first 686.Cm keep-state 687or 688.Cm limit 689rule. 690.It Cm count 691Update counters for all packets that match rule. 692The search continues with the next rule. 693.It Cm deny | drop 694Discard packets that match this rule. 695The search terminates. 696.It Cm divert Ar port 697Divert packets that match this rule to the 698.Xr divert 4 699socket bound to port 700.Ar port . 701The search terminates. 702.It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port 703Change the next-hop on matching packets to 704.Ar ipaddr , 705which can be an IP address or a host name. 706The next hop can also be supplied by the last table 707looked up for the packet by using the 708.Cm tablearg 709keyword instead of an explicit address. 710The search terminates if this rule matches. 711.Pp 712If 713.Ar ipaddr 714is a local address, then matching packets will be forwarded to 715.Ar port 716(or the port number in the packet if one is not specified in the rule) 717on the local machine. 718.br 719If 720.Ar ipaddr 721is not a local address, then the port number 722(if specified) is ignored, and the packet will be 723forwarded to the remote address, using the route as found in 724the local routing table for that IP. 725.br 726A 727.Ar fwd 728rule will not match layer-2 packets (those received 729on ether_input, ether_output, or bridged). 730.br 731The 732.Cm fwd 733action does not change the contents of the packet at all. 734In particular, the destination address remains unmodified, so 735packets forwarded to another system will usually be rejected by that system 736unless there is a matching rule on that system to capture them. 737For packets forwarded locally, 738the local address of the socket will be 739set to the original destination address of the packet. 740This makes the 741.Xr netstat 1 742entry look rather weird but is intended for 743use with transparent proxy servers. 744.Pp 745To enable 746.Cm fwd 747a custom kernel needs to be compiled with the option 748.Cd "options IPFIREWALL_FORWARD" . 749.It Cm nat Ar nat_nr 750Pass packet to a 751nat instance 752(for network address translation, address redirect, etc.): 753see the 754.Sx NETWORK ADDRESS TRANSLATION (NAT) 755Section for further information. 756.It Cm pipe Ar pipe_nr 757Pass packet to a 758.Nm dummynet 759.Dq pipe 760(for bandwidth limitation, delay, etc.). 761See the 762.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 763Section for further information. 764The search terminates; however, on exit from the pipe and if 765the 766.Xr sysctl 8 767variable 768.Va net.inet.ip.fw.one_pass 769is not set, the packet is passed again to the firewall code 770starting from the next rule. 771.It Cm queue Ar queue_nr 772Pass packet to a 773.Nm dummynet 774.Dq queue 775(for bandwidth limitation using WF2Q+). 776.It Cm reject 777(Deprecated). 778Synonym for 779.Cm unreach host . 780.It Cm reset 781Discard packets that match this rule, and if the 782packet is a TCP packet, try to send a TCP reset (RST) notice. 783The search terminates. 784.It Cm reset6 785Discard packets that match this rule, and if the 786packet is a TCP packet, try to send a TCP reset (RST) notice. 787The search terminates. 788.It Cm skipto Ar number 789Skip all subsequent rules numbered less than 790.Ar number . 791The search continues with the first rule numbered 792.Ar number 793or higher. 794.It Cm tee Ar port 795Send a copy of packets matching this rule to the 796.Xr divert 4 797socket bound to port 798.Ar port . 799The search continues with the next rule. 800.It Cm unreach Ar code 801Discard packets that match this rule, and try to send an ICMP 802unreachable notice with code 803.Ar code , 804where 805.Ar code 806is a number from 0 to 255, or one of these aliases: 807.Cm net , host , protocol , port , 808.Cm needfrag , srcfail , net-unknown , host-unknown , 809.Cm isolated , net-prohib , host-prohib , tosnet , 810.Cm toshost , filter-prohib , host-precedence 811or 812.Cm precedence-cutoff . 813The search terminates. 814.It Cm unreach6 Ar code 815Discard packets that match this rule, and try to send an ICMPv6 816unreachable notice with code 817.Ar code , 818where 819.Ar code 820is a number from 0, 1, 3 or 4, or one of these aliases: 821.Cm no-route, admin-prohib, address 822or 823.Cm port . 824The search terminates. 825.It Cm netgraph Ar cookie 826Divert packet into netgraph with given 827.Ar cookie . 828The search terminates. 829If packet is later returned from netgraph it is either 830accepted or continues with the next rule, depending on 831.Va net.inet.ip.fw.one_pass 832sysctl variable. 833.It Cm ngtee Ar cookie 834A copy of packet is diverted into netgraph, original 835packet is either accepted or continues with the next rule, depending on 836.Va net.inet.ip.fw.one_pass 837sysctl variable. 838See 839.Xr ng_ipfw 4 840for more information on 841.Cm netgraph 842and 843.Cm ngtee 844actions. 845.El 846.Ss RULE BODY 847The body of a rule contains zero or more patterns (such as 848specific source and destination addresses or ports, 849protocol options, incoming or outgoing interfaces, etc.) 850that the packet must match in order to be recognised. 851In general, the patterns are connected by (implicit) 852.Cm and 853operators -- i.e., all must match in order for the 854rule to match. 855Individual patterns can be prefixed by the 856.Cm not 857operator to reverse the result of the match, as in 858.Pp 859.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any" 860.Pp 861Additionally, sets of alternative match patterns 862.Pq Em or-blocks 863can be constructed by putting the patterns in 864lists enclosed between parentheses ( ) or braces { }, and 865using the 866.Cm or 867operator as follows: 868.Pp 869.Dl "ipfw add 100 allow ip from { x or not y or z } to any" 870.Pp 871Only one level of parentheses is allowed. 872Beware that most shells have special meanings for parentheses 873or braces, so it is advisable to put a backslash \\ in front of them 874to prevent such interpretations. 875.Pp 876The body of a rule must in general include a source and destination 877address specifier. 878The keyword 879.Ar any 880can be used in various places to specify that the content of 881a required field is irrelevant. 882.Pp 883The rule body has the following format: 884.Bd -ragged -offset indent 885.Op Ar proto Cm from Ar src Cm to Ar dst 886.Op Ar options 887.Ed 888.Pp 889The first part (proto from src to dst) is for backward 890compatibility with earlier versions of 891.Fx . 892In modern 893.Fx 894any match pattern (including MAC headers, IP protocols, 895addresses and ports) can be specified in the 896.Ar options 897section. 898.Pp 899Rule fields have the following meaning: 900.Bl -tag -width indent 901.It Ar proto : protocol | Cm { Ar protocol Cm or ... } 902.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number 903An IP protocol specified by number or name 904(for a complete list see 905.Pa /etc/protocols ) , 906or one of the following keywords: 907.Bl -tag -width indent 908.It Cm ip4 | ipv4 909Matches IPv4 packets. 910.It Cm ip6 | ipv6 911Matches IPv6 packets. 912.It Cm ip | all 913Matches any packet. 914.El 915.Pp 916The 917.Cm ipv6 918in 919.Cm proto 920option will be treated as inner protocol. 921And, the 922.Cm ipv4 923is not available in 924.Cm proto 925option. 926.Pp 927The 928.Cm { Ar protocol Cm or ... } 929format (an 930.Em or-block ) 931is provided for convenience only but its use is deprecated. 932.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports 933An address (or a list, see below) 934optionally followed by 935.Ar ports 936specifiers. 937.Pp 938The second format 939.Em ( or-block 940with multiple addresses) is provided for convenience only and 941its use is discouraged. 942.It Ar addr : Oo Cm not Oc Bro 943.Cm any | me | me6 | 944.Cm table Ns Pq Ar number Ns Op , Ns Ar value 945.Ar | addr-list | addr-set 946.Brc 947.It Cm any 948matches any IP address. 949.It Cm me 950matches any IP address configured on an interface in the system. 951.It Cm me6 952matches any IPv6 address configured on an interface in the system. 953The address list is evaluated at the time the packet is 954analysed. 955.It Cm table Ns Pq Ar number Ns Op , Ns Ar value 956Matches any IPv4 address for which an entry exists in the lookup table 957.Ar number . 958If an optional 32-bit unsigned 959.Ar value 960is also specified, an entry will match only if it has this value. 961See the 962.Sx LOOKUP TABLES 963section below for more information on lookup tables. 964.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list 965.It Ar ip-addr : 966A host or subnet address specified in one of the following ways: 967.Bl -tag -width indent 968.It Ar numeric-ip | hostname 969Matches a single IPv4 address, specified as dotted-quad or a hostname. 970Hostnames are resolved at the time the rule is added to the firewall list. 971.It Ar addr Ns / Ns Ar masklen 972Matches all addresses with base 973.Ar addr 974(specified as an IP address, a network number, or a hostname) 975and mask width of 976.Cm masklen 977bits. 978As an example, 1.2.3.4/25 or 1.2.3.0/25 will match 979all IP numbers from 1.2.3.0 to 1.2.3.127 . 980.It Ar addr Ns : Ns Ar mask 981Matches all addresses with base 982.Ar addr 983(specified as an IP address, a network number, or a hostname) 984and the mask of 985.Ar mask , 986specified as a dotted quad. 987As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 9881.*.3.*. 989This form is advised only for non-contiguous 990masks. 991It is better to resort to the 992.Ar addr Ns / Ns Ar masklen 993format for contiguous masks, which is more compact and less 994error-prone. 995.El 996.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm } 997.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list 998Matches all addresses with base address 999.Ar addr 1000(specified as an IP address, a network number, or a hostname) 1001and whose last byte is in the list between braces { } . 1002Note that there must be no spaces between braces and 1003numbers (spaces after commas are allowed). 1004Elements of the list can be specified as single entries 1005or ranges. 1006The 1007.Ar masklen 1008field is used to limit the size of the set of addresses, 1009and can have any value between 24 and 32. 1010If not specified, 1011it will be assumed as 24. 1012.br 1013This format is particularly useful to handle sparse address sets 1014within a single rule. 1015Because the matching occurs using a 1016bitmask, it takes constant time and dramatically reduces 1017the complexity of rulesets. 1018.br 1019As an example, an address specified as 1.2.3.4/24{128,35-55,89} 1020or 1.2.3.0/24{128,35-55,89} 1021will match the following IP addresses: 1022.br 10231.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . 1024.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list 1025.It Ar ip6-addr : 1026A host or subnet specified one of the following ways: 1027.Pp 1028.Bl -tag -width indent 1029.It Ar numeric-ip | hostname 1030Matches a single IPv6 address as allowed by 1031.Xr inet_pton 3 1032or a hostname. 1033Hostnames are resolved at the time the rule is added to the firewall 1034list. 1035.It Ar addr Ns / Ns Ar masklen 1036Matches all IPv6 addresses with base 1037.Ar addr 1038(specified as allowed by 1039.Xr inet_pton 1040or a hostname) 1041and mask width of 1042.Cm masklen 1043bits. 1044.El 1045.Pp 1046No support for sets of IPv6 addresses is provided because IPv6 addresses 1047are typically random past the initial prefix. 1048.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports 1049For protocols which support port numbers (such as TCP and UDP), optional 1050.Cm ports 1051may be specified as one or more ports or port ranges, separated 1052by commas but no spaces, and an optional 1053.Cm not 1054operator. 1055The 1056.Ql \&- 1057notation specifies a range of ports (including boundaries). 1058.Pp 1059Service names (from 1060.Pa /etc/services ) 1061may be used instead of numeric port values. 1062The length of the port list is limited to 30 ports or ranges, 1063though one can specify larger ranges by using an 1064.Em or-block 1065in the 1066.Cm options 1067section of the rule. 1068.Pp 1069A backslash 1070.Pq Ql \e 1071can be used to escape the dash 1072.Pq Ql - 1073character in a service name (from a shell, the backslash must be 1074typed twice to avoid the shell itself interpreting it as an escape 1075character). 1076.Pp 1077.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any" 1078.Pp 1079Fragmented packets which have a non-zero offset (i.e., not the first 1080fragment) will never match a rule which has one or more port 1081specifications. 1082See the 1083.Cm frag 1084option for details on matching fragmented packets. 1085.El 1086.Ss RULE OPTIONS (MATCH PATTERNS) 1087Additional match patterns can be used within 1088rules. 1089Zero or more of these so-called 1090.Em options 1091can be present in a rule, optionally prefixed by the 1092.Cm not 1093operand, and possibly grouped into 1094.Em or-blocks . 1095.Pp 1096The following match patterns can be used (listed in alphabetical order): 1097.Bl -tag -width indent 1098.It Cm // this is a comment. 1099Inserts the specified text as a comment in the rule. 1100Everything following // is considered as a comment and stored in the rule. 1101You can have comment-only rules, which are listed as having a 1102.Cm count 1103action followed by the comment. 1104.It Cm bridged 1105Alias for 1106.Cm layer2 . 1107.It Cm diverted 1108Matches only packets generated by a divert socket. 1109.It Cm diverted-loopback 1110Matches only packets coming from a divert socket back into the IP stack 1111input for delivery. 1112.It Cm diverted-output 1113Matches only packets going from a divert socket back outward to the IP 1114stack output for delivery. 1115.It Cm dst-ip Ar ip-address 1116Matches IPv4 packets whose destination IP is one of the address(es) 1117specified as argument. 1118.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address 1119Matches IPv6 packets whose destination IP is one of the address(es) 1120specified as argument. 1121.It Cm dst-port Ar ports 1122Matches IP packets whose destination port is one of the port(s) 1123specified as argument. 1124.It Cm established 1125Matches TCP packets that have the RST or ACK bits set. 1126.It Cm ext6hdr Ar header 1127Matches IPv6 packets containing the extended header given by 1128.Ar header . 1129Supported headers are: 1130.Pp 1131Fragment, 1132.Pq Cm frag , 1133Hop-to-hop options 1134.Pq Cm hopopt , 1135any type of Routing Header 1136.Pq Cm route , 1137Source routing Routing Header Type 0 1138.Pq Cm rthdr0 , 1139Mobile IPv6 Routing Header Type 2 1140.Pq Cm rthdr2 , 1141Destination options 1142.Pq Cm dstopt , 1143IPSec authentication headers 1144.Pq Cm ah , 1145and IPSec encapsulated security payload headers 1146.Pq Cm esp . 1147.It Cm flow-id Ar labels 1148Matches IPv6 packets containing any of the flow labels given in 1149.Ar labels . 1150.Ar labels 1151is a comma seperate list of numeric flow labels. 1152.It Cm frag 1153Matches packets that are fragments and not the first 1154fragment of an IP datagram. 1155Note that these packets will not have 1156the next protocol header (e.g.\& TCP, UDP) so options that look into 1157these headers cannot match. 1158.It Cm gid Ar group 1159Matches all TCP or UDP packets sent by or received for a 1160.Ar group . 1161A 1162.Ar group 1163may be specified by name or number. 1164.It Cm jail Ar prisonID 1165Matches all TCP or UDP packets sent by or received for the 1166jail whos prison ID is 1167.Ar prisonID . 1168.It Cm icmptypes Ar types 1169Matches ICMP packets whose ICMP type is in the list 1170.Ar types . 1171The list may be specified as any combination of 1172individual types (numeric) separated by commas. 1173.Em Ranges are not allowed . 1174The supported ICMP types are: 1175.Pp 1176echo reply 1177.Pq Cm 0 , 1178destination unreachable 1179.Pq Cm 3 , 1180source quench 1181.Pq Cm 4 , 1182redirect 1183.Pq Cm 5 , 1184echo request 1185.Pq Cm 8 , 1186router advertisement 1187.Pq Cm 9 , 1188router solicitation 1189.Pq Cm 10 , 1190time-to-live exceeded 1191.Pq Cm 11 , 1192IP header bad 1193.Pq Cm 12 , 1194timestamp request 1195.Pq Cm 13 , 1196timestamp reply 1197.Pq Cm 14 , 1198information request 1199.Pq Cm 15 , 1200information reply 1201.Pq Cm 16 , 1202address mask request 1203.Pq Cm 17 1204and address mask reply 1205.Pq Cm 18 . 1206.It Cm icmp6types Ar types 1207Matches ICMP6 packets whose ICMP6 type is in the list of 1208.Ar types . 1209The list may be specified as any combination of 1210individual types (numeric) separated by commas. 1211.Em Ranges are not allowed . 1212.It Cm in | out 1213Matches incoming or outgoing packets, respectively. 1214.Cm in 1215and 1216.Cm out 1217are mutually exclusive (in fact, 1218.Cm out 1219is implemented as 1220.Cm not in Ns No ). 1221.It Cm ipid Ar id-list 1222Matches IPv4 packets whose 1223.Cm ip_id 1224field has value included in 1225.Ar id-list , 1226which is either a single value or a list of values or ranges 1227specified in the same way as 1228.Ar ports . 1229.It Cm iplen Ar len-list 1230Matches IP packets whose total length, including header and data, is 1231in the set 1232.Ar len-list , 1233which is either a single value or a list of values or ranges 1234specified in the same way as 1235.Ar ports . 1236.It Cm ipoptions Ar spec 1237Matches packets whose IPv4 header contains the comma separated list of 1238options specified in 1239.Ar spec . 1240The supported IP options are: 1241.Pp 1242.Cm ssrr 1243(strict source route), 1244.Cm lsrr 1245(loose source route), 1246.Cm rr 1247(record packet route) and 1248.Cm ts 1249(timestamp). 1250The absence of a particular option may be denoted 1251with a 1252.Ql \&! . 1253.It Cm ipprecedence Ar precedence 1254Matches IPv4 packets whose precedence field is equal to 1255.Ar precedence . 1256.It Cm ipsec 1257Matches packets that have IPSEC history associated with them 1258(i.e., the packet comes encapsulated in IPSEC, the kernel 1259has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly 1260decapsulate it). 1261.Pp 1262Note that specifying 1263.Cm ipsec 1264is different from specifying 1265.Cm proto Ar ipsec 1266as the latter will only look at the specific IP protocol field, 1267irrespective of IPSEC kernel support and the validity of the IPSEC data. 1268.Pp 1269Further note that this flag is silently ignored in kernels without 1270IPSEC support. 1271It does not affect rule processing when given and the 1272rules are handled as if with no 1273.Cm ipsec 1274flag. 1275.It Cm iptos Ar spec 1276Matches IPv4 packets whose 1277.Cm tos 1278field contains the comma separated list of 1279service types specified in 1280.Ar spec . 1281The supported IP types of service are: 1282.Pp 1283.Cm lowdelay 1284.Pq Dv IPTOS_LOWDELAY , 1285.Cm throughput 1286.Pq Dv IPTOS_THROUGHPUT , 1287.Cm reliability 1288.Pq Dv IPTOS_RELIABILITY , 1289.Cm mincost 1290.Pq Dv IPTOS_MINCOST , 1291.Cm congestion 1292.Pq Dv IPTOS_ECN_CE . 1293The absence of a particular type may be denoted 1294with a 1295.Ql \&! . 1296.It Cm ipttl Ar ttl-list 1297Matches IPv4 packets whose time to live is included in 1298.Ar ttl-list , 1299which is either a single value or a list of values or ranges 1300specified in the same way as 1301.Ar ports . 1302.It Cm ipversion Ar ver 1303Matches IP packets whose IP version field is 1304.Ar ver . 1305.It Cm keep-state 1306Upon a match, the firewall will create a dynamic rule, whose 1307default behaviour is to match bidirectional traffic between 1308source and destination IP/port using the same protocol. 1309The rule has a limited lifetime (controlled by a set of 1310.Xr sysctl 8 1311variables), and the lifetime is refreshed every time a matching 1312packet is found. 1313.It Cm layer2 1314Matches only layer2 packets, i.e., those passed to 1315.Nm 1316from ether_demux() and ether_output_frame(). 1317.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N 1318The firewall will only allow 1319.Ar N 1320connections with the same 1321set of parameters as specified in the rule. 1322One or more 1323of source and destination addresses and ports can be 1324specified. 1325Currently, 1326only IPv4 flows are supported. 1327.It Cm { MAC | mac } Ar dst-mac src-mac 1328Match packets with a given 1329.Ar dst-mac 1330and 1331.Ar src-mac 1332addresses, specified as the 1333.Cm any 1334keyword (matching any MAC address), or six groups of hex digits 1335separated by colons, 1336and optionally followed by a mask indicating the significant bits. 1337The mask may be specified using either of the following methods: 1338.Bl -enum -width indent 1339.It 1340A slash 1341.Pq / 1342followed by the number of significant bits. 1343For example, an address with 33 significant bits could be specified as: 1344.Pp 1345.Dl "MAC 10:20:30:40:50:60/33 any" 1346.Pp 1347.It 1348An ampersand 1349.Pq & 1350followed by a bitmask specified as six groups of hex digits separated 1351by colons. 1352For example, an address in which the last 16 bits are significant could 1353be specified as: 1354.Pp 1355.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any" 1356.Pp 1357Note that the ampersand character has a special meaning in many shells 1358and should generally be escaped. 1359.Pp 1360.El 1361Note that the order of MAC addresses (destination first, 1362source second) is 1363the same as on the wire, but the opposite of the one used for 1364IP addresses. 1365.It Cm mac-type Ar mac-type 1366Matches packets whose Ethernet Type field 1367corresponds to one of those specified as argument. 1368.Ar mac-type 1369is specified in the same way as 1370.Cm port numbers 1371(i.e., one or more comma-separated single values or ranges). 1372You can use symbolic names for known values such as 1373.Em vlan , ipv4, ipv6 . 1374Values can be entered as decimal or hexadecimal (if prefixed by 0x), 1375and they are always printed as hexadecimal (unless the 1376.Cm -N 1377option is used, in which case symbolic resolution will be attempted). 1378.It Cm proto Ar protocol 1379Matches packets with the corresponding IP protocol. 1380.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any 1381Matches packets received, transmitted or going through, 1382respectively, the interface specified by exact name 1383.Ns No ( Ar ifX Ns No ), 1384by device name 1385.Ns No ( Ar if Ns Ar * Ns No ), 1386by IP address, or through some interface. 1387.Pp 1388The 1389.Cm via 1390keyword causes the interface to always be checked. 1391If 1392.Cm recv 1393or 1394.Cm xmit 1395is used instead of 1396.Cm via , 1397then only the receive or transmit interface (respectively) 1398is checked. 1399By specifying both, it is possible to match packets based on 1400both receive and transmit interface, e.g.: 1401.Pp 1402.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1" 1403.Pp 1404The 1405.Cm recv 1406interface can be tested on either incoming or outgoing packets, 1407while the 1408.Cm xmit 1409interface can only be tested on outgoing packets. 1410So 1411.Cm out 1412is required (and 1413.Cm in 1414is invalid) whenever 1415.Cm xmit 1416is used. 1417.Pp 1418A packet may not have a receive or transmit interface: packets 1419originating from the local host have no receive interface, 1420while packets destined for the local host have no transmit 1421interface. 1422.It Cm setup 1423Matches TCP packets that have the SYN bit set but no ACK bit. 1424This is the short form of 1425.Dq Li tcpflags\ syn,!ack . 1426.It Cm src-ip Ar ip-address 1427Matches IPv4 packets whose source IP is one of the address(es) 1428specified as an argument. 1429.It Cm src-ip6 Ar ip6-address 1430Matches IPv6 packets whose source IP is one of the address(es) 1431specified as an argument. 1432.It Cm src-port Ar ports 1433Matches IP packets whose source port is one of the port(s) 1434specified as argument. 1435.It Cm tagged Ar tag-list 1436Matches packets whose tags are included in 1437.Ar tag-list , 1438which is either a single value or a list of values or ranges 1439specified in the same way as 1440.Ar ports . 1441Tags can be applied to the packet using 1442.Cm tag 1443rule action parameter (see it's description for details on tags). 1444.It Cm tcpack Ar ack 1445TCP packets only. 1446Match if the TCP header acknowledgment number field is set to 1447.Ar ack . 1448.It Cm tcpdatalen Ar tcpdatalen-list 1449Matches TCP packets whose length of TCP data is 1450.Ar tcpdatalen-list , 1451which is either a single value or a list of values or ranges 1452specified in the same way as 1453.Ar ports . 1454.It Cm tcpflags Ar spec 1455TCP packets only. 1456Match if the TCP header contains the comma separated list of 1457flags specified in 1458.Ar spec . 1459The supported TCP flags are: 1460.Pp 1461.Cm fin , 1462.Cm syn , 1463.Cm rst , 1464.Cm psh , 1465.Cm ack 1466and 1467.Cm urg . 1468The absence of a particular flag may be denoted 1469with a 1470.Ql \&! . 1471A rule which contains a 1472.Cm tcpflags 1473specification can never match a fragmented packet which has 1474a non-zero offset. 1475See the 1476.Cm frag 1477option for details on matching fragmented packets. 1478.It Cm tcpseq Ar seq 1479TCP packets only. 1480Match if the TCP header sequence number field is set to 1481.Ar seq . 1482.It Cm tcpwin Ar win 1483TCP packets only. 1484Match if the TCP header window field is set to 1485.Ar win . 1486.It Cm tcpoptions Ar spec 1487TCP packets only. 1488Match if the TCP header contains the comma separated list of 1489options specified in 1490.Ar spec . 1491The supported TCP options are: 1492.Pp 1493.Cm mss 1494(maximum segment size), 1495.Cm window 1496(tcp window advertisement), 1497.Cm sack 1498(selective ack), 1499.Cm ts 1500(rfc1323 timestamp) and 1501.Cm cc 1502(rfc1644 t/tcp connection count). 1503The absence of a particular option may be denoted 1504with a 1505.Ql \&! . 1506.It Cm uid Ar user 1507Match all TCP or UDP packets sent by or received for a 1508.Ar user . 1509A 1510.Ar user 1511may be matched by name or identification number. 1512.It Cm verrevpath 1513For incoming packets, 1514a routing table lookup is done on the packet's source address. 1515If the interface on which the packet entered the system matches the 1516outgoing interface for the route, 1517the packet matches. 1518If the interfaces do not match up, 1519the packet does not match. 1520All outgoing packets or packets with no incoming interface match. 1521.Pp 1522The name and functionality of the option is intentionally similar to 1523the Cisco IOS command: 1524.Pp 1525.Dl ip verify unicast reverse-path 1526.Pp 1527This option can be used to make anti-spoofing rules to reject all 1528packets with source addresses not from this interface. 1529See also the option 1530.Cm antispoof . 1531.It Cm versrcreach 1532For incoming packets, 1533a routing table lookup is done on the packet's source address. 1534If a route to the source address exists, but not the default route 1535or a blackhole/reject route, the packet matches. 1536Otherwise, the packet does not match. 1537All outgoing packets match. 1538.Pp 1539The name and functionality of the option is intentionally similar to 1540the Cisco IOS command: 1541.Pp 1542.Dl ip verify unicast source reachable-via any 1543.Pp 1544This option can be used to make anti-spoofing rules to reject all 1545packets whose source address is unreachable. 1546.It Cm antispoof 1547For incoming packets, the packet's source address is checked if it 1548belongs to a directly connected network. 1549If the network is directly connected, then the interface the packet 1550came on in is compared to the interface the network is connected to. 1551When incoming interface and directly connected interface are not the 1552same, the packet does not match. 1553Otherwise, the packet does match. 1554All outgoing packets match. 1555.Pp 1556This option can be used to make anti-spoofing rules to reject all 1557packets that pretend to be from a directly connected network but do 1558not come in through that interface. 1559This option is similar to but more restricted than 1560.Cm verrevpath 1561because it engages only on packets with source addresses of directly 1562connected networks instead of all source addresses. 1563.El 1564.Sh LOOKUP TABLES 1565Lookup tables are useful to handle large sparse address sets, 1566typically from a hundred to several thousands of entries. 1567There may be up to 128 different lookup tables, numbered 0 to 127. 1568.Pp 1569Each entry is represented by an 1570.Ar addr Ns Op / Ns Ar masklen 1571and will match all addresses with base 1572.Ar addr 1573(specified as an IP address or a hostname) 1574and mask width of 1575.Ar masklen 1576bits. 1577If 1578.Ar masklen 1579is not specified, it defaults to 32. 1580When looking up an IP address in a table, the most specific 1581entry will match. 1582Associated with each entry is a 32-bit unsigned 1583.Ar value , 1584which can optionally be checked by a rule matching code. 1585When adding an entry, if 1586.Ar value 1587is not specified, it defaults to 0. 1588.Pp 1589An entry can be added to a table 1590.Pq Cm add , 1591removed from a table 1592.Pq Cm delete , 1593a table can be examined 1594.Pq Cm list 1595or flushed 1596.Pq Cm flush . 1597.Pp 1598Internally, each table is stored in a Radix tree, the same way as 1599the routing table (see 1600.Xr route 4 ) . 1601.Pp 1602Lookup tables currently support IPv4 addresses only. 1603.Pp 1604The 1605.Cm tablearg 1606feature provides the ability to use a value, looked up in the table, as 1607the argument for a rule action, action parameter or rule option. 1608This can significantly reduce number of rules in some configurations. 1609The 1610.Cm tablearg 1611argument can be used with the following actions: 1612.Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd 1613action parameters: 1614.Cm tag, untag, 1615rule options: 1616.Cm limit, tagged. 1617.Pp 1618When used with 1619.Cm fwd 1620it is possible to supply table entries with values 1621that are in the form of IP addresses or hostnames. 1622See the 1623.Sx EXAMPLES 1624Section for example usage of tables and the tablearg keyword. 1625.Sh SETS OF RULES 1626Each rule belongs to one of 32 different 1627.Em sets 1628, numbered 0 to 31. 1629Set 31 is reserved for the default rule. 1630.Pp 1631By default, rules are put in set 0, unless you use the 1632.Cm set N 1633attribute when entering a new rule. 1634Sets can be individually and atomically enabled or disabled, 1635so this mechanism permits an easy way to store multiple configurations 1636of the firewall and quickly (and atomically) switch between them. 1637The command to enable/disable sets is 1638.Bd -ragged -offset indent 1639.Nm 1640.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 1641.Ed 1642.Pp 1643where multiple 1644.Cm enable 1645or 1646.Cm disable 1647sections can be specified. 1648Command execution is atomic on all the sets specified in the command. 1649By default, all sets are enabled. 1650.Pp 1651When you disable a set, its rules behave as if they do not exist 1652in the firewall configuration, with only one exception: 1653.Bd -ragged -offset indent 1654dynamic rules created from a rule before it had been disabled 1655will still be active until they expire. 1656In order to delete 1657dynamic rules you have to explicitly delete the parent rule 1658which generated them. 1659.Ed 1660.Pp 1661The set number of rules can be changed with the command 1662.Bd -ragged -offset indent 1663.Nm 1664.Cm set move 1665.Brq Cm rule Ar rule-number | old-set 1666.Cm to Ar new-set 1667.Ed 1668.Pp 1669Also, you can atomically swap two rulesets with the command 1670.Bd -ragged -offset indent 1671.Nm 1672.Cm set swap Ar first-set second-set 1673.Ed 1674.Pp 1675See the 1676.Sx EXAMPLES 1677Section on some possible uses of sets of rules. 1678.Sh STATEFUL FIREWALL 1679Stateful operation is a way for the firewall to dynamically 1680create rules for specific flows when packets that 1681match a given pattern are detected. 1682Support for stateful 1683operation comes through the 1684.Cm check-state , keep-state 1685and 1686.Cm limit 1687options of 1688.Nm rules . 1689.Pp 1690Dynamic rules are created when a packet matches a 1691.Cm keep-state 1692or 1693.Cm limit 1694rule, causing the creation of a 1695.Em dynamic 1696rule which will match all and only packets with 1697a given 1698.Em protocol 1699between a 1700.Em src-ip/src-port dst-ip/dst-port 1701pair of addresses 1702.Em ( src 1703and 1704.Em dst 1705are used here only to denote the initial match addresses, but they 1706are completely equivalent afterwards). 1707Dynamic rules will be checked at the first 1708.Cm check-state, keep-state 1709or 1710.Cm limit 1711occurrence, and the action performed upon a match will be the same 1712as in the parent rule. 1713.Pp 1714Note that no additional attributes other than protocol and IP addresses 1715and ports are checked on dynamic rules. 1716.Pp 1717The typical use of dynamic rules is to keep a closed firewall configuration, 1718but let the first TCP SYN packet from the inside network install a 1719dynamic rule for the flow so that packets belonging to that session 1720will be allowed through the firewall: 1721.Pp 1722.Dl "ipfw add check-state" 1723.Dl "ipfw add allow tcp from my-subnet to any setup keep-state" 1724.Dl "ipfw add deny tcp from any to any" 1725.Pp 1726A similar approach can be used for UDP, where an UDP packet coming 1727from the inside will install a dynamic rule to let the response through 1728the firewall: 1729.Pp 1730.Dl "ipfw add check-state" 1731.Dl "ipfw add allow udp from my-subnet to any keep-state" 1732.Dl "ipfw add deny udp from any to any" 1733.Pp 1734Dynamic rules expire after some time, which depends on the status 1735of the flow and the setting of some 1736.Cm sysctl 1737variables. 1738See Section 1739.Sx SYSCTL VARIABLES 1740for more details. 1741For TCP sessions, dynamic rules can be instructed to periodically 1742send keepalive packets to refresh the state of the rule when it is 1743about to expire. 1744.Pp 1745See Section 1746.Sx EXAMPLES 1747for more examples on how to use dynamic rules. 1748.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 1749.Nm 1750is also the user interface for the 1751.Nm dummynet 1752traffic shaper. 1753.Pp 1754.Nm dummynet 1755operates by first using the firewall to classify packets and divide them into 1756.Em flows , 1757using any match pattern that can be used in 1758.Nm 1759rules. 1760Depending on local policies, a flow can contain packets for a single 1761TCP connection, or from/to a given host, or entire subnet, or a 1762protocol type, etc. 1763.Pp 1764There are two modes of 1765.Nm dummynet 1766operation: 1767.Dq normal 1768and 1769.Dq fast . 1770The 1771.Dq normal 1772mode tries to emulate a real link: the 1773.Nm dummynet 1774scheduler ensures that the packet will not leave the pipe faster than it 1775would on the real link with a given bandwidth. 1776The 1777.Dq fast 1778mode allows certain packets to bypass the 1779.Nm dummynet 1780scheduler (if packet flow does not exceed pipe's bandwidth). 1781This is the reason why the 1782.Dq fast 1783mode requires less CPU cycles per packet (on average) and packet latency 1784can be significantly lower in comparison to a real link with the same 1785bandwidth. 1786The default mode is 1787.Dq normal . 1788The 1789.Dq fast 1790mode can be enabled by setting the 1791.Va net.inet.ip.dummynet.io_fast 1792.Xr sysctl 8 1793variable to a non-zero value. 1794.Pp 1795Packets belonging to the same flow are then passed to either of two 1796different objects, which implement the traffic regulation: 1797.Bl -hang -offset XXXX 1798.It Em pipe 1799A pipe emulates a link with given bandwidth, propagation delay, 1800queue size and packet loss rate. 1801Packets are queued in front of the pipe as they come out from the classifier, 1802and then transferred to the pipe according to the pipe's parameters. 1803.Pp 1804.It Em queue 1805A queue 1806is an abstraction used to implement the WF2Q+ 1807(Worst-case Fair Weighted Fair Queueing) policy, which is 1808an efficient variant of the WFQ policy. 1809.br 1810The queue associates a 1811.Em weight 1812and a reference pipe to each flow, and then all backlogged (i.e., 1813with packets queued) flows linked to the same pipe share the pipe's 1814bandwidth proportionally to their weights. 1815Note that weights are not priorities; a flow with a lower weight 1816is still guaranteed to get its fraction of the bandwidth even if a 1817flow with a higher weight is permanently backlogged. 1818.Pp 1819.El 1820In practice, 1821.Em pipes 1822can be used to set hard limits to the bandwidth that a flow can use, whereas 1823.Em queues 1824can be used to determine how different flow share the available bandwidth. 1825.Pp 1826The 1827.Em pipe 1828and 1829.Em queue 1830configuration commands are the following: 1831.Bd -ragged -offset indent 1832.Cm pipe Ar number Cm config Ar pipe-configuration 1833.Pp 1834.Cm queue Ar number Cm config Ar queue-configuration 1835.Ed 1836.Pp 1837The following parameters can be configured for a pipe: 1838.Pp 1839.Bl -tag -width indent -compact 1840.It Cm bw Ar bandwidth | device 1841Bandwidth, measured in 1842.Sm off 1843.Op Cm K | M 1844.Brq Cm bit/s | Byte/s . 1845.Sm on 1846.Pp 1847A value of 0 (default) means unlimited bandwidth. 1848The unit must immediately follow the number, as in 1849.Pp 1850.Dl "ipfw pipe 1 config bw 300Kbit/s" 1851.Pp 1852If a device name is specified instead of a numeric value, as in 1853.Pp 1854.Dl "ipfw pipe 1 config bw tun0" 1855.Pp 1856then the transmit clock is supplied by the specified device. 1857At the moment only the 1858.Xr tun 4 1859device supports this 1860functionality, for use in conjunction with 1861.Xr ppp 8 . 1862.Pp 1863.It Cm delay Ar ms-delay 1864Propagation delay, measured in milliseconds. 1865The value is rounded to the next multiple of the clock tick 1866(typically 10ms, but it is a good practice to run kernels 1867with 1868.Dq "options HZ=1000" 1869to reduce 1870the granularity to 1ms or less). 1871Default value is 0, meaning no delay. 1872.El 1873.Pp 1874The following parameters can be configured for a queue: 1875.Pp 1876.Bl -tag -width indent -compact 1877.It Cm pipe Ar pipe_nr 1878Connects a queue to the specified pipe. 1879Multiple queues (with the same or different weights) can be connected to 1880the same pipe, which specifies the aggregate rate for the set of queues. 1881.Pp 1882.It Cm weight Ar weight 1883Specifies the weight to be used for flows matching this queue. 1884The weight must be in the range 1..100, and defaults to 1. 1885.El 1886.Pp 1887Finally, the following parameters can be configured for both 1888pipes and queues: 1889.Pp 1890.Bl -tag -width XXXX -compact 1891.Pp 1892.It Cm buckets Ar hash-table-size 1893Specifies the size of the hash table used for storing the 1894various queues. 1895Default value is 64 controlled by the 1896.Xr sysctl 8 1897variable 1898.Va net.inet.ip.dummynet.hash_size , 1899allowed range is 16 to 65536. 1900.Pp 1901.It Cm mask Ar mask-specifier 1902Packets sent to a given pipe or queue by an 1903.Nm 1904rule can be further classified into multiple flows, each of which is then 1905sent to a different 1906.Em dynamic 1907pipe or queue. 1908A flow identifier is constructed by masking the IP addresses, 1909ports and protocol types as specified with the 1910.Cm mask 1911options in the configuration of the pipe or queue. 1912For each different flow identifier, a new pipe or queue is created 1913with the same parameters as the original object, and matching packets 1914are sent to it. 1915.Pp 1916Thus, when 1917.Em dynamic pipes 1918are used, each flow will get the same bandwidth as defined by the pipe, 1919whereas when 1920.Em dynamic queues 1921are used, each flow will share the parent's pipe bandwidth evenly 1922with other flows generated by the same queue (note that other queues 1923with different weights might be connected to the same pipe). 1924.br 1925Available mask specifiers are a combination of one or more of the following: 1926.Pp 1927.Cm dst-ip Ar mask , 1928.Cm dst-ip6 Ar mask , 1929.Cm src-ip Ar mask , 1930.Cm src-ip6 Ar mask , 1931.Cm dst-port Ar mask , 1932.Cm src-port Ar mask , 1933.Cm flow-id Ar mask , 1934.Cm proto Ar mask 1935or 1936.Cm all , 1937.Pp 1938where the latter means all bits in all fields are significant. 1939.Pp 1940.It Cm noerror 1941When a packet is dropped by a 1942.Nm dummynet 1943queue or pipe, the error 1944is normally reported to the caller routine in the kernel, in the 1945same way as it happens when a device queue fills up. 1946Setting this 1947option reports the packet as successfully delivered, which can be 1948needed for some experimental setups where you want to simulate 1949loss or congestion at a remote router. 1950.Pp 1951.It Cm plr Ar packet-loss-rate 1952Packet loss rate. 1953Argument 1954.Ar packet-loss-rate 1955is a floating-point number between 0 and 1, with 0 meaning no 1956loss, 1 meaning 100% loss. 1957The loss rate is internally represented on 31 bits. 1958.Pp 1959.It Cm queue Brq Ar slots | size Ns Cm Kbytes 1960Queue size, in 1961.Ar slots 1962or 1963.Cm KBytes . 1964Default value is 50 slots, which 1965is the typical queue size for Ethernet devices. 1966Note that for slow speed links you should keep the queue 1967size short or your traffic might be affected by a significant 1968queueing delay. 1969E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit 1970or 20s of queue on a 30Kbit/s pipe. 1971Even worse effects can result if you get packets from an 1972interface with a much larger MTU, e.g.\& the loopback interface 1973with its 16KB packets. 1974The 1975.Xr sysctl 8 1976variables 1977.Em net.inet.ip.dummynet.pipe_byte_limit 1978and 1979.Em net.inet.ip.dummynet.pipe_slot_limit 1980control the maximum lengths that can be specified. 1981.Pp 1982.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p 1983Make use of the RED (Random Early Detection) queue management algorithm. 1984.Ar w_q 1985and 1986.Ar max_p 1987are floating 1988point numbers between 0 and 1 (0 not included), while 1989.Ar min_th 1990and 1991.Ar max_th 1992are integer numbers specifying thresholds for queue management 1993(thresholds are computed in bytes if the queue has been defined 1994in bytes, in slots otherwise). 1995The 1996.Nm dummynet 1997also supports the gentle RED variant (gred). 1998Three 1999.Xr sysctl 8 2000variables can be used to control the RED behaviour: 2001.Bl -tag -width indent 2002.It Va net.inet.ip.dummynet.red_lookup_depth 2003specifies the accuracy in computing the average queue 2004when the link is idle (defaults to 256, must be greater than zero) 2005.It Va net.inet.ip.dummynet.red_avg_pkt_size 2006specifies the expected average packet size (defaults to 512, must be 2007greater than zero) 2008.It Va net.inet.ip.dummynet.red_max_pkt_size 2009specifies the expected maximum packet size, only used when queue 2010thresholds are in bytes (defaults to 1500, must be greater than zero). 2011.El 2012.El 2013.Pp 2014When used with IPv6 data, 2015.Nm dummynet 2016currently has several limitations. 2017Information necessary to route link-local packets to an 2018interface is not available after processing by 2019.Nm dummynet 2020so those packets are dropped in the output path. 2021Care should be taken to insure that link-local packets are not passed to 2022.Nm dummynet . 2023.Sh CHECKLIST 2024Here are some important points to consider when designing your 2025rules: 2026.Bl -bullet 2027.It 2028Remember that you filter both packets going 2029.Cm in 2030and 2031.Cm out . 2032Most connections need packets going in both directions. 2033.It 2034Remember to test very carefully. 2035It is a good idea to be near the console when doing this. 2036If you cannot be near the console, 2037use an auto-recovery script such as the one in 2038.Pa /usr/share/examples/ipfw/change_rules.sh . 2039.It 2040Do not forget the loopback interface. 2041.El 2042.Sh FINE POINTS 2043.Bl -bullet 2044.It 2045There are circumstances where fragmented datagrams are unconditionally 2046dropped. 2047TCP packets are dropped if they do not contain at least 20 bytes of 2048TCP header, UDP packets are dropped if they do not contain a full 8 2049byte UDP header, and ICMP packets are dropped if they do not contain 20504 bytes of ICMP header, enough to specify the ICMP type, code, and 2051checksum. 2052These packets are simply logged as 2053.Dq pullup failed 2054since there may not be enough good data in the packet to produce a 2055meaningful log entry. 2056.It 2057Another type of packet is unconditionally dropped, a TCP packet with a 2058fragment offset of one. 2059This is a valid packet, but it only has one use, to try 2060to circumvent firewalls. 2061When logging is enabled, these packets are 2062reported as being dropped by rule -1. 2063.It 2064If you are logged in over a network, loading the 2065.Xr kld 4 2066version of 2067.Nm 2068is probably not as straightforward as you would think. 2069I recommend the following command line: 2070.Bd -literal -offset indent 2071kldload ipfw && \e 2072ipfw add 32000 allow ip from any to any 2073.Ed 2074.Pp 2075Along the same lines, doing an 2076.Bd -literal -offset indent 2077ipfw flush 2078.Ed 2079.Pp 2080in similar surroundings is also a bad idea. 2081.It 2082The 2083.Nm 2084filter list may not be modified if the system security level 2085is set to 3 or higher 2086(see 2087.Xr init 8 2088for information on system security levels). 2089.El 2090.Sh PACKET DIVERSION 2091A 2092.Xr divert 4 2093socket bound to the specified port will receive all packets 2094diverted to that port. 2095If no socket is bound to the destination port, or if the divert module is 2096not loaded, or if the kernel was not compiled with divert socket support, 2097the packets are dropped. 2098.Sh NETWORK ADDRESS TRANSLATION (NAT) 2099The nat configuration command is the following: 2100.Bd -ragged -offset indent 2101.Bk -words 2102.Cm nat 2103.Ar nat_number 2104.Cm config 2105.Ar nat-configuration 2106.Ek 2107.Ed 2108.Pp 2109. 2110The following parameters can be configured: 2111.Bl -tag -width indent 2112.It Cm ip Ar ip_address 2113Define an ip address to use for aliasing. 2114.It Cm if Ar nic 2115Use ip addres of NIC for aliasing, dynamically changing 2116it if NIC's ip address change. 2117.It Cm log 2118Enable logging on this nat instance. 2119.It Cm deny_in 2120Deny any incoming connection from outside world. 2121.It Cm same_ports 2122Try to leave the alias port numbers unchanged from 2123the actual local port numbers. 2124.It Cm unreg_only 2125Traffic on the local network not originating from an 2126unregistered address spaces will be ignored. 2127.It Cm reset 2128Reset table of the packet aliasing engine on address change. 2129.It Cm reverse 2130Reverse the way libalias handles aliasing. 2131.It Cm proxy_only 2132Obey transparent proxy rules only, packet aliasing is not performed. 2133.El 2134.Pp 2135To let the packet continue after being (de)aliased, set the sysctl variable 2136.Va net.inet.ip.fw.one_pass 2137to 0. 2138For more information about aliasing modes, refer to 2139.Xr libalias 3 2140. 2141See Section 2142.Sx EXAMPLES 2143for some examples about nat usage. 2144.Sh REDIRECT AND LSNAT SUPPORT IN IPFW 2145Redirect and LSNAT support follow closely the syntax used in 2146.Xr natd 8 2147. 2148See Section 2149.Sx EXAMPLES 2150for some examples on how to do redirect and lsnat. 2151.Sh SYSCTL VARIABLES 2152A set of 2153.Xr sysctl 8 2154variables controls the behaviour of the firewall and 2155associated modules 2156.Pq Nm dummynet , bridge . 2157These are shown below together with their default value 2158(but always check with the 2159.Xr sysctl 8 2160command what value is actually in use) and meaning: 2161.Bl -tag -width indent 2162.It Va net.inet.ip.dummynet.expire : No 1 2163Lazily delete dynamic pipes/queue once they have no pending traffic. 2164You can disable this by setting the variable to 0, in which case 2165the pipes/queues will only be deleted when the threshold is reached. 2166.It Va net.inet.ip.dummynet.hash_size : No 64 2167Default size of the hash table used for dynamic pipes/queues. 2168This value is used when no 2169.Cm buckets 2170option is specified when configuring a pipe/queue. 2171.It Va net.inet.ip.dummynet.io_fast : No 0 2172If set to a non-zero value, 2173the 2174.Dq fast 2175mode of 2176.Nm dummynet 2177operation (see above) is enabled. 2178.It Va net.inet.ip.dummynet.io_pkt 2179Number of packets passed to 2180.Nm dummynet . 2181.It Va net.inet.ip.dummynet.io_pkt_drop 2182Number of packets dropped by 2183.Nm dummynet . 2184.It Va net.inet.ip.dummynet.io_pkt_fast 2185Number of packets bypassed by the 2186.Nm dummynet 2187scheduler. 2188.It Va net.inet.ip.dummynet.max_chain_len : No 16 2189Target value for the maximum number of pipes/queues in a hash bucket. 2190The product 2191.Cm max_chain_len*hash_size 2192is used to determine the threshold over which empty pipes/queues 2193will be expired even when 2194.Cm net.inet.ip.dummynet.expire=0 . 2195.It Va net.inet.ip.dummynet.red_lookup_depth : No 256 2196.It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512 2197.It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500 2198Parameters used in the computations of the drop probability 2199for the RED algorithm. 2200.It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576 2201.It Va net.inet.ip.dummynet.pipe_slot_limit : No 100 2202The maximum queue size that can be specified in bytes or packets. 2203These limits prevent accidental exhaustion of resources such as mbufs. 2204If you raise these limits, 2205you should make sure the system is configured so that sufficient resources 2206are available. 2207.It Va net.inet.ip.fw.autoinc_step : No 100 2208Delta between rule numbers when auto-generating them. 2209The value must be in the range 1..1000. 2210.It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets 2211The current number of buckets in the hash table for dynamic rules 2212(readonly). 2213.It Va net.inet.ip.fw.debug : No 1 2214Controls debugging messages produced by 2215.Nm . 2216.It Va net.inet.ip.fw.dyn_buckets : No 256 2217The number of buckets in the hash table for dynamic rules. 2218Must be a power of 2, up to 65536. 2219It only takes effect when all dynamic rules have expired, so you 2220are advised to use a 2221.Cm flush 2222command to make sure that the hash table is resized. 2223.It Va net.inet.ip.fw.dyn_count : No 3 2224Current number of dynamic rules 2225(read-only). 2226.It Va net.inet.ip.fw.dyn_keepalive : No 1 2227Enables generation of keepalive packets for 2228.Cm keep-state 2229rules on TCP sessions. 2230A keepalive is generated to both 2231sides of the connection every 5 seconds for the last 20 2232seconds of the lifetime of the rule. 2233.It Va net.inet.ip.fw.dyn_max : No 8192 2234Maximum number of dynamic rules. 2235When you hit this limit, no more dynamic rules can be 2236installed until old ones expire. 2237.It Va net.inet.ip.fw.dyn_ack_lifetime : No 300 2238.It Va net.inet.ip.fw.dyn_syn_lifetime : No 20 2239.It Va net.inet.ip.fw.dyn_fin_lifetime : No 1 2240.It Va net.inet.ip.fw.dyn_rst_lifetime : No 1 2241.It Va net.inet.ip.fw.dyn_udp_lifetime : No 5 2242.It Va net.inet.ip.fw.dyn_short_lifetime : No 30 2243These variables control the lifetime, in seconds, of dynamic 2244rules. 2245Upon the initial SYN exchange the lifetime is kept short, 2246then increased after both SYN have been seen, then decreased 2247again during the final FIN exchange or when a RST is received. 2248Both 2249.Em dyn_fin_lifetime 2250and 2251.Em dyn_rst_lifetime 2252must be strictly lower than 5 seconds, the period of 2253repetition of keepalives. 2254The firewall enforces that. 2255.It Va net.inet.ip.fw.enable : No 1 2256Enables the firewall. 2257Setting this variable to 0 lets you run your machine without 2258firewall even if compiled in. 2259.It Va net.inet6.ip6.fw.enable : No 1 2260provides the same functionality as above for the IPv6 case. 2261.It Va net.inet.ip.fw.one_pass : No 1 2262When set, the packet exiting from the 2263.Nm dummynet 2264pipe or from 2265.Xr ng_ipfw 4 2266node is not passed though the firewall again. 2267Otherwise, after an action, the packet is 2268reinjected into the firewall at the next rule. 2269.It Va net.inet.ip.fw.verbose : No 1 2270Enables verbose messages. 2271.It Va net.inet.ip.fw.verbose_limit : No 0 2272Limits the number of messages produced by a verbose firewall. 2273.It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1 2274If enabled packets with unknown IPv6 Extension Headers will be denied. 2275.It Va net.link.ether.ipfw : No 0 2276Controls whether layer-2 packets are passed to 2277.Nm . 2278Default is no. 2279.It Va net.link.bridge.ipfw : No 0 2280Controls whether bridged packets are passed to 2281.Nm . 2282Default is no. 2283.El 2284.Pp 2285.Sh EXAMPLES 2286There are far too many possible uses of 2287.Nm 2288so this Section will only give a small set of examples. 2289.Pp 2290.Ss BASIC PACKET FILTERING 2291This command adds an entry which denies all tcp packets from 2292.Em cracker.evil.org 2293to the telnet port of 2294.Em wolf.tambov.su 2295from being forwarded by the host: 2296.Pp 2297.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet" 2298.Pp 2299This one disallows any connection from the entire cracker's 2300network to my host: 2301.Pp 2302.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org" 2303.Pp 2304A first and efficient way to limit access (not using dynamic rules) 2305is the use of the following rules: 2306.Pp 2307.Dl "ipfw add allow tcp from any to any established" 2308.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup" 2309.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup" 2310.Dl "..." 2311.Dl "ipfw add deny tcp from any to any" 2312.Pp 2313The first rule will be a quick match for normal TCP packets, 2314but it will not match the initial SYN packet, which will be 2315matched by the 2316.Cm setup 2317rules only for selected source/destination pairs. 2318All other SYN packets will be rejected by the final 2319.Cm deny 2320rule. 2321.Pp 2322If you administer one or more subnets, you can take advantage 2323of the address sets and or-blocks and write extremely 2324compact rulesets which selectively enable services to blocks 2325of clients, as below: 2326.Pp 2327.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q" 2328.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q" 2329.Dl "" 2330.Dl "ipfw add allow ip from ${goodguys} to any" 2331.Dl "ipfw add deny ip from ${badguys} to any" 2332.Dl "... normal policies ..." 2333.Pp 2334The 2335.Cm verrevpath 2336option could be used to do automated anti-spoofing by adding the 2337following to the top of a ruleset: 2338.Pp 2339.Dl "ipfw add deny ip from any to any not verrevpath in" 2340.Pp 2341This rule drops all incoming packets that appear to be coming to the 2342system on the wrong interface. 2343For example, a packet with a source 2344address belonging to a host on a protected internal network would be 2345dropped if it tried to enter the system from an external interface. 2346.Pp 2347The 2348.Cm antispoof 2349option could be used to do similar but more restricted anti-spoofing 2350by adding the following to the top of a ruleset: 2351.Pp 2352.Dl "ipfw add deny ip from any to any not antispoof in" 2353.Pp 2354This rule drops all incoming packets that appear to be coming from another 2355directly connected system but on the wrong interface. 2356For example, a packet with a source address of 2357.Li 192.168.0.0/24 2358, configured on 2359.Li fxp0 2360, but coming in on 2361.Li fxp1 2362would be dropped. 2363.Ss DYNAMIC RULES 2364In order to protect a site from flood attacks involving fake 2365TCP packets, it is safer to use dynamic rules: 2366.Pp 2367.Dl "ipfw add check-state" 2368.Dl "ipfw add deny tcp from any to any established" 2369.Dl "ipfw add allow tcp from my-net to any setup keep-state" 2370.Pp 2371This will let the firewall install dynamic rules only for 2372those connection which start with a regular SYN packet coming 2373from the inside of our network. 2374Dynamic rules are checked when encountering the first 2375.Cm check-state 2376or 2377.Cm keep-state 2378rule. 2379A 2380.Cm check-state 2381rule should usually be placed near the beginning of the 2382ruleset to minimize the amount of work scanning the ruleset. 2383Your mileage may vary. 2384.Pp 2385To limit the number of connections a user can open 2386you can use the following type of rules: 2387.Pp 2388.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10" 2389.Dl "ipfw add allow tcp from any to me setup limit src-addr 4" 2390.Pp 2391The former (assuming it runs on a gateway) will allow each host 2392on a /24 network to open at most 10 TCP connections. 2393The latter can be placed on a server to make sure that a single 2394client does not use more than 4 simultaneous connections. 2395.Pp 2396.Em BEWARE : 2397stateful rules can be subject to denial-of-service attacks 2398by a SYN-flood which opens a huge number of dynamic rules. 2399The effects of such attacks can be partially limited by 2400acting on a set of 2401.Xr sysctl 8 2402variables which control the operation of the firewall. 2403.Pp 2404Here is a good usage of the 2405.Cm list 2406command to see accounting records and timestamp information: 2407.Pp 2408.Dl ipfw -at list 2409.Pp 2410or in short form without timestamps: 2411.Pp 2412.Dl ipfw -a list 2413.Pp 2414which is equivalent to: 2415.Pp 2416.Dl ipfw show 2417.Pp 2418Next rule diverts all incoming packets from 192.168.2.0/24 2419to divert port 5000: 2420.Pp 2421.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in 2422.Pp 2423.Ss TRAFFIC SHAPING 2424The following rules show some of the applications of 2425.Nm 2426and 2427.Nm dummynet 2428for simulations and the like. 2429.Pp 2430This rule drops random incoming packets with a probability 2431of 5%: 2432.Pp 2433.Dl "ipfw add prob 0.05 deny ip from any to any in" 2434.Pp 2435A similar effect can be achieved making use of 2436.Nm dummynet 2437pipes: 2438.Pp 2439.Dl "ipfw add pipe 10 ip from any to any" 2440.Dl "ipfw pipe 10 config plr 0.05" 2441.Pp 2442We can use pipes to artificially limit bandwidth, e.g.\& on a 2443machine acting as a router, if we want to limit traffic from 2444local clients on 192.168.2.0/24 we do: 2445.Pp 2446.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2447.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes" 2448.Pp 2449note that we use the 2450.Cm out 2451modifier so that the rule is not used twice. 2452Remember in fact that 2453.Nm 2454rules are checked both on incoming and outgoing packets. 2455.Pp 2456Should we want to simulate a bidirectional link with bandwidth 2457limitations, the correct way is the following: 2458.Pp 2459.Dl "ipfw add pipe 1 ip from any to any out" 2460.Dl "ipfw add pipe 2 ip from any to any in" 2461.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes" 2462.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes" 2463.Pp 2464The above can be very useful, e.g.\& if you want to see how 2465your fancy Web page will look for a residential user who 2466is connected only through a slow link. 2467You should not use only one pipe for both directions, unless 2468you want to simulate a half-duplex medium (e.g.\& AppleTalk, 2469Ethernet, IRDA). 2470It is not necessary that both pipes have the same configuration, 2471so we can also simulate asymmetric links. 2472.Pp 2473Should we want to verify network performance with the RED queue 2474management algorithm: 2475.Pp 2476.Dl "ipfw add pipe 1 ip from any to any" 2477.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1" 2478.Pp 2479Another typical application of the traffic shaper is to 2480introduce some delay in the communication. 2481This can significantly affect applications which do a lot of Remote 2482Procedure Calls, and where the round-trip-time of the 2483connection often becomes a limiting factor much more than 2484bandwidth: 2485.Pp 2486.Dl "ipfw add pipe 1 ip from any to any out" 2487.Dl "ipfw add pipe 2 ip from any to any in" 2488.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s" 2489.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s" 2490.Pp 2491Per-flow queueing can be useful for a variety of purposes. 2492A very simple one is counting traffic: 2493.Pp 2494.Dl "ipfw add pipe 1 tcp from any to any" 2495.Dl "ipfw add pipe 1 udp from any to any" 2496.Dl "ipfw add pipe 1 ip from any to any" 2497.Dl "ipfw pipe 1 config mask all" 2498.Pp 2499The above set of rules will create queues (and collect 2500statistics) for all traffic. 2501Because the pipes have no limitations, the only effect is 2502collecting statistics. 2503Note that we need 3 rules, not just the last one, because 2504when 2505.Nm 2506tries to match IP packets it will not consider ports, so we 2507would not see connections on separate ports as different 2508ones. 2509.Pp 2510A more sophisticated example is limiting the outbound traffic 2511on a net with per-host limits, rather than per-network limits: 2512.Pp 2513.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2514.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in" 2515.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2516.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2517.Ss LOOKUP TABLES 2518In the following example, we need to create several traffic bandwidth 2519classes and we need different hosts/networks to fall into different classes. 2520We create one pipe for each class and configure them accordingly. 2521Then we create a single table and fill it with IP subnets and addresses. 2522For each subnet/host we set the argument equal to the number of the pipe 2523that it should use. 2524Then we classify traffic using a single rule: 2525.Pp 2526.Dl "ipfw pipe 1 config bw 1000Kbyte/s" 2527.Dl "ipfw pipe 4 config bw 4000Kbyte/s" 2528.Dl "..." 2529.Dl "ipfw table 1 add 192.168.2.0/24 1" 2530.Dl "ipfw table 1 add 192.168.0.0/27 4" 2531.Dl "ipfw table 1 add 192.168.0.2 1" 2532.Dl "..." 2533.Dl "ipfw add pipe tablearg ip from table(1) to any" 2534.Pp 2535Using the 2536.Cm fwd 2537action, the table entries may include hostnames and IP addresses. 2538.Pp 2539.Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1" 2540.Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz" 2541.Dl "..." 2542.Dl "ipfw add 100 fwd tablearg ip from any to table(1)" 2543.Ss SETS OF RULES 2544To add a set of rules atomically, e.g.\& set 18: 2545.Pp 2546.Dl "ipfw set disable 18" 2547.Dl "ipfw add NN set 18 ... # repeat as needed" 2548.Dl "ipfw set enable 18" 2549.Pp 2550To delete a set of rules atomically the command is simply: 2551.Pp 2552.Dl "ipfw delete set 18" 2553.Pp 2554To test a ruleset and disable it and regain control if something goes wrong: 2555.Pp 2556.Dl "ipfw set disable 18" 2557.Dl "ipfw add NN set 18 ... # repeat as needed" 2558.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18" 2559.Pp 2560Here if everything goes well, you press control-C before the "sleep" 2561terminates, and your ruleset will be left active. 2562Otherwise, e.g.\& if 2563you cannot access your box, the ruleset will be disabled after 2564the sleep terminates thus restoring the previous situation. 2565.Pp 2566To show rules of the specific set: 2567.Pp 2568.Dl "ipfw set 18 show" 2569.Pp 2570To show rules of the disabled set: 2571.Pp 2572.Dl "ipfw -S set 18 show" 2573.Pp 2574To clear a specific rule counters of the specific set: 2575.Pp 2576.Dl "ipfw set 18 zero NN" 2577.Pp 2578To delete a specific rule of the specific set: 2579.Pp 2580.Dl "ipfw set 18 delete NN" 2581.Ss NAT, REDIRECT AND LSNAT 2582First redirect all the traffic to nat instance 123: 2583.Pp 2584.Dl "ipfw add nat 123 all from any to any" 2585.Pp 2586Then to configure nat instance 123 to alias all the outgoing traffic with ip 2587192.168.0.123, blocking all incoming connections, trying to keep 2588same ports on both sides, clearing aliasing table on address change 2589and keeping a log of traffic/link statistics: 2590.Pp 2591.Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports" 2592.Pp 2593Or to change address of instance 123, aliasing table will be cleared (see 2594reset option): 2595.Pp 2596.Dl "ipfw nat 123 config ip 10.0.0.1" 2597.Pp 2598To see configuration of nat instance 123: 2599.Pp 2600.Dl "ipfw nat 123 show config" 2601.Pp 2602To show logs of all the instances in range 111-999: 2603.Pp 2604.Dl "ipfw nat 111-999 show" 2605.Pp 2606To see configurations of all instances: 2607.Pp 2608.Dl "ipfw nat show config" 2609.Pp 2610Or a redirect rule with mixed modes could looks like: 2611.Pp 2612.Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66" 2613.Dl " redirect_port tcp 192.168.0.1:80 500" 2614.Dl " redirect_proto udp 192.168.1.43 192.168.1.1" 2615.Dl " redirect_addr 192.168.0.10,192.168.0.11" 2616.Dl " 10.0.0.100 # LSNAT" 2617.Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22" 2618.Dl " 500 # LSNAT" 2619.Pp 2620or it could be splitted in: 2621.Pp 2622.Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66" 2623.Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500" 2624.Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1" 2625.Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12" 2626.Dl " 10.0.0.100" 2627.Dl "ipfw nat 5 config redirect_port tcp" 2628.Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500" 2629.Pp 2630.Sh SEE ALSO 2631.Xr cpp 1 , 2632.Xr m4 1 , 2633.Xr altq 4 , 2634.Xr divert 4 , 2635.Xr dummynet 4 , 2636.Xr if_bridge 4 , 2637.Xr ip 4 , 2638.Xr ipfirewall 4 , 2639.Xr ng_ipfw 4 , 2640.Xr protocols 5 , 2641.Xr services 5 , 2642.Xr init 8 , 2643.Xr kldload 8 , 2644.Xr reboot 8 , 2645.Xr sysctl 8 , 2646.Xr syslogd 8 2647.Sh HISTORY 2648The 2649.Nm 2650utility first appeared in 2651.Fx 2.0 . 2652.Nm dummynet 2653was introduced in 2654.Fx 2.2.8 . 2655Stateful extensions were introduced in 2656.Fx 4.0 . 2657.Nm ipfw2 2658was introduced in Summer 2002. 2659.Sh AUTHORS 2660.An Ugen J. S. Antsilevich , 2661.An Poul-Henning Kamp , 2662.An Alex Nash , 2663.An Archie Cobbs , 2664.An Luigi Rizzo . 2665.Pp 2666.An -nosplit 2667API based upon code written by 2668.An Daniel Boulet 2669for BSDI. 2670.Pp 2671.An -nosplit 2672In-kernel NAT support written by 2673.An Paolo Pisati Aq piso@FreeBSD.org 2674as part of a Summer of Code 2005 project. 2675.Pp 2676Work on 2677.Nm dummynet 2678traffic shaper supported by Akamba Corp. 2679.Sh BUGS 2680The syntax has grown over the years and sometimes it might be confusing. 2681Unfortunately, backward compatibility prevents cleaning up mistakes 2682made in the definition of the syntax. 2683.Pp 2684.Em !!! WARNING !!! 2685.Pp 2686Misconfiguring the firewall can put your computer in an unusable state, 2687possibly shutting down network services and requiring console access to 2688regain control of it. 2689.Pp 2690Incoming packet fragments diverted by 2691.Cm divert 2692are reassembled before delivery to the socket. 2693The action used on those packet is the one from the 2694rule which matches the first fragment of the packet. 2695.Pp 2696Packets diverted to userland, and then reinserted by a userland process 2697may lose various packet attributes. 2698The packet source interface name 2699will be preserved if it is shorter than 8 bytes and the userland process 2700saves and reuses the sockaddr_in 2701(as does 2702.Xr natd 8 ) ; 2703otherwise, it may be lost. 2704If a packet is reinserted in this manner, later rules may be incorrectly 2705applied, making the order of 2706.Cm divert 2707rules in the rule sequence very important. 2708.Pp 2709Dummynet drops all packets with IPv6 link-local addresses. 2710.Pp 2711Rules using 2712.Cm uid 2713or 2714.Cm gid 2715may not behave as expected. 2716In particular, incoming SYN packets may 2717have no uid or gid associated with them since they do not yet belong 2718to a TCP connection, and the uid/gid associated with a packet may not 2719be as expected if the associated process calls 2720.Xr setuid 2 2721or similar system calls. 2722.Pp 2723Rule syntax is subject to the command line environment and some patterns 2724may need to be escaped with the backslash character 2725or quoted appropriately. 2726.Pp 2727Due to the architecture of 2728.Xr libalias 3 , 2729ipfw nat is not compatible with the tcp segmentation offloading 2730(TSO). Thus, to reliably nat your network traffic, please disable TSO 2731on your NICs using 2732.Xr ifconfig 8 . 2733.Pp 2734ICMP error messages are not implicitly matched by dynamic rules 2735for the respective conversations. 2736To avoid failures of network error detection and path MTU discovery, 2737ICMP error messages may need to be allowed explicitly through static 2738rules. 2739