1.\" 2.\" $FreeBSD$ 3.\" 4.Dd November 10, 2011 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.Pp 44.Nm 45.Cm enable 46.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 47.Nm 48.Cm disable 49.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 50.Pp 51.Ss LOOKUP TABLES 52.Nm 53.Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value 54.Nm 55.Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen 56.Nm 57.Cm table 58.Brq Ar number | all 59.Cm flush 60.Nm 61.Cm table 62.Brq Ar number | all 63.Cm list 64.Pp 65.Ss DUMMYNET CONFIGURATION (TRAFFIC SHAPER AND PACKET SCHEDULER) 66.Nm 67.Brq Cm pipe | queue | sched 68.Ar number 69.Cm config 70.Ar config-options 71.Nm 72.Op Fl s Op Ar field 73.Brq Cm pipe | queue | sched 74.Brq Cm delete | list | show 75.Op Ar number ... 76.Pp 77.Ss IN-KERNEL NAT 78.Nm 79.Op Fl q 80.Cm nat 81.Ar number 82.Cm config 83.Ar config-options 84.Pp 85.Nm 86.Op Fl cfnNqS 87.Oo 88.Fl p Ar preproc 89.Oo 90.Ar preproc-flags 91.Oc 92.Oc 93.Ar pathname 94.Sh DESCRIPTION 95The 96.Nm 97utility is the user interface for controlling the 98.Xr ipfw 4 99firewall, the 100.Xr dummynet 4 101traffic shaper/packet scheduler, and the 102in-kernel NAT services. 103.Pp 104A firewall configuration, or 105.Em ruleset , 106is made of a list of 107.Em rules 108numbered from 1 to 65535. 109Packets are passed to the firewall 110from a number of different places in the protocol stack 111(depending on the source and destination of the packet, 112it is possible for the firewall to be 113invoked multiple times on the same packet). 114The packet passed to the firewall is compared 115against each of the rules in the 116.Em ruleset , 117in rule-number order 118(multiple rules with the same number are permitted, in which case 119they are processed in order of insertion). 120When a match is found, the action corresponding to the 121matching rule is performed. 122.Pp 123Depending on the action and certain system settings, packets 124can be reinjected into the firewall at some rule after the 125matching one for further processing. 126.Pp 127A ruleset always includes a 128.Em default 129rule (numbered 65535) which cannot be modified or deleted, 130and matches all packets. 131The action associated with the 132.Em default 133rule can be either 134.Cm deny 135or 136.Cm allow 137depending on how the kernel is configured. 138.Pp 139If the ruleset includes one or more rules with the 140.Cm keep-state 141or 142.Cm limit 143option, 144the firewall will have a 145.Em stateful 146behaviour, i.e., upon a match it will create 147.Em dynamic rules , 148i.e. rules that match packets with the same 5-tuple 149(protocol, source and destination addresses and ports) 150as the packet which caused their creation. 151Dynamic rules, which have a limited lifetime, are checked 152at the first occurrence of a 153.Cm check-state , 154.Cm keep-state 155or 156.Cm limit 157rule, and are typically used to open the firewall on-demand to 158legitimate traffic only. 159See the 160.Sx STATEFUL FIREWALL 161and 162.Sx EXAMPLES 163Sections below for more information on the stateful behaviour of 164.Nm . 165.Pp 166All rules (including dynamic ones) have a few associated counters: 167a packet count, a byte count, a log count and a timestamp 168indicating the time of the last match. 169Counters can be displayed or reset with 170.Nm 171commands. 172.Pp 173Each rule belongs to one of 32 different 174.Em sets 175, and there are 176.Nm 177commands to atomically manipulate sets, such as enable, 178disable, swap sets, move all rules in a set to another 179one, delete all rules in a set. 180These can be useful to 181install temporary configurations, or to test them. 182See Section 183.Sx SETS OF RULES 184for more information on 185.Em sets . 186.Pp 187Rules can be added with the 188.Cm add 189command; deleted individually or in groups with the 190.Cm delete 191command, and globally (except those in set 31) with the 192.Cm flush 193command; displayed, optionally with the content of the 194counters, using the 195.Cm show 196and 197.Cm list 198commands. 199Finally, counters can be reset with the 200.Cm zero 201and 202.Cm resetlog 203commands. 204.Pp 205.Ss COMMAND OPTIONS 206The following general options are available when invoking 207.Nm : 208.Bl -tag -width indent 209.It Fl a 210Show counter values when listing rules. 211The 212.Cm show 213command implies this option. 214.It Fl b 215Only show the action and the comment, not the body of a rule. 216Implies 217.Fl c . 218.It Fl c 219When entering or showing rules, print them in compact form, 220i.e., omitting the "ip from any to any" string 221when this does not carry any additional information. 222.It Fl d 223When listing, show dynamic rules in addition to static ones. 224.It Fl e 225When listing and 226.Fl d 227is specified, also show expired dynamic rules. 228.It Fl f 229Do not ask for confirmation for commands that can cause problems 230if misused, 231.No i.e. Cm flush . 232If there is no tty associated with the process, this is implied. 233.It Fl i 234When listing a table (see the 235.Sx LOOKUP TABLES 236section below for more information on lookup tables), format values 237as IP addresses. By default, values are shown as integers. 238.It Fl n 239Only check syntax of the command strings, without actually passing 240them to the kernel. 241.It Fl N 242Try to resolve addresses and service names in output. 243.It Fl q 244Be quiet when executing the 245.Cm add , 246.Cm nat , 247.Cm zero , 248.Cm resetlog 249or 250.Cm flush 251commands; 252(implies 253.Fl f ) . 254This is useful when updating rulesets by executing multiple 255.Nm 256commands in a script 257(e.g., 258.Ql sh\ /etc/rc.firewall ) , 259or by processing a file with many 260.Nm 261rules across a remote login session. 262It also stops a table add or delete 263from failing if the entry already exists or is not present. 264.Pp 265The reason why this option may be important is that 266for some of these actions, 267.Nm 268may print a message; if the action results in blocking the 269traffic to the remote client, 270the remote login session will be closed 271and the rest of the ruleset will not be processed. 272Access to the console would then be required to recover. 273.It Fl S 274When listing rules, show the 275.Em set 276each rule belongs to. 277If this flag is not specified, disabled rules will not be 278listed. 279.It Fl s Op Ar field 280When listing pipes, sort according to one of the four 281counters (total or current packets or bytes). 282.It Fl t 283When listing, show last match timestamp converted with ctime(). 284.It Fl T 285When listing, show last match timestamp as seconds from the epoch. 286This form can be more convenient for postprocessing by scripts. 287.El 288.Pp 289.Ss LIST OF RULES AND PREPROCESSING 290To ease configuration, rules can be put into a file which is 291processed using 292.Nm 293as shown in the last synopsis line. 294An absolute 295.Ar pathname 296must be used. 297The file will be read line by line and applied as arguments to the 298.Nm 299utility. 300.Pp 301Optionally, a preprocessor can be specified using 302.Fl p Ar preproc 303where 304.Ar pathname 305is to be piped through. 306Useful preprocessors include 307.Xr cpp 1 308and 309.Xr m4 1 . 310If 311.Ar preproc 312does not start with a slash 313.Pq Ql / 314as its first character, the usual 315.Ev PATH 316name search is performed. 317Care should be taken with this in environments where not all 318file systems are mounted (yet) by the time 319.Nm 320is being run (e.g.\& when they are mounted over NFS). 321Once 322.Fl p 323has been specified, any additional arguments are passed on to the preprocessor 324for interpretation. 325This allows for flexible configuration files (like conditionalizing 326them on the local hostname) and the use of macros to centralize 327frequently required arguments like IP addresses. 328.Pp 329.Ss TRAFFIC SHAPER CONFIGURATION 330The 331.Nm 332.Cm pipe , queue 333and 334.Cm sched 335commands are used to configure the traffic shaper and packet scheduler. 336See the 337.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 338Section below for details. 339.Pp 340If the world and the kernel get out of sync the 341.Nm 342ABI may break, preventing you from being able to add any rules. 343This can 344adversely effect the booting process. 345You can use 346.Nm 347.Cm disable 348.Cm firewall 349to temporarily disable the firewall to regain access to the network, 350allowing you to fix the problem. 351.Sh PACKET FLOW 352A packet is checked against the active ruleset in multiple places 353in the protocol stack, under control of several sysctl variables. 354These places and variables are shown below, and it is important to 355have this picture in mind in order to design a correct ruleset. 356.Bd -literal -offset indent 357 ^ to upper layers V 358 | | 359 +----------->-----------+ 360 ^ V 361 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1 362 | | 363 ^ V 364 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 365 | | 366 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1 367 ^ V 368 | to devices | 369.Ed 370.Pp 371The number of 372times the same packet goes through the firewall can 373vary between 0 and 4 depending on packet source and 374destination, and system configuration. 375.Pp 376Note that as packets flow through the stack, headers can be 377stripped or added to it, and so they may or may not be available 378for inspection. 379E.g., incoming packets will include the MAC header when 380.Nm 381is invoked from 382.Cm ether_demux() , 383but the same packets will have the MAC header stripped off when 384.Nm 385is invoked from 386.Cm ip_input() 387or 388.Cm ip6_input() . 389.Pp 390Also note that each packet is always checked against the complete ruleset, 391irrespective of the place where the check occurs, or the source of the packet. 392If a rule contains some match patterns or actions which are not valid 393for the place of invocation (e.g.\& trying to match a MAC header within 394.Cm ip_input 395or 396.Cm ip6_input ), 397the match pattern will not match, but a 398.Cm not 399operator in front of such patterns 400.Em will 401cause the pattern to 402.Em always 403match on those packets. 404It is thus the responsibility of 405the programmer, if necessary, to write a suitable ruleset to 406differentiate among the possible places. 407.Cm skipto 408rules can be useful here, as an example: 409.Bd -literal -offset indent 410# packets from ether_demux or bdg_forward 411ipfw add 10 skipto 1000 all from any to any layer2 in 412# packets from ip_input 413ipfw add 10 skipto 2000 all from any to any not layer2 in 414# packets from ip_output 415ipfw add 10 skipto 3000 all from any to any not layer2 out 416# packets from ether_output_frame 417ipfw add 10 skipto 4000 all from any to any layer2 out 418.Ed 419.Pp 420(yes, at the moment there is no way to differentiate between 421ether_demux and bdg_forward). 422.Sh SYNTAX 423In general, each keyword or argument must be provided as 424a separate command line argument, with no leading or trailing 425spaces. 426Keywords are case-sensitive, whereas arguments may 427or may not be case-sensitive depending on their nature 428(e.g.\& uid's are, hostnames are not). 429.Pp 430Some arguments (e.g. port or address lists) are comma-separated 431lists of values. 432In this case, spaces after commas ',' are allowed to make 433the line more readable. 434You can also put the entire 435command (including flags) into a single argument. 436E.g., the following forms are equivalent: 437.Bd -literal -offset indent 438ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 439ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 440ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" 441.Ed 442.Sh RULE FORMAT 443The format of firewall rules is the following: 444.Bd -ragged -offset indent 445.Bk -words 446.Op Ar rule_number 447.Op Cm set Ar set_number 448.Op Cm prob Ar match_probability 449.Ar action 450.Op Cm log Op Cm logamount Ar number 451.Op Cm altq Ar queue 452.Oo 453.Bro Cm tag | untag 454.Brc Ar number 455.Oc 456.Ar body 457.Ek 458.Ed 459.Pp 460where the body of the rule specifies which information is used 461for filtering packets, among the following: 462.Pp 463.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact 464.It Layer-2 header fields 465When available 466.It IPv4 and IPv6 Protocol 467TCP, UDP, ICMP, etc. 468.It Source and dest. addresses and ports 469.It Direction 470See Section 471.Sx PACKET FLOW 472.It Transmit and receive interface 473By name or address 474.It Misc. IP header fields 475Version, type of service, datagram length, identification, 476fragment flag (non-zero IP offset), 477Time To Live 478.It IP options 479.It IPv6 Extension headers 480Fragmentation, Hop-by-Hop options, 481Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options. 482.It IPv6 Flow-ID 483.It Misc. TCP header fields 484TCP flags (SYN, FIN, ACK, RST, etc.), 485sequence number, acknowledgment number, 486window 487.It TCP options 488.It ICMP types 489for ICMP packets 490.It ICMP6 types 491for ICMP6 packets 492.It User/group ID 493When the packet can be associated with a local socket. 494.It Divert status 495Whether a packet came from a divert socket (e.g., 496.Xr natd 8 ) . 497.It Fib annotation state 498Whether a packet has been tagged for using a specific FIB (routing table) 499in future forwarding decisions. 500.El 501.Pp 502Note that some of the above information, e.g.\& source MAC or IP addresses and 503TCP/UDP ports, can be easily spoofed, so filtering on those fields 504alone might not guarantee the desired results. 505.Bl -tag -width indent 506.It Ar rule_number 507Each rule is associated with a 508.Ar rule_number 509in the range 1..65535, with the latter reserved for the 510.Em default 511rule. 512Rules are checked sequentially by rule number. 513Multiple rules can have the same number, in which case they are 514checked (and listed) according to the order in which they have 515been added. 516If a rule is entered without specifying a number, the kernel will 517assign one in such a way that the rule becomes the last one 518before the 519.Em default 520rule. 521Automatic rule numbers are assigned by incrementing the last 522non-default rule number by the value of the sysctl variable 523.Ar net.inet.ip.fw.autoinc_step 524which defaults to 100. 525If this is not possible (e.g.\& because we would go beyond the 526maximum allowed rule number), the number of the last 527non-default value is used instead. 528.It Cm set Ar set_number 529Each rule is associated with a 530.Ar set_number 531in the range 0..31. 532Sets can be individually disabled and enabled, so this parameter 533is of fundamental importance for atomic ruleset manipulation. 534It can be also used to simplify deletion of groups of rules. 535If a rule is entered without specifying a set number, 536set 0 will be used. 537.br 538Set 31 is special in that it cannot be disabled, 539and rules in set 31 are not deleted by the 540.Nm ipfw flush 541command (but you can delete them with the 542.Nm ipfw delete set 31 543command). 544Set 31 is also used for the 545.Em default 546rule. 547.It Cm prob Ar match_probability 548A match is only declared with the specified probability 549(floating point number between 0 and 1). 550This can be useful for a number of applications such as 551random packet drop or 552(in conjunction with 553.Nm dummynet ) 554to simulate the effect of multiple paths leading to out-of-order 555packet delivery. 556.Pp 557Note: this condition is checked before any other condition, including 558ones such as keep-state or check-state which might have side effects. 559.It Cm log Op Cm logamount Ar number 560Packets matching a rule with the 561.Cm log 562keyword will be made available for logging in two ways: 563if the sysctl variable 564.Va net.inet.ip.fw.verbose 565is set to 0 (default), one can use 566.Xr bpf 4 567attached to the 568.Li ipfw0 569pseudo interface. There is no overhead if no 570.Xr bpf 4 571is attached to the pseudo interface. 572.Pp 573If 574.Va net.inet.ip.fw.verbose 575is set to 1, packets will be logged to 576.Xr syslogd 8 577with a 578.Dv LOG_SECURITY 579facility up to a maximum of 580.Cm logamount 581packets. 582If no 583.Cm logamount 584is specified, the limit is taken from the sysctl variable 585.Va net.inet.ip.fw.verbose_limit . 586In both cases, a value of 0 means unlimited logging. 587.Pp 588Once the limit is reached, logging can be re-enabled by 589clearing the logging counter or the packet counter for that entry, see the 590.Cm resetlog 591command. 592.Pp 593Note: logging is done after all other packet matching conditions 594have been successfully verified, and before performing the final 595action (accept, deny, etc.) on the packet. 596.It Cm tag Ar number 597When a packet matches a rule with the 598.Cm tag 599keyword, the numeric tag for the given 600.Ar number 601in the range 1..65534 will be attached to the packet. 602The tag acts as an internal marker (it is not sent out over 603the wire) that can be used to identify these packets later on. 604This can be used, for example, to provide trust between interfaces 605and to start doing policy-based filtering. 606A packet can have multiple tags at the same time. 607Tags are "sticky", meaning once a tag is applied to a packet by a 608matching rule it exists until explicit removal. 609Tags are kept with the packet everywhere within the kernel, but are 610lost when packet leaves the kernel, for example, on transmitting 611packet out to the network or sending packet to a 612.Xr divert 4 613socket. 614.Pp 615To check for previously applied tags, use the 616.Cm tagged 617rule option. 618To delete previously applied tag, use the 619.Cm untag 620keyword. 621.Pp 622Note: since tags are kept with the packet everywhere in kernelspace, 623they can be set and unset anywhere in the kernel network subsystem 624(using the 625.Xr mbuf_tags 9 626facility), not only by means of the 627.Xr ipfw 4 628.Cm tag 629and 630.Cm untag 631keywords. 632For example, there can be a specialized 633.Xr netgraph 4 634node doing traffic analyzing and tagging for later inspecting 635in firewall. 636.It Cm untag Ar number 637When a packet matches a rule with the 638.Cm untag 639keyword, the tag with the number 640.Ar number 641is searched among the tags attached to this packet and, 642if found, removed from it. 643Other tags bound to packet, if present, are left untouched. 644.It Cm altq Ar queue 645When a packet matches a rule with the 646.Cm altq 647keyword, the ALTQ identifier for the given 648.Ar queue 649(see 650.Xr altq 4 ) 651will be attached. 652Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, 653and not being rejected or going to divert sockets. 654Note that if there is insufficient memory at the time the packet is 655processed, it will not be tagged, so it is wise to make your ALTQ 656"default" queue policy account for this. 657If multiple 658.Cm altq 659rules match a single packet, only the first one adds the ALTQ classification 660tag. 661In doing so, traffic may be shaped by using 662.Cm count Cm altq Ar queue 663rules for classification early in the ruleset, then later applying 664the filtering decision. 665For example, 666.Cm check-state 667and 668.Cm keep-state 669rules may come later and provide the actual filtering decisions in 670addition to the fallback ALTQ tag. 671.Pp 672You must run 673.Xr pfctl 8 674to set up the queues before IPFW will be able to look them up by name, 675and if the ALTQ disciplines are rearranged, the rules in containing the 676queue identifiers in the kernel will likely have gone stale and need 677to be reloaded. 678Stale queue identifiers will probably result in misclassification. 679.Pp 680All system ALTQ processing can be turned on or off via 681.Nm 682.Cm enable Ar altq 683and 684.Nm 685.Cm disable Ar altq . 686The usage of 687.Va net.inet.ip.fw.one_pass 688is irrelevant to ALTQ traffic shaping, as the actual rule action is followed 689always after adding an ALTQ tag. 690.El 691.Ss RULE ACTIONS 692A rule can be associated with one of the following actions, which 693will be executed when the packet matches the body of the rule. 694.Bl -tag -width indent 695.It Cm allow | accept | pass | permit 696Allow packets that match rule. 697The search terminates. 698.It Cm check-state 699Checks the packet against the dynamic ruleset. 700If a match is found, execute the action associated with 701the rule which generated this dynamic rule, otherwise 702move to the next rule. 703.br 704.Cm Check-state 705rules do not have a body. 706If no 707.Cm check-state 708rule is found, the dynamic ruleset is checked at the first 709.Cm keep-state 710or 711.Cm limit 712rule. 713.It Cm count 714Update counters for all packets that match rule. 715The search continues with the next rule. 716.It Cm deny | drop 717Discard packets that match this rule. 718The search terminates. 719.It Cm divert Ar port 720Divert packets that match this rule to the 721.Xr divert 4 722socket bound to port 723.Ar port . 724The search terminates. 725.It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port 726Change the next-hop on matching packets to 727.Ar ipaddr , 728which can be an IP address or a host name. 729For IPv4, the next hop can also be supplied by the last table 730looked up for the packet by using the 731.Cm tablearg 732keyword instead of an explicit address. 733The search terminates if this rule matches. 734.Pp 735If 736.Ar ipaddr 737is a local address, then matching packets will be forwarded to 738.Ar port 739(or the port number in the packet if one is not specified in the rule) 740on the local machine. 741.br 742If 743.Ar ipaddr 744is not a local address, then the port number 745(if specified) is ignored, and the packet will be 746forwarded to the remote address, using the route as found in 747the local routing table for that IP. 748.br 749A 750.Ar fwd 751rule will not match layer-2 packets (those received 752on ether_input, ether_output, or bridged). 753.br 754The 755.Cm fwd 756action does not change the contents of the packet at all. 757In particular, the destination address remains unmodified, so 758packets forwarded to another system will usually be rejected by that system 759unless there is a matching rule on that system to capture them. 760For packets forwarded locally, 761the local address of the socket will be 762set to the original destination address of the packet. 763This makes the 764.Xr netstat 1 765entry look rather weird but is intended for 766use with transparent proxy servers. 767.Pp 768To enable 769.Cm fwd 770a custom kernel needs to be compiled with the option 771.Cd "options IPFIREWALL_FORWARD" . 772.It Cm nat Ar nat_nr | tablearg 773Pass packet to a 774nat instance 775(for network address translation, address redirect, etc.): 776see the 777.Sx NETWORK ADDRESS TRANSLATION (NAT) 778Section for further information. 779.It Cm pipe Ar pipe_nr 780Pass packet to a 781.Nm dummynet 782.Dq pipe 783(for bandwidth limitation, delay, etc.). 784See the 785.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 786Section for further information. 787The search terminates; however, on exit from the pipe and if 788the 789.Xr sysctl 8 790variable 791.Va net.inet.ip.fw.one_pass 792is not set, the packet is passed again to the firewall code 793starting from the next rule. 794.It Cm queue Ar queue_nr 795Pass packet to a 796.Nm dummynet 797.Dq queue 798(for bandwidth limitation using WF2Q+). 799.It Cm reject 800(Deprecated). 801Synonym for 802.Cm unreach host . 803.It Cm reset 804Discard packets that match this rule, and if the 805packet is a TCP packet, try to send a TCP reset (RST) notice. 806The search terminates. 807.It Cm reset6 808Discard packets that match this rule, and if the 809packet is a TCP packet, try to send a TCP reset (RST) notice. 810The search terminates. 811.It Cm skipto Ar number | tablearg 812Skip all subsequent rules numbered less than 813.Ar number . 814The search continues with the first rule numbered 815.Ar number 816or higher. 817It is possible to use the 818.Cm tablearg 819keyword with a skipto for a 820.Em computed 821skipto, but care should be used, as no destination caching 822is possible in this case so the rules are always walked to find it, 823starting from the 824.Cm skipto . 825.It Cm call Ar number | tablearg 826The current rule number is saved in the internal stack and 827ruleset processing continues with the first rule numbered 828.Ar number 829or higher. 830If later a rule with the 831.Cm return 832action is encountered, the processing returns to the first rule 833with number of this 834.Cm call 835rule plus one or higher 836(the same behaviour as with packets returning from 837.Xr divert 4 838socket after a 839.Cm divert 840action). 841This could be used to make somewhat like an assembly language 842.Dq subroutine 843calls to rules with common checks for different interfaces, etc. 844.Pp 845Rule with any number could be called, not just forward jumps as with 846.Cm skipto . 847So, to prevent endless loops in case of mistakes, both 848.Cm call 849and 850.Cm return 851actions don't do any jumps and simply go to the next rule if memory 852can't be allocated or stack overflowed/undeflowed. 853.Pp 854Internally stack for rule numbers is implemented using 855.Xr mbuf_tags 9 856facility and currently has size of 16 entries. 857As mbuf tags are lost when packet leaves the kernel, 858.Cm divert 859should not be used in subroutines to avoid endless loops 860and other undesired effects. 861.It Cm return 862Takes rule number saved to internal stack by the last 863.Cm call 864action and returns ruleset processing to the first rule 865with number greater than number of corresponding 866.Cm call 867rule. See description of the 868.Cm call 869action for more details. 870.Pp 871Note that 872.Cm return 873rules usually end a 874.Dq subroutine 875and thus are unconditional, but 876.Nm 877command-line utility currently requires every action except 878.Cm check-state 879to have body. 880While it is sometimes useful to return only on some packets, 881usually you want to print just 882.Dq return 883for readability. 884A workaround for this is to use new syntax and 885.Fl c 886switch: 887.Pp 888.Bd -literal -offset indent 889# Add a rule without actual body 890ipfw add 2999 return via any 891 892# List rules without "from any to any" part 893ipfw -c list 894.Ed 895.Pp 896This cosmetic annoyance may be fixed in future releases. 897.It Cm tee Ar port 898Send a copy of packets matching this rule to the 899.Xr divert 4 900socket bound to port 901.Ar port . 902The search continues with the next rule. 903.It Cm unreach Ar code 904Discard packets that match this rule, and try to send an ICMP 905unreachable notice with code 906.Ar code , 907where 908.Ar code 909is a number from 0 to 255, or one of these aliases: 910.Cm net , host , protocol , port , 911.Cm needfrag , srcfail , net-unknown , host-unknown , 912.Cm isolated , net-prohib , host-prohib , tosnet , 913.Cm toshost , filter-prohib , host-precedence 914or 915.Cm precedence-cutoff . 916The search terminates. 917.It Cm unreach6 Ar code 918Discard packets that match this rule, and try to send an ICMPv6 919unreachable notice with code 920.Ar code , 921where 922.Ar code 923is a number from 0, 1, 3 or 4, or one of these aliases: 924.Cm no-route, admin-prohib, address 925or 926.Cm port . 927The search terminates. 928.It Cm netgraph Ar cookie 929Divert packet into netgraph with given 930.Ar cookie . 931The search terminates. 932If packet is later returned from netgraph it is either 933accepted or continues with the next rule, depending on 934.Va net.inet.ip.fw.one_pass 935sysctl variable. 936.It Cm ngtee Ar cookie 937A copy of packet is diverted into netgraph, original 938packet continues with the next rule. 939See 940.Xr ng_ipfw 4 941for more information on 942.Cm netgraph 943and 944.Cm ngtee 945actions. 946.It Cm setfib Ar fibnum | tablearg 947The packet is tagged so as to use the FIB (routing table) 948.Ar fibnum 949in any subsequent forwarding decisions. 950Initially this is limited to the values 0 through 15, see 951.Xr setfib 1 . 952Processing continues at the next rule. 953It is possible to use the 954.Cm tablearg 955keyword with a setfib. If tablearg value is not within compiled FIB range packet fib is set to 0. 956.It Cm reass 957Queue and reassemble ip fragments. 958If the packet is not fragmented, counters are updated and processing continues with the next rule. 959If the packet is the last logical fragment, the packet is reassembled and, if 960.Va net.inet.ip.fw.one_pass 961is set to 0, processing continues with the next rule, else packet is allowed to pass and search terminates. 962If the packet is a fragment in the middle, it is consumed and processing stops immediately. 963.Pp 964Fragments handling can be tuned via 965.Va net.inet.ip.maxfragpackets 966and 967.Va net.inet.ip.maxfragsperpacket 968which limit, respectively, the maximum number of processable fragments (default: 800) and 969the maximum number of fragments per packet (default: 16). 970.Pp 971NOTA BENE: since fragments do not contain port numbers, they should be avoided with the 972.Nm reass 973rule. 974Alternatively, direction-based (like 975.Nm in 976/ 977.Nm out 978) and source-based (like 979.Nm via 980) match patterns can be used to select fragments. 981.Pp 982Usually a simple rule like: 983.Bd -literal -offset indent 984# reassemble incoming fragments 985ipfw add reass all from any to any in 986.Ed 987.Pp 988is all you need at the beginning of your ruleset. 989.El 990.Ss RULE BODY 991The body of a rule contains zero or more patterns (such as 992specific source and destination addresses or ports, 993protocol options, incoming or outgoing interfaces, etc.) 994that the packet must match in order to be recognised. 995In general, the patterns are connected by (implicit) 996.Cm and 997operators -- i.e., all must match in order for the 998rule to match. 999Individual patterns can be prefixed by the 1000.Cm not 1001operator to reverse the result of the match, as in 1002.Pp 1003.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any" 1004.Pp 1005Additionally, sets of alternative match patterns 1006.Pq Em or-blocks 1007can be constructed by putting the patterns in 1008lists enclosed between parentheses ( ) or braces { }, and 1009using the 1010.Cm or 1011operator as follows: 1012.Pp 1013.Dl "ipfw add 100 allow ip from { x or not y or z } to any" 1014.Pp 1015Only one level of parentheses is allowed. 1016Beware that most shells have special meanings for parentheses 1017or braces, so it is advisable to put a backslash \\ in front of them 1018to prevent such interpretations. 1019.Pp 1020The body of a rule must in general include a source and destination 1021address specifier. 1022The keyword 1023.Ar any 1024can be used in various places to specify that the content of 1025a required field is irrelevant. 1026.Pp 1027The rule body has the following format: 1028.Bd -ragged -offset indent 1029.Op Ar proto Cm from Ar src Cm to Ar dst 1030.Op Ar options 1031.Ed 1032.Pp 1033The first part (proto from src to dst) is for backward 1034compatibility with earlier versions of 1035.Fx . 1036In modern 1037.Fx 1038any match pattern (including MAC headers, IP protocols, 1039addresses and ports) can be specified in the 1040.Ar options 1041section. 1042.Pp 1043Rule fields have the following meaning: 1044.Bl -tag -width indent 1045.It Ar proto : protocol | Cm { Ar protocol Cm or ... } 1046.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number 1047An IP protocol specified by number or name 1048(for a complete list see 1049.Pa /etc/protocols ) , 1050or one of the following keywords: 1051.Bl -tag -width indent 1052.It Cm ip4 | ipv4 1053Matches IPv4 packets. 1054.It Cm ip6 | ipv6 1055Matches IPv6 packets. 1056.It Cm ip | all 1057Matches any packet. 1058.El 1059.Pp 1060The 1061.Cm ipv6 1062in 1063.Cm proto 1064option will be treated as inner protocol. 1065And, the 1066.Cm ipv4 1067is not available in 1068.Cm proto 1069option. 1070.Pp 1071The 1072.Cm { Ar protocol Cm or ... } 1073format (an 1074.Em or-block ) 1075is provided for convenience only but its use is deprecated. 1076.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports 1077An address (or a list, see below) 1078optionally followed by 1079.Ar ports 1080specifiers. 1081.Pp 1082The second format 1083.Em ( or-block 1084with multiple addresses) is provided for convenience only and 1085its use is discouraged. 1086.It Ar addr : Oo Cm not Oc Bro 1087.Cm any | me | me6 | 1088.Cm table Ns Pq Ar number Ns Op , Ns Ar value 1089.Ar | addr-list | addr-set 1090.Brc 1091.Bl -tag -width indent 1092.It Cm any 1093matches any IP address. 1094.It Cm me 1095matches any IP address configured on an interface in the system. 1096.It Cm me6 1097matches any IPv6 address configured on an interface in the system. 1098The address list is evaluated at the time the packet is 1099analysed. 1100.It Cm table Ns Pq Ar number Ns Op , Ns Ar value 1101Matches any IPv4 address for which an entry exists in the lookup table 1102.Ar number . 1103If an optional 32-bit unsigned 1104.Ar value 1105is also specified, an entry will match only if it has this value. 1106See the 1107.Sx LOOKUP TABLES 1108section below for more information on lookup tables. 1109.El 1110.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list 1111.It Ar ip-addr : 1112A host or subnet address specified in one of the following ways: 1113.Bl -tag -width indent 1114.It Ar numeric-ip | hostname 1115Matches a single IPv4 address, specified as dotted-quad or a hostname. 1116Hostnames are resolved at the time the rule is added to the firewall list. 1117.It Ar addr Ns / Ns Ar masklen 1118Matches all addresses with base 1119.Ar addr 1120(specified as an IP address, a network number, or a hostname) 1121and mask width of 1122.Cm masklen 1123bits. 1124As an example, 1.2.3.4/25 or 1.2.3.0/25 will match 1125all IP numbers from 1.2.3.0 to 1.2.3.127 . 1126.It Ar addr Ns : Ns Ar mask 1127Matches all addresses with base 1128.Ar addr 1129(specified as an IP address, a network number, or a hostname) 1130and the mask of 1131.Ar mask , 1132specified as a dotted quad. 1133As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 11341.*.3.*. 1135This form is advised only for non-contiguous 1136masks. 1137It is better to resort to the 1138.Ar addr Ns / Ns Ar masklen 1139format for contiguous masks, which is more compact and less 1140error-prone. 1141.El 1142.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm } 1143.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list 1144Matches all addresses with base address 1145.Ar addr 1146(specified as an IP address, a network number, or a hostname) 1147and whose last byte is in the list between braces { } . 1148Note that there must be no spaces between braces and 1149numbers (spaces after commas are allowed). 1150Elements of the list can be specified as single entries 1151or ranges. 1152The 1153.Ar masklen 1154field is used to limit the size of the set of addresses, 1155and can have any value between 24 and 32. 1156If not specified, 1157it will be assumed as 24. 1158.br 1159This format is particularly useful to handle sparse address sets 1160within a single rule. 1161Because the matching occurs using a 1162bitmask, it takes constant time and dramatically reduces 1163the complexity of rulesets. 1164.br 1165As an example, an address specified as 1.2.3.4/24{128,35-55,89} 1166or 1.2.3.0/24{128,35-55,89} 1167will match the following IP addresses: 1168.br 11691.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . 1170.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list 1171.It Ar ip6-addr : 1172A host or subnet specified one of the following ways: 1173.Bl -tag -width indent 1174.It Ar numeric-ip | hostname 1175Matches a single IPv6 address as allowed by 1176.Xr inet_pton 3 1177or a hostname. 1178Hostnames are resolved at the time the rule is added to the firewall 1179list. 1180.It Ar addr Ns / Ns Ar masklen 1181Matches all IPv6 addresses with base 1182.Ar addr 1183(specified as allowed by 1184.Xr inet_pton 1185or a hostname) 1186and mask width of 1187.Cm masklen 1188bits. 1189.El 1190.Pp 1191No support for sets of IPv6 addresses is provided because IPv6 addresses 1192are typically random past the initial prefix. 1193.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports 1194For protocols which support port numbers (such as TCP and UDP), optional 1195.Cm ports 1196may be specified as one or more ports or port ranges, separated 1197by commas but no spaces, and an optional 1198.Cm not 1199operator. 1200The 1201.Ql \&- 1202notation specifies a range of ports (including boundaries). 1203.Pp 1204Service names (from 1205.Pa /etc/services ) 1206may be used instead of numeric port values. 1207The length of the port list is limited to 30 ports or ranges, 1208though one can specify larger ranges by using an 1209.Em or-block 1210in the 1211.Cm options 1212section of the rule. 1213.Pp 1214A backslash 1215.Pq Ql \e 1216can be used to escape the dash 1217.Pq Ql - 1218character in a service name (from a shell, the backslash must be 1219typed twice to avoid the shell itself interpreting it as an escape 1220character). 1221.Pp 1222.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any" 1223.Pp 1224Fragmented packets which have a non-zero offset (i.e., not the first 1225fragment) will never match a rule which has one or more port 1226specifications. 1227See the 1228.Cm frag 1229option for details on matching fragmented packets. 1230.El 1231.Ss RULE OPTIONS (MATCH PATTERNS) 1232Additional match patterns can be used within 1233rules. 1234Zero or more of these so-called 1235.Em options 1236can be present in a rule, optionally prefixed by the 1237.Cm not 1238operand, and possibly grouped into 1239.Em or-blocks . 1240.Pp 1241The following match patterns can be used (listed in alphabetical order): 1242.Bl -tag -width indent 1243.It Cm // this is a comment. 1244Inserts the specified text as a comment in the rule. 1245Everything following // is considered as a comment and stored in the rule. 1246You can have comment-only rules, which are listed as having a 1247.Cm count 1248action followed by the comment. 1249.It Cm bridged 1250Alias for 1251.Cm layer2 . 1252.It Cm diverted 1253Matches only packets generated by a divert socket. 1254.It Cm diverted-loopback 1255Matches only packets coming from a divert socket back into the IP stack 1256input for delivery. 1257.It Cm diverted-output 1258Matches only packets going from a divert socket back outward to the IP 1259stack output for delivery. 1260.It Cm dst-ip Ar ip-address 1261Matches IPv4 packets whose destination IP is one of the address(es) 1262specified as argument. 1263.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address 1264Matches IPv6 packets whose destination IP is one of the address(es) 1265specified as argument. 1266.It Cm dst-port Ar ports 1267Matches IP packets whose destination port is one of the port(s) 1268specified as argument. 1269.It Cm established 1270Matches TCP packets that have the RST or ACK bits set. 1271.It Cm ext6hdr Ar header 1272Matches IPv6 packets containing the extended header given by 1273.Ar header . 1274Supported headers are: 1275.Pp 1276Fragment, 1277.Pq Cm frag , 1278Hop-to-hop options 1279.Pq Cm hopopt , 1280any type of Routing Header 1281.Pq Cm route , 1282Source routing Routing Header Type 0 1283.Pq Cm rthdr0 , 1284Mobile IPv6 Routing Header Type 2 1285.Pq Cm rthdr2 , 1286Destination options 1287.Pq Cm dstopt , 1288IPSec authentication headers 1289.Pq Cm ah , 1290and IPsec encapsulated security payload headers 1291.Pq Cm esp . 1292.It Cm fib Ar fibnum 1293Matches a packet that has been tagged to use 1294the given FIB (routing table) number. 1295.It Cm flow-id Ar labels 1296Matches IPv6 packets containing any of the flow labels given in 1297.Ar labels . 1298.Ar labels 1299is a comma separated list of numeric flow labels. 1300.It Cm frag 1301Matches packets that are fragments and not the first 1302fragment of an IP datagram. 1303Note that these packets will not have 1304the next protocol header (e.g.\& TCP, UDP) so options that look into 1305these headers cannot match. 1306.It Cm gid Ar group 1307Matches all TCP or UDP packets sent by or received for a 1308.Ar group . 1309A 1310.Ar group 1311may be specified by name or number. 1312.It Cm jail Ar prisonID 1313Matches all TCP or UDP packets sent by or received for the 1314jail whos prison ID is 1315.Ar prisonID . 1316.It Cm icmptypes Ar types 1317Matches ICMP packets whose ICMP type is in the list 1318.Ar types . 1319The list may be specified as any combination of 1320individual types (numeric) separated by commas. 1321.Em Ranges are not allowed . 1322The supported ICMP types are: 1323.Pp 1324echo reply 1325.Pq Cm 0 , 1326destination unreachable 1327.Pq Cm 3 , 1328source quench 1329.Pq Cm 4 , 1330redirect 1331.Pq Cm 5 , 1332echo request 1333.Pq Cm 8 , 1334router advertisement 1335.Pq Cm 9 , 1336router solicitation 1337.Pq Cm 10 , 1338time-to-live exceeded 1339.Pq Cm 11 , 1340IP header bad 1341.Pq Cm 12 , 1342timestamp request 1343.Pq Cm 13 , 1344timestamp reply 1345.Pq Cm 14 , 1346information request 1347.Pq Cm 15 , 1348information reply 1349.Pq Cm 16 , 1350address mask request 1351.Pq Cm 17 1352and address mask reply 1353.Pq Cm 18 . 1354.It Cm icmp6types Ar types 1355Matches ICMP6 packets whose ICMP6 type is in the list of 1356.Ar types . 1357The list may be specified as any combination of 1358individual types (numeric) separated by commas. 1359.Em Ranges are not allowed . 1360.It Cm in | out 1361Matches incoming or outgoing packets, respectively. 1362.Cm in 1363and 1364.Cm out 1365are mutually exclusive (in fact, 1366.Cm out 1367is implemented as 1368.Cm not in Ns No ). 1369.It Cm ipid Ar id-list 1370Matches IPv4 packets whose 1371.Cm ip_id 1372field has value included in 1373.Ar id-list , 1374which is either a single value or a list of values or ranges 1375specified in the same way as 1376.Ar ports . 1377.It Cm iplen Ar len-list 1378Matches IP packets whose total length, including header and data, is 1379in the set 1380.Ar len-list , 1381which is either a single value or a list of values or ranges 1382specified in the same way as 1383.Ar ports . 1384.It Cm ipoptions Ar spec 1385Matches packets whose IPv4 header contains the comma separated list of 1386options specified in 1387.Ar spec . 1388The supported IP options are: 1389.Pp 1390.Cm ssrr 1391(strict source route), 1392.Cm lsrr 1393(loose source route), 1394.Cm rr 1395(record packet route) and 1396.Cm ts 1397(timestamp). 1398The absence of a particular option may be denoted 1399with a 1400.Ql \&! . 1401.It Cm ipprecedence Ar precedence 1402Matches IPv4 packets whose precedence field is equal to 1403.Ar precedence . 1404.It Cm ipsec 1405Matches packets that have IPSEC history associated with them 1406(i.e., the packet comes encapsulated in IPSEC, the kernel 1407has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly 1408decapsulate it). 1409.Pp 1410Note that specifying 1411.Cm ipsec 1412is different from specifying 1413.Cm proto Ar ipsec 1414as the latter will only look at the specific IP protocol field, 1415irrespective of IPSEC kernel support and the validity of the IPSEC data. 1416.Pp 1417Further note that this flag is silently ignored in kernels without 1418IPSEC support. 1419It does not affect rule processing when given and the 1420rules are handled as if with no 1421.Cm ipsec 1422flag. 1423.It Cm iptos Ar spec 1424Matches IPv4 packets whose 1425.Cm tos 1426field contains the comma separated list of 1427service types specified in 1428.Ar spec . 1429The supported IP types of service are: 1430.Pp 1431.Cm lowdelay 1432.Pq Dv IPTOS_LOWDELAY , 1433.Cm throughput 1434.Pq Dv IPTOS_THROUGHPUT , 1435.Cm reliability 1436.Pq Dv IPTOS_RELIABILITY , 1437.Cm mincost 1438.Pq Dv IPTOS_MINCOST , 1439.Cm congestion 1440.Pq Dv IPTOS_ECN_CE . 1441The absence of a particular type may be denoted 1442with a 1443.Ql \&! . 1444.It Cm ipttl Ar ttl-list 1445Matches IPv4 packets whose time to live is included in 1446.Ar ttl-list , 1447which is either a single value or a list of values or ranges 1448specified in the same way as 1449.Ar ports . 1450.It Cm ipversion Ar ver 1451Matches IP packets whose IP version field is 1452.Ar ver . 1453.It Cm keep-state 1454Upon a match, the firewall will create a dynamic rule, whose 1455default behaviour is to match bidirectional traffic between 1456source and destination IP/port using the same protocol. 1457The rule has a limited lifetime (controlled by a set of 1458.Xr sysctl 8 1459variables), and the lifetime is refreshed every time a matching 1460packet is found. 1461.It Cm layer2 1462Matches only layer2 packets, i.e., those passed to 1463.Nm 1464from ether_demux() and ether_output_frame(). 1465.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N 1466The firewall will only allow 1467.Ar N 1468connections with the same 1469set of parameters as specified in the rule. 1470One or more 1471of source and destination addresses and ports can be 1472specified. 1473Currently, 1474only IPv4 flows are supported. 1475.It Cm lookup Bro Cm dst-ip | dst-port | src-ip | src-port | uid | jail Brc Ar N 1476Search an entry in lookup table 1477.Ar N 1478that matches the field specified as argument. 1479If not found, the match fails. 1480Otherwise, the match succeeds and 1481.Cm tablearg 1482is set to the value extracted from the table. 1483.Pp 1484This option can be useful to quickly dispatch traffic based on 1485certain packet fields. 1486See the 1487.Sx LOOKUP TABLES 1488section below for more information on lookup tables. 1489.It Cm { MAC | mac } Ar dst-mac src-mac 1490Match packets with a given 1491.Ar dst-mac 1492and 1493.Ar src-mac 1494addresses, specified as the 1495.Cm any 1496keyword (matching any MAC address), or six groups of hex digits 1497separated by colons, 1498and optionally followed by a mask indicating the significant bits. 1499The mask may be specified using either of the following methods: 1500.Bl -enum -width indent 1501.It 1502A slash 1503.Pq / 1504followed by the number of significant bits. 1505For example, an address with 33 significant bits could be specified as: 1506.Pp 1507.Dl "MAC 10:20:30:40:50:60/33 any" 1508.Pp 1509.It 1510An ampersand 1511.Pq & 1512followed by a bitmask specified as six groups of hex digits separated 1513by colons. 1514For example, an address in which the last 16 bits are significant could 1515be specified as: 1516.Pp 1517.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any" 1518.Pp 1519Note that the ampersand character has a special meaning in many shells 1520and should generally be escaped. 1521.Pp 1522.El 1523Note that the order of MAC addresses (destination first, 1524source second) is 1525the same as on the wire, but the opposite of the one used for 1526IP addresses. 1527.It Cm mac-type Ar mac-type 1528Matches packets whose Ethernet Type field 1529corresponds to one of those specified as argument. 1530.Ar mac-type 1531is specified in the same way as 1532.Cm port numbers 1533(i.e., one or more comma-separated single values or ranges). 1534You can use symbolic names for known values such as 1535.Em vlan , ipv4, ipv6 . 1536Values can be entered as decimal or hexadecimal (if prefixed by 0x), 1537and they are always printed as hexadecimal (unless the 1538.Cm -N 1539option is used, in which case symbolic resolution will be attempted). 1540.It Cm proto Ar protocol 1541Matches packets with the corresponding IP protocol. 1542.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any 1543Matches packets received, transmitted or going through, 1544respectively, the interface specified by exact name 1545.Ns No ( Ar ifX Ns No ), 1546by device name 1547.Ns No ( Ar if Ns Ar * Ns No ), 1548by IP address, or through some interface. 1549.Pp 1550The 1551.Cm via 1552keyword causes the interface to always be checked. 1553If 1554.Cm recv 1555or 1556.Cm xmit 1557is used instead of 1558.Cm via , 1559then only the receive or transmit interface (respectively) 1560is checked. 1561By specifying both, it is possible to match packets based on 1562both receive and transmit interface, e.g.: 1563.Pp 1564.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1" 1565.Pp 1566The 1567.Cm recv 1568interface can be tested on either incoming or outgoing packets, 1569while the 1570.Cm xmit 1571interface can only be tested on outgoing packets. 1572So 1573.Cm out 1574is required (and 1575.Cm in 1576is invalid) whenever 1577.Cm xmit 1578is used. 1579.Pp 1580A packet might not have a receive or transmit interface: packets 1581originating from the local host have no receive interface, 1582while packets destined for the local host have no transmit 1583interface. 1584.It Cm setup 1585Matches TCP packets that have the SYN bit set but no ACK bit. 1586This is the short form of 1587.Dq Li tcpflags\ syn,!ack . 1588.It Cm sockarg 1589Matches packets that are associated to a local socket and 1590for which the SO_USER_COOKIE socket option has been set 1591to a non-zero value. As a side effect, the value of the 1592option is made available as 1593.Cm tablearg 1594value, which in turn can be used as 1595.Cm skipto 1596or 1597.Cm pipe 1598number. 1599.It Cm src-ip Ar ip-address 1600Matches IPv4 packets whose source IP is one of the address(es) 1601specified as an argument. 1602.It Cm src-ip6 Ar ip6-address 1603Matches IPv6 packets whose source IP is one of the address(es) 1604specified as an argument. 1605.It Cm src-port Ar ports 1606Matches IP packets whose source port is one of the port(s) 1607specified as argument. 1608.It Cm tagged Ar tag-list 1609Matches packets whose tags are included in 1610.Ar tag-list , 1611which is either a single value or a list of values or ranges 1612specified in the same way as 1613.Ar ports . 1614Tags can be applied to the packet using 1615.Cm tag 1616rule action parameter (see it's description for details on tags). 1617.It Cm tcpack Ar ack 1618TCP packets only. 1619Match if the TCP header acknowledgment number field is set to 1620.Ar ack . 1621.It Cm tcpdatalen Ar tcpdatalen-list 1622Matches TCP packets whose length of TCP data is 1623.Ar tcpdatalen-list , 1624which is either a single value or a list of values or ranges 1625specified in the same way as 1626.Ar ports . 1627.It Cm tcpflags Ar spec 1628TCP packets only. 1629Match if the TCP header contains the comma separated list of 1630flags specified in 1631.Ar spec . 1632The supported TCP flags are: 1633.Pp 1634.Cm fin , 1635.Cm syn , 1636.Cm rst , 1637.Cm psh , 1638.Cm ack 1639and 1640.Cm urg . 1641The absence of a particular flag may be denoted 1642with a 1643.Ql \&! . 1644A rule which contains a 1645.Cm tcpflags 1646specification can never match a fragmented packet which has 1647a non-zero offset. 1648See the 1649.Cm frag 1650option for details on matching fragmented packets. 1651.It Cm tcpseq Ar seq 1652TCP packets only. 1653Match if the TCP header sequence number field is set to 1654.Ar seq . 1655.It Cm tcpwin Ar win 1656TCP packets only. 1657Match if the TCP header window field is set to 1658.Ar win . 1659.It Cm tcpoptions Ar spec 1660TCP packets only. 1661Match if the TCP header contains the comma separated list of 1662options specified in 1663.Ar spec . 1664The supported TCP options are: 1665.Pp 1666.Cm mss 1667(maximum segment size), 1668.Cm window 1669(tcp window advertisement), 1670.Cm sack 1671(selective ack), 1672.Cm ts 1673(rfc1323 timestamp) and 1674.Cm cc 1675(rfc1644 t/tcp connection count). 1676The absence of a particular option may be denoted 1677with a 1678.Ql \&! . 1679.It Cm uid Ar user 1680Match all TCP or UDP packets sent by or received for a 1681.Ar user . 1682A 1683.Ar user 1684may be matched by name or identification number. 1685.It Cm verrevpath 1686For incoming packets, 1687a routing table lookup is done on the packet's source address. 1688If the interface on which the packet entered the system matches the 1689outgoing interface for the route, 1690the packet matches. 1691If the interfaces do not match up, 1692the packet does not match. 1693All outgoing packets or packets with no incoming interface match. 1694.Pp 1695The name and functionality of the option is intentionally similar to 1696the Cisco IOS command: 1697.Pp 1698.Dl ip verify unicast reverse-path 1699.Pp 1700This option can be used to make anti-spoofing rules to reject all 1701packets with source addresses not from this interface. 1702See also the option 1703.Cm antispoof . 1704.It Cm versrcreach 1705For incoming packets, 1706a routing table lookup is done on the packet's source address. 1707If a route to the source address exists, but not the default route 1708or a blackhole/reject route, the packet matches. 1709Otherwise, the packet does not match. 1710All outgoing packets match. 1711.Pp 1712The name and functionality of the option is intentionally similar to 1713the Cisco IOS command: 1714.Pp 1715.Dl ip verify unicast source reachable-via any 1716.Pp 1717This option can be used to make anti-spoofing rules to reject all 1718packets whose source address is unreachable. 1719.It Cm antispoof 1720For incoming packets, the packet's source address is checked if it 1721belongs to a directly connected network. 1722If the network is directly connected, then the interface the packet 1723came on in is compared to the interface the network is connected to. 1724When incoming interface and directly connected interface are not the 1725same, the packet does not match. 1726Otherwise, the packet does match. 1727All outgoing packets match. 1728.Pp 1729This option can be used to make anti-spoofing rules to reject all 1730packets that pretend to be from a directly connected network but do 1731not come in through that interface. 1732This option is similar to but more restricted than 1733.Cm verrevpath 1734because it engages only on packets with source addresses of directly 1735connected networks instead of all source addresses. 1736.El 1737.Sh LOOKUP TABLES 1738Lookup tables are useful to handle large sparse sets of 1739addresses or other search keys (e.g. ports, jail IDs). 1740In the rest of this section we will use the term ``address'' 1741to mean any unsigned value of up to 32-bit. 1742There may be up to 128 different lookup tables, numbered 0 to 127. 1743.Pp 1744Each entry is represented by an 1745.Ar addr Ns Op / Ns Ar masklen 1746and will match all addresses with base 1747.Ar addr 1748(specified as an IP address, a hostname or an unsigned integer) 1749and mask width of 1750.Ar masklen 1751bits. 1752If 1753.Ar masklen 1754is not specified, it defaults to 32. 1755When looking up an IP address in a table, the most specific 1756entry will match. 1757Associated with each entry is a 32-bit unsigned 1758.Ar value , 1759which can optionally be checked by a rule matching code. 1760When adding an entry, if 1761.Ar value 1762is not specified, it defaults to 0. 1763.Pp 1764An entry can be added to a table 1765.Pq Cm add , 1766or removed from a table 1767.Pq Cm delete . 1768A table can be examined 1769.Pq Cm list 1770or flushed 1771.Pq Cm flush . 1772.Pp 1773Internally, each table is stored in a Radix tree, the same way as 1774the routing table (see 1775.Xr route 4 ) . 1776.Pp 1777Lookup tables currently support only ports, jail IDs and IPv4 addresses. 1778.Pp 1779The 1780.Cm tablearg 1781feature provides the ability to use a value, looked up in the table, as 1782the argument for a rule action, action parameter or rule option. 1783This can significantly reduce number of rules in some configurations. 1784If two tables are used in a rule, the result of the second (destination) 1785is used. 1786The 1787.Cm tablearg 1788argument can be used with the following actions: 1789.Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto, setfib, 1790action parameters: 1791.Cm tag, untag, 1792rule options: 1793.Cm limit, tagged. 1794.Pp 1795When used with 1796.Cm fwd 1797it is possible to supply table entries with values 1798that are in the form of IP addresses or hostnames. 1799See the 1800.Sx EXAMPLES 1801Section for example usage of tables and the tablearg keyword. 1802.Pp 1803When used with the 1804.Cm skipto 1805action, the user should be aware that the code will walk the ruleset 1806up to a rule equal to, or past, the given number, and should therefore try keep the 1807ruleset compact between the skipto and the target rules. 1808.Sh SETS OF RULES 1809Each rule belongs to one of 32 different 1810.Em sets 1811, numbered 0 to 31. 1812Set 31 is reserved for the default rule. 1813.Pp 1814By default, rules are put in set 0, unless you use the 1815.Cm set N 1816attribute when entering a new rule. 1817Sets can be individually and atomically enabled or disabled, 1818so this mechanism permits an easy way to store multiple configurations 1819of the firewall and quickly (and atomically) switch between them. 1820The command to enable/disable sets is 1821.Bd -ragged -offset indent 1822.Nm 1823.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 1824.Ed 1825.Pp 1826where multiple 1827.Cm enable 1828or 1829.Cm disable 1830sections can be specified. 1831Command execution is atomic on all the sets specified in the command. 1832By default, all sets are enabled. 1833.Pp 1834When you disable a set, its rules behave as if they do not exist 1835in the firewall configuration, with only one exception: 1836.Bd -ragged -offset indent 1837dynamic rules created from a rule before it had been disabled 1838will still be active until they expire. 1839In order to delete 1840dynamic rules you have to explicitly delete the parent rule 1841which generated them. 1842.Ed 1843.Pp 1844The set number of rules can be changed with the command 1845.Bd -ragged -offset indent 1846.Nm 1847.Cm set move 1848.Brq Cm rule Ar rule-number | old-set 1849.Cm to Ar new-set 1850.Ed 1851.Pp 1852Also, you can atomically swap two rulesets with the command 1853.Bd -ragged -offset indent 1854.Nm 1855.Cm set swap Ar first-set second-set 1856.Ed 1857.Pp 1858See the 1859.Sx EXAMPLES 1860Section on some possible uses of sets of rules. 1861.Sh STATEFUL FIREWALL 1862Stateful operation is a way for the firewall to dynamically 1863create rules for specific flows when packets that 1864match a given pattern are detected. 1865Support for stateful 1866operation comes through the 1867.Cm check-state , keep-state 1868and 1869.Cm limit 1870options of 1871.Nm rules . 1872.Pp 1873Dynamic rules are created when a packet matches a 1874.Cm keep-state 1875or 1876.Cm limit 1877rule, causing the creation of a 1878.Em dynamic 1879rule which will match all and only packets with 1880a given 1881.Em protocol 1882between a 1883.Em src-ip/src-port dst-ip/dst-port 1884pair of addresses 1885.Em ( src 1886and 1887.Em dst 1888are used here only to denote the initial match addresses, but they 1889are completely equivalent afterwards). 1890Dynamic rules will be checked at the first 1891.Cm check-state, keep-state 1892or 1893.Cm limit 1894occurrence, and the action performed upon a match will be the same 1895as in the parent rule. 1896.Pp 1897Note that no additional attributes other than protocol and IP addresses 1898and ports are checked on dynamic rules. 1899.Pp 1900The typical use of dynamic rules is to keep a closed firewall configuration, 1901but let the first TCP SYN packet from the inside network install a 1902dynamic rule for the flow so that packets belonging to that session 1903will be allowed through the firewall: 1904.Pp 1905.Dl "ipfw add check-state" 1906.Dl "ipfw add allow tcp from my-subnet to any setup keep-state" 1907.Dl "ipfw add deny tcp from any to any" 1908.Pp 1909A similar approach can be used for UDP, where an UDP packet coming 1910from the inside will install a dynamic rule to let the response through 1911the firewall: 1912.Pp 1913.Dl "ipfw add check-state" 1914.Dl "ipfw add allow udp from my-subnet to any keep-state" 1915.Dl "ipfw add deny udp from any to any" 1916.Pp 1917Dynamic rules expire after some time, which depends on the status 1918of the flow and the setting of some 1919.Cm sysctl 1920variables. 1921See Section 1922.Sx SYSCTL VARIABLES 1923for more details. 1924For TCP sessions, dynamic rules can be instructed to periodically 1925send keepalive packets to refresh the state of the rule when it is 1926about to expire. 1927.Pp 1928See Section 1929.Sx EXAMPLES 1930for more examples on how to use dynamic rules. 1931.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 1932.Nm 1933is also the user interface for the 1934.Nm dummynet 1935traffic shaper, packet scheduler and network emulator, a subsystem that 1936can artificially queue, delay or drop packets 1937emulating the behaviour of certain network links 1938or queueing systems. 1939.Pp 1940.Nm dummynet 1941operates by first using the firewall to select packets 1942using any match pattern that can be used in 1943.Nm 1944rules. 1945Matching packets are then passed to either of two 1946different objects, which implement the traffic regulation: 1947.Bl -hang -offset XXXX 1948.It Em pipe 1949A 1950.Em pipe 1951emulates a 1952.Em link 1953with given bandwidth and propagation delay, 1954driven by a FIFO scheduler and a single queue with programmable 1955queue size and packet loss rate. 1956Packets are appended to the queue as they come out from 1957.Nm ipfw , 1958and then transferred in FIFO order to the link at the desired rate. 1959.It Em queue 1960A 1961.Em queue 1962is an abstraction used to implement packet scheduling 1963using one of several packet scheduling algorithms. 1964Packets sent to a 1965.Em queue 1966are first grouped into flows according to a mask on the 5-tuple. 1967Flows are then passed to the scheduler associated to the 1968.Em queue , 1969and each flow uses scheduling parameters (weight and others) 1970as configured in the 1971.Em queue 1972itself. 1973A scheduler in turn is connected to an emulated link, 1974and arbitrates the link's bandwidth among backlogged flows according to 1975weights and to the features of the scheduling algorithm in use. 1976.El 1977.Pp 1978In practice, 1979.Em pipes 1980can be used to set hard limits to the bandwidth that a flow can use, whereas 1981.Em queues 1982can be used to determine how different flows share the available bandwidth. 1983.Pp 1984A graphical representation of the binding of queues, 1985flows, schedulers and links is below. 1986.Bd -literal -offset indent 1987 (flow_mask|sched_mask) sched_mask 1988 +---------+ weight Wx +-------------+ 1989 | |->-[flow]-->--| |-+ 1990 -->--| QUEUE x | ... | | | 1991 | |->-[flow]-->--| SCHEDuler N | | 1992 +---------+ | | | 1993 ... | +--[LINK N]-->-- 1994 +---------+ weight Wy | | +--[LINK N]-->-- 1995 | |->-[flow]-->--| | | 1996 -->--| QUEUE y | ... | | | 1997 | |->-[flow]-->--| | | 1998 +---------+ +-------------+ | 1999 +-------------+ 2000.Ed 2001It is important to understand the role of the SCHED_MASK 2002and FLOW_MASK, which are configured through the commands 2003.Dl "ipfw sched N config mask SCHED_MASK ..." 2004and 2005.Dl "ipfw queue X config mask FLOW_MASK ..." . 2006.Pp 2007The SCHED_MASK is used to assign flows to one or more 2008scheduler instances, one for each 2009value of the packet's 5-tuple after applying SCHED_MASK. 2010As an example, using ``src-ip 0xffffff00'' creates one instance 2011for each /24 destination subnet. 2012.Pp 2013The FLOW_MASK, together with the SCHED_MASK, is used to split 2014packets into flows. As an example, using 2015``src-ip 0x000000ff'' 2016together with the previous SCHED_MASK makes a flow for 2017each individual source address. In turn, flows for each /24 2018subnet will be sent to the same scheduler instance. 2019.Pp 2020The above diagram holds even for the 2021.Em pipe 2022case, with the only restriction that a 2023.Em pipe 2024only supports a SCHED_MASK, and forces the use of a FIFO 2025scheduler (these are for backward compatibility reasons; 2026in fact, internally, a 2027.Nm dummynet's 2028pipe is implemented exactly as above). 2029.Pp 2030There are two modes of 2031.Nm dummynet 2032operation: 2033.Dq normal 2034and 2035.Dq fast . 2036The 2037.Dq normal 2038mode tries to emulate a real link: the 2039.Nm dummynet 2040scheduler ensures that the packet will not leave the pipe faster than it 2041would on the real link with a given bandwidth. 2042The 2043.Dq fast 2044mode allows certain packets to bypass the 2045.Nm dummynet 2046scheduler (if packet flow does not exceed pipe's bandwidth). 2047This is the reason why the 2048.Dq fast 2049mode requires less CPU cycles per packet (on average) and packet latency 2050can be significantly lower in comparison to a real link with the same 2051bandwidth. 2052The default mode is 2053.Dq normal . 2054The 2055.Dq fast 2056mode can be enabled by setting the 2057.Va net.inet.ip.dummynet.io_fast 2058.Xr sysctl 8 2059variable to a non-zero value. 2060.Pp 2061.Ss PIPE, QUEUE AND SCHEDULER CONFIGURATION 2062The 2063.Em pipe , 2064.Em queue 2065and 2066.Em scheduler 2067configuration commands are the following: 2068.Bd -ragged -offset indent 2069.Cm pipe Ar number Cm config Ar pipe-configuration 2070.Pp 2071.Cm queue Ar number Cm config Ar queue-configuration 2072.Pp 2073.Cm sched Ar number Cm config Ar sched-configuration 2074.Ed 2075.Pp 2076The following parameters can be configured for a pipe: 2077.Pp 2078.Bl -tag -width indent -compact 2079.It Cm bw Ar bandwidth | device 2080Bandwidth, measured in 2081.Sm off 2082.Op Cm K | M 2083.Brq Cm bit/s | Byte/s . 2084.Sm on 2085.Pp 2086A value of 0 (default) means unlimited bandwidth. 2087The unit must immediately follow the number, as in 2088.Pp 2089.Dl "ipfw pipe 1 config bw 300Kbit/s" 2090.Pp 2091If a device name is specified instead of a numeric value, as in 2092.Pp 2093.Dl "ipfw pipe 1 config bw tun0" 2094.Pp 2095then the transmit clock is supplied by the specified device. 2096At the moment only the 2097.Xr tun 4 2098device supports this 2099functionality, for use in conjunction with 2100.Xr ppp 8 . 2101.Pp 2102.It Cm delay Ar ms-delay 2103Propagation delay, measured in milliseconds. 2104The value is rounded to the next multiple of the clock tick 2105(typically 10ms, but it is a good practice to run kernels 2106with 2107.Dq "options HZ=1000" 2108to reduce 2109the granularity to 1ms or less). 2110The default value is 0, meaning no delay. 2111.Pp 2112.It Cm burst Ar size 2113If the data to be sent exceeds the pipe's bandwidth limit 2114(and the pipe was previously idle), up to 2115.Ar size 2116bytes of data are allowed to bypass the 2117.Nm dummynet 2118scheduler, and will be sent as fast as the physical link allows. 2119Any additional data will be transmitted at the rate specified 2120by the 2121.Nm pipe 2122bandwidth. 2123The burst size depends on how long the pipe has been idle; 2124the effective burst size is calculated as follows: 2125MAX( 2126.Ar size 2127, 2128.Nm bw 2129* pipe_idle_time). 2130.Pp 2131.It Cm profile Ar filename 2132A file specifying the additional overhead incurred in the transmission 2133of a packet on the link. 2134.Pp 2135Some link types introduce extra delays in the transmission 2136of a packet, e.g. because of MAC level framing, contention on 2137the use of the channel, MAC level retransmissions and so on. 2138From our point of view, the channel is effectively unavailable 2139for this extra time, which is constant or variable depending 2140on the link type. Additionally, packets may be dropped after this 2141time (e.g. on a wireless link after too many retransmissions). 2142We can model the additional delay with an empirical curve 2143that represents its distribution. 2144.Bd -literal -offset indent 2145 cumulative probability 2146 1.0 ^ 2147 | 2148 L +-- loss-level x 2149 | ****** 2150 | * 2151 | ***** 2152 | * 2153 | ** 2154 | * 2155 +-------*-------------------> 2156 delay 2157.Ed 2158The empirical curve may have both vertical and horizontal lines. 2159Vertical lines represent constant delay for a range of 2160probabilities. 2161Horizontal lines correspond to a discontinuity in the delay 2162distribution: the pipe will use the largest delay for a 2163given probability. 2164.Pp 2165The file format is the following, with whitespace acting as 2166a separator and '#' indicating the beginning a comment: 2167.Bl -tag -width indent 2168.It Cm name Ar identifier 2169optional name (listed by "ipfw pipe show") 2170to identify the delay distribution; 2171.It Cm bw Ar value 2172the bandwidth used for the pipe. 2173If not specified here, it must be present 2174explicitly as a configuration parameter for the pipe; 2175.It Cm loss-level Ar L 2176the probability above which packets are lost. 2177(0.0 <= L <= 1.0, default 1.0 i.e. no loss); 2178.It Cm samples Ar N 2179the number of samples used in the internal 2180representation of the curve (2..1024; default 100); 2181.It Cm "delay prob" | "prob delay" 2182One of these two lines is mandatory and defines 2183the format of the following lines with data points. 2184.It Ar XXX Ar YYY 21852 or more lines representing points in the curve, 2186with either delay or probability first, according 2187to the chosen format. 2188The unit for delay is milliseconds. 2189Data points do not need to be sorted. 2190Also, the number of actual lines can be different 2191from the value of the "samples" parameter: 2192.Nm 2193utility will sort and interpolate 2194the curve as needed. 2195.El 2196.Pp 2197Example of a profile file: 2198.Bd -literal -offset indent 2199name bla_bla_bla 2200samples 100 2201loss-level 0.86 2202prob delay 22030 200 # minimum overhead is 200ms 22040.5 200 22050.5 300 22060.8 1000 22070.9 1300 22081 1300 2209#configuration file end 2210.Ed 2211.El 2212.Pp 2213The following parameters can be configured for a queue: 2214.Pp 2215.Bl -tag -width indent -compact 2216.It Cm pipe Ar pipe_nr 2217Connects a queue to the specified pipe. 2218Multiple queues (with the same or different weights) can be connected to 2219the same pipe, which specifies the aggregate rate for the set of queues. 2220.Pp 2221.It Cm weight Ar weight 2222Specifies the weight to be used for flows matching this queue. 2223The weight must be in the range 1..100, and defaults to 1. 2224.El 2225.Pp 2226The following parameters can be configured for a scheduler: 2227.Pp 2228.Bl -tag -width indent -compact 2229.It Cm type Ar {fifo | wf2qp | rr | qfq} 2230specifies the scheduling algorithm to use. 2231.Bl -tag -width indent -compact 2232.It cm fifo 2233is just a FIFO scheduler (which means that all packets 2234are stored in the same queue as they arrive to the scheduler). 2235FIFO has O(1) per-packet time complexity, with very low 2236constants (estimate 60-80ns on a 2Ghz desktop machine) 2237but gives no service guarantees. 2238.It Cm wf2qp 2239implements the WF2Q+ algorithm, which is a Weighted Fair Queueing 2240algorithm which permits flows to share bandwidth according to 2241their weights. Note that weights are not priorities; even a flow 2242with a minuscule weight will never starve. 2243WF2Q+ has O(log N) per-packet processing cost, where N is the number 2244of flows, and is the default algorithm used by previous versions 2245dummynet's queues. 2246.It Cm rr 2247implements the Deficit Round Robin algorithm, which has O(1) processing 2248costs (roughly, 100-150ns per packet) 2249and permits bandwidth allocation according to weights, but 2250with poor service guarantees. 2251.It Cm qfq 2252implements the QFQ algorithm, which is a very fast variant of 2253WF2Q+, with similar service guarantees and O(1) processing 2254costs (roughly, 200-250ns per packet). 2255.El 2256.El 2257.Pp 2258In addition to the type, all parameters allowed for a pipe can also 2259be specified for a scheduler. 2260.Pp 2261Finally, the following parameters can be configured for both 2262pipes and queues: 2263.Pp 2264.Bl -tag -width XXXX -compact 2265.It Cm buckets Ar hash-table-size 2266Specifies the size of the hash table used for storing the 2267various queues. 2268Default value is 64 controlled by the 2269.Xr sysctl 8 2270variable 2271.Va net.inet.ip.dummynet.hash_size , 2272allowed range is 16 to 65536. 2273.Pp 2274.It Cm mask Ar mask-specifier 2275Packets sent to a given pipe or queue by an 2276.Nm 2277rule can be further classified into multiple flows, each of which is then 2278sent to a different 2279.Em dynamic 2280pipe or queue. 2281A flow identifier is constructed by masking the IP addresses, 2282ports and protocol types as specified with the 2283.Cm mask 2284options in the configuration of the pipe or queue. 2285For each different flow identifier, a new pipe or queue is created 2286with the same parameters as the original object, and matching packets 2287are sent to it. 2288.Pp 2289Thus, when 2290.Em dynamic pipes 2291are used, each flow will get the same bandwidth as defined by the pipe, 2292whereas when 2293.Em dynamic queues 2294are used, each flow will share the parent's pipe bandwidth evenly 2295with other flows generated by the same queue (note that other queues 2296with different weights might be connected to the same pipe). 2297.br 2298Available mask specifiers are a combination of one or more of the following: 2299.Pp 2300.Cm dst-ip Ar mask , 2301.Cm dst-ip6 Ar mask , 2302.Cm src-ip Ar mask , 2303.Cm src-ip6 Ar mask , 2304.Cm dst-port Ar mask , 2305.Cm src-port Ar mask , 2306.Cm flow-id Ar mask , 2307.Cm proto Ar mask 2308or 2309.Cm all , 2310.Pp 2311where the latter means all bits in all fields are significant. 2312.Pp 2313.It Cm noerror 2314When a packet is dropped by a 2315.Nm dummynet 2316queue or pipe, the error 2317is normally reported to the caller routine in the kernel, in the 2318same way as it happens when a device queue fills up. 2319Setting this 2320option reports the packet as successfully delivered, which can be 2321needed for some experimental setups where you want to simulate 2322loss or congestion at a remote router. 2323.Pp 2324.It Cm plr Ar packet-loss-rate 2325Packet loss rate. 2326Argument 2327.Ar packet-loss-rate 2328is a floating-point number between 0 and 1, with 0 meaning no 2329loss, 1 meaning 100% loss. 2330The loss rate is internally represented on 31 bits. 2331.Pp 2332.It Cm queue Brq Ar slots | size Ns Cm Kbytes 2333Queue size, in 2334.Ar slots 2335or 2336.Cm KBytes . 2337Default value is 50 slots, which 2338is the typical queue size for Ethernet devices. 2339Note that for slow speed links you should keep the queue 2340size short or your traffic might be affected by a significant 2341queueing delay. 2342E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit 2343or 20s of queue on a 30Kbit/s pipe. 2344Even worse effects can result if you get packets from an 2345interface with a much larger MTU, e.g.\& the loopback interface 2346with its 16KB packets. 2347The 2348.Xr sysctl 8 2349variables 2350.Em net.inet.ip.dummynet.pipe_byte_limit 2351and 2352.Em net.inet.ip.dummynet.pipe_slot_limit 2353control the maximum lengths that can be specified. 2354.Pp 2355.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p 2356Make use of the RED (Random Early Detection) queue management algorithm. 2357.Ar w_q 2358and 2359.Ar max_p 2360are floating 2361point numbers between 0 and 1 (0 not included), while 2362.Ar min_th 2363and 2364.Ar max_th 2365are integer numbers specifying thresholds for queue management 2366(thresholds are computed in bytes if the queue has been defined 2367in bytes, in slots otherwise). 2368The 2369.Nm dummynet 2370also supports the gentle RED variant (gred). 2371Three 2372.Xr sysctl 8 2373variables can be used to control the RED behaviour: 2374.Bl -tag -width indent 2375.It Va net.inet.ip.dummynet.red_lookup_depth 2376specifies the accuracy in computing the average queue 2377when the link is idle (defaults to 256, must be greater than zero) 2378.It Va net.inet.ip.dummynet.red_avg_pkt_size 2379specifies the expected average packet size (defaults to 512, must be 2380greater than zero) 2381.It Va net.inet.ip.dummynet.red_max_pkt_size 2382specifies the expected maximum packet size, only used when queue 2383thresholds are in bytes (defaults to 1500, must be greater than zero). 2384.El 2385.El 2386.Pp 2387When used with IPv6 data, 2388.Nm dummynet 2389currently has several limitations. 2390Information necessary to route link-local packets to an 2391interface is not available after processing by 2392.Nm dummynet 2393so those packets are dropped in the output path. 2394Care should be taken to ensure that link-local packets are not passed to 2395.Nm dummynet . 2396.Sh CHECKLIST 2397Here are some important points to consider when designing your 2398rules: 2399.Bl -bullet 2400.It 2401Remember that you filter both packets going 2402.Cm in 2403and 2404.Cm out . 2405Most connections need packets going in both directions. 2406.It 2407Remember to test very carefully. 2408It is a good idea to be near the console when doing this. 2409If you cannot be near the console, 2410use an auto-recovery script such as the one in 2411.Pa /usr/share/examples/ipfw/change_rules.sh . 2412.It 2413Do not forget the loopback interface. 2414.El 2415.Sh FINE POINTS 2416.Bl -bullet 2417.It 2418There are circumstances where fragmented datagrams are unconditionally 2419dropped. 2420TCP packets are dropped if they do not contain at least 20 bytes of 2421TCP header, UDP packets are dropped if they do not contain a full 8 2422byte UDP header, and ICMP packets are dropped if they do not contain 24234 bytes of ICMP header, enough to specify the ICMP type, code, and 2424checksum. 2425These packets are simply logged as 2426.Dq pullup failed 2427since there may not be enough good data in the packet to produce a 2428meaningful log entry. 2429.It 2430Another type of packet is unconditionally dropped, a TCP packet with a 2431fragment offset of one. 2432This is a valid packet, but it only has one use, to try 2433to circumvent firewalls. 2434When logging is enabled, these packets are 2435reported as being dropped by rule -1. 2436.It 2437If you are logged in over a network, loading the 2438.Xr kld 4 2439version of 2440.Nm 2441is probably not as straightforward as you would think. 2442The following command line is recommended: 2443.Bd -literal -offset indent 2444kldload ipfw && \e 2445ipfw add 32000 allow ip from any to any 2446.Ed 2447.Pp 2448Along the same lines, doing an 2449.Bd -literal -offset indent 2450ipfw flush 2451.Ed 2452.Pp 2453in similar surroundings is also a bad idea. 2454.It 2455The 2456.Nm 2457filter list may not be modified if the system security level 2458is set to 3 or higher 2459(see 2460.Xr init 8 2461for information on system security levels). 2462.El 2463.Sh PACKET DIVERSION 2464A 2465.Xr divert 4 2466socket bound to the specified port will receive all packets 2467diverted to that port. 2468If no socket is bound to the destination port, or if the divert module is 2469not loaded, or if the kernel was not compiled with divert socket support, 2470the packets are dropped. 2471.Sh NETWORK ADDRESS TRANSLATION (NAT) 2472.Pp 2473.Nm 2474support in-kernel NAT using the kernel version of 2475.Xr libalias 3 . 2476.Pp 2477The nat configuration command is the following: 2478.Bd -ragged -offset indent 2479.Bk -words 2480.Cm nat 2481.Ar nat_number 2482.Cm config 2483.Ar nat-configuration 2484.Ek 2485.Ed 2486.Pp 2487The following parameters can be configured: 2488.Bl -tag -width indent 2489.It Cm ip Ar ip_address 2490Define an ip address to use for aliasing. 2491.It Cm if Ar nic 2492Use ip address of NIC for aliasing, dynamically changing 2493it if NIC's ip address changes. 2494.It Cm log 2495Enable logging on this nat instance. 2496.It Cm deny_in 2497Deny any incoming connection from outside world. 2498.It Cm same_ports 2499Try to leave the alias port numbers unchanged from 2500the actual local port numbers. 2501.It Cm unreg_only 2502Traffic on the local network not originating from an 2503unregistered address spaces will be ignored. 2504.It Cm reset 2505Reset table of the packet aliasing engine on address change. 2506.It Cm reverse 2507Reverse the way libalias handles aliasing. 2508.It Cm proxy_only 2509Obey transparent proxy rules only, packet aliasing is not performed. 2510.It Cm skip_global 2511Skip instance in case of global state lookup (see below). 2512.El 2513.Pp 2514Some specials value can be supplied instead of 2515.Va nat_number: 2516.Bl -tag -width indent 2517.It Cm global 2518Looks up translation state in all configured nat instances. 2519If an entry is found, packet is aliased according to that entry. 2520If no entry was found in any of the instances, packet is passed unchanged, 2521and no new entry will be created. 2522See section 2523.Sx MULTIPLE INSTANCES 2524in 2525.Xr natd 8 2526for more information. 2527.It Cm tablearg 2528Uses argument supplied in lookup table. See 2529.Sx LOOKUP TABLES 2530section below for more information on lookup tables. 2531.El 2532.Pp 2533To let the packet continue after being (de)aliased, set the sysctl variable 2534.Va net.inet.ip.fw.one_pass 2535to 0. 2536For more information about aliasing modes, refer to 2537.Xr libalias 3 . 2538See Section 2539.Sx EXAMPLES 2540for some examples about nat usage. 2541.Ss REDIRECT AND LSNAT SUPPORT IN IPFW 2542Redirect and LSNAT support follow closely the syntax used in 2543.Xr natd 8 . 2544See Section 2545.Sx EXAMPLES 2546for some examples on how to do redirect and lsnat. 2547.Ss SCTP NAT SUPPORT 2548SCTP nat can be configured in a similar manner to TCP through the 2549.Nm 2550command line tool. 2551The main difference is that 2552.Nm sctp nat 2553does not do port translation. 2554Since the local and global side ports will be the same, 2555there is no need to specify both. 2556Ports are redirected as follows: 2557.Bd -ragged -offset indent 2558.Bk -words 2559.Cm nat 2560.Ar nat_number 2561.Cm config if 2562.Ar nic 2563.Cm redirect_port sctp 2564.Ar ip_address [,addr_list] {[port | port-port] [,ports]} 2565.Ek 2566.Ed 2567.Pp 2568Most 2569.Nm sctp nat 2570configuration can be done in real-time through the 2571.Xr sysctl 8 2572interface. 2573All may be changed dynamically, though the hash_table size will only 2574change for new 2575.Nm nat 2576instances. 2577See 2578.Sx SYSCTL VARIABLES 2579for more info. 2580.Sh SYSCTL VARIABLES 2581A set of 2582.Xr sysctl 8 2583variables controls the behaviour of the firewall and 2584associated modules 2585.Pq Nm dummynet , bridge , sctp nat . 2586These are shown below together with their default value 2587(but always check with the 2588.Xr sysctl 8 2589command what value is actually in use) and meaning: 2590.Bl -tag -width indent 2591.It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0 2592Defines how the 2593.Nm nat 2594responds to receipt of global OOTB ASCONF-AddIP: 2595.Bl -tag -width indent 2596.It Cm 0 2597No response (unless a partially matching association exists - 2598ports and vtags match but global address does not) 2599.It Cm 1 2600.Nm nat 2601will accept and process all OOTB global AddIP messages. 2602.El 2603.Pp 2604Option 1 should never be selected as this forms a security risk. 2605An attacker can 2606establish multiple fake associations by sending AddIP messages. 2607.It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5 2608Defines the maximum number of chunks in an SCTP packet that will be parsed for a 2609packet that matches an existing association. 2610This value is enforced to be greater or equal than 2611.Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit . 2612A high value is 2613a DoS risk yet setting too low a value may result in important control chunks in 2614the packet not being located and parsed. 2615.It Va net.inet.ip.alias.sctp.error_on_ootb: No 1 2616Defines when the 2617.Nm nat 2618responds to any Out-of-the-Blue (OOTB) packets with ErrorM packets. 2619An OOTB packet is a packet that arrives with no existing association 2620registered in the 2621.Nm nat 2622and is not an INIT or ASCONF-AddIP packet: 2623.Bl -tag -width indent 2624.It Cm 0 2625ErrorM is never sent in response to OOTB packets. 2626.It Cm 1 2627ErrorM is only sent to OOTB packets received on the local side. 2628.It Cm 2 2629ErrorM is sent to the local side and on the global side ONLY if there is a 2630partial match (ports and vtags match but the source global IP does not). 2631This value is only useful if the 2632.Nm nat 2633is tracking global IP addresses. 2634.It Cm 3 2635ErrorM is sent in response to all OOTB packets on both the local and global side 2636(DoS risk). 2637.El 2638.Pp 2639At the moment the default is 0, since the ErrorM packet is not yet 2640supported by most SCTP stacks. 2641When it is supported, and if not tracking 2642global addresses, we recommend setting this value to 1 to allow 2643multi-homed local hosts to function with the 2644.Nm nat . 2645To track global addresses, we recommend setting this value to 2 to 2646allow global hosts to be informed when they need to (re)send an 2647ASCONF-AddIP. 2648Value 3 should never be chosen (except for debugging) as the 2649.Nm nat 2650will respond to all OOTB global packets (a DoS risk). 2651.It Va net.inet.ip.alias.sctp.hashtable_size: No 2003 2652Size of hash tables used for 2653.Nm nat 2654lookups (100 < prime_number > 1000001). 2655This value sets the 2656.Nm hash table 2657size for any future created 2658.Nm nat 2659instance and therefore must be set prior to creating a 2660.Nm nat 2661instance. 2662The table sizes may be changed to suit specific needs. 2663If there will be few 2664concurrent associations, and memory is scarce, you may make these smaller. 2665If there will be many thousands (or millions) of concurrent associations, you 2666should make these larger. 2667A prime number is best for the table size. 2668The sysctl 2669update function will adjust your input value to the next highest prime number. 2670.It Va net.inet.ip.alias.sctp.holddown_time: No 0 2671Hold association in table for this many seconds after receiving a 2672SHUTDOWN-COMPLETE. 2673This allows endpoints to correct shutdown gracefully if a 2674shutdown_complete is lost and retransmissions are required. 2675.It Va net.inet.ip.alias.sctp.init_timer: No 15 2676Timeout value while waiting for (INIT-ACK|AddIP-ACK). 2677This value cannot be 0. 2678.It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2 2679Defines the maximum number of chunks in an SCTP packet that will be parsed when 2680no existing association exists that matches that packet. 2681Ideally this packet 2682will only be an INIT or ASCONF-AddIP packet. 2683A higher value may become a DoS 2684risk as malformed packets can consume processing resources. 2685.It Va net.inet.ip.alias.sctp.param_proc_limit: No 25 2686Defines the maximum number of parameters within a chunk that will be parsed in a 2687packet. 2688As for other similar sysctl variables, larger values pose a DoS risk. 2689.It Va net.inet.ip.alias.sctp.log_level: No 0 2690Level of detail in the system log messages (0 \- minimal, 1 \- event, 26912 \- info, 3 \- detail, 4 \- debug, 5 \- max debug). May be a good 2692option in high loss environments. 2693.It Va net.inet.ip.alias.sctp.shutdown_time: No 15 2694Timeout value while waiting for SHUTDOWN-COMPLETE. 2695This value cannot be 0. 2696.It Va net.inet.ip.alias.sctp.track_global_addresses: No 0 2697Enables/disables global IP address tracking within the 2698.Nm nat 2699and places an 2700upper limit on the number of addresses tracked for each association: 2701.Bl -tag -width indent 2702.It Cm 0 2703Global tracking is disabled 2704.It Cm >1 2705Enables tracking, the maximum number of addresses tracked for each 2706association is limited to this value 2707.El 2708.Pp 2709This variable is fully dynamic, the new value will be adopted for all newly 2710arriving associations, existing associations are treated as they were previously. 2711Global tracking will decrease the number of collisions within the 2712.Nm nat 2713at a cost 2714of increased processing load, memory usage, complexity, and possible 2715.Nm nat 2716state 2717problems in complex networks with multiple 2718.Nm nats . 2719We recommend not tracking 2720global IP addresses, this will still result in a fully functional 2721.Nm nat . 2722.It Va net.inet.ip.alias.sctp.up_timer: No 300 2723Timeout value to keep an association up with no traffic. 2724This value cannot be 0. 2725.It Va net.inet.ip.dummynet.expire : No 1 2726Lazily delete dynamic pipes/queue once they have no pending traffic. 2727You can disable this by setting the variable to 0, in which case 2728the pipes/queues will only be deleted when the threshold is reached. 2729.It Va net.inet.ip.dummynet.hash_size : No 64 2730Default size of the hash table used for dynamic pipes/queues. 2731This value is used when no 2732.Cm buckets 2733option is specified when configuring a pipe/queue. 2734.It Va net.inet.ip.dummynet.io_fast : No 0 2735If set to a non-zero value, 2736the 2737.Dq fast 2738mode of 2739.Nm dummynet 2740operation (see above) is enabled. 2741.It Va net.inet.ip.dummynet.io_pkt 2742Number of packets passed to 2743.Nm dummynet . 2744.It Va net.inet.ip.dummynet.io_pkt_drop 2745Number of packets dropped by 2746.Nm dummynet . 2747.It Va net.inet.ip.dummynet.io_pkt_fast 2748Number of packets bypassed by the 2749.Nm dummynet 2750scheduler. 2751.It Va net.inet.ip.dummynet.max_chain_len : No 16 2752Target value for the maximum number of pipes/queues in a hash bucket. 2753The product 2754.Cm max_chain_len*hash_size 2755is used to determine the threshold over which empty pipes/queues 2756will be expired even when 2757.Cm net.inet.ip.dummynet.expire=0 . 2758.It Va net.inet.ip.dummynet.red_lookup_depth : No 256 2759.It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512 2760.It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500 2761Parameters used in the computations of the drop probability 2762for the RED algorithm. 2763.It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576 2764.It Va net.inet.ip.dummynet.pipe_slot_limit : No 100 2765The maximum queue size that can be specified in bytes or packets. 2766These limits prevent accidental exhaustion of resources such as mbufs. 2767If you raise these limits, 2768you should make sure the system is configured so that sufficient resources 2769are available. 2770.It Va net.inet.ip.fw.autoinc_step : No 100 2771Delta between rule numbers when auto-generating them. 2772The value must be in the range 1..1000. 2773.It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets 2774The current number of buckets in the hash table for dynamic rules 2775(readonly). 2776.It Va net.inet.ip.fw.debug : No 1 2777Controls debugging messages produced by 2778.Nm . 2779.It Va net.inet.ip.fw.default_rule : No 65535 2780The default rule number (read-only). 2781By the design of 2782.Nm , the default rule is the last one, so its number 2783can also serve as the highest number allowed for a rule. 2784.It Va net.inet.ip.fw.dyn_buckets : No 256 2785The number of buckets in the hash table for dynamic rules. 2786Must be a power of 2, up to 65536. 2787It only takes effect when all dynamic rules have expired, so you 2788are advised to use a 2789.Cm flush 2790command to make sure that the hash table is resized. 2791.It Va net.inet.ip.fw.dyn_count : No 3 2792Current number of dynamic rules 2793(read-only). 2794.It Va net.inet.ip.fw.dyn_keepalive : No 1 2795Enables generation of keepalive packets for 2796.Cm keep-state 2797rules on TCP sessions. 2798A keepalive is generated to both 2799sides of the connection every 5 seconds for the last 20 2800seconds of the lifetime of the rule. 2801.It Va net.inet.ip.fw.dyn_max : No 8192 2802Maximum number of dynamic rules. 2803When you hit this limit, no more dynamic rules can be 2804installed until old ones expire. 2805.It Va net.inet.ip.fw.dyn_ack_lifetime : No 300 2806.It Va net.inet.ip.fw.dyn_syn_lifetime : No 20 2807.It Va net.inet.ip.fw.dyn_fin_lifetime : No 1 2808.It Va net.inet.ip.fw.dyn_rst_lifetime : No 1 2809.It Va net.inet.ip.fw.dyn_udp_lifetime : No 5 2810.It Va net.inet.ip.fw.dyn_short_lifetime : No 30 2811These variables control the lifetime, in seconds, of dynamic 2812rules. 2813Upon the initial SYN exchange the lifetime is kept short, 2814then increased after both SYN have been seen, then decreased 2815again during the final FIN exchange or when a RST is received. 2816Both 2817.Em dyn_fin_lifetime 2818and 2819.Em dyn_rst_lifetime 2820must be strictly lower than 5 seconds, the period of 2821repetition of keepalives. 2822The firewall enforces that. 2823.It Va net.inet.ip.fw.enable : No 1 2824Enables the firewall. 2825Setting this variable to 0 lets you run your machine without 2826firewall even if compiled in. 2827.It Va net.inet6.ip6.fw.enable : No 1 2828provides the same functionality as above for the IPv6 case. 2829.It Va net.inet.ip.fw.one_pass : No 1 2830When set, the packet exiting from the 2831.Nm dummynet 2832pipe or from 2833.Xr ng_ipfw 4 2834node is not passed though the firewall again. 2835Otherwise, after an action, the packet is 2836reinjected into the firewall at the next rule. 2837.It Va net.inet.ip.fw.tables_max : No 128 2838Maximum number of tables (read-only). 2839.It Va net.inet.ip.fw.verbose : No 1 2840Enables verbose messages. 2841.It Va net.inet.ip.fw.verbose_limit : No 0 2842Limits the number of messages produced by a verbose firewall. 2843.It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1 2844If enabled packets with unknown IPv6 Extension Headers will be denied. 2845.It Va net.link.ether.ipfw : No 0 2846Controls whether layer-2 packets are passed to 2847.Nm . 2848Default is no. 2849.It Va net.link.bridge.ipfw : No 0 2850Controls whether bridged packets are passed to 2851.Nm . 2852Default is no. 2853.El 2854.Pp 2855.Sh EXAMPLES 2856There are far too many possible uses of 2857.Nm 2858so this Section will only give a small set of examples. 2859.Pp 2860.Ss BASIC PACKET FILTERING 2861This command adds an entry which denies all tcp packets from 2862.Em cracker.evil.org 2863to the telnet port of 2864.Em wolf.tambov.su 2865from being forwarded by the host: 2866.Pp 2867.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet" 2868.Pp 2869This one disallows any connection from the entire cracker's 2870network to my host: 2871.Pp 2872.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org" 2873.Pp 2874A first and efficient way to limit access (not using dynamic rules) 2875is the use of the following rules: 2876.Pp 2877.Dl "ipfw add allow tcp from any to any established" 2878.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup" 2879.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup" 2880.Dl "..." 2881.Dl "ipfw add deny tcp from any to any" 2882.Pp 2883The first rule will be a quick match for normal TCP packets, 2884but it will not match the initial SYN packet, which will be 2885matched by the 2886.Cm setup 2887rules only for selected source/destination pairs. 2888All other SYN packets will be rejected by the final 2889.Cm deny 2890rule. 2891.Pp 2892If you administer one or more subnets, you can take advantage 2893of the address sets and or-blocks and write extremely 2894compact rulesets which selectively enable services to blocks 2895of clients, as below: 2896.Pp 2897.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q" 2898.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q" 2899.Dl "" 2900.Dl "ipfw add allow ip from ${goodguys} to any" 2901.Dl "ipfw add deny ip from ${badguys} to any" 2902.Dl "... normal policies ..." 2903.Pp 2904The 2905.Cm verrevpath 2906option could be used to do automated anti-spoofing by adding the 2907following to the top of a ruleset: 2908.Pp 2909.Dl "ipfw add deny ip from any to any not verrevpath in" 2910.Pp 2911This rule drops all incoming packets that appear to be coming to the 2912system on the wrong interface. 2913For example, a packet with a source 2914address belonging to a host on a protected internal network would be 2915dropped if it tried to enter the system from an external interface. 2916.Pp 2917The 2918.Cm antispoof 2919option could be used to do similar but more restricted anti-spoofing 2920by adding the following to the top of a ruleset: 2921.Pp 2922.Dl "ipfw add deny ip from any to any not antispoof in" 2923.Pp 2924This rule drops all incoming packets that appear to be coming from another 2925directly connected system but on the wrong interface. 2926For example, a packet with a source address of 2927.Li 192.168.0.0/24 , 2928configured on 2929.Li fxp0 , 2930but coming in on 2931.Li fxp1 2932would be dropped. 2933.Ss DYNAMIC RULES 2934In order to protect a site from flood attacks involving fake 2935TCP packets, it is safer to use dynamic rules: 2936.Pp 2937.Dl "ipfw add check-state" 2938.Dl "ipfw add deny tcp from any to any established" 2939.Dl "ipfw add allow tcp from my-net to any setup keep-state" 2940.Pp 2941This will let the firewall install dynamic rules only for 2942those connection which start with a regular SYN packet coming 2943from the inside of our network. 2944Dynamic rules are checked when encountering the first 2945.Cm check-state 2946or 2947.Cm keep-state 2948rule. 2949A 2950.Cm check-state 2951rule should usually be placed near the beginning of the 2952ruleset to minimize the amount of work scanning the ruleset. 2953Your mileage may vary. 2954.Pp 2955To limit the number of connections a user can open 2956you can use the following type of rules: 2957.Pp 2958.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10" 2959.Dl "ipfw add allow tcp from any to me setup limit src-addr 4" 2960.Pp 2961The former (assuming it runs on a gateway) will allow each host 2962on a /24 network to open at most 10 TCP connections. 2963The latter can be placed on a server to make sure that a single 2964client does not use more than 4 simultaneous connections. 2965.Pp 2966.Em BEWARE : 2967stateful rules can be subject to denial-of-service attacks 2968by a SYN-flood which opens a huge number of dynamic rules. 2969The effects of such attacks can be partially limited by 2970acting on a set of 2971.Xr sysctl 8 2972variables which control the operation of the firewall. 2973.Pp 2974Here is a good usage of the 2975.Cm list 2976command to see accounting records and timestamp information: 2977.Pp 2978.Dl ipfw -at list 2979.Pp 2980or in short form without timestamps: 2981.Pp 2982.Dl ipfw -a list 2983.Pp 2984which is equivalent to: 2985.Pp 2986.Dl ipfw show 2987.Pp 2988Next rule diverts all incoming packets from 192.168.2.0/24 2989to divert port 5000: 2990.Pp 2991.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in 2992.Pp 2993.Ss TRAFFIC SHAPING 2994The following rules show some of the applications of 2995.Nm 2996and 2997.Nm dummynet 2998for simulations and the like. 2999.Pp 3000This rule drops random incoming packets with a probability 3001of 5%: 3002.Pp 3003.Dl "ipfw add prob 0.05 deny ip from any to any in" 3004.Pp 3005A similar effect can be achieved making use of 3006.Nm dummynet 3007pipes: 3008.Pp 3009.Dl "ipfw add pipe 10 ip from any to any" 3010.Dl "ipfw pipe 10 config plr 0.05" 3011.Pp 3012We can use pipes to artificially limit bandwidth, e.g.\& on a 3013machine acting as a router, if we want to limit traffic from 3014local clients on 192.168.2.0/24 we do: 3015.Pp 3016.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 3017.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes" 3018.Pp 3019note that we use the 3020.Cm out 3021modifier so that the rule is not used twice. 3022Remember in fact that 3023.Nm 3024rules are checked both on incoming and outgoing packets. 3025.Pp 3026Should we want to simulate a bidirectional link with bandwidth 3027limitations, the correct way is the following: 3028.Pp 3029.Dl "ipfw add pipe 1 ip from any to any out" 3030.Dl "ipfw add pipe 2 ip from any to any in" 3031.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes" 3032.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes" 3033.Pp 3034The above can be very useful, e.g.\& if you want to see how 3035your fancy Web page will look for a residential user who 3036is connected only through a slow link. 3037You should not use only one pipe for both directions, unless 3038you want to simulate a half-duplex medium (e.g.\& AppleTalk, 3039Ethernet, IRDA). 3040It is not necessary that both pipes have the same configuration, 3041so we can also simulate asymmetric links. 3042.Pp 3043Should we want to verify network performance with the RED queue 3044management algorithm: 3045.Pp 3046.Dl "ipfw add pipe 1 ip from any to any" 3047.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1" 3048.Pp 3049Another typical application of the traffic shaper is to 3050introduce some delay in the communication. 3051This can significantly affect applications which do a lot of Remote 3052Procedure Calls, and where the round-trip-time of the 3053connection often becomes a limiting factor much more than 3054bandwidth: 3055.Pp 3056.Dl "ipfw add pipe 1 ip from any to any out" 3057.Dl "ipfw add pipe 2 ip from any to any in" 3058.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s" 3059.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s" 3060.Pp 3061Per-flow queueing can be useful for a variety of purposes. 3062A very simple one is counting traffic: 3063.Pp 3064.Dl "ipfw add pipe 1 tcp from any to any" 3065.Dl "ipfw add pipe 1 udp from any to any" 3066.Dl "ipfw add pipe 1 ip from any to any" 3067.Dl "ipfw pipe 1 config mask all" 3068.Pp 3069The above set of rules will create queues (and collect 3070statistics) for all traffic. 3071Because the pipes have no limitations, the only effect is 3072collecting statistics. 3073Note that we need 3 rules, not just the last one, because 3074when 3075.Nm 3076tries to match IP packets it will not consider ports, so we 3077would not see connections on separate ports as different 3078ones. 3079.Pp 3080A more sophisticated example is limiting the outbound traffic 3081on a net with per-host limits, rather than per-network limits: 3082.Pp 3083.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 3084.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in" 3085.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 3086.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 3087.Ss LOOKUP TABLES 3088In the following example, we need to create several traffic bandwidth 3089classes and we need different hosts/networks to fall into different classes. 3090We create one pipe for each class and configure them accordingly. 3091Then we create a single table and fill it with IP subnets and addresses. 3092For each subnet/host we set the argument equal to the number of the pipe 3093that it should use. 3094Then we classify traffic using a single rule: 3095.Pp 3096.Dl "ipfw pipe 1 config bw 1000Kbyte/s" 3097.Dl "ipfw pipe 4 config bw 4000Kbyte/s" 3098.Dl "..." 3099.Dl "ipfw table 1 add 192.168.2.0/24 1" 3100.Dl "ipfw table 1 add 192.168.0.0/27 4" 3101.Dl "ipfw table 1 add 192.168.0.2 1" 3102.Dl "..." 3103.Dl "ipfw add pipe tablearg ip from table(1) to any" 3104.Pp 3105Using the 3106.Cm fwd 3107action, the table entries may include hostnames and IP addresses. 3108.Pp 3109.Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1" 3110.Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz" 3111.Dl "..." 3112.Dl "ipfw add 100 fwd tablearg ip from any to table(1)" 3113.Ss SETS OF RULES 3114To add a set of rules atomically, e.g.\& set 18: 3115.Pp 3116.Dl "ipfw set disable 18" 3117.Dl "ipfw add NN set 18 ... # repeat as needed" 3118.Dl "ipfw set enable 18" 3119.Pp 3120To delete a set of rules atomically the command is simply: 3121.Pp 3122.Dl "ipfw delete set 18" 3123.Pp 3124To test a ruleset and disable it and regain control if something goes wrong: 3125.Pp 3126.Dl "ipfw set disable 18" 3127.Dl "ipfw add NN set 18 ... # repeat as needed" 3128.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18" 3129.Pp 3130Here if everything goes well, you press control-C before the "sleep" 3131terminates, and your ruleset will be left active. 3132Otherwise, e.g.\& if 3133you cannot access your box, the ruleset will be disabled after 3134the sleep terminates thus restoring the previous situation. 3135.Pp 3136To show rules of the specific set: 3137.Pp 3138.Dl "ipfw set 18 show" 3139.Pp 3140To show rules of the disabled set: 3141.Pp 3142.Dl "ipfw -S set 18 show" 3143.Pp 3144To clear a specific rule counters of the specific set: 3145.Pp 3146.Dl "ipfw set 18 zero NN" 3147.Pp 3148To delete a specific rule of the specific set: 3149.Pp 3150.Dl "ipfw set 18 delete NN" 3151.Ss NAT, REDIRECT AND LSNAT 3152First redirect all the traffic to nat instance 123: 3153.Pp 3154.Dl "ipfw add nat 123 all from any to any" 3155.Pp 3156Then to configure nat instance 123 to alias all the outgoing traffic with ip 3157192.168.0.123, blocking all incoming connections, trying to keep 3158same ports on both sides, clearing aliasing table on address change 3159and keeping a log of traffic/link statistics: 3160.Pp 3161.Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports" 3162.Pp 3163Or to change address of instance 123, aliasing table will be cleared (see 3164reset option): 3165.Pp 3166.Dl "ipfw nat 123 config ip 10.0.0.1" 3167.Pp 3168To see configuration of nat instance 123: 3169.Pp 3170.Dl "ipfw nat 123 show config" 3171.Pp 3172To show logs of all the instances in range 111-999: 3173.Pp 3174.Dl "ipfw nat 111-999 show" 3175.Pp 3176To see configurations of all instances: 3177.Pp 3178.Dl "ipfw nat show config" 3179.Pp 3180Or a redirect rule with mixed modes could looks like: 3181.Pp 3182.Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66" 3183.Dl " redirect_port tcp 192.168.0.1:80 500" 3184.Dl " redirect_proto udp 192.168.1.43 192.168.1.1" 3185.Dl " redirect_addr 192.168.0.10,192.168.0.11" 3186.Dl " 10.0.0.100 # LSNAT" 3187.Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22" 3188.Dl " 500 # LSNAT" 3189.Pp 3190or it could be split in: 3191.Pp 3192.Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66" 3193.Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500" 3194.Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1" 3195.Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12" 3196.Dl " 10.0.0.100" 3197.Dl "ipfw nat 5 config redirect_port tcp" 3198.Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500" 3199.Pp 3200.Sh SEE ALSO 3201.Xr cpp 1 , 3202.Xr m4 1 , 3203.Xr altq 4 , 3204.Xr divert 4 , 3205.Xr dummynet 4 , 3206.Xr if_bridge 4 , 3207.Xr ip 4 , 3208.Xr ipfirewall 4 , 3209.Xr ng_ipfw 4 , 3210.Xr protocols 5 , 3211.Xr services 5 , 3212.Xr init 8 , 3213.Xr kldload 8 , 3214.Xr reboot 8 , 3215.Xr sysctl 8 , 3216.Xr syslogd 8 3217.Sh HISTORY 3218The 3219.Nm 3220utility first appeared in 3221.Fx 2.0 . 3222.Nm dummynet 3223was introduced in 3224.Fx 2.2.8 . 3225Stateful extensions were introduced in 3226.Fx 4.0 . 3227.Nm ipfw2 3228was introduced in Summer 2002. 3229.Sh AUTHORS 3230.An Ugen J. S. Antsilevich , 3231.An Poul-Henning Kamp , 3232.An Alex Nash , 3233.An Archie Cobbs , 3234.An Luigi Rizzo . 3235.Pp 3236.An -nosplit 3237API based upon code written by 3238.An Daniel Boulet 3239for BSDI. 3240.Pp 3241Dummynet has been introduced by Luigi Rizzo in 1997-1998. 3242.Pp 3243Some early work (1999-2000) on the 3244.Nm dummynet 3245traffic shaper supported by Akamba Corp. 3246.Pp 3247The ipfw core (ipfw2) has been completely redesigned and 3248reimplemented by Luigi Rizzo in summer 2002. Further 3249actions and 3250options have been added by various developer over the years. 3251.Pp 3252.An -nosplit 3253In-kernel NAT support written by 3254.An Paolo Pisati Aq piso@FreeBSD.org 3255as part of a Summer of Code 2005 project. 3256.Pp 3257SCTP 3258.Nm nat 3259support has been developed by 3260.An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au . 3261The primary developers and maintainers are David Hayes and Jason But. 3262For further information visit: 3263.Aq http://www.caia.swin.edu.au/urp/SONATA 3264.Pp 3265Delay profiles have been developed by Alessandro Cerri and 3266Luigi Rizzo, supported by the 3267European Commission within Projects Onelab and Onelab2. 3268.Sh BUGS 3269The syntax has grown over the years and sometimes it might be confusing. 3270Unfortunately, backward compatibility prevents cleaning up mistakes 3271made in the definition of the syntax. 3272.Pp 3273.Em !!! WARNING !!! 3274.Pp 3275Misconfiguring the firewall can put your computer in an unusable state, 3276possibly shutting down network services and requiring console access to 3277regain control of it. 3278.Pp 3279Incoming packet fragments diverted by 3280.Cm divert 3281are reassembled before delivery to the socket. 3282The action used on those packet is the one from the 3283rule which matches the first fragment of the packet. 3284.Pp 3285Packets diverted to userland, and then reinserted by a userland process 3286may lose various packet attributes. 3287The packet source interface name 3288will be preserved if it is shorter than 8 bytes and the userland process 3289saves and reuses the sockaddr_in 3290(as does 3291.Xr natd 8 ) ; 3292otherwise, it may be lost. 3293If a packet is reinserted in this manner, later rules may be incorrectly 3294applied, making the order of 3295.Cm divert 3296rules in the rule sequence very important. 3297.Pp 3298Dummynet drops all packets with IPv6 link-local addresses. 3299.Pp 3300Rules using 3301.Cm uid 3302or 3303.Cm gid 3304may not behave as expected. 3305In particular, incoming SYN packets may 3306have no uid or gid associated with them since they do not yet belong 3307to a TCP connection, and the uid/gid associated with a packet may not 3308be as expected if the associated process calls 3309.Xr setuid 2 3310or similar system calls. 3311.Pp 3312Rule syntax is subject to the command line environment and some patterns 3313may need to be escaped with the backslash character 3314or quoted appropriately. 3315.Pp 3316Due to the architecture of 3317.Xr libalias 3 , 3318ipfw nat is not compatible with the TCP segmentation offloading (TSO). 3319Thus, to reliably nat your network traffic, please disable TSO 3320on your NICs using 3321.Xr ifconfig 8 . 3322.Pp 3323ICMP error messages are not implicitly matched by dynamic rules 3324for the respective conversations. 3325To avoid failures of network error detection and path MTU discovery, 3326ICMP error messages may need to be allowed explicitly through static 3327rules. 3328.Pp 3329Rules using 3330.Cm call 3331and 3332.Cm return 3333actions may lead to confusing behaviour if ruleset has mistakes, 3334and/or interaction with other subsystems (netgraph, dummynet, etc.) is used. 3335One possible case for this is packet leaving 3336.Nm 3337in subroutine on the input pass, while later on output encountering unpaired 3338.Cm return 3339first. 3340As the call stack is kept intact after input pass, packet will suddenly 3341return to the rule number used on input pass, not on output one. 3342Order of processing should be checked carefully to avoid such mistakes. 3343