1.\" 2.\" $FreeBSD$ 3.\" 4.Dd June 24, 2009 5.Dt IPFW 8 6.Os 7.Sh NAME 8.Nm ipfw 9.Nd IP firewall and traffic shaper control program 10.Sh SYNOPSIS 11.Nm 12.Op Fl cq 13.Cm add 14.Ar rule 15.Nm 16.Op Fl acdefnNStT 17.Op Cm set Ar N 18.Brq Cm list | show 19.Op Ar rule | first-last ... 20.Nm 21.Op Fl f | q 22.Op Cm set Ar N 23.Cm flush 24.Nm 25.Op Fl q 26.Op Cm set Ar N 27.Brq Cm delete | zero | resetlog 28.Op Ar number ... 29.Nm 30.Cm enable 31.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 32.Nm 33.Cm disable 34.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 35.Pp 36.Nm 37.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 38.Nm 39.Cm set move 40.Op Cm rule 41.Ar number Cm to Ar number 42.Nm 43.Cm set swap Ar number number 44.Nm 45.Cm set show 46.Pp 47.Nm 48.Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value 49.Nm 50.Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen 51.Nm 52.Cm table 53.Brq Ar number | all 54.Cm flush 55.Nm 56.Cm table 57.Brq Ar number | all 58.Cm list 59.Pp 60.Nm 61.Brq Cm pipe | queue 62.Ar number 63.Cm config 64.Ar config-options 65.Nm 66.Op Fl s Op Ar field 67.Brq Cm pipe | queue 68.Brq Cm delete | list | show 69.Op Ar number ... 70.Pp 71.Nm 72.Op Fl q 73.Cm nat 74.Ar number 75.Cm config 76.Ar config-options 77.Pp 78.Nm 79.Op Fl cfnNqS 80.Oo 81.Fl p Ar preproc 82.Oo 83.Ar preproc-flags 84.Oc 85.Oc 86.Ar pathname 87.Sh DESCRIPTION 88The 89.Nm 90utility is the user interface for controlling the 91.Xr ipfw 4 92firewall and the 93.Xr dummynet 4 94traffic shaper in 95.Fx . 96.Pp 97An 98.Nm 99configuration, or 100.Em ruleset , 101is made of a list of 102.Em rules 103numbered from 1 to 65535. 104Packets are passed to 105.Nm 106from a number of different places in the protocol stack 107(depending on the source and destination of the packet, 108it is possible that 109.Nm 110is invoked multiple times on the same packet). 111The packet passed to the firewall is compared 112against each of the rules in the firewall 113.Em ruleset . 114When a match is found, the action corresponding to the 115matching rule is performed. 116.Pp 117Depending on the action and certain system settings, packets 118can be reinjected into the firewall at some rule after the 119matching one for further processing. 120.Pp 121An 122.Nm 123ruleset always includes a 124.Em default 125rule (numbered 65535) which cannot be modified or deleted, 126and matches all packets. 127The action associated with the 128.Em default 129rule can be either 130.Cm deny 131or 132.Cm allow 133depending on how the kernel is configured. 134.Pp 135If the ruleset includes one or more rules with the 136.Cm keep-state 137or 138.Cm limit 139option, 140.Nm 141will have a 142.Em stateful 143behaviour, i.e., upon a match it will create dynamic rules matching 144the exact parameters (source and destination addresses and ports) 145of the matching packet. 146.Pp 147These dynamic rules, which have a limited lifetime, are checked 148at the first occurrence of a 149.Cm check-state , 150.Cm keep-state 151or 152.Cm limit 153rule, and are typically used to open the firewall on-demand to 154legitimate traffic only. 155See the 156.Sx STATEFUL FIREWALL 157and 158.Sx EXAMPLES 159Sections below for more information on the stateful behaviour of 160.Nm . 161.Pp 162All rules (including dynamic ones) have a few associated counters: 163a packet count, a byte count, a log count and a timestamp 164indicating the time of the last match. 165Counters can be displayed or reset with 166.Nm 167commands. 168.Pp 169Each rule belongs to one of 32 different 170.Em sets 171, and there are 172.Nm 173commands to atomically manipulate sets, such as enable, 174disable, swap sets, move all rules in a set to another 175one, delete all rules in a set. 176These can be useful to 177install temporary configurations, or to test them. 178See Section 179.Sx SETS OF RULES 180for more information on 181.Em sets . 182.Pp 183.Pp 184Rules can be added with the 185.Cm add 186command; deleted individually or in groups with the 187.Cm delete 188command, and globally (except those in set 31) with the 189.Cm flush 190command; displayed, optionally with the content of the 191counters, using the 192.Cm show 193and 194.Cm list 195commands. 196Finally, counters can be reset with the 197.Cm zero 198and 199.Cm resetlog 200commands. 201.Pp 202.Ss COMMAND OPTIONS 203The following general options are available when invoking 204.Nm : 205.Bl -tag -width indent 206.It Fl a 207Show counter values when listing rules. 208The 209.Cm show 210command implies this option. 211.It Fl b 212Only show the action and the comment, not the body of a rule. 213Implies 214.Fl c . 215.It Fl c 216When entering or showing rules, print them in compact form, 217i.e., omitting the "ip from any to any" string 218when this does not carry any additional information. 219.It Fl d 220When listing, show dynamic rules in addition to static ones. 221.It Fl e 222When listing and 223.Fl d 224is specified, also show expired dynamic rules. 225.It Fl f 226Do not ask for confirmation for commands that can cause problems 227if misused, 228.No i.e. Cm flush . 229If there is no tty associated with the process, this is implied. 230.It Fl i 231When listing a table (see the 232.Sx LOOKUP TABLES 233section below for more information on lookup tables), format values 234as IP addresses. By default, values are shown as integers. 235.It Fl n 236Only check syntax of the command strings, without actually passing 237them to the kernel. 238.It Fl N 239Try to resolve addresses and service names in output. 240.It Fl q 241Be quiet when executing the 242.Cm add , 243.Cm nat , 244.Cm zero , 245.Cm resetlog 246or 247.Cm flush 248commands; 249(implies 250.Fl f ) . 251This is useful when updating rulesets by executing multiple 252.Nm 253commands in a script 254(e.g., 255.Ql sh\ /etc/rc.firewall ) , 256or by processing a file with many 257.Nm 258rules across a remote login session. 259It also stops a table add or delete 260from failing if the entry already exists or is not present. 261.Pp 262The reason why this option may be important is that 263for some of these actions, 264.Nm 265may print a message; if the action results in blocking the 266traffic to the remote client, 267the remote login session will be closed 268and the rest of the ruleset will not be processed. 269Access to the console would then be required to recover. 270.It Fl S 271When listing rules, show the 272.Em set 273each rule belongs to. 274If this flag is not specified, disabled rules will not be 275listed. 276.It Fl s Op Ar field 277When listing pipes, sort according to one of the four 278counters (total or current packets or bytes). 279.It Fl t 280When listing, show last match timestamp converted with ctime(). 281.It Fl T 282When listing, show last match timestamp as seconds from the epoch. 283This form can be more convenient for postprocessing by scripts. 284.El 285.Pp 286To ease configuration, rules can be put into a file which is 287processed using 288.Nm 289as shown in the last synopsis line. 290An absolute 291.Ar pathname 292must be used. 293The file will be read line by line and applied as arguments to the 294.Nm 295utility. 296.Pp 297Optionally, a preprocessor can be specified using 298.Fl p Ar preproc 299where 300.Ar pathname 301is to be piped through. 302Useful preprocessors include 303.Xr cpp 1 304and 305.Xr m4 1 . 306If 307.Ar preproc 308does not start with a slash 309.Pq Ql / 310as its first character, the usual 311.Ev PATH 312name search is performed. 313Care should be taken with this in environments where not all 314file systems are mounted (yet) by the time 315.Nm 316is being run (e.g.\& when they are mounted over NFS). 317Once 318.Fl p 319has been specified, any additional arguments are passed on to the preprocessor 320for interpretation. 321This allows for flexible configuration files (like conditionalizing 322them on the local hostname) and the use of macros to centralize 323frequently required arguments like IP addresses. 324.Pp 325The 326.Nm 327.Cm pipe 328and 329.Cm queue 330commands are used to configure the traffic shaper, as shown in the 331.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 332Section below. 333.Pp 334If the world and the kernel get out of sync the 335.Nm 336ABI may break, preventing you from being able to add any rules. 337This can 338adversely effect the booting process. 339You can use 340.Nm 341.Cm disable 342.Cm firewall 343to temporarily disable the firewall to regain access to the network, 344allowing you to fix the problem. 345.Sh PACKET FLOW 346A packet is checked against the active ruleset in multiple places 347in the protocol stack, under control of several sysctl variables. 348These places and variables are shown below, and it is important to 349have this picture in mind in order to design a correct ruleset. 350.Bd -literal -offset indent 351 ^ to upper layers V 352 | | 353 +----------->-----------+ 354 ^ V 355 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1 356 | | 357 ^ V 358 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 359 | | 360 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1 361 ^ V 362 | to devices | 363.Ed 364.Pp 365As can be noted from the above picture, the number of 366times the same packet goes through the firewall can 367vary between 0 and 4 depending on packet source and 368destination, and system configuration. 369.Pp 370Note that as packets flow through the stack, headers can be 371stripped or added to it, and so they may or may not be available 372for inspection. 373E.g., incoming packets will include the MAC header when 374.Nm 375is invoked from 376.Cm ether_demux() , 377but the same packets will have the MAC header stripped off when 378.Nm 379is invoked from 380.Cm ip_input() 381or 382.Cm ip6_input() . 383.Pp 384Also note that each packet is always checked against the complete ruleset, 385irrespective of the place where the check occurs, or the source of the packet. 386If a rule contains some match patterns or actions which are not valid 387for the place of invocation (e.g.\& trying to match a MAC header within 388.Cm ip_input 389or 390.Cm ip6_input ), 391the match pattern will not match, but a 392.Cm not 393operator in front of such patterns 394.Em will 395cause the pattern to 396.Em always 397match on those packets. 398It is thus the responsibility of 399the programmer, if necessary, to write a suitable ruleset to 400differentiate among the possible places. 401.Cm skipto 402rules can be useful here, as an example: 403.Bd -literal -offset indent 404# packets from ether_demux or bdg_forward 405ipfw add 10 skipto 1000 all from any to any layer2 in 406# packets from ip_input 407ipfw add 10 skipto 2000 all from any to any not layer2 in 408# packets from ip_output 409ipfw add 10 skipto 3000 all from any to any not layer2 out 410# packets from ether_output_frame 411ipfw add 10 skipto 4000 all from any to any layer2 out 412.Ed 413.Pp 414(yes, at the moment there is no way to differentiate between 415ether_demux and bdg_forward). 416.Sh SYNTAX 417In general, each keyword or argument must be provided as 418a separate command line argument, with no leading or trailing 419spaces. 420Keywords are case-sensitive, whereas arguments may 421or may not be case-sensitive depending on their nature 422(e.g.\& uid's are, hostnames are not). 423.Pp 424In 425.Nm ipfw2 426you can introduce spaces after commas ',' to make 427the line more readable. 428You can also put the entire 429command (including flags) into a single argument. 430E.g., the following forms are equivalent: 431.Bd -literal -offset indent 432ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 433ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 434ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" 435.Ed 436.Sh RULE FORMAT 437The format of 438.Nm 439rules is the following: 440.Bd -ragged -offset indent 441.Bk -words 442.Op Ar rule_number 443.Op Cm set Ar set_number 444.Op Cm prob Ar match_probability 445.Ar action 446.Op Cm log Op Cm logamount Ar number 447.Op Cm altq Ar queue 448.Oo 449.Bro Cm tag | untag 450.Brc Ar number 451.Oc 452.Ar body 453.Ek 454.Ed 455.Pp 456where the body of the rule specifies which information is used 457for filtering packets, among the following: 458.Pp 459.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact 460.It Layer-2 header fields 461When available 462.It IPv4 and IPv6 Protocol 463TCP, UDP, ICMP, etc. 464.It Source and dest. addresses and ports 465.It Direction 466See Section 467.Sx PACKET FLOW 468.It Transmit and receive interface 469By name or address 470.It Misc. IP header fields 471Version, type of service, datagram length, identification, 472fragment flag (non-zero IP offset), 473Time To Live 474.It IP options 475.It IPv6 Extension headers 476Fragmentation, Hop-by-Hop options, 477Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options. 478.It IPv6 Flow-ID 479.It Misc. TCP header fields 480TCP flags (SYN, FIN, ACK, RST, etc.), 481sequence number, acknowledgment number, 482window 483.It TCP options 484.It ICMP types 485for ICMP packets 486.It ICMP6 types 487for ICMP6 packets 488.It User/group ID 489When the packet can be associated with a local socket. 490.It Divert status 491Whether a packet came from a divert socket (e.g., 492.Xr natd 8 ) . 493.It Fib annotation state 494Whether a packet has been tagged for using a specific FIB (routing table) 495in future forwarding decisions. 496.El 497.Pp 498Note that some of the above information, e.g.\& source MAC or IP addresses and 499TCP/UDP ports, could easily be spoofed, so filtering on those fields 500alone might not guarantee the desired results. 501.Bl -tag -width indent 502.It Ar rule_number 503Each rule is associated with a 504.Ar rule_number 505in the range 1..65535, with the latter reserved for the 506.Em default 507rule. 508Rules are checked sequentially by rule number. 509Multiple rules can have the same number, in which case they are 510checked (and listed) according to the order in which they have 511been added. 512If a rule is entered without specifying a number, the kernel will 513assign one in such a way that the rule becomes the last one 514before the 515.Em default 516rule. 517Automatic rule numbers are assigned by incrementing the last 518non-default rule number by the value of the sysctl variable 519.Ar net.inet.ip.fw.autoinc_step 520which defaults to 100. 521If this is not possible (e.g.\& because we would go beyond the 522maximum allowed rule number), the number of the last 523non-default value is used instead. 524.It Cm set Ar set_number 525Each rule is associated with a 526.Ar set_number 527in the range 0..31. 528Sets can be individually disabled and enabled, so this parameter 529is of fundamental importance for atomic ruleset manipulation. 530It can be also used to simplify deletion of groups of rules. 531If a rule is entered without specifying a set number, 532set 0 will be used. 533.br 534Set 31 is special in that it cannot be disabled, 535and rules in set 31 are not deleted by the 536.Nm ipfw flush 537command (but you can delete them with the 538.Nm ipfw delete set 31 539command). 540Set 31 is also used for the 541.Em default 542rule. 543.It Cm prob Ar match_probability 544A match is only declared with the specified probability 545(floating point number between 0 and 1). 546This can be useful for a number of applications such as 547random packet drop or 548(in conjunction with 549.Nm dummynet ) 550to simulate the effect of multiple paths leading to out-of-order 551packet delivery. 552.Pp 553Note: this condition is checked before any other condition, including 554ones such as keep-state or check-state which might have side effects. 555.It Cm log Op Cm logamount Ar number 556When a packet matches a rule with the 557.Cm log 558keyword, a message will be 559logged to 560.Xr syslogd 8 561with a 562.Dv LOG_SECURITY 563facility. 564The logging only occurs if the sysctl variable 565.Va net.inet.ip.fw.verbose 566is set to 1 567(which is the default when the kernel is compiled with 568.Dv IPFIREWALL_VERBOSE ) 569and the number of packets logged so far for that 570particular rule does not exceed the 571.Cm logamount 572parameter. 573If no 574.Cm logamount 575is specified, the limit is taken from the sysctl variable 576.Va net.inet.ip.fw.verbose_limit . 577In both cases, a value of 0 removes the logging limit. 578.Pp 579Once the limit is reached, logging can be re-enabled by 580clearing the logging counter or the packet counter for that entry, see the 581.Cm resetlog 582command. 583.Pp 584Note: logging is done after all other packet matching conditions 585have been successfully verified, and before performing the final 586action (accept, deny, etc.) on the packet. 587.It Cm tag Ar number 588When a packet matches a rule with the 589.Cm tag 590keyword, the numeric tag for the given 591.Ar number 592in the range 1..65534 will be attached to the packet. 593The tag acts as an internal marker (it is not sent out over 594the wire) that can be used to identify these packets later on. 595This can be used, for example, to provide trust between interfaces 596and to start doing policy-based filtering. 597A packet can have multiple tags at the same time. 598Tags are "sticky", meaning once a tag is applied to a packet by a 599matching rule it exists until explicit removal. 600Tags are kept with the packet everywhere within the kernel, but are 601lost when packet leaves the kernel, for example, on transmitting 602packet out to the network or sending packet to a 603.Xr divert 4 604socket. 605.Pp 606To check for previously applied tags, use the 607.Cm tagged 608rule option. 609To delete previously applied tag, use the 610.Cm untag 611keyword. 612.Pp 613Note: since tags are kept with the packet everywhere in kernelspace, 614they can be set and unset anywhere in the kernel network subsystem 615(using the 616.Xr mbuf_tags 9 617facility), not only by means of the 618.Xr ipfw 4 619.Cm tag 620and 621.Cm untag 622keywords. 623For example, there can be a specialized 624.Xr netgraph 4 625node doing traffic analyzing and tagging for later inspecting 626in firewall. 627.It Cm untag Ar number 628When a packet matches a rule with the 629.Cm untag 630keyword, the tag with the number 631.Ar number 632is searched among the tags attached to this packet and, 633if found, removed from it. 634Other tags bound to packet, if present, are left untouched. 635.It Cm altq Ar queue 636When a packet matches a rule with the 637.Cm altq 638keyword, the ALTQ identifier for the given 639.Ar queue 640(see 641.Xr altq 4 ) 642will be attached. 643Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, 644and not being rejected or going to divert sockets. 645Note that if there is insufficient memory at the time the packet is 646processed, it will not be tagged, so it is wise to make your ALTQ 647"default" queue policy account for this. 648If multiple 649.Cm altq 650rules match a single packet, only the first one adds the ALTQ classification 651tag. 652In doing so, traffic may be shaped by using 653.Cm count Cm altq Ar queue 654rules for classification early in the ruleset, then later applying 655the filtering decision. 656For example, 657.Cm check-state 658and 659.Cm keep-state 660rules may come later and provide the actual filtering decisions in 661addition to the fallback ALTQ tag. 662.Pp 663You must run 664.Xr pfctl 8 665to set up the queues before IPFW will be able to look them up by name, 666and if the ALTQ disciplines are rearranged, the rules in containing the 667queue identifiers in the kernel will likely have gone stale and need 668to be reloaded. 669Stale queue identifiers will probably result in misclassification. 670.Pp 671All system ALTQ processing can be turned on or off via 672.Nm 673.Cm enable Ar altq 674and 675.Nm 676.Cm disable Ar altq . 677The usage of 678.Va net.inet.ip.fw.one_pass 679is irrelevant to ALTQ traffic shaping, as the actual rule action is followed 680always after adding an ALTQ tag. 681.El 682.Ss RULE ACTIONS 683A rule can be associated with one of the following actions, which 684will be executed when the packet matches the body of the rule. 685.Bl -tag -width indent 686.It Cm allow | accept | pass | permit 687Allow packets that match rule. 688The search terminates. 689.It Cm check-state 690Checks the packet against the dynamic ruleset. 691If a match is found, execute the action associated with 692the rule which generated this dynamic rule, otherwise 693move to the next rule. 694.br 695.Cm Check-state 696rules do not have a body. 697If no 698.Cm check-state 699rule is found, the dynamic ruleset is checked at the first 700.Cm keep-state 701or 702.Cm limit 703rule. 704.It Cm count 705Update counters for all packets that match rule. 706The search continues with the next rule. 707.It Cm deny | drop 708Discard packets that match this rule. 709The search terminates. 710.It Cm divert Ar port 711Divert packets that match this rule to the 712.Xr divert 4 713socket bound to port 714.Ar port . 715The search terminates. 716.It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port 717Change the next-hop on matching packets to 718.Ar ipaddr , 719which can be an IP address or a host name. 720The next hop can also be supplied by the last table 721looked up for the packet by using the 722.Cm tablearg 723keyword instead of an explicit address. 724The search terminates if this rule matches. 725.Pp 726If 727.Ar ipaddr 728is a local address, then matching packets will be forwarded to 729.Ar port 730(or the port number in the packet if one is not specified in the rule) 731on the local machine. 732.br 733If 734.Ar ipaddr 735is not a local address, then the port number 736(if specified) is ignored, and the packet will be 737forwarded to the remote address, using the route as found in 738the local routing table for that IP. 739.br 740A 741.Ar fwd 742rule will not match layer-2 packets (those received 743on ether_input, ether_output, or bridged). 744.br 745The 746.Cm fwd 747action does not change the contents of the packet at all. 748In particular, the destination address remains unmodified, so 749packets forwarded to another system will usually be rejected by that system 750unless there is a matching rule on that system to capture them. 751For packets forwarded locally, 752the local address of the socket will be 753set to the original destination address of the packet. 754This makes the 755.Xr netstat 1 756entry look rather weird but is intended for 757use with transparent proxy servers. 758.Pp 759To enable 760.Cm fwd 761a custom kernel needs to be compiled with the option 762.Cd "options IPFIREWALL_FORWARD" . 763.It Cm nat Ar nat_nr 764Pass packet to a 765nat instance 766(for network address translation, address redirect, etc.): 767see the 768.Sx NETWORK ADDRESS TRANSLATION (NAT) 769Section for further information. 770.It Cm pipe Ar pipe_nr 771Pass packet to a 772.Nm dummynet 773.Dq pipe 774(for bandwidth limitation, delay, etc.). 775See the 776.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 777Section for further information. 778The search terminates; however, on exit from the pipe and if 779the 780.Xr sysctl 8 781variable 782.Va net.inet.ip.fw.one_pass 783is not set, the packet is passed again to the firewall code 784starting from the next rule. 785.It Cm queue Ar queue_nr 786Pass packet to a 787.Nm dummynet 788.Dq queue 789(for bandwidth limitation using WF2Q+). 790.It Cm reject 791(Deprecated). 792Synonym for 793.Cm unreach host . 794.It Cm reset 795Discard packets that match this rule, and if the 796packet is a TCP packet, try to send a TCP reset (RST) notice. 797The search terminates. 798.It Cm reset6 799Discard packets that match this rule, and if the 800packet is a TCP packet, try to send a TCP reset (RST) notice. 801The search terminates. 802.It Cm skipto Ar number | tablearg 803Skip all subsequent rules numbered less than 804.Ar number . 805The search continues with the first rule numbered 806.Ar number 807or higher. 808It is possible to use the 809.Cm tablearg 810keyword with a skipto for a 811.Em computed 812skipto, but care should be used, as no destination caching 813is possible in this case so the rules are always walked to find it, 814starting from the 815.Cm skipto . 816.It Cm tee Ar port 817Send a copy of packets matching this rule to the 818.Xr divert 4 819socket bound to port 820.Ar port . 821The search continues with the next rule. 822.It Cm unreach Ar code 823Discard packets that match this rule, and try to send an ICMP 824unreachable notice with code 825.Ar code , 826where 827.Ar code 828is a number from 0 to 255, or one of these aliases: 829.Cm net , host , protocol , port , 830.Cm needfrag , srcfail , net-unknown , host-unknown , 831.Cm isolated , net-prohib , host-prohib , tosnet , 832.Cm toshost , filter-prohib , host-precedence 833or 834.Cm precedence-cutoff . 835The search terminates. 836.It Cm unreach6 Ar code 837Discard packets that match this rule, and try to send an ICMPv6 838unreachable notice with code 839.Ar code , 840where 841.Ar code 842is a number from 0, 1, 3 or 4, or one of these aliases: 843.Cm no-route, admin-prohib, address 844or 845.Cm port . 846The search terminates. 847.It Cm netgraph Ar cookie 848Divert packet into netgraph with given 849.Ar cookie . 850The search terminates. 851If packet is later returned from netgraph it is either 852accepted or continues with the next rule, depending on 853.Va net.inet.ip.fw.one_pass 854sysctl variable. 855.It Cm ngtee Ar cookie 856A copy of packet is diverted into netgraph, original 857packet is either accepted or continues with the next rule, depending on 858.Va net.inet.ip.fw.one_pass 859sysctl variable. 860See 861.Xr ng_ipfw 4 862for more information on 863.Cm netgraph 864and 865.Cm ngtee 866actions. 867.It Cm setfib Ar fibnum 868The packet is tagged so as to use the FIB (routing table) 869.Ar fibnum 870in any subsequent forwarding decisions. 871Initially this is limited to the values 0 through 15, see 872.Xr setfib 1 . 873Processing continues at the next rule. 874.It Cm reass 875Queue and reassemble ip fragments. 876If the packet is not fragmented, counters are updated and processing continues with the next rule. 877If the packet is the last logical fragment, the packet is reassembled and, if 878.Va net.inet.ip.fw.one_pass 879is set to 0, processing continues with the next rule, else packet is allowed to pass and search terminates. 880If the packet is a fragment in the middle, it is consumed and processing stops immediately. 881.Pp 882Fragments handling can be tuned via 883.Va net.inet.ip.maxfragpackets 884and 885.Va net.inet.ip.maxfragsperpacket 886which limit, respectively, the maximum number of processable fragments (default: 800) and 887the maximum number of fragments per packet (default: 16). 888.Pp 889NOTA BENE: since fragments do not contain port numbers, they should be avoided with the 890.Nm reass 891rule. 892Alternatively, direction-based (like 893.Nm in 894/ 895.Nm out 896) and source-based (like 897.Nm via 898) match patterns can be used to select fragments. 899.Pp 900Usually a simple rule like: 901.Bd -literal -offset indent 902# reassemble incoming fragments 903ipfw add reass all from any to any in 904.Ed 905.Pp 906is all you need at the beginning of your ruleset. 907.El 908.Ss RULE BODY 909The body of a rule contains zero or more patterns (such as 910specific source and destination addresses or ports, 911protocol options, incoming or outgoing interfaces, etc.) 912that the packet must match in order to be recognised. 913In general, the patterns are connected by (implicit) 914.Cm and 915operators -- i.e., all must match in order for the 916rule to match. 917Individual patterns can be prefixed by the 918.Cm not 919operator to reverse the result of the match, as in 920.Pp 921.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any" 922.Pp 923Additionally, sets of alternative match patterns 924.Pq Em or-blocks 925can be constructed by putting the patterns in 926lists enclosed between parentheses ( ) or braces { }, and 927using the 928.Cm or 929operator as follows: 930.Pp 931.Dl "ipfw add 100 allow ip from { x or not y or z } to any" 932.Pp 933Only one level of parentheses is allowed. 934Beware that most shells have special meanings for parentheses 935or braces, so it is advisable to put a backslash \\ in front of them 936to prevent such interpretations. 937.Pp 938The body of a rule must in general include a source and destination 939address specifier. 940The keyword 941.Ar any 942can be used in various places to specify that the content of 943a required field is irrelevant. 944.Pp 945The rule body has the following format: 946.Bd -ragged -offset indent 947.Op Ar proto Cm from Ar src Cm to Ar dst 948.Op Ar options 949.Ed 950.Pp 951The first part (proto from src to dst) is for backward 952compatibility with earlier versions of 953.Fx . 954In modern 955.Fx 956any match pattern (including MAC headers, IP protocols, 957addresses and ports) can be specified in the 958.Ar options 959section. 960.Pp 961Rule fields have the following meaning: 962.Bl -tag -width indent 963.It Ar proto : protocol | Cm { Ar protocol Cm or ... } 964.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number 965An IP protocol specified by number or name 966(for a complete list see 967.Pa /etc/protocols ) , 968or one of the following keywords: 969.Bl -tag -width indent 970.It Cm ip4 | ipv4 971Matches IPv4 packets. 972.It Cm ip6 | ipv6 973Matches IPv6 packets. 974.It Cm ip | all 975Matches any packet. 976.El 977.Pp 978The 979.Cm ipv6 980in 981.Cm proto 982option will be treated as inner protocol. 983And, the 984.Cm ipv4 985is not available in 986.Cm proto 987option. 988.Pp 989The 990.Cm { Ar protocol Cm or ... } 991format (an 992.Em or-block ) 993is provided for convenience only but its use is deprecated. 994.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports 995An address (or a list, see below) 996optionally followed by 997.Ar ports 998specifiers. 999.Pp 1000The second format 1001.Em ( or-block 1002with multiple addresses) is provided for convenience only and 1003its use is discouraged. 1004.It Ar addr : Oo Cm not Oc Bro 1005.Bl -tag -width indent 1006.Cm any | me | me6 | 1007.Cm table Ns Pq Ar number Ns Op , Ns Ar value 1008.Ar | addr-list | addr-set 1009.Brc 1010.It Cm any 1011matches any IP address. 1012.It Cm me 1013matches any IP address configured on an interface in the system. 1014.It Cm me6 1015matches any IPv6 address configured on an interface in the system. 1016The address list is evaluated at the time the packet is 1017analysed. 1018.It Cm table Ns Pq Ar number Ns Op , Ns Ar value 1019Matches any IPv4 address for which an entry exists in the lookup table 1020.Ar number . 1021If an optional 32-bit unsigned 1022.Ar value 1023is also specified, an entry will match only if it has this value. 1024See the 1025.Sx LOOKUP TABLES 1026section below for more information on lookup tables. 1027.El 1028.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list 1029.It Ar ip-addr : 1030A host or subnet address specified in one of the following ways: 1031.Bl -tag -width indent 1032.It Ar numeric-ip | hostname 1033Matches a single IPv4 address, specified as dotted-quad or a hostname. 1034Hostnames are resolved at the time the rule is added to the firewall list. 1035.It Ar addr Ns / Ns Ar masklen 1036Matches all addresses with base 1037.Ar addr 1038(specified as an IP address, a network number, or a hostname) 1039and mask width of 1040.Cm masklen 1041bits. 1042As an example, 1.2.3.4/25 or 1.2.3.0/25 will match 1043all IP numbers from 1.2.3.0 to 1.2.3.127 . 1044.It Ar addr Ns : Ns Ar mask 1045Matches all addresses with base 1046.Ar addr 1047(specified as an IP address, a network number, or a hostname) 1048and the mask of 1049.Ar mask , 1050specified as a dotted quad. 1051As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 10521.*.3.*. 1053This form is advised only for non-contiguous 1054masks. 1055It is better to resort to the 1056.Ar addr Ns / Ns Ar masklen 1057format for contiguous masks, which is more compact and less 1058error-prone. 1059.El 1060.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm } 1061.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list 1062Matches all addresses with base address 1063.Ar addr 1064(specified as an IP address, a network number, or a hostname) 1065and whose last byte is in the list between braces { } . 1066Note that there must be no spaces between braces and 1067numbers (spaces after commas are allowed). 1068Elements of the list can be specified as single entries 1069or ranges. 1070The 1071.Ar masklen 1072field is used to limit the size of the set of addresses, 1073and can have any value between 24 and 32. 1074If not specified, 1075it will be assumed as 24. 1076.br 1077This format is particularly useful to handle sparse address sets 1078within a single rule. 1079Because the matching occurs using a 1080bitmask, it takes constant time and dramatically reduces 1081the complexity of rulesets. 1082.br 1083As an example, an address specified as 1.2.3.4/24{128,35-55,89} 1084or 1.2.3.0/24{128,35-55,89} 1085will match the following IP addresses: 1086.br 10871.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . 1088.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list 1089.It Ar ip6-addr : 1090A host or subnet specified one of the following ways: 1091.Pp 1092.Bl -tag -width indent 1093.It Ar numeric-ip | hostname 1094Matches a single IPv6 address as allowed by 1095.Xr inet_pton 3 1096or a hostname. 1097Hostnames are resolved at the time the rule is added to the firewall 1098list. 1099.It Ar addr Ns / Ns Ar masklen 1100Matches all IPv6 addresses with base 1101.Ar addr 1102(specified as allowed by 1103.Xr inet_pton 1104or a hostname) 1105and mask width of 1106.Cm masklen 1107bits. 1108.El 1109.Pp 1110No support for sets of IPv6 addresses is provided because IPv6 addresses 1111are typically random past the initial prefix. 1112.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports 1113For protocols which support port numbers (such as TCP and UDP), optional 1114.Cm ports 1115may be specified as one or more ports or port ranges, separated 1116by commas but no spaces, and an optional 1117.Cm not 1118operator. 1119The 1120.Ql \&- 1121notation specifies a range of ports (including boundaries). 1122.Pp 1123Service names (from 1124.Pa /etc/services ) 1125may be used instead of numeric port values. 1126The length of the port list is limited to 30 ports or ranges, 1127though one can specify larger ranges by using an 1128.Em or-block 1129in the 1130.Cm options 1131section of the rule. 1132.Pp 1133A backslash 1134.Pq Ql \e 1135can be used to escape the dash 1136.Pq Ql - 1137character in a service name (from a shell, the backslash must be 1138typed twice to avoid the shell itself interpreting it as an escape 1139character). 1140.Pp 1141.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any" 1142.Pp 1143Fragmented packets which have a non-zero offset (i.e., not the first 1144fragment) will never match a rule which has one or more port 1145specifications. 1146See the 1147.Cm frag 1148option for details on matching fragmented packets. 1149.El 1150.Ss RULE OPTIONS (MATCH PATTERNS) 1151Additional match patterns can be used within 1152rules. 1153Zero or more of these so-called 1154.Em options 1155can be present in a rule, optionally prefixed by the 1156.Cm not 1157operand, and possibly grouped into 1158.Em or-blocks . 1159.Pp 1160The following match patterns can be used (listed in alphabetical order): 1161.Bl -tag -width indent 1162.It Cm // this is a comment. 1163Inserts the specified text as a comment in the rule. 1164Everything following // is considered as a comment and stored in the rule. 1165You can have comment-only rules, which are listed as having a 1166.Cm count 1167action followed by the comment. 1168.It Cm bridged 1169Alias for 1170.Cm layer2 . 1171.It Cm diverted 1172Matches only packets generated by a divert socket. 1173.It Cm diverted-loopback 1174Matches only packets coming from a divert socket back into the IP stack 1175input for delivery. 1176.It Cm diverted-output 1177Matches only packets going from a divert socket back outward to the IP 1178stack output for delivery. 1179.It Cm dst-ip Ar ip-address 1180Matches IPv4 packets whose destination IP is one of the address(es) 1181specified as argument. 1182.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address 1183Matches IPv6 packets whose destination IP is one of the address(es) 1184specified as argument. 1185.It Cm dst-port Ar ports 1186Matches IP packets whose destination port is one of the port(s) 1187specified as argument. 1188.It Cm established 1189Matches TCP packets that have the RST or ACK bits set. 1190.It Cm ext6hdr Ar header 1191Matches IPv6 packets containing the extended header given by 1192.Ar header . 1193Supported headers are: 1194.Pp 1195Fragment, 1196.Pq Cm frag , 1197Hop-to-hop options 1198.Pq Cm hopopt , 1199any type of Routing Header 1200.Pq Cm route , 1201Source routing Routing Header Type 0 1202.Pq Cm rthdr0 , 1203Mobile IPv6 Routing Header Type 2 1204.Pq Cm rthdr2 , 1205Destination options 1206.Pq Cm dstopt , 1207IPSec authentication headers 1208.Pq Cm ah , 1209and IPsec encapsulated security payload headers 1210.Pq Cm esp . 1211.It Cm fib Ar fibnum 1212Matches a packet that has been tagged to use 1213the given FIB (routing table) number. 1214.It Cm flow-id Ar labels 1215Matches IPv6 packets containing any of the flow labels given in 1216.Ar labels . 1217.Ar labels 1218is a comma separated list of numeric flow labels. 1219.It Cm frag 1220Matches packets that are fragments and not the first 1221fragment of an IP datagram. 1222Note that these packets will not have 1223the next protocol header (e.g.\& TCP, UDP) so options that look into 1224these headers cannot match. 1225.It Cm gid Ar group 1226Matches all TCP or UDP packets sent by or received for a 1227.Ar group . 1228A 1229.Ar group 1230may be specified by name or number. 1231.It Cm jail Ar prisonID 1232Matches all TCP or UDP packets sent by or received for the 1233jail whos prison ID is 1234.Ar prisonID . 1235.It Cm icmptypes Ar types 1236Matches ICMP packets whose ICMP type is in the list 1237.Ar types . 1238The list may be specified as any combination of 1239individual types (numeric) separated by commas. 1240.Em Ranges are not allowed . 1241The supported ICMP types are: 1242.Pp 1243echo reply 1244.Pq Cm 0 , 1245destination unreachable 1246.Pq Cm 3 , 1247source quench 1248.Pq Cm 4 , 1249redirect 1250.Pq Cm 5 , 1251echo request 1252.Pq Cm 8 , 1253router advertisement 1254.Pq Cm 9 , 1255router solicitation 1256.Pq Cm 10 , 1257time-to-live exceeded 1258.Pq Cm 11 , 1259IP header bad 1260.Pq Cm 12 , 1261timestamp request 1262.Pq Cm 13 , 1263timestamp reply 1264.Pq Cm 14 , 1265information request 1266.Pq Cm 15 , 1267information reply 1268.Pq Cm 16 , 1269address mask request 1270.Pq Cm 17 1271and address mask reply 1272.Pq Cm 18 . 1273.It Cm icmp6types Ar types 1274Matches ICMP6 packets whose ICMP6 type is in the list of 1275.Ar types . 1276The list may be specified as any combination of 1277individual types (numeric) separated by commas. 1278.Em Ranges are not allowed . 1279.It Cm in | out 1280Matches incoming or outgoing packets, respectively. 1281.Cm in 1282and 1283.Cm out 1284are mutually exclusive (in fact, 1285.Cm out 1286is implemented as 1287.Cm not in Ns No ). 1288.It Cm ipid Ar id-list 1289Matches IPv4 packets whose 1290.Cm ip_id 1291field has value included in 1292.Ar id-list , 1293which is either a single value or a list of values or ranges 1294specified in the same way as 1295.Ar ports . 1296.It Cm iplen Ar len-list 1297Matches IP packets whose total length, including header and data, is 1298in the set 1299.Ar len-list , 1300which is either a single value or a list of values or ranges 1301specified in the same way as 1302.Ar ports . 1303.It Cm ipoptions Ar spec 1304Matches packets whose IPv4 header contains the comma separated list of 1305options specified in 1306.Ar spec . 1307The supported IP options are: 1308.Pp 1309.Cm ssrr 1310(strict source route), 1311.Cm lsrr 1312(loose source route), 1313.Cm rr 1314(record packet route) and 1315.Cm ts 1316(timestamp). 1317The absence of a particular option may be denoted 1318with a 1319.Ql \&! . 1320.It Cm ipprecedence Ar precedence 1321Matches IPv4 packets whose precedence field is equal to 1322.Ar precedence . 1323.It Cm ipsec 1324Matches packets that have IPSEC history associated with them 1325(i.e., the packet comes encapsulated in IPSEC, the kernel 1326has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly 1327decapsulate it). 1328.Pp 1329Note that specifying 1330.Cm ipsec 1331is different from specifying 1332.Cm proto Ar ipsec 1333as the latter will only look at the specific IP protocol field, 1334irrespective of IPSEC kernel support and the validity of the IPSEC data. 1335.Pp 1336Further note that this flag is silently ignored in kernels without 1337IPSEC support. 1338It does not affect rule processing when given and the 1339rules are handled as if with no 1340.Cm ipsec 1341flag. 1342.It Cm iptos Ar spec 1343Matches IPv4 packets whose 1344.Cm tos 1345field contains the comma separated list of 1346service types specified in 1347.Ar spec . 1348The supported IP types of service are: 1349.Pp 1350.Cm lowdelay 1351.Pq Dv IPTOS_LOWDELAY , 1352.Cm throughput 1353.Pq Dv IPTOS_THROUGHPUT , 1354.Cm reliability 1355.Pq Dv IPTOS_RELIABILITY , 1356.Cm mincost 1357.Pq Dv IPTOS_MINCOST , 1358.Cm congestion 1359.Pq Dv IPTOS_ECN_CE . 1360The absence of a particular type may be denoted 1361with a 1362.Ql \&! . 1363.It Cm ipttl Ar ttl-list 1364Matches IPv4 packets whose time to live is included in 1365.Ar ttl-list , 1366which is either a single value or a list of values or ranges 1367specified in the same way as 1368.Ar ports . 1369.It Cm ipversion Ar ver 1370Matches IP packets whose IP version field is 1371.Ar ver . 1372.It Cm keep-state 1373Upon a match, the firewall will create a dynamic rule, whose 1374default behaviour is to match bidirectional traffic between 1375source and destination IP/port using the same protocol. 1376The rule has a limited lifetime (controlled by a set of 1377.Xr sysctl 8 1378variables), and the lifetime is refreshed every time a matching 1379packet is found. 1380.It Cm layer2 1381Matches only layer2 packets, i.e., those passed to 1382.Nm 1383from ether_demux() and ether_output_frame(). 1384.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N 1385The firewall will only allow 1386.Ar N 1387connections with the same 1388set of parameters as specified in the rule. 1389One or more 1390of source and destination addresses and ports can be 1391specified. 1392Currently, 1393only IPv4 flows are supported. 1394.It Cm lookup Bro Cm dst-ip | dst-port | src-ip | src-port | uid | jail Brc Ar N 1395Search an entry in lookup table 1396.Ar N 1397that matches the field specified as argument. 1398If not found, the match fails. 1399Otherwise, the match succeeds and 1400.Cm tablearg 1401is set to the value extracted from the table. 1402.Br 1403This option can be useful to quickly dispatch traffic based on 1404certain packet fields. 1405See the 1406.Sx LOOKUP TABLES 1407section below for more information on lookup tables. 1408.It Cm { MAC | mac } Ar dst-mac src-mac 1409Match packets with a given 1410.Ar dst-mac 1411and 1412.Ar src-mac 1413addresses, specified as the 1414.Cm any 1415keyword (matching any MAC address), or six groups of hex digits 1416separated by colons, 1417and optionally followed by a mask indicating the significant bits. 1418The mask may be specified using either of the following methods: 1419.Bl -enum -width indent 1420.It 1421A slash 1422.Pq / 1423followed by the number of significant bits. 1424For example, an address with 33 significant bits could be specified as: 1425.Pp 1426.Dl "MAC 10:20:30:40:50:60/33 any" 1427.Pp 1428.It 1429An ampersand 1430.Pq & 1431followed by a bitmask specified as six groups of hex digits separated 1432by colons. 1433For example, an address in which the last 16 bits are significant could 1434be specified as: 1435.Pp 1436.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any" 1437.Pp 1438Note that the ampersand character has a special meaning in many shells 1439and should generally be escaped. 1440.Pp 1441.El 1442Note that the order of MAC addresses (destination first, 1443source second) is 1444the same as on the wire, but the opposite of the one used for 1445IP addresses. 1446.It Cm mac-type Ar mac-type 1447Matches packets whose Ethernet Type field 1448corresponds to one of those specified as argument. 1449.Ar mac-type 1450is specified in the same way as 1451.Cm port numbers 1452(i.e., one or more comma-separated single values or ranges). 1453You can use symbolic names for known values such as 1454.Em vlan , ipv4, ipv6 . 1455Values can be entered as decimal or hexadecimal (if prefixed by 0x), 1456and they are always printed as hexadecimal (unless the 1457.Cm -N 1458option is used, in which case symbolic resolution will be attempted). 1459.It Cm proto Ar protocol 1460Matches packets with the corresponding IP protocol. 1461.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any 1462Matches packets received, transmitted or going through, 1463respectively, the interface specified by exact name 1464.Ns No ( Ar ifX Ns No ), 1465by device name 1466.Ns No ( Ar if Ns Ar * Ns No ), 1467by IP address, or through some interface. 1468.Pp 1469The 1470.Cm via 1471keyword causes the interface to always be checked. 1472If 1473.Cm recv 1474or 1475.Cm xmit 1476is used instead of 1477.Cm via , 1478then only the receive or transmit interface (respectively) 1479is checked. 1480By specifying both, it is possible to match packets based on 1481both receive and transmit interface, e.g.: 1482.Pp 1483.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1" 1484.Pp 1485The 1486.Cm recv 1487interface can be tested on either incoming or outgoing packets, 1488while the 1489.Cm xmit 1490interface can only be tested on outgoing packets. 1491So 1492.Cm out 1493is required (and 1494.Cm in 1495is invalid) whenever 1496.Cm xmit 1497is used. 1498.Pp 1499A packet may not have a receive or transmit interface: packets 1500originating from the local host have no receive interface, 1501while packets destined for the local host have no transmit 1502interface. 1503.It Cm setup 1504Matches TCP packets that have the SYN bit set but no ACK bit. 1505This is the short form of 1506.Dq Li tcpflags\ syn,!ack . 1507.It Cm src-ip Ar ip-address 1508Matches IPv4 packets whose source IP is one of the address(es) 1509specified as an argument. 1510.It Cm src-ip6 Ar ip6-address 1511Matches IPv6 packets whose source IP is one of the address(es) 1512specified as an argument. 1513.It Cm src-port Ar ports 1514Matches IP packets whose source port is one of the port(s) 1515specified as argument. 1516.It Cm tagged Ar tag-list 1517Matches packets whose tags are included in 1518.Ar tag-list , 1519which is either a single value or a list of values or ranges 1520specified in the same way as 1521.Ar ports . 1522Tags can be applied to the packet using 1523.Cm tag 1524rule action parameter (see it's description for details on tags). 1525.It Cm tcpack Ar ack 1526TCP packets only. 1527Match if the TCP header acknowledgment number field is set to 1528.Ar ack . 1529.It Cm tcpdatalen Ar tcpdatalen-list 1530Matches TCP packets whose length of TCP data is 1531.Ar tcpdatalen-list , 1532which is either a single value or a list of values or ranges 1533specified in the same way as 1534.Ar ports . 1535.It Cm tcpflags Ar spec 1536TCP packets only. 1537Match if the TCP header contains the comma separated list of 1538flags specified in 1539.Ar spec . 1540The supported TCP flags are: 1541.Pp 1542.Cm fin , 1543.Cm syn , 1544.Cm rst , 1545.Cm psh , 1546.Cm ack 1547and 1548.Cm urg . 1549The absence of a particular flag may be denoted 1550with a 1551.Ql \&! . 1552A rule which contains a 1553.Cm tcpflags 1554specification can never match a fragmented packet which has 1555a non-zero offset. 1556See the 1557.Cm frag 1558option for details on matching fragmented packets. 1559.It Cm tcpseq Ar seq 1560TCP packets only. 1561Match if the TCP header sequence number field is set to 1562.Ar seq . 1563.It Cm tcpwin Ar win 1564TCP packets only. 1565Match if the TCP header window field is set to 1566.Ar win . 1567.It Cm tcpoptions Ar spec 1568TCP packets only. 1569Match if the TCP header contains the comma separated list of 1570options specified in 1571.Ar spec . 1572The supported TCP options are: 1573.Pp 1574.Cm mss 1575(maximum segment size), 1576.Cm window 1577(tcp window advertisement), 1578.Cm sack 1579(selective ack), 1580.Cm ts 1581(rfc1323 timestamp) and 1582.Cm cc 1583(rfc1644 t/tcp connection count). 1584The absence of a particular option may be denoted 1585with a 1586.Ql \&! . 1587.It Cm uid Ar user 1588Match all TCP or UDP packets sent by or received for a 1589.Ar user . 1590A 1591.Ar user 1592may be matched by name or identification number. 1593.It Cm verrevpath 1594For incoming packets, 1595a routing table lookup is done on the packet's source address. 1596If the interface on which the packet entered the system matches the 1597outgoing interface for the route, 1598the packet matches. 1599If the interfaces do not match up, 1600the packet does not match. 1601All outgoing packets or packets with no incoming interface match. 1602.Pp 1603The name and functionality of the option is intentionally similar to 1604the Cisco IOS command: 1605.Pp 1606.Dl ip verify unicast reverse-path 1607.Pp 1608This option can be used to make anti-spoofing rules to reject all 1609packets with source addresses not from this interface. 1610See also the option 1611.Cm antispoof . 1612.It Cm versrcreach 1613For incoming packets, 1614a routing table lookup is done on the packet's source address. 1615If a route to the source address exists, but not the default route 1616or a blackhole/reject route, the packet matches. 1617Otherwise, the packet does not match. 1618All outgoing packets match. 1619.Pp 1620The name and functionality of the option is intentionally similar to 1621the Cisco IOS command: 1622.Pp 1623.Dl ip verify unicast source reachable-via any 1624.Pp 1625This option can be used to make anti-spoofing rules to reject all 1626packets whose source address is unreachable. 1627.It Cm antispoof 1628For incoming packets, the packet's source address is checked if it 1629belongs to a directly connected network. 1630If the network is directly connected, then the interface the packet 1631came on in is compared to the interface the network is connected to. 1632When incoming interface and directly connected interface are not the 1633same, the packet does not match. 1634Otherwise, the packet does match. 1635All outgoing packets match. 1636.Pp 1637This option can be used to make anti-spoofing rules to reject all 1638packets that pretend to be from a directly connected network but do 1639not come in through that interface. 1640This option is similar to but more restricted than 1641.Cm verrevpath 1642because it engages only on packets with source addresses of directly 1643connected networks instead of all source addresses. 1644.El 1645.Sh LOOKUP TABLES 1646Lookup tables are useful to handle large sparse address sets, 1647typically from a hundred to several thousands of entries. 1648There may be up to 128 different lookup tables, numbered 0 to 127. 1649.Pp 1650Each entry is represented by an 1651.Ar addr Ns Op / Ns Ar masklen 1652and will match all addresses with base 1653.Ar addr 1654(specified as an IP address or a hostname) 1655and mask width of 1656.Ar masklen 1657bits. 1658If 1659.Ar masklen 1660is not specified, it defaults to 32. 1661When looking up an IP address in a table, the most specific 1662entry will match. 1663Associated with each entry is a 32-bit unsigned 1664.Ar value , 1665which can optionally be checked by a rule matching code. 1666When adding an entry, if 1667.Ar value 1668is not specified, it defaults to 0. 1669.Pp 1670An entry can be added to a table 1671.Pq Cm add , 1672removed from a table 1673.Pq Cm delete , 1674a table can be examined 1675.Pq Cm list 1676or flushed 1677.Pq Cm flush . 1678.Pp 1679Internally, each table is stored in a Radix tree, the same way as 1680the routing table (see 1681.Xr route 4 ) . 1682.Pp 1683Lookup tables currently support IPv4 addresses only. 1684.Pp 1685The 1686.Cm tablearg 1687feature provides the ability to use a value, looked up in the table, as 1688the argument for a rule action, action parameter or rule option. 1689This can significantly reduce number of rules in some configurations. 1690If two tables are used in a rule, the result of the second (destination) 1691is used. 1692The 1693.Cm tablearg 1694argument can be used with the following actions: 1695.Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto 1696action parameters: 1697.Cm tag, untag, 1698rule options: 1699.Cm limit, tagged. 1700.Pp 1701When used with 1702.Cm fwd 1703it is possible to supply table entries with values 1704that are in the form of IP addresses or hostnames. 1705See the 1706.Sx EXAMPLES 1707Section for example usage of tables and the tablearg keyword. 1708.Pp 1709When used with the 1710.Cm skipto 1711action, the user should be aware that the code will walk the ruleset 1712up to a rule equal to, or past, the given number, and should therefore try keep the 1713ruleset compact between the skipto and the target rules. 1714.Sh SETS OF RULES 1715Each rule belongs to one of 32 different 1716.Em sets 1717, numbered 0 to 31. 1718Set 31 is reserved for the default rule. 1719.Pp 1720By default, rules are put in set 0, unless you use the 1721.Cm set N 1722attribute when entering a new rule. 1723Sets can be individually and atomically enabled or disabled, 1724so this mechanism permits an easy way to store multiple configurations 1725of the firewall and quickly (and atomically) switch between them. 1726The command to enable/disable sets is 1727.Bd -ragged -offset indent 1728.Nm 1729.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 1730.Ed 1731.Pp 1732where multiple 1733.Cm enable 1734or 1735.Cm disable 1736sections can be specified. 1737Command execution is atomic on all the sets specified in the command. 1738By default, all sets are enabled. 1739.Pp 1740When you disable a set, its rules behave as if they do not exist 1741in the firewall configuration, with only one exception: 1742.Bd -ragged -offset indent 1743dynamic rules created from a rule before it had been disabled 1744will still be active until they expire. 1745In order to delete 1746dynamic rules you have to explicitly delete the parent rule 1747which generated them. 1748.Ed 1749.Pp 1750The set number of rules can be changed with the command 1751.Bd -ragged -offset indent 1752.Nm 1753.Cm set move 1754.Brq Cm rule Ar rule-number | old-set 1755.Cm to Ar new-set 1756.Ed 1757.Pp 1758Also, you can atomically swap two rulesets with the command 1759.Bd -ragged -offset indent 1760.Nm 1761.Cm set swap Ar first-set second-set 1762.Ed 1763.Pp 1764See the 1765.Sx EXAMPLES 1766Section on some possible uses of sets of rules. 1767.Sh STATEFUL FIREWALL 1768Stateful operation is a way for the firewall to dynamically 1769create rules for specific flows when packets that 1770match a given pattern are detected. 1771Support for stateful 1772operation comes through the 1773.Cm check-state , keep-state 1774and 1775.Cm limit 1776options of 1777.Nm rules . 1778.Pp 1779Dynamic rules are created when a packet matches a 1780.Cm keep-state 1781or 1782.Cm limit 1783rule, causing the creation of a 1784.Em dynamic 1785rule which will match all and only packets with 1786a given 1787.Em protocol 1788between a 1789.Em src-ip/src-port dst-ip/dst-port 1790pair of addresses 1791.Em ( src 1792and 1793.Em dst 1794are used here only to denote the initial match addresses, but they 1795are completely equivalent afterwards). 1796Dynamic rules will be checked at the first 1797.Cm check-state, keep-state 1798or 1799.Cm limit 1800occurrence, and the action performed upon a match will be the same 1801as in the parent rule. 1802.Pp 1803Note that no additional attributes other than protocol and IP addresses 1804and ports are checked on dynamic rules. 1805.Pp 1806The typical use of dynamic rules is to keep a closed firewall configuration, 1807but let the first TCP SYN packet from the inside network install a 1808dynamic rule for the flow so that packets belonging to that session 1809will be allowed through the firewall: 1810.Pp 1811.Dl "ipfw add check-state" 1812.Dl "ipfw add allow tcp from my-subnet to any setup keep-state" 1813.Dl "ipfw add deny tcp from any to any" 1814.Pp 1815A similar approach can be used for UDP, where an UDP packet coming 1816from the inside will install a dynamic rule to let the response through 1817the firewall: 1818.Pp 1819.Dl "ipfw add check-state" 1820.Dl "ipfw add allow udp from my-subnet to any keep-state" 1821.Dl "ipfw add deny udp from any to any" 1822.Pp 1823Dynamic rules expire after some time, which depends on the status 1824of the flow and the setting of some 1825.Cm sysctl 1826variables. 1827See Section 1828.Sx SYSCTL VARIABLES 1829for more details. 1830For TCP sessions, dynamic rules can be instructed to periodically 1831send keepalive packets to refresh the state of the rule when it is 1832about to expire. 1833.Pp 1834See Section 1835.Sx EXAMPLES 1836for more examples on how to use dynamic rules. 1837.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 1838.Nm 1839is also the user interface for the 1840.Nm dummynet 1841traffic shaper and network emulator, a subsystem that 1842can artificially queue, delay or drop packets 1843emulator the behaviour of certain network links 1844or queueing systems. 1845.Pp 1846.Nm dummynet 1847operates by first using the firewall to select packets 1848using any match pattern that can be used in 1849.Nm 1850rules. 1851Matching packets are then passed to either of two 1852different objects, which implement the traffic regulation: 1853.Bl -hang -offset XXXX 1854.It Em pipe 1855A pipe emulates a link with given bandwidth, propagation delay, 1856queue size and packet loss rate. 1857Packets are queued in front of the pipe as they come out from the classifier, 1858and then transferred to the pipe according to the pipe's parameters. 1859.It Em queue 1860A queue 1861is an abstraction used to implement the WF2Q+ 1862(Worst-case Fair Weighted Fair Queueing) policy, which is 1863an efficient variant of the WFQ policy. 1864.Pp 1865The queue associates a 1866.Em weight 1867and a reference pipe to each flow (a flow is a set of packets 1868with the same addresses and ports after masking). 1869All backlogged flows (i.e., those 1870with packets queued) linked to the same pipe share the pipe's 1871bandwidth proportionally to their weights. 1872Note that weights are not priorities; a flow with a lower weight 1873is still guaranteed to get its fraction of the bandwidth even if a 1874flow with a higher weight is permanently backlogged. 1875.El 1876.Pp 1877In practice, 1878.Em pipes 1879can be used to set hard limits to the bandwidth that a flow can use, whereas 1880.Em queues 1881can be used to determine how different flows share the available bandwidth. 1882.Pp 1883There are two modes of 1884.Nm dummynet 1885operation: 1886.Dq normal 1887and 1888.Dq fast . 1889The 1890.Dq normal 1891mode tries to emulate a real link: the 1892.Nm dummynet 1893scheduler ensures that the packet will not leave the pipe faster than it 1894would on the real link with a given bandwidth. 1895The 1896.Dq fast 1897mode allows certain packets to bypass the 1898.Nm dummynet 1899scheduler (if packet flow does not exceed pipe's bandwidth). 1900This is the reason why the 1901.Dq fast 1902mode requires less CPU cycles per packet (on average) and packet latency 1903can be significantly lower in comparison to a real link with the same 1904bandwidth. 1905The default mode is 1906.Dq normal . 1907The 1908.Dq fast 1909mode can be enabled by setting the 1910.Va net.inet.ip.dummynet.io_fast 1911.Xr sysctl 8 1912variable to a non-zero value. 1913.Pp 1914.Ss PIPE AND QUEUE CONFIGURATION 1915The 1916.Em pipe 1917and 1918.Em queue 1919configuration commands are the following: 1920.Bd -ragged -offset indent 1921.Cm pipe Ar number Cm config Ar pipe-configuration 1922.Pp 1923.Cm queue Ar number Cm config Ar queue-configuration 1924.Ed 1925.Pp 1926The following parameters can be configured for a pipe: 1927.Pp 1928.Bl -tag -width indent -compact 1929.It Cm bw Ar bandwidth | device 1930Bandwidth, measured in 1931.Sm off 1932.Op Cm K | M 1933.Brq Cm bit/s | Byte/s . 1934.Sm on 1935.Pp 1936A value of 0 (default) means unlimited bandwidth. 1937The unit must immediately follow the number, as in 1938.Pp 1939.Dl "ipfw pipe 1 config bw 300Kbit/s" 1940.Pp 1941If a device name is specified instead of a numeric value, as in 1942.Pp 1943.Dl "ipfw pipe 1 config bw tun0" 1944.Pp 1945then the transmit clock is supplied by the specified device. 1946At the moment only the 1947.Xr tun 4 1948device supports this 1949functionality, for use in conjunction with 1950.Xr ppp 8 . 1951.Pp 1952.It Cm delay Ar ms-delay 1953Propagation delay, measured in milliseconds. 1954The value is rounded to the next multiple of the clock tick 1955(typically 10ms, but it is a good practice to run kernels 1956with 1957.Dq "options HZ=1000" 1958to reduce 1959the granularity to 1ms or less). 1960The default value is 0, meaning no delay. 1961.Pp 1962.It Cm burst Ar size 1963If the data to be sent exceeds the pipe's bandwidth limit 1964(and the pipe was previously idle), up to 1965.Ar size 1966bytes of data are allowed to bypass the 1967.Nm dummynet 1968scheduler, and will be sent as fast as the physical link allows. 1969Any additional data will be transmitted at the rate specified 1970by the 1971.Nm pipe 1972bandwidth. 1973The burst size depends on how long the pipe has been idle; 1974the effective burst size is calculated as follows: 1975MAX( 1976.Ar size 1977, 1978.Nm bw 1979* pipe_idle_time). 1980.Pp 1981.It Cm profile Ar filename 1982A file specifying the additional overhead incurred in the transmission 1983of a packet on the link. 1984.Pp 1985Some link types introduce extra delays in the transmission 1986of a packet, e.g. because of MAC level framing, contention on 1987the use of the channel, MAC level retransmissions and so on. 1988From our point of view, the channel is effectively unavailable 1989for this extra time, which is constant or variable depending 1990on the link type. Additionally, packets may be dropped after this 1991time (e.g. on a wireless link after too many retransmissions). 1992We can model the additional delay with an empirical curve 1993that represents its distribution. 1994.Bd -literal -offset indent 1995 cumulative probability 1996 1.0 ^ 1997 | 1998 L +-- loss-level x 1999 | ****** 2000 | * 2001 | ***** 2002 | * 2003 | ** 2004 | * 2005 +-------*-------------------> 2006 delay 2007.Ed 2008The empirical curve may have both vertical and horizontal lines. 2009Vertical lines represent constant delay for a range of 2010probabilities. 2011Horizontal lines correspond to a discontinuity in the delay 2012distribution: the pipe will use the largest delay for a 2013given probability. 2014.Pp 2015The file format is the following, with whitespace acting as 2016a separator and '#' indicating the beginning a comment: 2017.Bl -tag -width indent 2018.It Cm name Ar identifier 2019optional name (listed by "ipfw pipe show") 2020to identify the delay distribution; 2021.It Cm bw Ar value 2022the bandwidth used for the pipe. 2023If not specified here, it must be present 2024explicitly as a configuration parameter for the pipe; 2025.It Cm loss-level Ar L 2026the probability above which packets are lost. 2027(0.0 <= L <= 1.0, default 1.0 i.e. no loss); 2028.It Cm samples Ar N 2029the number of samples used in the internal 2030representation of the curve (2..1024; default 100); 2031.It Cm "delay prob" | "prob delay" 2032One of these two lines is mandatory and defines 2033the format of the following lines with data points. 2034.It Ar XXX Ar YYY 20352 or more lines representing points in the curve, 2036with either delay or probability first, according 2037to the chosen format. 2038The unit for delay is milliseconds. 2039Data points do not need to be sorted. 2040Also, tne number of actual lines can be different 2041from the value of the "samples" parameter: 2042.Nm 2043utility will sort and interpolate 2044the curve as needed. 2045.El 2046.Pp 2047Example of a profile file: 2048.Bd -literal -offset indent 2049name bla_bla_bla 2050samples 100 2051loss-level 0.86 2052prob delay 20530 200 # minimum overhead is 200ms 20540.5 200 20550.5 300 20560.8 1000 20570.9 1300 20581 1300 2059#configuration file end 2060.Ed 2061.El 2062.Pp 2063The following parameters can be configured for a queue: 2064.Pp 2065.Bl -tag -width indent -compact 2066.It Cm pipe Ar pipe_nr 2067Connects a queue to the specified pipe. 2068Multiple queues (with the same or different weights) can be connected to 2069the same pipe, which specifies the aggregate rate for the set of queues. 2070.Pp 2071.It Cm weight Ar weight 2072Specifies the weight to be used for flows matching this queue. 2073The weight must be in the range 1..100, and defaults to 1. 2074.El 2075.Pp 2076Finally, the following parameters can be configured for both 2077pipes and queues: 2078.Pp 2079.Bl -tag -width XXXX -compact 2080.Pp 2081.It Cm buckets Ar hash-table-size 2082Specifies the size of the hash table used for storing the 2083various queues. 2084Default value is 64 controlled by the 2085.Xr sysctl 8 2086variable 2087.Va net.inet.ip.dummynet.hash_size , 2088allowed range is 16 to 65536. 2089.Pp 2090.It Cm mask Ar mask-specifier 2091Packets sent to a given pipe or queue by an 2092.Nm 2093rule can be further classified into multiple flows, each of which is then 2094sent to a different 2095.Em dynamic 2096pipe or queue. 2097A flow identifier is constructed by masking the IP addresses, 2098ports and protocol types as specified with the 2099.Cm mask 2100options in the configuration of the pipe or queue. 2101For each different flow identifier, a new pipe or queue is created 2102with the same parameters as the original object, and matching packets 2103are sent to it. 2104.Pp 2105Thus, when 2106.Em dynamic pipes 2107are used, each flow will get the same bandwidth as defined by the pipe, 2108whereas when 2109.Em dynamic queues 2110are used, each flow will share the parent's pipe bandwidth evenly 2111with other flows generated by the same queue (note that other queues 2112with different weights might be connected to the same pipe). 2113.br 2114Available mask specifiers are a combination of one or more of the following: 2115.Pp 2116.Cm dst-ip Ar mask , 2117.Cm dst-ip6 Ar mask , 2118.Cm src-ip Ar mask , 2119.Cm src-ip6 Ar mask , 2120.Cm dst-port Ar mask , 2121.Cm src-port Ar mask , 2122.Cm flow-id Ar mask , 2123.Cm proto Ar mask 2124or 2125.Cm all , 2126.Pp 2127where the latter means all bits in all fields are significant. 2128.Pp 2129.It Cm noerror 2130When a packet is dropped by a 2131.Nm dummynet 2132queue or pipe, the error 2133is normally reported to the caller routine in the kernel, in the 2134same way as it happens when a device queue fills up. 2135Setting this 2136option reports the packet as successfully delivered, which can be 2137needed for some experimental setups where you want to simulate 2138loss or congestion at a remote router. 2139.Pp 2140.It Cm plr Ar packet-loss-rate 2141Packet loss rate. 2142Argument 2143.Ar packet-loss-rate 2144is a floating-point number between 0 and 1, with 0 meaning no 2145loss, 1 meaning 100% loss. 2146The loss rate is internally represented on 31 bits. 2147.Pp 2148.It Cm queue Brq Ar slots | size Ns Cm Kbytes 2149Queue size, in 2150.Ar slots 2151or 2152.Cm KBytes . 2153Default value is 50 slots, which 2154is the typical queue size for Ethernet devices. 2155Note that for slow speed links you should keep the queue 2156size short or your traffic might be affected by a significant 2157queueing delay. 2158E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit 2159or 20s of queue on a 30Kbit/s pipe. 2160Even worse effects can result if you get packets from an 2161interface with a much larger MTU, e.g.\& the loopback interface 2162with its 16KB packets. 2163The 2164.Xr sysctl 8 2165variables 2166.Em net.inet.ip.dummynet.pipe_byte_limit 2167and 2168.Em net.inet.ip.dummynet.pipe_slot_limit 2169control the maximum lengths that can be specified. 2170.Pp 2171.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p 2172Make use of the RED (Random Early Detection) queue management algorithm. 2173.Ar w_q 2174and 2175.Ar max_p 2176are floating 2177point numbers between 0 and 1 (0 not included), while 2178.Ar min_th 2179and 2180.Ar max_th 2181are integer numbers specifying thresholds for queue management 2182(thresholds are computed in bytes if the queue has been defined 2183in bytes, in slots otherwise). 2184The 2185.Nm dummynet 2186also supports the gentle RED variant (gred). 2187Three 2188.Xr sysctl 8 2189variables can be used to control the RED behaviour: 2190.Bl -tag -width indent 2191.It Va net.inet.ip.dummynet.red_lookup_depth 2192specifies the accuracy in computing the average queue 2193when the link is idle (defaults to 256, must be greater than zero) 2194.It Va net.inet.ip.dummynet.red_avg_pkt_size 2195specifies the expected average packet size (defaults to 512, must be 2196greater than zero) 2197.It Va net.inet.ip.dummynet.red_max_pkt_size 2198specifies the expected maximum packet size, only used when queue 2199thresholds are in bytes (defaults to 1500, must be greater than zero). 2200.El 2201.El 2202.Pp 2203When used with IPv6 data, 2204.Nm dummynet 2205currently has several limitations. 2206Information necessary to route link-local packets to an 2207interface is not available after processing by 2208.Nm dummynet 2209so those packets are dropped in the output path. 2210Care should be taken to insure that link-local packets are not passed to 2211.Nm dummynet . 2212.Sh CHECKLIST 2213Here are some important points to consider when designing your 2214rules: 2215.Bl -bullet 2216.It 2217Remember that you filter both packets going 2218.Cm in 2219and 2220.Cm out . 2221Most connections need packets going in both directions. 2222.It 2223Remember to test very carefully. 2224It is a good idea to be near the console when doing this. 2225If you cannot be near the console, 2226use an auto-recovery script such as the one in 2227.Pa /usr/share/examples/ipfw/change_rules.sh . 2228.It 2229Do not forget the loopback interface. 2230.El 2231.Sh FINE POINTS 2232.Bl -bullet 2233.It 2234There are circumstances where fragmented datagrams are unconditionally 2235dropped. 2236TCP packets are dropped if they do not contain at least 20 bytes of 2237TCP header, UDP packets are dropped if they do not contain a full 8 2238byte UDP header, and ICMP packets are dropped if they do not contain 22394 bytes of ICMP header, enough to specify the ICMP type, code, and 2240checksum. 2241These packets are simply logged as 2242.Dq pullup failed 2243since there may not be enough good data in the packet to produce a 2244meaningful log entry. 2245.It 2246Another type of packet is unconditionally dropped, a TCP packet with a 2247fragment offset of one. 2248This is a valid packet, but it only has one use, to try 2249to circumvent firewalls. 2250When logging is enabled, these packets are 2251reported as being dropped by rule -1. 2252.It 2253If you are logged in over a network, loading the 2254.Xr kld 4 2255version of 2256.Nm 2257is probably not as straightforward as you would think. 2258The following command line is recommended: 2259.Bd -literal -offset indent 2260kldload ipfw && \e 2261ipfw add 32000 allow ip from any to any 2262.Ed 2263.Pp 2264Along the same lines, doing an 2265.Bd -literal -offset indent 2266ipfw flush 2267.Ed 2268.Pp 2269in similar surroundings is also a bad idea. 2270.It 2271The 2272.Nm 2273filter list may not be modified if the system security level 2274is set to 3 or higher 2275(see 2276.Xr init 8 2277for information on system security levels). 2278.El 2279.Sh PACKET DIVERSION 2280A 2281.Xr divert 4 2282socket bound to the specified port will receive all packets 2283diverted to that port. 2284If no socket is bound to the destination port, or if the divert module is 2285not loaded, or if the kernel was not compiled with divert socket support, 2286the packets are dropped. 2287.Sh NETWORK ADDRESS TRANSLATION (NAT) 2288.Pp 2289.Nm 2290support in-kernel NAT using the kernel version of 2291.Xr libalias 3 . 2292.Pp 2293The nat configuration command is the following: 2294.Bd -ragged -offset indent 2295.Bk -words 2296.Cm nat 2297.Ar nat_number 2298.Cm config 2299.Ar nat-configuration 2300.Ek 2301.Ed 2302.Pp 2303The following parameters can be configured: 2304.Bl -tag -width indent 2305.It Cm ip Ar ip_address 2306Define an ip address to use for aliasing. 2307.It Cm if Ar nic 2308Use ip address of NIC for aliasing, dynamically changing 2309it if NIC's ip address changes. 2310.It Cm log 2311Enable logging on this nat instance. 2312.It Cm deny_in 2313Deny any incoming connection from outside world. 2314.It Cm same_ports 2315Try to leave the alias port numbers unchanged from 2316the actual local port numbers. 2317.It Cm unreg_only 2318Traffic on the local network not originating from an 2319unregistered address spaces will be ignored. 2320.It Cm reset 2321Reset table of the packet aliasing engine on address change. 2322.It Cm reverse 2323Reverse the way libalias handles aliasing. 2324.It Cm proxy_only 2325Obey transparent proxy rules only, packet aliasing is not performed. 2326.El 2327.Pp 2328To let the packet continue after being (de)aliased, set the sysctl variable 2329.Va net.inet.ip.fw.one_pass 2330to 0. 2331For more information about aliasing modes, refer to 2332.Xr libalias 3 . 2333See Section 2334.Sx EXAMPLES 2335for some examples about nat usage. 2336.Ss REDIRECT AND LSNAT SUPPORT IN IPFW 2337Redirect and LSNAT support follow closely the syntax used in 2338.Xr natd 8 . 2339See Section 2340.Sx EXAMPLES 2341for some examples on how to do redirect and lsnat. 2342.Ss SCTP NAT SUPPORT 2343SCTP nat can be configured in a similar manner to TCP through the 2344.Nm 2345command line tool. 2346The main difference is that 2347.Nm sctp nat 2348does not do port translation. 2349Since the local and global side ports will be the same, 2350there is no need to specify both. 2351Ports are redirected as follows: 2352.Bd -ragged -offset indent 2353.Bk -words 2354.Cm nat 2355.Ar nat_number 2356.Cm config if 2357.Ar nic 2358.Cm redirect_port sctp 2359.Ar ip_address [,addr_list] {[port | port-port] [,ports]} 2360.Ek 2361.Ed 2362.Pp 2363Most 2364.Nm sctp nat 2365configuration can be done in real-time through the 2366.Xr sysctl 8 2367interface. 2368All may be changed dynamically, though the hash_table size will only 2369change for new 2370.Nm nat 2371instances. 2372See 2373.Sx SYSCTL VARIABLES 2374for more info. 2375.Sh SYSCTL VARIABLES 2376A set of 2377.Xr sysctl 8 2378variables controls the behaviour of the firewall and 2379associated modules 2380.Pq Nm dummynet , bridge , sctp nat . 2381These are shown below together with their default value 2382(but always check with the 2383.Xr sysctl 8 2384command what value is actually in use) and meaning: 2385.Bl -tag -width indent 2386.It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0 2387Defines how the 2388.Nm nat 2389responds to receipt of global OOTB ASCONF-AddIP: 2390.Bl -tag -width indent 2391.It Cm 0 2392No response (unless a partially matching association exists - 2393ports and vtags match but global address does not) 2394.It Cm 1 2395.Nm nat 2396will accept and process all OOTB global AddIP messages. 2397.El 2398.Pp 2399Option 1 should never be selected as this forms a security risk. 2400An attacker can 2401establish multiple fake associations by sending AddIP messages. 2402.It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5 2403Defines the maximum number of chunks in an SCTP packet that will be parsed for a 2404packet that matches an existing association. 2405This value is enforced to be greater or equal than 2406.Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit . 2407A high value is 2408a DoS risk yet setting too low a value may result in important control chunks in 2409the packet not being located and parsed. 2410.It Va net.inet.ip.alias.sctp.error_on_ootb: No 1 2411Defines when the 2412.Nm nat 2413responds to any Out-of-the-Blue (OOTB) packets with ErrorM packets. 2414An OOTB packet is a packet that arrives with no existing association 2415registered in the 2416.Nm nat 2417and is not an INIT or ASCONF-AddIP packet: 2418.Bl -tag -width indent 2419.It Cm 0 2420ErrorM is never sent in response to OOTB packets. 2421.It Cm 1 2422ErrorM is only sent to OOTB packets received on the local side. 2423.It Cm 2 2424ErrorM is sent to the local side and on the global side ONLY if there is a 2425partial match (ports and vtags match but the source global IP does not). 2426This value is only useful if the 2427.Nm nat 2428is tracking global IP addresses. 2429.It Cm 3 2430ErrorM is sent in response to all OOTB packets on both the local and global side 2431(DoS risk). 2432.El 2433.Pp 2434At the moment the default is 0, since the ErrorM packet is not yet 2435supported by most SCTP stacks. 2436When it is supported, and if not tracking 2437global addresses, we recommend setting this value to 1 to allow 2438multi-homed local hosts to function with the 2439.Nm nat . 2440To track global addresses, we recommend setting this value to 2 to 2441allow global hosts to be informed when they need to (re)send an 2442ASCONF-AddIP. 2443Value 3 should never be chosen (except for debugging) as the 2444.Nm nat 2445will respond to all OOTB global packets (a DoS risk). 2446.It Va net.inet.ip.alias.sctp.hashtable_size: No 2003 2447Size of hash tables used for 2448.Nm nat 2449lookups (100 < prime_number > 1000001). 2450This value sets the 2451.Nm hash table 2452size for any future created 2453.Nm nat 2454instance and therefore must be set prior to creating a 2455.Nm nat 2456instance. 2457The table sizes may be changed to suit specific needs. 2458If there will be few 2459concurrent associations, and memory is scarce, you may make these smaller. 2460If there will be many thousands (or millions) of concurrent associations, you 2461should make these larger. 2462A prime number is best for the table size. 2463The sysctl 2464update function will adjust your input value to the next highest prime number. 2465.It Va net.inet.ip.alias.sctp.holddown_time: No 0 2466Hold association in table for this many seconds after receiving a 2467SHUTDOWN-COMPLETE. 2468This allows endpoints to correct shutdown gracefully if a 2469shutdown_complete is lost and retransmissions are required. 2470.It Va net.inet.ip.alias.sctp.init_timer: No 15 2471Timeout value while waiting for (INIT-ACK|AddIP-ACK). 2472This value cannot be 0. 2473.It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2 2474Defines the maximum number of chunks in an SCTP packet that will be parsed when 2475no existing association exists that matches that packet. 2476Ideally this packet 2477will only be an INIT or ASCONF-AddIP packet. 2478A higher value may become a DoS 2479risk as malformed packets can consume processing resources. 2480.It Va net.inet.ip.alias.sctp.param_proc_limit: No 25 2481Defines the maximum number of parameters within a chunk that will be parsed in a 2482packet. 2483As for other similar sysctl variables, larger values pose a DoS risk. 2484.It Va net.inet.ip.alias.sctp.log_level: No 0 2485Level of detail in the system log messages (0 \- minimal, 1 \- event, 24862 \- info, 3 \- detail, 4 \- debug, 5 \- max debug). May be a good 2487option in high loss environments. 2488.It Va net.inet.ip.alias.sctp.shutdown_time: No 15 2489Timeout value while waiting for SHUTDOWN-COMPLETE. 2490This value cannot be 0. 2491.It Va net.inet.ip.alias.sctp.track_global_addresses: No 0 2492Enables/disables global IP address tracking within the 2493.Nm nat 2494and places an 2495upper limit on the number of addresses tracked for each association: 2496.Bl -tag -width indent 2497.It Cm 0 2498Global tracking is disabled 2499.It Cm >1 2500Enables tracking, the maximum number of addresses tracked for each 2501association is limited to this value 2502.El 2503.Pp 2504This variable is fully dynamic, the new value will be adopted for all newly 2505arriving associations, existing associations are treated as they were previously. 2506Global tracking will decrease the number of collisions within the 2507.Nm nat 2508at a cost 2509of increased processing load, memory usage, complexity, and possible 2510.Nm nat 2511state 2512problems in complex networks with multiple 2513.Nm nats . 2514We recommend not tracking 2515global IP addresses, this will still result in a fully functional 2516.Nm nat . 2517.It Va net.inet.ip.alias.sctp.up_timer: No 300 2518Timeout value to keep an association up with no traffic. 2519This value cannot be 0. 2520.It Va net.inet.ip.dummynet.expire : No 1 2521Lazily delete dynamic pipes/queue once they have no pending traffic. 2522You can disable this by setting the variable to 0, in which case 2523the pipes/queues will only be deleted when the threshold is reached. 2524.It Va net.inet.ip.dummynet.hash_size : No 64 2525Default size of the hash table used for dynamic pipes/queues. 2526This value is used when no 2527.Cm buckets 2528option is specified when configuring a pipe/queue. 2529.It Va net.inet.ip.dummynet.io_fast : No 0 2530If set to a non-zero value, 2531the 2532.Dq fast 2533mode of 2534.Nm dummynet 2535operation (see above) is enabled. 2536.It Va net.inet.ip.dummynet.io_pkt 2537Number of packets passed to 2538.Nm dummynet . 2539.It Va net.inet.ip.dummynet.io_pkt_drop 2540Number of packets dropped by 2541.Nm dummynet . 2542.It Va net.inet.ip.dummynet.io_pkt_fast 2543Number of packets bypassed by the 2544.Nm dummynet 2545scheduler. 2546.It Va net.inet.ip.dummynet.max_chain_len : No 16 2547Target value for the maximum number of pipes/queues in a hash bucket. 2548The product 2549.Cm max_chain_len*hash_size 2550is used to determine the threshold over which empty pipes/queues 2551will be expired even when 2552.Cm net.inet.ip.dummynet.expire=0 . 2553.It Va net.inet.ip.dummynet.red_lookup_depth : No 256 2554.It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512 2555.It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500 2556Parameters used in the computations of the drop probability 2557for the RED algorithm. 2558.It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576 2559.It Va net.inet.ip.dummynet.pipe_slot_limit : No 100 2560The maximum queue size that can be specified in bytes or packets. 2561These limits prevent accidental exhaustion of resources such as mbufs. 2562If you raise these limits, 2563you should make sure the system is configured so that sufficient resources 2564are available. 2565.It Va net.inet.ip.fw.autoinc_step : No 100 2566Delta between rule numbers when auto-generating them. 2567The value must be in the range 1..1000. 2568.It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets 2569The current number of buckets in the hash table for dynamic rules 2570(readonly). 2571.It Va net.inet.ip.fw.debug : No 1 2572Controls debugging messages produced by 2573.Nm . 2574.It Va net.inet.ip.fw.default_rule : No 65535 2575The default rule number (read-only). 2576By the design of 2577.Nm , the default rule is the last one, so its number 2578can also serve as the highest number allowed for a rule. 2579.It Va net.inet.ip.fw.dyn_buckets : No 256 2580The number of buckets in the hash table for dynamic rules. 2581Must be a power of 2, up to 65536. 2582It only takes effect when all dynamic rules have expired, so you 2583are advised to use a 2584.Cm flush 2585command to make sure that the hash table is resized. 2586.It Va net.inet.ip.fw.dyn_count : No 3 2587Current number of dynamic rules 2588(read-only). 2589.It Va net.inet.ip.fw.dyn_keepalive : No 1 2590Enables generation of keepalive packets for 2591.Cm keep-state 2592rules on TCP sessions. 2593A keepalive is generated to both 2594sides of the connection every 5 seconds for the last 20 2595seconds of the lifetime of the rule. 2596.It Va net.inet.ip.fw.dyn_max : No 8192 2597Maximum number of dynamic rules. 2598When you hit this limit, no more dynamic rules can be 2599installed until old ones expire. 2600.It Va net.inet.ip.fw.dyn_ack_lifetime : No 300 2601.It Va net.inet.ip.fw.dyn_syn_lifetime : No 20 2602.It Va net.inet.ip.fw.dyn_fin_lifetime : No 1 2603.It Va net.inet.ip.fw.dyn_rst_lifetime : No 1 2604.It Va net.inet.ip.fw.dyn_udp_lifetime : No 5 2605.It Va net.inet.ip.fw.dyn_short_lifetime : No 30 2606These variables control the lifetime, in seconds, of dynamic 2607rules. 2608Upon the initial SYN exchange the lifetime is kept short, 2609then increased after both SYN have been seen, then decreased 2610again during the final FIN exchange or when a RST is received. 2611Both 2612.Em dyn_fin_lifetime 2613and 2614.Em dyn_rst_lifetime 2615must be strictly lower than 5 seconds, the period of 2616repetition of keepalives. 2617The firewall enforces that. 2618.It Va net.inet.ip.fw.enable : No 1 2619Enables the firewall. 2620Setting this variable to 0 lets you run your machine without 2621firewall even if compiled in. 2622.It Va net.inet6.ip6.fw.enable : No 1 2623provides the same functionality as above for the IPv6 case. 2624.It Va net.inet.ip.fw.one_pass : No 1 2625When set, the packet exiting from the 2626.Nm dummynet 2627pipe or from 2628.Xr ng_ipfw 4 2629node is not passed though the firewall again. 2630Otherwise, after an action, the packet is 2631reinjected into the firewall at the next rule. 2632.It Va net.inet.ip.fw.tables_max : No 128 2633Maximum number of tables (read-only). 2634.It Va net.inet.ip.fw.verbose : No 1 2635Enables verbose messages. 2636.It Va net.inet.ip.fw.verbose_limit : No 0 2637Limits the number of messages produced by a verbose firewall. 2638.It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1 2639If enabled packets with unknown IPv6 Extension Headers will be denied. 2640.It Va net.link.ether.ipfw : No 0 2641Controls whether layer-2 packets are passed to 2642.Nm . 2643Default is no. 2644.It Va net.link.bridge.ipfw : No 0 2645Controls whether bridged packets are passed to 2646.Nm . 2647Default is no. 2648.El 2649.Pp 2650.Sh EXAMPLES 2651There are far too many possible uses of 2652.Nm 2653so this Section will only give a small set of examples. 2654.Pp 2655.Ss BASIC PACKET FILTERING 2656This command adds an entry which denies all tcp packets from 2657.Em cracker.evil.org 2658to the telnet port of 2659.Em wolf.tambov.su 2660from being forwarded by the host: 2661.Pp 2662.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet" 2663.Pp 2664This one disallows any connection from the entire cracker's 2665network to my host: 2666.Pp 2667.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org" 2668.Pp 2669A first and efficient way to limit access (not using dynamic rules) 2670is the use of the following rules: 2671.Pp 2672.Dl "ipfw add allow tcp from any to any established" 2673.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup" 2674.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup" 2675.Dl "..." 2676.Dl "ipfw add deny tcp from any to any" 2677.Pp 2678The first rule will be a quick match for normal TCP packets, 2679but it will not match the initial SYN packet, which will be 2680matched by the 2681.Cm setup 2682rules only for selected source/destination pairs. 2683All other SYN packets will be rejected by the final 2684.Cm deny 2685rule. 2686.Pp 2687If you administer one or more subnets, you can take advantage 2688of the address sets and or-blocks and write extremely 2689compact rulesets which selectively enable services to blocks 2690of clients, as below: 2691.Pp 2692.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q" 2693.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q" 2694.Dl "" 2695.Dl "ipfw add allow ip from ${goodguys} to any" 2696.Dl "ipfw add deny ip from ${badguys} to any" 2697.Dl "... normal policies ..." 2698.Pp 2699The 2700.Cm verrevpath 2701option could be used to do automated anti-spoofing by adding the 2702following to the top of a ruleset: 2703.Pp 2704.Dl "ipfw add deny ip from any to any not verrevpath in" 2705.Pp 2706This rule drops all incoming packets that appear to be coming to the 2707system on the wrong interface. 2708For example, a packet with a source 2709address belonging to a host on a protected internal network would be 2710dropped if it tried to enter the system from an external interface. 2711.Pp 2712The 2713.Cm antispoof 2714option could be used to do similar but more restricted anti-spoofing 2715by adding the following to the top of a ruleset: 2716.Pp 2717.Dl "ipfw add deny ip from any to any not antispoof in" 2718.Pp 2719This rule drops all incoming packets that appear to be coming from another 2720directly connected system but on the wrong interface. 2721For example, a packet with a source address of 2722.Li 192.168.0.0/24 , 2723configured on 2724.Li fxp0 , 2725but coming in on 2726.Li fxp1 2727would be dropped. 2728.Ss DYNAMIC RULES 2729In order to protect a site from flood attacks involving fake 2730TCP packets, it is safer to use dynamic rules: 2731.Pp 2732.Dl "ipfw add check-state" 2733.Dl "ipfw add deny tcp from any to any established" 2734.Dl "ipfw add allow tcp from my-net to any setup keep-state" 2735.Pp 2736This will let the firewall install dynamic rules only for 2737those connection which start with a regular SYN packet coming 2738from the inside of our network. 2739Dynamic rules are checked when encountering the first 2740.Cm check-state 2741or 2742.Cm keep-state 2743rule. 2744A 2745.Cm check-state 2746rule should usually be placed near the beginning of the 2747ruleset to minimize the amount of work scanning the ruleset. 2748Your mileage may vary. 2749.Pp 2750To limit the number of connections a user can open 2751you can use the following type of rules: 2752.Pp 2753.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10" 2754.Dl "ipfw add allow tcp from any to me setup limit src-addr 4" 2755.Pp 2756The former (assuming it runs on a gateway) will allow each host 2757on a /24 network to open at most 10 TCP connections. 2758The latter can be placed on a server to make sure that a single 2759client does not use more than 4 simultaneous connections. 2760.Pp 2761.Em BEWARE : 2762stateful rules can be subject to denial-of-service attacks 2763by a SYN-flood which opens a huge number of dynamic rules. 2764The effects of such attacks can be partially limited by 2765acting on a set of 2766.Xr sysctl 8 2767variables which control the operation of the firewall. 2768.Pp 2769Here is a good usage of the 2770.Cm list 2771command to see accounting records and timestamp information: 2772.Pp 2773.Dl ipfw -at list 2774.Pp 2775or in short form without timestamps: 2776.Pp 2777.Dl ipfw -a list 2778.Pp 2779which is equivalent to: 2780.Pp 2781.Dl ipfw show 2782.Pp 2783Next rule diverts all incoming packets from 192.168.2.0/24 2784to divert port 5000: 2785.Pp 2786.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in 2787.Pp 2788.Ss TRAFFIC SHAPING 2789The following rules show some of the applications of 2790.Nm 2791and 2792.Nm dummynet 2793for simulations and the like. 2794.Pp 2795This rule drops random incoming packets with a probability 2796of 5%: 2797.Pp 2798.Dl "ipfw add prob 0.05 deny ip from any to any in" 2799.Pp 2800A similar effect can be achieved making use of 2801.Nm dummynet 2802pipes: 2803.Pp 2804.Dl "ipfw add pipe 10 ip from any to any" 2805.Dl "ipfw pipe 10 config plr 0.05" 2806.Pp 2807We can use pipes to artificially limit bandwidth, e.g.\& on a 2808machine acting as a router, if we want to limit traffic from 2809local clients on 192.168.2.0/24 we do: 2810.Pp 2811.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2812.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes" 2813.Pp 2814note that we use the 2815.Cm out 2816modifier so that the rule is not used twice. 2817Remember in fact that 2818.Nm 2819rules are checked both on incoming and outgoing packets. 2820.Pp 2821Should we want to simulate a bidirectional link with bandwidth 2822limitations, the correct way is the following: 2823.Pp 2824.Dl "ipfw add pipe 1 ip from any to any out" 2825.Dl "ipfw add pipe 2 ip from any to any in" 2826.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes" 2827.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes" 2828.Pp 2829The above can be very useful, e.g.\& if you want to see how 2830your fancy Web page will look for a residential user who 2831is connected only through a slow link. 2832You should not use only one pipe for both directions, unless 2833you want to simulate a half-duplex medium (e.g.\& AppleTalk, 2834Ethernet, IRDA). 2835It is not necessary that both pipes have the same configuration, 2836so we can also simulate asymmetric links. 2837.Pp 2838Should we want to verify network performance with the RED queue 2839management algorithm: 2840.Pp 2841.Dl "ipfw add pipe 1 ip from any to any" 2842.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1" 2843.Pp 2844Another typical application of the traffic shaper is to 2845introduce some delay in the communication. 2846This can significantly affect applications which do a lot of Remote 2847Procedure Calls, and where the round-trip-time of the 2848connection often becomes a limiting factor much more than 2849bandwidth: 2850.Pp 2851.Dl "ipfw add pipe 1 ip from any to any out" 2852.Dl "ipfw add pipe 2 ip from any to any in" 2853.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s" 2854.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s" 2855.Pp 2856Per-flow queueing can be useful for a variety of purposes. 2857A very simple one is counting traffic: 2858.Pp 2859.Dl "ipfw add pipe 1 tcp from any to any" 2860.Dl "ipfw add pipe 1 udp from any to any" 2861.Dl "ipfw add pipe 1 ip from any to any" 2862.Dl "ipfw pipe 1 config mask all" 2863.Pp 2864The above set of rules will create queues (and collect 2865statistics) for all traffic. 2866Because the pipes have no limitations, the only effect is 2867collecting statistics. 2868Note that we need 3 rules, not just the last one, because 2869when 2870.Nm 2871tries to match IP packets it will not consider ports, so we 2872would not see connections on separate ports as different 2873ones. 2874.Pp 2875A more sophisticated example is limiting the outbound traffic 2876on a net with per-host limits, rather than per-network limits: 2877.Pp 2878.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2879.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in" 2880.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2881.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2882.Ss LOOKUP TABLES 2883In the following example, we need to create several traffic bandwidth 2884classes and we need different hosts/networks to fall into different classes. 2885We create one pipe for each class and configure them accordingly. 2886Then we create a single table and fill it with IP subnets and addresses. 2887For each subnet/host we set the argument equal to the number of the pipe 2888that it should use. 2889Then we classify traffic using a single rule: 2890.Pp 2891.Dl "ipfw pipe 1 config bw 1000Kbyte/s" 2892.Dl "ipfw pipe 4 config bw 4000Kbyte/s" 2893.Dl "..." 2894.Dl "ipfw table 1 add 192.168.2.0/24 1" 2895.Dl "ipfw table 1 add 192.168.0.0/27 4" 2896.Dl "ipfw table 1 add 192.168.0.2 1" 2897.Dl "..." 2898.Dl "ipfw add pipe tablearg ip from table(1) to any" 2899.Pp 2900Using the 2901.Cm fwd 2902action, the table entries may include hostnames and IP addresses. 2903.Pp 2904.Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1" 2905.Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz" 2906.Dl "..." 2907.Dl "ipfw add 100 fwd tablearg ip from any to table(1)" 2908.Ss SETS OF RULES 2909To add a set of rules atomically, e.g.\& set 18: 2910.Pp 2911.Dl "ipfw set disable 18" 2912.Dl "ipfw add NN set 18 ... # repeat as needed" 2913.Dl "ipfw set enable 18" 2914.Pp 2915To delete a set of rules atomically the command is simply: 2916.Pp 2917.Dl "ipfw delete set 18" 2918.Pp 2919To test a ruleset and disable it and regain control if something goes wrong: 2920.Pp 2921.Dl "ipfw set disable 18" 2922.Dl "ipfw add NN set 18 ... # repeat as needed" 2923.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18" 2924.Pp 2925Here if everything goes well, you press control-C before the "sleep" 2926terminates, and your ruleset will be left active. 2927Otherwise, e.g.\& if 2928you cannot access your box, the ruleset will be disabled after 2929the sleep terminates thus restoring the previous situation. 2930.Pp 2931To show rules of the specific set: 2932.Pp 2933.Dl "ipfw set 18 show" 2934.Pp 2935To show rules of the disabled set: 2936.Pp 2937.Dl "ipfw -S set 18 show" 2938.Pp 2939To clear a specific rule counters of the specific set: 2940.Pp 2941.Dl "ipfw set 18 zero NN" 2942.Pp 2943To delete a specific rule of the specific set: 2944.Pp 2945.Dl "ipfw set 18 delete NN" 2946.Ss NAT, REDIRECT AND LSNAT 2947First redirect all the traffic to nat instance 123: 2948.Pp 2949.Dl "ipfw add nat 123 all from any to any" 2950.Pp 2951Then to configure nat instance 123 to alias all the outgoing traffic with ip 2952192.168.0.123, blocking all incoming connections, trying to keep 2953same ports on both sides, clearing aliasing table on address change 2954and keeping a log of traffic/link statistics: 2955.Pp 2956.Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports" 2957.Pp 2958Or to change address of instance 123, aliasing table will be cleared (see 2959reset option): 2960.Pp 2961.Dl "ipfw nat 123 config ip 10.0.0.1" 2962.Pp 2963To see configuration of nat instance 123: 2964.Pp 2965.Dl "ipfw nat 123 show config" 2966.Pp 2967To show logs of all the instances in range 111-999: 2968.Pp 2969.Dl "ipfw nat 111-999 show" 2970.Pp 2971To see configurations of all instances: 2972.Pp 2973.Dl "ipfw nat show config" 2974.Pp 2975Or a redirect rule with mixed modes could looks like: 2976.Pp 2977.Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66" 2978.Dl " redirect_port tcp 192.168.0.1:80 500" 2979.Dl " redirect_proto udp 192.168.1.43 192.168.1.1" 2980.Dl " redirect_addr 192.168.0.10,192.168.0.11" 2981.Dl " 10.0.0.100 # LSNAT" 2982.Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22" 2983.Dl " 500 # LSNAT" 2984.Pp 2985or it could be split in: 2986.Pp 2987.Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66" 2988.Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500" 2989.Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1" 2990.Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12" 2991.Dl " 10.0.0.100" 2992.Dl "ipfw nat 5 config redirect_port tcp" 2993.Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500" 2994.Pp 2995.Sh SEE ALSO 2996.Xr cpp 1 , 2997.Xr m4 1 , 2998.Xr altq 4 , 2999.Xr divert 4 , 3000.Xr dummynet 4 , 3001.Xr if_bridge 4 , 3002.Xr ip 4 , 3003.Xr ipfirewall 4 , 3004.Xr ng_ipfw 4 , 3005.Xr protocols 5 , 3006.Xr services 5 , 3007.Xr init 8 , 3008.Xr kldload 8 , 3009.Xr reboot 8 , 3010.Xr sysctl 8 , 3011.Xr syslogd 8 3012.Sh HISTORY 3013The 3014.Nm 3015utility first appeared in 3016.Fx 2.0 . 3017.Nm dummynet 3018was introduced in 3019.Fx 2.2.8 . 3020Stateful extensions were introduced in 3021.Fx 4.0 . 3022.Nm ipfw2 3023was introduced in Summer 2002. 3024.Sh AUTHORS 3025.An Ugen J. S. Antsilevich , 3026.An Poul-Henning Kamp , 3027.An Alex Nash , 3028.An Archie Cobbs , 3029.An Luigi Rizzo . 3030.Pp 3031.An -nosplit 3032API based upon code written by 3033.An Daniel Boulet 3034for BSDI. 3035.Pp 3036Dummynet has been introduced by Luigi Rizzo in 1997-1998. 3037.Pp 3038Some early work (1999-2000) on the 3039.Nm dummynet 3040traffic shaper supported by Akamba Corp. 3041.Pp 3042The ipfw core (ipfw2) has been completely redesigned and 3043reimplemented by Luigi Rizzo in summer 2002. Further 3044actions and 3045options have been added by various developer over the years. 3046.Pp 3047.An -nosplit 3048In-kernel NAT support written by 3049.An Paolo Pisati Aq piso@FreeBSD.org 3050as part of a Summer of Code 2005 project. 3051.Pp 3052SCTP 3053.Nm nat 3054support has been developed by 3055.An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au . 3056The primary developers and maintainers are David Hayes and Jason But. 3057For further information visit: 3058.Aq http://www.caia.swin.edu.au/urp/SONATA 3059.Pp 3060Delay profiles have been developed by Alessandro Cerri and 3061Luigi Rizzo, supported by the 3062European Commission within Projects Onelab and Onelab2. 3063.Sh BUGS 3064The syntax has grown over the years and sometimes it might be confusing. 3065Unfortunately, backward compatibility prevents cleaning up mistakes 3066made in the definition of the syntax. 3067.Pp 3068.Em !!! WARNING !!! 3069.Pp 3070Misconfiguring the firewall can put your computer in an unusable state, 3071possibly shutting down network services and requiring console access to 3072regain control of it. 3073.Pp 3074Incoming packet fragments diverted by 3075.Cm divert 3076are reassembled before delivery to the socket. 3077The action used on those packet is the one from the 3078rule which matches the first fragment of the packet. 3079.Pp 3080Packets diverted to userland, and then reinserted by a userland process 3081may lose various packet attributes. 3082The packet source interface name 3083will be preserved if it is shorter than 8 bytes and the userland process 3084saves and reuses the sockaddr_in 3085(as does 3086.Xr natd 8 ) ; 3087otherwise, it may be lost. 3088If a packet is reinserted in this manner, later rules may be incorrectly 3089applied, making the order of 3090.Cm divert 3091rules in the rule sequence very important. 3092.Pp 3093Dummynet drops all packets with IPv6 link-local addresses. 3094.Pp 3095Rules using 3096.Cm uid 3097or 3098.Cm gid 3099may not behave as expected. 3100In particular, incoming SYN packets may 3101have no uid or gid associated with them since they do not yet belong 3102to a TCP connection, and the uid/gid associated with a packet may not 3103be as expected if the associated process calls 3104.Xr setuid 2 3105or similar system calls. 3106.Pp 3107Rule syntax is subject to the command line environment and some patterns 3108may need to be escaped with the backslash character 3109or quoted appropriately. 3110.Pp 3111Due to the architecture of 3112.Xr libalias 3 , 3113ipfw nat is not compatible with the TCP segmentation offloading (TSO). 3114Thus, to reliably nat your network traffic, please disable TSO 3115on your NICs using 3116.Xr ifconfig 8 . 3117.Pp 3118ICMP error messages are not implicitly matched by dynamic rules 3119for the respective conversations. 3120To avoid failures of network error detection and path MTU discovery, 3121ICMP error messages may need to be allowed explicitly through static 3122rules. 3123