1.\" 2.\" $FreeBSD$ 3.\" 4.Dd September 27, 2008 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, then 140.Nm 141assumes a 142.Em stateful 143behaviour, i.e., upon a match it will create dynamic rules matching 144the exact parameters (addresses and ports) of the matching packet. 145.Pp 146These dynamic rules, which have a limited lifetime, are checked 147at the first occurrence of a 148.Cm check-state , 149.Cm keep-state 150or 151.Cm limit 152rule, and are typically used to open the firewall on-demand to 153legitimate traffic only. 154See the 155.Sx STATEFUL FIREWALL 156and 157.Sx EXAMPLES 158Sections below for more information on the stateful behaviour of 159.Nm . 160.Pp 161All rules (including dynamic ones) have a few associated counters: 162a packet count, a byte count, a log count and a timestamp 163indicating the time of the last match. 164Counters can be displayed or reset with 165.Nm 166commands. 167.Pp 168Rules can be added with the 169.Cm add 170command; deleted individually or in groups with the 171.Cm delete 172command, and globally (except those in set 31) with the 173.Cm flush 174command; displayed, optionally with the content of the 175counters, using the 176.Cm show 177and 178.Cm list 179commands. 180Finally, counters can be reset with the 181.Cm zero 182and 183.Cm resetlog 184commands. 185.Pp 186Also, each rule belongs to one of 32 different 187.Em sets 188, and there are 189.Nm 190commands to atomically manipulate sets, such as enable, 191disable, swap sets, move all rules in a set to another 192one, delete all rules in a set. 193These can be useful to 194install temporary configurations, or to test them. 195See Section 196.Sx SETS OF RULES 197for more information on 198.Em sets . 199.Pp 200The following options are available: 201.Bl -tag -width indent 202.It Fl a 203While listing, show counter values. 204The 205.Cm show 206command just implies this option. 207.It Fl b 208Only show the action and the comment, not the body of a rule. 209Implies 210.Fl c . 211.It Fl c 212When entering or showing rules, print them in compact form, 213i.e., without the optional "ip from any to any" string 214when this does not carry any additional information. 215.It Fl d 216While listing, show dynamic rules in addition to static ones. 217.It Fl e 218While listing, if the 219.Fl d 220option was specified, also show expired dynamic rules. 221.It Fl f 222Do not ask for confirmation for commands that can cause problems 223if misused, 224.No i.e. Cm flush . 225If there is no tty associated with the process, this is implied. 226.It Fl i 227While listing a table (see the 228.Sx LOOKUP TABLES 229section below for more information on lookup tables), format values 230as IP addresses. By default, values are shown as integers. 231.It Fl n 232Only check syntax of the command strings, without actually passing 233them to the kernel. 234.It Fl N 235Try to resolve addresses and service names in output. 236.It Fl q 237While 238.Cm add Ns ing , 239.Cm nat Ns ing , 240.Cm zero Ns ing , 241.Cm resetlog Ns ging 242or 243.Cm flush Ns ing , 244be quiet about actions 245(implies 246.Fl f ) . 247This is useful for adjusting rules by executing multiple 248.Nm 249commands in a script 250(e.g., 251.Ql sh\ /etc/rc.firewall ) , 252or by processing a file of many 253.Nm 254rules across a remote login session. 255It also stops a table add or delete 256from failing if the entry already exists or is not present. 257If a 258.Cm flush 259is performed in normal (verbose) mode (with the default kernel 260configuration), it prints a message. 261Because all rules are flushed, the message might not be delivered 262to the login session, causing the remote login session to be closed 263and the remainder of the ruleset to not be processed. 264Access to the console would then be required to recover. 265.It Fl S 266While listing rules, show the 267.Em set 268each rule belongs to. 269If this flag is not specified, disabled rules will not be 270listed. 271.It Fl s Op Ar field 272While listing pipes, sort according to one of the four 273counters (total or current packets or bytes). 274.It Fl t 275While listing, show last match timestamp (converted with ctime()). 276.It Fl T 277While listing, show last match timestamp (as seconds from the epoch). 278This form can be more convenient for postprocessing by scripts. 279.El 280.Pp 281To ease configuration, rules can be put into a file which is 282processed using 283.Nm 284as shown in the last synopsis line. 285An absolute 286.Ar pathname 287must be used. 288The file will be read line by line and applied as arguments to the 289.Nm 290utility. 291.Pp 292Optionally, a preprocessor can be specified using 293.Fl p Ar preproc 294where 295.Ar pathname 296is to be piped through. 297Useful preprocessors include 298.Xr cpp 1 299and 300.Xr m4 1 . 301If 302.Ar preproc 303does not start with a slash 304.Pq Ql / 305as its first character, the usual 306.Ev PATH 307name search is performed. 308Care should be taken with this in environments where not all 309file systems are mounted (yet) by the time 310.Nm 311is being run (e.g.\& when they are mounted over NFS). 312Once 313.Fl p 314has been specified, any additional arguments as passed on to the preprocessor 315for interpretation. 316This allows for flexible configuration files (like conditionalizing 317them on the local hostname) and the use of macros to centralize 318frequently required arguments like IP addresses. 319.Pp 320The 321.Nm 322.Cm pipe 323and 324.Cm queue 325commands are used to configure the traffic shaper, as shown in the 326.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 327Section below. 328.Pp 329If the world and the kernel get out of sync the 330.Nm 331ABI may break, preventing you from being able to add any rules. 332This can 333adversely effect the booting process. 334You can use 335.Nm 336.Cm disable 337.Cm firewall 338to temporarily disable the firewall to regain access to the network, 339allowing you to fix the problem. 340.Sh PACKET FLOW 341A packet is checked against the active ruleset in multiple places 342in the protocol stack, under control of several sysctl variables. 343These places and variables are shown below, and it is important to 344have this picture in mind in order to design a correct ruleset. 345.Bd -literal -offset indent 346 ^ to upper layers V 347 | | 348 +----------->-----------+ 349 ^ V 350 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1 351 | | 352 ^ V 353 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 354 | | 355 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1 356 ^ V 357 | to devices | 358.Ed 359.Pp 360As can be noted from the above picture, the number of 361times the same packet goes through the firewall can 362vary between 0 and 4 depending on packet source and 363destination, and system configuration. 364.Pp 365Note that as packets flow through the stack, headers can be 366stripped or added to it, and so they may or may not be available 367for inspection. 368E.g., incoming packets will include the MAC header when 369.Nm 370is invoked from 371.Cm ether_demux() , 372but the same packets will have the MAC header stripped off when 373.Nm 374is invoked from 375.Cm ip_input() 376or 377.Cm ip6_input() . 378.Pp 379Also note that each packet is always checked against the complete ruleset, 380irrespective of the place where the check occurs, or the source of the packet. 381If a rule contains some match patterns or actions which are not valid 382for the place of invocation (e.g.\& trying to match a MAC header within 383.Cm ip_input 384or 385.Cm ip6_input ), 386the match pattern will not match, but a 387.Cm not 388operator in front of such patterns 389.Em will 390cause the pattern to 391.Em always 392match on those packets. 393It is thus the responsibility of 394the programmer, if necessary, to write a suitable ruleset to 395differentiate among the possible places. 396.Cm skipto 397rules can be useful here, as an example: 398.Bd -literal -offset indent 399# packets from ether_demux or bdg_forward 400ipfw add 10 skipto 1000 all from any to any layer2 in 401# packets from ip_input 402ipfw add 10 skipto 2000 all from any to any not layer2 in 403# packets from ip_output 404ipfw add 10 skipto 3000 all from any to any not layer2 out 405# packets from ether_output_frame 406ipfw add 10 skipto 4000 all from any to any layer2 out 407.Ed 408.Pp 409(yes, at the moment there is no way to differentiate between 410ether_demux and bdg_forward). 411.Sh SYNTAX 412In general, each keyword or argument must be provided as 413a separate command line argument, with no leading or trailing 414spaces. 415Keywords are case-sensitive, whereas arguments may 416or may not be case-sensitive depending on their nature 417(e.g.\& uid's are, hostnames are not). 418.Pp 419In 420.Nm ipfw2 421you can introduce spaces after commas ',' to make 422the line more readable. 423You can also put the entire 424command (including flags) into a single argument. 425E.g., the following forms are equivalent: 426.Bd -literal -offset indent 427ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 428ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 429ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" 430.Ed 431.Sh RULE FORMAT 432The format of 433.Nm 434rules is the following: 435.Bd -ragged -offset indent 436.Bk -words 437.Op Ar rule_number 438.Op Cm set Ar set_number 439.Op Cm prob Ar match_probability 440.Ar action 441.Op Cm log Op Cm logamount Ar number 442.Op Cm altq Ar queue 443.Oo 444.Bro Cm tag | untag 445.Brc Ar number 446.Oc 447.Ar body 448.Ek 449.Ed 450.Pp 451where the body of the rule specifies which information is used 452for filtering packets, among the following: 453.Pp 454.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact 455.It Layer-2 header fields 456When available 457.It IPv4 and IPv6 Protocol 458TCP, UDP, ICMP, etc. 459.It Source and dest. addresses and ports 460.It Direction 461See Section 462.Sx PACKET FLOW 463.It Transmit and receive interface 464By name or address 465.It Misc. IP header fields 466Version, type of service, datagram length, identification, 467fragment flag (non-zero IP offset), 468Time To Live 469.It IP options 470.It IPv6 Extension headers 471Fragmentation, Hop-by-Hop options, 472Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options. 473.It IPv6 Flow-ID 474.It Misc. TCP header fields 475TCP flags (SYN, FIN, ACK, RST, etc.), 476sequence number, acknowledgment number, 477window 478.It TCP options 479.It ICMP types 480for ICMP packets 481.It ICMP6 types 482for ICMP6 packets 483.It User/group ID 484When the packet can be associated with a local socket. 485.It Divert status 486Whether a packet came from a divert socket (e.g., 487.Xr natd 8 ) . 488.It Fib annotation state 489Whether a packet has been tagged for using a specific FIB (routing table) 490in future forwarding decisions. 491.El 492.Pp 493Note that some of the above information, e.g.\& source MAC or IP addresses and 494TCP/UDP ports, could easily be spoofed, so filtering on those fields 495alone might not guarantee the desired results. 496.Bl -tag -width indent 497.It Ar rule_number 498Each rule is associated with a 499.Ar rule_number 500in the range 1..65535, with the latter reserved for the 501.Em default 502rule. 503Rules are checked sequentially by rule number. 504Multiple rules can have the same number, in which case they are 505checked (and listed) according to the order in which they have 506been added. 507If a rule is entered without specifying a number, the kernel will 508assign one in such a way that the rule becomes the last one 509before the 510.Em default 511rule. 512Automatic rule numbers are assigned by incrementing the last 513non-default rule number by the value of the sysctl variable 514.Ar net.inet.ip.fw.autoinc_step 515which defaults to 100. 516If this is not possible (e.g.\& because we would go beyond the 517maximum allowed rule number), the number of the last 518non-default value is used instead. 519.It Cm set Ar set_number 520Each rule is associated with a 521.Ar set_number 522in the range 0..31. 523Sets can be individually disabled and enabled, so this parameter 524is of fundamental importance for atomic ruleset manipulation. 525It can be also used to simplify deletion of groups of rules. 526If a rule is entered without specifying a set number, 527set 0 will be used. 528.br 529Set 31 is special in that it cannot be disabled, 530and rules in set 31 are not deleted by the 531.Nm ipfw flush 532command (but you can delete them with the 533.Nm ipfw delete set 31 534command). 535Set 31 is also used for the 536.Em default 537rule. 538.It Cm prob Ar match_probability 539A match is only declared with the specified probability 540(floating point number between 0 and 1). 541This can be useful for a number of applications such as 542random packet drop or 543(in conjunction with 544.Nm dummynet ) 545to simulate the effect of multiple paths leading to out-of-order 546packet delivery. 547.Pp 548Note: this condition is checked before any other condition, including 549ones such as keep-state or check-state which might have side effects. 550.It Cm log Op Cm logamount Ar number 551When a packet matches a rule with the 552.Cm log 553keyword, a message will be 554logged to 555.Xr syslogd 8 556with a 557.Dv LOG_SECURITY 558facility. 559The logging only occurs if the sysctl variable 560.Va net.inet.ip.fw.verbose 561is set to 1 562(which is the default when the kernel is compiled with 563.Dv IPFIREWALL_VERBOSE ) 564and the number of packets logged so far for that 565particular rule does not exceed the 566.Cm logamount 567parameter. 568If no 569.Cm logamount 570is specified, the limit is taken from the sysctl variable 571.Va net.inet.ip.fw.verbose_limit . 572In both cases, a value of 0 removes the logging limit. 573.Pp 574Once the limit is reached, logging can be re-enabled by 575clearing the logging counter or the packet counter for that entry, see the 576.Cm resetlog 577command. 578.Pp 579Note: logging is done after all other packet matching conditions 580have been successfully verified, and before performing the final 581action (accept, deny, etc.) on the packet. 582.It Cm tag Ar number 583When a packet matches a rule with the 584.Cm tag 585keyword, the numeric tag for the given 586.Ar number 587in the range 1..65534 will be attached to the packet. 588The tag acts as an internal marker (it is not sent out over 589the wire) that can be used to identify these packets later on. 590This can be used, for example, to provide trust between interfaces 591and to start doing policy-based filtering. 592A packet can have mutiple tags at the same time. 593Tags are "sticky", meaning once a tag is applied to a packet by a 594matching rule it exists until explicit removal. 595Tags are kept with the packet everywhere within the kernel, but are 596lost when packet leaves the kernel, for example, on transmitting 597packet out to the network or sending packet to a 598.Xr divert 4 599socket. 600.Pp 601To check for previously applied tags, use the 602.Cm tagged 603rule option. 604To delete previously applied tag, use the 605.Cm untag 606keyword. 607.Pp 608Note: since tags are kept with the packet everywhere in kernelspace, 609they can be set and unset anywhere in kernel network subsystem 610(using 611.Xr mbuf_tags 9 612facility), not only by means of 613.Xr ipfw 4 614.Cm tag 615and 616.Cm untag 617keywords. 618For example, there can be a specialized 619.Xr netgraph 4 620node doing traffic analyzing and tagging for later inspecting 621in firewall. 622.It Cm untag Ar number 623When a packet matches a rule with the 624.Cm untag 625keyword, the tag with the number 626.Ar number 627is searched among the tags attached to this packet and, 628if found, removed from it. 629Other tags bound to packet, if present, are left untouched. 630.It Cm altq Ar queue 631When a packet matches a rule with the 632.Cm altq 633keyword, the ALTQ identifier for the given 634.Ar queue 635(see 636.Xr altq 4 ) 637will be attached. 638Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, 639and not being rejected or going to divert sockets. 640Note that if there is insufficient memory at the time the packet is 641processed, it will not be tagged, so it is wise to make your ALTQ 642"default" queue policy account for this. 643If multiple 644.Cm altq 645rules match a single packet, only the first one adds the ALTQ classification 646tag. 647In doing so, traffic may be shaped by using 648.Cm count Cm altq Ar queue 649rules for classification early in the ruleset, then later applying 650the filtering decision. 651For example, 652.Cm check-state 653and 654.Cm keep-state 655rules may come later and provide the actual filtering decisions in 656addition to the fallback ALTQ tag. 657.Pp 658You must run 659.Xr pfctl 8 660to set up the queues before IPFW will be able to look them up by name, 661and if the ALTQ disciplines are rearranged, the rules in containing the 662queue identifiers in the kernel will likely have gone stale and need 663to be reloaded. 664Stale queue identifiers will probably result in misclassification. 665.Pp 666All system ALTQ processing can be turned on or off via 667.Nm 668.Cm enable Ar altq 669and 670.Nm 671.Cm disable Ar altq . 672The usage of 673.Va net.inet.ip.fw.one_pass 674is irrelevant to ALTQ traffic shaping, as the actual rule action is followed 675always after adding an ALTQ tag. 676.El 677.Ss RULE ACTIONS 678A rule can be associated with one of the following actions, which 679will be executed when the packet matches the body of the rule. 680.Bl -tag -width indent 681.It Cm allow | accept | pass | permit 682Allow packets that match rule. 683The search terminates. 684.It Cm check-state 685Checks the packet against the dynamic ruleset. 686If a match is found, execute the action associated with 687the rule which generated this dynamic rule, otherwise 688move to the next rule. 689.br 690.Cm Check-state 691rules do not have a body. 692If no 693.Cm check-state 694rule is found, the dynamic ruleset is checked at the first 695.Cm keep-state 696or 697.Cm limit 698rule. 699.It Cm count 700Update counters for all packets that match rule. 701The search continues with the next rule. 702.It Cm deny | drop 703Discard packets that match this rule. 704The search terminates. 705.It Cm divert Ar port 706Divert packets that match this rule to the 707.Xr divert 4 708socket bound to port 709.Ar port . 710The search terminates. 711.It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port 712Change the next-hop on matching packets to 713.Ar ipaddr , 714which can be an IP address or a host name. 715The next hop can also be supplied by the last table 716looked up for the packet by using the 717.Cm tablearg 718keyword instead of an explicit address. 719The search terminates if this rule matches. 720.Pp 721If 722.Ar ipaddr 723is a local address, then matching packets will be forwarded to 724.Ar port 725(or the port number in the packet if one is not specified in the rule) 726on the local machine. 727.br 728If 729.Ar ipaddr 730is not a local address, then the port number 731(if specified) is ignored, and the packet will be 732forwarded to the remote address, using the route as found in 733the local routing table for that IP. 734.br 735A 736.Ar fwd 737rule will not match layer-2 packets (those received 738on ether_input, ether_output, or bridged). 739.br 740The 741.Cm fwd 742action does not change the contents of the packet at all. 743In particular, the destination address remains unmodified, so 744packets forwarded to another system will usually be rejected by that system 745unless there is a matching rule on that system to capture them. 746For packets forwarded locally, 747the local address of the socket will be 748set to the original destination address of the packet. 749This makes the 750.Xr netstat 1 751entry look rather weird but is intended for 752use with transparent proxy servers. 753.Pp 754To enable 755.Cm fwd 756a custom kernel needs to be compiled with the option 757.Cd "options IPFIREWALL_FORWARD" . 758.It Cm nat Ar nat_nr 759Pass packet to a 760nat instance 761(for network address translation, address redirect, etc.): 762see the 763.Sx NETWORK ADDRESS TRANSLATION (NAT) 764Section for further information. 765.It Cm pipe Ar pipe_nr 766Pass packet to a 767.Nm dummynet 768.Dq pipe 769(for bandwidth limitation, delay, etc.). 770See the 771.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 772Section for further information. 773The search terminates; however, on exit from the pipe and if 774the 775.Xr sysctl 8 776variable 777.Va net.inet.ip.fw.one_pass 778is not set, the packet is passed again to the firewall code 779starting from the next rule. 780.It Cm queue Ar queue_nr 781Pass packet to a 782.Nm dummynet 783.Dq queue 784(for bandwidth limitation using WF2Q+). 785.It Cm reject 786(Deprecated). 787Synonym for 788.Cm unreach host . 789.It Cm reset 790Discard packets that match this rule, and if the 791packet is a TCP packet, try to send a TCP reset (RST) notice. 792The search terminates. 793.It Cm reset6 794Discard packets that match this rule, and if the 795packet is a TCP packet, try to send a TCP reset (RST) notice. 796The search terminates. 797.It Cm skipto Ar number | tablearg 798Skip all subsequent rules numbered less than 799.Ar number . 800The search continues with the first rule numbered 801.Ar number 802or higher. 803It is possible to use the 804.Cm tablearg 805keyword with a skipto for a 806.Em computed 807skipto, but care should be used, as no destination caching 808is possible in this case so the rules are always walked to find it, 809starting from the 810.Cm skipto . 811.It Cm tee Ar port 812Send a copy of packets matching this rule to the 813.Xr divert 4 814socket bound to port 815.Ar port . 816The search continues with the next rule. 817.It Cm unreach Ar code 818Discard packets that match this rule, and try to send an ICMP 819unreachable notice with code 820.Ar code , 821where 822.Ar code 823is a number from 0 to 255, or one of these aliases: 824.Cm net , host , protocol , port , 825.Cm needfrag , srcfail , net-unknown , host-unknown , 826.Cm isolated , net-prohib , host-prohib , tosnet , 827.Cm toshost , filter-prohib , host-precedence 828or 829.Cm precedence-cutoff . 830The search terminates. 831.It Cm unreach6 Ar code 832Discard packets that match this rule, and try to send an ICMPv6 833unreachable notice with code 834.Ar code , 835where 836.Ar code 837is a number from 0, 1, 3 or 4, or one of these aliases: 838.Cm no-route, admin-prohib, address 839or 840.Cm port . 841The search terminates. 842.It Cm netgraph Ar cookie 843Divert packet into netgraph with given 844.Ar cookie . 845The search terminates. 846If packet is later returned from netgraph it is either 847accepted or continues with the next rule, depending on 848.Va net.inet.ip.fw.one_pass 849sysctl variable. 850.It Cm ngtee Ar cookie 851A copy of packet is diverted into netgraph, original 852packet is either accepted or continues with the next rule, depending on 853.Va net.inet.ip.fw.one_pass 854sysctl variable. 855See 856.Xr ng_ipfw 4 857for more information on 858.Cm netgraph 859and 860.Cm ngtee 861actions. 862.It Cm setfib Ar fibnum 863The packet is tagged so as to use the FIB (routing table) 864.Ar fibnum 865in any subsequent forwarding decisions. Initially this is 866limited to the values 0 through 15. See 867.Xr setfib 8 . 868Processing continues at the next rule. 869.El 870.Ss RULE BODY 871The body of a rule contains zero or more patterns (such as 872specific source and destination addresses or ports, 873protocol options, incoming or outgoing interfaces, etc.) 874that the packet must match in order to be recognised. 875In general, the patterns are connected by (implicit) 876.Cm and 877operators -- i.e., all must match in order for the 878rule to match. 879Individual patterns can be prefixed by the 880.Cm not 881operator to reverse the result of the match, as in 882.Pp 883.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any" 884.Pp 885Additionally, sets of alternative match patterns 886.Pq Em or-blocks 887can be constructed by putting the patterns in 888lists enclosed between parentheses ( ) or braces { }, and 889using the 890.Cm or 891operator as follows: 892.Pp 893.Dl "ipfw add 100 allow ip from { x or not y or z } to any" 894.Pp 895Only one level of parentheses is allowed. 896Beware that most shells have special meanings for parentheses 897or braces, so it is advisable to put a backslash \\ in front of them 898to prevent such interpretations. 899.Pp 900The body of a rule must in general include a source and destination 901address specifier. 902The keyword 903.Ar any 904can be used in various places to specify that the content of 905a required field is irrelevant. 906.Pp 907The rule body has the following format: 908.Bd -ragged -offset indent 909.Op Ar proto Cm from Ar src Cm to Ar dst 910.Op Ar options 911.Ed 912.Pp 913The first part (proto from src to dst) is for backward 914compatibility with earlier versions of 915.Fx . 916In modern 917.Fx 918any match pattern (including MAC headers, IP protocols, 919addresses and ports) can be specified in the 920.Ar options 921section. 922.Pp 923Rule fields have the following meaning: 924.Bl -tag -width indent 925.It Ar proto : protocol | Cm { Ar protocol Cm or ... } 926.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number 927An IP protocol specified by number or name 928(for a complete list see 929.Pa /etc/protocols ) , 930or one of the following keywords: 931.Bl -tag -width indent 932.It Cm ip4 | ipv4 933Matches IPv4 packets. 934.It Cm ip6 | ipv6 935Matches IPv6 packets. 936.It Cm ip | all 937Matches any packet. 938.El 939.Pp 940The 941.Cm ipv6 942in 943.Cm proto 944option will be treated as inner protocol. 945And, the 946.Cm ipv4 947is not available in 948.Cm proto 949option. 950.Pp 951The 952.Cm { Ar protocol Cm or ... } 953format (an 954.Em or-block ) 955is provided for convenience only but its use is deprecated. 956.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports 957An address (or a list, see below) 958optionally followed by 959.Ar ports 960specifiers. 961.Pp 962The second format 963.Em ( or-block 964with multiple addresses) is provided for convenience only and 965its use is discouraged. 966.It Ar addr : Oo Cm not Oc Bro 967.Cm any | me | me6 | 968.Cm table Ns Pq Ar number Ns Op , Ns Ar value 969.Ar | addr-list | addr-set 970.Brc 971.It Cm any 972matches any IP address. 973.It Cm me 974matches any IP address configured on an interface in the system. 975.It Cm me6 976matches any IPv6 address configured on an interface in the system. 977The address list is evaluated at the time the packet is 978analysed. 979.It Cm table Ns Pq Ar number Ns Op , Ns Ar value 980Matches any IPv4 address for which an entry exists in the lookup table 981.Ar number . 982If an optional 32-bit unsigned 983.Ar value 984is also specified, an entry will match only if it has this value. 985See the 986.Sx LOOKUP TABLES 987section below for more information on lookup tables. 988.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list 989.It Ar ip-addr : 990A host or subnet address specified in one of the following ways: 991.Bl -tag -width indent 992.It Ar numeric-ip | hostname 993Matches a single IPv4 address, specified as dotted-quad or a hostname. 994Hostnames are resolved at the time the rule is added to the firewall list. 995.It Ar addr Ns / Ns Ar masklen 996Matches all addresses with base 997.Ar addr 998(specified as an IP address, a network number, or a hostname) 999and mask width of 1000.Cm masklen 1001bits. 1002As an example, 1.2.3.4/25 or 1.2.3.0/25 will match 1003all IP numbers from 1.2.3.0 to 1.2.3.127 . 1004.It Ar addr Ns : Ns Ar mask 1005Matches all addresses with base 1006.Ar addr 1007(specified as an IP address, a network number, or a hostname) 1008and the mask of 1009.Ar mask , 1010specified as a dotted quad. 1011As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 10121.*.3.*. 1013This form is advised only for non-contiguous 1014masks. 1015It is better to resort to the 1016.Ar addr Ns / Ns Ar masklen 1017format for contiguous masks, which is more compact and less 1018error-prone. 1019.El 1020.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm } 1021.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list 1022Matches all addresses with base address 1023.Ar addr 1024(specified as an IP address, a network number, or a hostname) 1025and whose last byte is in the list between braces { } . 1026Note that there must be no spaces between braces and 1027numbers (spaces after commas are allowed). 1028Elements of the list can be specified as single entries 1029or ranges. 1030The 1031.Ar masklen 1032field is used to limit the size of the set of addresses, 1033and can have any value between 24 and 32. 1034If not specified, 1035it will be assumed as 24. 1036.br 1037This format is particularly useful to handle sparse address sets 1038within a single rule. 1039Because the matching occurs using a 1040bitmask, it takes constant time and dramatically reduces 1041the complexity of rulesets. 1042.br 1043As an example, an address specified as 1.2.3.4/24{128,35-55,89} 1044or 1.2.3.0/24{128,35-55,89} 1045will match the following IP addresses: 1046.br 10471.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . 1048.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list 1049.It Ar ip6-addr : 1050A host or subnet specified one of the following ways: 1051.Pp 1052.Bl -tag -width indent 1053.It Ar numeric-ip | hostname 1054Matches a single IPv6 address as allowed by 1055.Xr inet_pton 3 1056or a hostname. 1057Hostnames are resolved at the time the rule is added to the firewall 1058list. 1059.It Ar addr Ns / Ns Ar masklen 1060Matches all IPv6 addresses with base 1061.Ar addr 1062(specified as allowed by 1063.Xr inet_pton 1064or a hostname) 1065and mask width of 1066.Cm masklen 1067bits. 1068.El 1069.Pp 1070No support for sets of IPv6 addresses is provided because IPv6 addresses 1071are typically random past the initial prefix. 1072.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports 1073For protocols which support port numbers (such as TCP and UDP), optional 1074.Cm ports 1075may be specified as one or more ports or port ranges, separated 1076by commas but no spaces, and an optional 1077.Cm not 1078operator. 1079The 1080.Ql \&- 1081notation specifies a range of ports (including boundaries). 1082.Pp 1083Service names (from 1084.Pa /etc/services ) 1085may be used instead of numeric port values. 1086The length of the port list is limited to 30 ports or ranges, 1087though one can specify larger ranges by using an 1088.Em or-block 1089in the 1090.Cm options 1091section of the rule. 1092.Pp 1093A backslash 1094.Pq Ql \e 1095can be used to escape the dash 1096.Pq Ql - 1097character in a service name (from a shell, the backslash must be 1098typed twice to avoid the shell itself interpreting it as an escape 1099character). 1100.Pp 1101.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any" 1102.Pp 1103Fragmented packets which have a non-zero offset (i.e., not the first 1104fragment) will never match a rule which has one or more port 1105specifications. 1106See the 1107.Cm frag 1108option for details on matching fragmented packets. 1109.El 1110.Ss RULE OPTIONS (MATCH PATTERNS) 1111Additional match patterns can be used within 1112rules. 1113Zero or more of these so-called 1114.Em options 1115can be present in a rule, optionally prefixed by the 1116.Cm not 1117operand, and possibly grouped into 1118.Em or-blocks . 1119.Pp 1120The following match patterns can be used (listed in alphabetical order): 1121.Bl -tag -width indent 1122.It Cm // this is a comment. 1123Inserts the specified text as a comment in the rule. 1124Everything following // is considered as a comment and stored in the rule. 1125You can have comment-only rules, which are listed as having a 1126.Cm count 1127action followed by the comment. 1128.It Cm bridged 1129Alias for 1130.Cm layer2 . 1131.It Cm diverted 1132Matches only packets generated by a divert socket. 1133.It Cm diverted-loopback 1134Matches only packets coming from a divert socket back into the IP stack 1135input for delivery. 1136.It Cm diverted-output 1137Matches only packets going from a divert socket back outward to the IP 1138stack output for delivery. 1139.It Cm dst-ip Ar ip-address 1140Matches IPv4 packets whose destination IP is one of the address(es) 1141specified as argument. 1142.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address 1143Matches IPv6 packets whose destination IP is one of the address(es) 1144specified as argument. 1145.It Cm dst-port Ar ports 1146Matches IP packets whose destination port is one of the port(s) 1147specified as argument. 1148.It Cm established 1149Matches TCP packets that have the RST or ACK bits set. 1150.It Cm ext6hdr Ar header 1151Matches IPv6 packets containing the extended header given by 1152.Ar header . 1153Supported headers are: 1154.Pp 1155Fragment, 1156.Pq Cm frag , 1157Hop-to-hop options 1158.Pq Cm hopopt , 1159any type of Routing Header 1160.Pq Cm route , 1161Source routing Routing Header Type 0 1162.Pq Cm rthdr0 , 1163Mobile IPv6 Routing Header Type 2 1164.Pq Cm rthdr2 , 1165Destination options 1166.Pq Cm dstopt , 1167IPSec authentication headers 1168.Pq Cm ah , 1169and IPSec encapsulated security payload headers 1170.Pq Cm esp . 1171.It Cm fib Ar fibnum 1172Matches a packet that has been tagged to use 1173the given FIB (routing table) number. 1174.It Cm flow-id Ar labels 1175Matches IPv6 packets containing any of the flow labels given in 1176.Ar labels . 1177.Ar labels 1178is a comma seperate list of numeric flow labels. 1179.It Cm frag 1180Matches packets that are fragments and not the first 1181fragment of an IP datagram. 1182Note that these packets will not have 1183the next protocol header (e.g.\& TCP, UDP) so options that look into 1184these headers cannot match. 1185.It Cm gid Ar group 1186Matches all TCP or UDP packets sent by or received for a 1187.Ar group . 1188A 1189.Ar group 1190may be specified by name or number. 1191.It Cm jail Ar prisonID 1192Matches all TCP or UDP packets sent by or received for the 1193jail whos prison ID is 1194.Ar prisonID . 1195.It Cm icmptypes Ar types 1196Matches ICMP packets whose ICMP type is in the list 1197.Ar types . 1198The list may be specified as any combination of 1199individual types (numeric) separated by commas. 1200.Em Ranges are not allowed . 1201The supported ICMP types are: 1202.Pp 1203echo reply 1204.Pq Cm 0 , 1205destination unreachable 1206.Pq Cm 3 , 1207source quench 1208.Pq Cm 4 , 1209redirect 1210.Pq Cm 5 , 1211echo request 1212.Pq Cm 8 , 1213router advertisement 1214.Pq Cm 9 , 1215router solicitation 1216.Pq Cm 10 , 1217time-to-live exceeded 1218.Pq Cm 11 , 1219IP header bad 1220.Pq Cm 12 , 1221timestamp request 1222.Pq Cm 13 , 1223timestamp reply 1224.Pq Cm 14 , 1225information request 1226.Pq Cm 15 , 1227information reply 1228.Pq Cm 16 , 1229address mask request 1230.Pq Cm 17 1231and address mask reply 1232.Pq Cm 18 . 1233.It Cm icmp6types Ar types 1234Matches ICMP6 packets whose ICMP6 type is in the list of 1235.Ar types . 1236The list may be specified as any combination of 1237individual types (numeric) separated by commas. 1238.Em Ranges are not allowed . 1239.It Cm in | out 1240Matches incoming or outgoing packets, respectively. 1241.Cm in 1242and 1243.Cm out 1244are mutually exclusive (in fact, 1245.Cm out 1246is implemented as 1247.Cm not in Ns No ). 1248.It Cm ipid Ar id-list 1249Matches IPv4 packets whose 1250.Cm ip_id 1251field has value included in 1252.Ar id-list , 1253which is either a single value or a list of values or ranges 1254specified in the same way as 1255.Ar ports . 1256.It Cm iplen Ar len-list 1257Matches IP packets whose total length, including header and data, is 1258in the set 1259.Ar len-list , 1260which is either a single value or a list of values or ranges 1261specified in the same way as 1262.Ar ports . 1263.It Cm ipoptions Ar spec 1264Matches packets whose IPv4 header contains the comma separated list of 1265options specified in 1266.Ar spec . 1267The supported IP options are: 1268.Pp 1269.Cm ssrr 1270(strict source route), 1271.Cm lsrr 1272(loose source route), 1273.Cm rr 1274(record packet route) and 1275.Cm ts 1276(timestamp). 1277The absence of a particular option may be denoted 1278with a 1279.Ql \&! . 1280.It Cm ipprecedence Ar precedence 1281Matches IPv4 packets whose precedence field is equal to 1282.Ar precedence . 1283.It Cm ipsec 1284Matches packets that have IPSEC history associated with them 1285(i.e., the packet comes encapsulated in IPSEC, the kernel 1286has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly 1287decapsulate it). 1288.Pp 1289Note that specifying 1290.Cm ipsec 1291is different from specifying 1292.Cm proto Ar ipsec 1293as the latter will only look at the specific IP protocol field, 1294irrespective of IPSEC kernel support and the validity of the IPSEC data. 1295.Pp 1296Further note that this flag is silently ignored in kernels without 1297IPSEC support. 1298It does not affect rule processing when given and the 1299rules are handled as if with no 1300.Cm ipsec 1301flag. 1302.It Cm iptos Ar spec 1303Matches IPv4 packets whose 1304.Cm tos 1305field contains the comma separated list of 1306service types specified in 1307.Ar spec . 1308The supported IP types of service are: 1309.Pp 1310.Cm lowdelay 1311.Pq Dv IPTOS_LOWDELAY , 1312.Cm throughput 1313.Pq Dv IPTOS_THROUGHPUT , 1314.Cm reliability 1315.Pq Dv IPTOS_RELIABILITY , 1316.Cm mincost 1317.Pq Dv IPTOS_MINCOST , 1318.Cm congestion 1319.Pq Dv IPTOS_ECN_CE . 1320The absence of a particular type may be denoted 1321with a 1322.Ql \&! . 1323.It Cm ipttl Ar ttl-list 1324Matches IPv4 packets whose time to live is included in 1325.Ar ttl-list , 1326which is either a single value or a list of values or ranges 1327specified in the same way as 1328.Ar ports . 1329.It Cm ipversion Ar ver 1330Matches IP packets whose IP version field is 1331.Ar ver . 1332.It Cm keep-state 1333Upon a match, the firewall will create a dynamic rule, whose 1334default behaviour is to match bidirectional traffic between 1335source and destination IP/port using the same protocol. 1336The rule has a limited lifetime (controlled by a set of 1337.Xr sysctl 8 1338variables), and the lifetime is refreshed every time a matching 1339packet is found. 1340.It Cm layer2 1341Matches only layer2 packets, i.e., those passed to 1342.Nm 1343from ether_demux() and ether_output_frame(). 1344.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N 1345The firewall will only allow 1346.Ar N 1347connections with the same 1348set of parameters as specified in the rule. 1349One or more 1350of source and destination addresses and ports can be 1351specified. 1352Currently, 1353only IPv4 flows are supported. 1354.It Cm { MAC | mac } Ar dst-mac src-mac 1355Match packets with a given 1356.Ar dst-mac 1357and 1358.Ar src-mac 1359addresses, specified as the 1360.Cm any 1361keyword (matching any MAC address), or six groups of hex digits 1362separated by colons, 1363and optionally followed by a mask indicating the significant bits. 1364The mask may be specified using either of the following methods: 1365.Bl -enum -width indent 1366.It 1367A slash 1368.Pq / 1369followed by the number of significant bits. 1370For example, an address with 33 significant bits could be specified as: 1371.Pp 1372.Dl "MAC 10:20:30:40:50:60/33 any" 1373.Pp 1374.It 1375An ampersand 1376.Pq & 1377followed by a bitmask specified as six groups of hex digits separated 1378by colons. 1379For example, an address in which the last 16 bits are significant could 1380be specified as: 1381.Pp 1382.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any" 1383.Pp 1384Note that the ampersand character has a special meaning in many shells 1385and should generally be escaped. 1386.Pp 1387.El 1388Note that the order of MAC addresses (destination first, 1389source second) is 1390the same as on the wire, but the opposite of the one used for 1391IP addresses. 1392.It Cm mac-type Ar mac-type 1393Matches packets whose Ethernet Type field 1394corresponds to one of those specified as argument. 1395.Ar mac-type 1396is specified in the same way as 1397.Cm port numbers 1398(i.e., one or more comma-separated single values or ranges). 1399You can use symbolic names for known values such as 1400.Em vlan , ipv4, ipv6 . 1401Values can be entered as decimal or hexadecimal (if prefixed by 0x), 1402and they are always printed as hexadecimal (unless the 1403.Cm -N 1404option is used, in which case symbolic resolution will be attempted). 1405.It Cm proto Ar protocol 1406Matches packets with the corresponding IP protocol. 1407.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any 1408Matches packets received, transmitted or going through, 1409respectively, the interface specified by exact name 1410.Ns No ( Ar ifX Ns No ), 1411by device name 1412.Ns No ( Ar if Ns Ar * Ns No ), 1413by IP address, or through some interface. 1414.Pp 1415The 1416.Cm via 1417keyword causes the interface to always be checked. 1418If 1419.Cm recv 1420or 1421.Cm xmit 1422is used instead of 1423.Cm via , 1424then only the receive or transmit interface (respectively) 1425is checked. 1426By specifying both, it is possible to match packets based on 1427both receive and transmit interface, e.g.: 1428.Pp 1429.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1" 1430.Pp 1431The 1432.Cm recv 1433interface can be tested on either incoming or outgoing packets, 1434while the 1435.Cm xmit 1436interface can only be tested on outgoing packets. 1437So 1438.Cm out 1439is required (and 1440.Cm in 1441is invalid) whenever 1442.Cm xmit 1443is used. 1444.Pp 1445A packet may not have a receive or transmit interface: packets 1446originating from the local host have no receive interface, 1447while packets destined for the local host have no transmit 1448interface. 1449.It Cm setup 1450Matches TCP packets that have the SYN bit set but no ACK bit. 1451This is the short form of 1452.Dq Li tcpflags\ syn,!ack . 1453.It Cm src-ip Ar ip-address 1454Matches IPv4 packets whose source IP is one of the address(es) 1455specified as an argument. 1456.It Cm src-ip6 Ar ip6-address 1457Matches IPv6 packets whose source IP is one of the address(es) 1458specified as an argument. 1459.It Cm src-port Ar ports 1460Matches IP packets whose source port is one of the port(s) 1461specified as argument. 1462.It Cm tagged Ar tag-list 1463Matches packets whose tags are included in 1464.Ar tag-list , 1465which is either a single value or a list of values or ranges 1466specified in the same way as 1467.Ar ports . 1468Tags can be applied to the packet using 1469.Cm tag 1470rule action parameter (see it's description for details on tags). 1471.It Cm tcpack Ar ack 1472TCP packets only. 1473Match if the TCP header acknowledgment number field is set to 1474.Ar ack . 1475.It Cm tcpdatalen Ar tcpdatalen-list 1476Matches TCP packets whose length of TCP data is 1477.Ar tcpdatalen-list , 1478which is either a single value or a list of values or ranges 1479specified in the same way as 1480.Ar ports . 1481.It Cm tcpflags Ar spec 1482TCP packets only. 1483Match if the TCP header contains the comma separated list of 1484flags specified in 1485.Ar spec . 1486The supported TCP flags are: 1487.Pp 1488.Cm fin , 1489.Cm syn , 1490.Cm rst , 1491.Cm psh , 1492.Cm ack 1493and 1494.Cm urg . 1495The absence of a particular flag may be denoted 1496with a 1497.Ql \&! . 1498A rule which contains a 1499.Cm tcpflags 1500specification can never match a fragmented packet which has 1501a non-zero offset. 1502See the 1503.Cm frag 1504option for details on matching fragmented packets. 1505.It Cm tcpseq Ar seq 1506TCP packets only. 1507Match if the TCP header sequence number field is set to 1508.Ar seq . 1509.It Cm tcpwin Ar win 1510TCP packets only. 1511Match if the TCP header window field is set to 1512.Ar win . 1513.It Cm tcpoptions Ar spec 1514TCP packets only. 1515Match if the TCP header contains the comma separated list of 1516options specified in 1517.Ar spec . 1518The supported TCP options are: 1519.Pp 1520.Cm mss 1521(maximum segment size), 1522.Cm window 1523(tcp window advertisement), 1524.Cm sack 1525(selective ack), 1526.Cm ts 1527(rfc1323 timestamp) and 1528.Cm cc 1529(rfc1644 t/tcp connection count). 1530The absence of a particular option may be denoted 1531with a 1532.Ql \&! . 1533.It Cm uid Ar user 1534Match all TCP or UDP packets sent by or received for a 1535.Ar user . 1536A 1537.Ar user 1538may be matched by name or identification number. 1539.It Cm verrevpath 1540For incoming packets, 1541a routing table lookup is done on the packet's source address. 1542If the interface on which the packet entered the system matches the 1543outgoing interface for the route, 1544the packet matches. 1545If the interfaces do not match up, 1546the packet does not match. 1547All outgoing packets or packets with no incoming interface match. 1548.Pp 1549The name and functionality of the option is intentionally similar to 1550the Cisco IOS command: 1551.Pp 1552.Dl ip verify unicast reverse-path 1553.Pp 1554This option can be used to make anti-spoofing rules to reject all 1555packets with source addresses not from this interface. 1556See also the option 1557.Cm antispoof . 1558.It Cm versrcreach 1559For incoming packets, 1560a routing table lookup is done on the packet's source address. 1561If a route to the source address exists, but not the default route 1562or a blackhole/reject route, the packet matches. 1563Otherwise, the packet does not match. 1564All outgoing packets match. 1565.Pp 1566The name and functionality of the option is intentionally similar to 1567the Cisco IOS command: 1568.Pp 1569.Dl ip verify unicast source reachable-via any 1570.Pp 1571This option can be used to make anti-spoofing rules to reject all 1572packets whose source address is unreachable. 1573.It Cm antispoof 1574For incoming packets, the packet's source address is checked if it 1575belongs to a directly connected network. 1576If the network is directly connected, then the interface the packet 1577came on in is compared to the interface the network is connected to. 1578When incoming interface and directly connected interface are not the 1579same, the packet does not match. 1580Otherwise, the packet does match. 1581All outgoing packets match. 1582.Pp 1583This option can be used to make anti-spoofing rules to reject all 1584packets that pretend to be from a directly connected network but do 1585not come in through that interface. 1586This option is similar to but more restricted than 1587.Cm verrevpath 1588because it engages only on packets with source addresses of directly 1589connected networks instead of all source addresses. 1590.El 1591.Sh LOOKUP TABLES 1592Lookup tables are useful to handle large sparse address sets, 1593typically from a hundred to several thousands of entries. 1594There may be up to 128 different lookup tables, numbered 0 to 127. 1595.Pp 1596Each entry is represented by an 1597.Ar addr Ns Op / Ns Ar masklen 1598and will match all addresses with base 1599.Ar addr 1600(specified as an IP address or a hostname) 1601and mask width of 1602.Ar masklen 1603bits. 1604If 1605.Ar masklen 1606is not specified, it defaults to 32. 1607When looking up an IP address in a table, the most specific 1608entry will match. 1609Associated with each entry is a 32-bit unsigned 1610.Ar value , 1611which can optionally be checked by a rule matching code. 1612When adding an entry, if 1613.Ar value 1614is not specified, it defaults to 0. 1615.Pp 1616An entry can be added to a table 1617.Pq Cm add , 1618removed from a table 1619.Pq Cm delete , 1620a table can be examined 1621.Pq Cm list 1622or flushed 1623.Pq Cm flush . 1624.Pp 1625Internally, each table is stored in a Radix tree, the same way as 1626the routing table (see 1627.Xr route 4 ) . 1628.Pp 1629Lookup tables currently support IPv4 addresses only. 1630.Pp 1631The 1632.Cm tablearg 1633feature provides the ability to use a value, looked up in the table, as 1634the argument for a rule action, action parameter or rule option. 1635This can significantly reduce number of rules in some configurations. 1636If two tables are used in a rule, the result of the second (destination) 1637is used. 1638The 1639.Cm tablearg 1640argument can be used with the following actions: 1641.Cm nat, pipe , queue, divert, tee, netgraph, ngtee, fwd, skipto 1642action parameters: 1643.Cm tag, untag, 1644rule options: 1645.Cm limit, tagged. 1646.Pp 1647When used with 1648.Cm fwd 1649it is possible to supply table entries with values 1650that are in the form of IP addresses or hostnames. 1651See the 1652.Sx EXAMPLES 1653Section for example usage of tables and the tablearg keyword. 1654.Pp 1655When used with the 1656.Cm skipto 1657action, the user should be aware that the code will walk the ruleset 1658up to a rule equal to, or past, the given number, and should therefore try keep the 1659ruleset compact between the skipto and the target rules. 1660.Sh SETS OF RULES 1661Each rule belongs to one of 32 different 1662.Em sets 1663, numbered 0 to 31. 1664Set 31 is reserved for the default rule. 1665.Pp 1666By default, rules are put in set 0, unless you use the 1667.Cm set N 1668attribute when entering a new rule. 1669Sets can be individually and atomically enabled or disabled, 1670so this mechanism permits an easy way to store multiple configurations 1671of the firewall and quickly (and atomically) switch between them. 1672The command to enable/disable sets is 1673.Bd -ragged -offset indent 1674.Nm 1675.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 1676.Ed 1677.Pp 1678where multiple 1679.Cm enable 1680or 1681.Cm disable 1682sections can be specified. 1683Command execution is atomic on all the sets specified in the command. 1684By default, all sets are enabled. 1685.Pp 1686When you disable a set, its rules behave as if they do not exist 1687in the firewall configuration, with only one exception: 1688.Bd -ragged -offset indent 1689dynamic rules created from a rule before it had been disabled 1690will still be active until they expire. 1691In order to delete 1692dynamic rules you have to explicitly delete the parent rule 1693which generated them. 1694.Ed 1695.Pp 1696The set number of rules can be changed with the command 1697.Bd -ragged -offset indent 1698.Nm 1699.Cm set move 1700.Brq Cm rule Ar rule-number | old-set 1701.Cm to Ar new-set 1702.Ed 1703.Pp 1704Also, you can atomically swap two rulesets with the command 1705.Bd -ragged -offset indent 1706.Nm 1707.Cm set swap Ar first-set second-set 1708.Ed 1709.Pp 1710See the 1711.Sx EXAMPLES 1712Section on some possible uses of sets of rules. 1713.Sh STATEFUL FIREWALL 1714Stateful operation is a way for the firewall to dynamically 1715create rules for specific flows when packets that 1716match a given pattern are detected. 1717Support for stateful 1718operation comes through the 1719.Cm check-state , keep-state 1720and 1721.Cm limit 1722options of 1723.Nm rules . 1724.Pp 1725Dynamic rules are created when a packet matches a 1726.Cm keep-state 1727or 1728.Cm limit 1729rule, causing the creation of a 1730.Em dynamic 1731rule which will match all and only packets with 1732a given 1733.Em protocol 1734between a 1735.Em src-ip/src-port dst-ip/dst-port 1736pair of addresses 1737.Em ( src 1738and 1739.Em dst 1740are used here only to denote the initial match addresses, but they 1741are completely equivalent afterwards). 1742Dynamic rules will be checked at the first 1743.Cm check-state, keep-state 1744or 1745.Cm limit 1746occurrence, and the action performed upon a match will be the same 1747as in the parent rule. 1748.Pp 1749Note that no additional attributes other than protocol and IP addresses 1750and ports are checked on dynamic rules. 1751.Pp 1752The typical use of dynamic rules is to keep a closed firewall configuration, 1753but let the first TCP SYN packet from the inside network install a 1754dynamic rule for the flow so that packets belonging to that session 1755will be allowed through the firewall: 1756.Pp 1757.Dl "ipfw add check-state" 1758.Dl "ipfw add allow tcp from my-subnet to any setup keep-state" 1759.Dl "ipfw add deny tcp from any to any" 1760.Pp 1761A similar approach can be used for UDP, where an UDP packet coming 1762from the inside will install a dynamic rule to let the response through 1763the firewall: 1764.Pp 1765.Dl "ipfw add check-state" 1766.Dl "ipfw add allow udp from my-subnet to any keep-state" 1767.Dl "ipfw add deny udp from any to any" 1768.Pp 1769Dynamic rules expire after some time, which depends on the status 1770of the flow and the setting of some 1771.Cm sysctl 1772variables. 1773See Section 1774.Sx SYSCTL VARIABLES 1775for more details. 1776For TCP sessions, dynamic rules can be instructed to periodically 1777send keepalive packets to refresh the state of the rule when it is 1778about to expire. 1779.Pp 1780See Section 1781.Sx EXAMPLES 1782for more examples on how to use dynamic rules. 1783.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 1784.Nm 1785is also the user interface for the 1786.Nm dummynet 1787traffic shaper. 1788.Pp 1789.Nm dummynet 1790operates by first using the firewall to classify packets and divide them into 1791.Em flows , 1792using any match pattern that can be used in 1793.Nm 1794rules. 1795Depending on local policies, a flow can contain packets for a single 1796TCP connection, or from/to a given host, or entire subnet, or a 1797protocol type, etc. 1798.Pp 1799There are two modes of 1800.Nm dummynet 1801operation: 1802.Dq normal 1803and 1804.Dq fast . 1805The 1806.Dq normal 1807mode tries to emulate a real link: the 1808.Nm dummynet 1809scheduler ensures that the packet will not leave the pipe faster than it 1810would on the real link with a given bandwidth. 1811The 1812.Dq fast 1813mode allows certain packets to bypass the 1814.Nm dummynet 1815scheduler (if packet flow does not exceed pipe's bandwidth). 1816This is the reason why the 1817.Dq fast 1818mode requires less CPU cycles per packet (on average) and packet latency 1819can be significantly lower in comparison to a real link with the same 1820bandwidth. 1821The default mode is 1822.Dq normal . 1823The 1824.Dq fast 1825mode can be enabled by setting the 1826.Va net.inet.ip.dummynet.io_fast 1827.Xr sysctl 8 1828variable to a non-zero value. 1829.Pp 1830Packets belonging to the same flow are then passed to either of two 1831different objects, which implement the traffic regulation: 1832.Bl -hang -offset XXXX 1833.It Em pipe 1834A pipe emulates a link with given bandwidth, propagation delay, 1835queue size and packet loss rate. 1836Packets are queued in front of the pipe as they come out from the classifier, 1837and then transferred to the pipe according to the pipe's parameters. 1838.Pp 1839.It Em queue 1840A queue 1841is an abstraction used to implement the WF2Q+ 1842(Worst-case Fair Weighted Fair Queueing) policy, which is 1843an efficient variant of the WFQ policy. 1844.br 1845The queue associates a 1846.Em weight 1847and a reference pipe to each flow, and then all backlogged (i.e., 1848with packets queued) flows linked to the same pipe share the pipe's 1849bandwidth proportionally to their weights. 1850Note that weights are not priorities; a flow with a lower weight 1851is still guaranteed to get its fraction of the bandwidth even if a 1852flow with a higher weight is permanently backlogged. 1853.Pp 1854.El 1855In practice, 1856.Em pipes 1857can be used to set hard limits to the bandwidth that a flow can use, whereas 1858.Em queues 1859can be used to determine how different flows share the available bandwidth. 1860.Pp 1861The 1862.Em pipe 1863and 1864.Em queue 1865configuration commands are the following: 1866.Bd -ragged -offset indent 1867.Cm pipe Ar number Cm config Ar pipe-configuration 1868.Pp 1869.Cm queue Ar number Cm config Ar queue-configuration 1870.Ed 1871.Pp 1872The following parameters can be configured for a pipe: 1873.Pp 1874.Bl -tag -width indent -compact 1875.It Cm bw Ar bandwidth | device 1876Bandwidth, measured in 1877.Sm off 1878.Op Cm K | M 1879.Brq Cm bit/s | Byte/s . 1880.Sm on 1881.Pp 1882A value of 0 (default) means unlimited bandwidth. 1883The unit must immediately follow the number, as in 1884.Pp 1885.Dl "ipfw pipe 1 config bw 300Kbit/s" 1886.Pp 1887If a device name is specified instead of a numeric value, as in 1888.Pp 1889.Dl "ipfw pipe 1 config bw tun0" 1890.Pp 1891then the transmit clock is supplied by the specified device. 1892At the moment only the 1893.Xr tun 4 1894device supports this 1895functionality, for use in conjunction with 1896.Xr ppp 8 . 1897.Pp 1898.It Cm delay Ar ms-delay 1899Propagation delay, measured in milliseconds. 1900The value is rounded to the next multiple of the clock tick 1901(typically 10ms, but it is a good practice to run kernels 1902with 1903.Dq "options HZ=1000" 1904to reduce 1905the granularity to 1ms or less). 1906Default value is 0, meaning no delay. 1907.El 1908.Pp 1909The following parameters can be configured for a queue: 1910.Pp 1911.Bl -tag -width indent -compact 1912.It Cm pipe Ar pipe_nr 1913Connects a queue to the specified pipe. 1914Multiple queues (with the same or different weights) can be connected to 1915the same pipe, which specifies the aggregate rate for the set of queues. 1916.Pp 1917.It Cm weight Ar weight 1918Specifies the weight to be used for flows matching this queue. 1919The weight must be in the range 1..100, and defaults to 1. 1920.El 1921.Pp 1922Finally, the following parameters can be configured for both 1923pipes and queues: 1924.Pp 1925.Bl -tag -width XXXX -compact 1926.Pp 1927.It Cm buckets Ar hash-table-size 1928Specifies the size of the hash table used for storing the 1929various queues. 1930Default value is 64 controlled by the 1931.Xr sysctl 8 1932variable 1933.Va net.inet.ip.dummynet.hash_size , 1934allowed range is 16 to 65536. 1935.Pp 1936.It Cm mask Ar mask-specifier 1937Packets sent to a given pipe or queue by an 1938.Nm 1939rule can be further classified into multiple flows, each of which is then 1940sent to a different 1941.Em dynamic 1942pipe or queue. 1943A flow identifier is constructed by masking the IP addresses, 1944ports and protocol types as specified with the 1945.Cm mask 1946options in the configuration of the pipe or queue. 1947For each different flow identifier, a new pipe or queue is created 1948with the same parameters as the original object, and matching packets 1949are sent to it. 1950.Pp 1951Thus, when 1952.Em dynamic pipes 1953are used, each flow will get the same bandwidth as defined by the pipe, 1954whereas when 1955.Em dynamic queues 1956are used, each flow will share the parent's pipe bandwidth evenly 1957with other flows generated by the same queue (note that other queues 1958with different weights might be connected to the same pipe). 1959.br 1960Available mask specifiers are a combination of one or more of the following: 1961.Pp 1962.Cm dst-ip Ar mask , 1963.Cm dst-ip6 Ar mask , 1964.Cm src-ip Ar mask , 1965.Cm src-ip6 Ar mask , 1966.Cm dst-port Ar mask , 1967.Cm src-port Ar mask , 1968.Cm flow-id Ar mask , 1969.Cm proto Ar mask 1970or 1971.Cm all , 1972.Pp 1973where the latter means all bits in all fields are significant. 1974.Pp 1975.It Cm noerror 1976When a packet is dropped by a 1977.Nm dummynet 1978queue or pipe, the error 1979is normally reported to the caller routine in the kernel, in the 1980same way as it happens when a device queue fills up. 1981Setting this 1982option reports the packet as successfully delivered, which can be 1983needed for some experimental setups where you want to simulate 1984loss or congestion at a remote router. 1985.Pp 1986.It Cm plr Ar packet-loss-rate 1987Packet loss rate. 1988Argument 1989.Ar packet-loss-rate 1990is a floating-point number between 0 and 1, with 0 meaning no 1991loss, 1 meaning 100% loss. 1992The loss rate is internally represented on 31 bits. 1993.Pp 1994.It Cm queue Brq Ar slots | size Ns Cm Kbytes 1995Queue size, in 1996.Ar slots 1997or 1998.Cm KBytes . 1999Default value is 50 slots, which 2000is the typical queue size for Ethernet devices. 2001Note that for slow speed links you should keep the queue 2002size short or your traffic might be affected by a significant 2003queueing delay. 2004E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit 2005or 20s of queue on a 30Kbit/s pipe. 2006Even worse effects can result if you get packets from an 2007interface with a much larger MTU, e.g.\& the loopback interface 2008with its 16KB packets. 2009The 2010.Xr sysctl 8 2011variables 2012.Em net.inet.ip.dummynet.pipe_byte_limit 2013and 2014.Em net.inet.ip.dummynet.pipe_slot_limit 2015control the maximum lengths that can be specified. 2016.Pp 2017.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p 2018Make use of the RED (Random Early Detection) queue management algorithm. 2019.Ar w_q 2020and 2021.Ar max_p 2022are floating 2023point numbers between 0 and 1 (0 not included), while 2024.Ar min_th 2025and 2026.Ar max_th 2027are integer numbers specifying thresholds for queue management 2028(thresholds are computed in bytes if the queue has been defined 2029in bytes, in slots otherwise). 2030The 2031.Nm dummynet 2032also supports the gentle RED variant (gred). 2033Three 2034.Xr sysctl 8 2035variables can be used to control the RED behaviour: 2036.Bl -tag -width indent 2037.It Va net.inet.ip.dummynet.red_lookup_depth 2038specifies the accuracy in computing the average queue 2039when the link is idle (defaults to 256, must be greater than zero) 2040.It Va net.inet.ip.dummynet.red_avg_pkt_size 2041specifies the expected average packet size (defaults to 512, must be 2042greater than zero) 2043.It Va net.inet.ip.dummynet.red_max_pkt_size 2044specifies the expected maximum packet size, only used when queue 2045thresholds are in bytes (defaults to 1500, must be greater than zero). 2046.El 2047.El 2048.Pp 2049When used with IPv6 data, 2050.Nm dummynet 2051currently has several limitations. 2052Information necessary to route link-local packets to an 2053interface is not available after processing by 2054.Nm dummynet 2055so those packets are dropped in the output path. 2056Care should be taken to insure that link-local packets are not passed to 2057.Nm dummynet . 2058.Sh CHECKLIST 2059Here are some important points to consider when designing your 2060rules: 2061.Bl -bullet 2062.It 2063Remember that you filter both packets going 2064.Cm in 2065and 2066.Cm out . 2067Most connections need packets going in both directions. 2068.It 2069Remember to test very carefully. 2070It is a good idea to be near the console when doing this. 2071If you cannot be near the console, 2072use an auto-recovery script such as the one in 2073.Pa /usr/share/examples/ipfw/change_rules.sh . 2074.It 2075Do not forget the loopback interface. 2076.El 2077.Sh FINE POINTS 2078.Bl -bullet 2079.It 2080There are circumstances where fragmented datagrams are unconditionally 2081dropped. 2082TCP packets are dropped if they do not contain at least 20 bytes of 2083TCP header, UDP packets are dropped if they do not contain a full 8 2084byte UDP header, and ICMP packets are dropped if they do not contain 20854 bytes of ICMP header, enough to specify the ICMP type, code, and 2086checksum. 2087These packets are simply logged as 2088.Dq pullup failed 2089since there may not be enough good data in the packet to produce a 2090meaningful log entry. 2091.It 2092Another type of packet is unconditionally dropped, a TCP packet with a 2093fragment offset of one. 2094This is a valid packet, but it only has one use, to try 2095to circumvent firewalls. 2096When logging is enabled, these packets are 2097reported as being dropped by rule -1. 2098.It 2099If you are logged in over a network, loading the 2100.Xr kld 4 2101version of 2102.Nm 2103is probably not as straightforward as you would think. 2104I recommend the following command line: 2105.Bd -literal -offset indent 2106kldload ipfw && \e 2107ipfw add 32000 allow ip from any to any 2108.Ed 2109.Pp 2110Along the same lines, doing an 2111.Bd -literal -offset indent 2112ipfw flush 2113.Ed 2114.Pp 2115in similar surroundings is also a bad idea. 2116.It 2117The 2118.Nm 2119filter list may not be modified if the system security level 2120is set to 3 or higher 2121(see 2122.Xr init 8 2123for information on system security levels). 2124.El 2125.Sh PACKET DIVERSION 2126A 2127.Xr divert 4 2128socket bound to the specified port will receive all packets 2129diverted to that port. 2130If no socket is bound to the destination port, or if the divert module is 2131not loaded, or if the kernel was not compiled with divert socket support, 2132the packets are dropped. 2133.Sh NETWORK ADDRESS TRANSLATION (NAT) 2134The nat configuration command is the following: 2135.Bd -ragged -offset indent 2136.Bk -words 2137.Cm nat 2138.Ar nat_number 2139.Cm config 2140.Ar nat-configuration 2141.Ek 2142.Ed 2143.Pp 2144. 2145The following parameters can be configured: 2146.Bl -tag -width indent 2147.It Cm ip Ar ip_address 2148Define an ip address to use for aliasing. 2149.It Cm if Ar nic 2150Use ip addres of NIC for aliasing, dynamically changing 2151it if NIC's ip address change. 2152.It Cm log 2153Enable logging on this nat instance. 2154.It Cm deny_in 2155Deny any incoming connection from outside world. 2156.It Cm same_ports 2157Try to leave the alias port numbers unchanged from 2158the actual local port numbers. 2159.It Cm unreg_only 2160Traffic on the local network not originating from an 2161unregistered address spaces will be ignored. 2162.It Cm reset 2163Reset table of the packet aliasing engine on address change. 2164.It Cm reverse 2165Reverse the way libalias handles aliasing. 2166.It Cm proxy_only 2167Obey transparent proxy rules only, packet aliasing is not performed. 2168.El 2169.Pp 2170To let the packet continue after being (de)aliased, set the sysctl variable 2171.Va net.inet.ip.fw.one_pass 2172to 0. 2173For more information about aliasing modes, refer to 2174.Xr libalias 3 2175. 2176See Section 2177.Sx EXAMPLES 2178for some examples about nat usage. 2179.Sh REDIRECT AND LSNAT SUPPORT IN IPFW 2180Redirect and LSNAT support follow closely the syntax used in 2181.Xr natd 8 2182. 2183See Section 2184.Sx EXAMPLES 2185for some examples on how to do redirect and lsnat. 2186.Sh SCTP NAT SUPPORT 2187Sctp nat can be configured in a simillar manner to TCP through the 2188ipfw command line tool 2189.Xr ipfw 8 2190, the main difference is that 2191.Nm sctp nat 2192does not do port 2193translation. Since the local and global side ports will be the same, 2194there is no need to specify both. Ports are redirected as follows: 2195.Bd -ragged -offset indent 2196.Bk -words 2197.Cm nat 2198.Ar nat_number 2199.Cm config if 2200.Ar nic 2201.Cm redirect_port sctp 2202.Ar ip_address [,addr_list] {[port | port-port] [,ports]} 2203.Ek 2204.Ed 2205.Pp 2206. 2207Most 2208.B sctp nat 2209configuration can be done in real-time through the 2210.B sysctl(8) 2211interface. All may be changed dynamically, though the hash_table size will only 2212change for new 2213.Nm nat 2214instances. See 2215.Sx SYSCTL VARIABLES 2216for more info. 2217.Sh SYSCTL VARIABLES 2218A set of 2219.Xr sysctl 8 2220variables controls the behaviour of the firewall and 2221associated modules 2222.Pq Nm dummynet , bridge , sctp nat . 2223These are shown below together with their default value 2224(but always check with the 2225.Xr sysctl 8 2226command what value is actually in use) and meaning: 2227.Bl -tag -width indent 2228.It Va net.inet.ip.alias.sctp.accept_global_ootb_addip: No 0 2229Defines how the 2230.Nm nat 2231responds to receipt of global OOTB ASCONF-AddIP: 2232.Bl -tag -width indent 2233.It Cm 0 2234No response (unless a partially matching association exists - 2235ports and vtags match but global address does not) 2236.It Cm 1 2237.Nm nat 2238will accept and process all OOTB global AddIP messages. 2239.El 2240.Pp 2241Option 1 should never be selected as this forms a security risk. An attacker can 2242establish multiple fake associations by sending AddIP messages. 2243.It Va net.inet.ip.alias.sctp.chunk_proc_limit: No 5 2244Defines the maximum number of chunks in an SCTP packet that will be parsed for a 2245packet that matches an existing association. This value is enforced to be greater or equal 2246than 2247.Cm net.inet.ip.alias.sctp.initialising_chunk_proc_limit . 2248A high value is 2249a DoS risk yet setting too low a value may result in important control chunks in 2250the packet not being located and parsed. 2251.It Va net.inet.ip.alias.sctp.error_on_ootb: No 1 2252Defines when the 2253.Nm nat 2254responds to any Out-of-the-Blue (OOTB) packets with ErrorM 2255packets. An OOTB packet is a packet that arrives with no existing association 2256registered in the 2257.Nm nat 2258and is not an INIT or ASCONF-AddIP packet: 2259.Bl -tag -width indent 2260.It Cm 0 2261ErrorM is never sent in response to OOTB packets. 2262.It Cm 1 2263ErrorM is only sent to OOTB packets received on the local side. 2264.It Cm 2 2265ErrorM is sent to the local side and on the global side ONLY if there is a 2266partial match (ports and vtags match but the source global IP does not). This 2267value is only useful if the 2268.Nm nat 2269is tracking global IP addresses. 2270.It Cm 3 2271ErrorM is sent in response to all OOTB packets on both the local and global side 2272(DoS risk). 2273.El 2274.Pp 2275At the moment the default is 0, since the ErrorM packet is not yet 2276supported by most SCTP stacks. When it is supported, and if not tracking 2277global addresses, we recommend setting this value to 1 to allow 2278multi-homed local hosts to function with the 2279.Nm nat . 2280To track global addresses, we recommend setting this value to 2 to 2281allow global hosts to be informed when they need to (re)send an 2282ASCONF-AddIP. Value 3 should never be chosen (except for debugging) as 2283the 2284.Nm nat 2285will respond to all OOTB global packets (a DoS risk). 2286.It Va net.inet.ip.alias.sctp.hashtable_size: No 2003 2287Size of hash tables used for 2288.Nm nat 2289lookups (100 < prime_number > 1000001) 2290This value sets the 2291.Nm hash table 2292size for any future created 2293.Nm nat 2294instance and therefore must be set prior to creating a 2295.Nm nat 2296instance. 2297The table sizes my be changed to suit specific needs. If there will be few 2298concurrent associations, and memory is scarce, you may make these smaller. If 2299there will be many thousands (or millions) of concurrent associations, you 2300should make these larger. A prime number is best for the table size. The sysctl 2301update function will adjust your input value to the next highest prime number. 2302.It Va net.inet.ip.alias.sctp.holddown_time: No 0 2303Hold association in table for this many seconds after receiving a 2304SHUTDOWN-COMPLETE. This allows endpoints to correct shutdown gracefully if a 2305shutdown_complete is lost and retransmissions are required. 2306.It Va net.inet.ip.alias.sctp.init_timer: No 15 2307Timeout value while waiting for (INIT-ACK|AddIP-ACK). 2308This value cannot be 0. 2309.It Va net.inet.ip.alias.sctp.initialising_chunk_proc_limit: No 2 2310Defines the maximum number of chunks in an SCTP packet that will be parsed when 2311no existing association exists that matches that packet. Ideally this packet 2312will only be an INIT or ASCONF-AddIP packet. A higher value may become a DoS 2313risk as malformed packets can consume processing resources. 2314.It Va net.inet.ip.alias.sctp.param_proc_limit: No 25 2315Defines the maximum number of parameters within a chunk that will be parsed in a 2316packet. As for other similar sysctl variables, larger values pose a DoS risk. 2317.It Va net.inet.ip.alias.sctp.log_level: No 0 2318Level of detail in the system log messages (0 \- minimal, 1 \- event, 23192 \- info, 3 \- detail, 4 \- debug, 5 \- max debug). May be a good 2320option in high loss environments. 2321.It Va net.inet.ip.alias.sctp.shutdown_time: No 15 2322Timeout value while waiting for SHUTDOWN-COMPLETE. 2323This value cannot be 0. 2324.It Va net.inet.ip.alias.sctp.track_global_addresses: No 0 2325Enables/disables global IP address tracking within the 2326.Nm nat 2327and places an 2328upper limit on the number of addresses tracked for each association: 2329.Bl -tag -width indent 2330.It Cm 0 2331Global tracking is disabled 2332.It Cm >1 2333Enables tracking, the maximum number of addresses tracked for each 2334association is limited to this value 2335.El 2336.Pp 2337This variable is fully dynamic, the new value will be adopted for all newly 2338arriving associations, existing association are treated as they were previously. 2339Global tracking will decrease the number of collisions within the 2340.Nm nat 2341at a cost 2342of increased processing load, memory usage, complexity, and possible 2343.Nm nat 2344state 2345problems in complex networks with multiple 2346.Nm nats . 2347We recommend not tracking 2348global IP addresses, this will still result in a fully functional 2349.Nm nat . 2350.It Va net.inet.ip.alias.sctp.up_timer: No 300 2351Timeout value to keep an association up with no traffic. 2352This value cannot be 0. 2353.It Va net.inet.ip.dummynet.expire : No 1 2354Lazily delete dynamic pipes/queue once they have no pending traffic. 2355You can disable this by setting the variable to 0, in which case 2356the pipes/queues will only be deleted when the threshold is reached. 2357.It Va net.inet.ip.dummynet.hash_size : No 64 2358Default size of the hash table used for dynamic pipes/queues. 2359This value is used when no 2360.Cm buckets 2361option is specified when configuring a pipe/queue. 2362.It Va net.inet.ip.dummynet.io_fast : No 0 2363If set to a non-zero value, 2364the 2365.Dq fast 2366mode of 2367.Nm dummynet 2368operation (see above) is enabled. 2369.It Va net.inet.ip.dummynet.io_pkt 2370Number of packets passed to 2371.Nm dummynet . 2372.It Va net.inet.ip.dummynet.io_pkt_drop 2373Number of packets dropped by 2374.Nm dummynet . 2375.It Va net.inet.ip.dummynet.io_pkt_fast 2376Number of packets bypassed by the 2377.Nm dummynet 2378scheduler. 2379.It Va net.inet.ip.dummynet.max_chain_len : No 16 2380Target value for the maximum number of pipes/queues in a hash bucket. 2381The product 2382.Cm max_chain_len*hash_size 2383is used to determine the threshold over which empty pipes/queues 2384will be expired even when 2385.Cm net.inet.ip.dummynet.expire=0 . 2386.It Va net.inet.ip.dummynet.red_lookup_depth : No 256 2387.It Va net.inet.ip.dummynet.red_avg_pkt_size : No 512 2388.It Va net.inet.ip.dummynet.red_max_pkt_size : No 1500 2389Parameters used in the computations of the drop probability 2390for the RED algorithm. 2391.It Va net.inet.ip.dummynet.pipe_byte_limit : No 1048576 2392.It Va net.inet.ip.dummynet.pipe_slot_limit : No 100 2393The maximum queue size that can be specified in bytes or packets. 2394These limits prevent accidental exhaustion of resources such as mbufs. 2395If you raise these limits, 2396you should make sure the system is configured so that sufficient resources 2397are available. 2398.It Va net.inet.ip.fw.autoinc_step : No 100 2399Delta between rule numbers when auto-generating them. 2400The value must be in the range 1..1000. 2401.It Va net.inet.ip.fw.curr_dyn_buckets : Va net.inet.ip.fw.dyn_buckets 2402The current number of buckets in the hash table for dynamic rules 2403(readonly). 2404.It Va net.inet.ip.fw.debug : No 1 2405Controls debugging messages produced by 2406.Nm . 2407.It Va net.inet.ip.fw.default_rule : No 65535 2408The default rule number (read-only). 2409By the design of 2410.Nm , the default rule is the last one, so its number 2411can also serve as the highest number allowed for a rule. 2412.It Va net.inet.ip.fw.dyn_buckets : No 256 2413The number of buckets in the hash table for dynamic rules. 2414Must be a power of 2, up to 65536. 2415It only takes effect when all dynamic rules have expired, so you 2416are advised to use a 2417.Cm flush 2418command to make sure that the hash table is resized. 2419.It Va net.inet.ip.fw.dyn_count : No 3 2420Current number of dynamic rules 2421(read-only). 2422.It Va net.inet.ip.fw.dyn_keepalive : No 1 2423Enables generation of keepalive packets for 2424.Cm keep-state 2425rules on TCP sessions. 2426A keepalive is generated to both 2427sides of the connection every 5 seconds for the last 20 2428seconds of the lifetime of the rule. 2429.It Va net.inet.ip.fw.dyn_max : No 8192 2430Maximum number of dynamic rules. 2431When you hit this limit, no more dynamic rules can be 2432installed until old ones expire. 2433.It Va net.inet.ip.fw.dyn_ack_lifetime : No 300 2434.It Va net.inet.ip.fw.dyn_syn_lifetime : No 20 2435.It Va net.inet.ip.fw.dyn_fin_lifetime : No 1 2436.It Va net.inet.ip.fw.dyn_rst_lifetime : No 1 2437.It Va net.inet.ip.fw.dyn_udp_lifetime : No 5 2438.It Va net.inet.ip.fw.dyn_short_lifetime : No 30 2439These variables control the lifetime, in seconds, of dynamic 2440rules. 2441Upon the initial SYN exchange the lifetime is kept short, 2442then increased after both SYN have been seen, then decreased 2443again during the final FIN exchange or when a RST is received. 2444Both 2445.Em dyn_fin_lifetime 2446and 2447.Em dyn_rst_lifetime 2448must be strictly lower than 5 seconds, the period of 2449repetition of keepalives. 2450The firewall enforces that. 2451.It Va net.inet.ip.fw.enable : No 1 2452Enables the firewall. 2453Setting this variable to 0 lets you run your machine without 2454firewall even if compiled in. 2455.It Va net.inet6.ip6.fw.enable : No 1 2456provides the same functionality as above for the IPv6 case. 2457.It Va net.inet.ip.fw.one_pass : No 1 2458When set, the packet exiting from the 2459.Nm dummynet 2460pipe or from 2461.Xr ng_ipfw 4 2462node is not passed though the firewall again. 2463Otherwise, after an action, the packet is 2464reinjected into the firewall at the next rule. 2465.It Va net.inet.ip.fw.tables_max : No 128 2466Maximum number of tables (read-only). 2467.It Va net.inet.ip.fw.verbose : No 1 2468Enables verbose messages. 2469.It Va net.inet.ip.fw.verbose_limit : No 0 2470Limits the number of messages produced by a verbose firewall. 2471.It Va net.inet6.ip6.fw.deny_unknown_exthdrs : No 1 2472If enabled packets with unknown IPv6 Extension Headers will be denied. 2473.It Va net.link.ether.ipfw : No 0 2474Controls whether layer-2 packets are passed to 2475.Nm . 2476Default is no. 2477.It Va net.link.bridge.ipfw : No 0 2478Controls whether bridged packets are passed to 2479.Nm . 2480Default is no. 2481.El 2482.Pp 2483.Sh EXAMPLES 2484There are far too many possible uses of 2485.Nm 2486so this Section will only give a small set of examples. 2487.Pp 2488.Ss BASIC PACKET FILTERING 2489This command adds an entry which denies all tcp packets from 2490.Em cracker.evil.org 2491to the telnet port of 2492.Em wolf.tambov.su 2493from being forwarded by the host: 2494.Pp 2495.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet" 2496.Pp 2497This one disallows any connection from the entire cracker's 2498network to my host: 2499.Pp 2500.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org" 2501.Pp 2502A first and efficient way to limit access (not using dynamic rules) 2503is the use of the following rules: 2504.Pp 2505.Dl "ipfw add allow tcp from any to any established" 2506.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup" 2507.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup" 2508.Dl "..." 2509.Dl "ipfw add deny tcp from any to any" 2510.Pp 2511The first rule will be a quick match for normal TCP packets, 2512but it will not match the initial SYN packet, which will be 2513matched by the 2514.Cm setup 2515rules only for selected source/destination pairs. 2516All other SYN packets will be rejected by the final 2517.Cm deny 2518rule. 2519.Pp 2520If you administer one or more subnets, you can take advantage 2521of the address sets and or-blocks and write extremely 2522compact rulesets which selectively enable services to blocks 2523of clients, as below: 2524.Pp 2525.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q" 2526.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q" 2527.Dl "" 2528.Dl "ipfw add allow ip from ${goodguys} to any" 2529.Dl "ipfw add deny ip from ${badguys} to any" 2530.Dl "... normal policies ..." 2531.Pp 2532The 2533.Cm verrevpath 2534option could be used to do automated anti-spoofing by adding the 2535following to the top of a ruleset: 2536.Pp 2537.Dl "ipfw add deny ip from any to any not verrevpath in" 2538.Pp 2539This rule drops all incoming packets that appear to be coming to the 2540system on the wrong interface. 2541For example, a packet with a source 2542address belonging to a host on a protected internal network would be 2543dropped if it tried to enter the system from an external interface. 2544.Pp 2545The 2546.Cm antispoof 2547option could be used to do similar but more restricted anti-spoofing 2548by adding the following to the top of a ruleset: 2549.Pp 2550.Dl "ipfw add deny ip from any to any not antispoof in" 2551.Pp 2552This rule drops all incoming packets that appear to be coming from another 2553directly connected system but on the wrong interface. 2554For example, a packet with a source address of 2555.Li 192.168.0.0/24 2556, configured on 2557.Li fxp0 2558, but coming in on 2559.Li fxp1 2560would be dropped. 2561.Ss DYNAMIC RULES 2562In order to protect a site from flood attacks involving fake 2563TCP packets, it is safer to use dynamic rules: 2564.Pp 2565.Dl "ipfw add check-state" 2566.Dl "ipfw add deny tcp from any to any established" 2567.Dl "ipfw add allow tcp from my-net to any setup keep-state" 2568.Pp 2569This will let the firewall install dynamic rules only for 2570those connection which start with a regular SYN packet coming 2571from the inside of our network. 2572Dynamic rules are checked when encountering the first 2573.Cm check-state 2574or 2575.Cm keep-state 2576rule. 2577A 2578.Cm check-state 2579rule should usually be placed near the beginning of the 2580ruleset to minimize the amount of work scanning the ruleset. 2581Your mileage may vary. 2582.Pp 2583To limit the number of connections a user can open 2584you can use the following type of rules: 2585.Pp 2586.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10" 2587.Dl "ipfw add allow tcp from any to me setup limit src-addr 4" 2588.Pp 2589The former (assuming it runs on a gateway) will allow each host 2590on a /24 network to open at most 10 TCP connections. 2591The latter can be placed on a server to make sure that a single 2592client does not use more than 4 simultaneous connections. 2593.Pp 2594.Em BEWARE : 2595stateful rules can be subject to denial-of-service attacks 2596by a SYN-flood which opens a huge number of dynamic rules. 2597The effects of such attacks can be partially limited by 2598acting on a set of 2599.Xr sysctl 8 2600variables which control the operation of the firewall. 2601.Pp 2602Here is a good usage of the 2603.Cm list 2604command to see accounting records and timestamp information: 2605.Pp 2606.Dl ipfw -at list 2607.Pp 2608or in short form without timestamps: 2609.Pp 2610.Dl ipfw -a list 2611.Pp 2612which is equivalent to: 2613.Pp 2614.Dl ipfw show 2615.Pp 2616Next rule diverts all incoming packets from 192.168.2.0/24 2617to divert port 5000: 2618.Pp 2619.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in 2620.Pp 2621.Ss TRAFFIC SHAPING 2622The following rules show some of the applications of 2623.Nm 2624and 2625.Nm dummynet 2626for simulations and the like. 2627.Pp 2628This rule drops random incoming packets with a probability 2629of 5%: 2630.Pp 2631.Dl "ipfw add prob 0.05 deny ip from any to any in" 2632.Pp 2633A similar effect can be achieved making use of 2634.Nm dummynet 2635pipes: 2636.Pp 2637.Dl "ipfw add pipe 10 ip from any to any" 2638.Dl "ipfw pipe 10 config plr 0.05" 2639.Pp 2640We can use pipes to artificially limit bandwidth, e.g.\& on a 2641machine acting as a router, if we want to limit traffic from 2642local clients on 192.168.2.0/24 we do: 2643.Pp 2644.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2645.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes" 2646.Pp 2647note that we use the 2648.Cm out 2649modifier so that the rule is not used twice. 2650Remember in fact that 2651.Nm 2652rules are checked both on incoming and outgoing packets. 2653.Pp 2654Should we want to simulate a bidirectional link with bandwidth 2655limitations, the correct way is the following: 2656.Pp 2657.Dl "ipfw add pipe 1 ip from any to any out" 2658.Dl "ipfw add pipe 2 ip from any to any in" 2659.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes" 2660.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes" 2661.Pp 2662The above can be very useful, e.g.\& if you want to see how 2663your fancy Web page will look for a residential user who 2664is connected only through a slow link. 2665You should not use only one pipe for both directions, unless 2666you want to simulate a half-duplex medium (e.g.\& AppleTalk, 2667Ethernet, IRDA). 2668It is not necessary that both pipes have the same configuration, 2669so we can also simulate asymmetric links. 2670.Pp 2671Should we want to verify network performance with the RED queue 2672management algorithm: 2673.Pp 2674.Dl "ipfw add pipe 1 ip from any to any" 2675.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1" 2676.Pp 2677Another typical application of the traffic shaper is to 2678introduce some delay in the communication. 2679This can significantly affect applications which do a lot of Remote 2680Procedure Calls, and where the round-trip-time of the 2681connection often becomes a limiting factor much more than 2682bandwidth: 2683.Pp 2684.Dl "ipfw add pipe 1 ip from any to any out" 2685.Dl "ipfw add pipe 2 ip from any to any in" 2686.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s" 2687.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s" 2688.Pp 2689Per-flow queueing can be useful for a variety of purposes. 2690A very simple one is counting traffic: 2691.Pp 2692.Dl "ipfw add pipe 1 tcp from any to any" 2693.Dl "ipfw add pipe 1 udp from any to any" 2694.Dl "ipfw add pipe 1 ip from any to any" 2695.Dl "ipfw pipe 1 config mask all" 2696.Pp 2697The above set of rules will create queues (and collect 2698statistics) for all traffic. 2699Because the pipes have no limitations, the only effect is 2700collecting statistics. 2701Note that we need 3 rules, not just the last one, because 2702when 2703.Nm 2704tries to match IP packets it will not consider ports, so we 2705would not see connections on separate ports as different 2706ones. 2707.Pp 2708A more sophisticated example is limiting the outbound traffic 2709on a net with per-host limits, rather than per-network limits: 2710.Pp 2711.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2712.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in" 2713.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2714.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2715.Ss LOOKUP TABLES 2716In the following example, we need to create several traffic bandwidth 2717classes and we need different hosts/networks to fall into different classes. 2718We create one pipe for each class and configure them accordingly. 2719Then we create a single table and fill it with IP subnets and addresses. 2720For each subnet/host we set the argument equal to the number of the pipe 2721that it should use. 2722Then we classify traffic using a single rule: 2723.Pp 2724.Dl "ipfw pipe 1 config bw 1000Kbyte/s" 2725.Dl "ipfw pipe 4 config bw 4000Kbyte/s" 2726.Dl "..." 2727.Dl "ipfw table 1 add 192.168.2.0/24 1" 2728.Dl "ipfw table 1 add 192.168.0.0/27 4" 2729.Dl "ipfw table 1 add 192.168.0.2 1" 2730.Dl "..." 2731.Dl "ipfw add pipe tablearg ip from table(1) to any" 2732.Pp 2733Using the 2734.Cm fwd 2735action, the table entries may include hostnames and IP addresses. 2736.Pp 2737.Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1" 2738.Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz" 2739.Dl "..." 2740.Dl "ipfw add 100 fwd tablearg ip from any to table(1)" 2741.Ss SETS OF RULES 2742To add a set of rules atomically, e.g.\& set 18: 2743.Pp 2744.Dl "ipfw set disable 18" 2745.Dl "ipfw add NN set 18 ... # repeat as needed" 2746.Dl "ipfw set enable 18" 2747.Pp 2748To delete a set of rules atomically the command is simply: 2749.Pp 2750.Dl "ipfw delete set 18" 2751.Pp 2752To test a ruleset and disable it and regain control if something goes wrong: 2753.Pp 2754.Dl "ipfw set disable 18" 2755.Dl "ipfw add NN set 18 ... # repeat as needed" 2756.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18" 2757.Pp 2758Here if everything goes well, you press control-C before the "sleep" 2759terminates, and your ruleset will be left active. 2760Otherwise, e.g.\& if 2761you cannot access your box, the ruleset will be disabled after 2762the sleep terminates thus restoring the previous situation. 2763.Pp 2764To show rules of the specific set: 2765.Pp 2766.Dl "ipfw set 18 show" 2767.Pp 2768To show rules of the disabled set: 2769.Pp 2770.Dl "ipfw -S set 18 show" 2771.Pp 2772To clear a specific rule counters of the specific set: 2773.Pp 2774.Dl "ipfw set 18 zero NN" 2775.Pp 2776To delete a specific rule of the specific set: 2777.Pp 2778.Dl "ipfw set 18 delete NN" 2779.Ss NAT, REDIRECT AND LSNAT 2780First redirect all the traffic to nat instance 123: 2781.Pp 2782.Dl "ipfw add nat 123 all from any to any" 2783.Pp 2784Then to configure nat instance 123 to alias all the outgoing traffic with ip 2785192.168.0.123, blocking all incoming connections, trying to keep 2786same ports on both sides, clearing aliasing table on address change 2787and keeping a log of traffic/link statistics: 2788.Pp 2789.Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports" 2790.Pp 2791Or to change address of instance 123, aliasing table will be cleared (see 2792reset option): 2793.Pp 2794.Dl "ipfw nat 123 config ip 10.0.0.1" 2795.Pp 2796To see configuration of nat instance 123: 2797.Pp 2798.Dl "ipfw nat 123 show config" 2799.Pp 2800To show logs of all the instances in range 111-999: 2801.Pp 2802.Dl "ipfw nat 111-999 show" 2803.Pp 2804To see configurations of all instances: 2805.Pp 2806.Dl "ipfw nat show config" 2807.Pp 2808Or a redirect rule with mixed modes could looks like: 2809.Pp 2810.Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66" 2811.Dl " redirect_port tcp 192.168.0.1:80 500" 2812.Dl " redirect_proto udp 192.168.1.43 192.168.1.1" 2813.Dl " redirect_addr 192.168.0.10,192.168.0.11" 2814.Dl " 10.0.0.100 # LSNAT" 2815.Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22" 2816.Dl " 500 # LSNAT" 2817.Pp 2818or it could be splitted in: 2819.Pp 2820.Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66" 2821.Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500" 2822.Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1" 2823.Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12" 2824.Dl " 10.0.0.100" 2825.Dl "ipfw nat 5 config redirect_port tcp" 2826.Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500" 2827.Pp 2828.Sh SEE ALSO 2829.Xr cpp 1 , 2830.Xr m4 1 , 2831.Xr altq 4 , 2832.Xr divert 4 , 2833.Xr dummynet 4 , 2834.Xr if_bridge 4 , 2835.Xr ip 4 , 2836.Xr ipfirewall 4 , 2837.Xr ng_ipfw 4 , 2838.Xr protocols 5 , 2839.Xr services 5 , 2840.Xr init 8 , 2841.Xr kldload 8 , 2842.Xr reboot 8 , 2843.Xr sysctl 8 , 2844.Xr syslogd 8 2845.Sh HISTORY 2846The 2847.Nm 2848utility first appeared in 2849.Fx 2.0 . 2850.Nm dummynet 2851was introduced in 2852.Fx 2.2.8 . 2853Stateful extensions were introduced in 2854.Fx 4.0 . 2855.Nm ipfw2 2856was introduced in Summer 2002. 2857.Sh AUTHORS 2858.An Ugen J. S. Antsilevich , 2859.An Poul-Henning Kamp , 2860.An Alex Nash , 2861.An Archie Cobbs , 2862.An Luigi Rizzo . 2863.Pp 2864.An -nosplit 2865API based upon code written by 2866.An Daniel Boulet 2867for BSDI. 2868.Pp 2869.An -nosplit 2870In-kernel NAT support written by 2871.An Paolo Pisati Aq piso@FreeBSD.org 2872as part of a Summer of Code 2005 project. 2873.Pp 2874Work on 2875.Nm dummynet 2876traffic shaper supported by Akamba Corp. 2877.Pp 2878Sctp 2879.Nm nat 2880support has been developed by 2881.An The Centre for Advanced Internet Architectures (CAIA) Aq http://www.caia.swin.edu.au . 2882The primary developers and maintainers are David Hayes and Jason But. 2883For further information visit: 2884.Aq http://www.caia.swin.edu.au/urp/SONATA 2885. 2886.Sh BUGS 2887The syntax has grown over the years and sometimes it might be confusing. 2888Unfortunately, backward compatibility prevents cleaning up mistakes 2889made in the definition of the syntax. 2890.Pp 2891.Em !!! WARNING !!! 2892.Pp 2893Misconfiguring the firewall can put your computer in an unusable state, 2894possibly shutting down network services and requiring console access to 2895regain control of it. 2896.Pp 2897Incoming packet fragments diverted by 2898.Cm divert 2899are reassembled before delivery to the socket. 2900The action used on those packet is the one from the 2901rule which matches the first fragment of the packet. 2902.Pp 2903Packets diverted to userland, and then reinserted by a userland process 2904may lose various packet attributes. 2905The packet source interface name 2906will be preserved if it is shorter than 8 bytes and the userland process 2907saves and reuses the sockaddr_in 2908(as does 2909.Xr natd 8 ) ; 2910otherwise, it may be lost. 2911If a packet is reinserted in this manner, later rules may be incorrectly 2912applied, making the order of 2913.Cm divert 2914rules in the rule sequence very important. 2915.Pp 2916Dummynet drops all packets with IPv6 link-local addresses. 2917.Pp 2918Rules using 2919.Cm uid 2920or 2921.Cm gid 2922may not behave as expected. 2923In particular, incoming SYN packets may 2924have no uid or gid associated with them since they do not yet belong 2925to a TCP connection, and the uid/gid associated with a packet may not 2926be as expected if the associated process calls 2927.Xr setuid 2 2928or similar system calls. 2929.Pp 2930Rule syntax is subject to the command line environment and some patterns 2931may need to be escaped with the backslash character 2932or quoted appropriately. 2933.Pp 2934Due to the architecture of 2935.Xr libalias 3 , 2936ipfw nat is not compatible with the tcp segmentation offloading 2937(TSO). Thus, to reliably nat your network traffic, please disable TSO 2938on your NICs using 2939.Xr ifconfig 8 . 2940.Pp 2941ICMP error messages are not implicitly matched by dynamic rules 2942for the respective conversations. 2943To avoid failures of network error detection and path MTU discovery, 2944ICMP error messages may need to be allowed explicitly through static 2945rules. 2946