1.\" 2.\" $FreeBSD$ 3.\" 4.Dd October 19, 2007 5.Dt IPFW 8 6.Os 7.Sh NAME 8.Nm ipfw 9.Nd IP firewall and traffic shaper control program 10.Sh SYNOPSIS 11.Nm 12.Op Fl cq 13.Cm add 14.Ar rule 15.Nm 16.Op Fl acdefnNStT 17.Op Cm set Ar N 18.Brq Cm list | show 19.Op Ar rule | first-last ... 20.Nm 21.Op Fl f | q 22.Op Cm set Ar N 23.Cm flush 24.Nm 25.Op Fl q 26.Op Cm set Ar N 27.Brq Cm delete | zero | resetlog 28.Op Ar number ... 29.Nm 30.Cm enable 31.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 32.Nm 33.Cm disable 34.Brq Cm firewall | altq | one_pass | debug | verbose | dyn_keepalive 35.Pp 36.Nm 37.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 38.Nm 39.Cm set move 40.Op Cm rule 41.Ar number Cm to Ar number 42.Nm 43.Cm set swap Ar number number 44.Nm 45.Cm set show 46.Pp 47.Nm 48.Cm table Ar number Cm add Ar addr Ns Oo / Ns Ar masklen Oc Op Ar value 49.Nm 50.Cm table Ar number Cm delete Ar addr Ns Op / Ns Ar masklen 51.Nm 52.Cm table Ar number Cm flush 53.Nm 54.Cm table Ar number Cm list 55.Pp 56.Nm 57.Brq Cm pipe | queue 58.Ar number 59.Cm config 60.Ar config-options 61.Nm 62.Op Fl s Op Ar field 63.Brq Cm pipe | queue 64.Brq Cm delete | list | show 65.Op Ar number ... 66.Pp 67.Nm 68.Cm nat 69.Ar number 70.Cm config 71.Ar config-options 72.Pp 73.Nm 74.Op Fl cfnNqS 75.Oo 76.Fl p Ar preproc 77.Oo 78.Ar preproc-flags 79.Oc 80.Oc 81.Ar pathname 82.Sh DESCRIPTION 83The 84.Nm 85utility is the user interface for controlling the 86.Xr ipfw 4 87firewall and the 88.Xr dummynet 4 89traffic shaper in 90.Fx . 91.Pp 92An 93.Nm 94configuration, or 95.Em ruleset , 96is made of a list of 97.Em rules 98numbered from 1 to 65535. 99Packets are passed to 100.Nm 101from a number of different places in the protocol stack 102(depending on the source and destination of the packet, 103it is possible that 104.Nm 105is invoked multiple times on the same packet). 106The packet passed to the firewall is compared 107against each of the rules in the firewall 108.Em ruleset . 109When a match is found, the action corresponding to the 110matching rule is performed. 111.Pp 112Depending on the action and certain system settings, packets 113can be reinjected into the firewall at some rule after the 114matching one for further processing. 115.Pp 116An 117.Nm 118ruleset always includes a 119.Em default 120rule (numbered 65535) which cannot be modified or deleted, 121and matches all packets. 122The action associated with the 123.Em default 124rule can be either 125.Cm deny 126or 127.Cm allow 128depending on how the kernel is configured. 129.Pp 130If the ruleset includes one or more rules with the 131.Cm keep-state 132or 133.Cm limit 134option, then 135.Nm 136assumes a 137.Em stateful 138behaviour, i.e., upon a match it will create dynamic rules matching 139the exact parameters (addresses and ports) of the matching packet. 140.Pp 141These dynamic rules, which have a limited lifetime, are checked 142at the first occurrence of a 143.Cm check-state , 144.Cm keep-state 145or 146.Cm limit 147rule, and are typically used to open the firewall on-demand to 148legitimate traffic only. 149See the 150.Sx STATEFUL FIREWALL 151and 152.Sx EXAMPLES 153Sections below for more information on the stateful behaviour of 154.Nm . 155.Pp 156All rules (including dynamic ones) have a few associated counters: 157a packet count, a byte count, a log count and a timestamp 158indicating the time of the last match. 159Counters can be displayed or reset with 160.Nm 161commands. 162.Pp 163Rules can be added with the 164.Cm add 165command; deleted individually or in groups with the 166.Cm delete 167command, and globally (except those in set 31) with the 168.Cm flush 169command; displayed, optionally with the content of the 170counters, using the 171.Cm show 172and 173.Cm list 174commands. 175Finally, counters can be reset with the 176.Cm zero 177and 178.Cm resetlog 179commands. 180.Pp 181Also, each rule belongs to one of 32 different 182.Em sets 183, and there are 184.Nm 185commands to atomically manipulate sets, such as enable, 186disable, swap sets, move all rules in a set to another 187one, delete all rules in a set. 188These can be useful to 189install temporary configurations, or to test them. 190See Section 191.Sx SETS OF RULES 192for more information on 193.Em sets . 194.Pp 195The following options are available: 196.Bl -tag -width indent 197.It Fl a 198While listing, show counter values. 199The 200.Cm show 201command just implies this option. 202.It Fl b 203Only show the action and the comment, not the body of a rule. 204Implies 205.Fl c . 206.It Fl c 207When entering or showing rules, print them in compact form, 208i.e., without the optional "ip from any to any" string 209when this does not carry any additional information. 210.It Fl d 211While listing, show dynamic rules in addition to static ones. 212.It Fl e 213While listing, if the 214.Fl d 215option was specified, also show expired dynamic rules. 216.It Fl f 217Do not ask for confirmation for commands that can cause problems 218if misused, 219.No i.e. Cm flush . 220If there is no tty associated with the process, this is implied. 221.It Fl n 222Only check syntax of the command strings, without actually passing 223them to the kernel. 224.It Fl N 225Try to resolve addresses and service names in output. 226.It Fl q 227While 228.Cm add Ns ing , 229.Cm zero Ns ing , 230.Cm resetlog Ns ging 231or 232.Cm flush Ns ing , 233be quiet about actions 234(implies 235.Fl f ) . 236This is useful for adjusting rules by executing multiple 237.Nm 238commands in a script 239(e.g., 240.Ql sh\ /etc/rc.firewall ) , 241or by processing a file of many 242.Nm 243rules across a remote login session. 244It also stops a table add or delete 245from failing if the entry already exists or is not present. 246If a 247.Cm flush 248is performed in normal (verbose) mode (with the default kernel 249configuration), it prints a message. 250Because all rules are flushed, the message might not be delivered 251to the login session, causing the remote login session to be closed 252and the remainder of the ruleset to not be processed. 253Access to the console would then be required to recover. 254.It Fl S 255While listing rules, show the 256.Em set 257each rule belongs to. 258If this flag is not specified, disabled rules will not be 259listed. 260.It Fl s Op Ar field 261While listing pipes, sort according to one of the four 262counters (total or current packets or bytes). 263.It Fl t 264While listing, show last match timestamp (converted with ctime()). 265.It Fl T 266While listing, show last match timestamp (as seconds from the epoch). 267This form can be more convenient for postprocessing by scripts. 268.El 269.Pp 270To ease configuration, rules can be put into a file which is 271processed using 272.Nm 273as shown in the last synopsis line. 274An absolute 275.Ar pathname 276must be used. 277The file will be read line by line and applied as arguments to the 278.Nm 279utility. 280.Pp 281Optionally, a preprocessor can be specified using 282.Fl p Ar preproc 283where 284.Ar pathname 285is to be piped through. 286Useful preprocessors include 287.Xr cpp 1 288and 289.Xr m4 1 . 290If 291.Ar preproc 292does not start with a slash 293.Pq Ql / 294as its first character, the usual 295.Ev PATH 296name search is performed. 297Care should be taken with this in environments where not all 298file systems are mounted (yet) by the time 299.Nm 300is being run (e.g.\& when they are mounted over NFS). 301Once 302.Fl p 303has been specified, any additional arguments as passed on to the preprocessor 304for interpretation. 305This allows for flexible configuration files (like conditionalizing 306them on the local hostname) and the use of macros to centralize 307frequently required arguments like IP addresses. 308.Pp 309The 310.Nm 311.Cm pipe 312and 313.Cm queue 314commands are used to configure the traffic shaper, as shown in the 315.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 316Section below. 317.Pp 318If the world and the kernel get out of sync the 319.Nm 320ABI may break, preventing you from being able to add any rules. 321This can 322adversely effect the booting process. 323You can use 324.Nm 325.Cm disable 326.Cm firewall 327to temporarily disable the firewall to regain access to the network, 328allowing you to fix the problem. 329.Sh PACKET FLOW 330A packet is checked against the active ruleset in multiple places 331in the protocol stack, under control of several sysctl variables. 332These places and variables are shown below, and it is important to 333have this picture in mind in order to design a correct ruleset. 334.Bd -literal -offset indent 335 ^ to upper layers V 336 | | 337 +----------->-----------+ 338 ^ V 339 [ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1 340 | | 341 ^ V 342 [ether_demux] [ether_output_frame] net.link.ether.ipfw=1 343 | | 344 +-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1 345 ^ V 346 | to devices | 347.Ed 348.Pp 349As can be noted from the above picture, the number of 350times the same packet goes through the firewall can 351vary between 0 and 4 depending on packet source and 352destination, and system configuration. 353.Pp 354Note that as packets flow through the stack, headers can be 355stripped or added to it, and so they may or may not be available 356for inspection. 357E.g., incoming packets will include the MAC header when 358.Nm 359is invoked from 360.Cm ether_demux() , 361but the same packets will have the MAC header stripped off when 362.Nm 363is invoked from 364.Cm ip_input() 365or 366.Cm ip6_input() . 367.Pp 368Also note that each packet is always checked against the complete ruleset, 369irrespective of the place where the check occurs, or the source of the packet. 370If a rule contains some match patterns or actions which are not valid 371for the place of invocation (e.g.\& trying to match a MAC header within 372.Cm ip_input 373or 374.Cm ip6_input ), 375the match pattern will not match, but a 376.Cm not 377operator in front of such patterns 378.Em will 379cause the pattern to 380.Em always 381match on those packets. 382It is thus the responsibility of 383the programmer, if necessary, to write a suitable ruleset to 384differentiate among the possible places. 385.Cm skipto 386rules can be useful here, as an example: 387.Bd -literal -offset indent 388# packets from ether_demux or bdg_forward 389ipfw add 10 skipto 1000 all from any to any layer2 in 390# packets from ip_input 391ipfw add 10 skipto 2000 all from any to any not layer2 in 392# packets from ip_output 393ipfw add 10 skipto 3000 all from any to any not layer2 out 394# packets from ether_output_frame 395ipfw add 10 skipto 4000 all from any to any layer2 out 396.Ed 397.Pp 398(yes, at the moment there is no way to differentiate between 399ether_demux and bdg_forward). 400.Sh SYNTAX 401In general, each keyword or argument must be provided as 402a separate command line argument, with no leading or trailing 403spaces. 404Keywords are case-sensitive, whereas arguments may 405or may not be case-sensitive depending on their nature 406(e.g.\& uid's are, hostnames are not). 407.Pp 408In 409.Nm ipfw2 410you can introduce spaces after commas ',' to make 411the line more readable. 412You can also put the entire 413command (including flags) into a single argument. 414E.g., the following forms are equivalent: 415.Bd -literal -offset indent 416ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 417ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 418ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8" 419.Ed 420.Sh RULE FORMAT 421The format of 422.Nm 423rules is the following: 424.Bd -ragged -offset indent 425.Bk -words 426.Op Ar rule_number 427.Op Cm set Ar set_number 428.Op Cm prob Ar match_probability 429.Ar action 430.Op Cm log Op Cm logamount Ar number 431.Op Cm altq Ar queue 432.Oo 433.Bro Cm tag | untag 434.Brc Ar number 435.Oc 436.Ar body 437.Ek 438.Ed 439.Pp 440where the body of the rule specifies which information is used 441for filtering packets, among the following: 442.Pp 443.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact 444.It Layer-2 header fields 445When available 446.It IPv4 and IPv6 Protocol 447TCP, UDP, ICMP, etc. 448.It Source and dest. addresses and ports 449.It Direction 450See Section 451.Sx PACKET FLOW 452.It Transmit and receive interface 453By name or address 454.It Misc. IP header fields 455Version, type of service, datagram length, identification, 456fragment flag (non-zero IP offset), 457Time To Live 458.It IP options 459.It IPv6 Extension headers 460Fragmentation, Hop-by-Hop options, 461Routing Headers, Source routing rthdr0, Mobile IPv6 rthdr2, IPSec options. 462.It IPv6 Flow-ID 463.It Misc. TCP header fields 464TCP flags (SYN, FIN, ACK, RST, etc.), 465sequence number, acknowledgment number, 466window 467.It TCP options 468.It ICMP types 469for ICMP packets 470.It ICMP6 types 471for ICMP6 packets 472.It User/group ID 473When the packet can be associated with a local socket. 474.It Divert status 475Whether a packet came from a divert socket (e.g., 476.Xr natd 8 ) . 477.El 478.Pp 479Note that some of the above information, e.g.\& source MAC or IP addresses and 480TCP/UDP ports, could easily be spoofed, so filtering on those fields 481alone might not guarantee the desired results. 482.Bl -tag -width indent 483.It Ar rule_number 484Each rule is associated with a 485.Ar rule_number 486in the range 1..65535, with the latter reserved for the 487.Em default 488rule. 489Rules are checked sequentially by rule number. 490Multiple rules can have the same number, in which case they are 491checked (and listed) according to the order in which they have 492been added. 493If a rule is entered without specifying a number, the kernel will 494assign one in such a way that the rule becomes the last one 495before the 496.Em default 497rule. 498Automatic rule numbers are assigned by incrementing the last 499non-default rule number by the value of the sysctl variable 500.Ar net.inet.ip.fw.autoinc_step 501which defaults to 100. 502If this is not possible (e.g.\& because we would go beyond the 503maximum allowed rule number), the number of the last 504non-default value is used instead. 505.It Cm set Ar set_number 506Each rule is associated with a 507.Ar set_number 508in the range 0..31. 509Sets can be individually disabled and enabled, so this parameter 510is of fundamental importance for atomic ruleset manipulation. 511It can be also used to simplify deletion of groups of rules. 512If a rule is entered without specifying a set number, 513set 0 will be used. 514.br 515Set 31 is special in that it cannot be disabled, 516and rules in set 31 are not deleted by the 517.Nm ipfw flush 518command (but you can delete them with the 519.Nm ipfw delete set 31 520command). 521Set 31 is also used for the 522.Em default 523rule. 524.It Cm prob Ar match_probability 525A match is only declared with the specified probability 526(floating point number between 0 and 1). 527This can be useful for a number of applications such as 528random packet drop or 529(in conjunction with 530.Xr dummynet 4 ) 531to simulate the effect of multiple paths leading to out-of-order 532packet delivery. 533.Pp 534Note: this condition is checked before any other condition, including 535ones such as keep-state or check-state which might have side effects. 536.It Cm log Op Cm logamount Ar number 537When a packet matches a rule with the 538.Cm log 539keyword, a message will be 540logged to 541.Xr syslogd 8 542with a 543.Dv LOG_SECURITY 544facility. 545The logging only occurs if the sysctl variable 546.Em net.inet.ip.fw.verbose 547is set to 1 548(which is the default when the kernel is compiled with 549.Dv IPFIREWALL_VERBOSE ) 550and the number of packets logged so far for that 551particular rule does not exceed the 552.Cm logamount 553parameter. 554If no 555.Cm logamount 556is specified, the limit is taken from the sysctl variable 557.Em net.inet.ip.fw.verbose_limit . 558In both cases, a value of 0 removes the logging limit. 559.Pp 560Once the limit is reached, logging can be re-enabled by 561clearing the logging counter or the packet counter for that entry, see the 562.Cm resetlog 563command. 564.Pp 565Note: logging is done after all other packet matching conditions 566have been successfully verified, and before performing the final 567action (accept, deny, etc.) on the packet. 568.It Cm tag Ar number 569When a packet matches a rule with the 570.Cm tag 571keyword, the numeric tag for the given 572.Ar number 573in the range 1..65534 will be attached to the packet. 574The tag acts as an internal marker (it is not sent out over 575the wire) that can be used to identify these packets later on. 576This can be used, for example, to provide trust between interfaces 577and to start doing policy-based filtering. 578A packet can have mutiple tags at the same time. 579Tags are "sticky", meaning once a tag is applied to a packet by a 580matching rule it exists until explicit removal. 581Tags are kept with the packet everywhere within the kernel, but are 582lost when packet leaves the kernel, for example, on transmitting 583packet out to the network or sending packet to a 584.Xr divert 4 585socket. 586.Pp 587To check for previously applied tags, use the 588.Cm tagged 589rule option. 590To delete previously applied tag, use the 591.Cm untag 592keyword. 593.Pp 594Note: since tags are kept with the packet everywhere in kernelspace, 595they can be set and unset anywhere in kernel network subsystem 596(using 597.Xr mbuf_tags 9 598facility), not only by means of 599.Xr ipfw 4 600.Cm tag 601and 602.Cm untag 603keywords. 604For example, there can be a specialized 605.Xr netgraph 4 606node doing traffic analyzing and tagging for later inspecting 607in firewall. 608.It Cm untag Ar number 609When a packet matches a rule with the 610.Cm untag 611keyword, the tag with the number 612.Ar number 613is searched among the tags attached to this packet and, 614if found, removed from it. 615Other tags bound to packet, if present, are left untouched. 616.It Cm altq Ar queue 617When a packet matches a rule with the 618.Cm altq 619keyword, the ALTQ identifier for the given 620.Ar queue 621(see 622.Xr altq 4 ) 623will be attached. 624Note that this ALTQ tag is only meaningful for packets going "out" of IPFW, 625and not being rejected or going to divert sockets. 626Note that if there is insufficient memory at the time the packet is 627processed, it will not be tagged, so it is wise to make your ALTQ 628"default" queue policy account for this. 629If multiple 630.Cm altq 631rules match a single packet, only the first one adds the ALTQ classification 632tag. 633In doing so, traffic may be shaped by using 634.Cm count Cm altq Ar queue 635rules for classification early in the ruleset, then later applying 636the filtering decision. 637For example, 638.Cm check-state 639and 640.Cm keep-state 641rules may come later and provide the actual filtering decisions in 642addition to the fallback ALTQ tag. 643.Pp 644You must run 645.Xr pfctl 8 646to set up the queues before IPFW will be able to look them up by name, 647and if the ALTQ disciplines are rearranged, the rules in containing the 648queue identifiers in the kernel will likely have gone stale and need 649to be reloaded. 650Stale queue identifiers will probably result in misclassification. 651.Pp 652All system ALTQ processing can be turned on or off via 653.Nm 654.Cm enable Ar altq 655and 656.Nm 657.Cm disable Ar altq . 658The usage of 659.Em net.inet.ip.fw.one_pass 660is irrelevant to ALTQ traffic shaping, as the actual rule action is followed 661always after adding an ALTQ tag. 662.El 663.Ss RULE ACTIONS 664A rule can be associated with one of the following actions, which 665will be executed when the packet matches the body of the rule. 666.Bl -tag -width indent 667.It Cm allow | accept | pass | permit 668Allow packets that match rule. 669The search terminates. 670.It Cm check-state 671Checks the packet against the dynamic ruleset. 672If a match is found, execute the action associated with 673the rule which generated this dynamic rule, otherwise 674move to the next rule. 675.br 676.Cm Check-state 677rules do not have a body. 678If no 679.Cm check-state 680rule is found, the dynamic ruleset is checked at the first 681.Cm keep-state 682or 683.Cm limit 684rule. 685.It Cm count 686Update counters for all packets that match rule. 687The search continues with the next rule. 688.It Cm deny | drop 689Discard packets that match this rule. 690The search terminates. 691.It Cm divert Ar port 692Divert packets that match this rule to the 693.Xr divert 4 694socket bound to port 695.Ar port . 696The search terminates. 697.It Cm fwd | forward Ar ipaddr | tablearg Ns Op , Ns Ar port 698Change the next-hop on matching packets to 699.Ar ipaddr , 700which can be an IP address or a host name. 701The next hop can also be supplied by the last table 702looked up for the packet by using the 703.Cm tablearg 704keyword instead of an explicit address. 705The search terminates if this rule matches. 706.Pp 707If 708.Ar ipaddr 709is a local address, then matching packets will be forwarded to 710.Ar port 711(or the port number in the packet if one is not specified in the rule) 712on the local machine. 713.br 714If 715.Ar ipaddr 716is not a local address, then the port number 717(if specified) is ignored, and the packet will be 718forwarded to the remote address, using the route as found in 719the local routing table for that IP. 720.br 721A 722.Ar fwd 723rule will not match layer-2 packets (those received 724on ether_input, ether_output, or bridged). 725.br 726The 727.Cm fwd 728action does not change the contents of the packet at all. 729In particular, the destination address remains unmodified, so 730packets forwarded to another system will usually be rejected by that system 731unless there is a matching rule on that system to capture them. 732For packets forwarded locally, 733the local address of the socket will be 734set to the original destination address of the packet. 735This makes the 736.Xr netstat 1 737entry look rather weird but is intended for 738use with transparent proxy servers. 739.Pp 740To enable 741.Cm fwd 742a custom kernel needs to be compiled with the option 743.Cd "options IPFIREWALL_FORWARD" . 744.It Cm nat Ar nat_nr 745Pass packet to a 746nat instance 747(for network address translation, address redirect, etc.): 748see the 749.Sx NETWORK ADDRESS TRANSLATION (NAT) 750Section for further information. 751.It Cm pipe Ar pipe_nr 752Pass packet to a 753.Xr dummynet 4 754.Dq pipe 755(for bandwidth limitation, delay, etc.). 756See the 757.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 758Section for further information. 759The search terminates; however, on exit from the pipe and if 760the 761.Xr sysctl 8 762variable 763.Em net.inet.ip.fw.one_pass 764is not set, the packet is passed again to the firewall code 765starting from the next rule. 766.It Cm queue Ar queue_nr 767Pass packet to a 768.Xr dummynet 4 769.Dq queue 770(for bandwidth limitation using WF2Q+). 771.It Cm reject 772(Deprecated). 773Synonym for 774.Cm unreach host . 775.It Cm reset 776Discard packets that match this rule, and if the 777packet is a TCP packet, try to send a TCP reset (RST) notice. 778The search terminates. 779.It Cm reset6 780Discard packets that match this rule, and if the 781packet is a TCP packet, try to send a TCP reset (RST) notice. 782The search terminates. 783.It Cm skipto Ar number 784Skip all subsequent rules numbered less than 785.Ar number . 786The search continues with the first rule numbered 787.Ar number 788or higher. 789.It Cm tee Ar port 790Send a copy of packets matching this rule to the 791.Xr divert 4 792socket bound to port 793.Ar port . 794The search continues with the next rule. 795.It Cm unreach Ar code 796Discard packets that match this rule, and try to send an ICMP 797unreachable notice with code 798.Ar code , 799where 800.Ar code 801is a number from 0 to 255, or one of these aliases: 802.Cm net , host , protocol , port , 803.Cm needfrag , srcfail , net-unknown , host-unknown , 804.Cm isolated , net-prohib , host-prohib , tosnet , 805.Cm toshost , filter-prohib , host-precedence 806or 807.Cm precedence-cutoff . 808The search terminates. 809.It Cm unreach6 Ar code 810Discard packets that match this rule, and try to send an ICMPv6 811unreachable notice with code 812.Ar code , 813where 814.Ar code 815is a number from 0, 1, 3 or 4, or one of these aliases: 816.Cm no-route, admin-prohib, address 817or 818.Cm port . 819The search terminates. 820.It Cm netgraph Ar cookie 821Divert packet into netgraph with given 822.Ar cookie . 823The search terminates. 824If packet is later returned from netgraph it is either 825accepted or continues with the next rule, depending on 826.Em net.inet.ip.fw.one_pass 827sysctl variable. 828.It Cm ngtee Ar cookie 829A copy of packet is diverted into netgraph, original 830packet is either accepted or continues with the next rule, depending on 831.Em net.inet.ip.fw.one_pass 832sysctl variable. 833See 834.Xr ng_ipfw 4 835for more information on 836.Cm netgraph 837and 838.Cm ngtee 839actions. 840.El 841.Ss RULE BODY 842The body of a rule contains zero or more patterns (such as 843specific source and destination addresses or ports, 844protocol options, incoming or outgoing interfaces, etc.) 845that the packet must match in order to be recognised. 846In general, the patterns are connected by (implicit) 847.Cm and 848operators -- i.e., all must match in order for the 849rule to match. 850Individual patterns can be prefixed by the 851.Cm not 852operator to reverse the result of the match, as in 853.Pp 854.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any" 855.Pp 856Additionally, sets of alternative match patterns 857.Pq Em or-blocks 858can be constructed by putting the patterns in 859lists enclosed between parentheses ( ) or braces { }, and 860using the 861.Cm or 862operator as follows: 863.Pp 864.Dl "ipfw add 100 allow ip from { x or not y or z } to any" 865.Pp 866Only one level of parentheses is allowed. 867Beware that most shells have special meanings for parentheses 868or braces, so it is advisable to put a backslash \\ in front of them 869to prevent such interpretations. 870.Pp 871The body of a rule must in general include a source and destination 872address specifier. 873The keyword 874.Ar any 875can be used in various places to specify that the content of 876a required field is irrelevant. 877.Pp 878The rule body has the following format: 879.Bd -ragged -offset indent 880.Op Ar proto Cm from Ar src Cm to Ar dst 881.Op Ar options 882.Ed 883.Pp 884The first part (proto from src to dst) is for backward 885compatibility with earlier versions of 886.Fx . 887In modern 888.Fx 889any match pattern (including MAC headers, IP protocols, 890addresses and ports) can be specified in the 891.Ar options 892section. 893.Pp 894Rule fields have the following meaning: 895.Bl -tag -width indent 896.It Ar proto : protocol | Cm { Ar protocol Cm or ... } 897.It Ar protocol : Oo Cm not Oc Ar protocol-name | protocol-number 898An IP protocol specified by number or name 899(for a complete list see 900.Pa /etc/protocols ) , 901or one of the following keywords: 902.Bl -tag -width indent 903.It Cm ip4 | ipv4 904Matches IPv4 packets. 905.It Cm ip6 | ipv6 906Matches IPv6 packets. 907.It Cm ip | all 908Matches any packet. 909.El 910.Pp 911The 912.Cm ipv6 913in 914.Cm proto 915option will be treated as inner protocol. 916And, the 917.Cm ipv4 918is not available in 919.Cm proto 920option. 921.Pp 922The 923.Cm { Ar protocol Cm or ... } 924format (an 925.Em or-block ) 926is provided for convenience only but its use is deprecated. 927.It Ar src No and Ar dst : Bro Cm addr | Cm { Ar addr Cm or ... } Brc Op Oo Cm not Oc Ar ports 928An address (or a list, see below) 929optionally followed by 930.Ar ports 931specifiers. 932.Pp 933The second format 934.Em ( or-block 935with multiple addresses) is provided for convenience only and 936its use is discouraged. 937.It Ar addr : Oo Cm not Oc Bro 938.Cm any | me | me6 | 939.Cm table Ns Pq Ar number Ns Op , Ns Ar value 940.Ar | addr-list | addr-set 941.Brc 942.It Cm any 943matches any IP address. 944.It Cm me 945matches any IP address configured on an interface in the system. 946.It Cm me6 947matches any IPv6 address configured on an interface in the system. 948The address list is evaluated at the time the packet is 949analysed. 950.It Cm table Ns Pq Ar number Ns Op , Ns Ar value 951Matches any IPv4 address for which an entry exists in the lookup table 952.Ar number . 953If an optional 32-bit unsigned 954.Ar value 955is also specified, an entry will match only if it has this value. 956See the 957.Sx LOOKUP TABLES 958section below for more information on lookup tables. 959.It Ar addr-list : ip-addr Ns Op Ns , Ns Ar addr-list 960.It Ar ip-addr : 961A host or subnet address specified in one of the following ways: 962.Bl -tag -width indent 963.It Ar numeric-ip | hostname 964Matches a single IPv4 address, specified as dotted-quad or a hostname. 965Hostnames are resolved at the time the rule is added to the firewall list. 966.It Ar addr Ns / Ns Ar masklen 967Matches all addresses with base 968.Ar addr 969(specified as an IP address, a network number, or a hostname) 970and mask width of 971.Cm masklen 972bits. 973As an example, 1.2.3.4/25 or 1.2.3.0/25 will match 974all IP numbers from 1.2.3.0 to 1.2.3.127 . 975.It Ar addr Ns : Ns Ar mask 976Matches all addresses with base 977.Ar addr 978(specified as an IP address, a network number, or a hostname) 979and the mask of 980.Ar mask , 981specified as a dotted quad. 982As an example, 1.2.3.4:255.0.255.0 or 1.0.3.0:255.0.255.0 will match 9831.*.3.*. 984This form is advised only for non-contiguous 985masks. 986It is better to resort to the 987.Ar addr Ns / Ns Ar masklen 988format for contiguous masks, which is more compact and less 989error-prone. 990.El 991.It Ar addr-set : addr Ns Oo Ns / Ns Ar masklen Oc Ns Cm { Ns Ar list Ns Cm } 992.It Ar list : Bro Ar num | num-num Brc Ns Op Ns , Ns Ar list 993Matches all addresses with base address 994.Ar addr 995(specified as an IP address, a network number, or a hostname) 996and whose last byte is in the list between braces { } . 997Note that there must be no spaces between braces and 998numbers (spaces after commas are allowed). 999Elements of the list can be specified as single entries 1000or ranges. 1001The 1002.Ar masklen 1003field is used to limit the size of the set of addresses, 1004and can have any value between 24 and 32. 1005If not specified, 1006it will be assumed as 24. 1007.br 1008This format is particularly useful to handle sparse address sets 1009within a single rule. 1010Because the matching occurs using a 1011bitmask, it takes constant time and dramatically reduces 1012the complexity of rulesets. 1013.br 1014As an example, an address specified as 1.2.3.4/24{128,35-55,89} 1015or 1.2.3.0/24{128,35-55,89} 1016will match the following IP addresses: 1017.br 10181.2.3.128, 1.2.3.35 to 1.2.3.55, 1.2.3.89 . 1019.It Ar addr6-list : ip6-addr Ns Op Ns , Ns Ar addr6-list 1020.It Ar ip6-addr : 1021A host or subnet specified one of the following ways: 1022.Pp 1023.Bl -tag -width indent 1024.It Ar numeric-ip | hostname 1025Matches a single IPv6 address as allowed by 1026.Xr inet_pton 3 1027or a hostname. 1028Hostnames are resolved at the time the rule is added to the firewall 1029list. 1030.It Ar addr Ns / Ns Ar masklen 1031Matches all IPv6 addresses with base 1032.Ar addr 1033(specified as allowed by 1034.Xr inet_pton 1035or a hostname) 1036and mask width of 1037.Cm masklen 1038bits. 1039.El 1040.Pp 1041No support for sets of IPv6 addresses is provided because IPv6 addresses 1042are typically random past the initial prefix. 1043.It Ar ports : Bro Ar port | port Ns \&- Ns Ar port Ns Brc Ns Op , Ns Ar ports 1044For protocols which support port numbers (such as TCP and UDP), optional 1045.Cm ports 1046may be specified as one or more ports or port ranges, separated 1047by commas but no spaces, and an optional 1048.Cm not 1049operator. 1050The 1051.Ql \&- 1052notation specifies a range of ports (including boundaries). 1053.Pp 1054Service names (from 1055.Pa /etc/services ) 1056may be used instead of numeric port values. 1057The length of the port list is limited to 30 ports or ranges, 1058though one can specify larger ranges by using an 1059.Em or-block 1060in the 1061.Cm options 1062section of the rule. 1063.Pp 1064A backslash 1065.Pq Ql \e 1066can be used to escape the dash 1067.Pq Ql - 1068character in a service name (from a shell, the backslash must be 1069typed twice to avoid the shell itself interpreting it as an escape 1070character). 1071.Pp 1072.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any" 1073.Pp 1074Fragmented packets which have a non-zero offset (i.e., not the first 1075fragment) will never match a rule which has one or more port 1076specifications. 1077See the 1078.Cm frag 1079option for details on matching fragmented packets. 1080.El 1081.Ss RULE OPTIONS (MATCH PATTERNS) 1082Additional match patterns can be used within 1083rules. 1084Zero or more of these so-called 1085.Em options 1086can be present in a rule, optionally prefixed by the 1087.Cm not 1088operand, and possibly grouped into 1089.Em or-blocks . 1090.Pp 1091The following match patterns can be used (listed in alphabetical order): 1092.Bl -tag -width indent 1093.It Cm // this is a comment. 1094Inserts the specified text as a comment in the rule. 1095Everything following // is considered as a comment and stored in the rule. 1096You can have comment-only rules, which are listed as having a 1097.Cm count 1098action followed by the comment. 1099.It Cm bridged 1100Alias for 1101.Cm layer2 . 1102.It Cm diverted 1103Matches only packets generated by a divert socket. 1104.It Cm diverted-loopback 1105Matches only packets coming from a divert socket back into the IP stack 1106input for delivery. 1107.It Cm diverted-output 1108Matches only packets going from a divert socket back outward to the IP 1109stack output for delivery. 1110.It Cm dst-ip Ar ip-address 1111Matches IPv4 packets whose destination IP is one of the address(es) 1112specified as argument. 1113.It Bro Cm dst-ip6 | dst-ipv6 Brc Ar ip6-address 1114Matches IPv6 packets whose destination IP is one of the address(es) 1115specified as argument. 1116.It Cm dst-port Ar ports 1117Matches IP packets whose destination port is one of the port(s) 1118specified as argument. 1119.It Cm established 1120Matches TCP packets that have the RST or ACK bits set. 1121.It Cm ext6hdr Ar header 1122Matches IPv6 packets containing the extended header given by 1123.Ar header . 1124Supported headers are: 1125.Pp 1126Fragment, 1127.Pq Cm frag , 1128Hop-to-hop options 1129.Pq Cm hopopt , 1130any type of Routing Header 1131.Pq Cm route , 1132Source routing Routing Header Type 0 1133.Pq Cm rthdr0 , 1134Mobile IPv6 Routing Header Type 2 1135.Pq Cm rthdr2 , 1136Destination options 1137.Pq Cm dstopt , 1138IPSec authentication headers 1139.Pq Cm ah , 1140and IPSec encapsulated security payload headers 1141.Pq Cm esp . 1142.It Cm flow-id Ar labels 1143Matches IPv6 packets containing any of the flow labels given in 1144.Ar labels . 1145.Ar labels 1146is a comma seperate list of numeric flow labels. 1147.It Cm frag 1148Matches packets that are fragments and not the first 1149fragment of an IP datagram. 1150Note that these packets will not have 1151the next protocol header (e.g.\& TCP, UDP) so options that look into 1152these headers cannot match. 1153.It Cm gid Ar group 1154Matches all TCP or UDP packets sent by or received for a 1155.Ar group . 1156A 1157.Ar group 1158may be specified by name or number. 1159.It Cm jail Ar prisonID 1160Matches all TCP or UDP packets sent by or received for the 1161jail whos prison ID is 1162.Ar prisonID . 1163.It Cm icmptypes Ar types 1164Matches ICMP packets whose ICMP type is in the list 1165.Ar types . 1166The list may be specified as any combination of 1167individual types (numeric) separated by commas. 1168.Em Ranges are not allowed. 1169The supported ICMP types are: 1170.Pp 1171echo reply 1172.Pq Cm 0 , 1173destination unreachable 1174.Pq Cm 3 , 1175source quench 1176.Pq Cm 4 , 1177redirect 1178.Pq Cm 5 , 1179echo request 1180.Pq Cm 8 , 1181router advertisement 1182.Pq Cm 9 , 1183router solicitation 1184.Pq Cm 10 , 1185time-to-live exceeded 1186.Pq Cm 11 , 1187IP header bad 1188.Pq Cm 12 , 1189timestamp request 1190.Pq Cm 13 , 1191timestamp reply 1192.Pq Cm 14 , 1193information request 1194.Pq Cm 15 , 1195information reply 1196.Pq Cm 16 , 1197address mask request 1198.Pq Cm 17 1199and address mask reply 1200.Pq Cm 18 . 1201.It Cm icmp6types Ar types 1202Matches ICMP6 packets whose ICMP6 type is in the list of 1203.Ar types . 1204The list may be specified as any combination of 1205individual types (numeric) separated by commas. 1206.Em Ranges are not allowed. 1207.It Cm in | out 1208Matches incoming or outgoing packets, respectively. 1209.Cm in 1210and 1211.Cm out 1212are mutually exclusive (in fact, 1213.Cm out 1214is implemented as 1215.Cm not in Ns No ). 1216.It Cm ipid Ar id-list 1217Matches IPv4 packets whose 1218.Cm ip_id 1219field has value included in 1220.Ar id-list , 1221which is either a single value or a list of values or ranges 1222specified in the same way as 1223.Ar ports . 1224.It Cm iplen Ar len-list 1225Matches IP packets whose total length, including header and data, is 1226in the set 1227.Ar len-list , 1228which is either a single value or a list of values or ranges 1229specified in the same way as 1230.Ar ports . 1231.It Cm ipoptions Ar spec 1232Matches packets whose IPv4 header contains the comma separated list of 1233options specified in 1234.Ar spec . 1235The supported IP options are: 1236.Pp 1237.Cm ssrr 1238(strict source route), 1239.Cm lsrr 1240(loose source route), 1241.Cm rr 1242(record packet route) and 1243.Cm ts 1244(timestamp). 1245The absence of a particular option may be denoted 1246with a 1247.Ql \&! . 1248.It Cm ipprecedence Ar precedence 1249Matches IPv4 packets whose precedence field is equal to 1250.Ar precedence . 1251.It Cm ipsec 1252Matches packets that have IPSEC history associated with them 1253(i.e., the packet comes encapsulated in IPSEC, the kernel 1254has IPSEC support and IPSEC_FILTERTUNNEL option, and can correctly 1255decapsulate it). 1256.Pp 1257Note that specifying 1258.Cm ipsec 1259is different from specifying 1260.Cm proto Ar ipsec 1261as the latter will only look at the specific IP protocol field, 1262irrespective of IPSEC kernel support and the validity of the IPSEC data. 1263.Pp 1264Further note that this flag is silently ignored in kernels without 1265IPSEC support. 1266It does not affect rule processing when given and the 1267rules are handled as if with no 1268.Cm ipsec 1269flag. 1270.It Cm iptos Ar spec 1271Matches IPv4 packets whose 1272.Cm tos 1273field contains the comma separated list of 1274service types specified in 1275.Ar spec . 1276The supported IP types of service are: 1277.Pp 1278.Cm lowdelay 1279.Pq Dv IPTOS_LOWDELAY , 1280.Cm throughput 1281.Pq Dv IPTOS_THROUGHPUT , 1282.Cm reliability 1283.Pq Dv IPTOS_RELIABILITY , 1284.Cm mincost 1285.Pq Dv IPTOS_MINCOST , 1286.Cm congestion 1287.Pq Dv IPTOS_ECN_CE . 1288The absence of a particular type may be denoted 1289with a 1290.Ql \&! . 1291.It Cm ipttl Ar ttl-list 1292Matches IPv4 packets whose time to live is included in 1293.Ar ttl-list , 1294which is either a single value or a list of values or ranges 1295specified in the same way as 1296.Ar ports . 1297.It Cm ipversion Ar ver 1298Matches IP packets whose IP version field is 1299.Ar ver . 1300.It Cm keep-state 1301Upon a match, the firewall will create a dynamic rule, whose 1302default behaviour is to match bidirectional traffic between 1303source and destination IP/port using the same protocol. 1304The rule has a limited lifetime (controlled by a set of 1305.Xr sysctl 8 1306variables), and the lifetime is refreshed every time a matching 1307packet is found. 1308.It Cm layer2 1309Matches only layer2 packets, i.e., those passed to 1310.Nm 1311from ether_demux() and ether_output_frame(). 1312.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N 1313The firewall will only allow 1314.Ar N 1315connections with the same 1316set of parameters as specified in the rule. 1317One or more 1318of source and destination addresses and ports can be 1319specified. 1320Currently, 1321only IPv4 flows are supported. 1322.It Cm { MAC | mac } Ar dst-mac src-mac 1323Match packets with a given 1324.Ar dst-mac 1325and 1326.Ar src-mac 1327addresses, specified as the 1328.Cm any 1329keyword (matching any MAC address), or six groups of hex digits 1330separated by colons, 1331and optionally followed by a mask indicating the significant bits. 1332The mask may be specified using either of the following methods: 1333.Bl -enum -width indent 1334.It 1335A slash 1336.Pq / 1337followed by the number of significant bits. 1338For example, an address with 33 significant bits could be specified as: 1339.Pp 1340.Dl "MAC 10:20:30:40:50:60/33 any" 1341.Pp 1342.It 1343An ampersand 1344.Pq & 1345followed by a bitmask specified as six groups of hex digits separated 1346by colons. 1347For example, an address in which the last 16 bits are significant could 1348be specified as: 1349.Pp 1350.Dl "MAC 10:20:30:40:50:60&00:00:00:00:ff:ff any" 1351.Pp 1352Note that the ampersand character has a special meaning in many shells 1353and should generally be escaped. 1354.Pp 1355.El 1356Note that the order of MAC addresses (destination first, 1357source second) is 1358the same as on the wire, but the opposite of the one used for 1359IP addresses. 1360.It Cm mac-type Ar mac-type 1361Matches packets whose Ethernet Type field 1362corresponds to one of those specified as argument. 1363.Ar mac-type 1364is specified in the same way as 1365.Cm port numbers 1366(i.e., one or more comma-separated single values or ranges). 1367You can use symbolic names for known values such as 1368.Em vlan , ipv4, ipv6 . 1369Values can be entered as decimal or hexadecimal (if prefixed by 0x), 1370and they are always printed as hexadecimal (unless the 1371.Cm -N 1372option is used, in which case symbolic resolution will be attempted). 1373.It Cm proto Ar protocol 1374Matches packets with the corresponding IP protocol. 1375.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any 1376Matches packets received, transmitted or going through, 1377respectively, the interface specified by exact name 1378.Ns No ( Ar ifX Ns No ), 1379by device name 1380.Ns No ( Ar if Ns Ar * Ns No ), 1381by IP address, or through some interface. 1382.Pp 1383The 1384.Cm via 1385keyword causes the interface to always be checked. 1386If 1387.Cm recv 1388or 1389.Cm xmit 1390is used instead of 1391.Cm via , 1392then only the receive or transmit interface (respectively) 1393is checked. 1394By specifying both, it is possible to match packets based on 1395both receive and transmit interface, e.g.: 1396.Pp 1397.Dl "ipfw add deny ip from any to any out recv ed0 xmit ed1" 1398.Pp 1399The 1400.Cm recv 1401interface can be tested on either incoming or outgoing packets, 1402while the 1403.Cm xmit 1404interface can only be tested on outgoing packets. 1405So 1406.Cm out 1407is required (and 1408.Cm in 1409is invalid) whenever 1410.Cm xmit 1411is used. 1412.Pp 1413A packet may not have a receive or transmit interface: packets 1414originating from the local host have no receive interface, 1415while packets destined for the local host have no transmit 1416interface. 1417.It Cm setup 1418Matches TCP packets that have the SYN bit set but no ACK bit. 1419This is the short form of 1420.Dq Li tcpflags\ syn,!ack . 1421.It Cm src-ip Ar ip-address 1422Matches IPv4 packets whose source IP is one of the address(es) 1423specified as an argument. 1424.It Cm src-ip6 Ar ip6-address 1425Matches IPv6 packets whose source IP is one of the address(es) 1426specified as an argument. 1427.It Cm src-port Ar ports 1428Matches IP packets whose source port is one of the port(s) 1429specified as argument. 1430.It Cm tagged Ar tag-list 1431Matches packets whose tags are included in 1432.Ar tag-list , 1433which is either a single value or a list of values or ranges 1434specified in the same way as 1435.Ar ports . 1436Tags can be applied to the packet using 1437.Cm tag 1438rule action parameter (see it's description for details on tags). 1439.It Cm tcpack Ar ack 1440TCP packets only. 1441Match if the TCP header acknowledgment number field is set to 1442.Ar ack . 1443.It Cm tcpdatalen Ar tcpdatalen-list 1444Matches TCP packets whose length of TCP data is 1445.Ar tcpdatalen-list , 1446which is either a single value or a list of values or ranges 1447specified in the same way as 1448.Ar ports . 1449.It Cm tcpflags Ar spec 1450TCP packets only. 1451Match if the TCP header contains the comma separated list of 1452flags specified in 1453.Ar spec . 1454The supported TCP flags are: 1455.Pp 1456.Cm fin , 1457.Cm syn , 1458.Cm rst , 1459.Cm psh , 1460.Cm ack 1461and 1462.Cm urg . 1463The absence of a particular flag may be denoted 1464with a 1465.Ql \&! . 1466A rule which contains a 1467.Cm tcpflags 1468specification can never match a fragmented packet which has 1469a non-zero offset. 1470See the 1471.Cm frag 1472option for details on matching fragmented packets. 1473.It Cm tcpseq Ar seq 1474TCP packets only. 1475Match if the TCP header sequence number field is set to 1476.Ar seq . 1477.It Cm tcpwin Ar win 1478TCP packets only. 1479Match if the TCP header window field is set to 1480.Ar win . 1481.It Cm tcpoptions Ar spec 1482TCP packets only. 1483Match if the TCP header contains the comma separated list of 1484options specified in 1485.Ar spec . 1486The supported TCP options are: 1487.Pp 1488.Cm mss 1489(maximum segment size), 1490.Cm window 1491(tcp window advertisement), 1492.Cm sack 1493(selective ack), 1494.Cm ts 1495(rfc1323 timestamp) and 1496.Cm cc 1497(rfc1644 t/tcp connection count). 1498The absence of a particular option may be denoted 1499with a 1500.Ql \&! . 1501.It Cm uid Ar user 1502Match all TCP or UDP packets sent by or received for a 1503.Ar user . 1504A 1505.Ar user 1506may be matched by name or identification number. 1507.It Cm verrevpath 1508For incoming packets, 1509a routing table lookup is done on the packet's source address. 1510If the interface on which the packet entered the system matches the 1511outgoing interface for the route, 1512the packet matches. 1513If the interfaces do not match up, 1514the packet does not match. 1515All outgoing packets or packets with no incoming interface match. 1516.Pp 1517The name and functionality of the option is intentionally similar to 1518the Cisco IOS command: 1519.Pp 1520.Dl ip verify unicast reverse-path 1521.Pp 1522This option can be used to make anti-spoofing rules to reject all 1523packets with source addresses not from this interface. 1524See also the option 1525.Cm antispoof . 1526.It Cm versrcreach 1527For incoming packets, 1528a routing table lookup is done on the packet's source address. 1529If a route to the source address exists, but not the default route 1530or a blackhole/reject route, the packet matches. 1531Otherwise, the packet does not match. 1532All outgoing packets match. 1533.Pp 1534The name and functionality of the option is intentionally similar to 1535the Cisco IOS command: 1536.Pp 1537.Dl ip verify unicast source reachable-via any 1538.Pp 1539This option can be used to make anti-spoofing rules to reject all 1540packets whose source address is unreachable. 1541.It Cm antispoof 1542For incoming packets, the packet's source address is checked if it 1543belongs to a directly connected network. 1544If the network is directly connected, then the interface the packet 1545came on in is compared to the interface the network is connected to. 1546When incoming interface and directly connected interface are not the 1547same, the packet does not match. 1548Otherwise, the packet does match. 1549All outgoing packets match. 1550.Pp 1551This option can be used to make anti-spoofing rules to reject all 1552packets that pretend to be from a directly connected network but do 1553not come in through that interface. 1554This option is similar to but more restricted than 1555.Cm verrevpath 1556because it engages only on packets with source addresses of directly 1557connected networks instead of all source addresses. 1558.El 1559.Sh LOOKUP TABLES 1560Lookup tables are useful to handle large sparse address sets, 1561typically from a hundred to several thousands of entries. 1562There may be up to 128 different lookup tables, numbered 0 to 127. 1563.Pp 1564Each entry is represented by an 1565.Ar addr Ns Op / Ns Ar masklen 1566and will match all addresses with base 1567.Ar addr 1568(specified as an IP address or a hostname) 1569and mask width of 1570.Ar masklen 1571bits. 1572If 1573.Ar masklen 1574is not specified, it defaults to 32. 1575When looking up an IP address in a table, the most specific 1576entry will match. 1577Associated with each entry is a 32-bit unsigned 1578.Ar value , 1579which can optionally be checked by a rule matching code. 1580When adding an entry, if 1581.Ar value 1582is not specified, it defaults to 0. 1583.Pp 1584An entry can be added to a table 1585.Pq Cm add , 1586removed from a table 1587.Pq Cm delete , 1588a table can be examined 1589.Pq Cm list 1590or flushed 1591.Pq Cm flush . 1592.Pp 1593Internally, each table is stored in a Radix tree, the same way as 1594the routing table (see 1595.Xr route 4 ) . 1596.Pp 1597Lookup tables currently support IPv4 addresses only. 1598.Pp 1599The 1600.Cm tablearg 1601feature provides the ability to use a value, looked up in the table, as 1602the argument for a rule action, action parameter or rule option. 1603This can significantly reduce number of rules in some configurations. 1604The 1605.Cm tablearg 1606argument can be used with the following actions: 1607.Cm pipe , queue, divert, tee, netgraph, ngtee, fwd 1608action parameters: 1609.Cm tag, untag, 1610rule options: 1611.Cm limit, tagged. 1612.Pp 1613When used with 1614.Cm fwd 1615it is possible to supply table entries with values 1616that are in the form of IP addresses or hostnames. 1617See the 1618.Sx EXAMPLES 1619Section for example usage of tables and the tablearg keyword. 1620.Sh SETS OF RULES 1621Each rule belongs to one of 32 different 1622.Em sets 1623, numbered 0 to 31. 1624Set 31 is reserved for the default rule. 1625.Pp 1626By default, rules are put in set 0, unless you use the 1627.Cm set N 1628attribute when entering a new rule. 1629Sets can be individually and atomically enabled or disabled, 1630so this mechanism permits an easy way to store multiple configurations 1631of the firewall and quickly (and atomically) switch between them. 1632The command to enable/disable sets is 1633.Bd -ragged -offset indent 1634.Nm 1635.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ... 1636.Ed 1637.Pp 1638where multiple 1639.Cm enable 1640or 1641.Cm disable 1642sections can be specified. 1643Command execution is atomic on all the sets specified in the command. 1644By default, all sets are enabled. 1645.Pp 1646When you disable a set, its rules behave as if they do not exist 1647in the firewall configuration, with only one exception: 1648.Bd -ragged -offset indent 1649dynamic rules created from a rule before it had been disabled 1650will still be active until they expire. 1651In order to delete 1652dynamic rules you have to explicitly delete the parent rule 1653which generated them. 1654.Ed 1655.Pp 1656The set number of rules can be changed with the command 1657.Bd -ragged -offset indent 1658.Nm 1659.Cm set move 1660.Brq Cm rule Ar rule-number | old-set 1661.Cm to Ar new-set 1662.Ed 1663.Pp 1664Also, you can atomically swap two rulesets with the command 1665.Bd -ragged -offset indent 1666.Nm 1667.Cm set swap Ar first-set second-set 1668.Ed 1669.Pp 1670See the 1671.Sx EXAMPLES 1672Section on some possible uses of sets of rules. 1673.Sh STATEFUL FIREWALL 1674Stateful operation is a way for the firewall to dynamically 1675create rules for specific flows when packets that 1676match a given pattern are detected. 1677Support for stateful 1678operation comes through the 1679.Cm check-state , keep-state 1680and 1681.Cm limit 1682options of 1683.Nm rules . 1684.Pp 1685Dynamic rules are created when a packet matches a 1686.Cm keep-state 1687or 1688.Cm limit 1689rule, causing the creation of a 1690.Em dynamic 1691rule which will match all and only packets with 1692a given 1693.Em protocol 1694between a 1695.Em src-ip/src-port dst-ip/dst-port 1696pair of addresses 1697.Em ( src 1698and 1699.Em dst 1700are used here only to denote the initial match addresses, but they 1701are completely equivalent afterwards). 1702Dynamic rules will be checked at the first 1703.Cm check-state, keep-state 1704or 1705.Cm limit 1706occurrence, and the action performed upon a match will be the same 1707as in the parent rule. 1708.Pp 1709Note that no additional attributes other than protocol and IP addresses 1710and ports are checked on dynamic rules. 1711.Pp 1712The typical use of dynamic rules is to keep a closed firewall configuration, 1713but let the first TCP SYN packet from the inside network install a 1714dynamic rule for the flow so that packets belonging to that session 1715will be allowed through the firewall: 1716.Pp 1717.Dl "ipfw add check-state" 1718.Dl "ipfw add allow tcp from my-subnet to any setup keep-state" 1719.Dl "ipfw add deny tcp from any to any" 1720.Pp 1721A similar approach can be used for UDP, where an UDP packet coming 1722from the inside will install a dynamic rule to let the response through 1723the firewall: 1724.Pp 1725.Dl "ipfw add check-state" 1726.Dl "ipfw add allow udp from my-subnet to any keep-state" 1727.Dl "ipfw add deny udp from any to any" 1728.Pp 1729Dynamic rules expire after some time, which depends on the status 1730of the flow and the setting of some 1731.Cm sysctl 1732variables. 1733See Section 1734.Sx SYSCTL VARIABLES 1735for more details. 1736For TCP sessions, dynamic rules can be instructed to periodically 1737send keepalive packets to refresh the state of the rule when it is 1738about to expire. 1739.Pp 1740See Section 1741.Sx EXAMPLES 1742for more examples on how to use dynamic rules. 1743.Sh TRAFFIC SHAPER (DUMMYNET) CONFIGURATION 1744.Nm 1745is also the user interface for the 1746.Xr dummynet 4 1747traffic shaper. 1748.Pp 1749.Nm dummynet 1750operates by first using the firewall to classify packets and divide them into 1751.Em flows , 1752using any match pattern that can be used in 1753.Nm 1754rules. 1755Depending on local policies, a flow can contain packets for a single 1756TCP connection, or from/to a given host, or entire subnet, or a 1757protocol type, etc. 1758.Pp 1759Packets belonging to the same flow are then passed to either of two 1760different objects, which implement the traffic regulation: 1761.Bl -hang -offset XXXX 1762.It Em pipe 1763A pipe emulates a link with given bandwidth, propagation delay, 1764queue size and packet loss rate. 1765Packets are queued in front of the pipe as they come out from the classifier, 1766and then transferred to the pipe according to the pipe's parameters. 1767.Pp 1768.It Em queue 1769A queue 1770is an abstraction used to implement the WF2Q+ 1771(Worst-case Fair Weighted Fair Queueing) policy, which is 1772an efficient variant of the WFQ policy. 1773.br 1774The queue associates a 1775.Em weight 1776and a reference pipe to each flow, and then all backlogged (i.e., 1777with packets queued) flows linked to the same pipe share the pipe's 1778bandwidth proportionally to their weights. 1779Note that weights are not priorities; a flow with a lower weight 1780is still guaranteed to get its fraction of the bandwidth even if a 1781flow with a higher weight is permanently backlogged. 1782.Pp 1783.El 1784In practice, 1785.Em pipes 1786can be used to set hard limits to the bandwidth that a flow can use, whereas 1787.Em queues 1788can be used to determine how different flow share the available bandwidth. 1789.Pp 1790The 1791.Em pipe 1792and 1793.Em queue 1794configuration commands are the following: 1795.Bd -ragged -offset indent 1796.Cm pipe Ar number Cm config Ar pipe-configuration 1797.Pp 1798.Cm queue Ar number Cm config Ar queue-configuration 1799.Ed 1800.Pp 1801The following parameters can be configured for a pipe: 1802.Pp 1803.Bl -tag -width indent -compact 1804.It Cm bw Ar bandwidth | device 1805Bandwidth, measured in 1806.Sm off 1807.Op Cm K | M 1808.Brq Cm bit/s | Byte/s . 1809.Sm on 1810.Pp 1811A value of 0 (default) means unlimited bandwidth. 1812The unit must immediately follow the number, as in 1813.Pp 1814.Dl "ipfw pipe 1 config bw 300Kbit/s" 1815.Pp 1816If a device name is specified instead of a numeric value, as in 1817.Pp 1818.Dl "ipfw pipe 1 config bw tun0" 1819.Pp 1820then the transmit clock is supplied by the specified device. 1821At the moment only the 1822.Xr tun 4 1823device supports this 1824functionality, for use in conjunction with 1825.Xr ppp 8 . 1826.Pp 1827.It Cm delay Ar ms-delay 1828Propagation delay, measured in milliseconds. 1829The value is rounded to the next multiple of the clock tick 1830(typically 10ms, but it is a good practice to run kernels 1831with 1832.Dq "options HZ=1000" 1833to reduce 1834the granularity to 1ms or less). 1835Default value is 0, meaning no delay. 1836.El 1837.Pp 1838The following parameters can be configured for a queue: 1839.Pp 1840.Bl -tag -width indent -compact 1841.It Cm pipe Ar pipe_nr 1842Connects a queue to the specified pipe. 1843Multiple queues (with the same or different weights) can be connected to 1844the same pipe, which specifies the aggregate rate for the set of queues. 1845.Pp 1846.It Cm weight Ar weight 1847Specifies the weight to be used for flows matching this queue. 1848The weight must be in the range 1..100, and defaults to 1. 1849.El 1850.Pp 1851Finally, the following parameters can be configured for both 1852pipes and queues: 1853.Pp 1854.Bl -tag -width XXXX -compact 1855.Pp 1856.It Cm buckets Ar hash-table-size 1857Specifies the size of the hash table used for storing the 1858various queues. 1859Default value is 64 controlled by the 1860.Xr sysctl 8 1861variable 1862.Em net.inet.ip.dummynet.hash_size , 1863allowed range is 16 to 65536. 1864.Pp 1865.It Cm mask Ar mask-specifier 1866Packets sent to a given pipe or queue by an 1867.Nm 1868rule can be further classified into multiple flows, each of which is then 1869sent to a different 1870.Em dynamic 1871pipe or queue. 1872A flow identifier is constructed by masking the IP addresses, 1873ports and protocol types as specified with the 1874.Cm mask 1875options in the configuration of the pipe or queue. 1876For each different flow identifier, a new pipe or queue is created 1877with the same parameters as the original object, and matching packets 1878are sent to it. 1879.Pp 1880Thus, when 1881.Em dynamic pipes 1882are used, each flow will get the same bandwidth as defined by the pipe, 1883whereas when 1884.Em dynamic queues 1885are used, each flow will share the parent's pipe bandwidth evenly 1886with other flows generated by the same queue (note that other queues 1887with different weights might be connected to the same pipe). 1888.br 1889Available mask specifiers are a combination of one or more of the following: 1890.Pp 1891.Cm dst-ip Ar mask , 1892.Cm dst-ip6 Ar mask , 1893.Cm src-ip Ar mask , 1894.Cm src-ip6 Ar mask , 1895.Cm dst-port Ar mask , 1896.Cm src-port Ar mask , 1897.Cm flow-id Ar mask , 1898.Cm proto Ar mask 1899or 1900.Cm all , 1901.Pp 1902where the latter means all bits in all fields are significant. 1903.Pp 1904.It Cm noerror 1905When a packet is dropped by a dummynet queue or pipe, the error 1906is normally reported to the caller routine in the kernel, in the 1907same way as it happens when a device queue fills up. 1908Setting this 1909option reports the packet as successfully delivered, which can be 1910needed for some experimental setups where you want to simulate 1911loss or congestion at a remote router. 1912.Pp 1913.It Cm plr Ar packet-loss-rate 1914Packet loss rate. 1915Argument 1916.Ar packet-loss-rate 1917is a floating-point number between 0 and 1, with 0 meaning no 1918loss, 1 meaning 100% loss. 1919The loss rate is internally represented on 31 bits. 1920.Pp 1921.It Cm queue Brq Ar slots | size Ns Cm Kbytes 1922Queue size, in 1923.Ar slots 1924or 1925.Cm KBytes . 1926Default value is 50 slots, which 1927is the typical queue size for Ethernet devices. 1928Note that for slow speed links you should keep the queue 1929size short or your traffic might be affected by a significant 1930queueing delay. 1931E.g., 50 max-sized ethernet packets (1500 bytes) mean 600Kbit 1932or 20s of queue on a 30Kbit/s pipe. 1933Even worse effects can result if you get packets from an 1934interface with a much larger MTU, e.g.\& the loopback interface 1935with its 16KB packets. 1936.Pp 1937.It Cm red | gred Ar w_q Ns / Ns Ar min_th Ns / Ns Ar max_th Ns / Ns Ar max_p 1938Make use of the RED (Random Early Detection) queue management algorithm. 1939.Ar w_q 1940and 1941.Ar max_p 1942are floating 1943point numbers between 0 and 1 (0 not included), while 1944.Ar min_th 1945and 1946.Ar max_th 1947are integer numbers specifying thresholds for queue management 1948(thresholds are computed in bytes if the queue has been defined 1949in bytes, in slots otherwise). 1950The 1951.Xr dummynet 4 1952also supports the gentle RED variant (gred). 1953Three 1954.Xr sysctl 8 1955variables can be used to control the RED behaviour: 1956.Bl -tag -width indent 1957.It Em net.inet.ip.dummynet.red_lookup_depth 1958specifies the accuracy in computing the average queue 1959when the link is idle (defaults to 256, must be greater than zero) 1960.It Em net.inet.ip.dummynet.red_avg_pkt_size 1961specifies the expected average packet size (defaults to 512, must be 1962greater than zero) 1963.It Em net.inet.ip.dummynet.red_max_pkt_size 1964specifies the expected maximum packet size, only used when queue 1965thresholds are in bytes (defaults to 1500, must be greater than zero). 1966.El 1967.El 1968.Pp 1969When used with IPv6 data, dummynet currently has several limitations. 1970Information necessary to route link-local packets to an 1971interface is not avalable after processing by dummynet so those packets 1972are dropped in the output path. 1973Care should be taken to insure that link-local packets are not passed to 1974dummynet. 1975.Sh CHECKLIST 1976Here are some important points to consider when designing your 1977rules: 1978.Bl -bullet 1979.It 1980Remember that you filter both packets going 1981.Cm in 1982and 1983.Cm out . 1984Most connections need packets going in both directions. 1985.It 1986Remember to test very carefully. 1987It is a good idea to be near the console when doing this. 1988If you cannot be near the console, 1989use an auto-recovery script such as the one in 1990.Pa /usr/share/examples/ipfw/change_rules.sh . 1991.It 1992Do not forget the loopback interface. 1993.El 1994.Sh FINE POINTS 1995.Bl -bullet 1996.It 1997There are circumstances where fragmented datagrams are unconditionally 1998dropped. 1999TCP packets are dropped if they do not contain at least 20 bytes of 2000TCP header, UDP packets are dropped if they do not contain a full 8 2001byte UDP header, and ICMP packets are dropped if they do not contain 20024 bytes of ICMP header, enough to specify the ICMP type, code, and 2003checksum. 2004These packets are simply logged as 2005.Dq pullup failed 2006since there may not be enough good data in the packet to produce a 2007meaningful log entry. 2008.It 2009Another type of packet is unconditionally dropped, a TCP packet with a 2010fragment offset of one. 2011This is a valid packet, but it only has one use, to try 2012to circumvent firewalls. 2013When logging is enabled, these packets are 2014reported as being dropped by rule -1. 2015.It 2016If you are logged in over a network, loading the 2017.Xr kld 4 2018version of 2019.Nm 2020is probably not as straightforward as you would think. 2021I recommend the following command line: 2022.Bd -literal -offset indent 2023kldload ipfw && \e 2024ipfw add 32000 allow ip from any to any 2025.Ed 2026.Pp 2027Along the same lines, doing an 2028.Bd -literal -offset indent 2029ipfw flush 2030.Ed 2031.Pp 2032in similar surroundings is also a bad idea. 2033.It 2034The 2035.Nm 2036filter list may not be modified if the system security level 2037is set to 3 or higher 2038(see 2039.Xr init 8 2040for information on system security levels). 2041.El 2042.Sh PACKET DIVERSION 2043A 2044.Xr divert 4 2045socket bound to the specified port will receive all packets 2046diverted to that port. 2047If no socket is bound to the destination port, or if the divert module is 2048not loaded, or if the kernel was not compiled with divert socket support, 2049the packets are dropped. 2050.Sh NETWORK ADDRESS TRANSLATION (NAT) 2051The nat configuration command is the following: 2052.Bd -ragged -offset indent 2053.Bk -words 2054.Cm nat 2055.Ar nat_number 2056.Cm config 2057.Ar nat-configuration 2058.Ek 2059.Ed 2060.Pp 2061. 2062The following parameters can be configured: 2063.Bl -tag -width indent 2064.It Cm ip Ar ip_address 2065Define an ip address to use for aliasing. 2066.It Cm if Ar nic 2067Use ip addres of NIC for aliasing, dynamically changing 2068it if NIC's ip address change. 2069.It Cm log 2070Enable logging on this nat instance. 2071.It Cm deny_in 2072Deny any incoming connection from outside world. 2073.It Cm same_ports 2074Try to leave the alias port numbers unchanged from 2075the actual local port numbers. 2076.It Cm unreg_only 2077Traffic on the local network not originating from an 2078unregistered address spaces will be ignored. 2079.It Cm reset 2080Reset table of the packet aliasing engine on address change. 2081.It Cm reverse 2082Reverse the way libalias handles aliasing. 2083.It Cm proxy_only 2084Obey transparent proxy rules only, packet aliasing is not performed. 2085.El 2086.Pp 2087To let the packet continue after being (de)aliased, set the sysctl variable 2088.Em net.inet.ip.fw.one_pass 2089to 0. 2090For more information about aliasing modes, refer to 2091.Xr libalias 3 2092. 2093See Section 2094.Sx EXAMPLES 2095for some examples about nat usage. 2096.Sh REDIRECT AND LSNAT SUPPORT IN IPFW 2097Redirect and LSNAT support follow closely the syntax used in 2098.Xr natd 8 2099. 2100See Section 2101.Sx EXAMPLES 2102for some examples on how to do redirect and lsnat. 2103.Sh SYSCTL VARIABLES 2104A set of 2105.Xr sysctl 8 2106variables controls the behaviour of the firewall and 2107associated modules 2108.Pq Nm dummynet , bridge . 2109These are shown below together with their default value 2110(but always check with the 2111.Xr sysctl 8 2112command what value is actually in use) and meaning: 2113.Bl -tag -width indent 2114.It Em net.inet.ip.dummynet.expire : No 1 2115Lazily delete dynamic pipes/queue once they have no pending traffic. 2116You can disable this by setting the variable to 0, in which case 2117the pipes/queues will only be deleted when the threshold is reached. 2118.It Em net.inet.ip.dummynet.hash_size : No 64 2119Default size of the hash table used for dynamic pipes/queues. 2120This value is used when no 2121.Cm buckets 2122option is specified when configuring a pipe/queue. 2123.It Em net.inet.ip.dummynet.max_chain_len : No 16 2124Target value for the maximum number of pipes/queues in a hash bucket. 2125The product 2126.Cm max_chain_len*hash_size 2127is used to determine the threshold over which empty pipes/queues 2128will be expired even when 2129.Cm net.inet.ip.dummynet.expire=0 . 2130.It Em net.inet.ip.dummynet.red_lookup_depth : No 256 2131.It Em net.inet.ip.dummynet.red_avg_pkt_size : No 512 2132.It Em net.inet.ip.dummynet.red_max_pkt_size : No 1500 2133Parameters used in the computations of the drop probability 2134for the RED algorithm. 2135.It Em net.inet.ip.fw.autoinc_step : No 100 2136Delta between rule numbers when auto-generating them. 2137The value must be in the range 1..1000. 2138.It Em net.inet.ip.fw.curr_dyn_buckets : Em net.inet.ip.fw.dyn_buckets 2139The current number of buckets in the hash table for dynamic rules 2140(readonly). 2141.It Em net.inet.ip.fw.debug : No 1 2142Controls debugging messages produced by 2143.Nm . 2144.It Em net.inet.ip.fw.dyn_buckets : No 256 2145The number of buckets in the hash table for dynamic rules. 2146Must be a power of 2, up to 65536. 2147It only takes effect when all dynamic rules have expired, so you 2148are advised to use a 2149.Cm flush 2150command to make sure that the hash table is resized. 2151.It Em net.inet.ip.fw.dyn_count : No 3 2152Current number of dynamic rules 2153(read-only). 2154.It Em net.inet.ip.fw.dyn_keepalive : No 1 2155Enables generation of keepalive packets for 2156.Cm keep-state 2157rules on TCP sessions. 2158A keepalive is generated to both 2159sides of the connection every 5 seconds for the last 20 2160seconds of the lifetime of the rule. 2161.It Em net.inet.ip.fw.dyn_max : No 8192 2162Maximum number of dynamic rules. 2163When you hit this limit, no more dynamic rules can be 2164installed until old ones expire. 2165.It Em net.inet.ip.fw.dyn_ack_lifetime : No 300 2166.It Em net.inet.ip.fw.dyn_syn_lifetime : No 20 2167.It Em net.inet.ip.fw.dyn_fin_lifetime : No 1 2168.It Em net.inet.ip.fw.dyn_rst_lifetime : No 1 2169.It Em net.inet.ip.fw.dyn_udp_lifetime : No 5 2170.It Em net.inet.ip.fw.dyn_short_lifetime : No 30 2171These variables control the lifetime, in seconds, of dynamic 2172rules. 2173Upon the initial SYN exchange the lifetime is kept short, 2174then increased after both SYN have been seen, then decreased 2175again during the final FIN exchange or when a RST is received. 2176Both 2177.Em dyn_fin_lifetime 2178and 2179.Em dyn_rst_lifetime 2180must be strictly lower than 5 seconds, the period of 2181repetition of keepalives. 2182The firewall enforces that. 2183.It Em net.inet.ip.fw.enable : No 1 2184Enables the firewall. 2185Setting this variable to 0 lets you run your machine without 2186firewall even if compiled in. 2187.It Em net.inet6.ip6.fw.enable : No 1 2188provides the same functionality as above for the IPv6 case. 2189.It Em net.inet.ip.fw.one_pass : No 1 2190When set, the packet exiting from the 2191.Xr dummynet 4 2192pipe or from 2193.Xr ng_ipfw 4 2194node is not passed though the firewall again. 2195Otherwise, after an action, the packet is 2196reinjected into the firewall at the next rule. 2197.It Em net.inet.ip.fw.verbose : No 1 2198Enables verbose messages. 2199.It Em net.inet.ip.fw.verbose_limit : No 0 2200Limits the number of messages produced by a verbose firewall. 2201.It Em net.inet6.ip6.fw.deny_unknown_exthdrs : No 1 2202If enabled packets with unknown IPv6 Extension Headers will be denied. 2203.It Em net.link.ether.ipfw : No 0 2204Controls whether layer-2 packets are passed to 2205.Nm . 2206Default is no. 2207.It Em net.link.bridge.ipfw : No 0 2208Controls whether bridged packets are passed to 2209.Nm . 2210Default is no. 2211.El 2212.Pp 2213.Sh EXAMPLES 2214There are far too many possible uses of 2215.Nm 2216so this Section will only give a small set of examples. 2217.Pp 2218.Ss BASIC PACKET FILTERING 2219This command adds an entry which denies all tcp packets from 2220.Em cracker.evil.org 2221to the telnet port of 2222.Em wolf.tambov.su 2223from being forwarded by the host: 2224.Pp 2225.Dl "ipfw add deny tcp from cracker.evil.org to wolf.tambov.su telnet" 2226.Pp 2227This one disallows any connection from the entire cracker's 2228network to my host: 2229.Pp 2230.Dl "ipfw add deny ip from 123.45.67.0/24 to my.host.org" 2231.Pp 2232A first and efficient way to limit access (not using dynamic rules) 2233is the use of the following rules: 2234.Pp 2235.Dl "ipfw add allow tcp from any to any established" 2236.Dl "ipfw add allow tcp from net1 portlist1 to net2 portlist2 setup" 2237.Dl "ipfw add allow tcp from net3 portlist3 to net3 portlist3 setup" 2238.Dl "..." 2239.Dl "ipfw add deny tcp from any to any" 2240.Pp 2241The first rule will be a quick match for normal TCP packets, 2242but it will not match the initial SYN packet, which will be 2243matched by the 2244.Cm setup 2245rules only for selected source/destination pairs. 2246All other SYN packets will be rejected by the final 2247.Cm deny 2248rule. 2249.Pp 2250If you administer one or more subnets, you can take advantage 2251of the address sets and or-blocks and write extremely 2252compact rulesets which selectively enable services to blocks 2253of clients, as below: 2254.Pp 2255.Dl "goodguys=\*q{ 10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }\*q" 2256.Dl "badguys=\*q10.1.2.0/24{8,38,60}\*q" 2257.Dl "" 2258.Dl "ipfw add allow ip from ${goodguys} to any" 2259.Dl "ipfw add deny ip from ${badguys} to any" 2260.Dl "... normal policies ..." 2261.Pp 2262The 2263.Cm verrevpath 2264option could be used to do automated anti-spoofing by adding the 2265following to the top of a ruleset: 2266.Pp 2267.Dl "ipfw add deny ip from any to any not verrevpath in" 2268.Pp 2269This rule drops all incoming packets that appear to be coming to the 2270system on the wrong interface. 2271For example, a packet with a source 2272address belonging to a host on a protected internal network would be 2273dropped if it tried to enter the system from an external interface. 2274.Pp 2275The 2276.Cm antispoof 2277option could be used to do similar but more restricted anti-spoofing 2278by adding the following to the top of a ruleset: 2279.Pp 2280.Dl "ipfw add deny ip from any to any not antispoof in" 2281.Pp 2282This rule drops all incoming packets that appear to be coming from another 2283directly connected system but on the wrong interface. 2284For example, a packet with a source address of 2285.Li 192.168.0.0/24 2286, configured on 2287.Li fxp0 2288, but coming in on 2289.Li fxp1 2290would be dropped. 2291.Ss DYNAMIC RULES 2292In order to protect a site from flood attacks involving fake 2293TCP packets, it is safer to use dynamic rules: 2294.Pp 2295.Dl "ipfw add check-state" 2296.Dl "ipfw add deny tcp from any to any established" 2297.Dl "ipfw add allow tcp from my-net to any setup keep-state" 2298.Pp 2299This will let the firewall install dynamic rules only for 2300those connection which start with a regular SYN packet coming 2301from the inside of our network. 2302Dynamic rules are checked when encountering the first 2303.Cm check-state 2304or 2305.Cm keep-state 2306rule. 2307A 2308.Cm check-state 2309rule should usually be placed near the beginning of the 2310ruleset to minimize the amount of work scanning the ruleset. 2311Your mileage may vary. 2312.Pp 2313To limit the number of connections a user can open 2314you can use the following type of rules: 2315.Pp 2316.Dl "ipfw add allow tcp from my-net/24 to any setup limit src-addr 10" 2317.Dl "ipfw add allow tcp from any to me setup limit src-addr 4" 2318.Pp 2319The former (assuming it runs on a gateway) will allow each host 2320on a /24 network to open at most 10 TCP connections. 2321The latter can be placed on a server to make sure that a single 2322client does not use more than 4 simultaneous connections. 2323.Pp 2324.Em BEWARE : 2325stateful rules can be subject to denial-of-service attacks 2326by a SYN-flood which opens a huge number of dynamic rules. 2327The effects of such attacks can be partially limited by 2328acting on a set of 2329.Xr sysctl 8 2330variables which control the operation of the firewall. 2331.Pp 2332Here is a good usage of the 2333.Cm list 2334command to see accounting records and timestamp information: 2335.Pp 2336.Dl ipfw -at list 2337.Pp 2338or in short form without timestamps: 2339.Pp 2340.Dl ipfw -a list 2341.Pp 2342which is equivalent to: 2343.Pp 2344.Dl ipfw show 2345.Pp 2346Next rule diverts all incoming packets from 192.168.2.0/24 2347to divert port 5000: 2348.Pp 2349.Dl ipfw divert 5000 ip from 192.168.2.0/24 to any in 2350.Pp 2351.Ss TRAFFIC SHAPING 2352The following rules show some of the applications of 2353.Nm 2354and 2355.Xr dummynet 4 2356for simulations and the like. 2357.Pp 2358This rule drops random incoming packets with a probability 2359of 5%: 2360.Pp 2361.Dl "ipfw add prob 0.05 deny ip from any to any in" 2362.Pp 2363A similar effect can be achieved making use of dummynet pipes: 2364.Pp 2365.Dl "ipfw add pipe 10 ip from any to any" 2366.Dl "ipfw pipe 10 config plr 0.05" 2367.Pp 2368We can use pipes to artificially limit bandwidth, e.g.\& on a 2369machine acting as a router, if we want to limit traffic from 2370local clients on 192.168.2.0/24 we do: 2371.Pp 2372.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2373.Dl "ipfw pipe 1 config bw 300Kbit/s queue 50KBytes" 2374.Pp 2375note that we use the 2376.Cm out 2377modifier so that the rule is not used twice. 2378Remember in fact that 2379.Nm 2380rules are checked both on incoming and outgoing packets. 2381.Pp 2382Should we want to simulate a bidirectional link with bandwidth 2383limitations, the correct way is the following: 2384.Pp 2385.Dl "ipfw add pipe 1 ip from any to any out" 2386.Dl "ipfw add pipe 2 ip from any to any in" 2387.Dl "ipfw pipe 1 config bw 64Kbit/s queue 10Kbytes" 2388.Dl "ipfw pipe 2 config bw 64Kbit/s queue 10Kbytes" 2389.Pp 2390The above can be very useful, e.g.\& if you want to see how 2391your fancy Web page will look for a residential user who 2392is connected only through a slow link. 2393You should not use only one pipe for both directions, unless 2394you want to simulate a half-duplex medium (e.g.\& AppleTalk, 2395Ethernet, IRDA). 2396It is not necessary that both pipes have the same configuration, 2397so we can also simulate asymmetric links. 2398.Pp 2399Should we want to verify network performance with the RED queue 2400management algorithm: 2401.Pp 2402.Dl "ipfw add pipe 1 ip from any to any" 2403.Dl "ipfw pipe 1 config bw 500Kbit/s queue 100 red 0.002/30/80/0.1" 2404.Pp 2405Another typical application of the traffic shaper is to 2406introduce some delay in the communication. 2407This can significantly affect applications which do a lot of Remote 2408Procedure Calls, and where the round-trip-time of the 2409connection often becomes a limiting factor much more than 2410bandwidth: 2411.Pp 2412.Dl "ipfw add pipe 1 ip from any to any out" 2413.Dl "ipfw add pipe 2 ip from any to any in" 2414.Dl "ipfw pipe 1 config delay 250ms bw 1Mbit/s" 2415.Dl "ipfw pipe 2 config delay 250ms bw 1Mbit/s" 2416.Pp 2417Per-flow queueing can be useful for a variety of purposes. 2418A very simple one is counting traffic: 2419.Pp 2420.Dl "ipfw add pipe 1 tcp from any to any" 2421.Dl "ipfw add pipe 1 udp from any to any" 2422.Dl "ipfw add pipe 1 ip from any to any" 2423.Dl "ipfw pipe 1 config mask all" 2424.Pp 2425The above set of rules will create queues (and collect 2426statistics) for all traffic. 2427Because the pipes have no limitations, the only effect is 2428collecting statistics. 2429Note that we need 3 rules, not just the last one, because 2430when 2431.Nm 2432tries to match IP packets it will not consider ports, so we 2433would not see connections on separate ports as different 2434ones. 2435.Pp 2436A more sophisticated example is limiting the outbound traffic 2437on a net with per-host limits, rather than per-network limits: 2438.Pp 2439.Dl "ipfw add pipe 1 ip from 192.168.2.0/24 to any out" 2440.Dl "ipfw add pipe 2 ip from any to 192.168.2.0/24 in" 2441.Dl "ipfw pipe 1 config mask src-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2442.Dl "ipfw pipe 2 config mask dst-ip 0x000000ff bw 200Kbit/s queue 20Kbytes" 2443.Ss LOOKUP TABLES 2444In the following example, we need to create several traffic bandwidth 2445classes and we need different hosts/networks to fall into different classes. 2446We create one pipe for each class and configure them accordingly. 2447Then we create a single table and fill it with IP subnets and addresses. 2448For each subnet/host we set the argument equal to the number of the pipe 2449that it should use. 2450Then we classify traffic using a single rule: 2451.Pp 2452.Dl "ipfw pipe 1 config bw 1000Kbyte/s" 2453.Dl "ipfw pipe 4 config bw 4000Kbyte/s" 2454.Dl "..." 2455.Dl "ipfw table 1 add 192.168.2.0/24 1" 2456.Dl "ipfw table 1 add 192.168.0.0/27 4" 2457.Dl "ipfw table 1 add 192.168.0.2 1" 2458.Dl "..." 2459.Dl "ipfw add pipe tablearg ip from table(1) to any" 2460.Pp 2461Using the 2462.Cm fwd 2463action, the table entries may include hostnames and IP addresses. 2464.Pp 2465.Dl "ipfw table 1 add 192.168.2.0/24 10.23.2.1" 2466.Dl "ipfw table 1 add 192.168.0.0/27 router1.dmz" 2467.Dl "..." 2468.Dl "ipfw add 100 fwd tablearg ip from any to table(1)" 2469.Ss SETS OF RULES 2470To add a set of rules atomically, e.g.\& set 18: 2471.Pp 2472.Dl "ipfw set disable 18" 2473.Dl "ipfw add NN set 18 ... # repeat as needed" 2474.Dl "ipfw set enable 18" 2475.Pp 2476To delete a set of rules atomically the command is simply: 2477.Pp 2478.Dl "ipfw delete set 18" 2479.Pp 2480To test a ruleset and disable it and regain control if something goes wrong: 2481.Pp 2482.Dl "ipfw set disable 18" 2483.Dl "ipfw add NN set 18 ... # repeat as needed" 2484.Dl "ipfw set enable 18; echo done; sleep 30 && ipfw set disable 18" 2485.Pp 2486Here if everything goes well, you press control-C before the "sleep" 2487terminates, and your ruleset will be left active. 2488Otherwise, e.g.\& if 2489you cannot access your box, the ruleset will be disabled after 2490the sleep terminates thus restoring the previous situation. 2491.Pp 2492To show rules of the specific set: 2493.Pp 2494.Dl "ipfw set 18 show" 2495.Pp 2496To show rules of the disabled set: 2497.Pp 2498.Dl "ipfw -S set 18 show" 2499.Pp 2500To clear a specific rule counters of the specific set: 2501.Pp 2502.Dl "ipfw set 18 zero NN" 2503.Pp 2504To delete a specific rule of the specific set: 2505.Pp 2506.Dl "ipfw set 18 delete NN" 2507.Ss NAT, REDIRECT AND LSNAT 2508First redirect all the traffic to nat instance 123: 2509.Pp 2510.Dl "ipfw add nat 123 all from any to any" 2511.Pp 2512Then to configure nat instance 123 to alias all the outgoing traffic with ip 2513192.168.0.123, blocking all incoming connections, trying to keep 2514same ports on both sides, clearing aliasing table on address change 2515and keeping a log of traffic/link statistics: 2516.Pp 2517.Dl "ipfw nat 123 config ip 192.168.0.123 log deny_in reset same_ports" 2518.Pp 2519Or to change address of instance 123, aliasing table will be cleared (see 2520reset option): 2521.Pp 2522.Dl "ipfw nat 123 config ip 10.0.0.1" 2523.Pp 2524To see configuration of nat instance 123: 2525.Pp 2526.Dl "ipfw nat 123 show config" 2527.Pp 2528To show logs of all the instances in range 111-999: 2529.Pp 2530.Dl "ipfw nat 111-999 show" 2531.Pp 2532To see configurations of all instances: 2533.Pp 2534.Dl "ipfw nat show config" 2535.Pp 2536Or a redirect rule with mixed modes could looks like: 2537.Pp 2538.Dl "ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66" 2539.Dl " redirect_port tcp 192.168.0.1:80 500" 2540.Dl " redirect_proto udp 192.168.1.43 192.168.1.1" 2541.Dl " redirect_addr 192.168.0.10,192.168.0.11" 2542.Dl " 10.0.0.100 # LSNAT" 2543.Dl " redirect_port tcp 192.168.0.1:80,192.168.0.10:22" 2544.Dl " 500 # LSNAT" 2545.Pp 2546or it could be splitted in: 2547.Pp 2548.Dl "ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66" 2549.Dl "ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500" 2550.Dl "ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1" 2551.Dl "ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12" 2552.Dl " 10.0.0.100" 2553.Dl "ipfw nat 5 config redirect_port tcp" 2554.Dl " 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500" 2555.Pp 2556.Sh SEE ALSO 2557.Xr cpp 1 , 2558.Xr m4 1 , 2559.Xr altq 4 , 2560.Xr divert 4 , 2561.Xr dummynet 4 , 2562.Xr if_bridge 4 , 2563.Xr ip 4 , 2564.Xr ipfirewall 4 , 2565.Xr ng_ipfw 4 , 2566.Xr protocols 5 , 2567.Xr services 5 , 2568.Xr init 8 , 2569.Xr kldload 8 , 2570.Xr reboot 8 , 2571.Xr sysctl 8 , 2572.Xr syslogd 8 2573.Sh HISTORY 2574The 2575.Nm 2576utility first appeared in 2577.Fx 2.0 . 2578.Xr dummynet 4 2579was introduced in 2580.Fx 2.2.8 . 2581Stateful extensions were introduced in 2582.Fx 4.0 . 2583.Nm ipfw2 2584was introduced in Summer 2002. 2585.Sh AUTHORS 2586.An Ugen J. S. Antsilevich , 2587.An Poul-Henning Kamp , 2588.An Alex Nash , 2589.An Archie Cobbs , 2590.An Luigi Rizzo . 2591.Pp 2592.An -nosplit 2593API based upon code written by 2594.An Daniel Boulet 2595for BSDI. 2596.Pp 2597.An -nosplit 2598In-kernel NAT support written by 2599.An Paolo Pisati Aq piso@FreeBSD.org 2600as part of a Summer of Code 2005 project. 2601.Pp 2602Work on 2603.Xr dummynet 4 2604traffic shaper supported by Akamba Corp. 2605.Sh BUGS 2606The syntax has grown over the years and sometimes it might be confusing. 2607Unfortunately, backward compatibility prevents cleaning up mistakes 2608made in the definition of the syntax. 2609.Pp 2610.Em !!! WARNING !!! 2611.Pp 2612Misconfiguring the firewall can put your computer in an unusable state, 2613possibly shutting down network services and requiring console access to 2614regain control of it. 2615.Pp 2616Incoming packet fragments diverted by 2617.Cm divert 2618are reassembled before delivery to the socket. 2619The action used on those packet is the one from the 2620rule which matches the first fragment of the packet. 2621.Pp 2622Packets diverted to userland, and then reinserted by a userland process 2623may lose various packet attributes. 2624The packet source interface name 2625will be preserved if it is shorter than 8 bytes and the userland process 2626saves and reuses the sockaddr_in 2627(as does 2628.Xr natd 8 ) ; 2629otherwise, it may be lost. 2630If a packet is reinserted in this manner, later rules may be incorrectly 2631applied, making the order of 2632.Cm divert 2633rules in the rule sequence very important. 2634.Pp 2635Dummynet drops all packets with IPv6 link-local addresses. 2636.Pp 2637Rules using 2638.Cm uid 2639or 2640.Cm gid 2641may not behave as expected. 2642In particular, incoming SYN packets may 2643have no uid or gid associated with them since they do not yet belong 2644to a TCP connection, and the uid/gid associated with a packet may not 2645be as expected if the associated process calls 2646.Xr setuid 2 2647or similar system calls. 2648.Pp 2649Rule syntax is subject to the command line environment and some patterns 2650may need to be escaped with the backslash character 2651or quoted appropriately. 2652.Pp 2653Due to the architecture of 2654.Xr libalias 3 , 2655ipfw nat is not compatible with the tcp segmentation offloading 2656(TSO). Thus, to reliably nat your network traffic, please disable TSO 2657on your NICs using 2658.Xr ifconfig 8 . 2659