1.\" $OpenBSD: pf.conf.5,v 1.406 2009/01/31 19:37:12 sobrado Exp $ 2.\" 3.\" Copyright (c) 2002, Daniel Hartmeier 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 10.\" - Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" - Redistributions in binary form must reproduce the above 13.\" copyright notice, this list of conditions and the following 14.\" disclaimer in the documentation and/or other materials provided 15.\" with the distribution. 16.\" 17.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 18.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 19.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 20.\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 21.\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 22.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 23.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 24.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 25.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 27.\" ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd June 21, 2023 31.Dt PF.CONF 5 32.Os 33.Sh NAME 34.Nm pf.conf 35.Nd packet filter configuration file 36.Sh DESCRIPTION 37The 38.Xr pf 4 39packet filter modifies, drops or passes packets according to rules or 40definitions specified in 41.Nm pf.conf . 42.Sh STATEMENT ORDER 43There are eight types of statements in 44.Nm pf.conf : 45.Bl -tag -width xxxx 46.It Cm Macros 47User-defined variables may be defined and used later, simplifying 48the configuration file. 49Macros must be defined before they are referenced in 50.Nm pf.conf . 51.It Cm Tables 52Tables provide a mechanism for increasing the performance and flexibility of 53rules with large numbers of source or destination addresses. 54.It Cm Options 55Options tune the behaviour of the packet filtering engine. 56.It Cm Ethernet Filtering 57Ethernet filtering provides rule-based blocking or passing of Ethernet packets. 58.It Cm Traffic Normalization Li (e.g. Em scrub ) 59Traffic normalization protects internal machines against inconsistencies 60in Internet protocols and implementations. 61.It Cm Queueing 62Queueing provides rule-based bandwidth control. 63.It Cm Translation Li (Various forms of NAT) 64Translation rules specify how addresses are to be mapped or redirected to 65other addresses. 66.It Cm Packet Filtering 67Packet filtering provides rule-based blocking or passing of packets. 68.El 69.Pp 70With the exception of 71.Cm macros 72and 73.Cm tables , 74the types of statements should be grouped and appear in 75.Nm pf.conf 76in the order shown above, as this matches the operation of the underlying 77packet filtering engine. 78By default 79.Xr pfctl 8 80enforces this order (see 81.Ar set require-order 82below). 83.Pp 84Comments can be put anywhere in the file using a hash mark 85.Pq Sq # , 86and extend to the end of the current line. 87.Pp 88Additional configuration files can be included with the 89.Ic include 90keyword, for example: 91.Bd -literal -offset indent 92include "/etc/pf/sub.filter.conf" 93.Ed 94.Sh MACROS 95Macros can be defined that will later be expanded in context. 96Macro names must start with a letter, and may contain letters, digits 97and underscores. 98Macro names may not be reserved words (for example 99.Ar pass , 100.Ar in , 101.Ar out ) . 102Macros are not expanded inside quotes. 103.Pp 104For example, 105.Bd -literal -offset indent 106ext_if = \&"kue0\&" 107all_ifs = \&"{\&" $ext_if lo0 \&"}\&" 108pass out on $ext_if from any to any 109pass in on $ext_if proto tcp from any to any port 25 110.Ed 111.Sh TABLES 112Tables are named structures which can hold a collection of addresses and 113networks. 114Lookups against tables in 115.Xr pf 4 116are relatively fast, making a single rule with tables much more efficient, 117in terms of 118processor usage and memory consumption, than a large number of rules which 119differ only in IP address (either created explicitly or automatically by rule 120expansion). 121.Pp 122Tables can be used as the source or destination of filter rules, 123.Ar scrub 124rules 125or 126translation rules such as 127.Ar nat 128or 129.Ar rdr 130(see below for details on the various rule types). 131Tables can also be used for the redirect address of 132.Ar nat 133and 134.Ar rdr 135rules and in the routing options of filter rules, but only for 136.Ar round-robin 137pools. 138.Pp 139Tables can be defined with any of the following 140.Xr pfctl 8 141mechanisms. 142As with macros, reserved words may not be used as table names. 143.Bl -tag -width "manually" 144.It Ar manually 145Persistent tables can be manually created with the 146.Ar add 147or 148.Ar replace 149option of 150.Xr pfctl 8 , 151before or after the ruleset has been loaded. 152.It Pa pf.conf 153Table definitions can be placed directly in this file, and loaded at the 154same time as other rules are loaded, atomically. 155Table definitions inside 156.Nm pf.conf 157use the 158.Ar table 159statement, and are especially useful to define non-persistent tables. 160The contents of a pre-existing table defined without a list of addresses 161to initialize it is not altered when 162.Nm pf.conf 163is loaded. 164A table initialized with the empty list, 165.Li { } , 166will be cleared on load. 167.El 168.Pp 169Tables may be defined with the following attributes: 170.Bl -tag -width persist 171.It Ar persist 172The 173.Ar persist 174flag forces the kernel to keep the table even when no rules refer to it. 175If the flag is not set, the kernel will automatically remove the table 176when the last rule referring to it is flushed. 177.It Ar const 178The 179.Ar const 180flag prevents the user from altering the contents of the table once it 181has been created. 182Without that flag, 183.Xr pfctl 8 184can be used to add or remove addresses from the table at any time, even 185when running with 186.Xr securelevel 7 187= 2. 188.It Ar counters 189The 190.Ar counters 191flag enables per-address packet and byte counters which can be displayed with 192.Xr pfctl 8 . 193Note that this feature carries significant memory overhead for large tables. 194.El 195.Pp 196For example, 197.Bd -literal -offset indent 198table \*(Ltprivate\*(Gt const { 10/8, 172.16/12, 192.168/16 } 199table \*(Ltbadhosts\*(Gt persist 200block on fxp0 from { \*(Ltprivate\*(Gt, \*(Ltbadhosts\*(Gt } to any 201.Ed 202.Pp 203creates a table called private, to hold RFC 1918 private network 204blocks, and a table called badhosts, which is initially empty. 205A filter rule is set up to block all traffic coming from addresses listed in 206either table. 207The private table cannot have its contents changed and the badhosts table 208will exist even when no active filter rules reference it. 209Addresses may later be added to the badhosts table, so that traffic from 210these hosts can be blocked by using 211.Bd -literal -offset indent 212# pfctl -t badhosts -Tadd 204.92.77.111 213.Ed 214.Pp 215A table can also be initialized with an address list specified in one or more 216external files, using the following syntax: 217.Bd -literal -offset indent 218table \*(Ltspam\*(Gt persist file \&"/etc/spammers\&" file \&"/etc/openrelays\&" 219block on fxp0 from \*(Ltspam\*(Gt to any 220.Ed 221.Pp 222The files 223.Pa /etc/spammers 224and 225.Pa /etc/openrelays 226list IP addresses, one per line. 227Any lines beginning with a # are treated as comments and ignored. 228In addition to being specified by IP address, hosts may also be 229specified by their hostname. 230When the resolver is called to add a hostname to a table, 231.Em all 232resulting IPv4 and IPv6 addresses are placed into the table. 233IP addresses can also be entered in a table by specifying a valid interface 234name, a valid interface group or the 235.Em self 236keyword, in which case all addresses assigned to the interface(s) will be 237added to the table. 238.Sh OPTIONS 239.Xr pf 4 240may be tuned for various situations using the 241.Ar set 242command. 243.Bl -tag -width xxxx 244.It Ar set timeout 245.Pp 246.Bl -tag -width "src.track" -compact 247.It Ar interval 248Interval between purging expired states and fragments. 249.It Ar frag 250Seconds before an unassembled fragment is expired. 251.It Ar src.track 252Length of time to retain a source tracking entry after the last state 253expires. 254.El 255.Pp 256When a packet matches a stateful connection, the seconds to live for the 257connection will be updated to that of the 258.Ar proto.modifier 259which corresponds to the connection state. 260Each packet which matches this state will reset the TTL. 261Tuning these values may improve the performance of the 262firewall at the risk of dropping valid idle connections. 263.Pp 264.Bl -tag -width xxxx -compact 265.It Ar tcp.first 266The state after the first packet. 267.It Ar tcp.opening 268The state before the destination host ever sends a packet. 269.It Ar tcp.established 270The fully established state. 271.It Ar tcp.closing 272The state after the first FIN has been sent. 273.It Ar tcp.finwait 274The state after both FINs have been exchanged and the connection is closed. 275Some hosts (notably web servers on Solaris) send TCP packets even after closing 276the connection. 277Increasing 278.Ar tcp.finwait 279(and possibly 280.Ar tcp.closing ) 281can prevent blocking of such packets. 282.It Ar tcp.closed 283The state after one endpoint sends an RST. 284.El 285.Pp 286ICMP and UDP are handled in a fashion similar to TCP, but with a much more 287limited set of states: 288.Pp 289.Bl -tag -width xxxx -compact 290.It Ar udp.first 291The state after the first packet. 292.It Ar udp.single 293The state if the source host sends more than one packet but the destination 294host has never sent one back. 295.It Ar udp.multiple 296The state if both hosts have sent packets. 297.It Ar icmp.first 298The state after the first packet. 299.It Ar icmp.error 300The state after an ICMP error came back in response to an ICMP packet. 301.El 302.Pp 303Other protocols are handled similarly to UDP: 304.Pp 305.Bl -tag -width xxxx -compact 306.It Ar other.first 307.It Ar other.single 308.It Ar other.multiple 309.El 310.Pp 311Timeout values can be reduced adaptively as the number of state table 312entries grows. 313.Pp 314.Bl -tag -width xxxx -compact 315.It Ar adaptive.start 316When the number of state entries exceeds this value, adaptive scaling 317begins. 318All timeout values are scaled linearly with factor 319(adaptive.end - number of states) / (adaptive.end - adaptive.start). 320.It Ar adaptive.end 321When reaching this number of state entries, all timeout values become 322zero, effectively purging all state entries immediately. 323This value is used to define the scale factor, it should not actually 324be reached (set a lower state limit, see below). 325.El 326.Pp 327Adaptive timeouts are enabled by default, with an adaptive.start value 328equal to 60% of the state limit, and an adaptive.end value equal to 329120% of the state limit. 330They can be disabled by setting both adaptive.start and adaptive.end to 0. 331.Pp 332The adaptive timeout values can be defined both globally and for each rule. 333When used on a per-rule basis, the values relate to the number of 334states created by the rule, otherwise to the total number of 335states. 336.Pp 337For example: 338.Bd -literal -offset indent 339set timeout tcp.first 120 340set timeout tcp.established 86400 341set timeout { adaptive.start 6000, adaptive.end 12000 } 342set limit states 10000 343.Ed 344.Pp 345With 9000 state table entries, the timeout values are scaled to 50% 346(tcp.first 60, tcp.established 43200). 347.It Ar set loginterface 348Enable collection of packet and byte count statistics for the given 349interface or interface group. 350These statistics can be viewed using 351.Bd -literal -offset indent 352# pfctl -s info 353.Ed 354.Pp 355In this example 356.Xr pf 4 357collects statistics on the interface named dc0: 358.Bd -literal -offset indent 359set loginterface dc0 360.Ed 361.Pp 362One can disable the loginterface using: 363.Bd -literal -offset indent 364set loginterface none 365.Ed 366.It Ar set limit 367Sets hard limits on the memory pools used by the packet filter. 368See 369.Xr zone 9 370for an explanation of memory pools. 371.Pp 372For example, 373.Bd -literal -offset indent 374set limit states 20000 375.Ed 376.Pp 377sets the maximum number of entries in the memory pool used by state table 378entries (generated by 379.Ar pass 380rules which do not specify 381.Ar no state ) 382to 20000. 383Using 384.Bd -literal -offset indent 385set limit frags 20000 386.Ed 387.Pp 388sets the maximum number of entries in the memory pool used for fragment 389reassembly (generated by 390.Ar scrub 391rules) to 20000. 392Using 393.Bd -literal -offset indent 394set limit src-nodes 2000 395.Ed 396.Pp 397sets the maximum number of entries in the memory pool used for tracking 398source IP addresses (generated by the 399.Ar sticky-address 400and 401.Ar src.track 402options) to 2000. 403Using 404.Bd -literal -offset indent 405set limit tables 1000 406set limit table-entries 100000 407.Ed 408.Pp 409sets limits on the memory pools used by tables. 410The first limits the number of tables that can exist to 1000. 411The second limits the overall number of addresses that can be stored 412in tables to 100000. 413.Pp 414Various limits can be combined on a single line: 415.Bd -literal -offset indent 416set limit { states 20000, frags 20000, src-nodes 2000 } 417.Ed 418.It Ar set ruleset-optimization 419.Bl -tag -width xxxxxxxx -compact 420.It Ar none 421Disable the ruleset optimizer. 422.It Ar basic 423Enable basic ruleset optimization. 424This is the default behaviour. 425Basic ruleset optimization does four things to improve the 426performance of ruleset evaluations: 427.Pp 428.Bl -enum -compact 429.It 430remove duplicate rules 431.It 432remove rules that are a subset of another rule 433.It 434combine multiple rules into a table when advantageous 435.It 436re-order the rules to improve evaluation performance 437.El 438.Pp 439.It Ar profile 440Uses the currently loaded ruleset as a feedback profile to tailor the 441ordering of quick rules to actual network traffic. 442.El 443.Pp 444It is important to note that the ruleset optimizer will modify the ruleset 445to improve performance. 446A side effect of the ruleset modification is that per-rule accounting 447statistics will have different meanings than before. 448If per-rule accounting is important for billing purposes or whatnot, 449either the ruleset optimizer should not be used or a label field should 450be added to all of the accounting rules to act as optimization barriers. 451.Pp 452Optimization can also be set as a command-line argument to 453.Xr pfctl 8 , 454overriding the settings in 455.Nm . 456.It Ar set optimization 457Optimize state timeouts for one of the following network environments: 458.Pp 459.Bl -tag -width xxxx -compact 460.It Ar normal 461A normal network environment. 462Suitable for almost all networks. 463.It Ar high-latency 464A high-latency environment (such as a satellite connection). 465.It Ar satellite 466Alias for 467.Ar high-latency . 468.It Ar aggressive 469Aggressively expire connections. 470This can greatly reduce the memory usage of the firewall at the cost of 471dropping idle connections early. 472.It Ar conservative 473Extremely conservative settings. 474Avoid dropping legitimate connections at the 475expense of greater memory utilization (possibly much greater on a busy 476network) and slightly increased processor utilization. 477.El 478.Pp 479For example: 480.Bd -literal -offset indent 481set optimization aggressive 482.Ed 483.It Ar set block-policy 484The 485.Ar block-policy 486option sets the default behaviour for the packet 487.Ar block 488action: 489.Pp 490.Bl -tag -width xxxxxxxx -compact 491.It Ar drop 492Packet is silently dropped. 493.It Ar return 494A TCP RST is returned for blocked TCP packets, 495an SCTP ABORT chunk is returned for blocked SCTP packets, 496an ICMP UNREACHABLE is returned for blocked UDP packets, 497and all other packets are silently dropped. 498.El 499.Pp 500For example: 501.Bd -literal -offset indent 502set block-policy return 503.Ed 504.It Ar set fail-policy 505The 506.Ar fail-policy 507option sets the behaviour of rules which should pass a packet but were 508unable to do so. 509This might happen when a nat or route-to rule uses an empty table as list 510of targets or if a rule fails to create state or source node. 511The following 512.Ar block 513actions are possible: 514.Pp 515.Bl -tag -width xxxxxxxx -compact 516.It Ar drop 517Incoming packet is silently dropped. 518.It Ar return 519Incoming packet is dropped and TCP RST is returned for TCP packets, 520an SCTP ABORT chunk is returned for blocked SCTP packets, 521an ICMP UNREACHABLE is returned for UDP packets, 522and no response is sent for other packets. 523.El 524.Pp 525For example: 526.Bd -literal -offset indent 527set fail-policy return 528.Ed 529.It Ar set state-policy 530The 531.Ar state-policy 532option sets the default behaviour for states: 533.Pp 534.Bl -tag -width group-bound -compact 535.It Ar if-bound 536States are bound to interface. 537.It Ar floating 538States can match packets on any interfaces (the default). 539.El 540.Pp 541For example: 542.Bd -literal -offset indent 543set state-policy if-bound 544.Ed 545.It Ar set syncookies never | always | adaptive 546When 547.Cm syncookies 548are active, pf will answer each incoming TCP SYN with a syncookie SYNACK, 549without allocating any resources. 550Upon reception of the client's ACK in response to the syncookie 551SYNACK, pf will evaluate the ruleset and create state if the ruleset 552permits it, complete the three way handshake with the target host and 553continue the connection with synproxy in place. 554This allows pf to be resilient against large synflood attacks which would 555run the state table against its limits otherwise. 556Due to the blind answers to every incoming SYN syncookies share the caveats of 557synproxy, namely seemingly accepting connections that will be dropped later on. 558.Pp 559.Bl -tag -width adaptive -compact 560.It Cm never 561pf will never send syncookie SYNACKs (the default). 562.It Cm always 563pf will always send syncookie SYNACKs. 564.It Cm adaptive 565pf will enable syncookie mode when a given percentage of the state table 566is used up by half-open TCP connections, as in, those that saw the initial 567SYN but didn't finish the three way handshake. 568The thresholds for entering and leaving syncookie mode can be specified using 569.Bd -literal -offset indent 570set syncookies adaptive (start 25%, end 12%) 571.Ed 572.El 573.It Ar set state-defaults 574The 575.Ar state-defaults 576option sets the state options for states created from rules 577without an explicit 578.Ar keep state . 579For example: 580.Bd -literal -offset indent 581set state-defaults no-sync 582.Ed 583.It Ar set hostid 584The 32-bit 585.Ar hostid 586identifies this firewall's state table entries to other firewalls 587in a 588.Xr pfsync 4 589failover cluster. 590By default the hostid is set to a pseudo-random value, however it may be 591desirable to manually configure it, for example to more easily identify the 592source of state table entries. 593.Bd -literal -offset indent 594set hostid 1 595.Ed 596.Pp 597The hostid may be specified in either decimal or hexadecimal. 598.It Ar set require-order 599By default 600.Xr pfctl 8 601enforces an ordering of the statement types in the ruleset to: 602.Em options , 603.Em normalization , 604.Em queueing , 605.Em translation , 606.Em filtering . 607Setting this option to 608.Ar no 609disables this enforcement. 610There may be non-trivial and non-obvious implications to an out of 611order ruleset. 612Consider carefully before disabling the order enforcement. 613.It Ar set fingerprints 614Load fingerprints of known operating systems from the given filename. 615By default fingerprints of known operating systems are automatically 616loaded from 617.Xr pf.os 5 618in 619.Pa /etc 620but can be overridden via this option. 621Setting this option may leave a small period of time where the fingerprints 622referenced by the currently active ruleset are inconsistent until the new 623ruleset finishes loading. 624.Pp 625For example: 626.Pp 627.Dl set fingerprints \&"/etc/pf.os.devel\&" 628.It Ar set skip on Aq Ar ifspec 629List interfaces for which packets should not be filtered. 630Packets passing in or out on such interfaces are passed as if pf was 631disabled, i.e. pf does not process them in any way. 632This can be useful on loopback and other virtual interfaces, when 633packet filtering is not desired and can have unexpected effects. 634For example: 635.Pp 636.Dl set skip on lo0 637.It Ar set debug 638Set the debug 639.Ar level 640to one of the following: 641.Pp 642.Bl -tag -width xxxxxxxxxxxx -compact 643.It Ar none 644Don't generate debug messages. 645.It Ar urgent 646Generate debug messages only for serious errors. 647.It Ar misc 648Generate debug messages for various errors. 649.It Ar loud 650Generate debug messages for common conditions. 651.El 652.It Ar set keepcounters 653Preserve rule counters across rule updates. 654Usually rule counters are reset to zero on every update of the ruleset. 655With 656.Ar keepcounters 657set pf will attempt to find matching rules between old and new rulesets 658and preserve the rule counters. 659.El 660.Sh ETHERNET FILTERING 661.Xr pf 4 662has the ability to 663.Ar block 664and 665.Ar pass 666packets based on attributes of their Ethernet (layer 2) header. 667.Pp 668For each packet processed by the packet filter, the filter rules are 669evaluated in sequential order, from first to last. 670The last matching rule decides what action is taken. 671If no rule matches the packet, the default action is to pass 672the packet. 673.Pp 674The following actions can be used in the filter: 675.Bl -tag -width xxxx 676.It Ar block 677The packet is blocked. 678Unlike for layer 3 traffic the packet is always silently dropped. 679.It Ar pass 680The packet is passed; 681no state is created for layer 2 traffic. 682.El 683.Sh PARAMETERS 684The rule parameters specify the packets to which a rule applies. 685A packet always comes in on, or goes out through, one interface. 686Most parameters are optional. 687If a parameter is specified, the rule only applies to packets with 688matching attributes. 689Certain parameters can be expressed as lists, in which case 690.Xr pfctl 8 691generates all needed rule combinations. 692.Bl -tag -width xxxx 693.It Ar in No or Ar out 694This rule applies to incoming or outgoing packets. 695If neither 696.Ar in 697nor 698.Ar out 699are specified, the rule will match packets in both directions. 700.It Ar quick 701If a packet matches a rule which has the 702.Ar quick 703option set, this rule 704is considered the last matching rule, and evaluation of subsequent rules 705is skipped. 706.It Ar on Aq Ar ifspec 707This rule applies only to packets coming in on, or going out through, this 708particular interface or interface group. 709For more information on interface groups, 710see the 711.Ic group 712keyword in 713.Xr ifconfig 8 . 714.It Ar bridge-to Aq interface 715Packets matching this rule will be sent out of the specified interface without 716further processing. 717.It Ar proto Aq Ar protocol 718This rule applies only to packets of this protocol. 719Note that Ethernet protocol numbers are different from those used in 720.Xr ip 4 721and 722.Xr ip6 4 . 723.It Xo 724.Ar from Aq Ar source 725.Ar to Aq Ar dest 726.Xc 727This rule applies only to packets with the specified source and destination 728MAC addresses. 729.It Xo Ar queue Aq Ar queue 730.Xc 731Packets matching this rule will be assigned to the specified queue. 732See 733.Sx QUEUEING 734for setup details. 735.Pp 736.It Ar tag Aq Ar string 737Packets matching this rule will be tagged with the 738specified string. 739The tag acts as an internal marker that can be used to 740identify these packets later on. 741This can be used, for example, to provide trust between 742interfaces and to determine if packets have been 743processed by translation rules. 744Tags are 745.Qq sticky , 746meaning that the packet will be tagged even if the rule 747is not the last matching rule. 748Further matching rules can replace the tag with a 749new one but will not remove a previously applied tag. 750A packet is only ever assigned one tag at a time. 751.It Ar tagged Aq Ar string 752Used to specify that packets must already be tagged with the given tag in order 753to match the rule. 754Inverse tag matching can also be done by specifying the ! operator before the 755tagged keyword. 756.Sh TRAFFIC NORMALIZATION 757Traffic normalization is used to sanitize packet content in such 758a way that there are no ambiguities in packet interpretation on 759the receiving side. 760The normalizer does IP fragment reassembly to prevent attacks 761that confuse intrusion detection systems by sending overlapping 762IP fragments. 763Packet normalization is invoked with the 764.Ar scrub 765directive. 766.Pp 767.Ar scrub 768has the following options: 769.Bl -tag -width xxxx 770.It Ar no-df 771Clears the 772.Ar dont-fragment 773bit from a matching IP packet. 774Some operating systems are known to generate fragmented packets with the 775.Ar dont-fragment 776bit set. 777This is particularly true with NFS. 778.Ar Scrub 779will drop such fragmented 780.Ar dont-fragment 781packets unless 782.Ar no-df 783is specified. 784.Pp 785Unfortunately some operating systems also generate their 786.Ar dont-fragment 787packets with a zero IP identification field. 788Clearing the 789.Ar dont-fragment 790bit on packets with a zero IP ID may cause deleterious results if an 791upstream router later fragments the packet. 792Using the 793.Ar random-id 794modifier (see below) is recommended in combination with the 795.Ar no-df 796modifier to ensure unique IP identifiers. 797.It Ar min-ttl Aq Ar number 798Enforces a minimum TTL for matching IP packets. 799.It Ar max-mss Aq Ar number 800Enforces a maximum MSS for matching TCP packets. 801.It Xo Ar set-tos Aq Ar string 802.No \*(Ba Aq Ar number 803.Xc 804Enforces a 805.Em TOS 806for matching IP packets. 807.Em TOS 808may be 809given as one of 810.Ar critical , 811.Ar inetcontrol , 812.Ar lowdelay , 813.Ar netcontrol , 814.Ar throughput , 815.Ar reliability , 816or one of the DiffServ Code Points: 817.Ar ef , 818.Ar va , 819.Ar af11 No ... Ar af43 , 820.Ar cs0 No ... Ar cs7 ; 821or as either hex or decimal. 822.It Ar random-id 823Replaces the IP identification field with random values to compensate 824for predictable values generated by many hosts. 825This option only applies to packets that are not fragmented 826after the optional fragment reassembly. 827.It Ar fragment reassemble 828Using 829.Ar scrub 830rules, fragments can be reassembled by normalization. 831In this case, fragments are buffered until they form a complete 832packet, and only the completed packet is passed on to the filter. 833The advantage is that filter rules have to deal only with complete 834packets, and can ignore fragments. 835The drawback of caching fragments is the additional memory cost. 836This is the default behaviour unless no fragment reassemble is specified. 837.It Ar no fragment reassemble 838Do not reassemble fragments. 839.It Ar reassemble tcp 840Statefully normalizes TCP connections. 841.Ar scrub reassemble tcp 842rules may not have the direction (in/out) specified. 843.Ar reassemble tcp 844performs the following normalizations: 845.Pp 846.Bl -tag -width timeout -compact 847.It ttl 848Neither side of the connection is allowed to reduce their IP TTL. 849An attacker may send a packet such that it reaches the firewall, affects 850the firewall state, and expires before reaching the destination host. 851.Ar reassemble tcp 852will raise the TTL of all packets back up to the highest value seen on 853the connection. 854.It timestamp modulation 855Modern TCP stacks will send a timestamp on every TCP packet and echo 856the other endpoint's timestamp back to them. 857Many operating systems will merely start the timestamp at zero when 858first booted, and increment it several times a second. 859The uptime of the host can be deduced by reading the timestamp and multiplying 860by a constant. 861Also observing several different timestamps can be used to count hosts 862behind a NAT device. 863And spoofing TCP packets into a connection requires knowing or guessing 864valid timestamps. 865Timestamps merely need to be monotonically increasing and not derived off a 866guessable base time. 867.Ar reassemble tcp 868will cause 869.Ar scrub 870to modulate the TCP timestamps with a random number. 871.It extended PAWS checks 872There is a problem with TCP on long fat pipes, in that a packet might get 873delayed for longer than it takes the connection to wrap its 32-bit sequence 874space. 875In such an occurrence, the old packet would be indistinguishable from a 876new packet and would be accepted as such. 877The solution to this is called PAWS: Protection Against Wrapped Sequence 878numbers. 879It protects against it by making sure the timestamp on each packet does 880not go backwards. 881.Ar reassemble tcp 882also makes sure the timestamp on the packet does not go forward more 883than the RFC allows. 884By doing this, 885.Xr pf 4 886artificially extends the security of TCP sequence numbers by 10 to 18 887bits when the host uses appropriately randomized timestamps, since a 888blind attacker would have to guess the timestamp as well. 889.El 890.El 891.Pp 892For example, 893.Bd -literal -offset indent 894scrub in on $ext_if all fragment reassemble 895.Ed 896.Pp 897The 898.Ar no 899option prefixed to a scrub rule causes matching packets to remain unscrubbed, 900much in the same way as 901.Ar drop quick 902works in the packet filter (see below). 903This mechanism should be used when it is necessary to exclude specific packets 904from broader scrub rules. 905.Sh QUEUEING with ALTQ 906The ALTQ system is currently not available in the GENERIC kernel nor as 907loadable modules. 908In order to use the herein after called queueing options one has to use a 909custom built kernel. 910Please refer to 911.Xr altq 4 912to learn about the related kernel options. 913.Pp 914Packets can be assigned to queues for the purpose of bandwidth 915control. 916At least two declarations are required to configure queues, and later 917any packet filtering rule can reference the defined queues by name. 918During the filtering component of 919.Nm pf.conf , 920the last referenced 921.Ar queue 922name is where any packets from 923.Ar pass 924rules will be queued, while for 925.Ar block 926rules it specifies where any resulting ICMP or TCP RST 927packets should be queued. 928The 929.Ar scheduler 930defines the algorithm used to decide which packets get delayed, dropped, or 931sent out immediately. 932There are three 933.Ar schedulers 934currently supported. 935.Bl -tag -width xxxx 936.It Ar cbq 937Class Based Queueing. 938.Ar Queues 939attached to an interface build a tree, thus each 940.Ar queue 941can have further child 942.Ar queues . 943Each queue can have a 944.Ar priority 945and a 946.Ar bandwidth 947assigned. 948.Ar Priority 949mainly controls the time packets take to get sent out, while 950.Ar bandwidth 951has primarily effects on throughput. 952.Ar cbq 953achieves both partitioning and sharing of link bandwidth 954by hierarchically structured classes. 955Each class has its own 956.Ar queue 957and is assigned its share of 958.Ar bandwidth . 959A child class can borrow bandwidth from its parent class 960as long as excess bandwidth is available 961(see the option 962.Ar borrow , 963below). 964.It Ar priq 965Priority Queueing. 966.Ar Queues 967are flat attached to the interface, thus, 968.Ar queues 969cannot have further child 970.Ar queues . 971Each 972.Ar queue 973has a unique 974.Ar priority 975assigned, ranging from 0 to 15. 976Packets in the 977.Ar queue 978with the highest 979.Ar priority 980are processed first. 981.It Ar hfsc 982Hierarchical Fair Service Curve. 983.Ar Queues 984attached to an interface build a tree, thus each 985.Ar queue 986can have further child 987.Ar queues . 988Each queue can have a 989.Ar priority 990and a 991.Ar bandwidth 992assigned. 993.Ar Priority 994mainly controls the time packets take to get sent out, while 995.Ar bandwidth 996primarily affects throughput. 997.Ar hfsc 998supports both link-sharing and guaranteed real-time services. 999It employs a service curve based QoS model, 1000and its unique feature is an ability to decouple 1001.Ar delay 1002and 1003.Ar bandwidth 1004allocation. 1005.El 1006.Pp 1007The interfaces on which queueing should be activated are declared using 1008the 1009.Ar altq on 1010declaration. 1011.Ar altq on 1012has the following keywords: 1013.Bl -tag -width xxxx 1014.It Aq Ar interface 1015Queueing is enabled on the named interface. 1016.It Aq Ar scheduler 1017Specifies which queueing scheduler to use. 1018Currently supported values 1019are 1020.Ar cbq 1021for Class Based Queueing, 1022.Ar priq 1023for Priority Queueing and 1024.Ar hfsc 1025for the Hierarchical Fair Service Curve scheduler. 1026.It Ar bandwidth Aq Ar bw 1027The maximum bitrate for all queues on an 1028interface may be specified using the 1029.Ar bandwidth 1030keyword. 1031The value can be specified as an absolute value or as a 1032percentage of the interface bandwidth. 1033When using an absolute value, the suffixes 1034.Ar b , 1035.Ar Kb , 1036.Ar Mb , 1037and 1038.Ar Gb 1039are used to represent bits, kilobits, megabits, and 1040gigabits per second, respectively. 1041The value must not exceed the interface bandwidth. 1042If 1043.Ar bandwidth 1044is not specified, the interface bandwidth is used 1045(but take note that some interfaces do not know their bandwidth, 1046or can adapt their bandwidth rates). 1047.It Ar qlimit Aq Ar limit 1048The maximum number of packets held in the queue. 1049The default is 50. 1050.It Ar tbrsize Aq Ar size 1051Adjusts the size, in bytes, of the token bucket regulator. 1052If not specified, heuristics based on the 1053interface bandwidth are used to determine the size. 1054.It Ar queue Aq Ar list 1055Defines a list of subqueues to create on an interface. 1056.El 1057.Pp 1058In the following example, the interface dc0 1059should queue up to 5Mbps in four second-level queues using 1060Class Based Queueing. 1061Those four queues will be shown in a later example. 1062.Bd -literal -offset indent 1063altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh } 1064.Ed 1065.Pp 1066Once interfaces are activated for queueing using the 1067.Ar altq 1068directive, a sequence of 1069.Ar queue 1070directives may be defined. 1071The name associated with a 1072.Ar queue 1073must match a queue defined in the 1074.Ar altq 1075directive (e.g. mail), or, except for the 1076.Ar priq 1077.Ar scheduler , 1078in a parent 1079.Ar queue 1080declaration. 1081The following keywords can be used: 1082.Bl -tag -width xxxx 1083.It Ar on Aq Ar interface 1084Specifies the interface the queue operates on. 1085If not given, it operates on all matching interfaces. 1086.It Ar bandwidth Aq Ar bw 1087Specifies the maximum bitrate to be processed by the queue. 1088This value must not exceed the value of the parent 1089.Ar queue 1090and can be specified as an absolute value or a percentage of the parent 1091queue's bandwidth. 1092If not specified, defaults to 100% of the parent queue's bandwidth. 1093The 1094.Ar priq 1095scheduler does not support bandwidth specification. 1096.It Ar priority Aq Ar level 1097Between queues a priority level can be set. 1098For 1099.Ar cbq 1100and 1101.Ar hfsc , 1102the range is 0 to 7 and for 1103.Ar priq , 1104the range is 0 to 15. 1105The default for all is 1. 1106.Ar Priq 1107queues with a higher priority are always served first. 1108.Ar Cbq 1109and 1110.Ar Hfsc 1111queues with a higher priority are preferred in the case of overload. 1112.It Ar qlimit Aq Ar limit 1113The maximum number of packets held in the queue. 1114The default is 50. 1115.El 1116.Pp 1117The 1118.Ar scheduler 1119can get additional parameters with 1120.Xo Aq Ar scheduler 1121.Pf ( Aq Ar parameters ) . 1122.Xc 1123Parameters are as follows: 1124.Bl -tag -width Fl 1125.It Ar default 1126Packets not matched by another queue are assigned to this one. 1127Exactly one default queue is required. 1128.It Ar red 1129Enable RED (Random Early Detection) on this queue. 1130RED drops packets with a probability proportional to the average 1131queue length. 1132.It Ar rio 1133Enables RIO on this queue. 1134RIO is RED with IN/OUT, thus running 1135RED two times more than RIO would achieve the same effect. 1136RIO is currently not supported in the GENERIC kernel. 1137.It Ar ecn 1138Enables ECN (Explicit Congestion Notification) on this queue. 1139ECN implies RED. 1140.El 1141.Pp 1142The 1143.Ar cbq 1144.Ar scheduler 1145supports an additional option: 1146.Bl -tag -width Fl 1147.It Ar borrow 1148The queue can borrow bandwidth from the parent. 1149.El 1150.Pp 1151The 1152.Ar hfsc 1153.Ar scheduler 1154supports some additional options: 1155.Bl -tag -width Fl 1156.It Ar realtime Aq Ar sc 1157The minimum required bandwidth for the queue. 1158.It Ar upperlimit Aq Ar sc 1159The maximum allowed bandwidth for the queue. 1160.It Ar linkshare Aq Ar sc 1161The bandwidth share of a backlogged queue. 1162.El 1163.Pp 1164.Aq Ar sc 1165is an acronym for 1166.Ar service curve . 1167.Pp 1168The format for service curve specifications is 1169.Ar ( m1 , d , m2 ) . 1170.Ar m2 1171controls the bandwidth assigned to the queue. 1172.Ar m1 1173and 1174.Ar d 1175are optional and can be used to control the initial bandwidth assignment. 1176For the first 1177.Ar d 1178milliseconds the queue gets the bandwidth given as 1179.Ar m1 , 1180afterwards the value given in 1181.Ar m2 . 1182.Pp 1183Furthermore, with 1184.Ar cbq 1185and 1186.Ar hfsc , 1187child queues can be specified as in an 1188.Ar altq 1189declaration, thus building a tree of queues using a part of 1190their parent's bandwidth. 1191.Pp 1192Packets can be assigned to queues based on filter rules by using the 1193.Ar queue 1194keyword. 1195Normally only one 1196.Ar queue 1197is specified; when a second one is specified it will instead be used for 1198packets which have a 1199.Em TOS 1200of 1201.Em lowdelay 1202and for TCP ACKs with no data payload. 1203.Pp 1204To continue the previous example, the examples below would specify the 1205four referenced 1206queues, plus a few child queues. 1207Interactive 1208.Xr ssh 1 1209sessions get priority over bulk transfers like 1210.Xr scp 1 1211and 1212.Xr sftp 1 . 1213The queues may then be referenced by filtering rules (see 1214.Sx PACKET FILTERING 1215below). 1216.Bd -literal 1217queue std bandwidth 10% cbq(default) 1218queue http bandwidth 60% priority 2 cbq(borrow red) \e 1219 { employees, developers } 1220queue developers bandwidth 75% cbq(borrow) 1221queue employees bandwidth 15% 1222queue mail bandwidth 10% priority 0 cbq(borrow ecn) 1223queue ssh bandwidth 20% cbq(borrow) { ssh_interactive, ssh_bulk } 1224queue ssh_interactive bandwidth 50% priority 7 cbq(borrow) 1225queue ssh_bulk bandwidth 50% priority 0 cbq(borrow) 1226 1227block return out on dc0 inet all queue std 1228pass out on dc0 inet proto tcp from $developerhosts to any port 80 \e 1229 queue developers 1230pass out on dc0 inet proto tcp from $employeehosts to any port 80 \e 1231 queue employees 1232pass out on dc0 inet proto tcp from any to any port 22 \e 1233 queue(ssh_bulk, ssh_interactive) 1234pass out on dc0 inet proto tcp from any to any port 25 \e 1235 queue mail 1236.Ed 1237.Sh QUEUEING with dummynet 1238Queueing can also be done with 1239.Xr dummynet 4 . 1240Queues and pipes can be created with 1241.Xr dnctl 8 . 1242.Pp 1243Packets can be assigned to queues and pipes using 1244.Ar dnqueue 1245and 1246.Ar dnpipe 1247respectively. 1248.Pp 1249Both 1250.Ar dnqueue 1251and 1252.Ar dnpipe 1253take either a single pipe or queue number or two numbers as arguments. 1254The first pipe or queue number will be used to shape the traffic in the rule 1255direction, the second will be used to shape the traffic in the reverse 1256direction. 1257If the rule does not specify a direction the first packet to create state will 1258be shaped according to the first number, and the response traffic according to 1259the second. 1260.Pp 1261If the 1262.Xr dummynet 4 1263module is not loaded any traffic sent into a queue or pipe will be dropped. 1264.Sh TRANSLATION 1265Translation rules modify either the source or destination address of the 1266packets associated with a stateful connection. 1267A stateful connection is automatically created to track packets matching 1268such a rule as long as they are not blocked by the filtering section of 1269.Nm pf.conf . 1270The translation engine modifies the specified address and/or port in the 1271packet, recalculates IP, TCP and UDP checksums as necessary, and passes 1272it to the packet filter for evaluation. 1273.Pp 1274Since translation occurs before filtering the filter 1275engine will see packets as they look after any 1276addresses and ports have been translated. 1277Filter rules will therefore have to filter based on the translated 1278address and port number. 1279Packets that match a translation rule are only automatically passed if 1280the 1281.Ar pass 1282modifier is given, otherwise they are 1283still subject to 1284.Ar block 1285and 1286.Ar pass 1287rules. 1288.Pp 1289The state entry created permits 1290.Xr pf 4 1291to keep track of the original address for traffic associated with that state 1292and correctly direct return traffic for that connection. 1293.Pp 1294Various types of translation are possible with pf: 1295.Bl -tag -width xxxx 1296.It Ar binat 1297A 1298.Ar binat 1299rule specifies a bidirectional mapping between an external IP netblock 1300and an internal IP netblock. 1301.It Ar nat 1302A 1303.Ar nat 1304rule specifies that IP addresses are to be changed as the packet 1305traverses the given interface. 1306This technique allows one or more IP addresses 1307on the translating host to support network traffic for a larger range of 1308machines on an "inside" network. 1309Although in theory any IP address can be used on the inside, it is strongly 1310recommended that one of the address ranges defined by RFC 1918 be used. 1311These netblocks are: 1312.Bd -literal 131310.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8) 1314172.16.0.0 - 172.31.255.255 (i.e., 172.16/12) 1315192.168.0.0 - 192.168.255.255 (i.e., 192.168/16) 1316.Ed 1317.It Pa rdr 1318The packet is redirected to another destination and possibly a 1319different port. 1320.Ar rdr 1321rules can optionally specify port ranges instead of single ports. 1322rdr ... port 2000:2999 -\*(Gt ... port 4000 1323redirects ports 2000 to 2999 (inclusive) to port 4000. 1324rdr ... port 2000:2999 -\*(Gt ... port 4000:* 1325redirects port 2000 to 4000, 2001 to 4001, ..., 2999 to 4999. 1326.El 1327.Pp 1328In addition to modifying the address, some translation rules may modify 1329source or destination ports for 1330.Xr tcp 4 1331or 1332.Xr udp 4 1333connections; implicitly in the case of 1334.Ar nat 1335rules and explicitly in the case of 1336.Ar rdr 1337rules. 1338Port numbers are never translated with a 1339.Ar binat 1340rule. 1341.Pp 1342Evaluation order of the translation rules is dependent on the type 1343of the translation rules and of the direction of a packet. 1344.Ar binat 1345rules are always evaluated first. 1346Then either the 1347.Ar rdr 1348rules are evaluated on an inbound packet or the 1349.Ar nat 1350rules on an outbound packet. 1351Rules of the same type are evaluated in the same order in which they 1352appear in the ruleset. 1353The first matching rule decides what action is taken. 1354.Pp 1355The 1356.Ar no 1357option prefixed to a translation rule causes packets to remain untranslated, 1358much in the same way as 1359.Ar drop quick 1360works in the packet filter (see below). 1361If no rule matches the packet it is passed to the filter engine unmodified. 1362.Pp 1363Translation rules apply only to packets that pass through 1364the specified interface, and if no interface is specified, 1365translation is applied to packets on all interfaces. 1366For instance, redirecting port 80 on an external interface to an internal 1367web server will only work for connections originating from the outside. 1368Connections to the address of the external interface from local hosts will 1369not be redirected, since such packets do not actually pass through the 1370external interface. 1371Redirections cannot reflect packets back through the interface they arrive 1372on, they can only be redirected to hosts connected to different interfaces 1373or to the firewall itself. 1374.Pp 1375Note that redirecting external incoming connections to the loopback 1376address, as in 1377.Bd -literal -offset indent 1378rdr on ne3 inet proto tcp to port smtp -\*(Gt 127.0.0.1 port spamd 1379.Ed 1380.Pp 1381will effectively allow an external host to connect to daemons 1382bound solely to the loopback address, circumventing the traditional 1383blocking of such connections on a real interface. 1384Unless this effect is desired, any of the local non-loopback addresses 1385should be used as redirection target instead, which allows external 1386connections only to daemons bound to this address or not bound to 1387any address. 1388.Pp 1389See 1390.Sx TRANSLATION EXAMPLES 1391below. 1392.Sh PACKET FILTERING 1393.Xr pf 4 1394has the ability to 1395.Ar block 1396, 1397.Ar pass 1398and 1399.Ar match 1400packets based on attributes of their layer 3 (see 1401.Xr ip 4 1402and 1403.Xr ip6 4 ) 1404and layer 4 (see 1405.Xr icmp 4 , 1406.Xr icmp6 4 , 1407.Xr tcp 4 , 1408.Xr sctp 4 , 1409.Xr udp 4 ) 1410headers. 1411In addition, packets may also be 1412assigned to queues for the purpose of bandwidth control. 1413.Pp 1414For each packet processed by the packet filter, the filter rules are 1415evaluated in sequential order, from first to last. 1416For 1417.Ar block 1418and 1419.Ar pass 1420, the last matching rule decides what action is taken. 1421For 1422.Ar match 1423, rules are evaluated every time they match; the pass/block state of a packet 1424remains unchanged. 1425If no rule matches the packet, the default action is to pass 1426the packet. 1427.Pp 1428The following actions can be used in the filter: 1429.Bl -tag -width xxxx 1430.It Ar block 1431The packet is blocked. 1432There are a number of ways in which a 1433.Ar block 1434rule can behave when blocking a packet. 1435The default behaviour is to 1436.Ar drop 1437packets silently, however this can be overridden or made 1438explicit either globally, by setting the 1439.Ar block-policy 1440option, or on a per-rule basis with one of the following options: 1441.Pp 1442.Bl -tag -width xxxx -compact 1443.It Ar drop 1444The packet is silently dropped. 1445.It Ar return-rst 1446This applies only to 1447.Xr tcp 4 1448packets, and issues a TCP RST which closes the 1449connection. 1450.It Ar return-icmp 1451.It Ar return-icmp6 1452This causes ICMP messages to be returned for packets which match the rule. 1453By default this is an ICMP UNREACHABLE message, however this 1454can be overridden by specifying a message as a code or number. 1455.It Ar return 1456This causes a TCP RST to be returned for 1457.Xr tcp 4 1458packets, an SCTP ABORT for SCTP 1459and an ICMP UNREACHABLE for UDP and other packets. 1460.El 1461.Pp 1462Options returning ICMP packets currently have no effect if 1463.Xr pf 4 1464operates on a 1465.Xr if_bridge 4 , 1466as the code to support this feature has not yet been implemented. 1467.Pp 1468The simplest mechanism to block everything by default and only pass 1469packets that match explicit rules is specify a first filter rule of: 1470.Bd -literal -offset indent 1471block all 1472.Ed 1473.It Ar match 1474The packet is matched. 1475This mechanism is used to provide fine grained filtering without altering the 1476block/pass state of a packet. 1477.Ar match 1478rules differ from 1479.Ar block 1480and 1481.Ar pass 1482rules in that parameters are set every time a packet matches the rule, not only 1483on the last matching rule. 1484For the following parameters, this means that the parameter effectively becomes 1485"sticky" until explicitly overridden: 1486.Ar queue , 1487.Ar dnpipe , 1488.Ar dnqueue 1489. 1490.It Ar pass 1491The packet is passed; 1492state is created unless the 1493.Ar no state 1494option is specified. 1495.It Ar match 1496Action is unaltered, the previously matched rule's action still matters. 1497Match rules apply queue and rtable assignments for every matched packet, 1498subsequent matching pass or match rules can overwrite the assignment, 1499if they don't specify a queue or an rtable, respectively, the previously 1500set value remains. 1501Additionally, match rules can contain log statements; the is logging done 1502for each and every matching match rule, so it is possible to log a single 1503packet multiple times. 1504.El 1505.Pp 1506By default 1507.Xr pf 4 1508filters packets statefully; the first time a packet matches a 1509.Ar pass 1510rule, a state entry is created; for subsequent packets the filter checks 1511whether the packet matches any state. 1512If it does, the packet is passed without evaluation of any rules. 1513After the connection is closed or times out, the state entry is automatically 1514removed. 1515.Pp 1516This has several advantages. 1517For TCP connections, comparing a packet to a state involves checking 1518its sequence numbers, as well as TCP timestamps if a 1519.Ar scrub reassemble tcp 1520rule applies to the connection. 1521If these values are outside the narrow windows of expected 1522values, the packet is dropped. 1523This prevents spoofing attacks, such as when an attacker sends packets with 1524a fake source address/port but does not know the connection's sequence 1525numbers. 1526Similarly, 1527.Xr pf 4 1528knows how to match ICMP replies to states. 1529For example, 1530.Bd -literal -offset indent 1531pass out inet proto icmp all icmp-type echoreq 1532.Ed 1533.Pp 1534allows echo requests (such as those created by 1535.Xr ping 8 ) 1536out statefully, and matches incoming echo replies correctly to states. 1537.Pp 1538Also, looking up states is usually faster than evaluating rules. 1539If there are 50 rules, all of them are evaluated sequentially in O(n). 1540Even with 50000 states, only 16 comparisons are needed to match a 1541state, since states are stored in a binary search tree that allows 1542searches in O(log2 n). 1543.Pp 1544Furthermore, correct handling of ICMP error messages is critical to 1545many protocols, particularly TCP. 1546.Xr pf 4 1547matches ICMP error messages to the correct connection, checks them against 1548connection parameters, and passes them if appropriate. 1549For example if an ICMP source quench message referring to a stateful TCP 1550connection arrives, it will be matched to the state and get passed. 1551.Pp 1552Finally, state tracking is required for 1553.Ar nat , binat No and Ar rdr 1554rules, in order to track address and port translations and reverse the 1555translation on returning packets. 1556.Pp 1557.Xr pf 4 1558will also create state for other protocols which are effectively stateless by 1559nature. 1560UDP packets are matched to states using only host addresses and ports, 1561and other protocols are matched to states using only the host addresses. 1562.Pp 1563If stateless filtering of individual packets is desired, 1564the 1565.Ar no state 1566keyword can be used to specify that state will not be created 1567if this is the last matching rule. 1568A number of parameters can also be set to affect how 1569.Xr pf 4 1570handles state tracking. 1571See 1572.Sx STATEFUL TRACKING OPTIONS 1573below for further details. 1574.Sh PARAMETERS 1575The rule parameters specify the packets to which a rule applies. 1576A packet always comes in on, or goes out through, one interface. 1577Most parameters are optional. 1578If a parameter is specified, the rule only applies to packets with 1579matching attributes. 1580Certain parameters can be expressed as lists, in which case 1581.Xr pfctl 8 1582generates all needed rule combinations. 1583.Bl -tag -width xxxx 1584.It Ar in No or Ar out 1585This rule applies to incoming or outgoing packets. 1586If neither 1587.Ar in 1588nor 1589.Ar out 1590are specified, the rule will match packets in both directions. 1591.It Ar log 1592In addition to the action specified, a log message is generated. 1593Only the packet that establishes the state is logged, 1594unless the 1595.Ar no state 1596option is specified. 1597The logged packets are sent to a 1598.Xr pflog 4 1599interface, by default 1600.Ar pflog0 . 1601This interface is monitored by the 1602.Xr pflogd 8 1603logging daemon, which dumps the logged packets to the file 1604.Pa /var/log/pflog 1605in 1606.Xr pcap 3 1607binary format. 1608.It Ar log (all) 1609Used to force logging of all packets for a connection. 1610This is not necessary when 1611.Ar no state 1612is explicitly specified. 1613As with 1614.Ar log , 1615packets are logged to 1616.Xr pflog 4 . 1617.It Ar log (user) 1618Logs the 1619.Ux 1620user ID of the user that owns the socket and the PID of the process that 1621has the socket open where the packet is sourced from or destined to 1622(depending on which socket is local). 1623This is in addition to the normal information logged. 1624.Pp 1625Only the first packet 1626logged via 1627.Ar log (all, user) 1628will have the user credentials logged when using stateful matching. 1629.It Ar log (to Aq Ar interface ) 1630Send logs to the specified 1631.Xr pflog 4 1632interface instead of 1633.Ar pflog0 . 1634.It Ar quick 1635If a packet matches a rule which has the 1636.Ar quick 1637option set, this rule 1638is considered the last matching rule, and evaluation of subsequent rules 1639is skipped. 1640.It Ar on Aq Ar interface 1641This rule applies only to packets coming in on, or going out through, this 1642particular interface or interface group. 1643For more information on interface groups, 1644see the 1645.Ic group 1646keyword in 1647.Xr ifconfig 8 . 1648.It Aq Ar af 1649This rule applies only to packets of this address family. 1650Supported values are 1651.Ar inet 1652and 1653.Ar inet6 . 1654.It Ar proto Aq Ar protocol 1655This rule applies only to packets of this protocol. 1656Common protocols are 1657.Xr icmp 4 , 1658.Xr icmp6 4 , 1659.Xr tcp 4 , 1660.Xr sctp 4 , 1661and 1662.Xr udp 4 . 1663For a list of all the protocol name to number mappings used by 1664.Xr pfctl 8 , 1665see the file 1666.Pa /etc/protocols . 1667.It Xo 1668.Ar from Aq Ar source 1669.Ar port Aq Ar source 1670.Ar os Aq Ar source 1671.Ar to Aq Ar dest 1672.Ar port Aq Ar dest 1673.Xc 1674This rule applies only to packets with the specified source and destination 1675addresses and ports. 1676.Pp 1677Addresses can be specified in CIDR notation (matching netblocks), as 1678symbolic host names, interface names or interface group names, or as any 1679of the following keywords: 1680.Pp 1681.Bl -tag -width xxxxxxxxxxxxxx -compact 1682.It Ar any 1683Any address. 1684.It Ar no-route 1685Any address which is not currently routable. 1686.It Ar urpf-failed 1687Any source address that fails a unicast reverse path forwarding (URPF) 1688check, i.e. packets coming in on an interface other than that which holds 1689the route back to the packet's source address. 1690.It Aq Ar table 1691Any address that matches the given table. 1692.El 1693.Pp 1694Ranges of addresses are specified by using the 1695.Sq - 1696operator. 1697For instance: 1698.Dq 10.1.1.10 - 10.1.1.12 1699means all addresses from 10.1.1.10 to 10.1.1.12, 1700hence addresses 10.1.1.10, 10.1.1.11, and 10.1.1.12. 1701.Pp 1702Interface names and interface group names can have modifiers appended: 1703.Pp 1704.Bl -tag -width xxxxxxxxxxxx -compact 1705.It Ar :network 1706Translates to the network(s) attached to the interface. 1707.It Ar :broadcast 1708Translates to the interface's broadcast address(es). 1709.It Ar :peer 1710Translates to the point-to-point interface's peer address(es). 1711.It Ar :0 1712Do not include interface aliases. 1713.El 1714.Pp 1715Host names may also have the 1716.Ar :0 1717option appended to restrict the name resolution to the first of each 1718v4 and non-link-local v6 address found. 1719.Pp 1720Host name resolution and interface to address translation are done at 1721ruleset load-time. 1722When the address of an interface (or host name) changes (under DHCP or PPP, 1723for instance), the ruleset must be reloaded for the change to be reflected 1724in the kernel. 1725Surrounding the interface name (and optional modifiers) in parentheses 1726changes this behaviour. 1727When the interface name is surrounded by parentheses, the rule is 1728automatically updated whenever the interface changes its address. 1729The ruleset does not need to be reloaded. 1730This is especially useful with 1731.Ar nat . 1732.Pp 1733Ports can be specified either by number or by name. 1734For example, port 80 can be specified as 1735.Em www . 1736For a list of all port name to number mappings used by 1737.Xr pfctl 8 , 1738see the file 1739.Pa /etc/services . 1740.Pp 1741Ports and ranges of ports are specified by using these operators: 1742.Bd -literal -offset indent 1743= (equal) 1744!= (unequal) 1745\*(Lt (less than) 1746\*(Le (less than or equal) 1747\*(Gt (greater than) 1748\*(Ge (greater than or equal) 1749: (range including boundaries) 1750\*(Gt\*(Lt (range excluding boundaries) 1751\*(Lt\*(Gt (except range) 1752.Ed 1753.Pp 1754.Sq \*(Gt\*(Lt , 1755.Sq \*(Lt\*(Gt 1756and 1757.Sq \&: 1758are binary operators (they take two arguments). 1759For instance: 1760.Bl -tag -width Fl 1761.It Ar port 2000:2004 1762means 1763.Sq all ports \*(Ge 2000 and \*(Le 2004 , 1764hence ports 2000, 2001, 2002, 2003 and 2004. 1765.It Ar port 2000 \*(Gt\*(Lt 2004 1766means 1767.Sq all ports \*(Gt 2000 and \*(Lt 2004 , 1768hence ports 2001, 2002 and 2003. 1769.It Ar port 2000 \*(Lt\*(Gt 2004 1770means 1771.Sq all ports \*(Lt 2000 or \*(Gt 2004 , 1772hence ports 1-1999 and 2005-65535. 1773.El 1774.Pp 1775The operating system of the source host can be specified in the case of TCP 1776rules with the 1777.Ar OS 1778modifier. 1779See the 1780.Sx OPERATING SYSTEM FINGERPRINTING 1781section for more information. 1782.Pp 1783The host, port and OS specifications are optional, as in the following examples: 1784.Bd -literal -offset indent 1785pass in all 1786pass in from any to any 1787pass in proto tcp from any port \*(Le 1024 to any 1788pass in proto tcp from any to any port 25 1789pass in proto tcp from 10.0.0.0/8 port \*(Gt 1024 \e 1790 to ! 10.1.2.3 port != ssh 1791pass in proto tcp from any os "OpenBSD" 1792.Ed 1793.It Ar all 1794This is equivalent to "from any to any". 1795.It Ar group Aq Ar group 1796Similar to 1797.Ar user , 1798this rule only applies to packets of sockets owned by the specified group. 1799.It Ar user Aq Ar user 1800This rule only applies to packets of sockets owned by the specified user. 1801For outgoing connections initiated from the firewall, this is the user 1802that opened the connection. 1803For incoming connections to the firewall itself, this is the user that 1804listens on the destination port. 1805For forwarded connections, where the firewall is not a connection endpoint, 1806the user and group are 1807.Em unknown . 1808.Pp 1809All packets, both outgoing and incoming, of one connection are associated 1810with the same user and group. 1811Only TCP and UDP packets can be associated with users; for other protocols 1812these parameters are ignored. 1813.Pp 1814User and group refer to the effective (as opposed to the real) IDs, in 1815case the socket is created by a setuid/setgid process. 1816User and group IDs are stored when a socket is created; 1817when a process creates a listening socket as root (for instance, by 1818binding to a privileged port) and subsequently changes to another 1819user ID (to drop privileges), the credentials will remain root. 1820.Pp 1821User and group IDs can be specified as either numbers or names. 1822The syntax is similar to the one for ports. 1823The value 1824.Em unknown 1825matches packets of forwarded connections. 1826.Em unknown 1827can only be used with the operators 1828.Cm = 1829and 1830.Cm != . 1831Other constructs like 1832.Cm user \*(Ge unknown 1833are invalid. 1834Forwarded packets with unknown user and group ID match only rules 1835that explicitly compare against 1836.Em unknown 1837with the operators 1838.Cm = 1839or 1840.Cm != . 1841For instance 1842.Cm user \*(Ge 0 1843does not match forwarded packets. 1844The following example allows only selected users to open outgoing 1845connections: 1846.Bd -literal -offset indent 1847block out proto { tcp, udp } all 1848pass out proto { tcp, udp } all user { \*(Lt 1000, dhartmei } 1849.Ed 1850.It Xo Ar flags Aq Ar a 1851.Pf / Ns Aq Ar b 1852.No \*(Ba / Ns Aq Ar b 1853.No \*(Ba any 1854.Xc 1855This rule only applies to TCP packets that have the flags 1856.Aq Ar a 1857set out of set 1858.Aq Ar b . 1859Flags not specified in 1860.Aq Ar b 1861are ignored. 1862For stateful connections, the default is 1863.Ar flags S/SA . 1864To indicate that flags should not be checked at all, specify 1865.Ar flags any . 1866The flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R. 1867.Bl -tag -width Fl 1868.It Ar flags S/S 1869Flag SYN is set. 1870The other flags are ignored. 1871.It Ar flags S/SA 1872This is the default setting for stateful connections. 1873Out of SYN and ACK, exactly SYN may be set. 1874SYN, SYN+PSH and SYN+RST match, but SYN+ACK, ACK and ACK+RST do not. 1875This is more restrictive than the previous example. 1876.It Ar flags /SFRA 1877If the first set is not specified, it defaults to none. 1878All of SYN, FIN, RST and ACK must be unset. 1879.El 1880.Pp 1881Because 1882.Ar flags S/SA 1883is applied by default (unless 1884.Ar no state 1885is specified), only the initial SYN packet of a TCP handshake will create 1886a state for a TCP connection. 1887It is possible to be less restrictive, and allow state creation from 1888intermediate 1889.Pq non-SYN 1890packets, by specifying 1891.Ar flags any . 1892This will cause 1893.Xr pf 4 1894to synchronize to existing connections, for instance 1895if one flushes the state table. 1896However, states created from such intermediate packets may be missing 1897connection details such as the TCP window scaling factor. 1898States which modify the packet flow, such as those affected by 1899.Ar nat , binat No or Ar rdr 1900rules, 1901.Ar modulate No or Ar synproxy state 1902options, or scrubbed with 1903.Ar reassemble tcp 1904will also not be recoverable from intermediate packets. 1905Such connections will stall and time out. 1906.It Xo Ar icmp-type Aq Ar type 1907.Ar code Aq Ar code 1908.Xc 1909.It Xo Ar icmp6-type Aq Ar type 1910.Ar code Aq Ar code 1911.Xc 1912This rule only applies to ICMP or ICMPv6 packets with the specified type 1913and code. 1914Text names for ICMP types and codes are listed in 1915.Xr icmp 4 1916and 1917.Xr icmp6 4 . 1918This parameter is only valid for rules that cover protocols ICMP or 1919ICMP6. 1920The protocol and the ICMP type indicator 1921.Po 1922.Ar icmp-type 1923or 1924.Ar icmp6-type 1925.Pc 1926must match. 1927.It Xo Ar tos Aq Ar string 1928.No \*(Ba Aq Ar number 1929.Xc 1930This rule applies to packets with the specified 1931.Em TOS 1932bits set. 1933.Em TOS 1934may be 1935given as one of 1936.Ar critical , 1937.Ar inetcontrol , 1938.Ar lowdelay , 1939.Ar netcontrol , 1940.Ar throughput , 1941.Ar reliability , 1942or one of the DiffServ Code Points: 1943.Ar ef , 1944.Ar va , 1945.Ar af11 No ... Ar af43 , 1946.Ar cs0 No ... Ar cs7 ; 1947or as either hex or decimal. 1948.Pp 1949For example, the following rules are identical: 1950.Bd -literal -offset indent 1951pass all tos lowdelay 1952pass all tos 0x10 1953pass all tos 16 1954.Ed 1955.It Ar allow-opts 1956By default, IPv4 packets with IP options or IPv6 packets with routing 1957extension headers are blocked. 1958When 1959.Ar allow-opts 1960is specified for a 1961.Ar pass 1962rule, packets that pass the filter based on that rule (last matching) 1963do so even if they contain IP options or routing extension headers. 1964For packets that match state, the rule that initially created the 1965state is used. 1966The implicit 1967.Ar pass 1968rule that is used when a packet does not match any rules does not 1969allow IP options. 1970.It Ar label Aq Ar string 1971Adds a label (name) to the rule, which can be used to identify the rule. 1972For instance, 1973pfctl -s labels 1974shows per-rule statistics for rules that have labels. 1975.Pp 1976The following macros can be used in labels: 1977.Pp 1978.Bl -tag -width $srcaddr -compact -offset indent 1979.It Ar $if 1980The interface. 1981.It Ar $srcaddr 1982The source IP address. 1983.It Ar $dstaddr 1984The destination IP address. 1985.It Ar $srcport 1986The source port specification. 1987.It Ar $dstport 1988The destination port specification. 1989.It Ar $proto 1990The protocol name. 1991.It Ar $nr 1992The rule number. 1993.El 1994.Pp 1995For example: 1996.Bd -literal -offset indent 1997ips = \&"{ 1.2.3.4, 1.2.3.5 }\&" 1998pass in proto tcp from any to $ips \e 1999 port \*(Gt 1023 label \&"$dstaddr:$dstport\&" 2000.Ed 2001.Pp 2002expands to 2003.Bd -literal -offset indent 2004pass in inet proto tcp from any to 1.2.3.4 \e 2005 port \*(Gt 1023 label \&"1.2.3.4:\*(Gt1023\&" 2006pass in inet proto tcp from any to 1.2.3.5 \e 2007 port \*(Gt 1023 label \&"1.2.3.5:\*(Gt1023\&" 2008.Ed 2009.Pp 2010The macro expansion for the 2011.Ar label 2012directive occurs only at configuration file parse time, not during runtime. 2013.It Ar ridentifier Aq Ar number 2014Add an identifier (number) to the rule, which can be used to correlate the rule 2015to pflog entries, even after ruleset updates. 2016.It Xo Ar queue Aq Ar queue 2017.No \*(Ba ( Aq Ar queue , 2018.Aq Ar queue ) 2019.Xc 2020Packets matching this rule will be assigned to the specified queue. 2021If two queues are given, packets which have a 2022.Em TOS 2023of 2024.Em lowdelay 2025and TCP ACKs with no data payload will be assigned to the second one. 2026See 2027.Sx QUEUEING 2028for setup details. 2029.Pp 2030For example: 2031.Bd -literal -offset indent 2032pass in proto tcp to port 25 queue mail 2033pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio) 2034.Ed 2035.It Cm set prio Ar priority | Pq Ar priority , priority 2036Packets matching this rule will be assigned a specific queueing priority. 2037Priorities are assigned as integers 0 through 7. 2038If the packet is transmitted on a 2039.Xr vlan 4 2040interface, the queueing priority will be written as the priority 2041code point in the 802.1Q VLAN header. 2042If two priorities are given, packets which have a TOS of 2043.Cm lowdelay 2044and TCP ACKs with no data payload will be assigned to the second one. 2045.Pp 2046For example: 2047.Bd -literal -offset indent 2048pass in proto tcp to port 25 set prio 2 2049pass in proto tcp to port 22 set prio (2, 5) 2050.Ed 2051.It Ar tag Aq Ar string 2052Packets matching this rule will be tagged with the 2053specified string. 2054The tag acts as an internal marker that can be used to 2055identify these packets later on. 2056This can be used, for example, to provide trust between 2057interfaces and to determine if packets have been 2058processed by translation rules. 2059Tags are 2060.Qq sticky , 2061meaning that the packet will be tagged even if the rule 2062is not the last matching rule. 2063Further matching rules can replace the tag with a 2064new one but will not remove a previously applied tag. 2065A packet is only ever assigned one tag at a time. 2066Packet tagging can be done during 2067.Ar nat , 2068.Ar rdr , 2069.Ar binat 2070or 2071.Ar ether 2072rules in addition to filter rules. 2073Tags take the same macros as labels (see above). 2074.It Ar tagged Aq Ar string 2075Used with filter, translation or scrub rules 2076to specify that packets must already 2077be tagged with the given tag in order to match the rule. 2078Inverse tag matching can also be done 2079by specifying the 2080.Cm !\& 2081operator before the 2082.Ar tagged 2083keyword. 2084.It Ar rtable Aq Ar number 2085Used to select an alternate routing table for the routing lookup. 2086Only effective before the route lookup happened, i.e. when filtering inbound. 2087.It Xo Ar divert-to Aq Ar host 2088.Ar port Aq Ar port 2089.Xc 2090Used to redirect packets to a local socket bound to 2091.Ar host 2092and 2093.Ar port . 2094The packets will not be modified, so 2095.Xr getsockname 2 2096on the socket will return the original destination address of the packet. 2097.It Ar divert-reply 2098Used to receive replies for sockets that are bound to addresses 2099which are not local to the machine. 2100See 2101.Xr setsockopt 2 2102for information on how to bind these sockets. 2103.It Ar probability Aq Ar number 2104A probability attribute can be attached to a rule, with a value set between 21050 and 1, bounds not included. 2106In that case, the rule will be honoured using the given probability value 2107only. 2108For example, the following rule will drop 20% of incoming ICMP packets: 2109.Bd -literal -offset indent 2110block in proto icmp probability 20% 2111.Ed 2112.It Ar prio Aq Ar number 2113Only match packets which have the given queueing priority assigned. 2114.El 2115.Sh ROUTING 2116If a packet matches a rule with a route option set, the packet filter will 2117route the packet according to the type of route option. 2118When such a rule creates state, the route option is also applied to all 2119packets matching the same connection. 2120.Bl -tag -width xxxx 2121.It Ar route-to 2122The 2123.Ar route-to 2124option routes the packet to the specified interface with an optional address 2125for the next hop. 2126When a 2127.Ar route-to 2128rule creates state, only packets that pass in the same direction as the 2129filter rule specifies will be routed in this way. 2130Packets passing in the opposite direction (replies) are not affected 2131and are routed normally. 2132.It Ar reply-to 2133The 2134.Ar reply-to 2135option is similar to 2136.Ar route-to , 2137but routes packets that pass in the opposite direction (replies) to the 2138specified interface. 2139Opposite direction is only defined in the context of a state entry, and 2140.Ar reply-to 2141is useful only in rules that create state. 2142It can be used on systems with multiple external connections to 2143route all outgoing packets of a connection through the interface 2144the incoming connection arrived through (symmetric routing enforcement). 2145.It Ar dup-to 2146The 2147.Ar dup-to 2148option creates a duplicate of the packet and routes it like 2149.Ar route-to . 2150The original packet gets routed as it normally would. 2151.El 2152.Sh POOL OPTIONS 2153For 2154.Ar nat 2155and 2156.Ar rdr 2157rules, (as well as for the 2158.Ar route-to , 2159.Ar reply-to 2160and 2161.Ar dup-to 2162rule options) for which there is a single redirection address which has a 2163subnet mask smaller than 32 for IPv4 or 128 for IPv6 (more than one IP 2164address), a variety of different methods for assigning this address can be 2165used: 2166.Bl -tag -width xxxx 2167.It Ar bitmask 2168The 2169.Ar bitmask 2170option applies the network portion of the redirection address to the address 2171to be modified (source with 2172.Ar nat , 2173destination with 2174.Ar rdr ) . 2175.It Ar random 2176The 2177.Ar random 2178option selects an address at random within the defined block of addresses. 2179.It Ar source-hash 2180The 2181.Ar source-hash 2182option uses a hash of the source address to determine the redirection address, 2183ensuring that the redirection address is always the same for a given source. 2184An optional key can be specified after this keyword either in hex or as a 2185string; by default 2186.Xr pfctl 8 2187randomly generates a key for source-hash every time the 2188ruleset is reloaded. 2189.It Ar round-robin 2190The 2191.Ar round-robin 2192option loops through the redirection address(es). 2193.Pp 2194When more than one redirection address is specified, 2195.Ar round-robin 2196is the only permitted pool type. 2197.It Ar static-port 2198With 2199.Ar nat 2200rules, the 2201.Ar static-port 2202option prevents 2203.Xr pf 4 2204from modifying the source port on TCP and UDP packets. 2205.It Xo Ar map-e-portset Aq Ar psid-offset 2206.No / Aq Ar psid-len 2207.No / Aq Ar psid 2208.Xc 2209With 2210.Ar nat 2211rules, the 2212.Ar map-e-portset 2213option enables the source port translation of MAP-E (RFC 7597) Customer Edge. 2214In order to make the host act as a MAP-E Customer Edge, setting up a tunneling 2215interface and pass rules for encapsulated packets are required in addition 2216to the map-e-portset nat rule. 2217.Pp 2218For example: 2219.Bd -literal -offset indent 2220nat on $gif_mape_if from $int_if:network to any \e 2221 -> $ipv4_mape_src map-e-portset 6/8/0x34 2222.Ed 2223.Pp 2224sets PSID offset 6, PSID length 8, PSID 0x34. 2225.El 2226.Pp 2227Additionally, the 2228.Ar sticky-address 2229option can be specified to help ensure that multiple connections from the 2230same source are mapped to the same redirection address. 2231This option can be used with the 2232.Ar random 2233and 2234.Ar round-robin 2235pool options. 2236Note that by default these associations are destroyed as soon as there are 2237no longer states which refer to them; in order to make the mappings last 2238beyond the lifetime of the states, increase the global options with 2239.Ar set timeout src.track . 2240See 2241.Sx STATEFUL TRACKING OPTIONS 2242for more ways to control the source tracking. 2243.Sh STATE MODULATION 2244Much of the security derived from TCP is attributable to how well the 2245initial sequence numbers (ISNs) are chosen. 2246Some popular stack implementations choose 2247.Em very 2248poor ISNs and thus are normally susceptible to ISN prediction exploits. 2249By applying a 2250.Ar modulate state 2251rule to a TCP connection, 2252.Xr pf 4 2253will create a high quality random sequence number for each connection 2254endpoint. 2255.Pp 2256The 2257.Ar modulate state 2258directive implicitly keeps state on the rule and is 2259only applicable to TCP connections. 2260.Pp 2261For instance: 2262.Bd -literal -offset indent 2263block all 2264pass out proto tcp from any to any modulate state 2265pass in proto tcp from any to any port 25 flags S/SFRA modulate state 2266.Ed 2267.Pp 2268Note that modulated connections will not recover when the state table 2269is lost (firewall reboot, flushing the state table, etc...). 2270.Xr pf 4 2271will not be able to infer a connection again after the state table flushes 2272the connection's modulator. 2273When the state is lost, the connection may be left dangling until the 2274respective endpoints time out the connection. 2275It is possible on a fast local network for the endpoints to start an ACK 2276storm while trying to resynchronize after the loss of the modulator. 2277The default 2278.Ar flags 2279settings (or a more strict equivalent) should be used on 2280.Ar modulate state 2281rules to prevent ACK storms. 2282.Pp 2283Note that alternative methods are available 2284to prevent loss of the state table 2285and allow for firewall failover. 2286See 2287.Xr carp 4 2288and 2289.Xr pfsync 4 2290for further information. 2291.Sh SYN PROXY 2292By default, 2293.Xr pf 4 2294passes packets that are part of a 2295.Xr tcp 4 2296handshake between the endpoints. 2297The 2298.Ar synproxy state 2299option can be used to cause 2300.Xr pf 4 2301itself to complete the handshake with the active endpoint, perform a handshake 2302with the passive endpoint, and then forward packets between the endpoints. 2303.Pp 2304No packets are sent to the passive endpoint before the active endpoint has 2305completed the handshake, hence so-called SYN floods with spoofed source 2306addresses will not reach the passive endpoint, as the sender can't complete the 2307handshake. 2308.Pp 2309The proxy is transparent to both endpoints, they each see a single 2310connection from/to the other endpoint. 2311.Xr pf 4 2312chooses random initial sequence numbers for both handshakes. 2313Once the handshakes are completed, the sequence number modulators 2314(see previous section) are used to translate further packets of the 2315connection. 2316.Ar synproxy state 2317includes 2318.Ar modulate state . 2319.Pp 2320Rules with 2321.Ar synproxy 2322will not work if 2323.Xr pf 4 2324operates on a 2325.Xr bridge 4 . 2326.Pp 2327Example: 2328.Bd -literal -offset indent 2329pass in proto tcp from any to any port www synproxy state 2330.Ed 2331.Sh STATEFUL TRACKING OPTIONS 2332A number of options related to stateful tracking can be applied on a 2333per-rule basis. 2334.Ar keep state , 2335.Ar modulate state 2336and 2337.Ar synproxy state 2338support these options, and 2339.Ar keep state 2340must be specified explicitly to apply options to a rule. 2341.Pp 2342.Bl -tag -width xxxx -compact 2343.It Ar max Aq Ar number 2344Limits the number of concurrent states the rule may create. 2345When this limit is reached, further packets that would create 2346state will not match this rule until existing states time out. 2347.It Ar no-sync 2348Prevent state changes for states created by this rule from appearing on the 2349.Xr pfsync 4 2350interface. 2351.It Xo Aq Ar timeout 2352.Aq Ar seconds 2353.Xc 2354Changes the timeout values used for states created by this rule. 2355For a list of all valid timeout names, see 2356.Sx OPTIONS 2357above. 2358.It Ar sloppy 2359Uses a sloppy TCP connection tracker that does not check sequence 2360numbers at all, which makes insertion and ICMP teardown attacks way 2361easier. 2362This is intended to be used in situations where one does not see all 2363packets of a connection, e.g. in asymmetric routing situations. 2364Cannot be used with modulate or synproxy state. 2365.El 2366.Pp 2367Multiple options can be specified, separated by commas: 2368.Bd -literal -offset indent 2369pass in proto tcp from any to any \e 2370 port www keep state \e 2371 (max 100, source-track rule, max-src-nodes 75, \e 2372 max-src-states 3, tcp.established 60, tcp.closing 5) 2373.Ed 2374.Pp 2375When the 2376.Ar source-track 2377keyword is specified, the number of states per source IP is tracked. 2378.Pp 2379.Bl -tag -width xxxx -compact 2380.It Ar source-track rule 2381The maximum number of states created by this rule is limited by the rule's 2382.Ar max-src-nodes 2383and 2384.Ar max-src-states 2385options. 2386Only state entries created by this particular rule count toward the rule's 2387limits. 2388.It Ar source-track global 2389The number of states created by all rules that use this option is limited. 2390Each rule can specify different 2391.Ar max-src-nodes 2392and 2393.Ar max-src-states 2394options, however state entries created by any participating rule count towards 2395each individual rule's limits. 2396.El 2397.Pp 2398The following limits can be set: 2399.Pp 2400.Bl -tag -width xxxx -compact 2401.It Ar max-src-nodes Aq Ar number 2402Limits the maximum number of source addresses which can simultaneously 2403have state table entries. 2404.It Ar max-src-states Aq Ar number 2405Limits the maximum number of simultaneous state entries that a single 2406source address can create with this rule. 2407.El 2408.Pp 2409For stateful TCP connections, limits on established connections (connections 2410which have completed the TCP 3-way handshake) can also be enforced 2411per source IP. 2412.Pp 2413.Bl -tag -width xxxx -compact 2414.It Ar max-src-conn Aq Ar number 2415Limits the maximum number of simultaneous TCP connections which have 2416completed the 3-way handshake that a single host can make. 2417.It Xo Ar max-src-conn-rate Aq Ar number 2418.No / Aq Ar seconds 2419.Xc 2420Limit the rate of new connections over a time interval. 2421The connection rate is an approximation calculated as a moving average. 2422.El 2423.Pp 2424Because the 3-way handshake ensures that the source address is not being 2425spoofed, more aggressive action can be taken based on these limits. 2426With the 2427.Ar overload Aq Ar table 2428state option, source IP addresses which hit either of the limits on 2429established connections will be added to the named table. 2430This table can be used in the ruleset to block further activity from 2431the offending host, redirect it to a tarpit process, or restrict its 2432bandwidth. 2433.Pp 2434The optional 2435.Ar flush 2436keyword kills all states created by the matching rule which originate 2437from the host which exceeds these limits. 2438The 2439.Ar global 2440modifier to the flush command kills all states originating from the 2441offending host, regardless of which rule created the state. 2442.Pp 2443For example, the following rules will protect the webserver against 2444hosts making more than 100 connections in 10 seconds. 2445Any host which connects faster than this rate will have its address added 2446to the 2447.Aq bad_hosts 2448table and have all states originating from it flushed. 2449Any new packets arriving from this host will be dropped unconditionally 2450by the block rule. 2451.Bd -literal -offset indent 2452block quick from \*(Ltbad_hosts\*(Gt 2453pass in on $ext_if proto tcp to $webserver port www keep state \e 2454 (max-src-conn-rate 100/10, overload \*(Ltbad_hosts\*(Gt flush global) 2455.Ed 2456.Sh OPERATING SYSTEM FINGERPRINTING 2457Passive OS Fingerprinting is a mechanism to inspect nuances of a TCP 2458connection's initial SYN packet and guess at the host's operating system. 2459Unfortunately these nuances are easily spoofed by an attacker so the 2460fingerprint is not useful in making security decisions. 2461But the fingerprint is typically accurate enough to make policy decisions 2462upon. 2463.Pp 2464The fingerprints may be specified by operating system class, by 2465version, or by subtype/patchlevel. 2466The class of an operating system is typically the vendor or genre 2467and would be 2468.Ox 2469for the 2470.Xr pf 4 2471firewall itself. 2472The version of the oldest available 2473.Ox 2474release on the main FTP site 2475would be 2.6 and the fingerprint would be written 2476.Pp 2477.Dl \&"OpenBSD 2.6\&" 2478.Pp 2479The subtype of an operating system is typically used to describe the 2480patchlevel if that patch led to changes in the TCP stack behavior. 2481In the case of 2482.Ox , 2483the only subtype is for a fingerprint that was 2484normalized by the 2485.Ar no-df 2486scrub option and would be specified as 2487.Pp 2488.Dl \&"OpenBSD 3.3 no-df\&" 2489.Pp 2490Fingerprints for most popular operating systems are provided by 2491.Xr pf.os 5 . 2492Once 2493.Xr pf 4 2494is running, a complete list of known operating system fingerprints may 2495be listed by running: 2496.Pp 2497.Dl # pfctl -so 2498.Pp 2499Filter rules can enforce policy at any level of operating system specification 2500assuming a fingerprint is present. 2501Policy could limit traffic to approved operating systems or even ban traffic 2502from hosts that aren't at the latest service pack. 2503.Pp 2504The 2505.Ar unknown 2506class can also be used as the fingerprint which will match packets for 2507which no operating system fingerprint is known. 2508.Pp 2509Examples: 2510.Bd -literal -offset indent 2511pass out proto tcp from any os OpenBSD 2512block out proto tcp from any os Doors 2513block out proto tcp from any os "Doors PT" 2514block out proto tcp from any os "Doors PT SP3" 2515block out from any os "unknown" 2516pass on lo0 proto tcp from any os "OpenBSD 3.3 lo0" 2517.Ed 2518.Pp 2519Operating system fingerprinting is limited only to the TCP SYN packet. 2520This means that it will not work on other protocols and will not match 2521a currently established connection. 2522.Pp 2523Caveat: operating system fingerprints are occasionally wrong. 2524There are three problems: an attacker can trivially craft his packets to 2525appear as any operating system he chooses; 2526an operating system patch could change the stack behavior and no fingerprints 2527will match it until the database is updated; 2528and multiple operating systems may have the same fingerprint. 2529.Sh BLOCKING SPOOFED TRAFFIC 2530"Spoofing" is the faking of IP addresses, typically for malicious 2531purposes. 2532The 2533.Ar antispoof 2534directive expands to a set of filter rules which will block all 2535traffic with a source IP from the network(s) directly connected 2536to the specified interface(s) from entering the system through 2537any other interface. 2538.Pp 2539For example, the line 2540.Bd -literal -offset indent 2541antispoof for lo0 2542.Ed 2543.Pp 2544expands to 2545.Bd -literal -offset indent 2546block drop in on ! lo0 inet from 127.0.0.1/8 to any 2547block drop in on ! lo0 inet6 from ::1 to any 2548.Ed 2549.Pp 2550For non-loopback interfaces, there are additional rules to block incoming 2551packets with a source IP address identical to the interface's IP(s). 2552For example, assuming the interface wi0 had an IP address of 10.0.0.1 and a 2553netmask of 255.255.255.0, 2554the line 2555.Bd -literal -offset indent 2556antispoof for wi0 inet 2557.Ed 2558.Pp 2559expands to 2560.Bd -literal -offset indent 2561block drop in on ! wi0 inet from 10.0.0.0/24 to any 2562block drop in inet from 10.0.0.1 to any 2563.Ed 2564.Pp 2565Caveat: Rules created by the 2566.Ar antispoof 2567directive interfere with packets sent over loopback interfaces 2568to local addresses. 2569One should pass these explicitly. 2570.Sh FRAGMENT HANDLING 2571The size of IP datagrams (packets) can be significantly larger than the 2572maximum transmission unit (MTU) of the network. 2573In cases when it is necessary or more efficient to send such large packets, 2574the large packet will be fragmented into many smaller packets that will each 2575fit onto the wire. 2576Unfortunately for a firewalling device, only the first logical fragment will 2577contain the necessary header information for the subprotocol that allows 2578.Xr pf 4 2579to filter on things such as TCP ports or to perform NAT. 2580.Pp 2581Besides the use of 2582.Ar scrub 2583rules as described in 2584.Sx TRAFFIC NORMALIZATION 2585above, there are three options for handling fragments in the packet filter. 2586.Pp 2587One alternative is to filter individual fragments with filter rules. 2588If no 2589.Ar scrub 2590rule applies to a fragment, it is passed to the filter. 2591Filter rules with matching IP header parameters decide whether the 2592fragment is passed or blocked, in the same way as complete packets 2593are filtered. 2594Without reassembly, fragments can only be filtered based on IP header 2595fields (source/destination address, protocol), since subprotocol header 2596fields are not available (TCP/UDP port numbers, ICMP code/type). 2597The 2598.Ar fragment 2599option can be used to restrict filter rules to apply only to 2600fragments, but not complete packets. 2601Filter rules without the 2602.Ar fragment 2603option still apply to fragments, if they only specify IP header fields. 2604For instance, the rule 2605.Bd -literal -offset indent 2606pass in proto tcp from any to any port 80 2607.Ed 2608.Pp 2609never applies to a fragment, even if the fragment is part of a TCP 2610packet with destination port 80, because without reassembly this information 2611is not available for each fragment. 2612This also means that fragments cannot create new or match existing 2613state table entries, which makes stateful filtering and address 2614translation (NAT, redirection) for fragments impossible. 2615.Pp 2616It's also possible to reassemble only certain fragments by specifying 2617source or destination addresses or protocols as parameters in 2618.Ar scrub 2619rules. 2620.Pp 2621In most cases, the benefits of reassembly outweigh the additional 2622memory cost, and it's recommended to use 2623.Ar scrub 2624rules to reassemble 2625all fragments via the 2626.Ar fragment reassemble 2627modifier. 2628.Pp 2629The memory allocated for fragment caching can be limited using 2630.Xr pfctl 8 . 2631Once this limit is reached, fragments that would have to be cached 2632are dropped until other entries time out. 2633The timeout value can also be adjusted. 2634.Pp 2635When forwarding reassembled IPv6 packets, pf refragments them with 2636the original maximum fragment size. 2637This allows the sender to determine the optimal fragment size by 2638path MTU discovery. 2639.Sh ANCHORS 2640Besides the main ruleset, 2641.Xr pfctl 8 2642can load rulesets into 2643.Ar anchor 2644attachment points. 2645An 2646.Ar anchor 2647is a container that can hold rules, address tables, and other anchors. 2648.Pp 2649An 2650.Ar anchor 2651has a name which specifies the path where 2652.Xr pfctl 8 2653can be used to access the anchor to perform operations on it, such as 2654attaching child anchors to it or loading rules into it. 2655Anchors may be nested, with components separated by 2656.Sq / 2657characters, similar to how file system hierarchies are laid out. 2658The main ruleset is actually the default anchor, so filter and 2659translation rules, for example, may also be contained in any anchor. 2660.Pp 2661An anchor can reference another 2662.Ar anchor 2663attachment point 2664using the following kinds 2665of rules: 2666.Bl -tag -width xxxx 2667.It Ar nat-anchor Aq Ar name 2668Evaluates the 2669.Ar nat 2670rules in the specified 2671.Ar anchor . 2672.It Ar rdr-anchor Aq Ar name 2673Evaluates the 2674.Ar rdr 2675rules in the specified 2676.Ar anchor . 2677.It Ar binat-anchor Aq Ar name 2678Evaluates the 2679.Ar binat 2680rules in the specified 2681.Ar anchor . 2682.It Ar anchor Aq Ar name 2683Evaluates the filter rules in the specified 2684.Ar anchor . 2685.It Xo Ar load anchor 2686.Aq Ar name 2687.Ar from Aq Ar file 2688.Xc 2689Loads the rules from the specified file into the 2690anchor 2691.Ar name . 2692.El 2693.Pp 2694When evaluation of the main ruleset reaches an 2695.Ar anchor 2696rule, 2697.Xr pf 4 2698will proceed to evaluate all rules specified in that anchor. 2699.Pp 2700Matching filter and translation rules marked with the 2701.Ar quick 2702option are final and abort the evaluation of the rules in other 2703anchors and the main ruleset. 2704If the 2705.Ar anchor 2706itself is marked with the 2707.Ar quick 2708option, 2709ruleset evaluation will terminate when the anchor is exited if the packet is 2710matched by any rule within the anchor. 2711.Pp 2712.Ar anchor 2713rules are evaluated relative to the anchor in which they are contained. 2714For example, all 2715.Ar anchor 2716rules specified in the main ruleset will reference anchor 2717attachment points underneath the main ruleset, and 2718.Ar anchor 2719rules specified in a file loaded from a 2720.Ar load anchor 2721rule will be attached under that anchor point. 2722.Pp 2723Rules may be contained in 2724.Ar anchor 2725attachment points which do not contain any rules when the main ruleset 2726is loaded, and later such anchors can be manipulated through 2727.Xr pfctl 8 2728without reloading the main ruleset or other anchors. 2729For example, 2730.Bd -literal -offset indent 2731ext_if = \&"kue0\&" 2732block on $ext_if all 2733anchor spam 2734pass out on $ext_if all 2735pass in on $ext_if proto tcp from any \e 2736 to $ext_if port smtp 2737.Ed 2738.Pp 2739blocks all packets on the external interface by default, then evaluates 2740all rules in the 2741.Ar anchor 2742named "spam", and finally passes all outgoing connections and 2743incoming connections to port 25. 2744.Bd -literal -offset indent 2745# echo \&"block in quick from 1.2.3.4 to any\&" \&| \e 2746 pfctl -a spam -f - 2747.Ed 2748.Pp 2749This loads a single rule into the 2750.Ar anchor , 2751which blocks all packets from a specific address. 2752.Pp 2753The anchor can also be populated by adding a 2754.Ar load anchor 2755rule after the 2756.Ar anchor 2757rule: 2758.Bd -literal -offset indent 2759anchor spam 2760load anchor spam from "/etc/pf-spam.conf" 2761.Ed 2762.Pp 2763When 2764.Xr pfctl 8 2765loads 2766.Nm pf.conf , 2767it will also load all the rules from the file 2768.Pa /etc/pf-spam.conf 2769into the anchor. 2770.Pp 2771Optionally, 2772.Ar anchor 2773rules can specify packet filtering parameters using the same syntax as 2774filter rules. 2775When parameters are used, the 2776.Ar anchor 2777rule is only evaluated for matching packets. 2778This allows conditional evaluation of anchors, like: 2779.Bd -literal -offset indent 2780block on $ext_if all 2781anchor spam proto tcp from any to any port smtp 2782pass out on $ext_if all 2783pass in on $ext_if proto tcp from any to $ext_if port smtp 2784.Ed 2785.Pp 2786The rules inside 2787.Ar anchor 2788spam are only evaluated for 2789.Ar tcp 2790packets with destination port 25. 2791Hence, 2792.Bd -literal -offset indent 2793# echo \&"block in quick from 1.2.3.4 to any" \&| \e 2794 pfctl -a spam -f - 2795.Ed 2796.Pp 2797will only block connections from 1.2.3.4 to port 25. 2798.Pp 2799Anchors may end with the asterisk 2800.Pq Sq * 2801character, which signifies that all anchors attached at that point 2802should be evaluated in the alphabetical ordering of their anchor name. 2803For example, 2804.Bd -literal -offset indent 2805anchor "spam/*" 2806.Ed 2807.Pp 2808will evaluate each rule in each anchor attached to the 2809.Li spam 2810anchor. 2811Note that it will only evaluate anchors that are directly attached to the 2812.Li spam 2813anchor, and will not descend to evaluate anchors recursively. 2814.Pp 2815Since anchors are evaluated relative to the anchor in which they are 2816contained, there is a mechanism for accessing the parent and ancestor 2817anchors of a given anchor. 2818Similar to file system path name resolution, if the sequence 2819.Dq .. 2820appears as an anchor path component, the parent anchor of the current 2821anchor in the path evaluation at that point will become the new current 2822anchor. 2823As an example, consider the following: 2824.Bd -literal -offset indent 2825# echo ' anchor "spam/allowed" ' | pfctl -f - 2826# echo -e ' anchor "../banned" \en pass' | \e 2827 pfctl -a spam/allowed -f - 2828.Ed 2829.Pp 2830Evaluation of the main ruleset will lead into the 2831.Li spam/allowed 2832anchor, which will evaluate the rules in the 2833.Li spam/banned 2834anchor, if any, before finally evaluating the 2835.Ar pass 2836rule. 2837.Pp 2838Filter rule 2839.Ar anchors 2840can also be loaded inline in the ruleset within a brace ('{' '}') delimited 2841block. 2842Brace delimited blocks may contain rules or other brace-delimited blocks. 2843When anchors are loaded this way the anchor name becomes optional. 2844.Bd -literal -offset indent 2845anchor "external" on $ext_if { 2846 block 2847 anchor out { 2848 pass proto tcp from any to port { 25, 80, 443 } 2849 } 2850 pass in proto tcp to any port 22 2851} 2852.Ed 2853.Pp 2854Since the parser specification for anchor names is a string, any 2855reference to an anchor name containing 2856.Sq / 2857characters will require double quote 2858.Pq Sq \&" 2859characters around the anchor name. 2860.Sh SCTP CONSIDERATIONS 2861.Xr pf 4 2862supports 2863.Xr sctp 4 2864connections. 2865It can match ports, track state and NAT SCTP traffic. 2866However, it will not alter port numbers during nat or rdr translations. 2867Doing so would break SCTP multihoming. 2868.Sh TRANSLATION EXAMPLES 2869This example maps incoming requests on port 80 to port 8080, on 2870which a daemon is running (because, for example, it is not run as root, 2871and therefore lacks permission to bind to port 80). 2872.Bd -literal 2873# use a macro for the interface name, so it can be changed easily 2874ext_if = \&"ne3\&" 2875 2876# map daemon on 8080 to appear to be on 80 2877rdr on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 port 8080 2878.Ed 2879.Pp 2880If the 2881.Ar pass 2882modifier is given, packets matching the translation rule are passed without 2883inspecting the filter rules: 2884.Bd -literal 2885rdr pass on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 \e 2886 port 8080 2887.Ed 2888.Pp 2889In the example below, vlan12 is configured as 192.168.168.1; 2890the machine translates all packets coming from 192.168.168.0/24 to 204.92.77.111 2891when they are going out any interface except vlan12. 2892This has the net effect of making traffic from the 192.168.168.0/24 2893network appear as though it is the Internet routable address 2894204.92.77.111 to nodes behind any interface on the router except 2895for the nodes on vlan12. 2896(Thus, 192.168.168.1 can talk to the 192.168.168.0/24 nodes.) 2897.Bd -literal 2898nat on ! vlan12 from 192.168.168.0/24 to any -\*(Gt 204.92.77.111 2899.Ed 2900.Pp 2901In the example below, the machine sits between a fake internal 144.19.74.* 2902network, and a routable external IP of 204.92.77.100. 2903The 2904.Ar no nat 2905rule excludes protocol AH from being translated. 2906.Bd -literal 2907# NO NAT 2908no nat on $ext_if proto ah from 144.19.74.0/24 to any 2909nat on $ext_if from 144.19.74.0/24 to any -\*(Gt 204.92.77.100 2910.Ed 2911.Pp 2912In the example below, packets bound for one specific server, as well as those 2913generated by the sysadmins are not proxied; all other connections are. 2914.Bd -literal 2915# NO RDR 2916no rdr on $int_if proto { tcp, udp } from any to $server port 80 2917no rdr on $int_if proto { tcp, udp } from $sysadmins to any port 80 2918rdr on $int_if proto { tcp, udp } from any to any port 80 -\*(Gt 127.0.0.1 \e 2919 port 80 2920.Ed 2921.Pp 2922This longer example uses both a NAT and a redirection. 2923The external interface has the address 157.161.48.183. 2924On localhost, we are running 2925.Xr ftp-proxy 8 , 2926waiting for FTP sessions to be redirected to it. 2927The three mandatory anchors for 2928.Xr ftp-proxy 8 2929are omitted from this example; see the 2930.Xr ftp-proxy 8 2931manpage. 2932.Bd -literal 2933# NAT 2934# Translate outgoing packets' source addresses (any protocol). 2935# In this case, any address but the gateway's external address is mapped. 2936nat on $ext_if inet from ! ($ext_if) to any -\*(Gt ($ext_if) 2937 2938# NAT PROXYING 2939# Map outgoing packets' source port to an assigned proxy port instead of 2940# an arbitrary port. 2941# In this case, proxy outgoing isakmp with port 500 on the gateway. 2942nat on $ext_if inet proto udp from any port = isakmp to any -\*(Gt ($ext_if) \e 2943 port 500 2944 2945# BINAT 2946# Translate outgoing packets' source address (any protocol). 2947# Translate incoming packets' destination address to an internal machine 2948# (bidirectional). 2949binat on $ext_if from 10.1.2.150 to any -\*(Gt $ext_if 2950 2951# Translate packets arriving on $peer_if addressed to 172.22.16.0/20 2952# to the corresponding address in 172.21.16.0/20 (bidirectional). 2953binat on $peer_if from 172.21.16.0/20 to any -> 172.22.16.0/20 2954 2955# RDR 2956# Translate incoming packets' destination addresses. 2957# As an example, redirect a TCP and UDP port to an internal machine. 2958rdr on $ext_if inet proto tcp from any to ($ext_if) port 8080 \e 2959 -\*(Gt 10.1.2.151 port 22 2960rdr on $ext_if inet proto udp from any to ($ext_if) port 8080 \e 2961 -\*(Gt 10.1.2.151 port 53 2962 2963# RDR 2964# Translate outgoing ftp control connections to send them to localhost 2965# for proxying with ftp-proxy(8) running on port 8021. 2966rdr on $int_if proto tcp from any to any port 21 -\*(Gt 127.0.0.1 port 8021 2967.Ed 2968.Pp 2969In this example, a NAT gateway is set up to translate internal addresses 2970using a pool of public addresses (192.0.2.16/28) and to redirect 2971incoming web server connections to a group of web servers on the internal 2972network. 2973.Bd -literal 2974# NAT LOAD BALANCE 2975# Translate outgoing packets' source addresses using an address pool. 2976# A given source address is always translated to the same pool address by 2977# using the source-hash keyword. 2978nat on $ext_if inet from any to any -\*(Gt 192.0.2.16/28 source-hash 2979 2980# RDR ROUND ROBIN 2981# Translate incoming web server connections to a group of web servers on 2982# the internal network. 2983rdr on $ext_if proto tcp from any to any port 80 \e 2984 -\*(Gt { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin 2985.Ed 2986.Sh FILTER EXAMPLES 2987.Bd -literal 2988# The external interface is kue0 2989# (157.161.48.183, the only routable address) 2990# and the private network is 10.0.0.0/8, for which we are doing NAT. 2991 2992# use a macro for the interface name, so it can be changed easily 2993ext_if = \&"kue0\&" 2994 2995# normalize all incoming traffic 2996scrub in on $ext_if all fragment reassemble 2997 2998# block and log everything by default 2999block return log on $ext_if all 3000 3001# block anything coming from source we have no back routes for 3002block in from no-route to any 3003 3004# block packets whose ingress interface does not match the one in 3005# the route back to their source address 3006block in from urpf-failed to any 3007 3008# block and log outgoing packets that do not have our address as source, 3009# they are either spoofed or something is misconfigured (NAT disabled, 3010# for instance), we want to be nice and do not send out garbage. 3011block out log quick on $ext_if from ! 157.161.48.183 to any 3012 3013# silently drop broadcasts (cable modem noise) 3014block in quick on $ext_if from any to 255.255.255.255 3015 3016# block and log incoming packets from reserved address space and invalid 3017# addresses, they are either spoofed or misconfigured, we cannot reply to 3018# them anyway (hence, no return-rst). 3019block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \e 3020 192.168.0.0/16, 255.255.255.255/32 } to any 3021 3022# ICMP 3023 3024# pass out/in certain ICMP queries and keep state (ping) 3025# state matching is done on host addresses and ICMP id (not type/code), 3026# so replies (like 0/0 for 8/0) will match queries 3027# ICMP error messages (which always refer to a TCP/UDP packet) are 3028# handled by the TCP/UDP states 3029pass on $ext_if inet proto icmp all icmp-type 8 code 0 3030 3031# UDP 3032 3033# pass out all UDP connections and keep state 3034pass out on $ext_if proto udp all 3035 3036# pass in certain UDP connections and keep state (DNS) 3037pass in on $ext_if proto udp from any to any port domain 3038 3039# TCP 3040 3041# pass out all TCP connections and modulate state 3042pass out on $ext_if proto tcp all modulate state 3043 3044# pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT) 3045pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \e 3046 auth } 3047 3048# Do not allow Windows 9x SMTP connections since they are typically 3049# a viral worm. Alternately we could limit these OSes to 1 connection each. 3050block in on $ext_if proto tcp from any os {"Windows 95", "Windows 98"} \e 3051 to any port smtp 3052 3053# IPv6 3054# pass in/out all IPv6 traffic: note that we have to enable this in two 3055# different ways, on both our physical interface and our tunnel 3056pass quick on gif0 inet6 3057pass quick on $ext_if proto ipv6 3058 3059# Packet Tagging 3060 3061# three interfaces: $int_if, $ext_if, and $wifi_if (wireless). NAT is 3062# being done on $ext_if for all outgoing packets. tag packets in on 3063# $int_if and pass those tagged packets out on $ext_if. all other 3064# outgoing packets (i.e., packets from the wireless network) are only 3065# permitted to access port 80. 3066 3067pass in on $int_if from any to any tag INTNET 3068pass in on $wifi_if from any to any 3069 3070block out on $ext_if from any to any 3071pass out quick on $ext_if tagged INTNET 3072pass out on $ext_if proto tcp from any to any port 80 3073 3074# tag incoming packets as they are redirected to spamd(8). use the tag 3075# to pass those packets through the packet filter. 3076 3077rdr on $ext_if inet proto tcp from \*(Ltspammers\*(Gt to port smtp \e 3078 tag SPAMD -\*(Gt 127.0.0.1 port spamd 3079 3080block in on $ext_if 3081pass in on $ext_if inet proto tcp tagged SPAMD 3082.Ed 3083.Sh GRAMMAR 3084Syntax for 3085.Nm 3086in BNF: 3087.Bd -literal 3088line = ( option | ether-rule | pf-rule | nat-rule | binat-rule | 3089 rdr-rule | antispoof-rule | altq-rule | queue-rule | 3090 trans-anchors | anchor-rule | anchor-close | load-anchor | 3091 table-rule | include ) 3092 3093option = "set" ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] | 3094 [ "ruleset-optimization" [ "none" | "basic" | "profile" ]] | 3095 [ "optimization" [ "default" | "normal" | 3096 "high-latency" | "satellite" | 3097 "aggressive" | "conservative" ] ] 3098 [ "limit" ( limit-item | "{" limit-list "}" ) ] | 3099 [ "loginterface" ( interface-name | "none" ) ] | 3100 [ "block-policy" ( "drop" | "return" ) ] | 3101 [ "state-policy" ( "if-bound" | "floating" ) ] 3102 [ "state-defaults" state-opts ] 3103 [ "require-order" ( "yes" | "no" ) ] 3104 [ "fingerprints" filename ] | 3105 [ "skip on" ifspec ] | 3106 [ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] 3107 [ "keepcounters" ] ) 3108 3109ether-rule = "ether" etheraction [ ( "in" | "out" ) ] 3110 [ "quick" ] [ "on" ifspec ] [ "bridge-to" interface-name ] 3111 [ etherprotospec ] etherhosts [ "l3" hosts ] 3112 [ etherfilteropt-list ] 3113 3114pf-rule = action [ ( "in" | "out" ) ] 3115 [ "log" [ "(" logopts ")"] ] [ "quick" ] 3116 [ "on" ifspec ] [ route ] [ af ] [ protospec ] 3117 hosts [ filteropt-list ] 3118 3119logopts = logopt [ "," logopts ] 3120logopt = "all" | "user" | "to" interface-name 3121 3122etherfilteropt-list = etherfilteropt-list etherfilteropt | etherfilteropt 3123etherfilteropt = "tag" string | "tagged" string | "queue" ( string ) | 3124 "ridentifier" number | "label" string 3125 3126filteropt-list = filteropt-list filteropt | filteropt 3127filteropt = user | group | flags | icmp-type | icmp6-type | "tos" tos | 3128 ( "no" | "keep" | "modulate" | "synproxy" ) "state" 3129 [ "(" state-opts ")" ] | 3130 "fragment" | "no-df" | "min-ttl" number | "set-tos" tos | 3131 "max-mss" number | "random-id" | "reassemble tcp" | 3132 fragmentation | "allow-opts" | 3133 "label" string | "tag" string | [ ! ] "tagged" string | 3134 "set prio" ( number | "(" number [ [ "," ] number ] ")" ) | 3135 "queue" ( string | "(" string [ [ "," ] string ] ")" ) | 3136 "rtable" number | "probability" number"%" | "prio" number | 3137 "dnpipe" ( number | "(" number "," number ")" ) | 3138 "dnqueue" ( number | "(" number "," number ")" ) | 3139 "ridentifier" number 3140 3141nat-rule = [ "no" ] "nat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3142 [ "on" ifspec ] [ af ] 3143 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3144 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3145 [ portspec ] [ pooltype ] [ "static-port" ] 3146 [ "map-e-portset" number "/" number "/" number ] ] 3147 3148binat-rule = [ "no" ] "binat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3149 [ "on" interface-name ] [ af ] 3150 [ "proto" ( proto-name | proto-number ) ] 3151 "from" address [ "/" mask-bits ] "to" ipspec 3152 [ "tag" string ] [ "tagged" string ] 3153 [ "-\*(Gt" address [ "/" mask-bits ] ] 3154 3155rdr-rule = [ "no" ] "rdr" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3156 [ "on" ifspec ] [ af ] 3157 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3158 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3159 [ portspec ] [ pooltype ] ] 3160 3161antispoof-rule = "antispoof" [ "log" ] [ "quick" ] 3162 "for" ifspec [ af ] [ "label" string ] 3163 [ "ridentifier" number ] 3164 3165table-rule = "table" "\*(Lt" string "\*(Gt" [ tableopts-list ] 3166tableopts-list = tableopts-list tableopts | tableopts 3167tableopts = "persist" | "const" | "counters" | "file" string | 3168 "{" [ tableaddr-list ] "}" 3169tableaddr-list = tableaddr-list [ "," ] tableaddr-spec | tableaddr-spec 3170tableaddr-spec = [ "!" ] tableaddr [ "/" mask-bits ] 3171tableaddr = hostname | ifspec | "self" | 3172 ipv4-dotted-quad | ipv6-coloned-hex 3173 3174altq-rule = "altq on" interface-name queueopts-list 3175 "queue" subqueue 3176queue-rule = "queue" string [ "on" interface-name ] queueopts-list 3177 subqueue 3178 3179anchor-rule = "anchor" [ string ] [ ( "in" | "out" ) ] [ "on" ifspec ] 3180 [ af ] [ protospec ] [ hosts ] [ filteropt-list ] [ "{" ] 3181 3182anchor-close = "}" 3183 3184trans-anchors = ( "nat-anchor" | "rdr-anchor" | "binat-anchor" ) string 3185 [ "on" ifspec ] [ af ] [ "proto" ] [ protospec ] [ hosts ] 3186 3187load-anchor = "load anchor" string "from" filename 3188 3189queueopts-list = queueopts-list queueopts | queueopts 3190queueopts = [ "bandwidth" bandwidth-spec ] | 3191 [ "qlimit" number ] | [ "tbrsize" number ] | 3192 [ "priority" number ] | [ schedulers ] 3193schedulers = ( cbq-def | priq-def | hfsc-def ) 3194bandwidth-spec = "number" ( "b" | "Kb" | "Mb" | "Gb" | "%" ) 3195 3196etheraction = "pass" | "block" 3197action = "pass" | "match" | "block" [ return ] | [ "no" ] "scrub" 3198return = "drop" | "return" | "return-rst" [ "( ttl" number ")" ] | 3199 "return-icmp" [ "(" icmpcode [ [ "," ] icmp6code ] ")" ] | 3200 "return-icmp6" [ "(" icmp6code ")" ] 3201icmpcode = ( icmp-code-name | icmp-code-number ) 3202icmp6code = ( icmp6-code-name | icmp6-code-number ) 3203 3204ifspec = ( [ "!" ] ( interface-name | interface-group ) ) | 3205 "{" interface-list "}" 3206interface-list = [ "!" ] ( interface-name | interface-group ) 3207 [ [ "," ] interface-list ] 3208route = ( "route-to" | "reply-to" | "dup-to" ) 3209 ( routehost | "{" routehost-list "}" ) 3210 [ pooltype ] 3211af = "inet" | "inet6" 3212 3213etherprotospec = "proto" ( proto-number | "{" etherproto-list "}" ) 3214etherproto-list = proto-number [ [ "," ] etherproto-list ] 3215protospec = "proto" ( proto-name | proto-number | 3216 "{" proto-list "}" ) 3217proto-list = ( proto-name | proto-number ) [ [ "," ] proto-list ] 3218 3219etherhosts = "from" macaddress "to" macaddress 3220macaddress = mac | mac "/" masklen | mac "&" mask 3221 3222hosts = "all" | 3223 "from" ( "any" | "no-route" | "urpf-failed" | "self" | host | 3224 "{" host-list "}" ) [ port ] [ os ] 3225 "to" ( "any" | "no-route" | "self" | host | 3226 "{" host-list "}" ) [ port ] 3227 3228ipspec = "any" | host | "{" host-list "}" 3229host = [ "!" ] ( address [ "/" mask-bits ] | "\*(Lt" string "\*(Gt" ) 3230redirhost = address [ "/" mask-bits ] 3231routehost = "(" interface-name [ address [ "/" mask-bits ] ] ")" 3232address = ( interface-name | interface-group | 3233 "(" ( interface-name | interface-group ) ")" | 3234 hostname | ipv4-dotted-quad | ipv6-coloned-hex ) 3235host-list = host [ [ "," ] host-list ] 3236redirhost-list = redirhost [ [ "," ] redirhost-list ] 3237routehost-list = routehost [ [ "," ] routehost-list ] 3238 3239port = "port" ( unary-op | binary-op | "{" op-list "}" ) 3240portspec = "port" ( number | name ) [ ":" ( "*" | number | name ) ] 3241os = "os" ( os-name | "{" os-list "}" ) 3242user = "user" ( unary-op | binary-op | "{" op-list "}" ) 3243group = "group" ( unary-op | binary-op | "{" op-list "}" ) 3244 3245unary-op = [ "=" | "!=" | "\*(Lt" | "\*(Le" | "\*(Gt" | "\*(Ge" ] 3246 ( name | number ) 3247binary-op = number ( "\*(Lt\*(Gt" | "\*(Gt\*(Lt" | ":" ) number 3248op-list = ( unary-op | binary-op ) [ [ "," ] op-list ] 3249 3250os-name = operating-system-name 3251os-list = os-name [ [ "," ] os-list ] 3252 3253flags = "flags" ( [ flag-set ] "/" flag-set | "any" ) 3254flag-set = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ] 3255 [ "W" ] 3256 3257icmp-type = "icmp-type" ( icmp-type-code | "{" icmp-list "}" ) 3258icmp6-type = "icmp6-type" ( icmp-type-code | "{" icmp-list "}" ) 3259icmp-type-code = ( icmp-type-name | icmp-type-number ) 3260 [ "code" ( icmp-code-name | icmp-code-number ) ] 3261icmp-list = icmp-type-code [ [ "," ] icmp-list ] 3262 3263tos = ( "lowdelay" | "throughput" | "reliability" | 3264 [ "0x" ] number ) 3265 3266state-opts = state-opt [ [ "," ] state-opts ] 3267state-opt = ( "max" number | "no-sync" | timeout | "sloppy" | 3268 "source-track" [ ( "rule" | "global" ) ] | 3269 "max-src-nodes" number | "max-src-states" number | 3270 "max-src-conn" number | 3271 "max-src-conn-rate" number "/" number | 3272 "overload" "\*(Lt" string "\*(Gt" [ "flush" ] | 3273 "if-bound" | "floating" ) 3274 3275fragmentation = [ "fragment reassemble" ] 3276 3277timeout-list = timeout [ [ "," ] timeout-list ] 3278timeout = ( "tcp.first" | "tcp.opening" | "tcp.established" | 3279 "tcp.closing" | "tcp.finwait" | "tcp.closed" | 3280 "udp.first" | "udp.single" | "udp.multiple" | 3281 "icmp.first" | "icmp.error" | 3282 "other.first" | "other.single" | "other.multiple" | 3283 "frag" | "interval" | "src.track" | 3284 "adaptive.start" | "adaptive.end" ) number 3285 3286limit-list = limit-item [ [ "," ] limit-list ] 3287limit-item = ( "states" | "frags" | "src-nodes" ) number 3288 3289pooltype = ( "bitmask" | "random" | 3290 "source-hash" [ ( hex-key | string-key ) ] | 3291 "round-robin" ) [ sticky-address ] 3292 3293subqueue = string | "{" queue-list "}" 3294queue-list = string [ [ "," ] string ] 3295cbq-def = "cbq" [ "(" cbq-opt [ [ "," ] cbq-opt ] ")" ] 3296priq-def = "priq" [ "(" priq-opt [ [ "," ] priq-opt ] ")" ] 3297hfsc-def = "hfsc" [ "(" hfsc-opt [ [ "," ] hfsc-opt ] ")" ] 3298cbq-opt = ( "default" | "borrow" | "red" | "ecn" | "rio" ) 3299priq-opt = ( "default" | "red" | "ecn" | "rio" ) 3300hfsc-opt = ( "default" | "red" | "ecn" | "rio" | 3301 linkshare-sc | realtime-sc | upperlimit-sc ) 3302linkshare-sc = "linkshare" sc-spec 3303realtime-sc = "realtime" sc-spec 3304upperlimit-sc = "upperlimit" sc-spec 3305sc-spec = ( bandwidth-spec | 3306 "(" bandwidth-spec number bandwidth-spec ")" ) 3307include = "include" filename 3308.Ed 3309.Sh FILES 3310.Bl -tag -width "/etc/protocols" -compact 3311.It Pa /etc/hosts 3312Host name database. 3313.It Pa /etc/pf.conf 3314Default location of the ruleset file. 3315The file has to be created manually as it is not installed with a 3316standard installation. 3317.It Pa /etc/pf.os 3318Default location of OS fingerprints. 3319.It Pa /etc/protocols 3320Protocol name database. 3321.It Pa /etc/services 3322Service name database. 3323.El 3324.Sh SEE ALSO 3325.Xr altq 4 , 3326.Xr carp 4 , 3327.Xr icmp 4 , 3328.Xr icmp6 4 , 3329.Xr ip 4 , 3330.Xr ip6 4 , 3331.Xr pf 4 , 3332.Xr pfsync 4 , 3333.Xr tcp 4 , 3334.Xr sctp 4 , 3335.Xr udp 4 , 3336.Xr hosts 5 , 3337.Xr pf.os 5 , 3338.Xr protocols 5 , 3339.Xr services 5 , 3340.Xr ftp-proxy 8 , 3341.Xr pfctl 8 , 3342.Xr pflogd 8 3343.Sh HISTORY 3344The 3345.Nm 3346file format first appeared in 3347.Ox 3.0 . 3348