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 September 4, 2024 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 286SCTP timeout are handled similar to TCP, but with its own set of states: 287.Pp 288.Bl -tag -width xxxx -compact 289.It Ar sctp.first 290The state after the first packet. 291.It Ar sctp.opening 292The state before the destination host ever sends a packet. 293.It Ar sctp.established 294The fully established state. 295.It Ar sctp.closing 296The state after the first SHUTDOWN chunk has been sent. 297.It Ar sctp.closed 298The state after SHUTDOWN_ACK has been exchanged and the connection is closed. 299.El 300.Pp 301ICMP and UDP are handled in a fashion similar to TCP, but with a much more 302limited set of states: 303.Pp 304.Bl -tag -width xxxx -compact 305.It Ar udp.first 306The state after the first packet. 307.It Ar udp.single 308The state if the source host sends more than one packet but the destination 309host has never sent one back. 310.It Ar udp.multiple 311The state if both hosts have sent packets. 312.It Ar icmp.first 313The state after the first packet. 314.It Ar icmp.error 315The state after an ICMP error came back in response to an ICMP packet. 316.El 317.Pp 318Other protocols are handled similarly to UDP: 319.Pp 320.Bl -tag -width xxxx -compact 321.It Ar other.first 322.It Ar other.single 323.It Ar other.multiple 324.El 325.Pp 326Timeout values can be reduced adaptively as the number of state table 327entries grows. 328.Pp 329.Bl -tag -width xxxx -compact 330.It Ar adaptive.start 331When the number of state entries exceeds this value, adaptive scaling 332begins. 333All timeout values are scaled linearly with factor 334(adaptive.end - number of states) / (adaptive.end - adaptive.start). 335.It Ar adaptive.end 336When reaching this number of state entries, all timeout values become 337zero, effectively purging all state entries immediately. 338This value is used to define the scale factor, it should not actually 339be reached (set a lower state limit, see below). 340.El 341.Pp 342Adaptive timeouts are enabled by default, with an adaptive.start value 343equal to 60% of the state limit, and an adaptive.end value equal to 344120% of the state limit. 345They can be disabled by setting both adaptive.start and adaptive.end to 0. 346.Pp 347The adaptive timeout values can be defined both globally and for each rule. 348When used on a per-rule basis, the values relate to the number of 349states created by the rule, otherwise to the total number of 350states. 351.Pp 352For example: 353.Bd -literal -offset indent 354set timeout tcp.first 120 355set timeout tcp.established 86400 356set timeout { adaptive.start 6000, adaptive.end 12000 } 357set limit states 10000 358.Ed 359.Pp 360With 9000 state table entries, the timeout values are scaled to 50% 361(tcp.first 60, tcp.established 43200). 362.It Ar set loginterface 363Enable collection of packet and byte count statistics for the given 364interface or interface group. 365These statistics can be viewed using 366.Bd -literal -offset indent 367# pfctl -s info 368.Ed 369.Pp 370In this example 371.Xr pf 4 372collects statistics on the interface named dc0: 373.Bd -literal -offset indent 374set loginterface dc0 375.Ed 376.Pp 377One can disable the loginterface using: 378.Bd -literal -offset indent 379set loginterface none 380.Ed 381.It Ar set limit 382Sets hard limits on the memory pools used by the packet filter. 383See 384.Xr zone 9 385for an explanation of memory pools. 386.Pp 387For example, 388.Bd -literal -offset indent 389set limit states 20000 390.Ed 391.Pp 392sets the maximum number of entries in the memory pool used by state table 393entries (generated by 394.Ar pass 395rules which do not specify 396.Ar no state ) 397to 20000. 398Using 399.Bd -literal -offset indent 400set limit frags 20000 401.Ed 402.Pp 403sets the maximum number of entries in the memory pool used for fragment 404reassembly (generated by the 405.Ar set reassemble 406option or 407.Ar scrub 408rules) to 20000. 409Using 410.Bd -literal -offset indent 411set limit src-nodes 2000 412.Ed 413.Pp 414sets the maximum number of entries in the memory pool used for tracking 415source IP addresses (generated by the 416.Ar sticky-address 417and 418.Ar src.track 419options) to 2000. 420Using 421.Bd -literal -offset indent 422set limit table-entries 100000 423.Ed 424.Pp 425sets the limit on the overall number of addresses that can be stored 426in tables to 100000. 427.Pp 428Various limits can be combined on a single line: 429.Bd -literal -offset indent 430set limit { states 20000, frags 20000, src-nodes 2000 } 431.Ed 432.It Ar set ruleset-optimization 433.Bl -tag -width xxxxxxxx -compact 434.It Ar none 435Disable the ruleset optimizer. 436.It Ar basic 437Enable basic ruleset optimization. 438This is the default behaviour. 439Basic ruleset optimization does four things to improve the 440performance of ruleset evaluations: 441.Pp 442.Bl -enum -compact 443.It 444remove duplicate rules 445.It 446remove rules that are a subset of another rule 447.It 448combine multiple rules into a table when advantageous 449.It 450re-order the rules to improve evaluation performance 451.El 452.Pp 453.It Ar profile 454Uses the currently loaded ruleset as a feedback profile to tailor the 455ordering of quick rules to actual network traffic. 456.El 457.Pp 458It is important to note that the ruleset optimizer will modify the ruleset 459to improve performance. 460A side effect of the ruleset modification is that per-rule accounting 461statistics will have different meanings than before. 462If per-rule accounting is important for billing purposes or whatnot, 463either the ruleset optimizer should not be used or a label field should 464be added to all of the accounting rules to act as optimization barriers. 465.Pp 466Optimization can also be set as a command-line argument to 467.Xr pfctl 8 , 468overriding the settings in 469.Nm . 470.It Ar set optimization 471Optimize state timeouts for one of the following network environments: 472.Pp 473.Bl -tag -width xxxx -compact 474.It Ar normal 475A normal network environment. 476Suitable for almost all networks. 477.It Ar high-latency 478A high-latency environment (such as a satellite connection). 479.It Ar satellite 480Alias for 481.Ar high-latency . 482.It Ar aggressive 483Aggressively expire connections. 484This can greatly reduce the memory usage of the firewall at the cost of 485dropping idle connections early. 486.It Ar conservative 487Extremely conservative settings. 488Avoid dropping legitimate connections at the 489expense of greater memory utilization (possibly much greater on a busy 490network) and slightly increased processor utilization. 491.El 492.Pp 493For example: 494.Bd -literal -offset indent 495set optimization aggressive 496.Ed 497.It Ar set reassemble yes | no Op Cm no-df 498The 499.Cm reassemble 500option is used to enable or disable the reassembly of fragmented packets, 501and can be set to 502.Cm yes 503or 504.Cm no . 505If 506.Cm no-df 507is also specified, fragments with the 508.Dq dont-fragment 509bit set are reassembled too, 510instead of being dropped; 511the reassembled packet will have the 512.Dq dont-fragment 513bit cleared. 514The default value is 515.Cm no . 516.Pp 517This option is ignored if there are pre-FreeBSD 14 518.Cm scrub 519rules present. 520.It Ar set block-policy 521The 522.Ar block-policy 523option sets the default behaviour for the packet 524.Ar block 525action: 526.Pp 527.Bl -tag -width xxxxxxxx -compact 528.It Ar drop 529Packet is silently dropped. 530.It Ar return 531A TCP RST is returned for blocked TCP packets, 532an SCTP ABORT chunk is returned for blocked SCTP packets, 533an ICMP UNREACHABLE is returned for blocked UDP packets, 534and all other packets are silently dropped. 535.El 536.Pp 537For example: 538.Bd -literal -offset indent 539set block-policy return 540.Ed 541.It Ar set fail-policy 542The 543.Ar fail-policy 544option sets the behaviour of rules which should pass a packet but were 545unable to do so. 546This might happen when a nat or route-to rule uses an empty table as list 547of targets or if a rule fails to create state or source node. 548The following 549.Ar block 550actions are possible: 551.Pp 552.Bl -tag -width xxxxxxxx -compact 553.It Ar drop 554Incoming packet is silently dropped. 555.It Ar return 556Incoming packet is dropped and TCP RST is returned for TCP packets, 557an SCTP ABORT chunk is returned for blocked SCTP packets, 558an ICMP UNREACHABLE is returned for UDP packets, 559and no response is sent for other packets. 560.El 561.Pp 562For example: 563.Bd -literal -offset indent 564set fail-policy return 565.Ed 566.It Ar set state-policy 567The 568.Ar state-policy 569option sets the default behaviour for states: 570.Pp 571.Bl -tag -width group-bound -compact 572.It Ar if-bound 573States are bound to interface. 574.It Ar floating 575States can match packets on any interfaces (the default). 576.El 577.Pp 578For example: 579.Bd -literal -offset indent 580set state-policy if-bound 581.Ed 582.It Ar set syncookies never | always | adaptive 583When 584.Cm syncookies 585are active, pf will answer each incoming TCP SYN with a syncookie SYNACK, 586without allocating any resources. 587Upon reception of the client's ACK in response to the syncookie 588SYNACK, pf will evaluate the ruleset and create state if the ruleset 589permits it, complete the three way handshake with the target host and 590continue the connection with synproxy in place. 591This allows pf to be resilient against large synflood attacks which would 592run the state table against its limits otherwise. 593Due to the blind answers to every incoming SYN syncookies share the caveats of 594synproxy, namely seemingly accepting connections that will be dropped later on. 595.Pp 596.Bl -tag -width adaptive -compact 597.It Cm never 598pf will never send syncookie SYNACKs (the default). 599.It Cm always 600pf will always send syncookie SYNACKs. 601.It Cm adaptive 602pf will enable syncookie mode when a given percentage of the state table 603is used up by half-open TCP connections, as in, those that saw the initial 604SYN but didn't finish the three way handshake. 605The thresholds for entering and leaving syncookie mode can be specified using 606.Bd -literal -offset indent 607set syncookies adaptive (start 25%, end 12%) 608.Ed 609.El 610.It Ar set state-defaults 611The 612.Ar state-defaults 613option sets the state options for states created from rules 614without an explicit 615.Ar keep state . 616For example: 617.Bd -literal -offset indent 618set state-defaults no-sync 619.Ed 620.It Ar set hostid 621The 32-bit 622.Ar hostid 623identifies this firewall's state table entries to other firewalls 624in a 625.Xr pfsync 4 626failover cluster. 627By default the hostid is set to a pseudo-random value, however it may be 628desirable to manually configure it, for example to more easily identify the 629source of state table entries. 630.Bd -literal -offset indent 631set hostid 1 632.Ed 633.Pp 634The hostid may be specified in either decimal or hexadecimal. 635.It Ar set require-order 636By default 637.Xr pfctl 8 638enforces an ordering of the statement types in the ruleset to: 639.Em options , 640.Em normalization , 641.Em queueing , 642.Em translation , 643.Em filtering . 644Setting this option to 645.Ar no 646disables this enforcement. 647There may be non-trivial and non-obvious implications to an out of 648order ruleset. 649Consider carefully before disabling the order enforcement. 650.It Ar set fingerprints 651Load fingerprints of known operating systems from the given filename. 652By default fingerprints of known operating systems are automatically 653loaded from 654.Xr pf.os 5 655in 656.Pa /etc 657but can be overridden via this option. 658Setting this option may leave a small period of time where the fingerprints 659referenced by the currently active ruleset are inconsistent until the new 660ruleset finishes loading. 661.Pp 662For example: 663.Pp 664.Dl set fingerprints \&"/etc/pf.os.devel\&" 665.It Ar set skip on Aq Ar ifspec 666List interfaces for which packets should not be filtered. 667Packets passing in or out on such interfaces are passed as if pf was 668disabled, i.e. pf does not process them in any way. 669This can be useful on loopback and other virtual interfaces, when 670packet filtering is not desired and can have unexpected effects. 671For example: 672.Pp 673.Dl set skip on lo0 674.It Ar set debug 675Set the debug 676.Ar level 677to one of the following: 678.Pp 679.Bl -tag -width xxxxxxxxxxxx -compact 680.It Ar none 681Don't generate debug messages. 682.It Ar urgent 683Generate debug messages only for serious errors. 684.It Ar misc 685Generate debug messages for various errors. 686.It Ar loud 687Generate debug messages for common conditions. 688.El 689.It Ar set keepcounters 690Preserve rule counters across rule updates. 691Usually rule counters are reset to zero on every update of the ruleset. 692With 693.Ar keepcounters 694set pf will attempt to find matching rules between old and new rulesets 695and preserve the rule counters. 696.El 697.Sh ETHERNET FILTERING 698.Xr pf 4 699has the ability to 700.Ar block 701and 702.Ar pass 703packets based on attributes of their Ethernet (layer 2) header. 704.Pp 705For each packet processed by the packet filter, the filter rules are 706evaluated in sequential order, from first to last. 707The last matching rule decides what action is taken. 708If no rule matches the packet, the default action is to pass 709the packet. 710.Pp 711The following actions can be used in the filter: 712.Bl -tag -width xxxx 713.It Ar block 714The packet is blocked. 715Unlike for layer 3 traffic the packet is always silently dropped. 716.It Ar pass 717The packet is passed; 718no state is created for layer 2 traffic. 719.El 720.Sh PARAMETERS 721The rule parameters specify the packets to which a rule applies. 722A packet always comes in on, or goes out through, one interface. 723Most parameters are optional. 724If a parameter is specified, the rule only applies to packets with 725matching attributes. 726Certain parameters can be expressed as lists, in which case 727.Xr pfctl 8 728generates all needed rule combinations. 729.Bl -tag -width xxxx 730.It Ar in No or Ar out 731This rule applies to incoming or outgoing packets. 732If neither 733.Ar in 734nor 735.Ar out 736are specified, the rule will match packets in both directions. 737.It Ar quick 738If a packet matches a rule which has the 739.Ar quick 740option set, this rule 741is considered the last matching rule, and evaluation of subsequent rules 742is skipped. 743.It Ar on Aq Ar ifspec 744This rule applies only to packets coming in on, or going out through, this 745particular interface or interface group. 746For more information on interface groups, 747see the 748.Ic group 749keyword in 750.Xr ifconfig 8 . 751.It Ar bridge-to Aq interface 752Packets matching this rule will be sent out of the specified interface without 753further processing. 754.It Ar proto Aq Ar protocol 755This rule applies only to packets of this protocol. 756Note that Ethernet protocol numbers are different from those used in 757.Xr ip 4 758and 759.Xr ip6 4 . 760.It Xo 761.Ar from Aq Ar source 762.Ar to Aq Ar dest 763.Xc 764This rule applies only to packets with the specified source and destination 765MAC addresses. 766.It Xo Ar queue Aq Ar queue 767.Xc 768Packets matching this rule will be assigned to the specified queue. 769See 770.Sx QUEUEING 771for setup details. 772.Pp 773.It Ar tag Aq Ar string 774Packets matching this rule will be tagged with the 775specified string. 776The tag acts as an internal marker that can be used to 777identify these packets later on. 778This can be used, for example, to provide trust between 779interfaces and to determine if packets have been 780processed by translation rules. 781Tags are 782.Qq sticky , 783meaning that the packet will be tagged even if the rule 784is not the last matching rule. 785Further matching rules can replace the tag with a 786new one but will not remove a previously applied tag. 787A packet is only ever assigned one tag at a time. 788.It Ar tagged Aq Ar string 789Used to specify that packets must already be tagged with the given tag in order 790to match the rule. 791Inverse tag matching can also be done by specifying the ! operator before the 792tagged keyword. 793.El 794.Sh TRAFFIC NORMALIZATION 795Traffic normalization is a broad umbrella term 796for aspects of the packet filter which deal with 797verifying packets, packet fragments, spoofed traffic, 798and other irregularities. 799.Ss Scrub 800Scrub involves sanitising packet content in such a way 801that there are no ambiguities in packet interpretation on the receiving side. 802It is invoked with the 803.Cm scrub 804option, added to filter rules. 805.Pp 806Parameters are specified enclosed in parentheses. 807At least one of the following parameters must be specified: 808.Bl -tag -width xxxx 809.It Ar no-df 810Clears the 811.Ar dont-fragment 812bit from a matching IP packet. 813Some operating systems are known to generate fragmented packets with the 814.Ar dont-fragment 815bit set. 816This is particularly true with NFS. 817.Ar Scrub 818will drop such fragmented 819.Ar dont-fragment 820packets unless 821.Ar no-df 822is specified. 823.Pp 824Unfortunately some operating systems also generate their 825.Ar dont-fragment 826packets with a zero IP identification field. 827Clearing the 828.Ar dont-fragment 829bit on packets with a zero IP ID may cause deleterious results if an 830upstream router later fragments the packet. 831Using the 832.Ar random-id 833modifier (see below) is recommended in combination with the 834.Ar no-df 835modifier to ensure unique IP identifiers. 836.It Ar min-ttl Aq Ar number 837Enforces a minimum TTL for matching IP packets. 838.It Ar max-mss Aq Ar number 839Enforces a maximum MSS for matching TCP packets. 840.It Xo Ar set-tos Aq Ar string 841.No \*(Ba Aq Ar number 842.Xc 843Enforces a 844.Em TOS 845for matching IP packets. 846.Em TOS 847may be 848given as one of 849.Ar critical , 850.Ar inetcontrol , 851.Ar lowdelay , 852.Ar netcontrol , 853.Ar throughput , 854.Ar reliability , 855or one of the DiffServ Code Points: 856.Ar ef , 857.Ar va , 858.Ar af11 No ... Ar af43 , 859.Ar cs0 No ... Ar cs7 ; 860or as either hex or decimal. 861.It Ar random-id 862Replaces the IP identification field with random values to compensate 863for predictable values generated by many hosts. 864This option only applies to packets that are not fragmented 865after the optional fragment reassembly. 866.It Ar reassemble tcp 867Statefully normalizes TCP connections. 868.Ar reassemble tcp 869performs the following normalizations: 870.Pp 871.Bl -tag -width timeout -compact 872.It ttl 873Neither side of the connection is allowed to reduce their IP TTL. 874An attacker may send a packet such that it reaches the firewall, affects 875the firewall state, and expires before reaching the destination host. 876.Ar reassemble tcp 877will raise the TTL of all packets back up to the highest value seen on 878the connection. 879.It timestamp modulation 880Modern TCP stacks will send a timestamp on every TCP packet and echo 881the other endpoint's timestamp back to them. 882Many operating systems will merely start the timestamp at zero when 883first booted, and increment it several times a second. 884The uptime of the host can be deduced by reading the timestamp and multiplying 885by a constant. 886Also observing several different timestamps can be used to count hosts 887behind a NAT device. 888And spoofing TCP packets into a connection requires knowing or guessing 889valid timestamps. 890Timestamps merely need to be monotonically increasing and not derived off a 891guessable base time. 892.Ar reassemble tcp 893will cause 894.Ar scrub 895to modulate the TCP timestamps with a random number. 896.It extended PAWS checks 897There is a problem with TCP on long fat pipes, in that a packet might get 898delayed for longer than it takes the connection to wrap its 32-bit sequence 899space. 900In such an occurrence, the old packet would be indistinguishable from a 901new packet and would be accepted as such. 902The solution to this is called PAWS: Protection Against Wrapped Sequence 903numbers. 904It protects against it by making sure the timestamp on each packet does 905not go backwards. 906.Ar reassemble tcp 907also makes sure the timestamp on the packet does not go forward more 908than the RFC allows. 909By doing this, 910.Xr pf 4 911artificially extends the security of TCP sequence numbers by 10 to 18 912bits when the host uses appropriately randomized timestamps, since a 913blind attacker would have to guess the timestamp as well. 914.El 915.El 916.Pp 917For example, 918.Bd -literal -offset indent 919match in all scrub (no-df random-id max-mss 1440) 920.Ed 921.Ss Scrub ruleset (pre-FreeBSD 14) 922In order to maintain compatibility with older releases of FreeBSD 923.Ar scrub 924rules can also be specified in their own ruleset. 925In such case they are invoked with the 926.Ar scrub 927directive. 928If there are such rules present they determine packet reassembly behaviour. 929When no such rules are present the option 930.Ar set reassembly 931takes precedence. 932The 933.Ar scrub 934rules can take all parameters specified above for a 935.Ar scrub 936option of filter rules and 2 more parameters controlling fragment reassembly: 937.Bl -tag -width xxxx 938.It Ar fragment reassemble 939Using 940.Ar scrub 941rules, fragments can be reassembled by normalization. 942In this case, fragments are buffered until they form a complete 943packet, and only the completed packet is passed on to the filter. 944The advantage is that filter rules have to deal only with complete 945packets, and can ignore fragments. 946The drawback of caching fragments is the additional memory cost. 947This is the default behaviour unless no fragment reassemble is specified. 948.It Ar no fragment reassemble 949Do not reassemble fragments. 950.El 951.Pp 952For example, 953.Bd -literal -offset indent 954scrub in on $ext_if all fragment reassemble 955.Ed 956.Pp 957The 958.Ar no 959option prefixed to a scrub rule causes matching packets to remain unscrubbed, 960much in the same way as 961.Ar drop quick 962works in the packet filter (see below). 963This mechanism should be used when it is necessary to exclude specific packets 964from broader scrub rules. 965.Pp 966.Ar scrub 967rules in the 968.Ar scrub 969ruleset are evaluated for every packet before stateful filtering. 970This means excessive usage of them will cause performance penalty. 971.Ar scrub reassemble tcp 972rules must not have the direction (in/out) specified. 973.Sh QUEUEING with ALTQ 974The ALTQ system is currently not available in the GENERIC kernel nor as 975loadable modules. 976In order to use the herein after called queueing options one has to use a 977custom built kernel. 978Please refer to 979.Xr altq 4 980to learn about the related kernel options. 981.Pp 982Packets can be assigned to queues for the purpose of bandwidth 983control. 984At least two declarations are required to configure queues, and later 985any packet filtering rule can reference the defined queues by name. 986During the filtering component of 987.Nm pf.conf , 988the last referenced 989.Ar queue 990name is where any packets from 991.Ar pass 992rules will be queued, while for 993.Ar block 994rules it specifies where any resulting ICMP or TCP RST 995packets should be queued. 996The 997.Ar scheduler 998defines the algorithm used to decide which packets get delayed, dropped, or 999sent out immediately. 1000There are three 1001.Ar schedulers 1002currently supported. 1003.Bl -tag -width xxxx 1004.It Ar cbq 1005Class Based Queueing. 1006.Ar Queues 1007attached to an interface build a tree, thus each 1008.Ar queue 1009can have further child 1010.Ar queues . 1011Each queue can have a 1012.Ar priority 1013and a 1014.Ar bandwidth 1015assigned. 1016.Ar Priority 1017mainly controls the time packets take to get sent out, while 1018.Ar bandwidth 1019has primarily effects on throughput. 1020.Ar cbq 1021achieves both partitioning and sharing of link bandwidth 1022by hierarchically structured classes. 1023Each class has its own 1024.Ar queue 1025and is assigned its share of 1026.Ar bandwidth . 1027A child class can borrow bandwidth from its parent class 1028as long as excess bandwidth is available 1029(see the option 1030.Ar borrow , 1031below). 1032.It Ar priq 1033Priority Queueing. 1034.Ar Queues 1035are flat attached to the interface, thus, 1036.Ar queues 1037cannot have further child 1038.Ar queues . 1039Each 1040.Ar queue 1041has a unique 1042.Ar priority 1043assigned, ranging from 0 to 15. 1044Packets in the 1045.Ar queue 1046with the highest 1047.Ar priority 1048are processed first. 1049.It Ar hfsc 1050Hierarchical Fair Service Curve. 1051.Ar Queues 1052attached to an interface build a tree, thus each 1053.Ar queue 1054can have further child 1055.Ar queues . 1056Each queue can have a 1057.Ar priority 1058and a 1059.Ar bandwidth 1060assigned. 1061.Ar Priority 1062mainly controls the time packets take to get sent out, while 1063.Ar bandwidth 1064primarily affects throughput. 1065.Ar hfsc 1066supports both link-sharing and guaranteed real-time services. 1067It employs a service curve based QoS model, 1068and its unique feature is an ability to decouple 1069.Ar delay 1070and 1071.Ar bandwidth 1072allocation. 1073.El 1074.Pp 1075The interfaces on which queueing should be activated are declared using 1076the 1077.Ar altq on 1078declaration. 1079.Ar altq on 1080has the following keywords: 1081.Bl -tag -width xxxx 1082.It Aq Ar interface 1083Queueing is enabled on the named interface. 1084.It Aq Ar scheduler 1085Specifies which queueing scheduler to use. 1086Currently supported values 1087are 1088.Ar cbq 1089for Class Based Queueing, 1090.Ar priq 1091for Priority Queueing and 1092.Ar hfsc 1093for the Hierarchical Fair Service Curve scheduler. 1094.It Ar bandwidth Aq Ar bw 1095The maximum bitrate for all queues on an 1096interface may be specified using the 1097.Ar bandwidth 1098keyword. 1099The value can be specified as an absolute value or as a 1100percentage of the interface bandwidth. 1101When using an absolute value, the suffixes 1102.Ar b , 1103.Ar Kb , 1104.Ar Mb , 1105and 1106.Ar Gb 1107are used to represent bits, kilobits, megabits, and 1108gigabits per second, respectively. 1109The value must not exceed the interface bandwidth. 1110If 1111.Ar bandwidth 1112is not specified, the interface bandwidth is used 1113(but take note that some interfaces do not know their bandwidth, 1114or can adapt their bandwidth rates). 1115.It Ar qlimit Aq Ar limit 1116The maximum number of packets held in the queue. 1117The default is 50. 1118.It Ar tbrsize Aq Ar size 1119Adjusts the size, in bytes, of the token bucket regulator. 1120If not specified, heuristics based on the 1121interface bandwidth are used to determine the size. 1122.It Ar queue Aq Ar list 1123Defines a list of subqueues to create on an interface. 1124.El 1125.Pp 1126In the following example, the interface dc0 1127should queue up to 5Mbps in four second-level queues using 1128Class Based Queueing. 1129Those four queues will be shown in a later example. 1130.Bd -literal -offset indent 1131altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh } 1132.Ed 1133.Pp 1134Once interfaces are activated for queueing using the 1135.Ar altq 1136directive, a sequence of 1137.Ar queue 1138directives may be defined. 1139The name associated with a 1140.Ar queue 1141must match a queue defined in the 1142.Ar altq 1143directive (e.g. mail), or, except for the 1144.Ar priq 1145.Ar scheduler , 1146in a parent 1147.Ar queue 1148declaration. 1149The following keywords can be used: 1150.Bl -tag -width xxxx 1151.It Ar on Aq Ar interface 1152Specifies the interface the queue operates on. 1153If not given, it operates on all matching interfaces. 1154.It Ar bandwidth Aq Ar bw 1155Specifies the maximum bitrate to be processed by the queue. 1156This value must not exceed the value of the parent 1157.Ar queue 1158and can be specified as an absolute value or a percentage of the parent 1159queue's bandwidth. 1160If not specified, defaults to 100% of the parent queue's bandwidth. 1161The 1162.Ar priq 1163scheduler does not support bandwidth specification. 1164.It Ar priority Aq Ar level 1165Between queues a priority level can be set. 1166For 1167.Ar cbq 1168and 1169.Ar hfsc , 1170the range is 0 to 7 and for 1171.Ar priq , 1172the range is 0 to 15. 1173The default for all is 1. 1174.Ar Priq 1175queues with a higher priority are always served first. 1176.Ar Cbq 1177and 1178.Ar Hfsc 1179queues with a higher priority are preferred in the case of overload. 1180.It Ar qlimit Aq Ar limit 1181The maximum number of packets held in the queue. 1182The default is 50. 1183.El 1184.Pp 1185The 1186.Ar scheduler 1187can get additional parameters with 1188.Xo Aq Ar scheduler 1189.Pf ( Aq Ar parameters ) . 1190.Xc 1191Parameters are as follows: 1192.Bl -tag -width Fl 1193.It Ar default 1194Packets not matched by another queue are assigned to this one. 1195Exactly one default queue is required. 1196.It Ar red 1197Enable RED (Random Early Detection) on this queue. 1198RED drops packets with a probability proportional to the average 1199queue length. 1200.It Ar rio 1201Enables RIO on this queue. 1202RIO is RED with IN/OUT, thus running 1203RED two times more than RIO would achieve the same effect. 1204RIO is currently not supported in the GENERIC kernel. 1205.It Ar ecn 1206Enables ECN (Explicit Congestion Notification) on this queue. 1207ECN implies RED. 1208.El 1209.Pp 1210The 1211.Ar cbq 1212.Ar scheduler 1213supports an additional option: 1214.Bl -tag -width Fl 1215.It Ar borrow 1216The queue can borrow bandwidth from the parent. 1217.El 1218.Pp 1219The 1220.Ar hfsc 1221.Ar scheduler 1222supports some additional options: 1223.Bl -tag -width Fl 1224.It Ar realtime Aq Ar sc 1225The minimum required bandwidth for the queue. 1226.It Ar upperlimit Aq Ar sc 1227The maximum allowed bandwidth for the queue. 1228.It Ar linkshare Aq Ar sc 1229The bandwidth share of a backlogged queue. 1230.El 1231.Pp 1232.Aq Ar sc 1233is an acronym for 1234.Ar service curve . 1235.Pp 1236The format for service curve specifications is 1237.Ar ( m1 , d , m2 ) . 1238.Ar m2 1239controls the bandwidth assigned to the queue. 1240.Ar m1 1241and 1242.Ar d 1243are optional and can be used to control the initial bandwidth assignment. 1244For the first 1245.Ar d 1246milliseconds the queue gets the bandwidth given as 1247.Ar m1 , 1248afterwards the value given in 1249.Ar m2 . 1250.Pp 1251Furthermore, with 1252.Ar cbq 1253and 1254.Ar hfsc , 1255child queues can be specified as in an 1256.Ar altq 1257declaration, thus building a tree of queues using a part of 1258their parent's bandwidth. 1259.Pp 1260Packets can be assigned to queues based on filter rules by using the 1261.Ar queue 1262keyword. 1263Normally only one 1264.Ar queue 1265is specified; when a second one is specified it will instead be used for 1266packets which have a 1267.Em TOS 1268of 1269.Em lowdelay 1270and for TCP ACKs with no data payload. 1271.Pp 1272To continue the previous example, the examples below would specify the 1273four referenced 1274queues, plus a few child queues. 1275Interactive 1276.Xr ssh 1 1277sessions get priority over bulk transfers like 1278.Xr scp 1 1279and 1280.Xr sftp 1 . 1281The queues may then be referenced by filtering rules (see 1282.Sx PACKET FILTERING 1283below). 1284.Bd -literal 1285queue std bandwidth 10% cbq(default) 1286queue http bandwidth 60% priority 2 cbq(borrow red) \e 1287 { employees, developers } 1288queue developers bandwidth 75% cbq(borrow) 1289queue employees bandwidth 15% 1290queue mail bandwidth 10% priority 0 cbq(borrow ecn) 1291queue ssh bandwidth 20% cbq(borrow) { ssh_interactive, ssh_bulk } 1292queue ssh_interactive bandwidth 50% priority 7 cbq(borrow) 1293queue ssh_bulk bandwidth 50% priority 0 cbq(borrow) 1294 1295block return out on dc0 inet all queue std 1296pass out on dc0 inet proto tcp from $developerhosts to any port 80 \e 1297 queue developers 1298pass out on dc0 inet proto tcp from $employeehosts to any port 80 \e 1299 queue employees 1300pass out on dc0 inet proto tcp from any to any port 22 \e 1301 queue(ssh_bulk, ssh_interactive) 1302pass out on dc0 inet proto tcp from any to any port 25 \e 1303 queue mail 1304.Ed 1305.Sh QUEUEING with dummynet 1306Queueing can also be done with 1307.Xr dummynet 4 . 1308Queues and pipes can be created with 1309.Xr dnctl 8 . 1310.Pp 1311Packets can be assigned to queues and pipes using 1312.Ar dnqueue 1313and 1314.Ar dnpipe 1315respectively. 1316.Pp 1317Both 1318.Ar dnqueue 1319and 1320.Ar dnpipe 1321take either a single pipe or queue number or two numbers as arguments. 1322The first pipe or queue number will be used to shape the traffic in the rule 1323direction, the second will be used to shape the traffic in the reverse 1324direction. 1325If the rule does not specify a direction the first packet to create state will 1326be shaped according to the first number, and the response traffic according to 1327the second. 1328.Pp 1329If the 1330.Xr dummynet 4 1331module is not loaded any traffic sent into a queue or pipe will be dropped. 1332.Sh TRANSLATION 1333Translation rules modify either the source or destination address of the 1334packets associated with a stateful connection. 1335A stateful connection is automatically created to track packets matching 1336such a rule as long as they are not blocked by the filtering section of 1337.Nm pf.conf . 1338The translation engine modifies the specified address and/or port in the 1339packet, recalculates IP, TCP and UDP checksums as necessary, and passes 1340it to the packet filter for evaluation. 1341.Pp 1342Since translation occurs before filtering the filter 1343engine will see packets as they look after any 1344addresses and ports have been translated. 1345Filter rules will therefore have to filter based on the translated 1346address and port number. 1347Packets that match a translation rule are only automatically passed if 1348the 1349.Ar pass 1350modifier is given, otherwise they are 1351still subject to 1352.Ar block 1353and 1354.Ar pass 1355rules. 1356.Pp 1357The state entry created permits 1358.Xr pf 4 1359to keep track of the original address for traffic associated with that state 1360and correctly direct return traffic for that connection. 1361.Pp 1362Various types of translation are possible with pf: 1363.Bl -tag -width xxxx 1364.It Ar binat 1365A 1366.Ar binat 1367rule specifies a bidirectional mapping between an external IP netblock 1368and an internal IP netblock. 1369.It Ar nat 1370A 1371.Ar nat 1372rule specifies that IP addresses are to be changed as the packet 1373traverses the given interface. 1374This technique allows one or more IP addresses 1375on the translating host to support network traffic for a larger range of 1376machines on an "inside" network. 1377Although in theory any IP address can be used on the inside, it is strongly 1378recommended that one of the address ranges defined by RFC 1918 be used. 1379These netblocks are: 1380.Bd -literal 138110.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8) 1382172.16.0.0 - 172.31.255.255 (i.e., 172.16/12) 1383192.168.0.0 - 192.168.255.255 (i.e., 192.168/16) 1384.Ed 1385.It Pa rdr 1386The packet is redirected to another destination and possibly a 1387different port. 1388.Ar rdr 1389rules can optionally specify port ranges instead of single ports. 1390rdr ... port 2000:2999 -\*(Gt ... port 4000 1391redirects ports 2000 to 2999 (inclusive) to port 4000. 1392rdr ... port 2000:2999 -\*(Gt ... port 4000:* 1393redirects port 2000 to 4000, 2001 to 4001, ..., 2999 to 4999. 1394.El 1395.Pp 1396In addition to modifying the address, some translation rules may modify 1397source or destination ports for 1398.Xr tcp 4 1399or 1400.Xr udp 4 1401connections; implicitly in the case of 1402.Ar nat 1403rules and both implicitly and explicitly in the case of 1404.Ar rdr 1405rules. 1406A 1407.Ar rdr 1408rule may cause the source port to be modified if doing so avoids a conflict 1409with an existing connection. 1410A random source port in the range 50001-65535 is chosen in this case; to 1411avoid excessive CPU consumption, the number of searches for a free port is 1412limited by the 1413.Va net.pf.rdr_srcport_rewrite_tries 1414sysctl. 1415Port numbers are never translated with a 1416.Ar binat 1417rule. 1418.Pp 1419Evaluation order of the translation rules is dependent on the type 1420of the translation rules and of the direction of a packet. 1421.Ar binat 1422rules are always evaluated first. 1423Then either the 1424.Ar rdr 1425rules are evaluated on an inbound packet or the 1426.Ar nat 1427rules on an outbound packet. 1428Rules of the same type are evaluated in the same order in which they 1429appear in the ruleset. 1430The first matching rule decides what action is taken. 1431.Pp 1432The 1433.Ar no 1434option prefixed to a translation rule causes packets to remain untranslated, 1435much in the same way as 1436.Ar drop quick 1437works in the packet filter (see below). 1438If no rule matches the packet it is passed to the filter engine unmodified. 1439.Pp 1440Translation rules apply only to packets that pass through 1441the specified interface, and if no interface is specified, 1442translation is applied to packets on all interfaces. 1443For instance, redirecting port 80 on an external interface to an internal 1444web server will only work for connections originating from the outside. 1445Connections to the address of the external interface from local hosts will 1446not be redirected, since such packets do not actually pass through the 1447external interface. 1448Redirections cannot reflect packets back through the interface they arrive 1449on, they can only be redirected to hosts connected to different interfaces 1450or to the firewall itself. 1451.Pp 1452Note that redirecting external incoming connections to the loopback 1453address, as in 1454.Bd -literal -offset indent 1455rdr on ne3 inet proto tcp to port smtp -\*(Gt 127.0.0.1 port spamd 1456.Ed 1457.Pp 1458will effectively allow an external host to connect to daemons 1459bound solely to the loopback address, circumventing the traditional 1460blocking of such connections on a real interface. 1461Unless this effect is desired, any of the local non-loopback addresses 1462should be used as redirection target instead, which allows external 1463connections only to daemons bound to this address or not bound to 1464any address. 1465.Pp 1466See 1467.Sx TRANSLATION EXAMPLES 1468below. 1469.Sh PACKET FILTERING 1470.Xr pf 4 1471has the ability to 1472.Ar block 1473, 1474.Ar pass 1475and 1476.Ar match 1477packets based on attributes of their layer 3 (see 1478.Xr ip 4 1479and 1480.Xr ip6 4 ) 1481and layer 4 (see 1482.Xr icmp 4 , 1483.Xr icmp6 4 , 1484.Xr tcp 4 , 1485.Xr sctp 4 , 1486.Xr udp 4 ) 1487headers. 1488In addition, packets may also be 1489assigned to queues for the purpose of bandwidth control. 1490.Pp 1491For each packet processed by the packet filter, the filter rules are 1492evaluated in sequential order, from first to last. 1493For 1494.Ar block 1495and 1496.Ar pass 1497, the last matching rule decides what action is taken. 1498For 1499.Ar match 1500, rules are evaluated every time they match; the pass/block state of a packet 1501remains unchanged. 1502If no rule matches the packet, the default action is to pass 1503the packet. 1504.Pp 1505The following actions can be used in the filter: 1506.Bl -tag -width xxxx 1507.It Ar block 1508The packet is blocked. 1509There are a number of ways in which a 1510.Ar block 1511rule can behave when blocking a packet. 1512The default behaviour is to 1513.Ar drop 1514packets silently, however this can be overridden or made 1515explicit either globally, by setting the 1516.Ar block-policy 1517option, or on a per-rule basis with one of the following options: 1518.Pp 1519.Bl -tag -width xxxx -compact 1520.It Ar drop 1521The packet is silently dropped. 1522.It Ar return-rst 1523This applies only to 1524.Xr tcp 4 1525packets, and issues a TCP RST which closes the 1526connection. 1527.It Ar return-icmp 1528.It Ar return-icmp6 1529This causes ICMP messages to be returned for packets which match the rule. 1530By default this is an ICMP UNREACHABLE message, however this 1531can be overridden by specifying a message as a code or number. 1532.It Ar return 1533This causes a TCP RST to be returned for 1534.Xr tcp 4 1535packets, an SCTP ABORT for SCTP 1536and an ICMP UNREACHABLE for UDP and other packets. 1537.El 1538.Pp 1539Options returning ICMP packets currently have no effect if 1540.Xr pf 4 1541operates on a 1542.Xr if_bridge 4 , 1543as the code to support this feature has not yet been implemented. 1544.Pp 1545The simplest mechanism to block everything by default and only pass 1546packets that match explicit rules is specify a first filter rule of: 1547.Bd -literal -offset indent 1548block all 1549.Ed 1550.It Ar match 1551The packet is matched. 1552This mechanism is used to provide fine grained filtering without altering the 1553block/pass state of a packet. 1554.Ar match 1555rules differ from 1556.Ar block 1557and 1558.Ar pass 1559rules in that parameters are set for every rule a packet matches, not only 1560on the last matching rule. 1561For the following parameters, this means that the parameter effectively becomes 1562"sticky" until explicitly overridden: 1563.Ar queue , 1564.Ar dnpipe , 1565.Ar dnqueue , 1566.Ar rtable , 1567.Ar scrub 1568. 1569.It Ar pass 1570The packet is passed; 1571state is created unless the 1572.Ar no state 1573option is specified. 1574.El 1575.Pp 1576By default 1577.Xr pf 4 1578filters packets statefully; the first time a packet matches a 1579.Ar pass 1580rule, a state entry is created; for subsequent packets the filter checks 1581whether the packet matches any state. 1582If it does, the packet is passed without evaluation of any rules. 1583After the connection is closed or times out, the state entry is automatically 1584removed. 1585.Pp 1586This has several advantages. 1587For TCP connections, comparing a packet to a state involves checking 1588its sequence numbers, as well as TCP timestamps if a 1589.Ar scrub reassemble tcp 1590rule applies to the connection. 1591If these values are outside the narrow windows of expected 1592values, the packet is dropped. 1593This prevents spoofing attacks, such as when an attacker sends packets with 1594a fake source address/port but does not know the connection's sequence 1595numbers. 1596Similarly, 1597.Xr pf 4 1598knows how to match ICMP replies to states. 1599For example, 1600.Bd -literal -offset indent 1601pass out inet proto icmp all icmp-type echoreq 1602.Ed 1603.Pp 1604allows echo requests (such as those created by 1605.Xr ping 8 ) 1606out statefully, and matches incoming echo replies correctly to states. 1607.Pp 1608Also, looking up states is usually faster than evaluating rules. 1609If there are 50 rules, all of them are evaluated sequentially in O(n). 1610Even with 50000 states, only 16 comparisons are needed to match a 1611state, since states are stored in a binary search tree that allows 1612searches in O(log2 n). 1613.Pp 1614Furthermore, correct handling of ICMP error messages is critical to 1615many protocols, particularly TCP. 1616.Xr pf 4 1617matches ICMP error messages to the correct connection, checks them against 1618connection parameters, and passes them if appropriate. 1619For example if an ICMP source quench message referring to a stateful TCP 1620connection arrives, it will be matched to the state and get passed. 1621.Pp 1622Finally, state tracking is required for 1623.Ar nat , binat No and Ar rdr 1624rules, in order to track address and port translations and reverse the 1625translation on returning packets. 1626.Pp 1627.Xr pf 4 1628will also create state for other protocols which are effectively stateless by 1629nature. 1630UDP packets are matched to states using only host addresses and ports, 1631and other protocols are matched to states using only the host addresses. 1632.Pp 1633If stateless filtering of individual packets is desired, 1634the 1635.Ar no state 1636keyword can be used to specify that state will not be created 1637if this is the last matching rule. 1638A number of parameters can also be set to affect how 1639.Xr pf 4 1640handles state tracking. 1641See 1642.Sx STATEFUL TRACKING OPTIONS 1643below for further details. 1644.Sh PARAMETERS 1645The rule parameters specify the packets to which a rule applies. 1646A packet always comes in on, or goes out through, one interface. 1647Most parameters are optional. 1648If a parameter is specified, the rule only applies to packets with 1649matching attributes. 1650Certain parameters can be expressed as lists, in which case 1651.Xr pfctl 8 1652generates all needed rule combinations. 1653.Bl -tag -width xxxx 1654.It Ar in No or Ar out 1655This rule applies to incoming or outgoing packets. 1656If neither 1657.Ar in 1658nor 1659.Ar out 1660are specified, the rule will match packets in both directions. 1661.It Ar log 1662In addition to the action specified, a log message is generated. 1663Only the packet that establishes the state is logged, 1664unless the 1665.Ar no state 1666option is specified. 1667The logged packets are sent to a 1668.Xr pflog 4 1669interface, by default 1670.Ar pflog0 . 1671This interface is monitored by the 1672.Xr pflogd 8 1673logging daemon, which dumps the logged packets to the file 1674.Pa /var/log/pflog 1675in 1676.Xr pcap 3 1677binary format. 1678.It Ar log (all) 1679Used to force logging of all packets for a connection. 1680This is not necessary when 1681.Ar no state 1682is explicitly specified. 1683As with 1684.Ar log , 1685packets are logged to 1686.Xr pflog 4 . 1687.It Ar log (user) 1688Logs the 1689.Ux 1690user ID of the user that owns the socket and the PID of the process that 1691has the socket open where the packet is sourced from or destined to 1692(depending on which socket is local). 1693This is in addition to the normal information logged. 1694.Pp 1695Only the first packet 1696logged via 1697.Ar log (all, user) 1698will have the user credentials logged when using stateful matching. 1699.It Ar log (to Aq Ar interface ) 1700Send logs to the specified 1701.Xr pflog 4 1702interface instead of 1703.Ar pflog0 . 1704.It Ar quick 1705If a packet matches a rule which has the 1706.Ar quick 1707option set, this rule 1708is considered the last matching rule, and evaluation of subsequent rules 1709is skipped. 1710.It Ar on Aq Ar interface 1711This rule applies only to packets coming in on, or going out through, this 1712particular interface or interface group. 1713For more information on interface groups, 1714see the 1715.Ic group 1716keyword in 1717.Xr ifconfig 8 . 1718.It Aq Ar af 1719This rule applies only to packets of this address family. 1720Supported values are 1721.Ar inet 1722and 1723.Ar inet6 . 1724.It Ar proto Aq Ar protocol 1725This rule applies only to packets of this protocol. 1726Common protocols are 1727.Xr icmp 4 , 1728.Xr icmp6 4 , 1729.Xr tcp 4 , 1730.Xr sctp 4 , 1731and 1732.Xr udp 4 . 1733For a list of all the protocol name to number mappings used by 1734.Xr pfctl 8 , 1735see the file 1736.Pa /etc/protocols . 1737.It Xo 1738.Ar from Aq Ar source 1739.Ar port Aq Ar source 1740.Ar os Aq Ar source 1741.Ar to Aq Ar dest 1742.Ar port Aq Ar dest 1743.Xc 1744This rule applies only to packets with the specified source and destination 1745addresses and ports. 1746.Pp 1747Addresses can be specified in CIDR notation (matching netblocks), as 1748symbolic host names, interface names or interface group names, or as any 1749of the following keywords: 1750.Pp 1751.Bl -tag -width xxxxxxxxxxxxxx -compact 1752.It Ar any 1753Any address. 1754.It Ar no-route 1755Any address which is not currently routable. 1756.It Ar urpf-failed 1757Any source address that fails a unicast reverse path forwarding (URPF) 1758check, i.e. packets coming in on an interface other than that which holds 1759the route back to the packet's source address. 1760.It Aq Ar table 1761Any address that matches the given table. 1762.El 1763.Pp 1764Ranges of addresses are specified by using the 1765.Sq - 1766operator. 1767For instance: 1768.Dq 10.1.1.10 - 10.1.1.12 1769means all addresses from 10.1.1.10 to 10.1.1.12, 1770hence addresses 10.1.1.10, 10.1.1.11, and 10.1.1.12. 1771.Pp 1772Interface names and interface group names can have modifiers appended: 1773.Pp 1774.Bl -tag -width xxxxxxxxxxxx -compact 1775.It Ar :network 1776Translates to the network(s) attached to the interface. 1777.It Ar :broadcast 1778Translates to the interface's broadcast address(es). 1779.It Ar :peer 1780Translates to the point-to-point interface's peer address(es). 1781.It Ar :0 1782Do not include interface aliases. 1783.El 1784.Pp 1785Host names may also have the 1786.Ar :0 1787option appended to restrict the name resolution to the first of each 1788v4 and non-link-local v6 address found. 1789.Pp 1790Host name resolution and interface to address translation are done at 1791ruleset load-time. 1792When the address of an interface (or host name) changes (under DHCP or PPP, 1793for instance), the ruleset must be reloaded for the change to be reflected 1794in the kernel. 1795Surrounding the interface name (and optional modifiers) in parentheses 1796changes this behaviour. 1797When the interface name is surrounded by parentheses, the rule is 1798automatically updated whenever the interface changes its address. 1799The ruleset does not need to be reloaded. 1800This is especially useful with 1801.Ar nat . 1802.Pp 1803Ports can be specified either by number or by name. 1804For example, port 80 can be specified as 1805.Em www . 1806For a list of all port name to number mappings used by 1807.Xr pfctl 8 , 1808see the file 1809.Pa /etc/services . 1810.Pp 1811Ports and ranges of ports are specified by using these operators: 1812.Bd -literal -offset indent 1813= (equal) 1814!= (unequal) 1815\*(Lt (less than) 1816\*(Le (less than or equal) 1817\*(Gt (greater than) 1818\*(Ge (greater than or equal) 1819: (range including boundaries) 1820\*(Gt\*(Lt (range excluding boundaries) 1821\*(Lt\*(Gt (except range) 1822.Ed 1823.Pp 1824.Sq \*(Gt\*(Lt , 1825.Sq \*(Lt\*(Gt 1826and 1827.Sq \&: 1828are binary operators (they take two arguments). 1829For instance: 1830.Bl -tag -width Fl 1831.It Ar port 2000:2004 1832means 1833.Sq all ports \*(Ge 2000 and \*(Le 2004 , 1834hence ports 2000, 2001, 2002, 2003 and 2004. 1835.It Ar port 2000 \*(Gt\*(Lt 2004 1836means 1837.Sq all ports \*(Gt 2000 and \*(Lt 2004 , 1838hence ports 2001, 2002 and 2003. 1839.It Ar port 2000 \*(Lt\*(Gt 2004 1840means 1841.Sq all ports \*(Lt 2000 or \*(Gt 2004 , 1842hence ports 1-1999 and 2005-65535. 1843.El 1844.Pp 1845The operating system of the source host can be specified in the case of TCP 1846rules with the 1847.Ar OS 1848modifier. 1849See the 1850.Sx OPERATING SYSTEM FINGERPRINTING 1851section for more information. 1852.Pp 1853The host, port and OS specifications are optional, as in the following examples: 1854.Bd -literal -offset indent 1855pass in all 1856pass in from any to any 1857pass in proto tcp from any port \*(Le 1024 to any 1858pass in proto tcp from any to any port 25 1859pass in proto tcp from 10.0.0.0/8 port \*(Gt 1024 \e 1860 to ! 10.1.2.3 port != ssh 1861pass in proto tcp from any os "OpenBSD" 1862.Ed 1863.It Ar all 1864This is equivalent to "from any to any". 1865.It Ar group Aq Ar group 1866Similar to 1867.Ar user , 1868this rule only applies to packets of sockets owned by the specified group. 1869.It Ar user Aq Ar user 1870This rule only applies to packets of sockets owned by the specified user. 1871For outgoing connections initiated from the firewall, this is the user 1872that opened the connection. 1873For incoming connections to the firewall itself, this is the user that 1874listens on the destination port. 1875For forwarded connections, where the firewall is not a connection endpoint, 1876the user and group are 1877.Em unknown . 1878.Pp 1879All packets, both outgoing and incoming, of one connection are associated 1880with the same user and group. 1881Only TCP and UDP packets can be associated with users; for other protocols 1882these parameters are ignored. 1883.Pp 1884User and group refer to the effective (as opposed to the real) IDs, in 1885case the socket is created by a setuid/setgid process. 1886User and group IDs are stored when a socket is created; 1887when a process creates a listening socket as root (for instance, by 1888binding to a privileged port) and subsequently changes to another 1889user ID (to drop privileges), the credentials will remain root. 1890.Pp 1891User and group IDs can be specified as either numbers or names. 1892The syntax is similar to the one for ports. 1893The value 1894.Em unknown 1895matches packets of forwarded connections. 1896.Em unknown 1897can only be used with the operators 1898.Cm = 1899and 1900.Cm != . 1901Other constructs like 1902.Cm user \*(Ge unknown 1903are invalid. 1904Forwarded packets with unknown user and group ID match only rules 1905that explicitly compare against 1906.Em unknown 1907with the operators 1908.Cm = 1909or 1910.Cm != . 1911For instance 1912.Cm user \*(Ge 0 1913does not match forwarded packets. 1914The following example allows only selected users to open outgoing 1915connections: 1916.Bd -literal -offset indent 1917block out proto { tcp, udp } all 1918pass out proto { tcp, udp } all user { \*(Lt 1000, dhartmei } 1919.Ed 1920.It Xo Ar flags Aq Ar a 1921.Pf / Ns Aq Ar b 1922.No \*(Ba / Ns Aq Ar b 1923.No \*(Ba any 1924.Xc 1925This rule only applies to TCP packets that have the flags 1926.Aq Ar a 1927set out of set 1928.Aq Ar b . 1929Flags not specified in 1930.Aq Ar b 1931are ignored. 1932For stateful connections, the default is 1933.Ar flags S/SA . 1934To indicate that flags should not be checked at all, specify 1935.Ar flags any . 1936The flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R. 1937.Bl -tag -width Fl 1938.It Ar flags S/S 1939Flag SYN is set. 1940The other flags are ignored. 1941.It Ar flags S/SA 1942This is the default setting for stateful connections. 1943Out of SYN and ACK, exactly SYN may be set. 1944SYN, SYN+PSH and SYN+RST match, but SYN+ACK, ACK and ACK+RST do not. 1945This is more restrictive than the previous example. 1946.It Ar flags /SFRA 1947If the first set is not specified, it defaults to none. 1948All of SYN, FIN, RST and ACK must be unset. 1949.El 1950.Pp 1951Because 1952.Ar flags S/SA 1953is applied by default (unless 1954.Ar no state 1955is specified), only the initial SYN packet of a TCP handshake will create 1956a state for a TCP connection. 1957It is possible to be less restrictive, and allow state creation from 1958intermediate 1959.Pq non-SYN 1960packets, by specifying 1961.Ar flags any . 1962This will cause 1963.Xr pf 4 1964to synchronize to existing connections, for instance 1965if one flushes the state table. 1966However, states created from such intermediate packets may be missing 1967connection details such as the TCP window scaling factor. 1968States which modify the packet flow, such as those affected by 1969.Ar nat , binat No or Ar rdr 1970rules, 1971.Ar modulate No or Ar synproxy state 1972options, or scrubbed with 1973.Ar reassemble tcp 1974will also not be recoverable from intermediate packets. 1975Such connections will stall and time out. 1976.It Xo Ar icmp-type Aq Ar type 1977.Ar code Aq Ar code 1978.Xc 1979.It Xo Ar icmp6-type Aq Ar type 1980.Ar code Aq Ar code 1981.Xc 1982This rule only applies to ICMP or ICMPv6 packets with the specified type 1983and code. 1984Text names for ICMP types and codes are listed in 1985.Xr icmp 4 1986and 1987.Xr icmp6 4 . 1988This parameter is only valid for rules that cover protocols ICMP or 1989ICMP6. 1990The protocol and the ICMP type indicator 1991.Po 1992.Ar icmp-type 1993or 1994.Ar icmp6-type 1995.Pc 1996must match. 1997.It Xo Ar tos Aq Ar string 1998.No \*(Ba Aq Ar number 1999.Xc 2000This rule applies to packets with the specified 2001.Em TOS 2002bits set. 2003.Em TOS 2004may be 2005given as one of 2006.Ar critical , 2007.Ar inetcontrol , 2008.Ar lowdelay , 2009.Ar netcontrol , 2010.Ar throughput , 2011.Ar reliability , 2012or one of the DiffServ Code Points: 2013.Ar ef , 2014.Ar va , 2015.Ar af11 No ... Ar af43 , 2016.Ar cs0 No ... Ar cs7 ; 2017or as either hex or decimal. 2018.Pp 2019For example, the following rules are identical: 2020.Bd -literal -offset indent 2021pass all tos lowdelay 2022pass all tos 0x10 2023pass all tos 16 2024.Ed 2025.It Ar allow-opts 2026By default, IPv4 packets with IP options or IPv6 packets with routing 2027extension headers are blocked. 2028When 2029.Ar allow-opts 2030is specified for a 2031.Ar pass 2032rule, packets that pass the filter based on that rule (last matching) 2033do so even if they contain IP options or routing extension headers. 2034For packets that match state, the rule that initially created the 2035state is used. 2036The implicit 2037.Ar pass 2038rule that is used when a packet does not match any rules does not 2039allow IP options. 2040.It Ar label Aq Ar string 2041Adds a label (name) to the rule, which can be used to identify the rule. 2042For instance, 2043pfctl -s labels 2044shows per-rule statistics for rules that have labels. 2045.Pp 2046The following macros can be used in labels: 2047.Pp 2048.Bl -tag -width $srcaddr -compact -offset indent 2049.It Ar $if 2050The interface. 2051.It Ar $srcaddr 2052The source IP address. 2053.It Ar $dstaddr 2054The destination IP address. 2055.It Ar $srcport 2056The source port specification. 2057.It Ar $dstport 2058The destination port specification. 2059.It Ar $proto 2060The protocol name. 2061.It Ar $nr 2062The rule number. 2063.El 2064.Pp 2065For example: 2066.Bd -literal -offset indent 2067ips = \&"{ 1.2.3.4, 1.2.3.5 }\&" 2068pass in proto tcp from any to $ips \e 2069 port \*(Gt 1023 label \&"$dstaddr:$dstport\&" 2070.Ed 2071.Pp 2072expands to 2073.Bd -literal -offset indent 2074pass in inet proto tcp from any to 1.2.3.4 \e 2075 port \*(Gt 1023 label \&"1.2.3.4:\*(Gt1023\&" 2076pass in inet proto tcp from any to 1.2.3.5 \e 2077 port \*(Gt 1023 label \&"1.2.3.5:\*(Gt1023\&" 2078.Ed 2079.Pp 2080The macro expansion for the 2081.Ar label 2082directive occurs only at configuration file parse time, not during runtime. 2083.It Ar ridentifier Aq Ar number 2084Add an identifier (number) to the rule, which can be used to correlate the rule 2085to pflog entries, even after ruleset updates. 2086.It Xo Ar queue Aq Ar queue 2087.No \*(Ba ( Aq Ar queue , 2088.Aq Ar queue ) 2089.Xc 2090Packets matching this rule will be assigned to the specified queue. 2091If two queues are given, packets which have a 2092.Em TOS 2093of 2094.Em lowdelay 2095and TCP ACKs with no data payload will be assigned to the second one. 2096See 2097.Sx QUEUEING 2098for setup details. 2099.Pp 2100For example: 2101.Bd -literal -offset indent 2102pass in proto tcp to port 25 queue mail 2103pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio) 2104.Ed 2105.It Cm set prio Ar priority | Pq Ar priority , priority 2106Packets matching this rule will be assigned a specific queueing priority. 2107Priorities are assigned as integers 0 through 7. 2108If the packet is transmitted on a 2109.Xr vlan 4 2110interface, the queueing priority will be written as the priority 2111code point in the 802.1Q VLAN header. 2112If two priorities are given, packets which have a TOS of 2113.Cm lowdelay 2114and TCP ACKs with no data payload will be assigned to the second one. 2115.Pp 2116For example: 2117.Bd -literal -offset indent 2118pass in proto tcp to port 25 set prio 2 2119pass in proto tcp to port 22 set prio (2, 5) 2120.Ed 2121.It Ar tag Aq Ar string 2122Packets matching this rule will be tagged with the 2123specified string. 2124The tag acts as an internal marker that can be used to 2125identify these packets later on. 2126This can be used, for example, to provide trust between 2127interfaces and to determine if packets have been 2128processed by translation rules. 2129Tags are 2130.Qq sticky , 2131meaning that the packet will be tagged even if the rule 2132is not the last matching rule. 2133Further matching rules can replace the tag with a 2134new one but will not remove a previously applied tag. 2135A packet is only ever assigned one tag at a time. 2136Packet tagging can be done during 2137.Ar nat , 2138.Ar rdr , 2139.Ar binat 2140or 2141.Ar ether 2142rules in addition to filter rules. 2143Tags take the same macros as labels (see above). 2144.It Ar tagged Aq Ar string 2145Used with filter, translation or scrub rules 2146to specify that packets must already 2147be tagged with the given tag in order to match the rule. 2148Inverse tag matching can also be done 2149by specifying the 2150.Cm !\& 2151operator before the 2152.Ar tagged 2153keyword. 2154.It Ar rtable Aq Ar number 2155Used to select an alternate routing table for the routing lookup. 2156Only effective before the route lookup happened, i.e. when filtering inbound. 2157.It Xo Ar divert-to Aq Ar host 2158.Ar port Aq Ar port 2159.Xc 2160Used to 2161.Xr divert 4 2162packets to the given divert 2163.Ar port . 2164Historically 2165.Ox pf has another meaning for this, and 2166.Fx pf uses 2167this syntax to support 2168.Xr divert 4 instead. Hence, 2169.Ar host 2170has no meaning and can be set to anything like 127.0.0.1. 2171If a packet is re-injected and does not change direction then it will not be 2172re-diverted. 2173.It Ar divert-reply 2174It has no meaning in 2175.Fx pf . 2176.It Ar probability Aq Ar number 2177A probability attribute can be attached to a rule, with a value set between 21780 and 1, bounds not included. 2179In that case, the rule will be honoured using the given probability value 2180only. 2181For example, the following rule will drop 20% of incoming ICMP packets: 2182.Bd -literal -offset indent 2183block in proto icmp probability 20% 2184.Ed 2185.It Ar prio Aq Ar number 2186Only match packets which have the given queueing priority assigned. 2187.El 2188.Sh ROUTING 2189If a packet matches a rule with a route option set, the packet filter will 2190route the packet according to the type of route option. 2191When such a rule creates state, the route option is also applied to all 2192packets matching the same connection. 2193.Bl -tag -width xxxx 2194.It Ar route-to 2195The 2196.Ar route-to 2197option routes the packet to the specified interface with an optional address 2198for the next hop. 2199When a 2200.Ar route-to 2201rule creates state, only packets that pass in the same direction as the 2202filter rule specifies will be routed in this way. 2203Packets passing in the opposite direction (replies) are not affected 2204and are routed normally. 2205.It Ar reply-to 2206The 2207.Ar reply-to 2208option is similar to 2209.Ar route-to , 2210but routes packets that pass in the opposite direction (replies) to the 2211specified interface. 2212Opposite direction is only defined in the context of a state entry, and 2213.Ar reply-to 2214is useful only in rules that create state. 2215It can be used on systems with multiple external connections to 2216route all outgoing packets of a connection through the interface 2217the incoming connection arrived through (symmetric routing enforcement). 2218.It Ar dup-to 2219The 2220.Ar dup-to 2221option creates a duplicate of the packet and routes it like 2222.Ar route-to . 2223The original packet gets routed as it normally would. 2224.El 2225.Sh POOL OPTIONS 2226For 2227.Ar nat 2228and 2229.Ar rdr 2230rules, (as well as for the 2231.Ar route-to , 2232.Ar reply-to 2233and 2234.Ar dup-to 2235rule options) for which there is a single redirection address which has a 2236subnet mask smaller than 32 for IPv4 or 128 for IPv6 (more than one IP 2237address), a variety of different methods for assigning this address can be 2238used: 2239.Bl -tag -width xxxx 2240.It Ar bitmask 2241The 2242.Ar bitmask 2243option applies the network portion of the redirection address to the address 2244to be modified (source with 2245.Ar nat , 2246destination with 2247.Ar rdr ) . 2248.It Ar random 2249The 2250.Ar random 2251option selects an address at random within the defined block of addresses. 2252.It Ar source-hash 2253The 2254.Ar source-hash 2255option uses a hash of the source address to determine the redirection address, 2256ensuring that the redirection address is always the same for a given source. 2257An optional key can be specified after this keyword either in hex or as a 2258string; by default 2259.Xr pfctl 8 2260randomly generates a key for source-hash every time the 2261ruleset is reloaded. 2262.It Ar round-robin 2263The 2264.Ar round-robin 2265option loops through the redirection address(es). 2266.Pp 2267When more than one redirection address is specified, 2268.Ar round-robin 2269is the only permitted pool type. 2270.It Ar static-port 2271With 2272.Ar nat 2273rules, the 2274.Ar static-port 2275option prevents 2276.Xr pf 4 2277from modifying the source port on TCP and UDP packets. 2278.It Xo Ar map-e-portset Aq Ar psid-offset 2279.No / Aq Ar psid-len 2280.No / Aq Ar psid 2281.Xc 2282With 2283.Ar nat 2284rules, the 2285.It Ar endpoint-independent 2286With 2287.Ar nat 2288rules, the 2289.Ar endpoint-independent 2290option caues 2291.Xr pf 4 2292to always map connections from a UDP source address and port to the same 2293NAT address and port. 2294This feature implements "full-cone" NAT behavior. 2295.Ar map-e-portset 2296option enables the source port translation of MAP-E (RFC 7597) Customer Edge. 2297In order to make the host act as a MAP-E Customer Edge, setting up a tunneling 2298interface and pass rules for encapsulated packets are required in addition 2299to the map-e-portset nat rule. 2300.Pp 2301For example: 2302.Bd -literal -offset indent 2303nat on $gif_mape_if from $int_if:network to any \e 2304 -> $ipv4_mape_src map-e-portset 6/8/0x34 2305.Ed 2306.Pp 2307sets PSID offset 6, PSID length 8, PSID 0x34. 2308.El 2309.Pp 2310Additionally, the 2311.Ar sticky-address 2312option can be specified to help ensure that multiple connections from the 2313same source are mapped to the same redirection address. 2314This option can be used with the 2315.Ar random 2316and 2317.Ar round-robin 2318pool options. 2319Note that by default these associations are destroyed as soon as there are 2320no longer states which refer to them; in order to make the mappings last 2321beyond the lifetime of the states, increase the global options with 2322.Ar set timeout src.track . 2323See 2324.Sx STATEFUL TRACKING OPTIONS 2325for more ways to control the source tracking. 2326.Sh STATE MODULATION 2327Much of the security derived from TCP is attributable to how well the 2328initial sequence numbers (ISNs) are chosen. 2329Some popular stack implementations choose 2330.Em very 2331poor ISNs and thus are normally susceptible to ISN prediction exploits. 2332By applying a 2333.Ar modulate state 2334rule to a TCP connection, 2335.Xr pf 4 2336will create a high quality random sequence number for each connection 2337endpoint. 2338.Pp 2339The 2340.Ar modulate state 2341directive implicitly keeps state on the rule and is 2342only applicable to TCP connections. 2343.Pp 2344For instance: 2345.Bd -literal -offset indent 2346block all 2347pass out proto tcp from any to any modulate state 2348pass in proto tcp from any to any port 25 flags S/SFRA modulate state 2349.Ed 2350.Pp 2351Note that modulated connections will not recover when the state table 2352is lost (firewall reboot, flushing the state table, etc...). 2353.Xr pf 4 2354will not be able to infer a connection again after the state table flushes 2355the connection's modulator. 2356When the state is lost, the connection may be left dangling until the 2357respective endpoints time out the connection. 2358It is possible on a fast local network for the endpoints to start an ACK 2359storm while trying to resynchronize after the loss of the modulator. 2360The default 2361.Ar flags 2362settings (or a more strict equivalent) should be used on 2363.Ar modulate state 2364rules to prevent ACK storms. 2365.Pp 2366Note that alternative methods are available 2367to prevent loss of the state table 2368and allow for firewall failover. 2369See 2370.Xr carp 4 2371and 2372.Xr pfsync 4 2373for further information. 2374.Sh SYN PROXY 2375By default, 2376.Xr pf 4 2377passes packets that are part of a 2378.Xr tcp 4 2379handshake between the endpoints. 2380The 2381.Ar synproxy state 2382option can be used to cause 2383.Xr pf 4 2384itself to complete the handshake with the active endpoint, perform a handshake 2385with the passive endpoint, and then forward packets between the endpoints. 2386.Pp 2387No packets are sent to the passive endpoint before the active endpoint has 2388completed the handshake, hence so-called SYN floods with spoofed source 2389addresses will not reach the passive endpoint, as the sender can't complete the 2390handshake. 2391.Pp 2392The proxy is transparent to both endpoints, they each see a single 2393connection from/to the other endpoint. 2394.Xr pf 4 2395chooses random initial sequence numbers for both handshakes. 2396Once the handshakes are completed, the sequence number modulators 2397(see previous section) are used to translate further packets of the 2398connection. 2399.Ar synproxy state 2400includes 2401.Ar modulate state . 2402.Pp 2403Rules with 2404.Ar synproxy 2405will not work if 2406.Xr pf 4 2407operates on a 2408.Xr bridge 4 . 2409.Pp 2410Example: 2411.Bd -literal -offset indent 2412pass in proto tcp from any to any port www synproxy state 2413.Ed 2414.Sh STATEFUL TRACKING OPTIONS 2415A number of options related to stateful tracking can be applied on a 2416per-rule basis. 2417.Ar keep state , 2418.Ar modulate state 2419and 2420.Ar synproxy state 2421support these options, and 2422.Ar keep state 2423must be specified explicitly to apply options to a rule. 2424.Pp 2425.Bl -tag -width xxxx -compact 2426.It Ar max Aq Ar number 2427Limits the number of concurrent states the rule may create. 2428When this limit is reached, further packets that would create 2429state will not match this rule until existing states time out. 2430.It Ar no-sync 2431Prevent state changes for states created by this rule from appearing on the 2432.Xr pfsync 4 2433interface. 2434.It Xo Aq Ar timeout 2435.Aq Ar seconds 2436.Xc 2437Changes the timeout values used for states created by this rule. 2438For a list of all valid timeout names, see 2439.Sx OPTIONS 2440above. 2441.It Ar sloppy 2442Uses a sloppy TCP connection tracker that does not check sequence 2443numbers at all, which makes insertion and ICMP teardown attacks way 2444easier. 2445This is intended to be used in situations where one does not see all 2446packets of a connection, e.g. in asymmetric routing situations. 2447Cannot be used with modulate or synproxy state. 2448.It Ar pflow 2449States created by this rule are exported on the 2450.Xr pflow 4 2451interface. 2452.El 2453.Pp 2454Multiple options can be specified, separated by commas: 2455.Bd -literal -offset indent 2456pass in proto tcp from any to any \e 2457 port www keep state \e 2458 (max 100, source-track rule, max-src-nodes 75, \e 2459 max-src-states 3, tcp.established 60, tcp.closing 5) 2460.Ed 2461.Pp 2462When the 2463.Ar source-track 2464keyword is specified, the number of states per source IP is tracked. 2465.Pp 2466.Bl -tag -width xxxx -compact 2467.It Ar source-track rule 2468The maximum number of states created by this rule is limited by the rule's 2469.Ar max-src-nodes 2470and 2471.Ar max-src-states 2472options. 2473Only state entries created by this particular rule count toward the rule's 2474limits. 2475.It Ar source-track global 2476The number of states created by all rules that use this option is limited. 2477Each rule can specify different 2478.Ar max-src-nodes 2479and 2480.Ar max-src-states 2481options, however state entries created by any participating rule count towards 2482each individual rule's limits. 2483.El 2484.Pp 2485The following limits can be set: 2486.Pp 2487.Bl -tag -width xxxx -compact 2488.It Ar max-src-nodes Aq Ar number 2489Limits the maximum number of source addresses which can simultaneously 2490have state table entries. 2491.It Ar max-src-states Aq Ar number 2492Limits the maximum number of simultaneous state entries that a single 2493source address can create with this rule. 2494.El 2495.Pp 2496For stateful TCP connections, limits on established connections (connections 2497which have completed the TCP 3-way handshake) can also be enforced 2498per source IP. 2499.Pp 2500.Bl -tag -width xxxx -compact 2501.It Ar max-src-conn Aq Ar number 2502Limits the maximum number of simultaneous TCP connections which have 2503completed the 3-way handshake that a single host can make. 2504.It Xo Ar max-src-conn-rate Aq Ar number 2505.No / Aq Ar seconds 2506.Xc 2507Limit the rate of new connections over a time interval. 2508The connection rate is an approximation calculated as a moving average. 2509.El 2510.Pp 2511Because the 3-way handshake ensures that the source address is not being 2512spoofed, more aggressive action can be taken based on these limits. 2513With the 2514.Ar overload Aq Ar table 2515state option, source IP addresses which hit either of the limits on 2516established connections will be added to the named table. 2517This table can be used in the ruleset to block further activity from 2518the offending host, redirect it to a tarpit process, or restrict its 2519bandwidth. 2520.Pp 2521The optional 2522.Ar flush 2523keyword kills all states created by the matching rule which originate 2524from the host which exceeds these limits. 2525The 2526.Ar global 2527modifier to the flush command kills all states originating from the 2528offending host, regardless of which rule created the state. 2529.Pp 2530For example, the following rules will protect the webserver against 2531hosts making more than 100 connections in 10 seconds. 2532Any host which connects faster than this rate will have its address added 2533to the 2534.Aq bad_hosts 2535table and have all states originating from it flushed. 2536Any new packets arriving from this host will be dropped unconditionally 2537by the block rule. 2538.Bd -literal -offset indent 2539block quick from \*(Ltbad_hosts\*(Gt 2540pass in on $ext_if proto tcp to $webserver port www keep state \e 2541 (max-src-conn-rate 100/10, overload \*(Ltbad_hosts\*(Gt flush global) 2542.Ed 2543.Sh OPERATING SYSTEM FINGERPRINTING 2544Passive OS Fingerprinting is a mechanism to inspect nuances of a TCP 2545connection's initial SYN packet and guess at the host's operating system. 2546Unfortunately these nuances are easily spoofed by an attacker so the 2547fingerprint is not useful in making security decisions. 2548But the fingerprint is typically accurate enough to make policy decisions 2549upon. 2550.Pp 2551The fingerprints may be specified by operating system class, by 2552version, or by subtype/patchlevel. 2553The class of an operating system is typically the vendor or genre 2554and would be 2555.Ox 2556for the 2557.Xr pf 4 2558firewall itself. 2559The version of the oldest available 2560.Ox 2561release on the main FTP site 2562would be 2.6 and the fingerprint would be written 2563.Pp 2564.Dl \&"OpenBSD 2.6\&" 2565.Pp 2566The subtype of an operating system is typically used to describe the 2567patchlevel if that patch led to changes in the TCP stack behavior. 2568In the case of 2569.Ox , 2570the only subtype is for a fingerprint that was 2571normalized by the 2572.Ar no-df 2573scrub option and would be specified as 2574.Pp 2575.Dl \&"OpenBSD 3.3 no-df\&" 2576.Pp 2577Fingerprints for most popular operating systems are provided by 2578.Xr pf.os 5 . 2579Once 2580.Xr pf 4 2581is running, a complete list of known operating system fingerprints may 2582be listed by running: 2583.Pp 2584.Dl # pfctl -so 2585.Pp 2586Filter rules can enforce policy at any level of operating system specification 2587assuming a fingerprint is present. 2588Policy could limit traffic to approved operating systems or even ban traffic 2589from hosts that aren't at the latest service pack. 2590.Pp 2591The 2592.Ar unknown 2593class can also be used as the fingerprint which will match packets for 2594which no operating system fingerprint is known. 2595.Pp 2596Examples: 2597.Bd -literal -offset indent 2598pass out proto tcp from any os OpenBSD 2599block out proto tcp from any os Doors 2600block out proto tcp from any os "Doors PT" 2601block out proto tcp from any os "Doors PT SP3" 2602block out from any os "unknown" 2603pass on lo0 proto tcp from any os "OpenBSD 3.3 lo0" 2604.Ed 2605.Pp 2606Operating system fingerprinting is limited only to the TCP SYN packet. 2607This means that it will not work on other protocols and will not match 2608a currently established connection. 2609.Pp 2610Caveat: operating system fingerprints are occasionally wrong. 2611There are three problems: an attacker can trivially craft his packets to 2612appear as any operating system he chooses; 2613an operating system patch could change the stack behavior and no fingerprints 2614will match it until the database is updated; 2615and multiple operating systems may have the same fingerprint. 2616.Sh BLOCKING SPOOFED TRAFFIC 2617"Spoofing" is the faking of IP addresses, typically for malicious 2618purposes. 2619The 2620.Ar antispoof 2621directive expands to a set of filter rules which will block all 2622traffic with a source IP from the network(s) directly connected 2623to the specified interface(s) from entering the system through 2624any other interface. 2625.Pp 2626For example, the line 2627.Bd -literal -offset indent 2628antispoof for lo0 2629.Ed 2630.Pp 2631expands to 2632.Bd -literal -offset indent 2633block drop in on ! lo0 inet from 127.0.0.1/8 to any 2634block drop in on ! lo0 inet6 from ::1 to any 2635.Ed 2636.Pp 2637For non-loopback interfaces, there are additional rules to block incoming 2638packets with a source IP address identical to the interface's IP(s). 2639For example, assuming the interface wi0 had an IP address of 10.0.0.1 and a 2640netmask of 255.255.255.0, 2641the line 2642.Bd -literal -offset indent 2643antispoof for wi0 inet 2644.Ed 2645.Pp 2646expands to 2647.Bd -literal -offset indent 2648block drop in on ! wi0 inet from 10.0.0.0/24 to any 2649block drop in inet from 10.0.0.1 to any 2650.Ed 2651.Pp 2652Caveat: Rules created by the 2653.Ar antispoof 2654directive interfere with packets sent over loopback interfaces 2655to local addresses. 2656One should pass these explicitly. 2657.Sh FRAGMENT HANDLING 2658The size of IP datagrams (packets) can be significantly larger than the 2659maximum transmission unit (MTU) of the network. 2660In cases when it is necessary or more efficient to send such large packets, 2661the large packet will be fragmented into many smaller packets that will each 2662fit onto the wire. 2663Unfortunately for a firewalling device, only the first logical fragment will 2664contain the necessary header information for the subprotocol that allows 2665.Xr pf 4 2666to filter on things such as TCP ports or to perform NAT. 2667.Pp 2668Besides the use of 2669.Ar set reassemble 2670option or 2671.Ar scrub 2672rules as described in 2673.Sx TRAFFIC NORMALIZATION 2674above, there are three options for handling fragments in the packet filter. 2675.Pp 2676One alternative is to filter individual fragments with filter rules. 2677If no 2678.Ar scrub 2679rule applies to a fragment or 2680.Ar set reassemble 2681is set to 2682.Cm no 2683, it is passed to the filter. 2684Filter rules with matching IP header parameters decide whether the 2685fragment is passed or blocked, in the same way as complete packets 2686are filtered. 2687Without reassembly, fragments can only be filtered based on IP header 2688fields (source/destination address, protocol), since subprotocol header 2689fields are not available (TCP/UDP port numbers, ICMP code/type). 2690The 2691.Ar fragment 2692option can be used to restrict filter rules to apply only to 2693fragments, but not complete packets. 2694Filter rules without the 2695.Ar fragment 2696option still apply to fragments, if they only specify IP header fields. 2697For instance, the rule 2698.Bd -literal -offset indent 2699pass in proto tcp from any to any port 80 2700.Ed 2701.Pp 2702never applies to a fragment, even if the fragment is part of a TCP 2703packet with destination port 80, because without reassembly this information 2704is not available for each fragment. 2705This also means that fragments cannot create new or match existing 2706state table entries, which makes stateful filtering and address 2707translation (NAT, redirection) for fragments impossible. 2708.Pp 2709It's also possible to reassemble only certain fragments by specifying 2710source or destination addresses or protocols as parameters in 2711.Ar scrub 2712rules. 2713.Pp 2714In most cases, the benefits of reassembly outweigh the additional 2715memory cost, and it's recommended to use 2716.Ar set reassemble 2717option or 2718.Ar scrub 2719rules with the 2720.Ar fragment reassemble 2721modifier to reassemble 2722all fragments. 2723.Pp 2724The memory allocated for fragment caching can be limited using 2725.Xr pfctl 8 . 2726Once this limit is reached, fragments that would have to be cached 2727are dropped until other entries time out. 2728The timeout value can also be adjusted. 2729.Pp 2730When forwarding reassembled IPv6 packets, pf refragments them with 2731the original maximum fragment size. 2732This allows the sender to determine the optimal fragment size by 2733path MTU discovery. 2734.Sh ANCHORS 2735Besides the main ruleset, 2736.Xr pfctl 8 2737can load rulesets into 2738.Ar anchor 2739attachment points. 2740An 2741.Ar anchor 2742is a container that can hold rules, address tables, and other anchors. 2743.Pp 2744An 2745.Ar anchor 2746has a name which specifies the path where 2747.Xr pfctl 8 2748can be used to access the anchor to perform operations on it, such as 2749attaching child anchors to it or loading rules into it. 2750Anchors may be nested, with components separated by 2751.Sq / 2752characters, similar to how file system hierarchies are laid out. 2753The main ruleset is actually the default anchor, so filter and 2754translation rules, for example, may also be contained in any anchor. 2755.Pp 2756An anchor can reference another 2757.Ar anchor 2758attachment point 2759using the following kinds 2760of rules: 2761.Bl -tag -width xxxx 2762.It Ar nat-anchor Aq Ar name 2763Evaluates the 2764.Ar nat 2765rules in the specified 2766.Ar anchor . 2767.It Ar rdr-anchor Aq Ar name 2768Evaluates the 2769.Ar rdr 2770rules in the specified 2771.Ar anchor . 2772.It Ar binat-anchor Aq Ar name 2773Evaluates the 2774.Ar binat 2775rules in the specified 2776.Ar anchor . 2777.It Ar anchor Aq Ar name 2778Evaluates the filter rules in the specified 2779.Ar anchor . 2780.It Xo Ar load anchor 2781.Aq Ar name 2782.Ar from Aq Ar file 2783.Xc 2784Loads the rules from the specified file into the 2785anchor 2786.Ar name . 2787.El 2788.Pp 2789When evaluation of the main ruleset reaches an 2790.Ar anchor 2791rule, 2792.Xr pf 4 2793will proceed to evaluate all rules specified in that anchor. 2794.Pp 2795Matching filter and translation rules marked with the 2796.Ar quick 2797option are final and abort the evaluation of the rules in other 2798anchors and the main ruleset. 2799If the 2800.Ar anchor 2801itself is marked with the 2802.Ar quick 2803option, 2804ruleset evaluation will terminate when the anchor is exited if the packet is 2805matched by any rule within the anchor. 2806.Pp 2807.Ar anchor 2808rules are evaluated relative to the anchor in which they are contained. 2809For example, all 2810.Ar anchor 2811rules specified in the main ruleset will reference anchor 2812attachment points underneath the main ruleset, and 2813.Ar anchor 2814rules specified in a file loaded from a 2815.Ar load anchor 2816rule will be attached under that anchor point. 2817.Pp 2818Rules may be contained in 2819.Ar anchor 2820attachment points which do not contain any rules when the main ruleset 2821is loaded, and later such anchors can be manipulated through 2822.Xr pfctl 8 2823without reloading the main ruleset or other anchors. 2824For example, 2825.Bd -literal -offset indent 2826ext_if = \&"kue0\&" 2827block on $ext_if all 2828anchor spam 2829pass out on $ext_if all 2830pass in on $ext_if proto tcp from any \e 2831 to $ext_if port smtp 2832.Ed 2833.Pp 2834blocks all packets on the external interface by default, then evaluates 2835all rules in the 2836.Ar anchor 2837named "spam", and finally passes all outgoing connections and 2838incoming connections to port 25. 2839.Bd -literal -offset indent 2840# echo \&"block in quick from 1.2.3.4 to any\&" \&| \e 2841 pfctl -a spam -f - 2842.Ed 2843.Pp 2844This loads a single rule into the 2845.Ar anchor , 2846which blocks all packets from a specific address. 2847.Pp 2848The anchor can also be populated by adding a 2849.Ar load anchor 2850rule after the 2851.Ar anchor 2852rule: 2853.Bd -literal -offset indent 2854anchor spam 2855load anchor spam from "/etc/pf-spam.conf" 2856.Ed 2857.Pp 2858When 2859.Xr pfctl 8 2860loads 2861.Nm pf.conf , 2862it will also load all the rules from the file 2863.Pa /etc/pf-spam.conf 2864into the anchor. 2865.Pp 2866Optionally, 2867.Ar anchor 2868rules can specify packet filtering parameters using the same syntax as 2869filter rules. 2870When parameters are used, the 2871.Ar anchor 2872rule is only evaluated for matching packets. 2873This allows conditional evaluation of anchors, like: 2874.Bd -literal -offset indent 2875block on $ext_if all 2876anchor spam proto tcp from any to any port smtp 2877pass out on $ext_if all 2878pass in on $ext_if proto tcp from any to $ext_if port smtp 2879.Ed 2880.Pp 2881The rules inside 2882.Ar anchor 2883spam are only evaluated for 2884.Ar tcp 2885packets with destination port 25. 2886Hence, 2887.Bd -literal -offset indent 2888# echo \&"block in quick from 1.2.3.4 to any" \&| \e 2889 pfctl -a spam -f - 2890.Ed 2891.Pp 2892will only block connections from 1.2.3.4 to port 25. 2893.Pp 2894Anchors may end with the asterisk 2895.Pq Sq * 2896character, which signifies that all anchors attached at that point 2897should be evaluated in the alphabetical ordering of their anchor name. 2898For example, 2899.Bd -literal -offset indent 2900anchor "spam/*" 2901.Ed 2902.Pp 2903will evaluate each rule in each anchor attached to the 2904.Li spam 2905anchor. 2906Note that it will only evaluate anchors that are directly attached to the 2907.Li spam 2908anchor, and will not descend to evaluate anchors recursively. 2909.Pp 2910Since anchors are evaluated relative to the anchor in which they are 2911contained, there is a mechanism for accessing the parent and ancestor 2912anchors of a given anchor. 2913Similar to file system path name resolution, if the sequence 2914.Dq .. 2915appears as an anchor path component, the parent anchor of the current 2916anchor in the path evaluation at that point will become the new current 2917anchor. 2918As an example, consider the following: 2919.Bd -literal -offset indent 2920# echo ' anchor "spam/allowed" ' | pfctl -f - 2921# echo -e ' anchor "../banned" \en pass' | \e 2922 pfctl -a spam/allowed -f - 2923.Ed 2924.Pp 2925Evaluation of the main ruleset will lead into the 2926.Li spam/allowed 2927anchor, which will evaluate the rules in the 2928.Li spam/banned 2929anchor, if any, before finally evaluating the 2930.Ar pass 2931rule. 2932.Pp 2933Filter rule 2934.Ar anchors 2935can also be loaded inline in the ruleset within a brace ('{' '}') delimited 2936block. 2937Brace delimited blocks may contain rules or other brace-delimited blocks. 2938When anchors are loaded this way the anchor name becomes optional. 2939.Bd -literal -offset indent 2940anchor "external" on $ext_if { 2941 block 2942 anchor out { 2943 pass proto tcp from any to port { 25, 80, 443 } 2944 } 2945 pass in proto tcp to any port 22 2946} 2947.Ed 2948.Pp 2949Since the parser specification for anchor names is a string, any 2950reference to an anchor name containing 2951.Sq / 2952characters will require double quote 2953.Pq Sq \&" 2954characters around the anchor name. 2955.Sh SCTP CONSIDERATIONS 2956.Xr pf 4 2957supports 2958.Xr sctp 4 2959connections. 2960It can match ports, track state and NAT SCTP traffic. 2961However, it will not alter port numbers during nat or rdr translations. 2962Doing so would break SCTP multihoming. 2963.Sh TRANSLATION EXAMPLES 2964This example maps incoming requests on port 80 to port 8080, on 2965which a daemon is running (because, for example, it is not run as root, 2966and therefore lacks permission to bind to port 80). 2967.Bd -literal 2968# use a macro for the interface name, so it can be changed easily 2969ext_if = \&"ne3\&" 2970 2971# map daemon on 8080 to appear to be on 80 2972rdr on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 port 8080 2973.Ed 2974.Pp 2975If the 2976.Ar pass 2977modifier is given, packets matching the translation rule are passed without 2978inspecting the filter rules: 2979.Bd -literal 2980rdr pass on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 \e 2981 port 8080 2982.Ed 2983.Pp 2984In the example below, vlan12 is configured as 192.168.168.1; 2985the machine translates all packets coming from 192.168.168.0/24 to 204.92.77.111 2986when they are going out any interface except vlan12. 2987This has the net effect of making traffic from the 192.168.168.0/24 2988network appear as though it is the Internet routable address 2989204.92.77.111 to nodes behind any interface on the router except 2990for the nodes on vlan12. 2991(Thus, 192.168.168.1 can talk to the 192.168.168.0/24 nodes.) 2992.Bd -literal 2993nat on ! vlan12 from 192.168.168.0/24 to any -\*(Gt 204.92.77.111 2994.Ed 2995.Pp 2996In the example below, the machine sits between a fake internal 144.19.74.* 2997network, and a routable external IP of 204.92.77.100. 2998The 2999.Ar no nat 3000rule excludes protocol AH from being translated. 3001.Bd -literal 3002# NO NAT 3003no nat on $ext_if proto ah from 144.19.74.0/24 to any 3004nat on $ext_if from 144.19.74.0/24 to any -\*(Gt 204.92.77.100 3005.Ed 3006.Pp 3007In the example below, packets bound for one specific server, as well as those 3008generated by the sysadmins are not proxied; all other connections are. 3009.Bd -literal 3010# NO RDR 3011no rdr on $int_if proto { tcp, udp } from any to $server port 80 3012no rdr on $int_if proto { tcp, udp } from $sysadmins to any port 80 3013rdr on $int_if proto { tcp, udp } from any to any port 80 -\*(Gt 127.0.0.1 \e 3014 port 80 3015.Ed 3016.Pp 3017This longer example uses both a NAT and a redirection. 3018The external interface has the address 157.161.48.183. 3019On localhost, we are running 3020.Xr ftp-proxy 8 , 3021waiting for FTP sessions to be redirected to it. 3022The three mandatory anchors for 3023.Xr ftp-proxy 8 3024are omitted from this example; see the 3025.Xr ftp-proxy 8 3026manpage. 3027.Bd -literal 3028# NAT 3029# Translate outgoing packets' source addresses (any protocol). 3030# In this case, any address but the gateway's external address is mapped. 3031nat on $ext_if inet from ! ($ext_if) to any -\*(Gt ($ext_if) 3032 3033# NAT PROXYING 3034# Map outgoing packets' source port to an assigned proxy port instead of 3035# an arbitrary port. 3036# In this case, proxy outgoing isakmp with port 500 on the gateway. 3037nat on $ext_if inet proto udp from any port = isakmp to any -\*(Gt ($ext_if) \e 3038 port 500 3039 3040# BINAT 3041# Translate outgoing packets' source address (any protocol). 3042# Translate incoming packets' destination address to an internal machine 3043# (bidirectional). 3044binat on $ext_if from 10.1.2.150 to any -\*(Gt $ext_if 3045 3046# Translate packets arriving on $peer_if addressed to 172.22.16.0/20 3047# to the corresponding address in 172.21.16.0/20 (bidirectional). 3048binat on $peer_if from 172.21.16.0/20 to any -> 172.22.16.0/20 3049 3050# RDR 3051# Translate incoming packets' destination addresses. 3052# As an example, redirect a TCP and UDP port to an internal machine. 3053rdr on $ext_if inet proto tcp from any to ($ext_if) port 8080 \e 3054 -\*(Gt 10.1.2.151 port 22 3055rdr on $ext_if inet proto udp from any to ($ext_if) port 8080 \e 3056 -\*(Gt 10.1.2.151 port 53 3057 3058# RDR 3059# Translate outgoing ftp control connections to send them to localhost 3060# for proxying with ftp-proxy(8) running on port 8021. 3061rdr on $int_if proto tcp from any to any port 21 -\*(Gt 127.0.0.1 port 8021 3062.Ed 3063.Pp 3064In this example, a NAT gateway is set up to translate internal addresses 3065using a pool of public addresses (192.0.2.16/28) and to redirect 3066incoming web server connections to a group of web servers on the internal 3067network. 3068.Bd -literal 3069# NAT LOAD BALANCE 3070# Translate outgoing packets' source addresses using an address pool. 3071# A given source address is always translated to the same pool address by 3072# using the source-hash keyword. 3073nat on $ext_if inet from any to any -\*(Gt 192.0.2.16/28 source-hash 3074 3075# RDR ROUND ROBIN 3076# Translate incoming web server connections to a group of web servers on 3077# the internal network. 3078rdr on $ext_if proto tcp from any to any port 80 \e 3079 -\*(Gt { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin 3080.Ed 3081.Sh FILTER EXAMPLES 3082.Bd -literal 3083# The external interface is kue0 3084# (157.161.48.183, the only routable address) 3085# and the private network is 10.0.0.0/8, for which we are doing NAT. 3086 3087# Reassemble incoming traffic 3088set reassemble yes 3089 3090# use a macro for the interface name, so it can be changed easily 3091ext_if = \&"kue0\&" 3092 3093# block and log everything by default 3094block return log on $ext_if all 3095 3096# block anything coming from source we have no back routes for 3097block in from no-route to any 3098 3099# block packets whose ingress interface does not match the one in 3100# the route back to their source address 3101block in from urpf-failed to any 3102 3103# block and log outgoing packets that do not have our address as source, 3104# they are either spoofed or something is misconfigured (NAT disabled, 3105# for instance), we want to be nice and do not send out garbage. 3106block out log quick on $ext_if from ! 157.161.48.183 to any 3107 3108# silently drop broadcasts (cable modem noise) 3109block in quick on $ext_if from any to 255.255.255.255 3110 3111# block and log incoming packets from reserved address space and invalid 3112# addresses, they are either spoofed or misconfigured, we cannot reply to 3113# them anyway (hence, no return-rst). 3114block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \e 3115 192.168.0.0/16, 255.255.255.255/32 } to any 3116 3117# ICMP 3118 3119# pass out/in certain ICMP queries and keep state (ping) 3120# state matching is done on host addresses and ICMP id (not type/code), 3121# so replies (like 0/0 for 8/0) will match queries 3122# ICMP error messages (which always refer to a TCP/UDP packet) are 3123# handled by the TCP/UDP states 3124pass on $ext_if inet proto icmp all icmp-type 8 code 0 3125 3126# UDP 3127 3128# pass out all UDP connections and keep state 3129pass out on $ext_if proto udp all 3130 3131# pass in certain UDP connections and keep state (DNS) 3132pass in on $ext_if proto udp from any to any port domain 3133 3134# TCP 3135 3136# pass out all TCP connections and modulate state 3137pass out on $ext_if proto tcp all modulate state 3138 3139# pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT) 3140pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \e 3141 auth } 3142 3143# Do not allow Windows 9x SMTP connections since they are typically 3144# a viral worm. Alternately we could limit these OSes to 1 connection each. 3145block in on $ext_if proto tcp from any os {"Windows 95", "Windows 98"} \e 3146 to any port smtp 3147 3148# IPv6 3149# pass in/out all IPv6 traffic: note that we have to enable this in two 3150# different ways, on both our physical interface and our tunnel 3151pass quick on gif0 inet6 3152pass quick on $ext_if proto ipv6 3153 3154# Packet Tagging 3155 3156# three interfaces: $int_if, $ext_if, and $wifi_if (wireless). NAT is 3157# being done on $ext_if for all outgoing packets. tag packets in on 3158# $int_if and pass those tagged packets out on $ext_if. all other 3159# outgoing packets (i.e., packets from the wireless network) are only 3160# permitted to access port 80. 3161 3162pass in on $int_if from any to any tag INTNET 3163pass in on $wifi_if from any to any 3164 3165block out on $ext_if from any to any 3166pass out quick on $ext_if tagged INTNET 3167pass out on $ext_if proto tcp from any to any port 80 3168 3169# tag incoming packets as they are redirected to spamd(8). use the tag 3170# to pass those packets through the packet filter. 3171 3172rdr on $ext_if inet proto tcp from \*(Ltspammers\*(Gt to port smtp \e 3173 tag SPAMD -\*(Gt 127.0.0.1 port spamd 3174 3175block in on $ext_if 3176pass in on $ext_if inet proto tcp tagged SPAMD 3177.Ed 3178.Sh GRAMMAR 3179Syntax for 3180.Nm 3181in BNF: 3182.Bd -literal 3183line = ( option | ether-rule | pf-rule | nat-rule | binat-rule | 3184 rdr-rule | antispoof-rule | altq-rule | queue-rule | 3185 trans-anchors | anchor-rule | anchor-close | load-anchor | 3186 table-rule | include ) 3187 3188option = "set" ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] | 3189 [ "ruleset-optimization" [ "none" | "basic" | "profile" ]] | 3190 [ "optimization" [ "default" | "normal" | 3191 "high-latency" | "satellite" | 3192 "aggressive" | "conservative" ] ] 3193 [ "limit" ( limit-item | "{" limit-list "}" ) ] | 3194 [ "loginterface" ( interface-name | "none" ) ] | 3195 [ "block-policy" ( "drop" | "return" ) ] | 3196 [ "state-policy" ( "if-bound" | "floating" ) ] 3197 [ "state-defaults" state-opts ] 3198 [ "require-order" ( "yes" | "no" ) ] 3199 [ "fingerprints" filename ] | 3200 [ "skip on" ifspec ] | 3201 [ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] 3202 [ "keepcounters" ] ) 3203 3204ether-rule = "ether" etheraction [ ( "in" | "out" ) ] 3205 [ "quick" ] [ "on" ifspec ] [ "bridge-to" interface-name ] 3206 [ etherprotospec ] etherhosts [ "l3" hosts ] 3207 [ etherfilteropt-list ] 3208 3209pf-rule = action [ ( "in" | "out" ) ] 3210 [ "log" [ "(" logopts ")"] ] [ "quick" ] 3211 [ "on" ifspec ] [ route ] [ af ] [ protospec ] 3212 hosts [ filteropt-list ] 3213 3214logopts = logopt [ "," logopts ] 3215logopt = "all" | "user" | "to" interface-name 3216 3217etherfilteropt-list = etherfilteropt-list etherfilteropt | etherfilteropt 3218etherfilteropt = "tag" string | "tagged" string | "queue" ( string ) | 3219 "ridentifier" number | "label" string 3220 3221filteropt-list = filteropt-list filteropt | filteropt 3222filteropt = user | group | flags | icmp-type | icmp6-type | "tos" tos | 3223 ( "no" | "keep" | "modulate" | "synproxy" ) "state" 3224 [ "(" state-opts ")" ] | 3225 "fragment" | "no-df" | "min-ttl" number | "set-tos" tos | 3226 "max-mss" number | "random-id" | "reassemble tcp" | 3227 fragmentation | "allow-opts" | 3228 "label" string | "tag" string | [ ! ] "tagged" string | 3229 "set prio" ( number | "(" number [ [ "," ] number ] ")" ) | 3230 "queue" ( string | "(" string [ [ "," ] string ] ")" ) | 3231 "rtable" number | "probability" number"%" | "prio" number | 3232 "dnpipe" ( number | "(" number "," number ")" ) | 3233 "dnqueue" ( number | "(" number "," number ")" ) | 3234 "ridentifier" number 3235 3236nat-rule = [ "no" ] "nat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3237 [ "on" ifspec ] [ af ] 3238 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3239 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3240 [ portspec ] [ pooltype ] [ "static-port" ] 3241 [ "map-e-portset" number "/" number "/" number ] ] 3242 3243binat-rule = [ "no" ] "binat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3244 [ "on" interface-name ] [ af ] 3245 [ "proto" ( proto-name | proto-number ) ] 3246 "from" address [ "/" mask-bits ] "to" ipspec 3247 [ "tag" string ] [ "tagged" string ] 3248 [ "-\*(Gt" address [ "/" mask-bits ] ] 3249 3250rdr-rule = [ "no" ] "rdr" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3251 [ "on" ifspec ] [ af ] 3252 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3253 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3254 [ portspec ] [ pooltype ] ] 3255 3256antispoof-rule = "antispoof" [ "log" ] [ "quick" ] 3257 "for" ifspec [ af ] [ "label" string ] 3258 [ "ridentifier" number ] 3259 3260table-rule = "table" "\*(Lt" string "\*(Gt" [ tableopts-list ] 3261tableopts-list = tableopts-list tableopts | tableopts 3262tableopts = "persist" | "const" | "counters" | "file" string | 3263 "{" [ tableaddr-list ] "}" 3264tableaddr-list = tableaddr-list [ "," ] tableaddr-spec | tableaddr-spec 3265tableaddr-spec = [ "!" ] tableaddr [ "/" mask-bits ] 3266tableaddr = hostname | ifspec | "self" | 3267 ipv4-dotted-quad | ipv6-coloned-hex 3268 3269altq-rule = "altq on" interface-name queueopts-list 3270 "queue" subqueue 3271queue-rule = "queue" string [ "on" interface-name ] queueopts-list 3272 subqueue 3273 3274anchor-rule = "anchor" [ string ] [ ( "in" | "out" ) ] [ "on" ifspec ] 3275 [ af ] [ protospec ] [ hosts ] [ filteropt-list ] [ "{" ] 3276 3277anchor-close = "}" 3278 3279trans-anchors = ( "nat-anchor" | "rdr-anchor" | "binat-anchor" ) string 3280 [ "on" ifspec ] [ af ] [ "proto" ] [ protospec ] [ hosts ] 3281 3282load-anchor = "load anchor" string "from" filename 3283 3284queueopts-list = queueopts-list queueopts | queueopts 3285queueopts = [ "bandwidth" bandwidth-spec ] | 3286 [ "qlimit" number ] | [ "tbrsize" number ] | 3287 [ "priority" number ] | [ schedulers ] 3288schedulers = ( cbq-def | priq-def | hfsc-def ) 3289bandwidth-spec = "number" ( "b" | "Kb" | "Mb" | "Gb" | "%" ) 3290 3291etheraction = "pass" | "block" 3292action = "pass" | "match" | "block" [ return ] | [ "no" ] "scrub" 3293return = "drop" | "return" | "return-rst" [ "( ttl" number ")" ] | 3294 "return-icmp" [ "(" icmpcode [ [ "," ] icmp6code ] ")" ] | 3295 "return-icmp6" [ "(" icmp6code ")" ] 3296icmpcode = ( icmp-code-name | icmp-code-number ) 3297icmp6code = ( icmp6-code-name | icmp6-code-number ) 3298 3299ifspec = ( [ "!" ] ( interface-name | interface-group ) ) | 3300 "{" interface-list "}" 3301interface-list = [ "!" ] ( interface-name | interface-group ) 3302 [ [ "," ] interface-list ] 3303route = ( "route-to" | "reply-to" | "dup-to" ) 3304 ( routehost | "{" routehost-list "}" ) 3305 [ pooltype ] 3306af = "inet" | "inet6" 3307 3308etherprotospec = "proto" ( proto-number | "{" etherproto-list "}" ) 3309etherproto-list = proto-number [ [ "," ] etherproto-list ] 3310protospec = "proto" ( proto-name | proto-number | 3311 "{" proto-list "}" ) 3312proto-list = ( proto-name | proto-number ) [ [ "," ] proto-list ] 3313 3314etherhosts = "from" macaddress "to" macaddress 3315macaddress = mac | mac "/" masklen | mac "&" mask 3316 3317hosts = "all" | 3318 "from" ( "any" | "no-route" | "urpf-failed" | "self" | host | 3319 "{" host-list "}" ) [ port ] [ os ] 3320 "to" ( "any" | "no-route" | "self" | host | 3321 "{" host-list "}" ) [ port ] 3322 3323ipspec = "any" | host | "{" host-list "}" 3324host = [ "!" ] ( address [ "/" mask-bits ] | "\*(Lt" string "\*(Gt" ) 3325redirhost = address [ "/" mask-bits ] 3326routehost = "(" interface-name [ address [ "/" mask-bits ] ] ")" 3327address = ( interface-name | interface-group | 3328 "(" ( interface-name | interface-group ) ")" | 3329 hostname | ipv4-dotted-quad | ipv6-coloned-hex ) 3330host-list = host [ [ "," ] host-list ] 3331redirhost-list = redirhost [ [ "," ] redirhost-list ] 3332routehost-list = routehost [ [ "," ] routehost-list ] 3333 3334port = "port" ( unary-op | binary-op | "{" op-list "}" ) 3335portspec = "port" ( number | name ) [ ":" ( "*" | number | name ) ] 3336os = "os" ( os-name | "{" os-list "}" ) 3337user = "user" ( unary-op | binary-op | "{" op-list "}" ) 3338group = "group" ( unary-op | binary-op | "{" op-list "}" ) 3339 3340unary-op = [ "=" | "!=" | "\*(Lt" | "\*(Le" | "\*(Gt" | "\*(Ge" ] 3341 ( name | number ) 3342binary-op = number ( "\*(Lt\*(Gt" | "\*(Gt\*(Lt" | ":" ) number 3343op-list = ( unary-op | binary-op ) [ [ "," ] op-list ] 3344 3345os-name = operating-system-name 3346os-list = os-name [ [ "," ] os-list ] 3347 3348flags = "flags" ( [ flag-set ] "/" flag-set | "any" ) 3349flag-set = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ] 3350 [ "W" ] 3351 3352icmp-type = "icmp-type" ( icmp-type-code | "{" icmp-list "}" ) 3353icmp6-type = "icmp6-type" ( icmp-type-code | "{" icmp-list "}" ) 3354icmp-type-code = ( icmp-type-name | icmp-type-number ) 3355 [ "code" ( icmp-code-name | icmp-code-number ) ] 3356icmp-list = icmp-type-code [ [ "," ] icmp-list ] 3357 3358tos = ( "lowdelay" | "throughput" | "reliability" | 3359 [ "0x" ] number ) 3360 3361state-opts = state-opt [ [ "," ] state-opts ] 3362state-opt = ( "max" number | "no-sync" | timeout | "sloppy" | 3363 "source-track" [ ( "rule" | "global" ) ] | 3364 "max-src-nodes" number | "max-src-states" number | 3365 "max-src-conn" number | 3366 "max-src-conn-rate" number "/" number | 3367 "overload" "\*(Lt" string "\*(Gt" [ "flush" ] | 3368 "if-bound" | "floating" | "pflow" ) 3369 3370fragmentation = [ "fragment reassemble" ] 3371 3372timeout-list = timeout [ [ "," ] timeout-list ] 3373timeout = ( "tcp.first" | "tcp.opening" | "tcp.established" | 3374 "tcp.closing" | "tcp.finwait" | "tcp.closed" | 3375 "sctp.first" | "sctp.opening" | "sctp.established" | 3376 "sctp.closing" | "sctp.closed" | 3377 "udp.first" | "udp.single" | "udp.multiple" | 3378 "icmp.first" | "icmp.error" | 3379 "other.first" | "other.single" | "other.multiple" | 3380 "frag" | "interval" | "src.track" | 3381 "adaptive.start" | "adaptive.end" ) number 3382 3383limit-list = limit-item [ [ "," ] limit-list ] 3384limit-item = ( "states" | "frags" | "src-nodes" ) number 3385 3386pooltype = ( "bitmask" | "random" | 3387 "source-hash" [ ( hex-key | string-key ) ] | 3388 "round-robin" ) [ sticky-address ] 3389 3390subqueue = string | "{" queue-list "}" 3391queue-list = string [ [ "," ] string ] 3392cbq-def = "cbq" [ "(" cbq-opt [ [ "," ] cbq-opt ] ")" ] 3393priq-def = "priq" [ "(" priq-opt [ [ "," ] priq-opt ] ")" ] 3394hfsc-def = "hfsc" [ "(" hfsc-opt [ [ "," ] hfsc-opt ] ")" ] 3395cbq-opt = ( "default" | "borrow" | "red" | "ecn" | "rio" ) 3396priq-opt = ( "default" | "red" | "ecn" | "rio" ) 3397hfsc-opt = ( "default" | "red" | "ecn" | "rio" | 3398 linkshare-sc | realtime-sc | upperlimit-sc ) 3399linkshare-sc = "linkshare" sc-spec 3400realtime-sc = "realtime" sc-spec 3401upperlimit-sc = "upperlimit" sc-spec 3402sc-spec = ( bandwidth-spec | 3403 "(" bandwidth-spec number bandwidth-spec ")" ) 3404include = "include" filename 3405.Ed 3406.Sh FILES 3407.Bl -tag -width "/etc/protocols" -compact 3408.It Pa /etc/hosts 3409Host name database. 3410.It Pa /etc/pf.conf 3411Default location of the ruleset file. 3412The file has to be created manually as it is not installed with a 3413standard installation. 3414.It Pa /etc/pf.os 3415Default location of OS fingerprints. 3416.It Pa /etc/protocols 3417Protocol name database. 3418.It Pa /etc/services 3419Service name database. 3420.El 3421.Sh SEE ALSO 3422.Xr altq 4 , 3423.Xr carp 4 , 3424.Xr icmp 4 , 3425.Xr icmp6 4 , 3426.Xr ip 4 , 3427.Xr ip6 4 , 3428.Xr pf 4 , 3429.Xr pflow 4 , 3430.Xr pfsync 4 , 3431.Xr tcp 4 , 3432.Xr sctp 4 , 3433.Xr udp 4 , 3434.Xr hosts 5 , 3435.Xr pf.os 5 , 3436.Xr protocols 5 , 3437.Xr services 5 , 3438.Xr ftp-proxy 8 , 3439.Xr pfctl 8 , 3440.Xr pflogd 8 3441.Sh HISTORY 3442The 3443.Nm 3444file format first appeared in 3445.Ox 3.0 . 3446