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. 1411Port numbers are never translated with a 1412.Ar binat 1413rule. 1414.Pp 1415Evaluation order of the translation rules is dependent on the type 1416of the translation rules and of the direction of a packet. 1417.Ar binat 1418rules are always evaluated first. 1419Then either the 1420.Ar rdr 1421rules are evaluated on an inbound packet or the 1422.Ar nat 1423rules on an outbound packet. 1424Rules of the same type are evaluated in the same order in which they 1425appear in the ruleset. 1426The first matching rule decides what action is taken. 1427.Pp 1428The 1429.Ar no 1430option prefixed to a translation rule causes packets to remain untranslated, 1431much in the same way as 1432.Ar drop quick 1433works in the packet filter (see below). 1434If no rule matches the packet it is passed to the filter engine unmodified. 1435.Pp 1436Translation rules apply only to packets that pass through 1437the specified interface, and if no interface is specified, 1438translation is applied to packets on all interfaces. 1439For instance, redirecting port 80 on an external interface to an internal 1440web server will only work for connections originating from the outside. 1441Connections to the address of the external interface from local hosts will 1442not be redirected, since such packets do not actually pass through the 1443external interface. 1444Redirections cannot reflect packets back through the interface they arrive 1445on, they can only be redirected to hosts connected to different interfaces 1446or to the firewall itself. 1447.Pp 1448Note that redirecting external incoming connections to the loopback 1449address, as in 1450.Bd -literal -offset indent 1451rdr on ne3 inet proto tcp to port smtp -\*(Gt 127.0.0.1 port spamd 1452.Ed 1453.Pp 1454will effectively allow an external host to connect to daemons 1455bound solely to the loopback address, circumventing the traditional 1456blocking of such connections on a real interface. 1457Unless this effect is desired, any of the local non-loopback addresses 1458should be used as redirection target instead, which allows external 1459connections only to daemons bound to this address or not bound to 1460any address. 1461.Pp 1462See 1463.Sx TRANSLATION EXAMPLES 1464below. 1465.Sh PACKET FILTERING 1466.Xr pf 4 1467has the ability to 1468.Ar block 1469, 1470.Ar pass 1471and 1472.Ar match 1473packets based on attributes of their layer 3 (see 1474.Xr ip 4 1475and 1476.Xr ip6 4 ) 1477and layer 4 (see 1478.Xr icmp 4 , 1479.Xr icmp6 4 , 1480.Xr tcp 4 , 1481.Xr sctp 4 , 1482.Xr udp 4 ) 1483headers. 1484In addition, packets may also be 1485assigned to queues for the purpose of bandwidth control. 1486.Pp 1487For each packet processed by the packet filter, the filter rules are 1488evaluated in sequential order, from first to last. 1489For 1490.Ar block 1491and 1492.Ar pass 1493, the last matching rule decides what action is taken. 1494For 1495.Ar match 1496, rules are evaluated every time they match; the pass/block state of a packet 1497remains unchanged. 1498If no rule matches the packet, the default action is to pass 1499the packet. 1500.Pp 1501The following actions can be used in the filter: 1502.Bl -tag -width xxxx 1503.It Ar block 1504The packet is blocked. 1505There are a number of ways in which a 1506.Ar block 1507rule can behave when blocking a packet. 1508The default behaviour is to 1509.Ar drop 1510packets silently, however this can be overridden or made 1511explicit either globally, by setting the 1512.Ar block-policy 1513option, or on a per-rule basis with one of the following options: 1514.Pp 1515.Bl -tag -width xxxx -compact 1516.It Ar drop 1517The packet is silently dropped. 1518.It Ar return-rst 1519This applies only to 1520.Xr tcp 4 1521packets, and issues a TCP RST which closes the 1522connection. 1523.It Ar return-icmp 1524.It Ar return-icmp6 1525This causes ICMP messages to be returned for packets which match the rule. 1526By default this is an ICMP UNREACHABLE message, however this 1527can be overridden by specifying a message as a code or number. 1528.It Ar return 1529This causes a TCP RST to be returned for 1530.Xr tcp 4 1531packets, an SCTP ABORT for SCTP 1532and an ICMP UNREACHABLE for UDP and other packets. 1533.El 1534.Pp 1535Options returning ICMP packets currently have no effect if 1536.Xr pf 4 1537operates on a 1538.Xr if_bridge 4 , 1539as the code to support this feature has not yet been implemented. 1540.Pp 1541The simplest mechanism to block everything by default and only pass 1542packets that match explicit rules is specify a first filter rule of: 1543.Bd -literal -offset indent 1544block all 1545.Ed 1546.It Ar match 1547The packet is matched. 1548This mechanism is used to provide fine grained filtering without altering the 1549block/pass state of a packet. 1550.Ar match 1551rules differ from 1552.Ar block 1553and 1554.Ar pass 1555rules in that parameters are set for every rule a packet matches, not only 1556on the last matching rule. 1557For the following parameters, this means that the parameter effectively becomes 1558"sticky" until explicitly overridden: 1559.Ar queue , 1560.Ar dnpipe , 1561.Ar dnqueue , 1562.Ar rtable , 1563.Ar scrub 1564. 1565.It Ar pass 1566The packet is passed; 1567state is created unless the 1568.Ar no state 1569option is specified. 1570.El 1571.Pp 1572By default 1573.Xr pf 4 1574filters packets statefully; the first time a packet matches a 1575.Ar pass 1576rule, a state entry is created; for subsequent packets the filter checks 1577whether the packet matches any state. 1578If it does, the packet is passed without evaluation of any rules. 1579After the connection is closed or times out, the state entry is automatically 1580removed. 1581.Pp 1582This has several advantages. 1583For TCP connections, comparing a packet to a state involves checking 1584its sequence numbers, as well as TCP timestamps if a 1585.Ar scrub reassemble tcp 1586rule applies to the connection. 1587If these values are outside the narrow windows of expected 1588values, the packet is dropped. 1589This prevents spoofing attacks, such as when an attacker sends packets with 1590a fake source address/port but does not know the connection's sequence 1591numbers. 1592Similarly, 1593.Xr pf 4 1594knows how to match ICMP replies to states. 1595For example, 1596.Bd -literal -offset indent 1597pass out inet proto icmp all icmp-type echoreq 1598.Ed 1599.Pp 1600allows echo requests (such as those created by 1601.Xr ping 8 ) 1602out statefully, and matches incoming echo replies correctly to states. 1603.Pp 1604Also, looking up states is usually faster than evaluating rules. 1605If there are 50 rules, all of them are evaluated sequentially in O(n). 1606Even with 50000 states, only 16 comparisons are needed to match a 1607state, since states are stored in a binary search tree that allows 1608searches in O(log2 n). 1609.Pp 1610Furthermore, correct handling of ICMP error messages is critical to 1611many protocols, particularly TCP. 1612.Xr pf 4 1613matches ICMP error messages to the correct connection, checks them against 1614connection parameters, and passes them if appropriate. 1615For example if an ICMP source quench message referring to a stateful TCP 1616connection arrives, it will be matched to the state and get passed. 1617.Pp 1618Finally, state tracking is required for 1619.Ar nat , binat No and Ar rdr 1620rules, in order to track address and port translations and reverse the 1621translation on returning packets. 1622.Pp 1623.Xr pf 4 1624will also create state for other protocols which are effectively stateless by 1625nature. 1626UDP packets are matched to states using only host addresses and ports, 1627and other protocols are matched to states using only the host addresses. 1628.Pp 1629If stateless filtering of individual packets is desired, 1630the 1631.Ar no state 1632keyword can be used to specify that state will not be created 1633if this is the last matching rule. 1634A number of parameters can also be set to affect how 1635.Xr pf 4 1636handles state tracking. 1637See 1638.Sx STATEFUL TRACKING OPTIONS 1639below for further details. 1640.Sh PARAMETERS 1641The rule parameters specify the packets to which a rule applies. 1642A packet always comes in on, or goes out through, one interface. 1643Most parameters are optional. 1644If a parameter is specified, the rule only applies to packets with 1645matching attributes. 1646Certain parameters can be expressed as lists, in which case 1647.Xr pfctl 8 1648generates all needed rule combinations. 1649.Bl -tag -width xxxx 1650.It Ar in No or Ar out 1651This rule applies to incoming or outgoing packets. 1652If neither 1653.Ar in 1654nor 1655.Ar out 1656are specified, the rule will match packets in both directions. 1657.It Ar log 1658In addition to the action specified, a log message is generated. 1659Only the packet that establishes the state is logged, 1660unless the 1661.Ar no state 1662option is specified. 1663The logged packets are sent to a 1664.Xr pflog 4 1665interface, by default 1666.Ar pflog0 . 1667This interface is monitored by the 1668.Xr pflogd 8 1669logging daemon, which dumps the logged packets to the file 1670.Pa /var/log/pflog 1671in 1672.Xr pcap 3 1673binary format. 1674.It Ar log (all) 1675Used to force logging of all packets for a connection. 1676This is not necessary when 1677.Ar no state 1678is explicitly specified. 1679As with 1680.Ar log , 1681packets are logged to 1682.Xr pflog 4 . 1683.It Ar log (user) 1684Logs the 1685.Ux 1686user ID of the user that owns the socket and the PID of the process that 1687has the socket open where the packet is sourced from or destined to 1688(depending on which socket is local). 1689This is in addition to the normal information logged. 1690.Pp 1691Only the first packet 1692logged via 1693.Ar log (all, user) 1694will have the user credentials logged when using stateful matching. 1695.It Ar log (to Aq Ar interface ) 1696Send logs to the specified 1697.Xr pflog 4 1698interface instead of 1699.Ar pflog0 . 1700.It Ar quick 1701If a packet matches a rule which has the 1702.Ar quick 1703option set, this rule 1704is considered the last matching rule, and evaluation of subsequent rules 1705is skipped. 1706.It Ar on Aq Ar interface 1707This rule applies only to packets coming in on, or going out through, this 1708particular interface or interface group. 1709For more information on interface groups, 1710see the 1711.Ic group 1712keyword in 1713.Xr ifconfig 8 . 1714.It Aq Ar af 1715This rule applies only to packets of this address family. 1716Supported values are 1717.Ar inet 1718and 1719.Ar inet6 . 1720.It Ar proto Aq Ar protocol 1721This rule applies only to packets of this protocol. 1722Common protocols are 1723.Xr icmp 4 , 1724.Xr icmp6 4 , 1725.Xr tcp 4 , 1726.Xr sctp 4 , 1727and 1728.Xr udp 4 . 1729For a list of all the protocol name to number mappings used by 1730.Xr pfctl 8 , 1731see the file 1732.Pa /etc/protocols . 1733.It Xo 1734.Ar from Aq Ar source 1735.Ar port Aq Ar source 1736.Ar os Aq Ar source 1737.Ar to Aq Ar dest 1738.Ar port Aq Ar dest 1739.Xc 1740This rule applies only to packets with the specified source and destination 1741addresses and ports. 1742.Pp 1743Addresses can be specified in CIDR notation (matching netblocks), as 1744symbolic host names, interface names or interface group names, or as any 1745of the following keywords: 1746.Pp 1747.Bl -tag -width xxxxxxxxxxxxxx -compact 1748.It Ar any 1749Any address. 1750.It Ar no-route 1751Any address which is not currently routable. 1752.It Ar urpf-failed 1753Any source address that fails a unicast reverse path forwarding (URPF) 1754check, i.e. packets coming in on an interface other than that which holds 1755the route back to the packet's source address. 1756.It Aq Ar table 1757Any address that matches the given table. 1758.El 1759.Pp 1760Ranges of addresses are specified by using the 1761.Sq - 1762operator. 1763For instance: 1764.Dq 10.1.1.10 - 10.1.1.12 1765means all addresses from 10.1.1.10 to 10.1.1.12, 1766hence addresses 10.1.1.10, 10.1.1.11, and 10.1.1.12. 1767.Pp 1768Interface names and interface group names can have modifiers appended: 1769.Pp 1770.Bl -tag -width xxxxxxxxxxxx -compact 1771.It Ar :network 1772Translates to the network(s) attached to the interface. 1773.It Ar :broadcast 1774Translates to the interface's broadcast address(es). 1775.It Ar :peer 1776Translates to the point-to-point interface's peer address(es). 1777.It Ar :0 1778Do not include interface aliases. 1779.El 1780.Pp 1781Host names may also have the 1782.Ar :0 1783option appended to restrict the name resolution to the first of each 1784v4 and non-link-local v6 address found. 1785.Pp 1786Host name resolution and interface to address translation are done at 1787ruleset load-time. 1788When the address of an interface (or host name) changes (under DHCP or PPP, 1789for instance), the ruleset must be reloaded for the change to be reflected 1790in the kernel. 1791Surrounding the interface name (and optional modifiers) in parentheses 1792changes this behaviour. 1793When the interface name is surrounded by parentheses, the rule is 1794automatically updated whenever the interface changes its address. 1795The ruleset does not need to be reloaded. 1796This is especially useful with 1797.Ar nat . 1798.Pp 1799Ports can be specified either by number or by name. 1800For example, port 80 can be specified as 1801.Em www . 1802For a list of all port name to number mappings used by 1803.Xr pfctl 8 , 1804see the file 1805.Pa /etc/services . 1806.Pp 1807Ports and ranges of ports are specified by using these operators: 1808.Bd -literal -offset indent 1809= (equal) 1810!= (unequal) 1811\*(Lt (less than) 1812\*(Le (less than or equal) 1813\*(Gt (greater than) 1814\*(Ge (greater than or equal) 1815: (range including boundaries) 1816\*(Gt\*(Lt (range excluding boundaries) 1817\*(Lt\*(Gt (except range) 1818.Ed 1819.Pp 1820.Sq \*(Gt\*(Lt , 1821.Sq \*(Lt\*(Gt 1822and 1823.Sq \&: 1824are binary operators (they take two arguments). 1825For instance: 1826.Bl -tag -width Fl 1827.It Ar port 2000:2004 1828means 1829.Sq all ports \*(Ge 2000 and \*(Le 2004 , 1830hence ports 2000, 2001, 2002, 2003 and 2004. 1831.It Ar port 2000 \*(Gt\*(Lt 2004 1832means 1833.Sq all ports \*(Gt 2000 and \*(Lt 2004 , 1834hence ports 2001, 2002 and 2003. 1835.It Ar port 2000 \*(Lt\*(Gt 2004 1836means 1837.Sq all ports \*(Lt 2000 or \*(Gt 2004 , 1838hence ports 1-1999 and 2005-65535. 1839.El 1840.Pp 1841The operating system of the source host can be specified in the case of TCP 1842rules with the 1843.Ar OS 1844modifier. 1845See the 1846.Sx OPERATING SYSTEM FINGERPRINTING 1847section for more information. 1848.Pp 1849The host, port and OS specifications are optional, as in the following examples: 1850.Bd -literal -offset indent 1851pass in all 1852pass in from any to any 1853pass in proto tcp from any port \*(Le 1024 to any 1854pass in proto tcp from any to any port 25 1855pass in proto tcp from 10.0.0.0/8 port \*(Gt 1024 \e 1856 to ! 10.1.2.3 port != ssh 1857pass in proto tcp from any os "OpenBSD" 1858.Ed 1859.It Ar all 1860This is equivalent to "from any to any". 1861.It Ar group Aq Ar group 1862Similar to 1863.Ar user , 1864this rule only applies to packets of sockets owned by the specified group. 1865.It Ar user Aq Ar user 1866This rule only applies to packets of sockets owned by the specified user. 1867For outgoing connections initiated from the firewall, this is the user 1868that opened the connection. 1869For incoming connections to the firewall itself, this is the user that 1870listens on the destination port. 1871For forwarded connections, where the firewall is not a connection endpoint, 1872the user and group are 1873.Em unknown . 1874.Pp 1875All packets, both outgoing and incoming, of one connection are associated 1876with the same user and group. 1877Only TCP and UDP packets can be associated with users; for other protocols 1878these parameters are ignored. 1879.Pp 1880User and group refer to the effective (as opposed to the real) IDs, in 1881case the socket is created by a setuid/setgid process. 1882User and group IDs are stored when a socket is created; 1883when a process creates a listening socket as root (for instance, by 1884binding to a privileged port) and subsequently changes to another 1885user ID (to drop privileges), the credentials will remain root. 1886.Pp 1887User and group IDs can be specified as either numbers or names. 1888The syntax is similar to the one for ports. 1889The value 1890.Em unknown 1891matches packets of forwarded connections. 1892.Em unknown 1893can only be used with the operators 1894.Cm = 1895and 1896.Cm != . 1897Other constructs like 1898.Cm user \*(Ge unknown 1899are invalid. 1900Forwarded packets with unknown user and group ID match only rules 1901that explicitly compare against 1902.Em unknown 1903with the operators 1904.Cm = 1905or 1906.Cm != . 1907For instance 1908.Cm user \*(Ge 0 1909does not match forwarded packets. 1910The following example allows only selected users to open outgoing 1911connections: 1912.Bd -literal -offset indent 1913block out proto { tcp, udp } all 1914pass out proto { tcp, udp } all user { \*(Lt 1000, dhartmei } 1915.Ed 1916.It Xo Ar flags Aq Ar a 1917.Pf / Ns Aq Ar b 1918.No \*(Ba / Ns Aq Ar b 1919.No \*(Ba any 1920.Xc 1921This rule only applies to TCP packets that have the flags 1922.Aq Ar a 1923set out of set 1924.Aq Ar b . 1925Flags not specified in 1926.Aq Ar b 1927are ignored. 1928For stateful connections, the default is 1929.Ar flags S/SA . 1930To indicate that flags should not be checked at all, specify 1931.Ar flags any . 1932The flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R. 1933.Bl -tag -width Fl 1934.It Ar flags S/S 1935Flag SYN is set. 1936The other flags are ignored. 1937.It Ar flags S/SA 1938This is the default setting for stateful connections. 1939Out of SYN and ACK, exactly SYN may be set. 1940SYN, SYN+PSH and SYN+RST match, but SYN+ACK, ACK and ACK+RST do not. 1941This is more restrictive than the previous example. 1942.It Ar flags /SFRA 1943If the first set is not specified, it defaults to none. 1944All of SYN, FIN, RST and ACK must be unset. 1945.El 1946.Pp 1947Because 1948.Ar flags S/SA 1949is applied by default (unless 1950.Ar no state 1951is specified), only the initial SYN packet of a TCP handshake will create 1952a state for a TCP connection. 1953It is possible to be less restrictive, and allow state creation from 1954intermediate 1955.Pq non-SYN 1956packets, by specifying 1957.Ar flags any . 1958This will cause 1959.Xr pf 4 1960to synchronize to existing connections, for instance 1961if one flushes the state table. 1962However, states created from such intermediate packets may be missing 1963connection details such as the TCP window scaling factor. 1964States which modify the packet flow, such as those affected by 1965.Ar nat , binat No or Ar rdr 1966rules, 1967.Ar modulate No or Ar synproxy state 1968options, or scrubbed with 1969.Ar reassemble tcp 1970will also not be recoverable from intermediate packets. 1971Such connections will stall and time out. 1972.It Xo Ar icmp-type Aq Ar type 1973.Ar code Aq Ar code 1974.Xc 1975.It Xo Ar icmp6-type Aq Ar type 1976.Ar code Aq Ar code 1977.Xc 1978This rule only applies to ICMP or ICMPv6 packets with the specified type 1979and code. 1980Text names for ICMP types and codes are listed in 1981.Xr icmp 4 1982and 1983.Xr icmp6 4 . 1984This parameter is only valid for rules that cover protocols ICMP or 1985ICMP6. 1986The protocol and the ICMP type indicator 1987.Po 1988.Ar icmp-type 1989or 1990.Ar icmp6-type 1991.Pc 1992must match. 1993.It Xo Ar tos Aq Ar string 1994.No \*(Ba Aq Ar number 1995.Xc 1996This rule applies to packets with the specified 1997.Em TOS 1998bits set. 1999.Em TOS 2000may be 2001given as one of 2002.Ar critical , 2003.Ar inetcontrol , 2004.Ar lowdelay , 2005.Ar netcontrol , 2006.Ar throughput , 2007.Ar reliability , 2008or one of the DiffServ Code Points: 2009.Ar ef , 2010.Ar va , 2011.Ar af11 No ... Ar af43 , 2012.Ar cs0 No ... Ar cs7 ; 2013or as either hex or decimal. 2014.Pp 2015For example, the following rules are identical: 2016.Bd -literal -offset indent 2017pass all tos lowdelay 2018pass all tos 0x10 2019pass all tos 16 2020.Ed 2021.It Ar allow-opts 2022By default, IPv4 packets with IP options or IPv6 packets with routing 2023extension headers are blocked. 2024When 2025.Ar allow-opts 2026is specified for a 2027.Ar pass 2028rule, packets that pass the filter based on that rule (last matching) 2029do so even if they contain IP options or routing extension headers. 2030For packets that match state, the rule that initially created the 2031state is used. 2032The implicit 2033.Ar pass 2034rule that is used when a packet does not match any rules does not 2035allow IP options. 2036.It Ar label Aq Ar string 2037Adds a label (name) to the rule, which can be used to identify the rule. 2038For instance, 2039pfctl -s labels 2040shows per-rule statistics for rules that have labels. 2041.Pp 2042The following macros can be used in labels: 2043.Pp 2044.Bl -tag -width $srcaddr -compact -offset indent 2045.It Ar $if 2046The interface. 2047.It Ar $srcaddr 2048The source IP address. 2049.It Ar $dstaddr 2050The destination IP address. 2051.It Ar $srcport 2052The source port specification. 2053.It Ar $dstport 2054The destination port specification. 2055.It Ar $proto 2056The protocol name. 2057.It Ar $nr 2058The rule number. 2059.El 2060.Pp 2061For example: 2062.Bd -literal -offset indent 2063ips = \&"{ 1.2.3.4, 1.2.3.5 }\&" 2064pass in proto tcp from any to $ips \e 2065 port \*(Gt 1023 label \&"$dstaddr:$dstport\&" 2066.Ed 2067.Pp 2068expands to 2069.Bd -literal -offset indent 2070pass in inet proto tcp from any to 1.2.3.4 \e 2071 port \*(Gt 1023 label \&"1.2.3.4:\*(Gt1023\&" 2072pass in inet proto tcp from any to 1.2.3.5 \e 2073 port \*(Gt 1023 label \&"1.2.3.5:\*(Gt1023\&" 2074.Ed 2075.Pp 2076The macro expansion for the 2077.Ar label 2078directive occurs only at configuration file parse time, not during runtime. 2079.It Ar ridentifier Aq Ar number 2080Add an identifier (number) to the rule, which can be used to correlate the rule 2081to pflog entries, even after ruleset updates. 2082.It Xo Ar queue Aq Ar queue 2083.No \*(Ba ( Aq Ar queue , 2084.Aq Ar queue ) 2085.Xc 2086Packets matching this rule will be assigned to the specified queue. 2087If two queues are given, packets which have a 2088.Em TOS 2089of 2090.Em lowdelay 2091and TCP ACKs with no data payload will be assigned to the second one. 2092See 2093.Sx QUEUEING 2094for setup details. 2095.Pp 2096For example: 2097.Bd -literal -offset indent 2098pass in proto tcp to port 25 queue mail 2099pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio) 2100.Ed 2101.It Cm set prio Ar priority | Pq Ar priority , priority 2102Packets matching this rule will be assigned a specific queueing priority. 2103Priorities are assigned as integers 0 through 7. 2104If the packet is transmitted on a 2105.Xr vlan 4 2106interface, the queueing priority will be written as the priority 2107code point in the 802.1Q VLAN header. 2108If two priorities are given, packets which have a TOS of 2109.Cm lowdelay 2110and TCP ACKs with no data payload will be assigned to the second one. 2111.Pp 2112For example: 2113.Bd -literal -offset indent 2114pass in proto tcp to port 25 set prio 2 2115pass in proto tcp to port 22 set prio (2, 5) 2116.Ed 2117.It Ar tag Aq Ar string 2118Packets matching this rule will be tagged with the 2119specified string. 2120The tag acts as an internal marker that can be used to 2121identify these packets later on. 2122This can be used, for example, to provide trust between 2123interfaces and to determine if packets have been 2124processed by translation rules. 2125Tags are 2126.Qq sticky , 2127meaning that the packet will be tagged even if the rule 2128is not the last matching rule. 2129Further matching rules can replace the tag with a 2130new one but will not remove a previously applied tag. 2131A packet is only ever assigned one tag at a time. 2132Packet tagging can be done during 2133.Ar nat , 2134.Ar rdr , 2135.Ar binat 2136or 2137.Ar ether 2138rules in addition to filter rules. 2139Tags take the same macros as labels (see above). 2140.It Ar tagged Aq Ar string 2141Used with filter, translation or scrub rules 2142to specify that packets must already 2143be tagged with the given tag in order to match the rule. 2144Inverse tag matching can also be done 2145by specifying the 2146.Cm !\& 2147operator before the 2148.Ar tagged 2149keyword. 2150.It Ar rtable Aq Ar number 2151Used to select an alternate routing table for the routing lookup. 2152Only effective before the route lookup happened, i.e. when filtering inbound. 2153.It Xo Ar divert-to Aq Ar host 2154.Ar port Aq Ar port 2155.Xc 2156Used to 2157.Xr divert 4 2158packets to the given divert 2159.Ar port . 2160Historically 2161.Ox pf has another meaning for this, and 2162.Fx pf uses 2163this syntax to support 2164.Xr divert 4 instead. Hence, 2165.Ar host 2166has no meaning and can be set to anything like 127.0.0.1. 2167If a packet is re-injected and does not change direction then it will not be 2168re-diverted. 2169.It Ar divert-reply 2170It has no meaning in 2171.Fx pf . 2172.It Ar probability Aq Ar number 2173A probability attribute can be attached to a rule, with a value set between 21740 and 1, bounds not included. 2175In that case, the rule will be honoured using the given probability value 2176only. 2177For example, the following rule will drop 20% of incoming ICMP packets: 2178.Bd -literal -offset indent 2179block in proto icmp probability 20% 2180.Ed 2181.It Ar prio Aq Ar number 2182Only match packets which have the given queueing priority assigned. 2183.El 2184.Sh ROUTING 2185If a packet matches a rule with a route option set, the packet filter will 2186route the packet according to the type of route option. 2187When such a rule creates state, the route option is also applied to all 2188packets matching the same connection. 2189.Bl -tag -width xxxx 2190.It Ar route-to 2191The 2192.Ar route-to 2193option routes the packet to the specified interface with an optional address 2194for the next hop. 2195When a 2196.Ar route-to 2197rule creates state, only packets that pass in the same direction as the 2198filter rule specifies will be routed in this way. 2199Packets passing in the opposite direction (replies) are not affected 2200and are routed normally. 2201.It Ar reply-to 2202The 2203.Ar reply-to 2204option is similar to 2205.Ar route-to , 2206but routes packets that pass in the opposite direction (replies) to the 2207specified interface. 2208Opposite direction is only defined in the context of a state entry, and 2209.Ar reply-to 2210is useful only in rules that create state. 2211It can be used on systems with multiple external connections to 2212route all outgoing packets of a connection through the interface 2213the incoming connection arrived through (symmetric routing enforcement). 2214.It Ar dup-to 2215The 2216.Ar dup-to 2217option creates a duplicate of the packet and routes it like 2218.Ar route-to . 2219The original packet gets routed as it normally would. 2220.El 2221.Sh POOL OPTIONS 2222For 2223.Ar nat 2224and 2225.Ar rdr 2226rules, (as well as for the 2227.Ar route-to , 2228.Ar reply-to 2229and 2230.Ar dup-to 2231rule options) for which there is a single redirection address which has a 2232subnet mask smaller than 32 for IPv4 or 128 for IPv6 (more than one IP 2233address), a variety of different methods for assigning this address can be 2234used: 2235.Bl -tag -width xxxx 2236.It Ar bitmask 2237The 2238.Ar bitmask 2239option applies the network portion of the redirection address to the address 2240to be modified (source with 2241.Ar nat , 2242destination with 2243.Ar rdr ) . 2244.It Ar random 2245The 2246.Ar random 2247option selects an address at random within the defined block of addresses. 2248.It Ar source-hash 2249The 2250.Ar source-hash 2251option uses a hash of the source address to determine the redirection address, 2252ensuring that the redirection address is always the same for a given source. 2253An optional key can be specified after this keyword either in hex or as a 2254string; by default 2255.Xr pfctl 8 2256randomly generates a key for source-hash every time the 2257ruleset is reloaded. 2258.It Ar round-robin 2259The 2260.Ar round-robin 2261option loops through the redirection address(es). 2262.Pp 2263When more than one redirection address is specified, 2264.Ar round-robin 2265is the only permitted pool type. 2266.It Ar static-port 2267With 2268.Ar nat 2269rules, the 2270.Ar static-port 2271option prevents 2272.Xr pf 4 2273from modifying the source port on TCP and UDP packets. 2274.It Xo Ar map-e-portset Aq Ar psid-offset 2275.No / Aq Ar psid-len 2276.No / Aq Ar psid 2277.Xc 2278With 2279.Ar nat 2280rules, the 2281.It Ar endpoint-independent 2282With 2283.Ar nat 2284rules, the 2285.Ar endpoint-independent 2286option caues 2287.Xr pf 4 2288to always map connections from a UDP source address and port to the same 2289NAT address and port. 2290This feature implements "full-cone" NAT behavior. 2291.Ar map-e-portset 2292option enables the source port translation of MAP-E (RFC 7597) Customer Edge. 2293In order to make the host act as a MAP-E Customer Edge, setting up a tunneling 2294interface and pass rules for encapsulated packets are required in addition 2295to the map-e-portset nat rule. 2296.Pp 2297For example: 2298.Bd -literal -offset indent 2299nat on $gif_mape_if from $int_if:network to any \e 2300 -> $ipv4_mape_src map-e-portset 6/8/0x34 2301.Ed 2302.Pp 2303sets PSID offset 6, PSID length 8, PSID 0x34. 2304.El 2305.Pp 2306Additionally, the 2307.Ar sticky-address 2308option can be specified to help ensure that multiple connections from the 2309same source are mapped to the same redirection address. 2310This option can be used with the 2311.Ar random 2312and 2313.Ar round-robin 2314pool options. 2315Note that by default these associations are destroyed as soon as there are 2316no longer states which refer to them; in order to make the mappings last 2317beyond the lifetime of the states, increase the global options with 2318.Ar set timeout src.track . 2319See 2320.Sx STATEFUL TRACKING OPTIONS 2321for more ways to control the source tracking. 2322.Sh STATE MODULATION 2323Much of the security derived from TCP is attributable to how well the 2324initial sequence numbers (ISNs) are chosen. 2325Some popular stack implementations choose 2326.Em very 2327poor ISNs and thus are normally susceptible to ISN prediction exploits. 2328By applying a 2329.Ar modulate state 2330rule to a TCP connection, 2331.Xr pf 4 2332will create a high quality random sequence number for each connection 2333endpoint. 2334.Pp 2335The 2336.Ar modulate state 2337directive implicitly keeps state on the rule and is 2338only applicable to TCP connections. 2339.Pp 2340For instance: 2341.Bd -literal -offset indent 2342block all 2343pass out proto tcp from any to any modulate state 2344pass in proto tcp from any to any port 25 flags S/SFRA modulate state 2345.Ed 2346.Pp 2347Note that modulated connections will not recover when the state table 2348is lost (firewall reboot, flushing the state table, etc...). 2349.Xr pf 4 2350will not be able to infer a connection again after the state table flushes 2351the connection's modulator. 2352When the state is lost, the connection may be left dangling until the 2353respective endpoints time out the connection. 2354It is possible on a fast local network for the endpoints to start an ACK 2355storm while trying to resynchronize after the loss of the modulator. 2356The default 2357.Ar flags 2358settings (or a more strict equivalent) should be used on 2359.Ar modulate state 2360rules to prevent ACK storms. 2361.Pp 2362Note that alternative methods are available 2363to prevent loss of the state table 2364and allow for firewall failover. 2365See 2366.Xr carp 4 2367and 2368.Xr pfsync 4 2369for further information. 2370.Sh SYN PROXY 2371By default, 2372.Xr pf 4 2373passes packets that are part of a 2374.Xr tcp 4 2375handshake between the endpoints. 2376The 2377.Ar synproxy state 2378option can be used to cause 2379.Xr pf 4 2380itself to complete the handshake with the active endpoint, perform a handshake 2381with the passive endpoint, and then forward packets between the endpoints. 2382.Pp 2383No packets are sent to the passive endpoint before the active endpoint has 2384completed the handshake, hence so-called SYN floods with spoofed source 2385addresses will not reach the passive endpoint, as the sender can't complete the 2386handshake. 2387.Pp 2388The proxy is transparent to both endpoints, they each see a single 2389connection from/to the other endpoint. 2390.Xr pf 4 2391chooses random initial sequence numbers for both handshakes. 2392Once the handshakes are completed, the sequence number modulators 2393(see previous section) are used to translate further packets of the 2394connection. 2395.Ar synproxy state 2396includes 2397.Ar modulate state . 2398.Pp 2399Rules with 2400.Ar synproxy 2401will not work if 2402.Xr pf 4 2403operates on a 2404.Xr bridge 4 . 2405.Pp 2406Example: 2407.Bd -literal -offset indent 2408pass in proto tcp from any to any port www synproxy state 2409.Ed 2410.Sh STATEFUL TRACKING OPTIONS 2411A number of options related to stateful tracking can be applied on a 2412per-rule basis. 2413.Ar keep state , 2414.Ar modulate state 2415and 2416.Ar synproxy state 2417support these options, and 2418.Ar keep state 2419must be specified explicitly to apply options to a rule. 2420.Pp 2421.Bl -tag -width xxxx -compact 2422.It Ar max Aq Ar number 2423Limits the number of concurrent states the rule may create. 2424When this limit is reached, further packets that would create 2425state will not match this rule until existing states time out. 2426.It Ar no-sync 2427Prevent state changes for states created by this rule from appearing on the 2428.Xr pfsync 4 2429interface. 2430.It Xo Aq Ar timeout 2431.Aq Ar seconds 2432.Xc 2433Changes the timeout values used for states created by this rule. 2434For a list of all valid timeout names, see 2435.Sx OPTIONS 2436above. 2437.It Ar sloppy 2438Uses a sloppy TCP connection tracker that does not check sequence 2439numbers at all, which makes insertion and ICMP teardown attacks way 2440easier. 2441This is intended to be used in situations where one does not see all 2442packets of a connection, e.g. in asymmetric routing situations. 2443Cannot be used with modulate or synproxy state. 2444.It Ar pflow 2445States created by this rule are exported on the 2446.Xr pflow 4 2447interface. 2448.El 2449.Pp 2450Multiple options can be specified, separated by commas: 2451.Bd -literal -offset indent 2452pass in proto tcp from any to any \e 2453 port www keep state \e 2454 (max 100, source-track rule, max-src-nodes 75, \e 2455 max-src-states 3, tcp.established 60, tcp.closing 5) 2456.Ed 2457.Pp 2458When the 2459.Ar source-track 2460keyword is specified, the number of states per source IP is tracked. 2461.Pp 2462.Bl -tag -width xxxx -compact 2463.It Ar source-track rule 2464The maximum number of states created by this rule is limited by the rule's 2465.Ar max-src-nodes 2466and 2467.Ar max-src-states 2468options. 2469Only state entries created by this particular rule count toward the rule's 2470limits. 2471.It Ar source-track global 2472The number of states created by all rules that use this option is limited. 2473Each rule can specify different 2474.Ar max-src-nodes 2475and 2476.Ar max-src-states 2477options, however state entries created by any participating rule count towards 2478each individual rule's limits. 2479.El 2480.Pp 2481The following limits can be set: 2482.Pp 2483.Bl -tag -width xxxx -compact 2484.It Ar max-src-nodes Aq Ar number 2485Limits the maximum number of source addresses which can simultaneously 2486have state table entries. 2487.It Ar max-src-states Aq Ar number 2488Limits the maximum number of simultaneous state entries that a single 2489source address can create with this rule. 2490.El 2491.Pp 2492For stateful TCP connections, limits on established connections (connections 2493which have completed the TCP 3-way handshake) can also be enforced 2494per source IP. 2495.Pp 2496.Bl -tag -width xxxx -compact 2497.It Ar max-src-conn Aq Ar number 2498Limits the maximum number of simultaneous TCP connections which have 2499completed the 3-way handshake that a single host can make. 2500.It Xo Ar max-src-conn-rate Aq Ar number 2501.No / Aq Ar seconds 2502.Xc 2503Limit the rate of new connections over a time interval. 2504The connection rate is an approximation calculated as a moving average. 2505.El 2506.Pp 2507Because the 3-way handshake ensures that the source address is not being 2508spoofed, more aggressive action can be taken based on these limits. 2509With the 2510.Ar overload Aq Ar table 2511state option, source IP addresses which hit either of the limits on 2512established connections will be added to the named table. 2513This table can be used in the ruleset to block further activity from 2514the offending host, redirect it to a tarpit process, or restrict its 2515bandwidth. 2516.Pp 2517The optional 2518.Ar flush 2519keyword kills all states created by the matching rule which originate 2520from the host which exceeds these limits. 2521The 2522.Ar global 2523modifier to the flush command kills all states originating from the 2524offending host, regardless of which rule created the state. 2525.Pp 2526For example, the following rules will protect the webserver against 2527hosts making more than 100 connections in 10 seconds. 2528Any host which connects faster than this rate will have its address added 2529to the 2530.Aq bad_hosts 2531table and have all states originating from it flushed. 2532Any new packets arriving from this host will be dropped unconditionally 2533by the block rule. 2534.Bd -literal -offset indent 2535block quick from \*(Ltbad_hosts\*(Gt 2536pass in on $ext_if proto tcp to $webserver port www keep state \e 2537 (max-src-conn-rate 100/10, overload \*(Ltbad_hosts\*(Gt flush global) 2538.Ed 2539.Sh OPERATING SYSTEM FINGERPRINTING 2540Passive OS Fingerprinting is a mechanism to inspect nuances of a TCP 2541connection's initial SYN packet and guess at the host's operating system. 2542Unfortunately these nuances are easily spoofed by an attacker so the 2543fingerprint is not useful in making security decisions. 2544But the fingerprint is typically accurate enough to make policy decisions 2545upon. 2546.Pp 2547The fingerprints may be specified by operating system class, by 2548version, or by subtype/patchlevel. 2549The class of an operating system is typically the vendor or genre 2550and would be 2551.Ox 2552for the 2553.Xr pf 4 2554firewall itself. 2555The version of the oldest available 2556.Ox 2557release on the main FTP site 2558would be 2.6 and the fingerprint would be written 2559.Pp 2560.Dl \&"OpenBSD 2.6\&" 2561.Pp 2562The subtype of an operating system is typically used to describe the 2563patchlevel if that patch led to changes in the TCP stack behavior. 2564In the case of 2565.Ox , 2566the only subtype is for a fingerprint that was 2567normalized by the 2568.Ar no-df 2569scrub option and would be specified as 2570.Pp 2571.Dl \&"OpenBSD 3.3 no-df\&" 2572.Pp 2573Fingerprints for most popular operating systems are provided by 2574.Xr pf.os 5 . 2575Once 2576.Xr pf 4 2577is running, a complete list of known operating system fingerprints may 2578be listed by running: 2579.Pp 2580.Dl # pfctl -so 2581.Pp 2582Filter rules can enforce policy at any level of operating system specification 2583assuming a fingerprint is present. 2584Policy could limit traffic to approved operating systems or even ban traffic 2585from hosts that aren't at the latest service pack. 2586.Pp 2587The 2588.Ar unknown 2589class can also be used as the fingerprint which will match packets for 2590which no operating system fingerprint is known. 2591.Pp 2592Examples: 2593.Bd -literal -offset indent 2594pass out proto tcp from any os OpenBSD 2595block out proto tcp from any os Doors 2596block out proto tcp from any os "Doors PT" 2597block out proto tcp from any os "Doors PT SP3" 2598block out from any os "unknown" 2599pass on lo0 proto tcp from any os "OpenBSD 3.3 lo0" 2600.Ed 2601.Pp 2602Operating system fingerprinting is limited only to the TCP SYN packet. 2603This means that it will not work on other protocols and will not match 2604a currently established connection. 2605.Pp 2606Caveat: operating system fingerprints are occasionally wrong. 2607There are three problems: an attacker can trivially craft his packets to 2608appear as any operating system he chooses; 2609an operating system patch could change the stack behavior and no fingerprints 2610will match it until the database is updated; 2611and multiple operating systems may have the same fingerprint. 2612.Sh BLOCKING SPOOFED TRAFFIC 2613"Spoofing" is the faking of IP addresses, typically for malicious 2614purposes. 2615The 2616.Ar antispoof 2617directive expands to a set of filter rules which will block all 2618traffic with a source IP from the network(s) directly connected 2619to the specified interface(s) from entering the system through 2620any other interface. 2621.Pp 2622For example, the line 2623.Bd -literal -offset indent 2624antispoof for lo0 2625.Ed 2626.Pp 2627expands to 2628.Bd -literal -offset indent 2629block drop in on ! lo0 inet from 127.0.0.1/8 to any 2630block drop in on ! lo0 inet6 from ::1 to any 2631.Ed 2632.Pp 2633For non-loopback interfaces, there are additional rules to block incoming 2634packets with a source IP address identical to the interface's IP(s). 2635For example, assuming the interface wi0 had an IP address of 10.0.0.1 and a 2636netmask of 255.255.255.0, 2637the line 2638.Bd -literal -offset indent 2639antispoof for wi0 inet 2640.Ed 2641.Pp 2642expands to 2643.Bd -literal -offset indent 2644block drop in on ! wi0 inet from 10.0.0.0/24 to any 2645block drop in inet from 10.0.0.1 to any 2646.Ed 2647.Pp 2648Caveat: Rules created by the 2649.Ar antispoof 2650directive interfere with packets sent over loopback interfaces 2651to local addresses. 2652One should pass these explicitly. 2653.Sh FRAGMENT HANDLING 2654The size of IP datagrams (packets) can be significantly larger than the 2655maximum transmission unit (MTU) of the network. 2656In cases when it is necessary or more efficient to send such large packets, 2657the large packet will be fragmented into many smaller packets that will each 2658fit onto the wire. 2659Unfortunately for a firewalling device, only the first logical fragment will 2660contain the necessary header information for the subprotocol that allows 2661.Xr pf 4 2662to filter on things such as TCP ports or to perform NAT. 2663.Pp 2664Besides the use of 2665.Ar set reassemble 2666option or 2667.Ar scrub 2668rules as described in 2669.Sx TRAFFIC NORMALIZATION 2670above, there are three options for handling fragments in the packet filter. 2671.Pp 2672One alternative is to filter individual fragments with filter rules. 2673If no 2674.Ar scrub 2675rule applies to a fragment or 2676.Ar set reassemble 2677is set to 2678.Cm no 2679, it is passed to the filter. 2680Filter rules with matching IP header parameters decide whether the 2681fragment is passed or blocked, in the same way as complete packets 2682are filtered. 2683Without reassembly, fragments can only be filtered based on IP header 2684fields (source/destination address, protocol), since subprotocol header 2685fields are not available (TCP/UDP port numbers, ICMP code/type). 2686The 2687.Ar fragment 2688option can be used to restrict filter rules to apply only to 2689fragments, but not complete packets. 2690Filter rules without the 2691.Ar fragment 2692option still apply to fragments, if they only specify IP header fields. 2693For instance, the rule 2694.Bd -literal -offset indent 2695pass in proto tcp from any to any port 80 2696.Ed 2697.Pp 2698never applies to a fragment, even if the fragment is part of a TCP 2699packet with destination port 80, because without reassembly this information 2700is not available for each fragment. 2701This also means that fragments cannot create new or match existing 2702state table entries, which makes stateful filtering and address 2703translation (NAT, redirection) for fragments impossible. 2704.Pp 2705It's also possible to reassemble only certain fragments by specifying 2706source or destination addresses or protocols as parameters in 2707.Ar scrub 2708rules. 2709.Pp 2710In most cases, the benefits of reassembly outweigh the additional 2711memory cost, and it's recommended to use 2712.Ar set reassemble 2713option or 2714.Ar scrub 2715rules with the 2716.Ar fragment reassemble 2717modifier to reassemble 2718all fragments. 2719.Pp 2720The memory allocated for fragment caching can be limited using 2721.Xr pfctl 8 . 2722Once this limit is reached, fragments that would have to be cached 2723are dropped until other entries time out. 2724The timeout value can also be adjusted. 2725.Pp 2726When forwarding reassembled IPv6 packets, pf refragments them with 2727the original maximum fragment size. 2728This allows the sender to determine the optimal fragment size by 2729path MTU discovery. 2730.Sh ANCHORS 2731Besides the main ruleset, 2732.Xr pfctl 8 2733can load rulesets into 2734.Ar anchor 2735attachment points. 2736An 2737.Ar anchor 2738is a container that can hold rules, address tables, and other anchors. 2739.Pp 2740An 2741.Ar anchor 2742has a name which specifies the path where 2743.Xr pfctl 8 2744can be used to access the anchor to perform operations on it, such as 2745attaching child anchors to it or loading rules into it. 2746Anchors may be nested, with components separated by 2747.Sq / 2748characters, similar to how file system hierarchies are laid out. 2749The main ruleset is actually the default anchor, so filter and 2750translation rules, for example, may also be contained in any anchor. 2751.Pp 2752An anchor can reference another 2753.Ar anchor 2754attachment point 2755using the following kinds 2756of rules: 2757.Bl -tag -width xxxx 2758.It Ar nat-anchor Aq Ar name 2759Evaluates the 2760.Ar nat 2761rules in the specified 2762.Ar anchor . 2763.It Ar rdr-anchor Aq Ar name 2764Evaluates the 2765.Ar rdr 2766rules in the specified 2767.Ar anchor . 2768.It Ar binat-anchor Aq Ar name 2769Evaluates the 2770.Ar binat 2771rules in the specified 2772.Ar anchor . 2773.It Ar anchor Aq Ar name 2774Evaluates the filter rules in the specified 2775.Ar anchor . 2776.It Xo Ar load anchor 2777.Aq Ar name 2778.Ar from Aq Ar file 2779.Xc 2780Loads the rules from the specified file into the 2781anchor 2782.Ar name . 2783.El 2784.Pp 2785When evaluation of the main ruleset reaches an 2786.Ar anchor 2787rule, 2788.Xr pf 4 2789will proceed to evaluate all rules specified in that anchor. 2790.Pp 2791Matching filter and translation rules marked with the 2792.Ar quick 2793option are final and abort the evaluation of the rules in other 2794anchors and the main ruleset. 2795If the 2796.Ar anchor 2797itself is marked with the 2798.Ar quick 2799option, 2800ruleset evaluation will terminate when the anchor is exited if the packet is 2801matched by any rule within the anchor. 2802.Pp 2803.Ar anchor 2804rules are evaluated relative to the anchor in which they are contained. 2805For example, all 2806.Ar anchor 2807rules specified in the main ruleset will reference anchor 2808attachment points underneath the main ruleset, and 2809.Ar anchor 2810rules specified in a file loaded from a 2811.Ar load anchor 2812rule will be attached under that anchor point. 2813.Pp 2814Rules may be contained in 2815.Ar anchor 2816attachment points which do not contain any rules when the main ruleset 2817is loaded, and later such anchors can be manipulated through 2818.Xr pfctl 8 2819without reloading the main ruleset or other anchors. 2820For example, 2821.Bd -literal -offset indent 2822ext_if = \&"kue0\&" 2823block on $ext_if all 2824anchor spam 2825pass out on $ext_if all 2826pass in on $ext_if proto tcp from any \e 2827 to $ext_if port smtp 2828.Ed 2829.Pp 2830blocks all packets on the external interface by default, then evaluates 2831all rules in the 2832.Ar anchor 2833named "spam", and finally passes all outgoing connections and 2834incoming connections to port 25. 2835.Bd -literal -offset indent 2836# echo \&"block in quick from 1.2.3.4 to any\&" \&| \e 2837 pfctl -a spam -f - 2838.Ed 2839.Pp 2840This loads a single rule into the 2841.Ar anchor , 2842which blocks all packets from a specific address. 2843.Pp 2844The anchor can also be populated by adding a 2845.Ar load anchor 2846rule after the 2847.Ar anchor 2848rule: 2849.Bd -literal -offset indent 2850anchor spam 2851load anchor spam from "/etc/pf-spam.conf" 2852.Ed 2853.Pp 2854When 2855.Xr pfctl 8 2856loads 2857.Nm pf.conf , 2858it will also load all the rules from the file 2859.Pa /etc/pf-spam.conf 2860into the anchor. 2861.Pp 2862Optionally, 2863.Ar anchor 2864rules can specify packet filtering parameters using the same syntax as 2865filter rules. 2866When parameters are used, the 2867.Ar anchor 2868rule is only evaluated for matching packets. 2869This allows conditional evaluation of anchors, like: 2870.Bd -literal -offset indent 2871block on $ext_if all 2872anchor spam proto tcp from any to any port smtp 2873pass out on $ext_if all 2874pass in on $ext_if proto tcp from any to $ext_if port smtp 2875.Ed 2876.Pp 2877The rules inside 2878.Ar anchor 2879spam are only evaluated for 2880.Ar tcp 2881packets with destination port 25. 2882Hence, 2883.Bd -literal -offset indent 2884# echo \&"block in quick from 1.2.3.4 to any" \&| \e 2885 pfctl -a spam -f - 2886.Ed 2887.Pp 2888will only block connections from 1.2.3.4 to port 25. 2889.Pp 2890Anchors may end with the asterisk 2891.Pq Sq * 2892character, which signifies that all anchors attached at that point 2893should be evaluated in the alphabetical ordering of their anchor name. 2894For example, 2895.Bd -literal -offset indent 2896anchor "spam/*" 2897.Ed 2898.Pp 2899will evaluate each rule in each anchor attached to the 2900.Li spam 2901anchor. 2902Note that it will only evaluate anchors that are directly attached to the 2903.Li spam 2904anchor, and will not descend to evaluate anchors recursively. 2905.Pp 2906Since anchors are evaluated relative to the anchor in which they are 2907contained, there is a mechanism for accessing the parent and ancestor 2908anchors of a given anchor. 2909Similar to file system path name resolution, if the sequence 2910.Dq .. 2911appears as an anchor path component, the parent anchor of the current 2912anchor in the path evaluation at that point will become the new current 2913anchor. 2914As an example, consider the following: 2915.Bd -literal -offset indent 2916# echo ' anchor "spam/allowed" ' | pfctl -f - 2917# echo -e ' anchor "../banned" \en pass' | \e 2918 pfctl -a spam/allowed -f - 2919.Ed 2920.Pp 2921Evaluation of the main ruleset will lead into the 2922.Li spam/allowed 2923anchor, which will evaluate the rules in the 2924.Li spam/banned 2925anchor, if any, before finally evaluating the 2926.Ar pass 2927rule. 2928.Pp 2929Filter rule 2930.Ar anchors 2931can also be loaded inline in the ruleset within a brace ('{' '}') delimited 2932block. 2933Brace delimited blocks may contain rules or other brace-delimited blocks. 2934When anchors are loaded this way the anchor name becomes optional. 2935.Bd -literal -offset indent 2936anchor "external" on $ext_if { 2937 block 2938 anchor out { 2939 pass proto tcp from any to port { 25, 80, 443 } 2940 } 2941 pass in proto tcp to any port 22 2942} 2943.Ed 2944.Pp 2945Since the parser specification for anchor names is a string, any 2946reference to an anchor name containing 2947.Sq / 2948characters will require double quote 2949.Pq Sq \&" 2950characters around the anchor name. 2951.Sh SCTP CONSIDERATIONS 2952.Xr pf 4 2953supports 2954.Xr sctp 4 2955connections. 2956It can match ports, track state and NAT SCTP traffic. 2957However, it will not alter port numbers during nat or rdr translations. 2958Doing so would break SCTP multihoming. 2959.Sh TRANSLATION EXAMPLES 2960This example maps incoming requests on port 80 to port 8080, on 2961which a daemon is running (because, for example, it is not run as root, 2962and therefore lacks permission to bind to port 80). 2963.Bd -literal 2964# use a macro for the interface name, so it can be changed easily 2965ext_if = \&"ne3\&" 2966 2967# map daemon on 8080 to appear to be on 80 2968rdr on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 port 8080 2969.Ed 2970.Pp 2971If the 2972.Ar pass 2973modifier is given, packets matching the translation rule are passed without 2974inspecting the filter rules: 2975.Bd -literal 2976rdr pass on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 \e 2977 port 8080 2978.Ed 2979.Pp 2980In the example below, vlan12 is configured as 192.168.168.1; 2981the machine translates all packets coming from 192.168.168.0/24 to 204.92.77.111 2982when they are going out any interface except vlan12. 2983This has the net effect of making traffic from the 192.168.168.0/24 2984network appear as though it is the Internet routable address 2985204.92.77.111 to nodes behind any interface on the router except 2986for the nodes on vlan12. 2987(Thus, 192.168.168.1 can talk to the 192.168.168.0/24 nodes.) 2988.Bd -literal 2989nat on ! vlan12 from 192.168.168.0/24 to any -\*(Gt 204.92.77.111 2990.Ed 2991.Pp 2992In the example below, the machine sits between a fake internal 144.19.74.* 2993network, and a routable external IP of 204.92.77.100. 2994The 2995.Ar no nat 2996rule excludes protocol AH from being translated. 2997.Bd -literal 2998# NO NAT 2999no nat on $ext_if proto ah from 144.19.74.0/24 to any 3000nat on $ext_if from 144.19.74.0/24 to any -\*(Gt 204.92.77.100 3001.Ed 3002.Pp 3003In the example below, packets bound for one specific server, as well as those 3004generated by the sysadmins are not proxied; all other connections are. 3005.Bd -literal 3006# NO RDR 3007no rdr on $int_if proto { tcp, udp } from any to $server port 80 3008no rdr on $int_if proto { tcp, udp } from $sysadmins to any port 80 3009rdr on $int_if proto { tcp, udp } from any to any port 80 -\*(Gt 127.0.0.1 \e 3010 port 80 3011.Ed 3012.Pp 3013This longer example uses both a NAT and a redirection. 3014The external interface has the address 157.161.48.183. 3015On localhost, we are running 3016.Xr ftp-proxy 8 , 3017waiting for FTP sessions to be redirected to it. 3018The three mandatory anchors for 3019.Xr ftp-proxy 8 3020are omitted from this example; see the 3021.Xr ftp-proxy 8 3022manpage. 3023.Bd -literal 3024# NAT 3025# Translate outgoing packets' source addresses (any protocol). 3026# In this case, any address but the gateway's external address is mapped. 3027nat on $ext_if inet from ! ($ext_if) to any -\*(Gt ($ext_if) 3028 3029# NAT PROXYING 3030# Map outgoing packets' source port to an assigned proxy port instead of 3031# an arbitrary port. 3032# In this case, proxy outgoing isakmp with port 500 on the gateway. 3033nat on $ext_if inet proto udp from any port = isakmp to any -\*(Gt ($ext_if) \e 3034 port 500 3035 3036# BINAT 3037# Translate outgoing packets' source address (any protocol). 3038# Translate incoming packets' destination address to an internal machine 3039# (bidirectional). 3040binat on $ext_if from 10.1.2.150 to any -\*(Gt $ext_if 3041 3042# Translate packets arriving on $peer_if addressed to 172.22.16.0/20 3043# to the corresponding address in 172.21.16.0/20 (bidirectional). 3044binat on $peer_if from 172.21.16.0/20 to any -> 172.22.16.0/20 3045 3046# RDR 3047# Translate incoming packets' destination addresses. 3048# As an example, redirect a TCP and UDP port to an internal machine. 3049rdr on $ext_if inet proto tcp from any to ($ext_if) port 8080 \e 3050 -\*(Gt 10.1.2.151 port 22 3051rdr on $ext_if inet proto udp from any to ($ext_if) port 8080 \e 3052 -\*(Gt 10.1.2.151 port 53 3053 3054# RDR 3055# Translate outgoing ftp control connections to send them to localhost 3056# for proxying with ftp-proxy(8) running on port 8021. 3057rdr on $int_if proto tcp from any to any port 21 -\*(Gt 127.0.0.1 port 8021 3058.Ed 3059.Pp 3060In this example, a NAT gateway is set up to translate internal addresses 3061using a pool of public addresses (192.0.2.16/28) and to redirect 3062incoming web server connections to a group of web servers on the internal 3063network. 3064.Bd -literal 3065# NAT LOAD BALANCE 3066# Translate outgoing packets' source addresses using an address pool. 3067# A given source address is always translated to the same pool address by 3068# using the source-hash keyword. 3069nat on $ext_if inet from any to any -\*(Gt 192.0.2.16/28 source-hash 3070 3071# RDR ROUND ROBIN 3072# Translate incoming web server connections to a group of web servers on 3073# the internal network. 3074rdr on $ext_if proto tcp from any to any port 80 \e 3075 -\*(Gt { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin 3076.Ed 3077.Sh FILTER EXAMPLES 3078.Bd -literal 3079# The external interface is kue0 3080# (157.161.48.183, the only routable address) 3081# and the private network is 10.0.0.0/8, for which we are doing NAT. 3082 3083# Reassemble incoming traffic 3084set reassemble yes 3085 3086# use a macro for the interface name, so it can be changed easily 3087ext_if = \&"kue0\&" 3088 3089# block and log everything by default 3090block return log on $ext_if all 3091 3092# block anything coming from source we have no back routes for 3093block in from no-route to any 3094 3095# block packets whose ingress interface does not match the one in 3096# the route back to their source address 3097block in from urpf-failed to any 3098 3099# block and log outgoing packets that do not have our address as source, 3100# they are either spoofed or something is misconfigured (NAT disabled, 3101# for instance), we want to be nice and do not send out garbage. 3102block out log quick on $ext_if from ! 157.161.48.183 to any 3103 3104# silently drop broadcasts (cable modem noise) 3105block in quick on $ext_if from any to 255.255.255.255 3106 3107# block and log incoming packets from reserved address space and invalid 3108# addresses, they are either spoofed or misconfigured, we cannot reply to 3109# them anyway (hence, no return-rst). 3110block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \e 3111 192.168.0.0/16, 255.255.255.255/32 } to any 3112 3113# ICMP 3114 3115# pass out/in certain ICMP queries and keep state (ping) 3116# state matching is done on host addresses and ICMP id (not type/code), 3117# so replies (like 0/0 for 8/0) will match queries 3118# ICMP error messages (which always refer to a TCP/UDP packet) are 3119# handled by the TCP/UDP states 3120pass on $ext_if inet proto icmp all icmp-type 8 code 0 3121 3122# UDP 3123 3124# pass out all UDP connections and keep state 3125pass out on $ext_if proto udp all 3126 3127# pass in certain UDP connections and keep state (DNS) 3128pass in on $ext_if proto udp from any to any port domain 3129 3130# TCP 3131 3132# pass out all TCP connections and modulate state 3133pass out on $ext_if proto tcp all modulate state 3134 3135# pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT) 3136pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \e 3137 auth } 3138 3139# Do not allow Windows 9x SMTP connections since they are typically 3140# a viral worm. Alternately we could limit these OSes to 1 connection each. 3141block in on $ext_if proto tcp from any os {"Windows 95", "Windows 98"} \e 3142 to any port smtp 3143 3144# IPv6 3145# pass in/out all IPv6 traffic: note that we have to enable this in two 3146# different ways, on both our physical interface and our tunnel 3147pass quick on gif0 inet6 3148pass quick on $ext_if proto ipv6 3149 3150# Packet Tagging 3151 3152# three interfaces: $int_if, $ext_if, and $wifi_if (wireless). NAT is 3153# being done on $ext_if for all outgoing packets. tag packets in on 3154# $int_if and pass those tagged packets out on $ext_if. all other 3155# outgoing packets (i.e., packets from the wireless network) are only 3156# permitted to access port 80. 3157 3158pass in on $int_if from any to any tag INTNET 3159pass in on $wifi_if from any to any 3160 3161block out on $ext_if from any to any 3162pass out quick on $ext_if tagged INTNET 3163pass out on $ext_if proto tcp from any to any port 80 3164 3165# tag incoming packets as they are redirected to spamd(8). use the tag 3166# to pass those packets through the packet filter. 3167 3168rdr on $ext_if inet proto tcp from \*(Ltspammers\*(Gt to port smtp \e 3169 tag SPAMD -\*(Gt 127.0.0.1 port spamd 3170 3171block in on $ext_if 3172pass in on $ext_if inet proto tcp tagged SPAMD 3173.Ed 3174.Sh GRAMMAR 3175Syntax for 3176.Nm 3177in BNF: 3178.Bd -literal 3179line = ( option | ether-rule | pf-rule | nat-rule | binat-rule | 3180 rdr-rule | antispoof-rule | altq-rule | queue-rule | 3181 trans-anchors | anchor-rule | anchor-close | load-anchor | 3182 table-rule | include ) 3183 3184option = "set" ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] | 3185 [ "ruleset-optimization" [ "none" | "basic" | "profile" ]] | 3186 [ "optimization" [ "default" | "normal" | 3187 "high-latency" | "satellite" | 3188 "aggressive" | "conservative" ] ] 3189 [ "limit" ( limit-item | "{" limit-list "}" ) ] | 3190 [ "loginterface" ( interface-name | "none" ) ] | 3191 [ "block-policy" ( "drop" | "return" ) ] | 3192 [ "state-policy" ( "if-bound" | "floating" ) ] 3193 [ "state-defaults" state-opts ] 3194 [ "require-order" ( "yes" | "no" ) ] 3195 [ "fingerprints" filename ] | 3196 [ "skip on" ifspec ] | 3197 [ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] 3198 [ "keepcounters" ] ) 3199 3200ether-rule = "ether" etheraction [ ( "in" | "out" ) ] 3201 [ "quick" ] [ "on" ifspec ] [ "bridge-to" interface-name ] 3202 [ etherprotospec ] etherhosts [ "l3" hosts ] 3203 [ etherfilteropt-list ] 3204 3205pf-rule = action [ ( "in" | "out" ) ] 3206 [ "log" [ "(" logopts ")"] ] [ "quick" ] 3207 [ "on" ifspec ] [ route ] [ af ] [ protospec ] 3208 hosts [ filteropt-list ] 3209 3210logopts = logopt [ "," logopts ] 3211logopt = "all" | "user" | "to" interface-name 3212 3213etherfilteropt-list = etherfilteropt-list etherfilteropt | etherfilteropt 3214etherfilteropt = "tag" string | "tagged" string | "queue" ( string ) | 3215 "ridentifier" number | "label" string 3216 3217filteropt-list = filteropt-list filteropt | filteropt 3218filteropt = user | group | flags | icmp-type | icmp6-type | "tos" tos | 3219 ( "no" | "keep" | "modulate" | "synproxy" ) "state" 3220 [ "(" state-opts ")" ] | 3221 "fragment" | "no-df" | "min-ttl" number | "set-tos" tos | 3222 "max-mss" number | "random-id" | "reassemble tcp" | 3223 fragmentation | "allow-opts" | 3224 "label" string | "tag" string | [ ! ] "tagged" string | 3225 "set prio" ( number | "(" number [ [ "," ] number ] ")" ) | 3226 "queue" ( string | "(" string [ [ "," ] string ] ")" ) | 3227 "rtable" number | "probability" number"%" | "prio" number | 3228 "dnpipe" ( number | "(" number "," number ")" ) | 3229 "dnqueue" ( number | "(" number "," number ")" ) | 3230 "ridentifier" number 3231 3232nat-rule = [ "no" ] "nat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3233 [ "on" ifspec ] [ af ] 3234 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3235 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3236 [ portspec ] [ pooltype ] [ "static-port" ] 3237 [ "map-e-portset" number "/" number "/" number ] ] 3238 3239binat-rule = [ "no" ] "binat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3240 [ "on" interface-name ] [ af ] 3241 [ "proto" ( proto-name | proto-number ) ] 3242 "from" address [ "/" mask-bits ] "to" ipspec 3243 [ "tag" string ] [ "tagged" string ] 3244 [ "-\*(Gt" address [ "/" mask-bits ] ] 3245 3246rdr-rule = [ "no" ] "rdr" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3247 [ "on" ifspec ] [ af ] 3248 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3249 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3250 [ portspec ] [ pooltype ] ] 3251 3252antispoof-rule = "antispoof" [ "log" ] [ "quick" ] 3253 "for" ifspec [ af ] [ "label" string ] 3254 [ "ridentifier" number ] 3255 3256table-rule = "table" "\*(Lt" string "\*(Gt" [ tableopts-list ] 3257tableopts-list = tableopts-list tableopts | tableopts 3258tableopts = "persist" | "const" | "counters" | "file" string | 3259 "{" [ tableaddr-list ] "}" 3260tableaddr-list = tableaddr-list [ "," ] tableaddr-spec | tableaddr-spec 3261tableaddr-spec = [ "!" ] tableaddr [ "/" mask-bits ] 3262tableaddr = hostname | ifspec | "self" | 3263 ipv4-dotted-quad | ipv6-coloned-hex 3264 3265altq-rule = "altq on" interface-name queueopts-list 3266 "queue" subqueue 3267queue-rule = "queue" string [ "on" interface-name ] queueopts-list 3268 subqueue 3269 3270anchor-rule = "anchor" [ string ] [ ( "in" | "out" ) ] [ "on" ifspec ] 3271 [ af ] [ protospec ] [ hosts ] [ filteropt-list ] [ "{" ] 3272 3273anchor-close = "}" 3274 3275trans-anchors = ( "nat-anchor" | "rdr-anchor" | "binat-anchor" ) string 3276 [ "on" ifspec ] [ af ] [ "proto" ] [ protospec ] [ hosts ] 3277 3278load-anchor = "load anchor" string "from" filename 3279 3280queueopts-list = queueopts-list queueopts | queueopts 3281queueopts = [ "bandwidth" bandwidth-spec ] | 3282 [ "qlimit" number ] | [ "tbrsize" number ] | 3283 [ "priority" number ] | [ schedulers ] 3284schedulers = ( cbq-def | priq-def | hfsc-def ) 3285bandwidth-spec = "number" ( "b" | "Kb" | "Mb" | "Gb" | "%" ) 3286 3287etheraction = "pass" | "block" 3288action = "pass" | "match" | "block" [ return ] | [ "no" ] "scrub" 3289return = "drop" | "return" | "return-rst" [ "( ttl" number ")" ] | 3290 "return-icmp" [ "(" icmpcode [ [ "," ] icmp6code ] ")" ] | 3291 "return-icmp6" [ "(" icmp6code ")" ] 3292icmpcode = ( icmp-code-name | icmp-code-number ) 3293icmp6code = ( icmp6-code-name | icmp6-code-number ) 3294 3295ifspec = ( [ "!" ] ( interface-name | interface-group ) ) | 3296 "{" interface-list "}" 3297interface-list = [ "!" ] ( interface-name | interface-group ) 3298 [ [ "," ] interface-list ] 3299route = ( "route-to" | "reply-to" | "dup-to" ) 3300 ( routehost | "{" routehost-list "}" ) 3301 [ pooltype ] 3302af = "inet" | "inet6" 3303 3304etherprotospec = "proto" ( proto-number | "{" etherproto-list "}" ) 3305etherproto-list = proto-number [ [ "," ] etherproto-list ] 3306protospec = "proto" ( proto-name | proto-number | 3307 "{" proto-list "}" ) 3308proto-list = ( proto-name | proto-number ) [ [ "," ] proto-list ] 3309 3310etherhosts = "from" macaddress "to" macaddress 3311macaddress = mac | mac "/" masklen | mac "&" mask 3312 3313hosts = "all" | 3314 "from" ( "any" | "no-route" | "urpf-failed" | "self" | host | 3315 "{" host-list "}" ) [ port ] [ os ] 3316 "to" ( "any" | "no-route" | "self" | host | 3317 "{" host-list "}" ) [ port ] 3318 3319ipspec = "any" | host | "{" host-list "}" 3320host = [ "!" ] ( address [ "/" mask-bits ] | "\*(Lt" string "\*(Gt" ) 3321redirhost = address [ "/" mask-bits ] 3322routehost = "(" interface-name [ address [ "/" mask-bits ] ] ")" 3323address = ( interface-name | interface-group | 3324 "(" ( interface-name | interface-group ) ")" | 3325 hostname | ipv4-dotted-quad | ipv6-coloned-hex ) 3326host-list = host [ [ "," ] host-list ] 3327redirhost-list = redirhost [ [ "," ] redirhost-list ] 3328routehost-list = routehost [ [ "," ] routehost-list ] 3329 3330port = "port" ( unary-op | binary-op | "{" op-list "}" ) 3331portspec = "port" ( number | name ) [ ":" ( "*" | number | name ) ] 3332os = "os" ( os-name | "{" os-list "}" ) 3333user = "user" ( unary-op | binary-op | "{" op-list "}" ) 3334group = "group" ( unary-op | binary-op | "{" op-list "}" ) 3335 3336unary-op = [ "=" | "!=" | "\*(Lt" | "\*(Le" | "\*(Gt" | "\*(Ge" ] 3337 ( name | number ) 3338binary-op = number ( "\*(Lt\*(Gt" | "\*(Gt\*(Lt" | ":" ) number 3339op-list = ( unary-op | binary-op ) [ [ "," ] op-list ] 3340 3341os-name = operating-system-name 3342os-list = os-name [ [ "," ] os-list ] 3343 3344flags = "flags" ( [ flag-set ] "/" flag-set | "any" ) 3345flag-set = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ] 3346 [ "W" ] 3347 3348icmp-type = "icmp-type" ( icmp-type-code | "{" icmp-list "}" ) 3349icmp6-type = "icmp6-type" ( icmp-type-code | "{" icmp-list "}" ) 3350icmp-type-code = ( icmp-type-name | icmp-type-number ) 3351 [ "code" ( icmp-code-name | icmp-code-number ) ] 3352icmp-list = icmp-type-code [ [ "," ] icmp-list ] 3353 3354tos = ( "lowdelay" | "throughput" | "reliability" | 3355 [ "0x" ] number ) 3356 3357state-opts = state-opt [ [ "," ] state-opts ] 3358state-opt = ( "max" number | "no-sync" | timeout | "sloppy" | 3359 "source-track" [ ( "rule" | "global" ) ] | 3360 "max-src-nodes" number | "max-src-states" number | 3361 "max-src-conn" number | 3362 "max-src-conn-rate" number "/" number | 3363 "overload" "\*(Lt" string "\*(Gt" [ "flush" ] | 3364 "if-bound" | "floating" | "pflow" ) 3365 3366fragmentation = [ "fragment reassemble" ] 3367 3368timeout-list = timeout [ [ "," ] timeout-list ] 3369timeout = ( "tcp.first" | "tcp.opening" | "tcp.established" | 3370 "tcp.closing" | "tcp.finwait" | "tcp.closed" | 3371 "sctp.first" | "sctp.opening" | "sctp.established" | 3372 "sctp.closing" | "sctp.closed" | 3373 "udp.first" | "udp.single" | "udp.multiple" | 3374 "icmp.first" | "icmp.error" | 3375 "other.first" | "other.single" | "other.multiple" | 3376 "frag" | "interval" | "src.track" | 3377 "adaptive.start" | "adaptive.end" ) number 3378 3379limit-list = limit-item [ [ "," ] limit-list ] 3380limit-item = ( "states" | "frags" | "src-nodes" ) number 3381 3382pooltype = ( "bitmask" | "random" | 3383 "source-hash" [ ( hex-key | string-key ) ] | 3384 "round-robin" ) [ sticky-address ] 3385 3386subqueue = string | "{" queue-list "}" 3387queue-list = string [ [ "," ] string ] 3388cbq-def = "cbq" [ "(" cbq-opt [ [ "," ] cbq-opt ] ")" ] 3389priq-def = "priq" [ "(" priq-opt [ [ "," ] priq-opt ] ")" ] 3390hfsc-def = "hfsc" [ "(" hfsc-opt [ [ "," ] hfsc-opt ] ")" ] 3391cbq-opt = ( "default" | "borrow" | "red" | "ecn" | "rio" ) 3392priq-opt = ( "default" | "red" | "ecn" | "rio" ) 3393hfsc-opt = ( "default" | "red" | "ecn" | "rio" | 3394 linkshare-sc | realtime-sc | upperlimit-sc ) 3395linkshare-sc = "linkshare" sc-spec 3396realtime-sc = "realtime" sc-spec 3397upperlimit-sc = "upperlimit" sc-spec 3398sc-spec = ( bandwidth-spec | 3399 "(" bandwidth-spec number bandwidth-spec ")" ) 3400include = "include" filename 3401.Ed 3402.Sh FILES 3403.Bl -tag -width "/etc/protocols" -compact 3404.It Pa /etc/hosts 3405Host name database. 3406.It Pa /etc/pf.conf 3407Default location of the ruleset file. 3408The file has to be created manually as it is not installed with a 3409standard installation. 3410.It Pa /etc/pf.os 3411Default location of OS fingerprints. 3412.It Pa /etc/protocols 3413Protocol name database. 3414.It Pa /etc/services 3415Service name database. 3416.El 3417.Sh SEE ALSO 3418.Xr altq 4 , 3419.Xr carp 4 , 3420.Xr icmp 4 , 3421.Xr icmp6 4 , 3422.Xr ip 4 , 3423.Xr ip6 4 , 3424.Xr pf 4 , 3425.Xr pflow 4 , 3426.Xr pfsync 4 , 3427.Xr tcp 4 , 3428.Xr sctp 4 , 3429.Xr udp 4 , 3430.Xr hosts 5 , 3431.Xr pf.os 5 , 3432.Xr protocols 5 , 3433.Xr services 5 , 3434.Xr ftp-proxy 8 , 3435.Xr pfctl 8 , 3436.Xr pflogd 8 3437.Sh HISTORY 3438The 3439.Nm 3440file format first appeared in 3441.Ox 3.0 . 3442