1.\" $FreeBSD$ 2.\" $OpenBSD: pf.conf.5,v 1.406 2009/01/31 19:37:12 sobrado Exp $ 3.\" 4.\" Copyright (c) 2002, Daniel Hartmeier 5.\" All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 11.\" - Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" - Redistributions in binary form must reproduce the above 14.\" copyright notice, this list of conditions and the following 15.\" disclaimer in the documentation and/or other materials provided 16.\" with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19.\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 21.\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 22.\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 23.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 24.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 25.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 26.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 28.\" ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29.\" POSSIBILITY OF SUCH DAMAGE. 30.\" 31.Dd June 21, 2023 32.Dt PF.CONF 5 33.Os 34.Sh NAME 35.Nm pf.conf 36.Nd packet filter configuration file 37.Sh DESCRIPTION 38The 39.Xr pf 4 40packet filter modifies, drops or passes packets according to rules or 41definitions specified in 42.Nm pf.conf . 43.Sh STATEMENT ORDER 44There are eight types of statements in 45.Nm pf.conf : 46.Bl -tag -width xxxx 47.It Cm Macros 48User-defined variables may be defined and used later, simplifying 49the configuration file. 50Macros must be defined before they are referenced in 51.Nm pf.conf . 52.It Cm Tables 53Tables provide a mechanism for increasing the performance and flexibility of 54rules with large numbers of source or destination addresses. 55.It Cm Options 56Options tune the behaviour of the packet filtering engine. 57.It Cm Ethernet Filtering 58Ethernet filtering provides rule-based blocking or passing of Ethernet packets. 59.It Cm Traffic Normalization Li (e.g. Em scrub ) 60Traffic normalization protects internal machines against inconsistencies 61in Internet protocols and implementations. 62.It Cm Queueing 63Queueing provides rule-based bandwidth control. 64.It Cm Translation Li (Various forms of NAT) 65Translation rules specify how addresses are to be mapped or redirected to 66other addresses. 67.It Cm Packet Filtering 68Packet filtering provides rule-based blocking or passing of packets. 69.El 70.Pp 71With the exception of 72.Cm macros 73and 74.Cm tables , 75the types of statements should be grouped and appear in 76.Nm pf.conf 77in the order shown above, as this matches the operation of the underlying 78packet filtering engine. 79By default 80.Xr pfctl 8 81enforces this order (see 82.Ar set require-order 83below). 84.Pp 85Comments can be put anywhere in the file using a hash mark 86.Pq Sq # , 87and extend to the end of the current line. 88.Pp 89Additional configuration files can be included with the 90.Ic include 91keyword, for example: 92.Bd -literal -offset indent 93include "/etc/pf/sub.filter.conf" 94.Ed 95.Sh MACROS 96Macros can be defined that will later be expanded in context. 97Macro names must start with a letter, and may contain letters, digits 98and underscores. 99Macro names may not be reserved words (for example 100.Ar pass , 101.Ar in , 102.Ar out ) . 103Macros are not expanded inside quotes. 104.Pp 105For example, 106.Bd -literal -offset indent 107ext_if = \&"kue0\&" 108all_ifs = \&"{\&" $ext_if lo0 \&"}\&" 109pass out on $ext_if from any to any 110pass in on $ext_if proto tcp from any to any port 25 111.Ed 112.Sh TABLES 113Tables are named structures which can hold a collection of addresses and 114networks. 115Lookups against tables in 116.Xr pf 4 117are relatively fast, making a single rule with tables much more efficient, 118in terms of 119processor usage and memory consumption, than a large number of rules which 120differ only in IP address (either created explicitly or automatically by rule 121expansion). 122.Pp 123Tables can be used as the source or destination of filter rules, 124.Ar scrub 125rules 126or 127translation rules such as 128.Ar nat 129or 130.Ar rdr 131(see below for details on the various rule types). 132Tables can also be used for the redirect address of 133.Ar nat 134and 135.Ar rdr 136rules and in the routing options of filter rules, but only for 137.Ar round-robin 138pools. 139.Pp 140Tables can be defined with any of the following 141.Xr pfctl 8 142mechanisms. 143As with macros, reserved words may not be used as table names. 144.Bl -tag -width "manually" 145.It Ar manually 146Persistent tables can be manually created with the 147.Ar add 148or 149.Ar replace 150option of 151.Xr pfctl 8 , 152before or after the ruleset has been loaded. 153.It Pa pf.conf 154Table definitions can be placed directly in this file, and loaded at the 155same time as other rules are loaded, atomically. 156Table definitions inside 157.Nm pf.conf 158use the 159.Ar table 160statement, and are especially useful to define non-persistent tables. 161The contents of a pre-existing table defined without a list of addresses 162to initialize it is not altered when 163.Nm pf.conf 164is loaded. 165A table initialized with the empty list, 166.Li { } , 167will be cleared on load. 168.El 169.Pp 170Tables may be defined with the following attributes: 171.Bl -tag -width persist 172.It Ar persist 173The 174.Ar persist 175flag forces the kernel to keep the table even when no rules refer to it. 176If the flag is not set, the kernel will automatically remove the table 177when the last rule referring to it is flushed. 178.It Ar const 179The 180.Ar const 181flag prevents the user from altering the contents of the table once it 182has been created. 183Without that flag, 184.Xr pfctl 8 185can be used to add or remove addresses from the table at any time, even 186when running with 187.Xr securelevel 7 188= 2. 189.It Ar counters 190The 191.Ar counters 192flag enables per-address packet and byte counters which can be displayed with 193.Xr pfctl 8 . 194Note that this feature carries significant memory overhead for large tables. 195.El 196.Pp 197For example, 198.Bd -literal -offset indent 199table \*(Ltprivate\*(Gt const { 10/8, 172.16/12, 192.168/16 } 200table \*(Ltbadhosts\*(Gt persist 201block on fxp0 from { \*(Ltprivate\*(Gt, \*(Ltbadhosts\*(Gt } to any 202.Ed 203.Pp 204creates a table called private, to hold RFC 1918 private network 205blocks, and a table called badhosts, which is initially empty. 206A filter rule is set up to block all traffic coming from addresses listed in 207either table. 208The private table cannot have its contents changed and the badhosts table 209will exist even when no active filter rules reference it. 210Addresses may later be added to the badhosts table, so that traffic from 211these hosts can be blocked by using 212.Bd -literal -offset indent 213# pfctl -t badhosts -Tadd 204.92.77.111 214.Ed 215.Pp 216A table can also be initialized with an address list specified in one or more 217external files, using the following syntax: 218.Bd -literal -offset indent 219table \*(Ltspam\*(Gt persist file \&"/etc/spammers\&" file \&"/etc/openrelays\&" 220block on fxp0 from \*(Ltspam\*(Gt to any 221.Ed 222.Pp 223The files 224.Pa /etc/spammers 225and 226.Pa /etc/openrelays 227list IP addresses, one per line. 228Any lines beginning with a # are treated as comments and ignored. 229In addition to being specified by IP address, hosts may also be 230specified by their hostname. 231When the resolver is called to add a hostname to a table, 232.Em all 233resulting IPv4 and IPv6 addresses are placed into the table. 234IP addresses can also be entered in a table by specifying a valid interface 235name, a valid interface group or the 236.Em self 237keyword, in which case all addresses assigned to the interface(s) will be 238added to the table. 239.Sh OPTIONS 240.Xr pf 4 241may be tuned for various situations using the 242.Ar set 243command. 244.Bl -tag -width xxxx 245.It Ar set timeout 246.Pp 247.Bl -tag -width "src.track" -compact 248.It Ar interval 249Interval between purging expired states and fragments. 250.It Ar frag 251Seconds before an unassembled fragment is expired. 252.It Ar src.track 253Length of time to retain a source tracking entry after the last state 254expires. 255.El 256.Pp 257When a packet matches a stateful connection, the seconds to live for the 258connection will be updated to that of the 259.Ar proto.modifier 260which corresponds to the connection state. 261Each packet which matches this state will reset the TTL. 262Tuning these values may improve the performance of the 263firewall at the risk of dropping valid idle connections. 264.Pp 265.Bl -tag -width xxxx -compact 266.It Ar tcp.first 267The state after the first packet. 268.It Ar tcp.opening 269The state before the destination host ever sends a packet. 270.It Ar tcp.established 271The fully established state. 272.It Ar tcp.closing 273The state after the first FIN has been sent. 274.It Ar tcp.finwait 275The state after both FINs have been exchanged and the connection is closed. 276Some hosts (notably web servers on Solaris) send TCP packets even after closing 277the connection. 278Increasing 279.Ar tcp.finwait 280(and possibly 281.Ar tcp.closing ) 282can prevent blocking of such packets. 283.It Ar tcp.closed 284The state after one endpoint sends an RST. 285.El 286.Pp 287ICMP and UDP are handled in a fashion similar to TCP, but with a much more 288limited set of states: 289.Pp 290.Bl -tag -width xxxx -compact 291.It Ar udp.first 292The state after the first packet. 293.It Ar udp.single 294The state if the source host sends more than one packet but the destination 295host has never sent one back. 296.It Ar udp.multiple 297The state if both hosts have sent packets. 298.It Ar icmp.first 299The state after the first packet. 300.It Ar icmp.error 301The state after an ICMP error came back in response to an ICMP packet. 302.El 303.Pp 304Other protocols are handled similarly to UDP: 305.Pp 306.Bl -tag -width xxxx -compact 307.It Ar other.first 308.It Ar other.single 309.It Ar other.multiple 310.El 311.Pp 312Timeout values can be reduced adaptively as the number of state table 313entries grows. 314.Pp 315.Bl -tag -width xxxx -compact 316.It Ar adaptive.start 317When the number of state entries exceeds this value, adaptive scaling 318begins. 319All timeout values are scaled linearly with factor 320(adaptive.end - number of states) / (adaptive.end - adaptive.start). 321.It Ar adaptive.end 322When reaching this number of state entries, all timeout values become 323zero, effectively purging all state entries immediately. 324This value is used to define the scale factor, it should not actually 325be reached (set a lower state limit, see below). 326.El 327.Pp 328Adaptive timeouts are enabled by default, with an adaptive.start value 329equal to 60% of the state limit, and an adaptive.end value equal to 330120% of the state limit. 331They can be disabled by setting both adaptive.start and adaptive.end to 0. 332.Pp 333The adaptive timeout values can be defined both globally and for each rule. 334When used on a per-rule basis, the values relate to the number of 335states created by the rule, otherwise to the total number of 336states. 337.Pp 338For example: 339.Bd -literal -offset indent 340set timeout tcp.first 120 341set timeout tcp.established 86400 342set timeout { adaptive.start 6000, adaptive.end 12000 } 343set limit states 10000 344.Ed 345.Pp 346With 9000 state table entries, the timeout values are scaled to 50% 347(tcp.first 60, tcp.established 43200). 348.It Ar set loginterface 349Enable collection of packet and byte count statistics for the given 350interface or interface group. 351These statistics can be viewed using 352.Bd -literal -offset indent 353# pfctl -s info 354.Ed 355.Pp 356In this example 357.Xr pf 4 358collects statistics on the interface named dc0: 359.Bd -literal -offset indent 360set loginterface dc0 361.Ed 362.Pp 363One can disable the loginterface using: 364.Bd -literal -offset indent 365set loginterface none 366.Ed 367.It Ar set limit 368Sets hard limits on the memory pools used by the packet filter. 369See 370.Xr zone 9 371for an explanation of memory pools. 372.Pp 373For example, 374.Bd -literal -offset indent 375set limit states 20000 376.Ed 377.Pp 378sets the maximum number of entries in the memory pool used by state table 379entries (generated by 380.Ar pass 381rules which do not specify 382.Ar no state ) 383to 20000. 384Using 385.Bd -literal -offset indent 386set limit frags 20000 387.Ed 388.Pp 389sets the maximum number of entries in the memory pool used for fragment 390reassembly (generated by 391.Ar scrub 392rules) to 20000. 393Using 394.Bd -literal -offset indent 395set limit src-nodes 2000 396.Ed 397.Pp 398sets the maximum number of entries in the memory pool used for tracking 399source IP addresses (generated by the 400.Ar sticky-address 401and 402.Ar src.track 403options) to 2000. 404Using 405.Bd -literal -offset indent 406set limit tables 1000 407set limit table-entries 100000 408.Ed 409.Pp 410sets limits on the memory pools used by tables. 411The first limits the number of tables that can exist to 1000. 412The second limits the overall number of addresses that can be stored 413in tables to 100000. 414.Pp 415Various limits can be combined on a single line: 416.Bd -literal -offset indent 417set limit { states 20000, frags 20000, src-nodes 2000 } 418.Ed 419.It Ar set ruleset-optimization 420.Bl -tag -width xxxxxxxx -compact 421.It Ar none 422Disable the ruleset optimizer. 423.It Ar basic 424Enable basic ruleset optimization. 425This is the default behaviour. 426Basic ruleset optimization does four things to improve the 427performance of ruleset evaluations: 428.Pp 429.Bl -enum -compact 430.It 431remove duplicate rules 432.It 433remove rules that are a subset of another rule 434.It 435combine multiple rules into a table when advantageous 436.It 437re-order the rules to improve evaluation performance 438.El 439.Pp 440.It Ar profile 441Uses the currently loaded ruleset as a feedback profile to tailor the 442ordering of quick rules to actual network traffic. 443.El 444.Pp 445It is important to note that the ruleset optimizer will modify the ruleset 446to improve performance. 447A side effect of the ruleset modification is that per-rule accounting 448statistics will have different meanings than before. 449If per-rule accounting is important for billing purposes or whatnot, 450either the ruleset optimizer should not be used or a label field should 451be added to all of the accounting rules to act as optimization barriers. 452.Pp 453Optimization can also be set as a command-line argument to 454.Xr pfctl 8 , 455overriding the settings in 456.Nm . 457.It Ar set optimization 458Optimize state timeouts for one of the following network environments: 459.Pp 460.Bl -tag -width xxxx -compact 461.It Ar normal 462A normal network environment. 463Suitable for almost all networks. 464.It Ar high-latency 465A high-latency environment (such as a satellite connection). 466.It Ar satellite 467Alias for 468.Ar high-latency . 469.It Ar aggressive 470Aggressively expire connections. 471This can greatly reduce the memory usage of the firewall at the cost of 472dropping idle connections early. 473.It Ar conservative 474Extremely conservative settings. 475Avoid dropping legitimate connections at the 476expense of greater memory utilization (possibly much greater on a busy 477network) and slightly increased processor utilization. 478.El 479.Pp 480For example: 481.Bd -literal -offset indent 482set optimization aggressive 483.Ed 484.It Ar set block-policy 485The 486.Ar block-policy 487option sets the default behaviour for the packet 488.Ar block 489action: 490.Pp 491.Bl -tag -width xxxxxxxx -compact 492.It Ar drop 493Packet is silently dropped. 494.It Ar return 495A TCP RST is returned for blocked TCP packets, 496an SCTP ABORT chunk is returned for blocked SCTP packets, 497an ICMP UNREACHABLE is returned for blocked UDP packets, 498and all other packets are silently dropped. 499.El 500.Pp 501For example: 502.Bd -literal -offset indent 503set block-policy return 504.Ed 505.It Ar set fail-policy 506The 507.Ar fail-policy 508option sets the behaviour of rules which should pass a packet but were 509unable to do so. 510This might happen when a nat or route-to rule uses an empty table as list 511of targets or if a rule fails to create state or source node. 512The following 513.Ar block 514actions are possible: 515.Pp 516.Bl -tag -width xxxxxxxx -compact 517.It Ar drop 518Incoming packet is silently dropped. 519.It Ar return 520Incoming packet is dropped and TCP RST is returned for TCP packets, 521an SCTP ABORT chunk is returned for blocked SCTP packets, 522an ICMP UNREACHABLE is returned for UDP packets, 523and no response is sent for other packets. 524.El 525.Pp 526For example: 527.Bd -literal -offset indent 528set fail-policy return 529.Ed 530.It Ar set state-policy 531The 532.Ar state-policy 533option sets the default behaviour for states: 534.Pp 535.Bl -tag -width group-bound -compact 536.It Ar if-bound 537States are bound to interface. 538.It Ar floating 539States can match packets on any interfaces (the default). 540.El 541.Pp 542For example: 543.Bd -literal -offset indent 544set state-policy if-bound 545.Ed 546.It Ar set syncookies never | always | adaptive 547When 548.Cm syncookies 549are active, pf will answer each incoming TCP SYN with a syncookie SYNACK, 550without allocating any resources. 551Upon reception of the client's ACK in response to the syncookie 552SYNACK, pf will evaluate the ruleset and create state if the ruleset 553permits it, complete the three way handshake with the target host and 554continue the connection with synproxy in place. 555This allows pf to be resilient against large synflood attacks which would 556run the state table against its limits otherwise. 557Due to the blind answers to every incoming SYN syncookies share the caveats of 558synproxy, namely seemingly accepting connections that will be dropped later on. 559.Pp 560.Bl -tag -width adaptive -compact 561.It Cm never 562pf will never send syncookie SYNACKs (the default). 563.It Cm always 564pf will always send syncookie SYNACKs. 565.It Cm adaptive 566pf will enable syncookie mode when a given percentage of the state table 567is used up by half-open TCP connections, as in, those that saw the initial 568SYN but didn't finish the three way handshake. 569The thresholds for entering and leaving syncookie mode can be specified using 570.Bd -literal -offset indent 571set syncookies adaptive (start 25%, end 12%) 572.Ed 573.El 574.It Ar set state-defaults 575The 576.Ar state-defaults 577option sets the state options for states created from rules 578without an explicit 579.Ar keep state . 580For example: 581.Bd -literal -offset indent 582set state-defaults no-sync 583.Ed 584.It Ar set hostid 585The 32-bit 586.Ar hostid 587identifies this firewall's state table entries to other firewalls 588in a 589.Xr pfsync 4 590failover cluster. 591By default the hostid is set to a pseudo-random value, however it may be 592desirable to manually configure it, for example to more easily identify the 593source of state table entries. 594.Bd -literal -offset indent 595set hostid 1 596.Ed 597.Pp 598The hostid may be specified in either decimal or hexadecimal. 599.It Ar set require-order 600By default 601.Xr pfctl 8 602enforces an ordering of the statement types in the ruleset to: 603.Em options , 604.Em normalization , 605.Em queueing , 606.Em translation , 607.Em filtering . 608Setting this option to 609.Ar no 610disables this enforcement. 611There may be non-trivial and non-obvious implications to an out of 612order ruleset. 613Consider carefully before disabling the order enforcement. 614.It Ar set fingerprints 615Load fingerprints of known operating systems from the given filename. 616By default fingerprints of known operating systems are automatically 617loaded from 618.Xr pf.os 5 619in 620.Pa /etc 621but can be overridden via this option. 622Setting this option may leave a small period of time where the fingerprints 623referenced by the currently active ruleset are inconsistent until the new 624ruleset finishes loading. 625.Pp 626For example: 627.Pp 628.Dl set fingerprints \&"/etc/pf.os.devel\&" 629.It Ar set skip on Aq Ar ifspec 630List interfaces for which packets should not be filtered. 631Packets passing in or out on such interfaces are passed as if pf was 632disabled, i.e. pf does not process them in any way. 633This can be useful on loopback and other virtual interfaces, when 634packet filtering is not desired and can have unexpected effects. 635For example: 636.Pp 637.Dl set skip on lo0 638.It Ar set debug 639Set the debug 640.Ar level 641to one of the following: 642.Pp 643.Bl -tag -width xxxxxxxxxxxx -compact 644.It Ar none 645Don't generate debug messages. 646.It Ar urgent 647Generate debug messages only for serious errors. 648.It Ar misc 649Generate debug messages for various errors. 650.It Ar loud 651Generate debug messages for common conditions. 652.El 653.It Ar set keepcounters 654Preserve rule counters across rule updates. 655Usually rule counters are reset to zero on every update of the ruleset. 656With 657.Ar keepcounters 658set pf will attempt to find matching rules between old and new rulesets 659and preserve the rule counters. 660.El 661.Sh ETHERNET FILTERING 662.Xr pf 4 663has the ability to 664.Ar block 665and 666.Ar pass 667packets based on attributes of their Ethernet (layer 2) header. 668.Pp 669For each packet processed by the packet filter, the filter rules are 670evaluated in sequential order, from first to last. 671The last matching rule decides what action is taken. 672If no rule matches the packet, the default action is to pass 673the packet. 674.Pp 675The following actions can be used in the filter: 676.Bl -tag -width xxxx 677.It Ar block 678The packet is blocked. 679Unlike for layer 3 traffic the packet is always silently dropped. 680.It Ar pass 681The packet is passed; 682no state is created for layer 2 traffic. 683.El 684.Sh PARAMETERS 685The rule parameters specify the packets to which a rule applies. 686A packet always comes in on, or goes out through, one interface. 687Most parameters are optional. 688If a parameter is specified, the rule only applies to packets with 689matching attributes. 690Certain parameters can be expressed as lists, in which case 691.Xr pfctl 8 692generates all needed rule combinations. 693.Bl -tag -width xxxx 694.It Ar in No or Ar out 695This rule applies to incoming or outgoing packets. 696If neither 697.Ar in 698nor 699.Ar out 700are specified, the rule will match packets in both directions. 701.It Ar quick 702If a packet matches a rule which has the 703.Ar quick 704option set, this rule 705is considered the last matching rule, and evaluation of subsequent rules 706is skipped. 707.It Ar on Aq Ar ifspec 708This rule applies only to packets coming in on, or going out through, this 709particular interface or interface group. 710For more information on interface groups, 711see the 712.Ic group 713keyword in 714.Xr ifconfig 8 . 715.It Ar bridge-to Aq interface 716Packets matching this rule will be sent out of the specified interface without 717further processing. 718.It Ar proto Aq Ar protocol 719This rule applies only to packets of this protocol. 720Note that Ethernet protocol numbers are different from those used in 721.Xr ip 4 722and 723.Xr ip6 4 . 724.It Xo 725.Ar from Aq Ar source 726.Ar to Aq Ar dest 727.Xc 728This rule applies only to packets with the specified source and destination 729MAC addresses. 730.It Xo Ar queue Aq Ar queue 731.Xc 732Packets matching this rule will be assigned to the specified queue. 733See 734.Sx QUEUEING 735for setup details. 736.Pp 737.It Ar tag Aq Ar string 738Packets matching this rule will be tagged with the 739specified string. 740The tag acts as an internal marker that can be used to 741identify these packets later on. 742This can be used, for example, to provide trust between 743interfaces and to determine if packets have been 744processed by translation rules. 745Tags are 746.Qq sticky , 747meaning that the packet will be tagged even if the rule 748is not the last matching rule. 749Further matching rules can replace the tag with a 750new one but will not remove a previously applied tag. 751A packet is only ever assigned one tag at a time. 752.It Ar tagged Aq Ar string 753Used to specify that packets must already be tagged with the given tag in order 754to match the rule. 755Inverse tag matching can also be done by specifying the ! operator before the 756tagged keyword. 757.Sh TRAFFIC NORMALIZATION 758Traffic normalization is used to sanitize packet content in such 759a way that there are no ambiguities in packet interpretation on 760the receiving side. 761The normalizer does IP fragment reassembly to prevent attacks 762that confuse intrusion detection systems by sending overlapping 763IP fragments. 764Packet normalization is invoked with the 765.Ar scrub 766directive. 767.Pp 768.Ar scrub 769has the following options: 770.Bl -tag -width xxxx 771.It Ar no-df 772Clears the 773.Ar dont-fragment 774bit from a matching IP packet. 775Some operating systems are known to generate fragmented packets with the 776.Ar dont-fragment 777bit set. 778This is particularly true with NFS. 779.Ar Scrub 780will drop such fragmented 781.Ar dont-fragment 782packets unless 783.Ar no-df 784is specified. 785.Pp 786Unfortunately some operating systems also generate their 787.Ar dont-fragment 788packets with a zero IP identification field. 789Clearing the 790.Ar dont-fragment 791bit on packets with a zero IP ID may cause deleterious results if an 792upstream router later fragments the packet. 793Using the 794.Ar random-id 795modifier (see below) is recommended in combination with the 796.Ar no-df 797modifier to ensure unique IP identifiers. 798.It Ar min-ttl Aq Ar number 799Enforces a minimum TTL for matching IP packets. 800.It Ar max-mss Aq Ar number 801Enforces a maximum MSS for matching TCP packets. 802.It Xo Ar set-tos Aq Ar string 803.No \*(Ba Aq Ar number 804.Xc 805Enforces a 806.Em TOS 807for matching IP packets. 808.Em TOS 809may be 810given as one of 811.Ar critical , 812.Ar inetcontrol , 813.Ar lowdelay , 814.Ar netcontrol , 815.Ar throughput , 816.Ar reliability , 817or one of the DiffServ Code Points: 818.Ar ef , 819.Ar va , 820.Ar af11 No ... Ar af43 , 821.Ar cs0 No ... Ar cs7 ; 822or as either hex or decimal. 823.It Ar random-id 824Replaces the IP identification field with random values to compensate 825for predictable values generated by many hosts. 826This option only applies to packets that are not fragmented 827after the optional fragment reassembly. 828.It Ar fragment reassemble 829Using 830.Ar scrub 831rules, fragments can be reassembled by normalization. 832In this case, fragments are buffered until they form a complete 833packet, and only the completed packet is passed on to the filter. 834The advantage is that filter rules have to deal only with complete 835packets, and can ignore fragments. 836The drawback of caching fragments is the additional memory cost. 837This is the default behaviour unless no fragment reassemble is specified. 838.It Ar no fragment reassemble 839Do not reassemble fragments. 840.It Ar reassemble tcp 841Statefully normalizes TCP connections. 842.Ar scrub reassemble tcp 843rules may not have the direction (in/out) specified. 844.Ar reassemble tcp 845performs the following normalizations: 846.Pp 847.Bl -tag -width timeout -compact 848.It ttl 849Neither side of the connection is allowed to reduce their IP TTL. 850An attacker may send a packet such that it reaches the firewall, affects 851the firewall state, and expires before reaching the destination host. 852.Ar reassemble tcp 853will raise the TTL of all packets back up to the highest value seen on 854the connection. 855.It timestamp modulation 856Modern TCP stacks will send a timestamp on every TCP packet and echo 857the other endpoint's timestamp back to them. 858Many operating systems will merely start the timestamp at zero when 859first booted, and increment it several times a second. 860The uptime of the host can be deduced by reading the timestamp and multiplying 861by a constant. 862Also observing several different timestamps can be used to count hosts 863behind a NAT device. 864And spoofing TCP packets into a connection requires knowing or guessing 865valid timestamps. 866Timestamps merely need to be monotonically increasing and not derived off a 867guessable base time. 868.Ar reassemble tcp 869will cause 870.Ar scrub 871to modulate the TCP timestamps with a random number. 872.It extended PAWS checks 873There is a problem with TCP on long fat pipes, in that a packet might get 874delayed for longer than it takes the connection to wrap its 32-bit sequence 875space. 876In such an occurrence, the old packet would be indistinguishable from a 877new packet and would be accepted as such. 878The solution to this is called PAWS: Protection Against Wrapped Sequence 879numbers. 880It protects against it by making sure the timestamp on each packet does 881not go backwards. 882.Ar reassemble tcp 883also makes sure the timestamp on the packet does not go forward more 884than the RFC allows. 885By doing this, 886.Xr pf 4 887artificially extends the security of TCP sequence numbers by 10 to 18 888bits when the host uses appropriately randomized timestamps, since a 889blind attacker would have to guess the timestamp as well. 890.El 891.El 892.Pp 893For example, 894.Bd -literal -offset indent 895scrub in on $ext_if all fragment reassemble 896.Ed 897.Pp 898The 899.Ar no 900option prefixed to a scrub rule causes matching packets to remain unscrubbed, 901much in the same way as 902.Ar drop quick 903works in the packet filter (see below). 904This mechanism should be used when it is necessary to exclude specific packets 905from broader scrub rules. 906.Sh QUEUEING with ALTQ 907The ALTQ system is currently not available in the GENERIC kernel nor as 908loadable modules. 909In order to use the herein after called queueing options one has to use a 910custom built kernel. 911Please refer to 912.Xr altq 4 913to learn about the related kernel options. 914.Pp 915Packets can be assigned to queues for the purpose of bandwidth 916control. 917At least two declarations are required to configure queues, and later 918any packet filtering rule can reference the defined queues by name. 919During the filtering component of 920.Nm pf.conf , 921the last referenced 922.Ar queue 923name is where any packets from 924.Ar pass 925rules will be queued, while for 926.Ar block 927rules it specifies where any resulting ICMP or TCP RST 928packets should be queued. 929The 930.Ar scheduler 931defines the algorithm used to decide which packets get delayed, dropped, or 932sent out immediately. 933There are three 934.Ar schedulers 935currently supported. 936.Bl -tag -width xxxx 937.It Ar cbq 938Class Based Queueing. 939.Ar Queues 940attached to an interface build a tree, thus each 941.Ar queue 942can have further child 943.Ar queues . 944Each queue can have a 945.Ar priority 946and a 947.Ar bandwidth 948assigned. 949.Ar Priority 950mainly controls the time packets take to get sent out, while 951.Ar bandwidth 952has primarily effects on throughput. 953.Ar cbq 954achieves both partitioning and sharing of link bandwidth 955by hierarchically structured classes. 956Each class has its own 957.Ar queue 958and is assigned its share of 959.Ar bandwidth . 960A child class can borrow bandwidth from its parent class 961as long as excess bandwidth is available 962(see the option 963.Ar borrow , 964below). 965.It Ar priq 966Priority Queueing. 967.Ar Queues 968are flat attached to the interface, thus, 969.Ar queues 970cannot have further child 971.Ar queues . 972Each 973.Ar queue 974has a unique 975.Ar priority 976assigned, ranging from 0 to 15. 977Packets in the 978.Ar queue 979with the highest 980.Ar priority 981are processed first. 982.It Ar hfsc 983Hierarchical Fair Service Curve. 984.Ar Queues 985attached to an interface build a tree, thus each 986.Ar queue 987can have further child 988.Ar queues . 989Each queue can have a 990.Ar priority 991and a 992.Ar bandwidth 993assigned. 994.Ar Priority 995mainly controls the time packets take to get sent out, while 996.Ar bandwidth 997primarily affects throughput. 998.Ar hfsc 999supports both link-sharing and guaranteed real-time services. 1000It employs a service curve based QoS model, 1001and its unique feature is an ability to decouple 1002.Ar delay 1003and 1004.Ar bandwidth 1005allocation. 1006.El 1007.Pp 1008The interfaces on which queueing should be activated are declared using 1009the 1010.Ar altq on 1011declaration. 1012.Ar altq on 1013has the following keywords: 1014.Bl -tag -width xxxx 1015.It Aq Ar interface 1016Queueing is enabled on the named interface. 1017.It Aq Ar scheduler 1018Specifies which queueing scheduler to use. 1019Currently supported values 1020are 1021.Ar cbq 1022for Class Based Queueing, 1023.Ar priq 1024for Priority Queueing and 1025.Ar hfsc 1026for the Hierarchical Fair Service Curve scheduler. 1027.It Ar bandwidth Aq Ar bw 1028The maximum bitrate for all queues on an 1029interface may be specified using the 1030.Ar bandwidth 1031keyword. 1032The value can be specified as an absolute value or as a 1033percentage of the interface bandwidth. 1034When using an absolute value, the suffixes 1035.Ar b , 1036.Ar Kb , 1037.Ar Mb , 1038and 1039.Ar Gb 1040are used to represent bits, kilobits, megabits, and 1041gigabits per second, respectively. 1042The value must not exceed the interface bandwidth. 1043If 1044.Ar bandwidth 1045is not specified, the interface bandwidth is used 1046(but take note that some interfaces do not know their bandwidth, 1047or can adapt their bandwidth rates). 1048.It Ar qlimit Aq Ar limit 1049The maximum number of packets held in the queue. 1050The default is 50. 1051.It Ar tbrsize Aq Ar size 1052Adjusts the size, in bytes, of the token bucket regulator. 1053If not specified, heuristics based on the 1054interface bandwidth are used to determine the size. 1055.It Ar queue Aq Ar list 1056Defines a list of subqueues to create on an interface. 1057.El 1058.Pp 1059In the following example, the interface dc0 1060should queue up to 5Mbps in four second-level queues using 1061Class Based Queueing. 1062Those four queues will be shown in a later example. 1063.Bd -literal -offset indent 1064altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh } 1065.Ed 1066.Pp 1067Once interfaces are activated for queueing using the 1068.Ar altq 1069directive, a sequence of 1070.Ar queue 1071directives may be defined. 1072The name associated with a 1073.Ar queue 1074must match a queue defined in the 1075.Ar altq 1076directive (e.g. mail), or, except for the 1077.Ar priq 1078.Ar scheduler , 1079in a parent 1080.Ar queue 1081declaration. 1082The following keywords can be used: 1083.Bl -tag -width xxxx 1084.It Ar on Aq Ar interface 1085Specifies the interface the queue operates on. 1086If not given, it operates on all matching interfaces. 1087.It Ar bandwidth Aq Ar bw 1088Specifies the maximum bitrate to be processed by the queue. 1089This value must not exceed the value of the parent 1090.Ar queue 1091and can be specified as an absolute value or a percentage of the parent 1092queue's bandwidth. 1093If not specified, defaults to 100% of the parent queue's bandwidth. 1094The 1095.Ar priq 1096scheduler does not support bandwidth specification. 1097.It Ar priority Aq Ar level 1098Between queues a priority level can be set. 1099For 1100.Ar cbq 1101and 1102.Ar hfsc , 1103the range is 0 to 7 and for 1104.Ar priq , 1105the range is 0 to 15. 1106The default for all is 1. 1107.Ar Priq 1108queues with a higher priority are always served first. 1109.Ar Cbq 1110and 1111.Ar Hfsc 1112queues with a higher priority are preferred in the case of overload. 1113.It Ar qlimit Aq Ar limit 1114The maximum number of packets held in the queue. 1115The default is 50. 1116.El 1117.Pp 1118The 1119.Ar scheduler 1120can get additional parameters with 1121.Xo Aq Ar scheduler 1122.Pf ( Aq Ar parameters ) . 1123.Xc 1124Parameters are as follows: 1125.Bl -tag -width Fl 1126.It Ar default 1127Packets not matched by another queue are assigned to this one. 1128Exactly one default queue is required. 1129.It Ar red 1130Enable RED (Random Early Detection) on this queue. 1131RED drops packets with a probability proportional to the average 1132queue length. 1133.It Ar rio 1134Enables RIO on this queue. 1135RIO is RED with IN/OUT, thus running 1136RED two times more than RIO would achieve the same effect. 1137RIO is currently not supported in the GENERIC kernel. 1138.It Ar ecn 1139Enables ECN (Explicit Congestion Notification) on this queue. 1140ECN implies RED. 1141.El 1142.Pp 1143The 1144.Ar cbq 1145.Ar scheduler 1146supports an additional option: 1147.Bl -tag -width Fl 1148.It Ar borrow 1149The queue can borrow bandwidth from the parent. 1150.El 1151.Pp 1152The 1153.Ar hfsc 1154.Ar scheduler 1155supports some additional options: 1156.Bl -tag -width Fl 1157.It Ar realtime Aq Ar sc 1158The minimum required bandwidth for the queue. 1159.It Ar upperlimit Aq Ar sc 1160The maximum allowed bandwidth for the queue. 1161.It Ar linkshare Aq Ar sc 1162The bandwidth share of a backlogged queue. 1163.El 1164.Pp 1165.Aq Ar sc 1166is an acronym for 1167.Ar service curve . 1168.Pp 1169The format for service curve specifications is 1170.Ar ( m1 , d , m2 ) . 1171.Ar m2 1172controls the bandwidth assigned to the queue. 1173.Ar m1 1174and 1175.Ar d 1176are optional and can be used to control the initial bandwidth assignment. 1177For the first 1178.Ar d 1179milliseconds the queue gets the bandwidth given as 1180.Ar m1 , 1181afterwards the value given in 1182.Ar m2 . 1183.Pp 1184Furthermore, with 1185.Ar cbq 1186and 1187.Ar hfsc , 1188child queues can be specified as in an 1189.Ar altq 1190declaration, thus building a tree of queues using a part of 1191their parent's bandwidth. 1192.Pp 1193Packets can be assigned to queues based on filter rules by using the 1194.Ar queue 1195keyword. 1196Normally only one 1197.Ar queue 1198is specified; when a second one is specified it will instead be used for 1199packets which have a 1200.Em TOS 1201of 1202.Em lowdelay 1203and for TCP ACKs with no data payload. 1204.Pp 1205To continue the previous example, the examples below would specify the 1206four referenced 1207queues, plus a few child queues. 1208Interactive 1209.Xr ssh 1 1210sessions get priority over bulk transfers like 1211.Xr scp 1 1212and 1213.Xr sftp 1 . 1214The queues may then be referenced by filtering rules (see 1215.Sx PACKET FILTERING 1216below). 1217.Bd -literal 1218queue std bandwidth 10% cbq(default) 1219queue http bandwidth 60% priority 2 cbq(borrow red) \e 1220 { employees, developers } 1221queue developers bandwidth 75% cbq(borrow) 1222queue employees bandwidth 15% 1223queue mail bandwidth 10% priority 0 cbq(borrow ecn) 1224queue ssh bandwidth 20% cbq(borrow) { ssh_interactive, ssh_bulk } 1225queue ssh_interactive bandwidth 50% priority 7 cbq(borrow) 1226queue ssh_bulk bandwidth 50% priority 0 cbq(borrow) 1227 1228block return out on dc0 inet all queue std 1229pass out on dc0 inet proto tcp from $developerhosts to any port 80 \e 1230 queue developers 1231pass out on dc0 inet proto tcp from $employeehosts to any port 80 \e 1232 queue employees 1233pass out on dc0 inet proto tcp from any to any port 22 \e 1234 queue(ssh_bulk, ssh_interactive) 1235pass out on dc0 inet proto tcp from any to any port 25 \e 1236 queue mail 1237.Ed 1238.Sh QUEUEING with dummynet 1239Queueing can also be done with 1240.Xr dummynet 4 . 1241Queues and pipes can be created with 1242.Xr dnctl 8 . 1243.Pp 1244Packets can be assigned to queues and pipes using 1245.Ar dnqueue 1246and 1247.Ar dnpipe 1248respectively. 1249.Pp 1250Both 1251.Ar dnqueue 1252and 1253.Ar dnpipe 1254take either a single pipe or queue number or two numbers as arguments. 1255The first pipe or queue number will be used to shape the traffic in the rule 1256direction, the second will be used to shape the traffic in the reverse 1257direction. 1258If the rule does not specify a direction the first packet to create state will 1259be shaped according to the first number, and the response traffic according to 1260the second. 1261.Pp 1262If the 1263.Xr dummynet 4 1264module is not loaded any traffic sent into a queue or pipe will be dropped. 1265.Sh TRANSLATION 1266Translation rules modify either the source or destination address of the 1267packets associated with a stateful connection. 1268A stateful connection is automatically created to track packets matching 1269such a rule as long as they are not blocked by the filtering section of 1270.Nm pf.conf . 1271The translation engine modifies the specified address and/or port in the 1272packet, recalculates IP, TCP and UDP checksums as necessary, and passes 1273it to the packet filter for evaluation. 1274.Pp 1275Since translation occurs before filtering the filter 1276engine will see packets as they look after any 1277addresses and ports have been translated. 1278Filter rules will therefore have to filter based on the translated 1279address and port number. 1280Packets that match a translation rule are only automatically passed if 1281the 1282.Ar pass 1283modifier is given, otherwise they are 1284still subject to 1285.Ar block 1286and 1287.Ar pass 1288rules. 1289.Pp 1290The state entry created permits 1291.Xr pf 4 1292to keep track of the original address for traffic associated with that state 1293and correctly direct return traffic for that connection. 1294.Pp 1295Various types of translation are possible with pf: 1296.Bl -tag -width xxxx 1297.It Ar binat 1298A 1299.Ar binat 1300rule specifies a bidirectional mapping between an external IP netblock 1301and an internal IP netblock. 1302.It Ar nat 1303A 1304.Ar nat 1305rule specifies that IP addresses are to be changed as the packet 1306traverses the given interface. 1307This technique allows one or more IP addresses 1308on the translating host to support network traffic for a larger range of 1309machines on an "inside" network. 1310Although in theory any IP address can be used on the inside, it is strongly 1311recommended that one of the address ranges defined by RFC 1918 be used. 1312These netblocks are: 1313.Bd -literal 131410.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8) 1315172.16.0.0 - 172.31.255.255 (i.e., 172.16/12) 1316192.168.0.0 - 192.168.255.255 (i.e., 192.168/16) 1317.Ed 1318.It Pa rdr 1319The packet is redirected to another destination and possibly a 1320different port. 1321.Ar rdr 1322rules can optionally specify port ranges instead of single ports. 1323rdr ... port 2000:2999 -\*(Gt ... port 4000 1324redirects ports 2000 to 2999 (inclusive) to port 4000. 1325rdr ... port 2000:2999 -\*(Gt ... port 4000:* 1326redirects port 2000 to 4000, 2001 to 4001, ..., 2999 to 4999. 1327.El 1328.Pp 1329In addition to modifying the address, some translation rules may modify 1330source or destination ports for 1331.Xr tcp 4 1332or 1333.Xr udp 4 1334connections; implicitly in the case of 1335.Ar nat 1336rules and explicitly in the case of 1337.Ar rdr 1338rules. 1339Port numbers are never translated with a 1340.Ar binat 1341rule. 1342.Pp 1343Evaluation order of the translation rules is dependent on the type 1344of the translation rules and of the direction of a packet. 1345.Ar binat 1346rules are always evaluated first. 1347Then either the 1348.Ar rdr 1349rules are evaluated on an inbound packet or the 1350.Ar nat 1351rules on an outbound packet. 1352Rules of the same type are evaluated in the same order in which they 1353appear in the ruleset. 1354The first matching rule decides what action is taken. 1355.Pp 1356The 1357.Ar no 1358option prefixed to a translation rule causes packets to remain untranslated, 1359much in the same way as 1360.Ar drop quick 1361works in the packet filter (see below). 1362If no rule matches the packet it is passed to the filter engine unmodified. 1363.Pp 1364Translation rules apply only to packets that pass through 1365the specified interface, and if no interface is specified, 1366translation is applied to packets on all interfaces. 1367For instance, redirecting port 80 on an external interface to an internal 1368web server will only work for connections originating from the outside. 1369Connections to the address of the external interface from local hosts will 1370not be redirected, since such packets do not actually pass through the 1371external interface. 1372Redirections cannot reflect packets back through the interface they arrive 1373on, they can only be redirected to hosts connected to different interfaces 1374or to the firewall itself. 1375.Pp 1376Note that redirecting external incoming connections to the loopback 1377address, as in 1378.Bd -literal -offset indent 1379rdr on ne3 inet proto tcp to port smtp -\*(Gt 127.0.0.1 port spamd 1380.Ed 1381.Pp 1382will effectively allow an external host to connect to daemons 1383bound solely to the loopback address, circumventing the traditional 1384blocking of such connections on a real interface. 1385Unless this effect is desired, any of the local non-loopback addresses 1386should be used as redirection target instead, which allows external 1387connections only to daemons bound to this address or not bound to 1388any address. 1389.Pp 1390See 1391.Sx TRANSLATION EXAMPLES 1392below. 1393.Sh PACKET FILTERING 1394.Xr pf 4 1395has the ability to 1396.Ar block 1397, 1398.Ar pass 1399and 1400.Ar match 1401packets based on attributes of their layer 3 (see 1402.Xr ip 4 1403and 1404.Xr ip6 4 ) 1405and layer 4 (see 1406.Xr icmp 4 , 1407.Xr icmp6 4 , 1408.Xr tcp 4 , 1409.Xr sctp 4 , 1410.Xr udp 4 ) 1411headers. 1412In addition, packets may also be 1413assigned to queues for the purpose of bandwidth control. 1414.Pp 1415For each packet processed by the packet filter, the filter rules are 1416evaluated in sequential order, from first to last. 1417For 1418.Ar block 1419and 1420.Ar pass 1421, the last matching rule decides what action is taken. 1422For 1423.Ar match 1424, rules are evaluated every time they match; the pass/block state of a packet 1425remains unchanged. 1426If no rule matches the packet, the default action is to pass 1427the packet. 1428.Pp 1429The following actions can be used in the filter: 1430.Bl -tag -width xxxx 1431.It Ar block 1432The packet is blocked. 1433There are a number of ways in which a 1434.Ar block 1435rule can behave when blocking a packet. 1436The default behaviour is to 1437.Ar drop 1438packets silently, however this can be overridden or made 1439explicit either globally, by setting the 1440.Ar block-policy 1441option, or on a per-rule basis with one of the following options: 1442.Pp 1443.Bl -tag -width xxxx -compact 1444.It Ar drop 1445The packet is silently dropped. 1446.It Ar return-rst 1447This applies only to 1448.Xr tcp 4 1449packets, and issues a TCP RST which closes the 1450connection. 1451.It Ar return-icmp 1452.It Ar return-icmp6 1453This causes ICMP messages to be returned for packets which match the rule. 1454By default this is an ICMP UNREACHABLE message, however this 1455can be overridden by specifying a message as a code or number. 1456.It Ar return 1457This causes a TCP RST to be returned for 1458.Xr tcp 4 1459packets, an SCTP ABORT for SCTP 1460and an ICMP UNREACHABLE for UDP and other packets. 1461.El 1462.Pp 1463Options returning ICMP packets currently have no effect if 1464.Xr pf 4 1465operates on a 1466.Xr if_bridge 4 , 1467as the code to support this feature has not yet been implemented. 1468.Pp 1469The simplest mechanism to block everything by default and only pass 1470packets that match explicit rules is specify a first filter rule of: 1471.Bd -literal -offset indent 1472block all 1473.Ed 1474.It Ar match 1475The packet is matched. 1476This mechanism is used to provide fine grained filtering without altering the 1477block/pass state of a packet. 1478.Ar match 1479rules differ from 1480.Ar block 1481and 1482.Ar pass 1483rules in that parameters are set every time a packet matches the rule, not only 1484on the last matching rule. 1485For the following parameters, this means that the parameter effectively becomes 1486"sticky" until explicitly overridden: 1487.Ar queue , 1488.Ar dnpipe , 1489.Ar dnqueue 1490. 1491.It Ar pass 1492The packet is passed; 1493state is created unless the 1494.Ar no state 1495option is specified. 1496.It Ar match 1497Action is unaltered, the previously matched rule's action still matters. 1498Match rules apply queue and rtable assignments for every matched packet, 1499subsequent matching pass or match rules can overwrite the assignment, 1500if they don't specify a queue or an rtable, respectively, the previously 1501set value remains. 1502Additionally, match rules can contain log statements; the is logging done 1503for each and every matching match rule, so it is possible to log a single 1504packet multiple times. 1505.El 1506.Pp 1507By default 1508.Xr pf 4 1509filters packets statefully; the first time a packet matches a 1510.Ar pass 1511rule, a state entry is created; for subsequent packets the filter checks 1512whether the packet matches any state. 1513If it does, the packet is passed without evaluation of any rules. 1514After the connection is closed or times out, the state entry is automatically 1515removed. 1516.Pp 1517This has several advantages. 1518For TCP connections, comparing a packet to a state involves checking 1519its sequence numbers, as well as TCP timestamps if a 1520.Ar scrub reassemble tcp 1521rule applies to the connection. 1522If these values are outside the narrow windows of expected 1523values, the packet is dropped. 1524This prevents spoofing attacks, such as when an attacker sends packets with 1525a fake source address/port but does not know the connection's sequence 1526numbers. 1527Similarly, 1528.Xr pf 4 1529knows how to match ICMP replies to states. 1530For example, 1531.Bd -literal -offset indent 1532pass out inet proto icmp all icmp-type echoreq 1533.Ed 1534.Pp 1535allows echo requests (such as those created by 1536.Xr ping 8 ) 1537out statefully, and matches incoming echo replies correctly to states. 1538.Pp 1539Also, looking up states is usually faster than evaluating rules. 1540If there are 50 rules, all of them are evaluated sequentially in O(n). 1541Even with 50000 states, only 16 comparisons are needed to match a 1542state, since states are stored in a binary search tree that allows 1543searches in O(log2 n). 1544.Pp 1545Furthermore, correct handling of ICMP error messages is critical to 1546many protocols, particularly TCP. 1547.Xr pf 4 1548matches ICMP error messages to the correct connection, checks them against 1549connection parameters, and passes them if appropriate. 1550For example if an ICMP source quench message referring to a stateful TCP 1551connection arrives, it will be matched to the state and get passed. 1552.Pp 1553Finally, state tracking is required for 1554.Ar nat , binat No and Ar rdr 1555rules, in order to track address and port translations and reverse the 1556translation on returning packets. 1557.Pp 1558.Xr pf 4 1559will also create state for other protocols which are effectively stateless by 1560nature. 1561UDP packets are matched to states using only host addresses and ports, 1562and other protocols are matched to states using only the host addresses. 1563.Pp 1564If stateless filtering of individual packets is desired, 1565the 1566.Ar no state 1567keyword can be used to specify that state will not be created 1568if this is the last matching rule. 1569A number of parameters can also be set to affect how 1570.Xr pf 4 1571handles state tracking. 1572See 1573.Sx STATEFUL TRACKING OPTIONS 1574below for further details. 1575.Sh PARAMETERS 1576The rule parameters specify the packets to which a rule applies. 1577A packet always comes in on, or goes out through, one interface. 1578Most parameters are optional. 1579If a parameter is specified, the rule only applies to packets with 1580matching attributes. 1581Certain parameters can be expressed as lists, in which case 1582.Xr pfctl 8 1583generates all needed rule combinations. 1584.Bl -tag -width xxxx 1585.It Ar in No or Ar out 1586This rule applies to incoming or outgoing packets. 1587If neither 1588.Ar in 1589nor 1590.Ar out 1591are specified, the rule will match packets in both directions. 1592.It Ar log 1593In addition to the action specified, a log message is generated. 1594Only the packet that establishes the state is logged, 1595unless the 1596.Ar no state 1597option is specified. 1598The logged packets are sent to a 1599.Xr pflog 4 1600interface, by default 1601.Ar pflog0 . 1602This interface is monitored by the 1603.Xr pflogd 8 1604logging daemon, which dumps the logged packets to the file 1605.Pa /var/log/pflog 1606in 1607.Xr pcap 3 1608binary format. 1609.It Ar log (all) 1610Used to force logging of all packets for a connection. 1611This is not necessary when 1612.Ar no state 1613is explicitly specified. 1614As with 1615.Ar log , 1616packets are logged to 1617.Xr pflog 4 . 1618.It Ar log (user) 1619Logs the 1620.Ux 1621user ID of the user that owns the socket and the PID of the process that 1622has the socket open where the packet is sourced from or destined to 1623(depending on which socket is local). 1624This is in addition to the normal information logged. 1625.Pp 1626Only the first packet 1627logged via 1628.Ar log (all, user) 1629will have the user credentials logged when using stateful matching. 1630.It Ar log (to Aq Ar interface ) 1631Send logs to the specified 1632.Xr pflog 4 1633interface instead of 1634.Ar pflog0 . 1635.It Ar quick 1636If a packet matches a rule which has the 1637.Ar quick 1638option set, this rule 1639is considered the last matching rule, and evaluation of subsequent rules 1640is skipped. 1641.It Ar on Aq Ar interface 1642This rule applies only to packets coming in on, or going out through, this 1643particular interface or interface group. 1644For more information on interface groups, 1645see the 1646.Ic group 1647keyword in 1648.Xr ifconfig 8 . 1649.It Aq Ar af 1650This rule applies only to packets of this address family. 1651Supported values are 1652.Ar inet 1653and 1654.Ar inet6 . 1655.It Ar proto Aq Ar protocol 1656This rule applies only to packets of this protocol. 1657Common protocols are 1658.Xr icmp 4 , 1659.Xr icmp6 4 , 1660.Xr tcp 4 , 1661.Xr sctp 4 , 1662and 1663.Xr udp 4 . 1664For a list of all the protocol name to number mappings used by 1665.Xr pfctl 8 , 1666see the file 1667.Pa /etc/protocols . 1668.It Xo 1669.Ar from Aq Ar source 1670.Ar port Aq Ar source 1671.Ar os Aq Ar source 1672.Ar to Aq Ar dest 1673.Ar port Aq Ar dest 1674.Xc 1675This rule applies only to packets with the specified source and destination 1676addresses and ports. 1677.Pp 1678Addresses can be specified in CIDR notation (matching netblocks), as 1679symbolic host names, interface names or interface group names, or as any 1680of the following keywords: 1681.Pp 1682.Bl -tag -width xxxxxxxxxxxxxx -compact 1683.It Ar any 1684Any address. 1685.It Ar no-route 1686Any address which is not currently routable. 1687.It Ar urpf-failed 1688Any source address that fails a unicast reverse path forwarding (URPF) 1689check, i.e. packets coming in on an interface other than that which holds 1690the route back to the packet's source address. 1691.It Aq Ar table 1692Any address that matches the given table. 1693.El 1694.Pp 1695Ranges of addresses are specified by using the 1696.Sq - 1697operator. 1698For instance: 1699.Dq 10.1.1.10 - 10.1.1.12 1700means all addresses from 10.1.1.10 to 10.1.1.12, 1701hence addresses 10.1.1.10, 10.1.1.11, and 10.1.1.12. 1702.Pp 1703Interface names and interface group names can have modifiers appended: 1704.Pp 1705.Bl -tag -width xxxxxxxxxxxx -compact 1706.It Ar :network 1707Translates to the network(s) attached to the interface. 1708.It Ar :broadcast 1709Translates to the interface's broadcast address(es). 1710.It Ar :peer 1711Translates to the point-to-point interface's peer address(es). 1712.It Ar :0 1713Do not include interface aliases. 1714.El 1715.Pp 1716Host names may also have the 1717.Ar :0 1718option appended to restrict the name resolution to the first of each 1719v4 and non-link-local v6 address found. 1720.Pp 1721Host name resolution and interface to address translation are done at 1722ruleset load-time. 1723When the address of an interface (or host name) changes (under DHCP or PPP, 1724for instance), the ruleset must be reloaded for the change to be reflected 1725in the kernel. 1726Surrounding the interface name (and optional modifiers) in parentheses 1727changes this behaviour. 1728When the interface name is surrounded by parentheses, the rule is 1729automatically updated whenever the interface changes its address. 1730The ruleset does not need to be reloaded. 1731This is especially useful with 1732.Ar nat . 1733.Pp 1734Ports can be specified either by number or by name. 1735For example, port 80 can be specified as 1736.Em www . 1737For a list of all port name to number mappings used by 1738.Xr pfctl 8 , 1739see the file 1740.Pa /etc/services . 1741.Pp 1742Ports and ranges of ports are specified by using these operators: 1743.Bd -literal -offset indent 1744= (equal) 1745!= (unequal) 1746\*(Lt (less than) 1747\*(Le (less than or equal) 1748\*(Gt (greater than) 1749\*(Ge (greater than or equal) 1750: (range including boundaries) 1751\*(Gt\*(Lt (range excluding boundaries) 1752\*(Lt\*(Gt (except range) 1753.Ed 1754.Pp 1755.Sq \*(Gt\*(Lt , 1756.Sq \*(Lt\*(Gt 1757and 1758.Sq \&: 1759are binary operators (they take two arguments). 1760For instance: 1761.Bl -tag -width Fl 1762.It Ar port 2000:2004 1763means 1764.Sq all ports \*(Ge 2000 and \*(Le 2004 , 1765hence ports 2000, 2001, 2002, 2003 and 2004. 1766.It Ar port 2000 \*(Gt\*(Lt 2004 1767means 1768.Sq all ports \*(Gt 2000 and \*(Lt 2004 , 1769hence ports 2001, 2002 and 2003. 1770.It Ar port 2000 \*(Lt\*(Gt 2004 1771means 1772.Sq all ports \*(Lt 2000 or \*(Gt 2004 , 1773hence ports 1-1999 and 2005-65535. 1774.El 1775.Pp 1776The operating system of the source host can be specified in the case of TCP 1777rules with the 1778.Ar OS 1779modifier. 1780See the 1781.Sx OPERATING SYSTEM FINGERPRINTING 1782section for more information. 1783.Pp 1784The host, port and OS specifications are optional, as in the following examples: 1785.Bd -literal -offset indent 1786pass in all 1787pass in from any to any 1788pass in proto tcp from any port \*(Le 1024 to any 1789pass in proto tcp from any to any port 25 1790pass in proto tcp from 10.0.0.0/8 port \*(Gt 1024 \e 1791 to ! 10.1.2.3 port != ssh 1792pass in proto tcp from any os "OpenBSD" 1793.Ed 1794.It Ar all 1795This is equivalent to "from any to any". 1796.It Ar group Aq Ar group 1797Similar to 1798.Ar user , 1799this rule only applies to packets of sockets owned by the specified group. 1800.It Ar user Aq Ar user 1801This rule only applies to packets of sockets owned by the specified user. 1802For outgoing connections initiated from the firewall, this is the user 1803that opened the connection. 1804For incoming connections to the firewall itself, this is the user that 1805listens on the destination port. 1806For forwarded connections, where the firewall is not a connection endpoint, 1807the user and group are 1808.Em unknown . 1809.Pp 1810All packets, both outgoing and incoming, of one connection are associated 1811with the same user and group. 1812Only TCP and UDP packets can be associated with users; for other protocols 1813these parameters are ignored. 1814.Pp 1815User and group refer to the effective (as opposed to the real) IDs, in 1816case the socket is created by a setuid/setgid process. 1817User and group IDs are stored when a socket is created; 1818when a process creates a listening socket as root (for instance, by 1819binding to a privileged port) and subsequently changes to another 1820user ID (to drop privileges), the credentials will remain root. 1821.Pp 1822User and group IDs can be specified as either numbers or names. 1823The syntax is similar to the one for ports. 1824The value 1825.Em unknown 1826matches packets of forwarded connections. 1827.Em unknown 1828can only be used with the operators 1829.Cm = 1830and 1831.Cm != . 1832Other constructs like 1833.Cm user \*(Ge unknown 1834are invalid. 1835Forwarded packets with unknown user and group ID match only rules 1836that explicitly compare against 1837.Em unknown 1838with the operators 1839.Cm = 1840or 1841.Cm != . 1842For instance 1843.Cm user \*(Ge 0 1844does not match forwarded packets. 1845The following example allows only selected users to open outgoing 1846connections: 1847.Bd -literal -offset indent 1848block out proto { tcp, udp } all 1849pass out proto { tcp, udp } all user { \*(Lt 1000, dhartmei } 1850.Ed 1851.It Xo Ar flags Aq Ar a 1852.Pf / Ns Aq Ar b 1853.No \*(Ba / Ns Aq Ar b 1854.No \*(Ba any 1855.Xc 1856This rule only applies to TCP packets that have the flags 1857.Aq Ar a 1858set out of set 1859.Aq Ar b . 1860Flags not specified in 1861.Aq Ar b 1862are ignored. 1863For stateful connections, the default is 1864.Ar flags S/SA . 1865To indicate that flags should not be checked at all, specify 1866.Ar flags any . 1867The flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R. 1868.Bl -tag -width Fl 1869.It Ar flags S/S 1870Flag SYN is set. 1871The other flags are ignored. 1872.It Ar flags S/SA 1873This is the default setting for stateful connections. 1874Out of SYN and ACK, exactly SYN may be set. 1875SYN, SYN+PSH and SYN+RST match, but SYN+ACK, ACK and ACK+RST do not. 1876This is more restrictive than the previous example. 1877.It Ar flags /SFRA 1878If the first set is not specified, it defaults to none. 1879All of SYN, FIN, RST and ACK must be unset. 1880.El 1881.Pp 1882Because 1883.Ar flags S/SA 1884is applied by default (unless 1885.Ar no state 1886is specified), only the initial SYN packet of a TCP handshake will create 1887a state for a TCP connection. 1888It is possible to be less restrictive, and allow state creation from 1889intermediate 1890.Pq non-SYN 1891packets, by specifying 1892.Ar flags any . 1893This will cause 1894.Xr pf 4 1895to synchronize to existing connections, for instance 1896if one flushes the state table. 1897However, states created from such intermediate packets may be missing 1898connection details such as the TCP window scaling factor. 1899States which modify the packet flow, such as those affected by 1900.Ar nat , binat No or Ar rdr 1901rules, 1902.Ar modulate No or Ar synproxy state 1903options, or scrubbed with 1904.Ar reassemble tcp 1905will also not be recoverable from intermediate packets. 1906Such connections will stall and time out. 1907.It Xo Ar icmp-type Aq Ar type 1908.Ar code Aq Ar code 1909.Xc 1910.It Xo Ar icmp6-type Aq Ar type 1911.Ar code Aq Ar code 1912.Xc 1913This rule only applies to ICMP or ICMPv6 packets with the specified type 1914and code. 1915Text names for ICMP types and codes are listed in 1916.Xr icmp 4 1917and 1918.Xr icmp6 4 . 1919This parameter is only valid for rules that cover protocols ICMP or 1920ICMP6. 1921The protocol and the ICMP type indicator 1922.Po 1923.Ar icmp-type 1924or 1925.Ar icmp6-type 1926.Pc 1927must match. 1928.It Xo Ar tos Aq Ar string 1929.No \*(Ba Aq Ar number 1930.Xc 1931This rule applies to packets with the specified 1932.Em TOS 1933bits set. 1934.Em TOS 1935may be 1936given as one of 1937.Ar critical , 1938.Ar inetcontrol , 1939.Ar lowdelay , 1940.Ar netcontrol , 1941.Ar throughput , 1942.Ar reliability , 1943or one of the DiffServ Code Points: 1944.Ar ef , 1945.Ar va , 1946.Ar af11 No ... Ar af43 , 1947.Ar cs0 No ... Ar cs7 ; 1948or as either hex or decimal. 1949.Pp 1950For example, the following rules are identical: 1951.Bd -literal -offset indent 1952pass all tos lowdelay 1953pass all tos 0x10 1954pass all tos 16 1955.Ed 1956.It Ar allow-opts 1957By default, IPv4 packets with IP options or IPv6 packets with routing 1958extension headers are blocked. 1959When 1960.Ar allow-opts 1961is specified for a 1962.Ar pass 1963rule, packets that pass the filter based on that rule (last matching) 1964do so even if they contain IP options or routing extension headers. 1965For packets that match state, the rule that initially created the 1966state is used. 1967The implicit 1968.Ar pass 1969rule that is used when a packet does not match any rules does not 1970allow IP options. 1971.It Ar label Aq Ar string 1972Adds a label (name) to the rule, which can be used to identify the rule. 1973For instance, 1974pfctl -s labels 1975shows per-rule statistics for rules that have labels. 1976.Pp 1977The following macros can be used in labels: 1978.Pp 1979.Bl -tag -width $srcaddr -compact -offset indent 1980.It Ar $if 1981The interface. 1982.It Ar $srcaddr 1983The source IP address. 1984.It Ar $dstaddr 1985The destination IP address. 1986.It Ar $srcport 1987The source port specification. 1988.It Ar $dstport 1989The destination port specification. 1990.It Ar $proto 1991The protocol name. 1992.It Ar $nr 1993The rule number. 1994.El 1995.Pp 1996For example: 1997.Bd -literal -offset indent 1998ips = \&"{ 1.2.3.4, 1.2.3.5 }\&" 1999pass in proto tcp from any to $ips \e 2000 port \*(Gt 1023 label \&"$dstaddr:$dstport\&" 2001.Ed 2002.Pp 2003expands to 2004.Bd -literal -offset indent 2005pass in inet proto tcp from any to 1.2.3.4 \e 2006 port \*(Gt 1023 label \&"1.2.3.4:\*(Gt1023\&" 2007pass in inet proto tcp from any to 1.2.3.5 \e 2008 port \*(Gt 1023 label \&"1.2.3.5:\*(Gt1023\&" 2009.Ed 2010.Pp 2011The macro expansion for the 2012.Ar label 2013directive occurs only at configuration file parse time, not during runtime. 2014.It Ar ridentifier Aq Ar number 2015Add an identifier (number) to the rule, which can be used to correlate the rule 2016to pflog entries, even after ruleset updates. 2017.It Xo Ar queue Aq Ar queue 2018.No \*(Ba ( Aq Ar queue , 2019.Aq Ar queue ) 2020.Xc 2021Packets matching this rule will be assigned to the specified queue. 2022If two queues are given, packets which have a 2023.Em TOS 2024of 2025.Em lowdelay 2026and TCP ACKs with no data payload will be assigned to the second one. 2027See 2028.Sx QUEUEING 2029for setup details. 2030.Pp 2031For example: 2032.Bd -literal -offset indent 2033pass in proto tcp to port 25 queue mail 2034pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio) 2035.Ed 2036.It Cm set prio Ar priority | Pq Ar priority , priority 2037Packets matching this rule will be assigned a specific queueing priority. 2038Priorities are assigned as integers 0 through 7. 2039If the packet is transmitted on a 2040.Xr vlan 4 2041interface, the queueing priority will be written as the priority 2042code point in the 802.1Q VLAN header. 2043If two priorities are given, packets which have a TOS of 2044.Cm lowdelay 2045and TCP ACKs with no data payload will be assigned to the second one. 2046.Pp 2047For example: 2048.Bd -literal -offset indent 2049pass in proto tcp to port 25 set prio 2 2050pass in proto tcp to port 22 set prio (2, 5) 2051.Ed 2052.It Ar tag Aq Ar string 2053Packets matching this rule will be tagged with the 2054specified string. 2055The tag acts as an internal marker that can be used to 2056identify these packets later on. 2057This can be used, for example, to provide trust between 2058interfaces and to determine if packets have been 2059processed by translation rules. 2060Tags are 2061.Qq sticky , 2062meaning that the packet will be tagged even if the rule 2063is not the last matching rule. 2064Further matching rules can replace the tag with a 2065new one but will not remove a previously applied tag. 2066A packet is only ever assigned one tag at a time. 2067Packet tagging can be done during 2068.Ar nat , 2069.Ar rdr , 2070.Ar binat 2071or 2072.Ar ether 2073rules in addition to filter rules. 2074Tags take the same macros as labels (see above). 2075.It Ar tagged Aq Ar string 2076Used with filter, translation or scrub rules 2077to specify that packets must already 2078be tagged with the given tag in order to match the rule. 2079Inverse tag matching can also be done 2080by specifying the 2081.Cm !\& 2082operator before the 2083.Ar tagged 2084keyword. 2085.It Ar rtable Aq Ar number 2086Used to select an alternate routing table for the routing lookup. 2087Only effective before the route lookup happened, i.e. when filtering inbound. 2088.It Xo Ar divert-to Aq Ar host 2089.Ar port Aq Ar port 2090.Xc 2091Used to redirect packets to a local socket bound to 2092.Ar host 2093and 2094.Ar port . 2095The packets will not be modified, so 2096.Xr getsockname 2 2097on the socket will return the original destination address of the packet. 2098.It Ar divert-reply 2099Used to receive replies for sockets that are bound to addresses 2100which are not local to the machine. 2101See 2102.Xr setsockopt 2 2103for information on how to bind these sockets. 2104.It Ar probability Aq Ar number 2105A probability attribute can be attached to a rule, with a value set between 21060 and 1, bounds not included. 2107In that case, the rule will be honoured using the given probability value 2108only. 2109For example, the following rule will drop 20% of incoming ICMP packets: 2110.Bd -literal -offset indent 2111block in proto icmp probability 20% 2112.Ed 2113.It Ar prio Aq Ar number 2114Only match packets which have the given queueing priority assigned. 2115.El 2116.Sh ROUTING 2117If a packet matches a rule with a route option set, the packet filter will 2118route the packet according to the type of route option. 2119When such a rule creates state, the route option is also applied to all 2120packets matching the same connection. 2121.Bl -tag -width xxxx 2122.It Ar route-to 2123The 2124.Ar route-to 2125option routes the packet to the specified interface with an optional address 2126for the next hop. 2127When a 2128.Ar route-to 2129rule creates state, only packets that pass in the same direction as the 2130filter rule specifies will be routed in this way. 2131Packets passing in the opposite direction (replies) are not affected 2132and are routed normally. 2133.It Ar reply-to 2134The 2135.Ar reply-to 2136option is similar to 2137.Ar route-to , 2138but routes packets that pass in the opposite direction (replies) to the 2139specified interface. 2140Opposite direction is only defined in the context of a state entry, and 2141.Ar reply-to 2142is useful only in rules that create state. 2143It can be used on systems with multiple external connections to 2144route all outgoing packets of a connection through the interface 2145the incoming connection arrived through (symmetric routing enforcement). 2146.It Ar dup-to 2147The 2148.Ar dup-to 2149option creates a duplicate of the packet and routes it like 2150.Ar route-to . 2151The original packet gets routed as it normally would. 2152.El 2153.Sh POOL OPTIONS 2154For 2155.Ar nat 2156and 2157.Ar rdr 2158rules, (as well as for the 2159.Ar route-to , 2160.Ar reply-to 2161and 2162.Ar dup-to 2163rule options) for which there is a single redirection address which has a 2164subnet mask smaller than 32 for IPv4 or 128 for IPv6 (more than one IP 2165address), a variety of different methods for assigning this address can be 2166used: 2167.Bl -tag -width xxxx 2168.It Ar bitmask 2169The 2170.Ar bitmask 2171option applies the network portion of the redirection address to the address 2172to be modified (source with 2173.Ar nat , 2174destination with 2175.Ar rdr ) . 2176.It Ar random 2177The 2178.Ar random 2179option selects an address at random within the defined block of addresses. 2180.It Ar source-hash 2181The 2182.Ar source-hash 2183option uses a hash of the source address to determine the redirection address, 2184ensuring that the redirection address is always the same for a given source. 2185An optional key can be specified after this keyword either in hex or as a 2186string; by default 2187.Xr pfctl 8 2188randomly generates a key for source-hash every time the 2189ruleset is reloaded. 2190.It Ar round-robin 2191The 2192.Ar round-robin 2193option loops through the redirection address(es). 2194.Pp 2195When more than one redirection address is specified, 2196.Ar round-robin 2197is the only permitted pool type. 2198.It Ar static-port 2199With 2200.Ar nat 2201rules, the 2202.Ar static-port 2203option prevents 2204.Xr pf 4 2205from modifying the source port on TCP and UDP packets. 2206.It Xo Ar map-e-portset Aq Ar psid-offset 2207.No / Aq Ar psid-len 2208.No / Aq Ar psid 2209.Xc 2210With 2211.Ar nat 2212rules, the 2213.Ar map-e-portset 2214option enables the source port translation of MAP-E (RFC 7597) Customer Edge. 2215In order to make the host act as a MAP-E Customer Edge, setting up a tunneling 2216interface and pass rules for encapsulated packets are required in addition 2217to the map-e-portset nat rule. 2218.Pp 2219For example: 2220.Bd -literal -offset indent 2221nat on $gif_mape_if from $int_if:network to any \e 2222 -> $ipv4_mape_src map-e-portset 6/8/0x34 2223.Ed 2224.Pp 2225sets PSID offset 6, PSID length 8, PSID 0x34. 2226.El 2227.Pp 2228Additionally, the 2229.Ar sticky-address 2230option can be specified to help ensure that multiple connections from the 2231same source are mapped to the same redirection address. 2232This option can be used with the 2233.Ar random 2234and 2235.Ar round-robin 2236pool options. 2237Note that by default these associations are destroyed as soon as there are 2238no longer states which refer to them; in order to make the mappings last 2239beyond the lifetime of the states, increase the global options with 2240.Ar set timeout src.track . 2241See 2242.Sx STATEFUL TRACKING OPTIONS 2243for more ways to control the source tracking. 2244.Sh STATE MODULATION 2245Much of the security derived from TCP is attributable to how well the 2246initial sequence numbers (ISNs) are chosen. 2247Some popular stack implementations choose 2248.Em very 2249poor ISNs and thus are normally susceptible to ISN prediction exploits. 2250By applying a 2251.Ar modulate state 2252rule to a TCP connection, 2253.Xr pf 4 2254will create a high quality random sequence number for each connection 2255endpoint. 2256.Pp 2257The 2258.Ar modulate state 2259directive implicitly keeps state on the rule and is 2260only applicable to TCP connections. 2261.Pp 2262For instance: 2263.Bd -literal -offset indent 2264block all 2265pass out proto tcp from any to any modulate state 2266pass in proto tcp from any to any port 25 flags S/SFRA modulate state 2267.Ed 2268.Pp 2269Note that modulated connections will not recover when the state table 2270is lost (firewall reboot, flushing the state table, etc...). 2271.Xr pf 4 2272will not be able to infer a connection again after the state table flushes 2273the connection's modulator. 2274When the state is lost, the connection may be left dangling until the 2275respective endpoints time out the connection. 2276It is possible on a fast local network for the endpoints to start an ACK 2277storm while trying to resynchronize after the loss of the modulator. 2278The default 2279.Ar flags 2280settings (or a more strict equivalent) should be used on 2281.Ar modulate state 2282rules to prevent ACK storms. 2283.Pp 2284Note that alternative methods are available 2285to prevent loss of the state table 2286and allow for firewall failover. 2287See 2288.Xr carp 4 2289and 2290.Xr pfsync 4 2291for further information. 2292.Sh SYN PROXY 2293By default, 2294.Xr pf 4 2295passes packets that are part of a 2296.Xr tcp 4 2297handshake between the endpoints. 2298The 2299.Ar synproxy state 2300option can be used to cause 2301.Xr pf 4 2302itself to complete the handshake with the active endpoint, perform a handshake 2303with the passive endpoint, and then forward packets between the endpoints. 2304.Pp 2305No packets are sent to the passive endpoint before the active endpoint has 2306completed the handshake, hence so-called SYN floods with spoofed source 2307addresses will not reach the passive endpoint, as the sender can't complete the 2308handshake. 2309.Pp 2310The proxy is transparent to both endpoints, they each see a single 2311connection from/to the other endpoint. 2312.Xr pf 4 2313chooses random initial sequence numbers for both handshakes. 2314Once the handshakes are completed, the sequence number modulators 2315(see previous section) are used to translate further packets of the 2316connection. 2317.Ar synproxy state 2318includes 2319.Ar modulate state . 2320.Pp 2321Rules with 2322.Ar synproxy 2323will not work if 2324.Xr pf 4 2325operates on a 2326.Xr bridge 4 . 2327.Pp 2328Example: 2329.Bd -literal -offset indent 2330pass in proto tcp from any to any port www synproxy state 2331.Ed 2332.Sh STATEFUL TRACKING OPTIONS 2333A number of options related to stateful tracking can be applied on a 2334per-rule basis. 2335.Ar keep state , 2336.Ar modulate state 2337and 2338.Ar synproxy state 2339support these options, and 2340.Ar keep state 2341must be specified explicitly to apply options to a rule. 2342.Pp 2343.Bl -tag -width xxxx -compact 2344.It Ar max Aq Ar number 2345Limits the number of concurrent states the rule may create. 2346When this limit is reached, further packets that would create 2347state will not match this rule until existing states time out. 2348.It Ar no-sync 2349Prevent state changes for states created by this rule from appearing on the 2350.Xr pfsync 4 2351interface. 2352.It Xo Aq Ar timeout 2353.Aq Ar seconds 2354.Xc 2355Changes the timeout values used for states created by this rule. 2356For a list of all valid timeout names, see 2357.Sx OPTIONS 2358above. 2359.It Ar sloppy 2360Uses a sloppy TCP connection tracker that does not check sequence 2361numbers at all, which makes insertion and ICMP teardown attacks way 2362easier. 2363This is intended to be used in situations where one does not see all 2364packets of a connection, e.g. in asymmetric routing situations. 2365Cannot be used with modulate or synproxy state. 2366.El 2367.Pp 2368Multiple options can be specified, separated by commas: 2369.Bd -literal -offset indent 2370pass in proto tcp from any to any \e 2371 port www keep state \e 2372 (max 100, source-track rule, max-src-nodes 75, \e 2373 max-src-states 3, tcp.established 60, tcp.closing 5) 2374.Ed 2375.Pp 2376When the 2377.Ar source-track 2378keyword is specified, the number of states per source IP is tracked. 2379.Pp 2380.Bl -tag -width xxxx -compact 2381.It Ar source-track rule 2382The maximum number of states created by this rule is limited by the rule's 2383.Ar max-src-nodes 2384and 2385.Ar max-src-states 2386options. 2387Only state entries created by this particular rule count toward the rule's 2388limits. 2389.It Ar source-track global 2390The number of states created by all rules that use this option is limited. 2391Each rule can specify different 2392.Ar max-src-nodes 2393and 2394.Ar max-src-states 2395options, however state entries created by any participating rule count towards 2396each individual rule's limits. 2397.El 2398.Pp 2399The following limits can be set: 2400.Pp 2401.Bl -tag -width xxxx -compact 2402.It Ar max-src-nodes Aq Ar number 2403Limits the maximum number of source addresses which can simultaneously 2404have state table entries. 2405.It Ar max-src-states Aq Ar number 2406Limits the maximum number of simultaneous state entries that a single 2407source address can create with this rule. 2408.El 2409.Pp 2410For stateful TCP connections, limits on established connections (connections 2411which have completed the TCP 3-way handshake) can also be enforced 2412per source IP. 2413.Pp 2414.Bl -tag -width xxxx -compact 2415.It Ar max-src-conn Aq Ar number 2416Limits the maximum number of simultaneous TCP connections which have 2417completed the 3-way handshake that a single host can make. 2418.It Xo Ar max-src-conn-rate Aq Ar number 2419.No / Aq Ar seconds 2420.Xc 2421Limit the rate of new connections over a time interval. 2422The connection rate is an approximation calculated as a moving average. 2423.El 2424.Pp 2425Because the 3-way handshake ensures that the source address is not being 2426spoofed, more aggressive action can be taken based on these limits. 2427With the 2428.Ar overload Aq Ar table 2429state option, source IP addresses which hit either of the limits on 2430established connections will be added to the named table. 2431This table can be used in the ruleset to block further activity from 2432the offending host, redirect it to a tarpit process, or restrict its 2433bandwidth. 2434.Pp 2435The optional 2436.Ar flush 2437keyword kills all states created by the matching rule which originate 2438from the host which exceeds these limits. 2439The 2440.Ar global 2441modifier to the flush command kills all states originating from the 2442offending host, regardless of which rule created the state. 2443.Pp 2444For example, the following rules will protect the webserver against 2445hosts making more than 100 connections in 10 seconds. 2446Any host which connects faster than this rate will have its address added 2447to the 2448.Aq bad_hosts 2449table and have all states originating from it flushed. 2450Any new packets arriving from this host will be dropped unconditionally 2451by the block rule. 2452.Bd -literal -offset indent 2453block quick from \*(Ltbad_hosts\*(Gt 2454pass in on $ext_if proto tcp to $webserver port www keep state \e 2455 (max-src-conn-rate 100/10, overload \*(Ltbad_hosts\*(Gt flush global) 2456.Ed 2457.Sh OPERATING SYSTEM FINGERPRINTING 2458Passive OS Fingerprinting is a mechanism to inspect nuances of a TCP 2459connection's initial SYN packet and guess at the host's operating system. 2460Unfortunately these nuances are easily spoofed by an attacker so the 2461fingerprint is not useful in making security decisions. 2462But the fingerprint is typically accurate enough to make policy decisions 2463upon. 2464.Pp 2465The fingerprints may be specified by operating system class, by 2466version, or by subtype/patchlevel. 2467The class of an operating system is typically the vendor or genre 2468and would be 2469.Ox 2470for the 2471.Xr pf 4 2472firewall itself. 2473The version of the oldest available 2474.Ox 2475release on the main FTP site 2476would be 2.6 and the fingerprint would be written 2477.Pp 2478.Dl \&"OpenBSD 2.6\&" 2479.Pp 2480The subtype of an operating system is typically used to describe the 2481patchlevel if that patch led to changes in the TCP stack behavior. 2482In the case of 2483.Ox , 2484the only subtype is for a fingerprint that was 2485normalized by the 2486.Ar no-df 2487scrub option and would be specified as 2488.Pp 2489.Dl \&"OpenBSD 3.3 no-df\&" 2490.Pp 2491Fingerprints for most popular operating systems are provided by 2492.Xr pf.os 5 . 2493Once 2494.Xr pf 4 2495is running, a complete list of known operating system fingerprints may 2496be listed by running: 2497.Pp 2498.Dl # pfctl -so 2499.Pp 2500Filter rules can enforce policy at any level of operating system specification 2501assuming a fingerprint is present. 2502Policy could limit traffic to approved operating systems or even ban traffic 2503from hosts that aren't at the latest service pack. 2504.Pp 2505The 2506.Ar unknown 2507class can also be used as the fingerprint which will match packets for 2508which no operating system fingerprint is known. 2509.Pp 2510Examples: 2511.Bd -literal -offset indent 2512pass out proto tcp from any os OpenBSD 2513block out proto tcp from any os Doors 2514block out proto tcp from any os "Doors PT" 2515block out proto tcp from any os "Doors PT SP3" 2516block out from any os "unknown" 2517pass on lo0 proto tcp from any os "OpenBSD 3.3 lo0" 2518.Ed 2519.Pp 2520Operating system fingerprinting is limited only to the TCP SYN packet. 2521This means that it will not work on other protocols and will not match 2522a currently established connection. 2523.Pp 2524Caveat: operating system fingerprints are occasionally wrong. 2525There are three problems: an attacker can trivially craft his packets to 2526appear as any operating system he chooses; 2527an operating system patch could change the stack behavior and no fingerprints 2528will match it until the database is updated; 2529and multiple operating systems may have the same fingerprint. 2530.Sh BLOCKING SPOOFED TRAFFIC 2531"Spoofing" is the faking of IP addresses, typically for malicious 2532purposes. 2533The 2534.Ar antispoof 2535directive expands to a set of filter rules which will block all 2536traffic with a source IP from the network(s) directly connected 2537to the specified interface(s) from entering the system through 2538any other interface. 2539.Pp 2540For example, the line 2541.Bd -literal -offset indent 2542antispoof for lo0 2543.Ed 2544.Pp 2545expands to 2546.Bd -literal -offset indent 2547block drop in on ! lo0 inet from 127.0.0.1/8 to any 2548block drop in on ! lo0 inet6 from ::1 to any 2549.Ed 2550.Pp 2551For non-loopback interfaces, there are additional rules to block incoming 2552packets with a source IP address identical to the interface's IP(s). 2553For example, assuming the interface wi0 had an IP address of 10.0.0.1 and a 2554netmask of 255.255.255.0, 2555the line 2556.Bd -literal -offset indent 2557antispoof for wi0 inet 2558.Ed 2559.Pp 2560expands to 2561.Bd -literal -offset indent 2562block drop in on ! wi0 inet from 10.0.0.0/24 to any 2563block drop in inet from 10.0.0.1 to any 2564.Ed 2565.Pp 2566Caveat: Rules created by the 2567.Ar antispoof 2568directive interfere with packets sent over loopback interfaces 2569to local addresses. 2570One should pass these explicitly. 2571.Sh FRAGMENT HANDLING 2572The size of IP datagrams (packets) can be significantly larger than the 2573maximum transmission unit (MTU) of the network. 2574In cases when it is necessary or more efficient to send such large packets, 2575the large packet will be fragmented into many smaller packets that will each 2576fit onto the wire. 2577Unfortunately for a firewalling device, only the first logical fragment will 2578contain the necessary header information for the subprotocol that allows 2579.Xr pf 4 2580to filter on things such as TCP ports or to perform NAT. 2581.Pp 2582Besides the use of 2583.Ar scrub 2584rules as described in 2585.Sx TRAFFIC NORMALIZATION 2586above, there are three options for handling fragments in the packet filter. 2587.Pp 2588One alternative is to filter individual fragments with filter rules. 2589If no 2590.Ar scrub 2591rule applies to a fragment, it is passed to the filter. 2592Filter rules with matching IP header parameters decide whether the 2593fragment is passed or blocked, in the same way as complete packets 2594are filtered. 2595Without reassembly, fragments can only be filtered based on IP header 2596fields (source/destination address, protocol), since subprotocol header 2597fields are not available (TCP/UDP port numbers, ICMP code/type). 2598The 2599.Ar fragment 2600option can be used to restrict filter rules to apply only to 2601fragments, but not complete packets. 2602Filter rules without the 2603.Ar fragment 2604option still apply to fragments, if they only specify IP header fields. 2605For instance, the rule 2606.Bd -literal -offset indent 2607pass in proto tcp from any to any port 80 2608.Ed 2609.Pp 2610never applies to a fragment, even if the fragment is part of a TCP 2611packet with destination port 80, because without reassembly this information 2612is not available for each fragment. 2613This also means that fragments cannot create new or match existing 2614state table entries, which makes stateful filtering and address 2615translation (NAT, redirection) for fragments impossible. 2616.Pp 2617It's also possible to reassemble only certain fragments by specifying 2618source or destination addresses or protocols as parameters in 2619.Ar scrub 2620rules. 2621.Pp 2622In most cases, the benefits of reassembly outweigh the additional 2623memory cost, and it's recommended to use 2624.Ar scrub 2625rules to reassemble 2626all fragments via the 2627.Ar fragment reassemble 2628modifier. 2629.Pp 2630The memory allocated for fragment caching can be limited using 2631.Xr pfctl 8 . 2632Once this limit is reached, fragments that would have to be cached 2633are dropped until other entries time out. 2634The timeout value can also be adjusted. 2635.Pp 2636When forwarding reassembled IPv6 packets, pf refragments them with 2637the original maximum fragment size. 2638This allows the sender to determine the optimal fragment size by 2639path MTU discovery. 2640.Sh ANCHORS 2641Besides the main ruleset, 2642.Xr pfctl 8 2643can load rulesets into 2644.Ar anchor 2645attachment points. 2646An 2647.Ar anchor 2648is a container that can hold rules, address tables, and other anchors. 2649.Pp 2650An 2651.Ar anchor 2652has a name which specifies the path where 2653.Xr pfctl 8 2654can be used to access the anchor to perform operations on it, such as 2655attaching child anchors to it or loading rules into it. 2656Anchors may be nested, with components separated by 2657.Sq / 2658characters, similar to how file system hierarchies are laid out. 2659The main ruleset is actually the default anchor, so filter and 2660translation rules, for example, may also be contained in any anchor. 2661.Pp 2662An anchor can reference another 2663.Ar anchor 2664attachment point 2665using the following kinds 2666of rules: 2667.Bl -tag -width xxxx 2668.It Ar nat-anchor Aq Ar name 2669Evaluates the 2670.Ar nat 2671rules in the specified 2672.Ar anchor . 2673.It Ar rdr-anchor Aq Ar name 2674Evaluates the 2675.Ar rdr 2676rules in the specified 2677.Ar anchor . 2678.It Ar binat-anchor Aq Ar name 2679Evaluates the 2680.Ar binat 2681rules in the specified 2682.Ar anchor . 2683.It Ar anchor Aq Ar name 2684Evaluates the filter rules in the specified 2685.Ar anchor . 2686.It Xo Ar load anchor 2687.Aq Ar name 2688.Ar from Aq Ar file 2689.Xc 2690Loads the rules from the specified file into the 2691anchor 2692.Ar name . 2693.El 2694.Pp 2695When evaluation of the main ruleset reaches an 2696.Ar anchor 2697rule, 2698.Xr pf 4 2699will proceed to evaluate all rules specified in that anchor. 2700.Pp 2701Matching filter and translation rules marked with the 2702.Ar quick 2703option are final and abort the evaluation of the rules in other 2704anchors and the main ruleset. 2705If the 2706.Ar anchor 2707itself is marked with the 2708.Ar quick 2709option, 2710ruleset evaluation will terminate when the anchor is exited if the packet is 2711matched by any rule within the anchor. 2712.Pp 2713.Ar anchor 2714rules are evaluated relative to the anchor in which they are contained. 2715For example, all 2716.Ar anchor 2717rules specified in the main ruleset will reference anchor 2718attachment points underneath the main ruleset, and 2719.Ar anchor 2720rules specified in a file loaded from a 2721.Ar load anchor 2722rule will be attached under that anchor point. 2723.Pp 2724Rules may be contained in 2725.Ar anchor 2726attachment points which do not contain any rules when the main ruleset 2727is loaded, and later such anchors can be manipulated through 2728.Xr pfctl 8 2729without reloading the main ruleset or other anchors. 2730For example, 2731.Bd -literal -offset indent 2732ext_if = \&"kue0\&" 2733block on $ext_if all 2734anchor spam 2735pass out on $ext_if all 2736pass in on $ext_if proto tcp from any \e 2737 to $ext_if port smtp 2738.Ed 2739.Pp 2740blocks all packets on the external interface by default, then evaluates 2741all rules in the 2742.Ar anchor 2743named "spam", and finally passes all outgoing connections and 2744incoming connections to port 25. 2745.Bd -literal -offset indent 2746# echo \&"block in quick from 1.2.3.4 to any\&" \&| \e 2747 pfctl -a spam -f - 2748.Ed 2749.Pp 2750This loads a single rule into the 2751.Ar anchor , 2752which blocks all packets from a specific address. 2753.Pp 2754The anchor can also be populated by adding a 2755.Ar load anchor 2756rule after the 2757.Ar anchor 2758rule: 2759.Bd -literal -offset indent 2760anchor spam 2761load anchor spam from "/etc/pf-spam.conf" 2762.Ed 2763.Pp 2764When 2765.Xr pfctl 8 2766loads 2767.Nm pf.conf , 2768it will also load all the rules from the file 2769.Pa /etc/pf-spam.conf 2770into the anchor. 2771.Pp 2772Optionally, 2773.Ar anchor 2774rules can specify packet filtering parameters using the same syntax as 2775filter rules. 2776When parameters are used, the 2777.Ar anchor 2778rule is only evaluated for matching packets. 2779This allows conditional evaluation of anchors, like: 2780.Bd -literal -offset indent 2781block on $ext_if all 2782anchor spam proto tcp from any to any port smtp 2783pass out on $ext_if all 2784pass in on $ext_if proto tcp from any to $ext_if port smtp 2785.Ed 2786.Pp 2787The rules inside 2788.Ar anchor 2789spam are only evaluated for 2790.Ar tcp 2791packets with destination port 25. 2792Hence, 2793.Bd -literal -offset indent 2794# echo \&"block in quick from 1.2.3.4 to any" \&| \e 2795 pfctl -a spam -f - 2796.Ed 2797.Pp 2798will only block connections from 1.2.3.4 to port 25. 2799.Pp 2800Anchors may end with the asterisk 2801.Pq Sq * 2802character, which signifies that all anchors attached at that point 2803should be evaluated in the alphabetical ordering of their anchor name. 2804For example, 2805.Bd -literal -offset indent 2806anchor "spam/*" 2807.Ed 2808.Pp 2809will evaluate each rule in each anchor attached to the 2810.Li spam 2811anchor. 2812Note that it will only evaluate anchors that are directly attached to the 2813.Li spam 2814anchor, and will not descend to evaluate anchors recursively. 2815.Pp 2816Since anchors are evaluated relative to the anchor in which they are 2817contained, there is a mechanism for accessing the parent and ancestor 2818anchors of a given anchor. 2819Similar to file system path name resolution, if the sequence 2820.Dq .. 2821appears as an anchor path component, the parent anchor of the current 2822anchor in the path evaluation at that point will become the new current 2823anchor. 2824As an example, consider the following: 2825.Bd -literal -offset indent 2826# echo ' anchor "spam/allowed" ' | pfctl -f - 2827# echo -e ' anchor "../banned" \en pass' | \e 2828 pfctl -a spam/allowed -f - 2829.Ed 2830.Pp 2831Evaluation of the main ruleset will lead into the 2832.Li spam/allowed 2833anchor, which will evaluate the rules in the 2834.Li spam/banned 2835anchor, if any, before finally evaluating the 2836.Ar pass 2837rule. 2838.Pp 2839Filter rule 2840.Ar anchors 2841can also be loaded inline in the ruleset within a brace ('{' '}') delimited 2842block. 2843Brace delimited blocks may contain rules or other brace-delimited blocks. 2844When anchors are loaded this way the anchor name becomes optional. 2845.Bd -literal -offset indent 2846anchor "external" on $ext_if { 2847 block 2848 anchor out { 2849 pass proto tcp from any to port { 25, 80, 443 } 2850 } 2851 pass in proto tcp to any port 22 2852} 2853.Ed 2854.Pp 2855Since the parser specification for anchor names is a string, any 2856reference to an anchor name containing 2857.Sq / 2858characters will require double quote 2859.Pq Sq \&" 2860characters around the anchor name. 2861.Sh SCTP CONSIDERATIONS 2862.Xr pf 4 2863supports 2864.Xr sctp 4 2865connections. 2866It can match ports, track state and NAT SCTP traffic. 2867However, it will not alter port numbers during nat or rdr translations. 2868Doing so would break SCTP multihoming. 2869.Sh TRANSLATION EXAMPLES 2870This example maps incoming requests on port 80 to port 8080, on 2871which a daemon is running (because, for example, it is not run as root, 2872and therefore lacks permission to bind to port 80). 2873.Bd -literal 2874# use a macro for the interface name, so it can be changed easily 2875ext_if = \&"ne3\&" 2876 2877# map daemon on 8080 to appear to be on 80 2878rdr on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 port 8080 2879.Ed 2880.Pp 2881If the 2882.Ar pass 2883modifier is given, packets matching the translation rule are passed without 2884inspecting the filter rules: 2885.Bd -literal 2886rdr pass on $ext_if proto tcp from any to any port 80 -\*(Gt 127.0.0.1 \e 2887 port 8080 2888.Ed 2889.Pp 2890In the example below, vlan12 is configured as 192.168.168.1; 2891the machine translates all packets coming from 192.168.168.0/24 to 204.92.77.111 2892when they are going out any interface except vlan12. 2893This has the net effect of making traffic from the 192.168.168.0/24 2894network appear as though it is the Internet routable address 2895204.92.77.111 to nodes behind any interface on the router except 2896for the nodes on vlan12. 2897(Thus, 192.168.168.1 can talk to the 192.168.168.0/24 nodes.) 2898.Bd -literal 2899nat on ! vlan12 from 192.168.168.0/24 to any -\*(Gt 204.92.77.111 2900.Ed 2901.Pp 2902In the example below, the machine sits between a fake internal 144.19.74.* 2903network, and a routable external IP of 204.92.77.100. 2904The 2905.Ar no nat 2906rule excludes protocol AH from being translated. 2907.Bd -literal 2908# NO NAT 2909no nat on $ext_if proto ah from 144.19.74.0/24 to any 2910nat on $ext_if from 144.19.74.0/24 to any -\*(Gt 204.92.77.100 2911.Ed 2912.Pp 2913In the example below, packets bound for one specific server, as well as those 2914generated by the sysadmins are not proxied; all other connections are. 2915.Bd -literal 2916# NO RDR 2917no rdr on $int_if proto { tcp, udp } from any to $server port 80 2918no rdr on $int_if proto { tcp, udp } from $sysadmins to any port 80 2919rdr on $int_if proto { tcp, udp } from any to any port 80 -\*(Gt 127.0.0.1 \e 2920 port 80 2921.Ed 2922.Pp 2923This longer example uses both a NAT and a redirection. 2924The external interface has the address 157.161.48.183. 2925On localhost, we are running 2926.Xr ftp-proxy 8 , 2927waiting for FTP sessions to be redirected to it. 2928The three mandatory anchors for 2929.Xr ftp-proxy 8 2930are omitted from this example; see the 2931.Xr ftp-proxy 8 2932manpage. 2933.Bd -literal 2934# NAT 2935# Translate outgoing packets' source addresses (any protocol). 2936# In this case, any address but the gateway's external address is mapped. 2937nat on $ext_if inet from ! ($ext_if) to any -\*(Gt ($ext_if) 2938 2939# NAT PROXYING 2940# Map outgoing packets' source port to an assigned proxy port instead of 2941# an arbitrary port. 2942# In this case, proxy outgoing isakmp with port 500 on the gateway. 2943nat on $ext_if inet proto udp from any port = isakmp to any -\*(Gt ($ext_if) \e 2944 port 500 2945 2946# BINAT 2947# Translate outgoing packets' source address (any protocol). 2948# Translate incoming packets' destination address to an internal machine 2949# (bidirectional). 2950binat on $ext_if from 10.1.2.150 to any -\*(Gt $ext_if 2951 2952# Translate packets arriving on $peer_if addressed to 172.22.16.0/20 2953# to the corresponding address in 172.21.16.0/20 (bidirectional). 2954binat on $peer_if from 172.21.16.0/20 to any -> 172.22.16.0/20 2955 2956# RDR 2957# Translate incoming packets' destination addresses. 2958# As an example, redirect a TCP and UDP port to an internal machine. 2959rdr on $ext_if inet proto tcp from any to ($ext_if) port 8080 \e 2960 -\*(Gt 10.1.2.151 port 22 2961rdr on $ext_if inet proto udp from any to ($ext_if) port 8080 \e 2962 -\*(Gt 10.1.2.151 port 53 2963 2964# RDR 2965# Translate outgoing ftp control connections to send them to localhost 2966# for proxying with ftp-proxy(8) running on port 8021. 2967rdr on $int_if proto tcp from any to any port 21 -\*(Gt 127.0.0.1 port 8021 2968.Ed 2969.Pp 2970In this example, a NAT gateway is set up to translate internal addresses 2971using a pool of public addresses (192.0.2.16/28) and to redirect 2972incoming web server connections to a group of web servers on the internal 2973network. 2974.Bd -literal 2975# NAT LOAD BALANCE 2976# Translate outgoing packets' source addresses using an address pool. 2977# A given source address is always translated to the same pool address by 2978# using the source-hash keyword. 2979nat on $ext_if inet from any to any -\*(Gt 192.0.2.16/28 source-hash 2980 2981# RDR ROUND ROBIN 2982# Translate incoming web server connections to a group of web servers on 2983# the internal network. 2984rdr on $ext_if proto tcp from any to any port 80 \e 2985 -\*(Gt { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin 2986.Ed 2987.Sh FILTER EXAMPLES 2988.Bd -literal 2989# The external interface is kue0 2990# (157.161.48.183, the only routable address) 2991# and the private network is 10.0.0.0/8, for which we are doing NAT. 2992 2993# use a macro for the interface name, so it can be changed easily 2994ext_if = \&"kue0\&" 2995 2996# normalize all incoming traffic 2997scrub in on $ext_if all fragment reassemble 2998 2999# block and log everything by default 3000block return log on $ext_if all 3001 3002# block anything coming from source we have no back routes for 3003block in from no-route to any 3004 3005# block packets whose ingress interface does not match the one in 3006# the route back to their source address 3007block in from urpf-failed to any 3008 3009# block and log outgoing packets that do not have our address as source, 3010# they are either spoofed or something is misconfigured (NAT disabled, 3011# for instance), we want to be nice and do not send out garbage. 3012block out log quick on $ext_if from ! 157.161.48.183 to any 3013 3014# silently drop broadcasts (cable modem noise) 3015block in quick on $ext_if from any to 255.255.255.255 3016 3017# block and log incoming packets from reserved address space and invalid 3018# addresses, they are either spoofed or misconfigured, we cannot reply to 3019# them anyway (hence, no return-rst). 3020block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \e 3021 192.168.0.0/16, 255.255.255.255/32 } to any 3022 3023# ICMP 3024 3025# pass out/in certain ICMP queries and keep state (ping) 3026# state matching is done on host addresses and ICMP id (not type/code), 3027# so replies (like 0/0 for 8/0) will match queries 3028# ICMP error messages (which always refer to a TCP/UDP packet) are 3029# handled by the TCP/UDP states 3030pass on $ext_if inet proto icmp all icmp-type 8 code 0 3031 3032# UDP 3033 3034# pass out all UDP connections and keep state 3035pass out on $ext_if proto udp all 3036 3037# pass in certain UDP connections and keep state (DNS) 3038pass in on $ext_if proto udp from any to any port domain 3039 3040# TCP 3041 3042# pass out all TCP connections and modulate state 3043pass out on $ext_if proto tcp all modulate state 3044 3045# pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT) 3046pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \e 3047 auth } 3048 3049# Do not allow Windows 9x SMTP connections since they are typically 3050# a viral worm. Alternately we could limit these OSes to 1 connection each. 3051block in on $ext_if proto tcp from any os {"Windows 95", "Windows 98"} \e 3052 to any port smtp 3053 3054# IPv6 3055# pass in/out all IPv6 traffic: note that we have to enable this in two 3056# different ways, on both our physical interface and our tunnel 3057pass quick on gif0 inet6 3058pass quick on $ext_if proto ipv6 3059 3060# Packet Tagging 3061 3062# three interfaces: $int_if, $ext_if, and $wifi_if (wireless). NAT is 3063# being done on $ext_if for all outgoing packets. tag packets in on 3064# $int_if and pass those tagged packets out on $ext_if. all other 3065# outgoing packets (i.e., packets from the wireless network) are only 3066# permitted to access port 80. 3067 3068pass in on $int_if from any to any tag INTNET 3069pass in on $wifi_if from any to any 3070 3071block out on $ext_if from any to any 3072pass out quick on $ext_if tagged INTNET 3073pass out on $ext_if proto tcp from any to any port 80 3074 3075# tag incoming packets as they are redirected to spamd(8). use the tag 3076# to pass those packets through the packet filter. 3077 3078rdr on $ext_if inet proto tcp from \*(Ltspammers\*(Gt to port smtp \e 3079 tag SPAMD -\*(Gt 127.0.0.1 port spamd 3080 3081block in on $ext_if 3082pass in on $ext_if inet proto tcp tagged SPAMD 3083.Ed 3084.Sh GRAMMAR 3085Syntax for 3086.Nm 3087in BNF: 3088.Bd -literal 3089line = ( option | ether-rule | pf-rule | nat-rule | binat-rule | 3090 rdr-rule | antispoof-rule | altq-rule | queue-rule | 3091 trans-anchors | anchor-rule | anchor-close | load-anchor | 3092 table-rule | include ) 3093 3094option = "set" ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] | 3095 [ "ruleset-optimization" [ "none" | "basic" | "profile" ]] | 3096 [ "optimization" [ "default" | "normal" | 3097 "high-latency" | "satellite" | 3098 "aggressive" | "conservative" ] ] 3099 [ "limit" ( limit-item | "{" limit-list "}" ) ] | 3100 [ "loginterface" ( interface-name | "none" ) ] | 3101 [ "block-policy" ( "drop" | "return" ) ] | 3102 [ "state-policy" ( "if-bound" | "floating" ) ] 3103 [ "state-defaults" state-opts ] 3104 [ "require-order" ( "yes" | "no" ) ] 3105 [ "fingerprints" filename ] | 3106 [ "skip on" ifspec ] | 3107 [ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] 3108 [ "keepcounters" ] ) 3109 3110ether-rule = "ether" etheraction [ ( "in" | "out" ) ] 3111 [ "quick" ] [ "on" ifspec ] [ "bridge-to" interface-name ] 3112 [ etherprotospec ] etherhosts [ "l3" hosts ] 3113 [ etherfilteropt-list ] 3114 3115pf-rule = action [ ( "in" | "out" ) ] 3116 [ "log" [ "(" logopts ")"] ] [ "quick" ] 3117 [ "on" ifspec ] [ route ] [ af ] [ protospec ] 3118 hosts [ filteropt-list ] 3119 3120logopts = logopt [ "," logopts ] 3121logopt = "all" | "user" | "to" interface-name 3122 3123etherfilteropt-list = etherfilteropt-list etherfilteropt | etherfilteropt 3124etherfilteropt = "tag" string | "tagged" string | "queue" ( string ) | 3125 "ridentifier" number | "label" string 3126 3127filteropt-list = filteropt-list filteropt | filteropt 3128filteropt = user | group | flags | icmp-type | icmp6-type | "tos" tos | 3129 ( "no" | "keep" | "modulate" | "synproxy" ) "state" 3130 [ "(" state-opts ")" ] | 3131 "fragment" | "no-df" | "min-ttl" number | "set-tos" tos | 3132 "max-mss" number | "random-id" | "reassemble tcp" | 3133 fragmentation | "allow-opts" | 3134 "label" string | "tag" string | [ ! ] "tagged" string | 3135 "set prio" ( number | "(" number [ [ "," ] number ] ")" ) | 3136 "queue" ( string | "(" string [ [ "," ] string ] ")" ) | 3137 "rtable" number | "probability" number"%" | "prio" number | 3138 "dnpipe" ( number | "(" number "," number ")" ) | 3139 "dnqueue" ( number | "(" number "," number ")" ) | 3140 "ridentifier" number 3141 3142nat-rule = [ "no" ] "nat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3143 [ "on" ifspec ] [ af ] 3144 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3145 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3146 [ portspec ] [ pooltype ] [ "static-port" ] 3147 [ "map-e-portset" number "/" number "/" number ] ] 3148 3149binat-rule = [ "no" ] "binat" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3150 [ "on" interface-name ] [ af ] 3151 [ "proto" ( proto-name | proto-number ) ] 3152 "from" address [ "/" mask-bits ] "to" ipspec 3153 [ "tag" string ] [ "tagged" string ] 3154 [ "-\*(Gt" address [ "/" mask-bits ] ] 3155 3156rdr-rule = [ "no" ] "rdr" [ "pass" [ "log" [ "(" logopts ")" ] ] ] 3157 [ "on" ifspec ] [ af ] 3158 [ protospec ] hosts [ "tag" string ] [ "tagged" string ] 3159 [ "-\*(Gt" ( redirhost | "{" redirhost-list "}" ) 3160 [ portspec ] [ pooltype ] ] 3161 3162antispoof-rule = "antispoof" [ "log" ] [ "quick" ] 3163 "for" ifspec [ af ] [ "label" string ] 3164 [ "ridentifier" number ] 3165 3166table-rule = "table" "\*(Lt" string "\*(Gt" [ tableopts-list ] 3167tableopts-list = tableopts-list tableopts | tableopts 3168tableopts = "persist" | "const" | "counters" | "file" string | 3169 "{" [ tableaddr-list ] "}" 3170tableaddr-list = tableaddr-list [ "," ] tableaddr-spec | tableaddr-spec 3171tableaddr-spec = [ "!" ] tableaddr [ "/" mask-bits ] 3172tableaddr = hostname | ifspec | "self" | 3173 ipv4-dotted-quad | ipv6-coloned-hex 3174 3175altq-rule = "altq on" interface-name queueopts-list 3176 "queue" subqueue 3177queue-rule = "queue" string [ "on" interface-name ] queueopts-list 3178 subqueue 3179 3180anchor-rule = "anchor" [ string ] [ ( "in" | "out" ) ] [ "on" ifspec ] 3181 [ af ] [ protospec ] [ hosts ] [ filteropt-list ] [ "{" ] 3182 3183anchor-close = "}" 3184 3185trans-anchors = ( "nat-anchor" | "rdr-anchor" | "binat-anchor" ) string 3186 [ "on" ifspec ] [ af ] [ "proto" ] [ protospec ] [ hosts ] 3187 3188load-anchor = "load anchor" string "from" filename 3189 3190queueopts-list = queueopts-list queueopts | queueopts 3191queueopts = [ "bandwidth" bandwidth-spec ] | 3192 [ "qlimit" number ] | [ "tbrsize" number ] | 3193 [ "priority" number ] | [ schedulers ] 3194schedulers = ( cbq-def | priq-def | hfsc-def ) 3195bandwidth-spec = "number" ( "b" | "Kb" | "Mb" | "Gb" | "%" ) 3196 3197etheraction = "pass" | "block" 3198action = "pass" | "match" | "block" [ return ] | [ "no" ] "scrub" 3199return = "drop" | "return" | "return-rst" [ "( ttl" number ")" ] | 3200 "return-icmp" [ "(" icmpcode [ [ "," ] icmp6code ] ")" ] | 3201 "return-icmp6" [ "(" icmp6code ")" ] 3202icmpcode = ( icmp-code-name | icmp-code-number ) 3203icmp6code = ( icmp6-code-name | icmp6-code-number ) 3204 3205ifspec = ( [ "!" ] ( interface-name | interface-group ) ) | 3206 "{" interface-list "}" 3207interface-list = [ "!" ] ( interface-name | interface-group ) 3208 [ [ "," ] interface-list ] 3209route = ( "route-to" | "reply-to" | "dup-to" ) 3210 ( routehost | "{" routehost-list "}" ) 3211 [ pooltype ] 3212af = "inet" | "inet6" 3213 3214etherprotospec = "proto" ( proto-number | "{" etherproto-list "}" ) 3215etherproto-list = proto-number [ [ "," ] etherproto-list ] 3216protospec = "proto" ( proto-name | proto-number | 3217 "{" proto-list "}" ) 3218proto-list = ( proto-name | proto-number ) [ [ "," ] proto-list ] 3219 3220etherhosts = "from" macaddress "to" macaddress 3221macaddress = mac | mac "/" masklen | mac "&" mask 3222 3223hosts = "all" | 3224 "from" ( "any" | "no-route" | "urpf-failed" | "self" | host | 3225 "{" host-list "}" ) [ port ] [ os ] 3226 "to" ( "any" | "no-route" | "self" | host | 3227 "{" host-list "}" ) [ port ] 3228 3229ipspec = "any" | host | "{" host-list "}" 3230host = [ "!" ] ( address [ "/" mask-bits ] | "\*(Lt" string "\*(Gt" ) 3231redirhost = address [ "/" mask-bits ] 3232routehost = "(" interface-name [ address [ "/" mask-bits ] ] ")" 3233address = ( interface-name | interface-group | 3234 "(" ( interface-name | interface-group ) ")" | 3235 hostname | ipv4-dotted-quad | ipv6-coloned-hex ) 3236host-list = host [ [ "," ] host-list ] 3237redirhost-list = redirhost [ [ "," ] redirhost-list ] 3238routehost-list = routehost [ [ "," ] routehost-list ] 3239 3240port = "port" ( unary-op | binary-op | "{" op-list "}" ) 3241portspec = "port" ( number | name ) [ ":" ( "*" | number | name ) ] 3242os = "os" ( os-name | "{" os-list "}" ) 3243user = "user" ( unary-op | binary-op | "{" op-list "}" ) 3244group = "group" ( unary-op | binary-op | "{" op-list "}" ) 3245 3246unary-op = [ "=" | "!=" | "\*(Lt" | "\*(Le" | "\*(Gt" | "\*(Ge" ] 3247 ( name | number ) 3248binary-op = number ( "\*(Lt\*(Gt" | "\*(Gt\*(Lt" | ":" ) number 3249op-list = ( unary-op | binary-op ) [ [ "," ] op-list ] 3250 3251os-name = operating-system-name 3252os-list = os-name [ [ "," ] os-list ] 3253 3254flags = "flags" ( [ flag-set ] "/" flag-set | "any" ) 3255flag-set = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ] 3256 [ "W" ] 3257 3258icmp-type = "icmp-type" ( icmp-type-code | "{" icmp-list "}" ) 3259icmp6-type = "icmp6-type" ( icmp-type-code | "{" icmp-list "}" ) 3260icmp-type-code = ( icmp-type-name | icmp-type-number ) 3261 [ "code" ( icmp-code-name | icmp-code-number ) ] 3262icmp-list = icmp-type-code [ [ "," ] icmp-list ] 3263 3264tos = ( "lowdelay" | "throughput" | "reliability" | 3265 [ "0x" ] number ) 3266 3267state-opts = state-opt [ [ "," ] state-opts ] 3268state-opt = ( "max" number | "no-sync" | timeout | "sloppy" | 3269 "source-track" [ ( "rule" | "global" ) ] | 3270 "max-src-nodes" number | "max-src-states" number | 3271 "max-src-conn" number | 3272 "max-src-conn-rate" number "/" number | 3273 "overload" "\*(Lt" string "\*(Gt" [ "flush" ] | 3274 "if-bound" | "floating" ) 3275 3276fragmentation = [ "fragment reassemble" ] 3277 3278timeout-list = timeout [ [ "," ] timeout-list ] 3279timeout = ( "tcp.first" | "tcp.opening" | "tcp.established" | 3280 "tcp.closing" | "tcp.finwait" | "tcp.closed" | 3281 "udp.first" | "udp.single" | "udp.multiple" | 3282 "icmp.first" | "icmp.error" | 3283 "other.first" | "other.single" | "other.multiple" | 3284 "frag" | "interval" | "src.track" | 3285 "adaptive.start" | "adaptive.end" ) number 3286 3287limit-list = limit-item [ [ "," ] limit-list ] 3288limit-item = ( "states" | "frags" | "src-nodes" ) number 3289 3290pooltype = ( "bitmask" | "random" | 3291 "source-hash" [ ( hex-key | string-key ) ] | 3292 "round-robin" ) [ sticky-address ] 3293 3294subqueue = string | "{" queue-list "}" 3295queue-list = string [ [ "," ] string ] 3296cbq-def = "cbq" [ "(" cbq-opt [ [ "," ] cbq-opt ] ")" ] 3297priq-def = "priq" [ "(" priq-opt [ [ "," ] priq-opt ] ")" ] 3298hfsc-def = "hfsc" [ "(" hfsc-opt [ [ "," ] hfsc-opt ] ")" ] 3299cbq-opt = ( "default" | "borrow" | "red" | "ecn" | "rio" ) 3300priq-opt = ( "default" | "red" | "ecn" | "rio" ) 3301hfsc-opt = ( "default" | "red" | "ecn" | "rio" | 3302 linkshare-sc | realtime-sc | upperlimit-sc ) 3303linkshare-sc = "linkshare" sc-spec 3304realtime-sc = "realtime" sc-spec 3305upperlimit-sc = "upperlimit" sc-spec 3306sc-spec = ( bandwidth-spec | 3307 "(" bandwidth-spec number bandwidth-spec ")" ) 3308include = "include" filename 3309.Ed 3310.Sh FILES 3311.Bl -tag -width "/etc/protocols" -compact 3312.It Pa /etc/hosts 3313Host name database. 3314.It Pa /etc/pf.conf 3315Default location of the ruleset file. 3316The file has to be created manually as it is not installed with a 3317standard installation. 3318.It Pa /etc/pf.os 3319Default location of OS fingerprints. 3320.It Pa /etc/protocols 3321Protocol name database. 3322.It Pa /etc/services 3323Service name database. 3324.El 3325.Sh SEE ALSO 3326.Xr altq 4 , 3327.Xr carp 4 , 3328.Xr icmp 4 , 3329.Xr icmp6 4 , 3330.Xr ip 4 , 3331.Xr ip6 4 , 3332.Xr pf 4 , 3333.Xr pfsync 4 , 3334.Xr tcp 4 , 3335.Xr sctp 4 , 3336.Xr udp 4 , 3337.Xr hosts 5 , 3338.Xr pf.os 5 , 3339.Xr protocols 5 , 3340.Xr services 5 , 3341.Xr ftp-proxy 8 , 3342.Xr pfctl 8 , 3343.Xr pflogd 8 3344.Sh HISTORY 3345The 3346.Nm 3347file format first appeared in 3348.Ox 3.0 . 3349