.\" $OpenBSD: pf.conf.5,v 1.337 2005/08/06 19:52:36 jmc Exp $ .\" .\" Copyright (c) 2002, Daniel Hartmeier .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" .\" - Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" - Redistributions in binary form must reproduce the above .\" copyright notice, this list of conditions and the following .\" disclaimer in the documentation and/or other materials provided .\" with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS .\" "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT .\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS .\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE .\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, .\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; .\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER .\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN .\" ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE .\" POSSIBILITY OF SUCH DAMAGE. .\" .Dd November 19, 2002 .Dt PF.CONF 5 .Os .Sh NAME .Nm pf.conf .Nd packet filter configuration file .Sh DESCRIPTION The .Xr pf 4 packet filter modifies, drops or passes packets according to rules or definitions specified in .Nm pf.conf . .Sh STATEMENT ORDER There are seven types of statements in .Nm pf.conf : .Bl -tag -width xxxx .It Cm Macros User-defined variables may be defined and used later, simplifying the configuration file. Macros must be defined before they are referenced in .Nm pf.conf . .It Cm Tables Tables provide a mechanism for increasing the performance and flexibility of rules with large numbers of source or destination addresses. .It Cm Options Options tune the behaviour of the packet filtering engine. .It Cm Traffic Normalization Li (e.g. Em scrub ) Traffic normalization protects internal machines against inconsistencies in Internet protocols and implementations. .It Cm Queueing Queueing provides rule-based bandwidth control. .It Cm Translation Li (Various forms of NAT) Translation rules specify how addresses are to be mapped or redirected to other addresses. .It Cm Packet Filtering Stateful and stateless packet filtering provides rule-based blocking or passing of packets. .El .Pp With the exception of .Cm macros and .Cm tables , the types of statements should be grouped and appear in .Nm pf.conf in the order shown above, as this matches the operation of the underlying packet filtering engine. By default .Xr pfctl 8 enforces this order (see .Ar set require-order below). .Sh MACROS Much like .Xr cpp 1 or .Xr m4 1 , macros can be defined that will later be expanded in context. Macro names must start with a letter, and may contain letters, digits and underscores. Macro names may not be reserved words (for example .Ar pass , .Ar in , .Ar out ) . Macros are not expanded inside quotes. .Pp For example, .Bd -literal -offset indent ext_if = \&"kue0\&" all_ifs = \&"{\&" $ext_if lo0 \&"}\&" pass out on $ext_if from any to any keep state pass in on $ext_if proto tcp from any to any port 25 keep state .Ed .Sh TABLES Tables are named structures which can hold a collection of addresses and networks. Lookups against tables in .Xr pf 4 are relatively fast, making a single rule with tables much more efficient, in terms of processor usage and memory consumption, than a large number of rules which differ only in IP address (either created explicitly or automatically by rule expansion). .Pp Tables can be used as the source or destination of filter rules, .Ar scrub rules or translation rules such as .Ar nat or .Ar rdr (see below for details on the various rule types). Tables can also be used for the redirect address of .Ar nat and .Ar rdr rules and in the routing options of filter rules, but only for .Ar round-robin pools. .Pp Tables can be defined with any of the following .Xr pfctl 8 mechanisms. As with macros, reserved words may not be used as table names. .Bl -tag -width "manually" .It Ar manually Persistent tables can be manually created with the .Ar add or .Ar replace option of .Xr pfctl 8 , before or after the ruleset has been loaded. .It Pa pf.conf Table definitions can be placed directly in this file, and loaded at the same time as other rules are loaded, atomically. Table definitions inside .Nm pf.conf use the .Ar table statement, and are especially useful to define non-persistent tables. The contents of a pre-existing table defined without a list of addresses to initialize it is not altered when .Nm pf.conf is loaded. A table initialized with the empty list, .Li { } , will be cleared on load. .El .Pp Tables may be defined with the following two attributes: .Bl -tag -width persist .It Ar persist The .Ar persist flag forces the kernel to keep the table even when no rules refer to it. If the flag is not set, the kernel will automatically remove the table when the last rule referring to it is flushed. .It Ar const The .Ar const flag prevents the user from altering the contents of the table once it has been created. Without that flag, .Xr pfctl 8 can be used to add or remove addresses from the table at any time, even when running with .Xr securelevel 7 = 2. .El .Pp For example, .Bd -literal -offset indent table const { 10/8, 172.16/12, 192.168/16 } table persist block on fxp0 from { , } to any .Ed .Pp creates a table called private, to hold RFC 1918 private network blocks, and a table called badhosts, which is initially empty. A filter rule is set up to block all traffic coming from addresses listed in either table. The private table cannot have its contents changed and the badhosts table will exist even when no active filter rules reference it. Addresses may later be added to the badhosts table, so that traffic from these hosts can be blocked by using .Bd -literal -offset indent # pfctl -t badhosts -Tadd 204.92.77.111 .Ed .Pp A table can also be initialized with an address list specified in one or more external files, using the following syntax: .Bd -literal -offset indent table persist file \&"/etc/spammers\&" file \&"/etc/openrelays\&" block on fxp0 from to any .Ed .Pp The files .Pa /etc/spammers and .Pa /etc/openrelays list IP addresses, one per line. Any lines beginning with a # are treated as comments and ignored. In addition to being specified by IP address, hosts may also be specified by their hostname. When the resolver is called to add a hostname to a table, .Em all resulting IPv4 and IPv6 addresses are placed into the table. IP addresses can also be entered in a table by specifying a valid interface name, a valid interface group or the .Em self keyword, in which case all addresses assigned to the interface(s) will be added to the table. .Sh OPTIONS .Xr pf 4 may be tuned for various situations using the .Ar set command. .Bl -tag -width xxxx .It Ar set timeout .Pp .Bl -tag -width "src.track" -compact .It Ar interval Interval between purging expired states and fragments. .It Ar frag Seconds before an unassembled fragment is expired. .It Ar src.track Length of time to retain a source tracking entry after the last state expires. .El .Pp When a packet matches a stateful connection, the seconds to live for the connection will be updated to that of the .Ar proto.modifier which corresponds to the connection state. Each packet which matches this state will reset the TTL. Tuning these values may improve the performance of the firewall at the risk of dropping valid idle connections. .Pp .Bl -tag -width xxxx -compact .It Ar tcp.first The state after the first packet. .It Ar tcp.opening The state before the destination host ever sends a packet. .It Ar tcp.established The fully established state. .It Ar tcp.closing The state after the first FIN has been sent. .It Ar tcp.finwait The state after both FINs have been exchanged and the connection is closed. Some hosts (notably web servers on Solaris) send TCP packets even after closing the connection. Increasing .Ar tcp.finwait (and possibly .Ar tcp.closing ) can prevent blocking of such packets. .It Ar tcp.closed The state after one endpoint sends an RST. .El .Pp ICMP and UDP are handled in a fashion similar to TCP, but with a much more limited set of states: .Pp .Bl -tag -width xxxx -compact .It Ar udp.first The state after the first packet. .It Ar udp.single The state if the source host sends more than one packet but the destination host has never sent one back. .It Ar udp.multiple The state if both hosts have sent packets. .It Ar icmp.first The state after the first packet. .It Ar icmp.error The state after an ICMP error came back in response to an ICMP packet. .El .Pp Other protocols are handled similarly to UDP: .Pp .Bl -tag -width xxxx -compact .It Ar other.first .It Ar other.single .It Ar other.multiple .El .Pp Timeout values can be reduced adaptively as the number of state table entries grows. .Pp .Bl -tag -width xxxx -compact .It Ar adaptive.start When the number of state entries exceeds this value, adaptive scaling begins. All timeout values are scaled linearly with factor (adaptive.end - number of states) / (adaptive.end - adaptive.start). .It Ar adaptive.end When reaching this number of state entries, all timeout values become zero, effectively purging all state entries immediately. This value is used to define the scale factor, it should not actually be reached (set a lower state limit, see below). .El .Pp These values can be defined both globally and for each rule. When used on a per-rule basis, the values relate to the number of states created by the rule, otherwise to the total number of states. .Pp For example: .Bd -literal -offset indent set timeout tcp.first 120 set timeout tcp.established 86400 set timeout { adaptive.start 6000, adaptive.end 12000 } set limit states 10000 .Ed .Pp With 9000 state table entries, the timeout values are scaled to 50% (tcp.first 60, tcp.established 43200). .Pp .It Ar set loginterface Enable collection of packet and byte count statistics for the given interface. These statistics can be viewed using .Bd -literal -offset indent # pfctl -s info .Ed .Pp In this example .Xr pf 4 collects statistics on the interface named dc0: .Bd -literal -offset indent set loginterface dc0 .Ed .Pp One can disable the loginterface using: .Bd -literal -offset indent set loginterface none .Ed .Pp .It Ar set limit Sets hard limits on the memory pools used by the packet filter. See .Xr pool 9 for an explanation of memory pools. .Pp For example, .Bd -literal -offset indent set limit states 20000 .Ed .Pp sets the maximum number of entries in the memory pool used by state table entries (generated by .Ar keep state rules) to 20000. Using .Bd -literal -offset indent set limit frags 20000 .Ed .Pp sets the maximum number of entries in the memory pool used for fragment reassembly (generated by .Ar scrub rules) to 20000. Finally, .Bd -literal -offset indent set limit src-nodes 2000 .Ed .Pp sets the maximum number of entries in the memory pool used for tracking source IP addresses (generated by the .Ar sticky-address and .Ar source-track options) to 2000. .Pp These can be combined: .Bd -literal -offset indent set limit { states 20000, frags 20000, src-nodes 2000 } .Ed .Pp .It Ar set optimization Optimize the engine for one of the following network environments: .Pp .Bl -tag -width xxxx -compact .It Ar normal A normal network environment. Suitable for almost all networks. .It Ar high-latency A high-latency environment (such as a satellite connection). .It Ar satellite Alias for .Ar high-latency . .It Ar aggressive Aggressively expire connections. This can greatly reduce the memory usage of the firewall at the cost of dropping idle connections early. .It Ar conservative Extremely conservative settings. Avoid dropping legitimate connections at the expense of greater memory utilization (possibly much greater on a busy network) and slightly increased processor utilization. .El .Pp For example: .Bd -literal -offset indent set optimization aggressive .Ed .Pp .It Ar set block-policy The .Ar block-policy option sets the default behaviour for the packet .Ar block action: .Pp .Bl -tag -width xxxxxxxx -compact .It Ar drop Packet is silently dropped. .It Ar return A TCP RST is returned for blocked TCP packets, an ICMP UNREACHABLE is returned for blocked UDP packets, and all other packets are silently dropped. .El .Pp For example: .Bd -literal -offset indent set block-policy return .Ed .It Ar set state-policy The .Ar state-policy option sets the default behaviour for states: .Pp .Bl -tag -width group-bound -compact .It Ar if-bound States are bound to interface. .It Ar floating States can match packets on any interfaces (the default). .El .Pp For example: .Bd -literal -offset indent set state-policy if-bound .Ed .It Ar set require-order By default .Xr pfctl 8 enforces an ordering of the statement types in the ruleset to: .Em options , .Em normalization , .Em queueing , .Em translation , .Em filtering . Setting this option to .Ar no disables this enforcement. There may be non-trivial and non-obvious implications to an out of order ruleset. Consider carefully before disabling the order enforcement. .It Ar set fingerprints Load fingerprints of known operating systems from the given filename. By default fingerprints of known operating systems are automatically loaded from .Xr pf.os 5 in .Pa /etc but can be overridden via this option. Setting this option may leave a small period of time where the fingerprints referenced by the currently active ruleset are inconsistent until the new ruleset finishes loading. .Pp For example: .Pp .Dl set fingerprints \&"/etc/pf.os.devel\&" .Pp .It Ar set skip on List interfaces for which packets should not be filtered. Packets passing in or out on such interfaces are passed as if pf was disabled, i.e. pf does not process them in any way. This can be useful on loopback and other virtual interfaces, when packet filtering is not desired and can have unexpected effects. For example: .Pp .Dl set skip on lo0 .Pp .It Ar set debug Set the debug .Ar level to one of the following: .Pp .Bl -tag -width xxxxxxxxxxxx -compact .It Ar none Don't generate debug messages. .It Ar urgent Generate debug messages only for serious errors. .It Ar misc Generate debug messages for various errors. .It Ar loud Generate debug messages for common conditions. .El .El .Sh TRAFFIC NORMALIZATION Traffic normalization is used to sanitize packet content in such a way that there are no ambiguities in packet interpretation on the receiving side. The normalizer does IP fragment reassembly to prevent attacks that confuse intrusion detection systems by sending overlapping IP fragments. Packet normalization is invoked with the .Ar scrub directive. .Pp .Ar scrub has the following options: .Bl -tag -width xxxx .It Ar no-df Clears the .Ar dont-fragment bit from a matching IP packet. Some operating systems are known to generate fragmented packets with the .Ar dont-fragment bit set. This is particularly true with NFS. .Ar Scrub will drop such fragmented .Ar dont-fragment packets unless .Ar no-df is specified. .Pp Unfortunately some operating systems also generate their .Ar dont-fragment packets with a zero IP identification field. Clearing the .Ar dont-fragment bit on packets with a zero IP ID may cause deleterious results if an upstream router later fragments the packet. Using the .Ar random-id modifier (see below) is recommended in combination with the .Ar no-df modifier to ensure unique IP identifiers. .It Ar min-ttl Enforces a minimum TTL for matching IP packets. .It Ar max-mss Enforces a maximum MSS for matching TCP packets. .It Ar random-id Replaces the IP identification field with random values to compensate for predictable values generated by many hosts. This option only applies to packets that are not fragmented after the optional fragment reassembly. .It Ar fragment reassemble Using .Ar scrub rules, fragments can be reassembled by normalization. In this case, fragments are buffered until they form a complete packet, and only the completed packet is passed on to the filter. The advantage is that filter rules have to deal only with complete packets, and can ignore fragments. The drawback of caching fragments is the additional memory cost. But the full reassembly method is the only method that currently works with NAT. This is the default behavior of a .Ar scrub rule if no fragmentation modifier is supplied. .It Ar fragment crop The default fragment reassembly method is expensive, hence the option to crop is provided. In this case, .Xr pf 4 will track the fragments and cache a small range descriptor. Duplicate fragments are dropped and overlaps are cropped. Thus data will only occur once on the wire with ambiguities resolving to the first occurrence. Unlike the .Ar fragment reassemble modifier, fragments are not buffered, they are passed as soon as they are received. The .Ar fragment crop reassembly mechanism does not yet work with NAT. .Pp .It Ar fragment drop-ovl This option is similar to the .Ar fragment crop modifier except that all overlapping or duplicate fragments will be dropped, and all further corresponding fragments will be dropped as well. .It Ar reassemble tcp Statefully normalizes TCP connections. .Ar scrub reassemble tcp rules may not have the direction (in/out) specified. .Ar reassemble tcp performs the following normalizations: .Pp .Bl -tag -width timeout -compact .It ttl Neither side of the connection is allowed to reduce their IP TTL. An attacker may send a packet such that it reaches the firewall, affects the firewall state, and expires before reaching the destination host. .Ar reassemble tcp will raise the TTL of all packets back up to the highest value seen on the connection. .It timestamp modulation Modern TCP stacks will send a timestamp on every TCP packet and echo the other endpoint's timestamp back to them. Many operating systems will merely start the timestamp at zero when first booted, and increment it several times a second. The uptime of the host can be deduced by reading the timestamp and multiplying by a constant. Also observing several different timestamps can be used to count hosts behind a NAT device. And spoofing TCP packets into a connection requires knowing or guessing valid timestamps. Timestamps merely need to be monotonically increasing and not derived off a guessable base time. .Ar reassemble tcp will cause .Ar scrub to modulate the TCP timestamps with a random number. .It extended PAWS checks There is a problem with TCP on long fat pipes, in that a packet might get delayed for longer than it takes the connection to wrap its 32-bit sequence space. In such an occurrence, the old packet would be indistinguishable from a new packet and would be accepted as such. The solution to this is called PAWS: Protection Against Wrapped Sequence numbers. It protects against it by making sure the timestamp on each packet does not go backwards. .Ar reassemble tcp also makes sure the timestamp on the packet does not go forward more than the RFC allows. By doing this, .Xr pf 4 artificially extends the security of TCP sequence numbers by 10 to 18 bits when the host uses appropriately randomized timestamps, since a blind attacker would have to guess the timestamp as well. .El .El .Pp For example, .Bd -literal -offset indent scrub in on $ext_if all fragment reassemble .Ed .Pp The .Ar no option prefixed to a scrub rule causes matching packets to remain unscrubbed, much in the same way as .Ar drop quick works in the packet filter (see below). This mechanism should be used when it is necessary to exclude specific packets from broader scrub rules. .Sh QUEUEING Packets can be assigned to queues for the purpose of bandwidth control. At least two declarations are required to configure queues, and later any packet filtering rule can reference the defined queues by name. During the filtering component of .Nm pf.conf , the last referenced .Ar queue name is where any packets from .Ar pass rules will be queued, while for .Ar block rules it specifies where any resulting ICMP or TCP RST packets should be queued. The .Ar scheduler defines the algorithm used to decide which packets get delayed, dropped, or sent out immediately. There are three .Ar schedulers currently supported. .Bl -tag -width xxxx .It Ar cbq Class Based Queueing. .Ar Queues attached to an interface build a tree, thus each .Ar queue can have further child .Ar queues . Each queue can have a .Ar priority and a .Ar bandwidth assigned. .Ar Priority mainly controls the time packets take to get sent out, while .Ar bandwidth has primarily effects on throughput. .Ar cbq achieves both partitioning and sharing of link bandwidth by hierarchically structured classes. Each class has its own .Ar queue and is assigned its share of .Ar bandwidth . A child class can borrow bandwidth from its parent class as long as excess bandwidth is available (see the option .Ar borrow , below). .It Ar priq Priority Queueing. .Ar Queues are flat attached to the interface, thus, .Ar queues cannot have further child .Ar queues . Each .Ar queue has a unique .Ar priority assigned, ranging from 0 to 15. Packets in the .Ar queue with the highest .Ar priority are processed first. .It Ar hfsc Hierarchical Fair Service Curve. .Ar Queues attached to an interface build a tree, thus each .Ar queue can have further child .Ar queues . Each queue can have a .Ar priority and a .Ar bandwidth assigned. .Ar Priority mainly controls the time packets take to get sent out, while .Ar bandwidth has primarily effects on throughput. .Ar hfsc supports both link-sharing and guaranteed real-time services. It employs a service curve based QoS model, and its unique feature is an ability to decouple .Ar delay and .Ar bandwidth allocation. .El .Pp The interfaces on which queueing should be activated are declared using the .Ar altq on declaration. .Ar altq on has the following keywords: .Bl -tag -width xxxx .It Ar Queueing is enabled on the named interface. .It Ar Specifies which queueing scheduler to use. Currently supported values are .Ar cbq for Class Based Queueing, .Ar priq for Priority Queueing and .Ar hfsc for the Hierarchical Fair Service Curve scheduler. .It Ar bandwidth The maximum bitrate for all queues on an interface may be specified using the .Ar bandwidth keyword. The value can be specified as an absolute value or as a percentage of the interface bandwidth. When using an absolute value, the suffixes .Ar b , .Ar Kb , .Ar Mb , and .Ar Gb are used to represent bits, kilobits, megabits, and gigabits per second, respectively. The value must not exceed the interface bandwidth. If .Ar bandwidth is not specified, the interface bandwidth is used. .It Ar qlimit The maximum number of packets held in the queue. The default is 50. .It Ar tbrsize Adjusts the size, in bytes, of the token bucket regulator. If not specified, heuristics based on the interface bandwidth are used to determine the size. .It Ar queue Defines a list of subqueues to create on an interface. .El .Pp In the following example, the interface dc0 should queue up to 5 Mbit/s in four second-level queues using Class Based Queueing. Those four queues will be shown in a later example. .Bd -literal -offset indent altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh } .Ed .Pp Once interfaces are activated for queueing using the .Ar altq directive, a sequence of .Ar queue directives may be defined. The name associated with a .Ar queue must match a queue defined in the .Ar altq directive (e.g. mail), or, except for the .Ar priq .Ar scheduler , in a parent .Ar queue declaration. The following keywords can be used: .Bl -tag -width xxxx .It Ar on Specifies the interface the queue operates on. If not given, it operates on all matching interfaces. .It Ar bandwidth Specifies the maximum bitrate to be processed by the queue. This value must not exceed the value of the parent .Ar queue and can be specified as an absolute value or a percentage of the parent queue's bandwidth. If not specified, defaults to 100% of the parent queue's bandwidth. The .Ar priq scheduler does not support bandwidth specification. .It Ar priority Between queues a priority level can be set. For .Ar cbq and .Ar hfsc , the range is 0 to 7 and for .Ar priq , the range is 0 to 15. The default for all is 1. .Ar Priq queues with a higher priority are always served first. .Ar Cbq and .Ar Hfsc queues with a higher priority are preferred in the case of overload. .It Ar qlimit The maximum number of packets held in the queue. The default is 50. .El .Pp The .Ar scheduler can get additional parameters with .Ar Ns Li (\& Ar No ) . Parameters are as follows: .Bl -tag -width Fl .It Ar default Packets not matched by another queue are assigned to this one. Exactly one default queue is required. .It Ar red Enable RED (Random Early Detection) on this queue. RED drops packets with a probability proportional to the average queue length. .It Ar rio Enables RIO on this queue. RIO is RED with IN/OUT, thus running RED two times more than RIO would achieve the same effect. RIO is currently not supported in the GENERIC kernel. .It Ar ecn Enables ECN (Explicit Congestion Notification) on this queue. ECN implies RED. .El .Pp The .Ar cbq .Ar scheduler supports an additional option: .Bl -tag -width Fl .It Ar borrow The queue can borrow bandwidth from the parent. .El .Pp The .Ar hfsc .Ar scheduler supports some additional options: .Bl -tag -width Fl .It Ar realtime The minimum required bandwidth for the queue. .It Ar upperlimit The maximum allowed bandwidth for the queue. .It Ar linkshare The bandwidth share of a backlogged queue. .El .Pp is an acronym for .Ar service curve . .Pp The format for service curve specifications is .Ar ( m1 , d , m2 ) . .Ar m2 controls the bandwidth assigned to the queue. .Ar m1 and .Ar d are optional and can be used to control the initial bandwidth assignment. For the first .Ar d milliseconds the queue gets the bandwidth given as .Ar m1 , afterwards the value given in .Ar m2 . .Pp Furthermore, with .Ar cbq and .Ar hfsc , child queues can be specified as in an .Ar altq declaration, thus building a tree of queues using a part of their parent's bandwidth. .Pp Packets can be assigned to queues based on filter rules by using the .Ar queue keyword. Normally only one .Ar queue is specified; when a second one is specified it will instead be used for packets which have a .Em TOS of .Em lowdelay and for TCP ACKs with no data payload. .Pp To continue the previous example, the examples below would specify the four referenced queues, plus a few child queues. Interactive .Xr ssh 1 sessions get priority over bulk transfers like .Xr scp 1 and .Xr sftp 1 . The queues may then be referenced by filtering rules (see .Sx PACKET FILTERING below). .Bd -literal queue std bandwidth 10% cbq(default) queue http bandwidth 60% priority 2 cbq(borrow red) \e { employees, developers } queue developers bandwidth 75% cbq(borrow) queue employees bandwidth 15% queue mail bandwidth 10% priority 0 cbq(borrow ecn) queue ssh bandwidth 20% cbq(borrow) { ssh_interactive, ssh_bulk } queue ssh_interactive bandwidth 50% priority 7 cbq(borrow) queue ssh_bulk bandwidth 50% priority 0 cbq(borrow) block return out on dc0 inet all queue std pass out on dc0 inet proto tcp from $developerhosts to any port 80 \e keep state queue developers pass out on dc0 inet proto tcp from $employeehosts to any port 80 \e keep state queue employees pass out on dc0 inet proto tcp from any to any port 22 \e keep state queue(ssh_bulk, ssh_interactive) pass out on dc0 inet proto tcp from any to any port 25 \e keep state queue mail .Ed .Sh TRANSLATION Translation rules modify either the source or destination address of the packets associated with a stateful connection. A stateful connection is automatically created to track packets matching such a rule as long as they are not blocked by the filtering section of .Nm pf.conf . The translation engine modifies the specified address and/or port in the packet, recalculates IP, TCP and UDP checksums as necessary, and passes it to the packet filter for evaluation. .Pp Since translation occurs before filtering the filter engine will see packets as they look after any addresses and ports have been translated. Filter rules will therefore have to filter based on the translated address and port number. Packets that match a translation rule are only automatically passed if the .Ar pass modifier is given, otherwise they are still subject to .Ar block and .Ar pass rules. .Pp The state entry created permits .Xr pf 4 to keep track of the original address for traffic associated with that state and correctly direct return traffic for that connection. .Pp Various types of translation are possible with pf: .Bl -tag -width xxxx .It Ar binat A .Ar binat rule specifies a bidirectional mapping between an external IP netblock and an internal IP netblock. .It Ar nat A .Ar nat rule specifies that IP addresses are to be changed as the packet traverses the given interface. This technique allows one or more IP addresses on the translating host to support network traffic for a larger range of machines on an "inside" network. Although in theory any IP address can be used on the inside, it is strongly recommended that one of the address ranges defined by RFC 1918 be used. These netblocks are: .Bd -literal 10.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8) 172.16.0.0 - 172.31.255.255 (i.e., 172.16/12) 192.168.0.0 - 192.168.255.255 (i.e., 192.168/16) .Ed .It Pa rdr The packet is redirected to another destination and possibly a different port. .Ar rdr rules can optionally specify port ranges instead of single ports. rdr ... port 2000:2999 -> ... port 4000 redirects ports 2000 to 2999 (inclusive) to port 4000. rdr ... port 2000:2999 -> ... port 4000:* redirects port 2000 to 4000, 2001 to 4001, ..., 2999 to 4999. .El .Pp In addition to modifying the address, some translation rules may modify source or destination ports for .Xr tcp 4 or .Xr udp 4 connections; implicitly in the case of .Ar nat rules and explicitly in the case of .Ar rdr rules. Port numbers are never translated with a .Ar binat rule. .Pp For each packet processed by the translator, the translation rules are evaluated in sequential order, from first to last. The first matching rule decides what action is taken. .Pp The .Ar no option prefixed to a translation rule causes packets to remain untranslated, much in the same way as .Ar drop quick works in the packet filter (see below). If no rule matches the packet it is passed to the filter engine unmodified. .Pp Translation rules apply only to packets that pass through the specified interface, and if no interface is specified, translation is applied to packets on all interfaces. For instance, redirecting port 80 on an external interface to an internal web server will only work for connections originating from the outside. Connections to the address of the external interface from local hosts will not be redirected, since such packets do not actually pass through the external interface. Redirections cannot reflect packets back through the interface they arrive on, they can only be redirected to hosts connected to different interfaces or to the firewall itself. .Pp Note that redirecting external incoming connections to the loopback address, as in .Bd -literal -offset indent rdr on ne3 inet proto tcp to port spamd -> 127.0.0.1 port smtp .Ed .Pp will effectively allow an external host to connect to daemons bound solely to the loopback address, circumventing the traditional blocking of such connections on a real interface. Unless this effect is desired, any of the local non-loopback addresses should be used as redirection target instead, which allows external connections only to daemons bound to this address or not bound to any address. .Pp See .Sx TRANSLATION EXAMPLES below. .Sh PACKET FILTERING .Xr pf 4 has the ability to .Ar block and .Ar pass packets based on attributes of their layer 3 (see .Xr ip 4 and .Xr ip6 4 ) and layer 4 (see .Xr icmp 4 , .Xr icmp6 4 , .Xr tcp 4 , .Xr udp 4 ) headers. In addition, packets may also be assigned to queues for the purpose of bandwidth control. .Pp For each packet processed by the packet filter, the filter rules are evaluated in sequential order, from first to last. The last matching rule decides what action is taken. .Pp The following actions can be used in the filter: .Bl -tag -width xxxx .It Ar block The packet is blocked. There are a number of ways in which a .Ar block rule can behave when blocking a packet. The default behaviour is to .Ar drop packets silently, however this can be overridden or made explicit either globally, by setting the .Ar block-policy option, or on a per-rule basis with one of the following options: .Pp .Bl -tag -width xxxx -compact .It Ar drop The packet is silently dropped. .It Ar return-rst This applies only to .Xr tcp 4 packets, and issues a TCP RST which closes the connection. .It Ar return-icmp .It Ar return-icmp6 This causes ICMP messages to be returned for packets which match the rule. By default this is an ICMP UNREACHABLE message, however this can be overridden by specifying a message as a code or number. .It Ar return This causes a TCP RST to be returned for .Xr tcp 4 packets and an ICMP UNREACHABLE for UDP and other packets. .El .Pp Options returning ICMP packets currently have no effect if .Xr pf 4 operates on a .Xr bridge 4 , as the code to support this feature has not yet been implemented. .It Ar pass The packet is passed. .El .Pp If no rule matches the packet, the default action is .Ar pass . .Pp To block everything by default and only pass packets that match explicit rules, one uses .Bd -literal -offset indent block all .Ed .Pp as the first filter rule. .Pp See .Sx FILTER EXAMPLES below. .Sh PARAMETERS The rule parameters specify the packets to which a rule applies. A packet always comes in on, or goes out through, one interface. Most parameters are optional. If a parameter is specified, the rule only applies to packets with matching attributes. Certain parameters can be expressed as lists, in which case .Xr pfctl 8 generates all needed rule combinations. .Bl -tag -width xxxx .It Ar in No or Ar out This rule applies to incoming or outgoing packets. If neither .Ar in nor .Ar out are specified, the rule will match packets in both directions. .It Ar log In addition to the action specified, a log message is generated. All packets for that connection are logged, unless the .Ar keep state , .Ar modulate state or .Ar synproxy state options are specified, in which case only the packet that establishes the state is logged. (See .Ar keep state , .Ar modulate state and .Ar synproxy state below). The logged packets are sent to the .Xr pflog 4 interface. This interface is monitored by the .Xr pflogd 8 logging daemon, which dumps the logged packets to the file .Pa /var/log/pflog in .Xr pcap 3 binary format. .It Ar log (all) Used with .Ar keep state , .Ar modulate state or .Ar synproxy state rules to force logging of all packets for a connection. As with .Ar log , packets are logged to .Xr pflog 4 . .It Ar quick If a packet matches a rule which has the .Ar quick option set, this rule is considered the last matching rule, and evaluation of subsequent rules is skipped. .It Ar on This rule applies only to packets coming in on, or going out through, this particular interface or interface group. .It Ar This rule applies only to packets of this address family. Supported values are .Ar inet and .Ar inet6 . .It Ar proto This rule applies only to packets of this protocol. Common protocols are .Xr icmp 4 , .Xr icmp6 4 , .Xr tcp 4 , and .Xr udp 4 . For a list of all the protocol name to number mappings used by .Xr pfctl 8 , see the file .Em /etc/protocols . .It Xo .Ar from port os .Ar to port .Xc This rule applies only to packets with the specified source and destination addresses and ports. .Pp Addresses can be specified in CIDR notation (matching netblocks), as symbolic host names or interface names, or as any of the following keywords: .Pp .Bl -tag -width xxxxxxxxxxxxxx -compact .It Ar any Any address. .It Ar route