PF.CONF(5)                OpenBSD Programmer's Manual               PF.CONF(5)

NAME
     pf.conf - packet filter configuration file

DESCRIPTION
     The pf(4) packet filter modifies, drops or passes packets according to
     rules or definitions specified in pf.conf.

STATEMENT ORDER
     There are seven types of statements in pf.conf:

     Macros
           User-defined variables may be defined and used later, simplifying
           the configuration file.  Macros must be defined before they are
           referenced in pf.conf.

     Tables
           Tables provide a mechanism for increasing the performance and flex-
           ibility of rules with large numbers of source or destination ad-
           dresses.

     Options
           Options tune the behaviour of the packet filtering engine.

     Traffic Normalization (e.g. scrub)
           Traffic normalization protects internal machines against inconsis-
           tencies in Internet protocols and implementations.

     Queueing
           Queueing provides rule-based bandwidth control.

     Translation (Various forms of NAT)
           Translation rules specify how addresses are to be mapped or redi-
           rected to other addresses.

     Packet Filtering
           Stateful and stateless packet filtering provides rule-based block-
           ing or passing of packets.

     With the exception of macros and tables, the types of statements should
     be grouped and appear in pf.conf in the order shown above, as this match-
     es the operation of the underlying packet filtering engine.  By default
     pfctl(8) enforces this order (see set require-order below).

MACROS
     Much like cpp(1) or m4(1), macros can be defined that will later be ex-
     panded 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 pass, in, out).  Macros are not expanded inside quotes.

     For example,

           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

TABLES
     Tables are named structures which can hold a collection of addresses and
     networks.  Lookups against tables in 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 expan-
     sion).

     Tables can be used as the source or destination of filter rules, scrub
     rules or translation rules such as nat or rdr (see below for details on
     the various rule types).  Tables can also be used for the redirect ad-
     dress of nat and rdr rules and in the routing options of filter rules,
     but only for round-robin pools.

     Tables can be defined with any of the following pfctl(8) mechanisms.  As
     with macros, reserved words may not be used as table names.

     manually  Persistent tables can be manually created with the add or
               replace option of pfctl(8), before or after the ruleset has
               been loaded.

     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 pf.conf use the table statement, and
               are especially useful to define non-persistent tables.  The
               contents of a pre-existing table defined without a list of ad-
               dresses to initialize it is not altered when pf.conf is loaded.
               A table initialized with the empty list, { }, will be cleared
               on load.

     Tables may be defined with the following two attributes:

     persist  The 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.

     const    The const flag prevents the user from altering the contents of
              the table once it has been created.  Without that flag, pfctl(8)
              can be used to add or remove addresses from the table at any
              time, even when running with securelevel(7) = 2.

     For example,

           table <private> const { 10/8, 172.16/12, 192.168/16 }
           table <badhosts> persist
           block on fxp0 from { <private>, <badhosts> } to any

     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

           # pfctl -t badhosts -Tadd 204.92.77.111

     A table can also be initialized with an address list specified in one or
     more external files, using the following syntax:

           table <spam> persist file "/etc/spammers" file "/etc/openrelays"
           block on fxp0 from <spam> to any

     The files /etc/spammers and /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, all resulting IPv4 and IPv6 addresses are placed into the table.
     IP addresses can also be entered in a table by specifying a valid inter-
     face name or the self keyword, in which case all addresses assigned to
     the interface(s) will be added to the table.

OPTIONS
     pf(4) may be tuned for various situations using the set command.

     set timeout

           interval  Interval between purging expired states and fragments.
           frag      Seconds before an unassembled fragment is expired.
           src.track
                     Length of time to retain a source tracking entry after
                     the last state expires.

           When a packet matches a stateful connection, the seconds to live
           for the connection will be updated to that of the proto.modifier
           which corresponds to the connection state.  Each packet which
           matches this state will reset the TTL.  Tuning these values may im-
           prove the performance of the firewall at the risk of dropping valid
           idle connections.

           tcp.first
                 The state after the first packet.
           tcp.opening
                 The state before the destination host ever sends a packet.
           tcp.established
                 The fully established state.
           tcp.closing
                 The state after the first FIN has been sent.
           tcp.finwait
                 The state after both FINs have been exchanged and the connec-
                 tion is closed.  Some hosts (notably web servers on Solaris)
                 send TCP packets even after closing the connection.  Increas-
                 ing tcp.finwait (and possibly tcp.closing) can prevent block-
                 ing of such packets.
           tcp.closed
                 The state after one endpoint sends an RST.

           ICMP and UDP are handled in a fashion similar to TCP, but with a
           much more limited set of states:

           udp.first
                 The state after the first packet.
           udp.single
                 The state if the source host sends more than one packet but
                 the destination host has never sent one back.
           udp.multiple
                 The state if both hosts have sent packets.
           icmp.first
                 The state after the first packet.
           icmp.error
                 The state after an ICMP error came back in response to an
                 ICMP packet.

           Other protocols are handled similarly to UDP:

           other.first
           other.single
           other.multiple

           Timeout values can be reduced adaptively as the number of state
           table entries grows.

           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).
           adaptive.end
                 When reaching this number of state entries, all timeout val-
                 ues become zero, effectively purging all state entries imme-
                 diately.  This value is used to define the scale factor, it
                 should not actually be reached (set a lower state limit, see
                 below).

           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.

           For example:

                 set timeout tcp.first 120
                 set timeout tcp.established 86400
                 set timeout { adaptive.start 6000, adaptive.end 12000 }
                 set limit states 10000

           With 9000 state table entries, the timeout values are scaled to 50%
           (tcp.first 60, tcp.established 43200).

     set loginterface
           Enable collection of packet and byte count statistics for the given
           interface.  These statistics can be viewed using

                 # pfctl -s info

           In this example pf(4) collects statistics on the interface named
           dc0:

                 set loginterface dc0

           One can disable the loginterface using:

                 set loginterface none

     set limit
           Sets hard limits on the memory pools used by the packet filter.
           See pool(9) for an explanation of memory pools.

           For example,

                 set limit states 20000

           sets the maximum number of entries in the memory pool used by state
           table entries (generated by keep state rules) to 20000.  Using

                 set limit frags 20000

           sets the maximum number of entries in the memory pool used for
           fragment reassembly (generated by scrub rules) to 20000.  Finally,

                 set limit src-nodes 2000

           sets the maximum number of entries in the memory pool used for
           tracking source IP addresses (generated by the sticky-address and
           source-track options) to 2000.

           These can be combined:

                 set limit { states 20000, frags 20000, src-nodes 2000 }

     set optimization
           Optimize the engine for one of the following network environments:

           normal
                 A normal network environment.  Suitable for almost all net-
                 works.
           high-latency
                 A high-latency environment (such as a satellite connection).
           satellite
                 Alias for high-latency.
           aggressive
                 Aggressively expire connections.  This can greatly reduce the
                 memory usage of the firewall at the cost of dropping idle
                 connections early.
           conservative
                 Extremely conservative settings.  Avoid dropping legitimate
                 connections at the expense of greater memory utilization
                 (possibly much greater on a busy network) and slightly in-
                 creased processor utilization.

           For example:

                 set optimization aggressive

     set block-policy
           The block-policy option sets the default behaviour for the packet
           block action:

           drop      Packet is silently dropped.
           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.

           For example:

                 set block-policy return

     set state-policy
           The state-policy option sets the default behaviour for states:

           if-bound     States are bound to interface.
           group-bound  States are bound to interface group (i.e. ppp)
           floating     States can match packets on any interfaces (the de-
                        fault).

           For example:

                 set state-policy if-bound

     set require-order
           By default pfctl(8) enforces an ordering of the statement types in
           the ruleset to: options, normalization, queueing, translation,
           filtering.  Setting this option to 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 en-
           forcement.

     set fingerprints
           Load fingerprints of known operating systems from the given file-
           name.  By default fingerprints of known operating systems are auto-
           matically loaded from pf.os(5) in /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.

           For example:

                 set fingerprints "/etc/pf.os.devel"

     set debug
           Set the debug level to one of the following:

           none          Don't generate debug messages.
           urgent        Generate debug messages only for serious errors.
           misc          Generate debug messages for various errors.
           loud          Generate debug messages for common conditions.

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 scrub directive.

     scrub has the following options:

     no-df
           Clears the dont-fragment bit from a matching IP packet.  Some oper-
           ating systems are known to generate fragmented packets with the
           dont-fragment bit set.  This is particularly true with NFS.  Scrub
           will drop such fragmented dont-fragment packets unless no-df is
           specified.

           Unfortunately some operating systems also generate their dont-
           fragment packets with a zero IP identification field.  Clearing the
           dont-fragment bit on packets with a zero IP ID may cause deleteri-
           ous results if an upstream router later fragments the packet.  Us-
           ing the random-id modifier (see below) is recommended in combina-
           tion with the no-df modifier to ensure unique IP identifiers.

     min-ttl <number>
           Enforces a minimum TTL for matching IP packets.

     max-mss <number>
           Enforces a maximum MSS for matching TCP packets.

     random-id
           Replaces the IP identification field with random values to compen-
           sate for predictable values generated by many hosts.  This option
           only applies to outgoing packets that are not fragmented after the
           optional fragment reassembly.

     fragment reassemble
           Using 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 frag-
           ments 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 scrub rule if no fragmentation modifier
           is supplied.

     fragment crop
           The default fragment reassembly method is expensive, hence the op-
           tion to crop is provided.  In this case, pf(4) will track the frag-
           ments 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 fragment reassemble modifier, fragments are not
           buffered, they are passed as soon as they are received.  The
           fragment crop reassembly mechanism does not yet work with NAT.

     fragment drop-ovl
           This option is similar to the fragment crop modifier except that
           all overlapping or duplicate fragments will be dropped, and all
           further corresponding fragments will be dropped as well.

     reassemble tcp
           Statefully normalizes TCP connections.  scrub reassemble tcp rules
           may not have the direction (in/out) specified.  reassemble tcp per-
           forms the following normalizations:

           ttl      Neither side of the connection is allowed to reduce their
                    IP TTL.  An attacker may send a packet such that it reach-
                    es the firewall, affects the firewall state, and expires
                    before reaching the destination host.  reassemble tcp will
                    raise the TTL of all packets back up to the highest value
                    seen on the connection.
           timeout modulation
                    Modern TCP stacks will send a timestamp on every TCP pack-
                    et 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 observ-
                    ing 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 times-
                    tamps.  Timestamps merely need to be monotonically in-
                    creasing and not derived off a guessable base time.
                    reassemble tcp will cause scrub to modulate the TCP times-
                    tamps with a random number.

     For example,

           scrub in on $ext_if all fragment reassemble

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 pf.conf, the last referenced queue name is
     where any packets from pass rules will be queued, while for block rules
     it specifies where any resulting ICMP or TCP RST packets should be
     queued.  The scheduler defines the algorithm used to decide which packets
     get delayed, dropped, or sent out immediately.  There are three
     schedulers currently supported.

     cbq   Class Based Queueing.  Queues attached to an interface build a
           tree, thus each queue can have further child queues.  Each queue
           can have a priority and a bandwidth assigned.  Priority mainly con-
           trols the time packets take to get sent out, while bandwidth has
           primarily effects on throughput.

     priq  Priority Queueing.  Queues are flat attached to the interface,
           thus, queues cannot have further child queues.  Each queue has a
           unique priority assigned, ranging from 0 to 15.  Packets in the
           queue with the highest priority are processed first.

     hfsc  Hierarchical Fair Service Curve.  Queues attached to an interface
           build a tree, thus each queue can have further child queues.  Each
           queue can have a priority and a bandwidth assigned.  Priority main-
           ly controls the time packets take to get sent out, while bandwidth
           has primarily effects on throughput.

     The interfaces on which queueing should be activated are declared using
     the altq on declaration.  altq on has the following keywords:

     <interface>
           Queueing is enabled on the named interface.

     <scheduler>
           Specifies which queueing scheduler to use.  Currently supported
           values are cbq for Class Based Queueing, priq for Priority Queueing
           and hfsc for the Hierarchical Fair Service Curve scheduler.

     bandwidth <bw>
           The maximum bitrate for all queues on an interface may be specified
           using the bandwidth keyword.  The value can be specified as an ab-
           solute value or as a percentage of the interface bandwidth.  When
           using an absolute value, the suffixes b, Kb, Mb, and Gb are used to
           represent bits, kilobits, megabits, and gigabits per second, re-
           spectively.  The value must not exceed the interface bandwidth.  If
           bandwidth is not specified, the interface bandwidth is used.

     qlimit <limit>
           The maximum number of packets held in the queue.  The default is
           50.

     tbrsize <size>
           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.

     queue <list>
           Defines a list of subqueues to create on an interface.

     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.

           altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh }

     Once interfaces are activated for queueing using the altq directive, a
     sequence of queue directives may be defined.  The name associated with a
     queue must match a queue defined in the altq directive (e.g. mail), or,
     except for the priq scheduler, in a parent queue declaration.  The fol-
     lowing keywords can be used:

     on <interface>
           Specifies the interface the queue operates on.  If not given, it
           operates on all matching interfaces.

     bandwidth <bw>
           Specifies the maximum bitrate to be processed by the queue.  This
           value must not exceed the value of the parent queue and can be
           specified as an absolute value or a percentage of the parent
           queue's bandwidth.  The priq scheduler does not support bandwidth
           specification.

     priority <level>
           Between queues a priority level can be set.  For cbq and hfsc, the
           range is 0 to 7 and for priq, the range is 0 to 15.  The default
           for all is 1.  Priq queues with a higher priority are always served
           first.  Cbq and Hfsc queues with a higher priority are preferred in
           the case of overload.

     qlimit <limit>
           The maximum number of packets held in the queue.  The default is
           50.

     The scheduler can get additional parameters with <scheduler>(
     <parameters> ).  Parameters are as follows:

     default     Packets not matched by another queue are assigned to this
                 one.  Exactly one default queue is required.

     red         Enable RED (Random Early Detection) on this queue.  RED drops
                 packets with a probability proportional to the average queue
                 length.

     rio         Enables RIO on this queue.  RIO is RED with IN/OUT, thus run-
                 ning RED two times more than RIO would achieve the same ef-
                 fect.  RIO is currently not supported in the GENERIC kernel.

     ecn         Enables ECN (Explicit Congestion Notification) on this queue.
                 ECN implies RED.

     The cbq scheduler supports an additional option:

     borrow      The queue can borrow bandwidth from the parent.

     The hfsc scheduler supports some additional options:

     realtime <sc>
                 The minimum required bandwidth for the queue.

     upperlimit <sc>
                 The maximum allowed bandwidth for the queue.

     linkshare <sc>
                 The bandwidth share of a backlogged queue.

     <sc> is an acronym for service curve.

     The format for service curve specifications is (m1, d, m2).  m2 controls
     the bandwidth assigned to the queue.  m1 and d are optional and can be
     used to control the initial bandwidth assignment.  For the first d mil-
     liseconds the queue gets the bandwidth given as m1, afterwards the value
     given in m2.

     Furthermore, with cbq and hfsc, child queues can be specified as in an
     altq declaration, thus building a tree of queues using a part of their
     parent's bandwidth.

     Packets can be assigned to queues based on filter rules by using the
     queue keyword.  Normally only one queue is specified; when a second one
     is specified it will instead be used for packets which have a TOS of
     lowdelay and for TCP ACKs with no data payload.

     To continue the previous example, the examples below would specify the
     four referenced queues, plus a few child queues.  Interactive ssh(1) ses-
     sions get priority over bulk transfers like scp(1) and sftp(1).  The
     queues may then be referenced by filtering rules (see PACKET FILTERING
     below).

     queue std bandwidth 10% cbq(default)
     queue http bandwidth 60% priority 2 cbq(borrow red) \
           { 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 priority 7
     queue  ssh_bulk priority 0

     block return out on dc0 inet all queue std
     pass out on dc0 inet proto tcp from $developerhosts to any port 80 \
           keep state queue developers
     pass out on dc0 inet proto tcp from $employeehosts to any port 80 \
           keep state queue employees
     pass out on dc0 inet proto tcp from any to any port 22 \
           keep state queue(ssh_bulk, ssh_interactive)
     pass out on dc0 inet proto tcp from any to any port 25 \
           keep state queue mail

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 pf.conf.  The transla-
     tion engine modifies the specified address and/or port in the packet, re-
     calculates IP, TCP and UDP checksums as necessary, and passes it to the
     packet filter for evaluation.

     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 ad-
     dress and port number.  Packets that match a translation rule are only
     automatically passed if the pass modifier is given, otherwise they are
     still subject to block and pass rules.

     The state entry created permits pf(4) to keep track of the original ad-
     dress for traffic associated with that state and correctly direct return
     traffic for that connection.

     Various types of translation are possible with pf:

     binat
           A binat rule specifies a bidirectional mapping between an external
           IP netblock and an internal IP netblock.

     nat   A 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 traf-
           fic for a larger range of machines on an "inside" network.  Al-
           though 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:

           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)

     rdr   The packet is redirected to another destination and possibly a dif-
           ferent port.  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.

     In addition to modifying the address, some translation rules may modify
     source or destination ports for tcp(4) or udp(4) connections; implicitly
     in the case of nat rules and explicitly in the case of rdr rules.  Port
     numbers are never translated with a binat rule.

     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.

     The no option prefixed to a translation rule causes packets to remain un-
     translated, much in the same way as drop quick works in the packet filter
     (see below).  If no rule matches the packet it is passed to the filter
     engine unmodified.

     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 ex-
     ternal 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 fire-
     wall itself.

     Note that redirecting external incoming connections to the loopback ad-
     dress, as in

           rdr on ne3 inet proto tcp to port 8025 -> 127.0.0.1 port 25

     will effectively allow an external host to connect to daemons bound sole-
     ly 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.

     See TRANSLATION EXAMPLES below.

PACKET FILTERING
     pf(4) has the ability to block and pass packets based on attributes of
     their layer 3 (see ip(4) and ip6(4)) and layer 4 (see icmp(4), icmp6(4),
     tcp(4), udp(4)) headers.  In addition, packets may also be assigned to
     queues for the purpose of bandwidth control.

     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.

     The following actions can be used in the filter:

     block
           The packet is blocked.  There are a number of ways in which a block
           rule can behave when blocking a packet.  The default behaviour is
           to drop packets silently, however this can be overridden or made
           explicit either globally, by setting the block-policy option, or on
           a per-rule basis with one of the following options:

           drop  The packet is silently dropped.
           return-rst
                 This applies only to tcp(4) packets, and issues a TCP RST
                 which closes the connection.
           return-icmp
           return-icmp6
                 This causes ICMP messages to be returned for packets which
                 match the rule.  By default this is an ICMP UNREACHABLE mes-
                 sage, however this can be overridden by specifying a message
                 as a code or number.
           return
                 This causes a TCP RST to be returned for tcp(4) packets and
                 an ICMP UNREACHABLE for UDP and other packets.

           Options returning packets have no effect if pf(4) operates on a
           bridge(4).

     pass  The packet is passed.

     If no rule matches the packet, the default action is pass.

     To block everything by default and only pass packets that match explicit
     rules, one uses

           block all

     as the first filter rule.

     See FILTER EXAMPLES below.

PARAMETERS
     The rule parameters specify the packets to which a rule applies.  A pack-
     et always comes in on, or goes out through, one interface.  Most parame-
     ters 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 pfctl(8) generates all needed rule combinations.

     in or out
           This rule applies to incoming or outgoing packets.  If neither in
           nor out are specified, the rule will match packets in both direc-
           tions.

     log   In addition to the action specified, a log message is generated.
           All packets for that connection are logged, unless the keep state,
           modulate state or synproxy state options are specified, in which
           case only the packet that establishes the state is logged.  (See
           keep state, modulate state and synproxy state below).  The logged
           packets are sent to the pflog(4) interface.  This interface is mon-
           itored by the pflogd(8) logging daemon, which dumps the logged
           packets to the file /var/log/pflog in pcap(3) binary format.

     log-all
           Used with keep state, modulate state or synproxy state rules to
           force logging of all packets for a connection.  As with log, pack-
           ets are logged to pflog(4).

     quick
           If a packet matches a rule which has the quick option set, this
           rule is considered the last matching rule, and evaluation of subse-
           quent rules is skipped.

     on <interface>
           This rule applies only to packets coming in on, or going out
           through, this particular interface.  It is also possible to simply
           give the interface driver name, like ppp or fxp, to make the rule
           match packets flowing through a group of interfaces.

     <af>  This rule applies only to packets of this address family.  Support-
           ed values are inet and inet6.

     proto <protocol>
           This rule applies only to packets of this protocol.  Common proto-
           cols are icmp(4), icmp6(4), tcp(4), and udp(4).  For a list of all
           the protocol name to number mappings used by pfctl(8), see the file
           /etc/protocols.

     from <source> port <source> os <source> to <dest> port <dest>
           This rule applies only to packets with the specified source and
           destination addresses and ports.

           Addresses can be specified in CIDR notation (matching netblocks),
           as symbolic host names or interface names, or as any of the follow-
           ing keywords:

           any           Any address.
           no-route      Any address which is not currently routable.
           <table>       Any address that matches the given table.

           Interface names can have modifiers appended:

           :network      Translates to the network(s) attached to the inter-
                         face.
           :broadcast    Translates to the interface's broadcast address(es).
           :peer         Translates to the point to point interface's peer ad-
                         dress(es).
           :0            Do not include interface aliases.

           Host names may also have the :0 option appended to restrict the
           name resolution to the first of each v4 and v6 address found.

           Host name resolution and interface to address translation are done
           at ruleset load-time.  When the address of an interface (or host
           name) changes (under DHCP or PPP, for instance), the ruleset must
           be reloaded for the change to be reflected in the kernel.  Sur-
           rounding the interface name (and optional modifiers) in parentheses
           changes this behaviour.  When the interface name is surrounded by
           parentheses, the rule is automatically updated whenever the inter-
           face changes its address.  The ruleset does not need to be reload-
           ed.  This is especially useful with nat.

           Ports can be specified either by number or by name.  For example,
           port 80 can be specified as www.  For a list of all port name to
           number mappings used by pfctl(8), see the file /etc/services.

           Ports and ranges of ports are specified by using these operators:

                 =       (equal)
                 !=      (unequal)
                 <       (less than)
                 <=      (less than or equal)
                 >       (greater than)
                 >=      (greater than or equal)
                 :       (range including boundaries)
                 ><      (range excluding boundaries)
                 <>      (except range)

           ><, <> and : are binary operators (they take two arguments).  For
           instance:

           port 2000:2004
                       means `all ports >= 2000 and <= 2004', hence ports
                       2000, 2001, 2002, 2003 and 2004.

           port 2000 >< 2004
                       means `all ports > 2000 and < 2004', hence ports 2001,
                       2002 and 2003.

           port 2000 <> 2004
                       means `all ports < 2000 or > 2004', hence ports 1-1999
                       and 2005-65535.

           The operating system of the source host can be specified in the
           case of TCP rules with the OS modifier.  See the OPERATING SYSTEM
           FINGERPRINTING section for more information.

           The host, port and OS specifications are optional, as in the fol-
           lowing examples:

                 pass in all
                 pass in from any to any
                 pass in proto tcp from any port <= 1024 to any
                 pass in proto tcp from any to any port 25
                 pass in proto tcp from 10.0.0.0/8 port > 1024 \
                       to ! 10.1.2.3 port != ssh
                 pass in proto tcp from any os "OpenBSD" flags S/SA

     all   This is equivalent to "from any to any".

     group <group>
           Similar to user, this rule only applies to packets of sockets owned
           by the specified group.

     user <user>
           This rule only applies to packets of sockets owned by the specified
           user.  For outgoing connections initiated from the firewall, this
           is the user that opened the connection.  For incoming connections
           to the firewall itself, this is the user that listens on the desti-
           nation port.  For forwarded connections, where the firewall is not
           a connection endpoint, the user and group are unknown.

           All packets, both outgoing and incoming, of one connection are as-
           sociated with the same user and group.  Only TCP and UDP packets
           can be associated with users; for other protocols these parameters
           are ignored.

           User and group refer to the effective (as opposed to the real) IDs,
           in case the socket is created by a setuid/setgid process.  User and
           group IDs are stored when a socket is created; when a process cre-
           ates a listening socket as root (for instance, by binding to a
           privileged port) and subsequently changes to another user ID (to
           drop privileges), the credentials will remain root.

           User and group IDs can be specified as either numbers or names.
           The syntax is similar to the one for ports.  The value unknown
           matches packets of forwarded connections.  unknown can only be used
           with the operators = and !=.  Other constructs like user >= unknown
           are invalid.  Forwarded packets with unknown user and group ID
           match only rules that explicitly compare against unknown with the
           operators = or !=.  For instance user >= 0 does not match forwarded
           packets.  The following example allows only selected users to open
           outgoing connections:

                 block out proto { tcp, udp } all
                 pass  out proto { tcp, udp } all \
                       user { < 1000, dhartmei } keep state

     flags <a>/<b> | /<b>
           This rule only applies to TCP packets that have the flags <a> set
           out of set <b>.  Flags not specified in <b> are ignored.  The flags
           are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R.

           flags S/S   Flag SYN is set.  The other flags are ignored.

           flags S/SA  Out of SYN and ACK, exactly SYN may be set.  SYN,
                       SYN+PSH and SYN+RST match, but SYN+ACK, ACK and ACK+RST
                       do not.  This is more restrictive than the previous ex-
                       ample.

           flags /SFRA
                       If the first set is not specified, it defaults to none.
                       All of SYN, FIN, RST and ACK must be unset.

     icmp-type <type> code <code>

     icmp6-type <type> code <code>
           This rule only applies to ICMP or ICMPv6 packets with the specified
           type and code.  This parameter is only valid for rules that cover
           protocols ICMP or ICMP6.  The protocol and the ICMP type indicator
           (icmp-type or icmp6-type) must match.

     allow-opts
           By default, packets which contain IP options are blocked.  When
           allow-opts is specified for a pass rule, packets that pass the fil-
           ter based on that rule (last matching) do so even if they contain
           IP options.  For packets that match state, the rule that initially
           created the state is used.  The implicit pass rule that is used
           when a packet does not match any rules does not allow IP options.

     label <string>
           Adds a label (name) to the rule, which can be used to identify the
           rule.  For instance, pfctl -s labels shows per-rule statistics for
           rules that have labels.

           The following macros can be used in labels:

                 $if       The interface.
                 $srcaddr  The source IP address.
                 $dstaddr  The destination IP address.
                 $srcport  The source port specification.
                 $dstport  The destination port specification.
                 $proto    The protocol name.
                 $nr       The rule number.

           For example:

                 ips = "{ 1.2.3.4, 1.2.3.5 }"
                 pass in proto tcp from any to $ips \
                       port > 1023 label "$dstaddr:$dstport"

           expands to

                 pass in inet proto tcp from any to 1.2.3.4 \
                       port > 1023 label "1.2.3.4:>1023"
                 pass in inet proto tcp from any to 1.2.3.5 \
                       port > 1023 label "1.2.3.5:>1023"

           The macro expansion for the label directive occurs only at configu-
           ration file parse time, not during runtime.

     queue <queue> | (<queue>, <queue>)
           Packets matching this rule will be assigned to the specified queue.
           If two queues are given, packets which have a tos of lowdelay and
           TCP ACKs with no data payload will be assigned to the second one.
           See QUEUEING for setup details.

           For example:

                 pass in proto tcp to port 25 queue mail
                 pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio)

     tag <string>
           Packets matching this rule will be tagged with the specified
           string.  The tag acts as an internal marker that can be used to
           identify these packets later on.  This can be used, for example, to
           provide trust between interfaces and to determine if packets have
           been processed by translation rules.  Tags are "sticky", meaning
           that the packet will be tagged even if the rule is not the last
           matching rule.  Further matching rules can replace the tag with a
           new one but will not remove a previously applied tag.  A packet is
           only ever assigned one tag at a time.  pass rules that use the tag
           keyword must also use keep state, modulate state or synproxy state.
           Packet tagging can be done during nat, rdr, or binat rules in addi-
           tion to filter rules.  Tags take the same macros as labels (see
           above).

     tagged <string>
           Used with filter rules to specify that packets must already be
           tagged with the given tag in order to match the rule.  Inverse tag
           matching can also be done by specifying the ! operator before the
           tagged keyword.

ROUTING
     If a packet matches a rule with a route option set, the packet filter
     will route the packet according to the type of route option.  When such a
     rule creates state, the route option is also applied to all packets
     matching the same connection.

     fastroute
           The fastroute option does a normal route lookup to find the next
           hop for the packet.

     route-to
           The route-to option routes the packet to the specified interface
           with an optional address for the next hop.  When a route-to rule
           creates state, only packets that pass in the same direction as the
           filter rule specifies will be routed in this way.  Packets passing
           in the opposite direction (replies) are not affected and are routed
           normally.

     reply-to
           The reply-to option is similar to route-to, but routes packets that
           pass in the opposite direction (replies) to the specified inter-
           face.  Opposite direction is only defined in the context of a state
           entry, and route-to is useful only in rules that create state.  It
           can be used on systems with multiple external connections to route
           all outgoing packets of a connection through the interface the in-
           coming connection arrived through (symmetric routing enforcement).

     dup-to
           The dup-to option creates a duplicate of the packet and routes it
           like route-to.  The original packet gets routed as it normally
           would.

POOL OPTIONS
     For nat and rdr rules, (as well as for the route-to, reply-to and dup-to
     rule options) for which there is a single redirection address which has a
     subnet mask smaller than 32 for IPv4 or 128 for IPv6 (more than one IP
     address), a variety of different methods for assigning this address can
     be used:

     bitmask
           The bitmask option applies the network portion of the redirection
           address to the address to be modified (source with nat, destination
           with rdr).

     random
           The random option selects an address at random within the defined
           block of addresses.

     source-hash
           The source-hash option uses a hash of the source address to deter-
           mine the redirection address, ensuring that the redirection address
           is always the same for a given source.  An optional key can be
           specified after this keyword either in hex or as a string; by de-
           fault pfctl(8) randomly generates a key for source-hash every time
           the ruleset is reloaded.

     round-robin
           The round-robin option loops through the redirection address(es).

           When more than one redirection address is specified, round-robin is
           the only permitted pool type.

     static-port
           With nat rules, the static-port option prevents pf(4) from modify-
           ing the source port on TCP and UDP packets.

     Additionally, the sticky-address option can be specified to help ensure
     that multiple connections from the same source are mapped to the same
     redirection address.  This option can be used with the random and round-
     robin pool options.  Note that by default these associations are de-
     stroyed as soon as there are no longer states which refer to them; in or-
     der to make the mappings last beyond the lifetime of the states, increase
     the global options with set timeout source-track See STATEFUL TRACKING
     OPTIONS for more ways to control the source tracking.

STATEFUL INSPECTION
     pf(4) is a stateful packet filter, which means it can track the state of
     a connection.  Instead of passing all traffic to port 25, for instance,
     it is possible to pass only the initial packet, and then begin to keep
     state.  Subsequent traffic will flow because the filter is aware of the
     connection.

     If a packet matches a pass ... keep state rule, the filter creates a
     state for this connection and automatically lets pass all subsequent
     packets of that connection.

     Before any rules are evaluated, the filter checks whether the packet
     matches any state.  If it does, the packet is passed without evaluation
     of any rules.

     States are removed after the connection is closed or has timed out.

     This has several advantages.  Comparing a packet to a state involves
     checking its sequence numbers.  If the sequence numbers are outside the
     narrow windows of expected values, the packet is dropped.  This prevents
     spoofing attacks, such as when an attacker sends packets with a fake
     source address/port but does not know the connection's sequence numbers.

     Also, looking up states is usually faster than evaluating rules.  If
     there are 50 rules, all of them are evaluated sequentially in O(n).  Even
     with 50000 states, only 16 comparisons are needed to match a state, since
     states are stored in a binary search tree that allows searches in O(log2
     n).

     For instance:

           block all
           pass out proto tcp from any to any flags S/SA keep state
           pass in  proto tcp from any to any port 25 flags S/SA keep state

     This ruleset blocks everything by default.  Only outgoing connections and
     incoming connections to port 25 are allowed.  The initial packet of each
     connection has the SYN flag set, will be passed and creates state.  All
     further packets of these connections are passed if they match a state.

     By default, packets coming in and out of any interface can match a state,
     but it is also possible to change that behaviour by assigning states to a
     single interface or a group of interfaces.

     The default policy is specified by the state-policy global option, but
     this can be adjusted on a per-rule basis by adding one of the if-bound,
     group-bound or floating keywords to the keep state option.  For example,
     if a rule is defined as:

           pass out on ppp from any to 10.12/16 keep state (group-bound)

     A state created on ppp0 would match packets an all PPP interfaces, but
     not packets flowing through fxp0 or any other interface.

     Keeping rules floating is the more flexible option when the firewall is
     in a dynamic routing environment.  However, this has some security impli-
     cations since a state created by one trusted network could allow poten-
     tially hostile packets coming in from other interfaces.

     Specifying flags S/SA restricts state creation to the initial SYN packet
     of the TCP handshake.  One can also be less restrictive, and allow state
     creation from intermediate (non-SYN) packets.  This will cause pf(4) to
     synchronize to existing connections, for instance if one flushes the
     state table.

     For UDP, which is stateless by nature, keep state will create state as
     well.  UDP packets are matched to states using only host addresses and
     ports.

     ICMP messages fall into two categories: ICMP error messages, which always
     refer to a TCP or UDP packet, are matched against the referred to connec-
     tion.  If one keeps state on a TCP connection, and an ICMP source quench
     message referring to this TCP connection arrives, it will be matched to
     the right state and get passed.

     For ICMP queries, keep state creates an ICMP state, and pf(4) knows how
     to match ICMP replies to states.  For example,

           pass out inet proto icmp all icmp-type echoreq keep state

     allows echo requests (such as those created by ping(8)) out, creates
     state, and matches incoming echo replies correctly to states.

     Note: nat, binat and rdr rules implicitly create state for connections.

STATE MODULATION
     Much of the security derived from TCP is attributable to how well the
     initial sequence numbers (ISNs) are chosen.  Some popular stack implemen-
     tations choose very poor ISNs and thus are normally susceptible to ISN
     prediction exploits.  By applying a modulate state rule to a TCP connec-
     tion, pf(4) will create a high quality random sequence number for each
     connection endpoint.

     The modulate state directive implicitly keeps state on the rule and is
     only applicable to TCP connections.

     For instance:

           block all
           pass out proto tcp from any to any modulate state
           pass in  proto tcp from any to any port 25 flags S/SA modulate state

     There are two caveats associated with state modulation: A modulate state
     rule can not be applied to a pre-existing but unmodulated connection.
     Such an application would desynchronize TCP's strict sequencing between
     the two endpoints.  Instead, pf(4) will treat the modulate state modifier
     as a keep state modifier and the pre-existing connection will be inferred
     without the protection conferred by modulation.

     The other caveat affects currently modulated states when the state table
     is lost (firewall reboot, flushing the state table, etc...).  pf(4) will
     not be able to infer a connection again after the state table flushes the
     connection's modulator.  When the state is lost, the connection may be
     left dangling until the respective endpoints time out the connection.  It
     is possible on a fast local network for the endpoints to start an ACK
     storm while trying to resynchronize after the loss of the modulator.  Us-
     ing a flags S/SA modifier on modulate state rules between fast networks
     is suggested to prevent ACK storms.

SYN PROXY
     By default, pf(4) passes packets that are part of a tcp(4) handshake be-
     tween the endpoints.  The synproxy state option can be used to cause
     pf(4) itself to complete the handshake with the active endpoint, perform
     a handshake with the passive endpoint, and then forward packets between
     the endpoints.

     No packets are sent to the passive endpoint before the active endpoint
     has completed the handshake, hence so-called SYN floods with spoofed
     source addresses will not reach the passive endpoint, as the sender can't
     complete the handshake.

     The proxy is transparent to both endpoints, they each see a single con-
     nection from/to the other endpoint.  pf(4) chooses random initial se-
     quence numbers for both handshakes.  Once the handshakes are completed,
     the sequence number modulators (see previous section) are used to trans-
     late further packets of the connection.  Hence, synproxy state includes
     modulate state and keep state.

     Rules with synproxy will not work if pf(4) operates on a bridge(4).

     Example:

           pass in proto tcp from any to any port www flags S/SA synproxy state

STATEFUL TRACKING OPTIONS
     All three of keep state, modulate state and synproxy state support the
     following options:

     max <number>
           Limits the number of concurrent states the rule may create.  When
           this limit is reached, further packets matching the rule that would
           create state are dropped, until existing states time out.
     no-sync
           Prevent state changes for states created by this rule from appear-
           ing on the pfsync(4) interface.
     <timeout> <seconds>
           Changes the timeout values used for states created by this rule.

           When the source-track keyword is specified, the number of states
           per source IP is tracked.  The following limits can be set:

           max-src-nodes
                 Limits the maximum number of source addresses which can si-
                 multaneously have state table entries.
           max-src-states
                 Limits the maximum number of simultaneous state entries that
                 a single source address can create with this rule.
           For a list of all valid timeout names, see OPTIONS above.

           Multiple options can be specified, separated by commas:

           pass in proto tcp from any to any \
                 port www flags S/SA keep state \
                 (max 100, source-track rule, max-src-nodes 75, \
                 max-src-states 3, tcp.established 60, tcp.closing 5)

OPERATING SYSTEM FINGERPRINTING
     Passive OS Fingerprinting is a mechanism to inspect nuances of a TCP con-
     nection's initial SYN packet and guess at the host's operating system.
     Unfortunately these nuances are easily spoofed by an attacker so the fin-
     gerprint is not useful in making security decisions.  But the fingerprint
     is typically accurate enough to make policy decisions upon.

     The fingerprints may be specified by operating system class, by version,
     or by subtype/patchlevel.  The class of an operating system is typically
     the vender or genre and would be OpenBSD for the pf(4) firewall itself.
     The version of the oldest available OpenBSD release on the main ftp site
     would be 2.6 and the fingerprint would be written

           "OpenBSD 2.6"

     The subtype of an operating system is typically used to describe the
     patchlevel if that patch led to changes in the TCP stack behavior.  In
     the case of OpenBSD, the only subtype is for a fingerprint that was nor-
     malized by the no-df scrub option and would be specified as

           "OpenBSD 3.3 no-df"

     Fingerprints for most popular operating systems are provided by pf.os(5).
     Once pf(4) is running, a complete list of known operating system finger-
     prints may be listed by running:

           # pfctl -so

     Filter rules can enforce policy at any level of operating system specifi-
     cation assuming a fingerprint is present.  Policy could limit traffic to
     approved operating systems or even ban traffic from hosts that aren't at
     the latest service pack.

     The unknown class can also be used as the fingerprint which will match
     packets for which no operating system fingerprint is known.

     Examples:

           pass  out proto tcp from any os OpenBSD keep state
           block out proto tcp from any os Doors
           block out proto tcp from any os "Doors PT"
           block out proto tcp from any os "Doors PT SP3"
           block out from any os "unknown"
           pass on lo0 proto tcp from any os "OpenBSD 3.3 lo0" keep state

     Operating system fingerprinting is limited only to the TCP SYN packet.
     This means that it will not work on other protocols and will not match a
     currently established connection.

     Caveat: operating system fingerprints are occasionally wrong.  There are
     three problems: an attacker can trivially craft his packets to appear as
     any operating system he chooses; an operating system patch could change
     the stack behavior and no fingerprints will match it until the database
     is updated; and multiple operating systems may have the same fingerprint.

BLOCKING SPOOFED TRAFFIC
     "Spoofing" is the faking of IP addresses, typically for malicious purpos-
     es.  The antispoof directive expands to a set of filter rules which will
     block all traffic with a source IP from the network(s) directly connected
     to the specified interface(s) from entering the system through any other
     interface.

     For example, the line

           antispoof for lo0

     expands to

           block drop in on ! lo0 inet from 127.0.0.1/8 to any
           block drop in on ! lo0 inet6 from ::1 to any

     For non-loopback interfaces, there are additional rules to block incoming
     packets with a source IP address identical to the interface's IP(s).  For
     example, assuming the interface wi0 had an IP address of 10.0.0.1 and a
     netmask of 255.255.255.0, the line

           antispoof for wi0 inet

     expands to

           block drop in on ! wi0 inet from 10.0.0.0/24 to any
           block drop in inet from 10.0.0.1 to any

     Caveat: Rules created by the antispoof directive interfere with packets
     sent over loopback interfaces to local addresses.  One should pass these
     explicitly.

FRAGMENT HANDLING
     The size of IP datagrams (packets) can be significantly larger than the
     maximum transmission unit (MTU) of the network.  In cases when it is nec-
     essary or more efficient to send such large packets, the large packet
     will be fragmented into many smaller packets that will each fit onto the
     wire.  Unfortunately for a firewalling device, only the first logical
     fragment will contain the necessary header information for the subproto-
     col that allows pf(4) to filter on things such as TCP ports or to perform
     NAT.

     Besides the use of scrub rules as described in TRAFFIC NORMALIZATION
     above, there are three options for handling fragments in the packet fil-
     ter.

     One alternative is to filter individual fragments with filter rules.  If
     no scrub rule applies to a fragment, it is passed to the filter.  Filter
     rules with matching IP header parameters decide whether the fragment is
     passed or blocked, in the same way as complete packets are filtered.
     Without reassembly, fragments can only be filtered based on IP header
     fields (source/destination address, protocol), since subprotocol header
     fields are not available (TCP/UDP port numbers, ICMP code/type).  The
     fragment option can be used to restrict filter rules to apply only to
     fragments, but not complete packets.  Filter rules without the fragment
     option still apply to fragments, if they only specify IP header fields.
     For instance, the rule

           pass in proto tcp from any to any port 80

     never applies to a fragment, even if the fragment is part of a TCP packet
     with destination port 80, because without reassembly this information is
     not available for each fragment.  This also means that fragments cannot
     create new or match existing state table entries, which makes stateful
     filtering and address translation (NAT, redirection) for fragments impos-
     sible.

     It's also possible to reassemble only certain fragments by specifying
     source or destination addresses or protocols as parameters in scrub
     rules.

     In most cases, the benefits of reassembly outweigh the additional memory
     cost, and it's recommended to use scrub rules to reassemble all fragments
     via the fragment reassemble modifier.

     The memory allocated for fragment caching can be limited using pfctl(8).
     Once this limit is reached, fragments that would have to be cached are
     dropped until other entries time out.  The timeout value can also be ad-
     justed.

     Currently, only IPv4 fragments are supported and IPv6 fragments are
     blocked unconditionally.

ANCHORS AND NAMED RULESETS
     Besides the main ruleset, pfctl(8) can load named rulesets into anchor
     attachment points.  An anchor contains a list of named rulesets.  An
     anchor has a name which specifies where pfctl(8) can be used to attach
     sub-rulesets.  A named ruleset contains filter and translation rules,
     like the main ruleset.  The main ruleset can reference anchor attachment
     points using the following kinds of rules:

     nat-anchor <name>
           Evaluates the nat rules of all named rulesets in the specified
           anchor.

     rdr-anchor <name>
           Evaluates the rdr rules of all named rulesets in the specified
           anchor.

     binat-anchor <name>
           Evaluates the binat rules of all named rulesets in the specified
           anchor.

     anchor <name>
           Evaluates the filter rules of all named rulesets in the specified
           anchor.

     load anchor <name>:<ruleset> from <file>
           Loads the rules from the specified file into the named ruleset
           <ruleset> attached to the anchor <name>.

     When evaluation of the main ruleset reaches an anchor rule, pf(4) will
     proceed to evaluate all rules specified in the named rulesets attached to
     that anchor.

     Matching filter rules in named rulesets with the quick option and match-
     ing translation rules are final and abort the evaluation of both the
     rules in the anchor and the main ruleset.

     Only the main ruleset can contain anchor rules.

     When an anchor contains more than one named ruleset, they are evaluated
     in the alphabetical order of their names.

     Rules may contain anchor attachment points which do not contain any rules
     when the main ruleset is loaded, and later such named rulesets can be ma-
     nipulated through pfctl(8) without reloading the main ruleset.  For exam-
     ple,

           ext_if = "kue0"
           block on $ext_if all
           anchor spam
           pass out on $ext_if all keep state
           pass in on $ext_if proto tcp from any \
                 to $ext_if port smtp keep state

     blocks all packets on the external interface by default, then evaluates
     all rulesets in the anchor named "spam", and finally passes all outgoing
     connections and incoming connections to port 25.

           # echo "block in quick from 1.2.3.4 to any" | \
                 pfctl -a spam:manual -f -

     loads a single ruleset containing a single rule into the anchor, which
     blocks all packets from a specific address.

     The named ruleset can also be populated by adding a load anchor rule af-
     ter the anchor rule:

           anchor spam
           load anchor spam:manual from "/etc/pf-spam.conf"

     When pfctl(8) loads pf.conf, it will also load all the rules from the
     file /etc/pf-spam.conf into the named ruleset.

     Optionally, anchor rules can specify the parameter's direction, inter-
     face, address family, protocol and source/destination address/port using
     the same syntax as filter rules.  When parameters are used, the anchor
     rule is only evaluated for matching packets.  This allows conditional
     evaluation of named rulesets, like:

           block on $ext_if all
           anchor spam proto tcp from any to any port smtp
           pass out on $ext_if all keep state
           pass in on $ext_if proto tcp from any to $ext_if port smtp keep state

     The rules inside anchor spam are only evaluated for tcp packets with des-
     tination port 25.  Hence,

           # echo "block in quick from 1.2.3.4 to any" | \
                 pfctl -a spam:manual -f -

     will only block connections from 1.2.3.4 to port 25.

TRANSLATION EXAMPLES
     This example maps incoming requests on port 80 to port 8080, on which a
     daemon is running (because, for example, it is not run as root, and
     therefore lacks permission to bind to port 80).

     # use a macro for the interface name, so it can be changed easily
     ext_if = "ne3"

     # map daemon on 8080 to appear to be on 80
     rdr on $ext_if proto tcp from any to any port 80 -> 127.0.0.1 port 8080

     If the pass modifier is given, packets matching the translation rule are
     passed without inspecting the filter rules:

     rdr pass on $ext_if proto tcp from any to any port 80 -> 127.0.0.1 \
           port 8080

     In the example below, vlan12 is configured as 192.168.168.1; the machine
     translates all packets coming from 192.168.168.0/24 to 204.92.77.111 when
     they are going out any interface except vlan12.  This has the net effect
     of making traffic from the 192.168.168.0/24 network appear as though it
     is the Internet routable address 204.92.77.111 to nodes behind any inter-
     face on the router except for the nodes on vlan12.  (Thus, 192.168.168.1
     can talk to the 192.168.168.0/24 nodes.)

     nat on ! vlan12 from 192.168.168.0/24 to any -> 204.92.77.111

     In the example below, the machine sits between a fake internal
     144.19.74.*  network, and a routable external IP of 204.92.77.100.  The
     no nat rule excludes protocol AH from being translated.

     # NO NAT
     no nat on $ext_if proto ah from 144.19.74.0/24 to any
     nat on $ext_if from 144.19.74.0/24 to any -> 204.92.77.100

     In the example below, packets bound for one specific server, as well as
     those generated by the sysadmins are not proxied; all other connections
     are.

     # NO RDR
     no rdr on $int_if proto { tcp, udp } from any to $server port 80
     no rdr on $int_if proto { tcp, udp } from $sysadmins to any port 80
     rdr on $int_if proto { tcp, udp } from any to any port 80 -> 127.0.0.1 \
           port 80

     This longer example uses both a NAT and a redirection.  The external in-
     terface has the address 157.161.48.183.  On the internal interface, we
     are running ftp-proxy(8), listening for outbound ftp sessions captured to
     port 8021.

     # NAT
     # Translate outgoing packets' source addresses (any protocol).
     # In this case, any address but the gateway's external address is mapped.
     nat on $ext_if inet from ! ($ext_if) to any -> ($ext_if)

     # NAT PROXYING
     # Map outgoing packets' source port to an assigned proxy port instead of
     # an arbitrary port.
     # In this case, proxy outgoing isakmp with port 500 on the gateway.
     nat on $ext_if inet proto udp from any port = isakmp to any -> ($ext_if) \
           port 500

     # BINAT
     # Translate outgoing packets' source address (any protocol).
     # Translate incoming packets' destination address to an internal machine
     # (bidirectional).
     binat on $ext_if from 10.1.2.150 to any -> ($ext_if)

     # RDR
     # Translate incoming packets' destination addresses.
     # As an example, redirect a TCP and UDP port to an internal machine.
     rdr on $ext_if inet proto tcp from any to ($ext_if) port 8080 \
           -> 10.1.2.151 port 22
     rdr on $ext_if inet proto udp from any to ($ext_if) port 8080 \
           -> 10.1.2.151 port 53

     # RDR
     # Translate outgoing ftp control connections to send them to localhost
     # for proxying with ftp-proxy(8) running on port 8021.
     rdr on $int_if proto tcp from any to any port 21 -> 127.0.0.1 port 8021

     In this example, a NAT gateway is set up to translate internal addresses
     using a pool of public addresses (192.0.2.16/28) and to redirect incoming
     web server connections to a group of web servers on the internal network.

     # NAT LOAD BALANCE
     # Translate outgoing packets' source addresses using an address pool.
     # A given source address is always translated to the same pool address by
     # using the source-hash keyword.
     nat on $ext_if inet from any to any -> 192.0.2.16/28 source-hash

     # RDR ROUND ROBIN
     # Translate incoming web server connections to a group of web servers on
     # the internal network.
     rdr on $ext_if proto tcp from any to any port 80 \
           -> { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin

FILTER EXAMPLES
     # The external interface is kue0
     # (157.161.48.183, the only routable address)
     # and the private network is 10.0.0.0/8, for which we are doing NAT.

     # use a macro for the interface name, so it can be changed easily
     ext_if = "kue0"

     # normalize all incoming traffic
     scrub in on $ext_if all fragment reassemble

     # block and log everything by default
     block return log on $ext_if all

     # block anything coming from source we have no back routes for
     block in from no-route to any

     # block and log outgoing packets that do not have our address as source,
     # they are either spoofed or something is misconfigured (NAT disabled,
     # for instance), we want to be nice and do not send out garbage.
     block out log quick on $ext_if from ! 157.161.48.183 to any

     # silently drop broadcasts (cable modem noise)
     block in quick on $ext_if from any to 255.255.255.255

     # block and log incoming packets from reserved address space and invalid
     # addresses, they are either spoofed or misconfigured, we cannot reply to
     # them anyway (hence, no return-rst).
     block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \
           192.168.0.0/16, 255.255.255.255/32 } to any

     # ICMP

     # pass out/in certain ICMP queries and keep state (ping)
     # state matching is done on host addresses and ICMP id (not type/code),
     # so replies (like 0/0 for 8/0) will match queries
     # ICMP error messages (which always refer to a TCP/UDP packet) are
     # handled by the TCP/UDP states
     pass on $ext_if inet proto icmp all icmp-type 8 code 0 keep state

     # UDP

     # pass out all UDP connections and keep state
     pass out on $ext_if proto udp all keep state

     # pass in certain UDP connections and keep state (DNS)
     pass in on $ext_if proto udp from any to any port domain keep state

     # TCP

     # pass out all TCP connections and modulate state
     pass out on $ext_if proto tcp all modulate state

     # pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT)
     pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \
           auth } flags S/SA keep state

     # pass in data mode connections for ftp-proxy running on this host.
     # (see ftp-proxy(8) for details)
     pass in on $ext_if proto tcp from any to 157.161.48.183 port >= 49152 \
           flags S/SA keep state

     # Do not allow Windows 9x SMTP connections since they are typically
     # a viral worm. Alternately we could limit these OSes to 1 connection each.
     block in on $ext_if proto tcp from any os {"Windows 95", "Windows 98"} \
           to any port smtp

     # Packet Tagging

     # three interfaces: $int_if, $ext_if, and $wifi_if (wireless). NAT is
     # being done on $ext_if for all outgoing packets. tag packets in on
     # $int_if and pass those tagged packets out on $ext_if.  all other
     # outgoing packets (i.e., packets from the wireless network) are only
     # permitted to access port 80.

     pass in on $int_if from any to any tag INTNET keep state
     pass in on $wifi_if from any to any keep state

     block out on $ext_if from any to any
     pass out quick on $ext_if tagged INTNET keep state
     pass out on $ext_if from any to any port 80 keep state

     # tag incoming packets as they are redirected to spamd(8). use the tag
     # to pass those packets through the packet filter.

     rdr on $ext_if inet proto tcp from <spammers> to port smtp \
             tag SPAMD -> 127.0.0.1 port spamd

     block in on $ext_if
     pass in on $ext_if inet proto tcp tagged SPAMD keep state

GRAMMAR
     Syntax for pf.conf in BNF:

     line           = ( option | pf-rule | nat-rule | binat-rule | rdr-rule |
                      antispoof-rule | altq-rule | queue-rule | anchor-rule |
                      trans-anchors | load-anchors | table-rule )

     option         = "set" ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] |
                      [ "optimization" [ "default" | "normal" |
                      "high-latency" | "satellite" |
                      "aggressive" | "conservative" ] ]
                      [ "limit" ( limit-item | "{" limit-list "}" ) ] |
                      [ "loginterface" ( interface-name | "none" ) ] |
                      [ "block-policy" ( "drop" | "return" ) ] |
                      [ "state-policy" ( "if-bound" | "group-bound" |
                      "floating" ) ]
                      [ "require-order" ( "yes" | "no" ) ]
                      [ "fingerprints" filename ] |
                      [ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] )

     pf-rule        = action [ ( "in" | "out" ) ]
                      [ "log" | "log-all" ] [ "quick" ]
                      [ "on" ifspec ] [ route ] [ af ] [ protospec ]
                      hosts [ filteropt-list ]

     filteropt-list = filteropt-list filteropt | filteropt
     filteropt      = user | group | flags | icmp-type | icmp6-type | tos |
                      ( "keep" | "modulate" | "synproxy" ) "state"
                      [ "(" state-opts ")" ] |
                      "fragment" | "no-df" | "min-ttl" number |
                      "max-mss" number | "random-id" | "reassemble tcp" |
                      fragmentation | "allow-opts" |
                      "label" string | "tag" string | [ ! ] "tagged" string
                      "queue" ( string | "(" string [ [ "," ] string ] ")" )

     nat-rule       = [ "no" ] "nat" [ "pass" ] [ "on" ifspec ] [ af ]
                      [ protospec ] hosts [ "tag" string ]
                      [ "->" ( redirhost | "{" redirhost-list "}" )
                      [ portspec ] [ pooltype ] [ "static-port" ] ]

     binat-rule     = [ "no" ] "binat" [ "pass" ] [ "on" interface-name ]
                      [ af ] [ "proto" ( proto-name | proto-number ) ]
                      "from" address [ "/" mask-bits ] "to" ipspec
                      [ "tag" string ]
                      [ "->" address [ "/" mask-bits ] ]

     rdr-rule       = [ "no" ] "rdr" [ "pass" ] [ "on" ifspec ] [ af ]
                      [ protospec ] hosts [ "tag" string ]
                      [ "->" ( redirhost | "{" redirhost-list "}" )
                      [ portspec ] [ pooltype ] ]

     antispoof-rule = "antispoof" [ "log" ] [ "quick" ]
                      "for" ( interface-name | "{" interface-list "}" )
                      [ af ] [ "label" string ]

     table-rule     = "table" "<" string ">" [ tableopts-list ]
     tableopts-list = tableopts-list tableopts | tableopts
     tableopts      = "persist" | "const" | "file" string |
                      "{" [ tableaddr-list ] "}"
     tableaddr-list = tableaddr-list [ "," ] tableaddr-spec | tableaddr-spec
     tableaddr-spec = [ "!" ] tableaddr [ "/" mask-bits ]
     tableaddr      = hostname | ipv4-dotted-quad | ipv6-coloned-hex |
                      interface-name | "self"

     altq-rule      = "altq on" interface-name queueopts-list
                      "queue" subqueue
     queue-rule     = "queue" string [ "on" interface-name ] queueopts-list
                      subqueue

     anchor-rule    = "anchor" string [ ( "in" | "out" ) ] [ "on" ifspec ]
                      [ af ] [ "proto" ] [ protospec ] [ hosts ]

     trans-anchors  = ( "nat-anchor" | "rdr-anchor" | "binat-anchor" ) string
                      [ "on" ifspec ] [ af ] [ "proto" ] [ protospec ] [ hosts ]

     load-anchor    = "load anchor" anchorname:rulesetname "from" filename

     queueopts-list = queueopts-list queueopts | queueopts
     queueopts      = [ "bandwidth" bandwidth-spec ] |
                      [ "qlimit" number ] | [ "tbrsize" number ] |
                      [ "priority" number ] | [ schedulers ]
     schedulers     = ( cbq-def | priq-def | hfsc-def )
     bandwidth-spec = "number" ( "b" | "Kb" | "Mb" | "Gb" | "%" )

     action         = "pass" | "block" [ return ] | "scrub"
     return         = "drop" | "return" | "return-rst" [ "( ttl" number ")" ] |
                      "return-icmp" [ "(" icmpcode ["," icmp6code ] ")" ] |
                      "return-icmp6" [ "(" icmp6code ")" ]
     icmpcode       = ( icmp-code-name | icmp-code-number )
     icmp6code      = ( icmp6-code-name | icmp6-code-number )

     ifspec         = ( [ "!" ] interface-name ) | "{" interface-list "}"
     interface-list = [ "!" ] interface-name [ [ "," ] interface-list ]
     route          = "fastroute" |
                      ( "route-to" | "reply-to" | "dup-to" )
                      ( routehost | "{" routehost-list "}" )
                      [ pooltype ]
     af             = "inet" | "inet6"

     protospec      = "proto" ( proto-name | proto-number |
                      "{" proto-list "}" )
     proto-list     = ( proto-name | proto-number ) [ [ "," ] proto-list ]

     hosts          = "all" |
                      "from" ( "any" | "no-route" | "self" | host |
                      "{" host-list "}" ) [ port ] [ os ]
                      "to"   ( "any" | "no-route" | "self" | host |
                      "{" host-list "}" ) [ port ]

     ipspec         = "any" | host | "{" host-list "}"
     host           = [ "!" ] ( address [ "/" mask-bits ] | "<" string ">" )
     redirhost      = address [ "/" mask-bits ]
     routehost      = ( interface-name [ address [ "/" mask-bits ] ] )
     address        = ( interface-name | "(" interface-name ")" | hostname |
                      ipv4-dotted-quad | ipv6-coloned-hex )
     host-list      = host [ [ "," ] host-list ]
     redirhost-list = redirhost [ [ "," ] redirhost-list ]
     routehost-list = routehost [ [ "," ] routehost-list ]

     port           = "port" ( unary-op | binary-op | "{" op-list "}" )
     portspec       = "port" ( number | name ) [ ":" ( "*" | number | name ) ]
     os             = "os"  ( os-name | "{" os-list "}" )
     user           = "user" ( unary-op | binary-op | "{" op-list "}" )
     group          = "group" ( unary-op | binary-op | "{" op-list "}" )

     unary-op       = [ "=" | "!=" | "<" | "<=" | ">" | ">=" ]
                      ( name | number )
     binary-op      = number ( "<>" | "><" | ":" ) number
     op-list        = ( unary-op | binary-op ) [ [ "," ] op-list ]

     os-name        = operating-system-name
     os-list        = os-name [ [ "," ] os-list ]

     flags          = "flags" [ flag-set ] "/" flag-set
     flag-set       = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ]
                      [ "W" ]

     icmp-type      = "icmp-type" ( icmp-type-code | "{" icmp-list "}" )
     icmp6-type     = "icmp6-type" ( icmp-type-code | "{" icmp-list "}" )
     icmp-type-code = ( icmp-type-name | icmp-type-number )
                      [ "code" ( icmp-code-name | icmp-code-number ) ]
     icmp-list      = icmp-type-code [ [ "," ] icmp-list ]

     tos            = "tos" ( "lowdelay" | "throughput" | "reliability" |
                      [ "0x" ] number )

     state-opts     = state-opt [ [ "," ] state-opts ]
     state-opt      = ( "max" number | "no-sync" | timeout |
                      "source-track" [ ( "rule" | "global" ) ] |
                      "max-src-nodes" number | "max-src-states" number |
                      "if-bound" | "group-bound" | "floating" )

     fragmentation  = [ "fragment reassemble" | "fragment crop" |
                      "fragment drop-ovl" ]

     timeout-list   = timeout [ [ "," ] timeout-list ]
     timeout        = ( "tcp.first" | "tcp.opening" | "tcp.established" |
                      "tcp.closing" | "tcp.finwait" | "tcp.closed" |
                      "udp.first" | "udp.single" | "udp.multiple" |
                      "icmp.first" | "icmp.error" |
                      "other.first" | "other.single" | "other.multiple" |
                      "frag" | "interval" | "src.track" |
                      "adaptive.start" | "adaptive.end" ) number

     limit-list     = limit-item [ [ "," ] limit-list ]
     limit-item     = ( "states" | "frags" | "src-nodes" ) number

     pooltype       = ( "bitmask" | "random" |
                      "source-hash" [ ( hex-key | string-key ) ] |
                      "round-robin" ) [ sticky-address ]

     subqueue       = string | "{" queue-list "}"
     queue-list     = string [ [ "," ] string ]
     cbq-def        = "cbq" [ "(" cbq-opt [ [ "," ] cbq-opt ] ")" ]
     priq-def       = "priq" [ "(" priq-opt [ [ "," ] priq-opt ] ")" ]
     hfsc-def       = "hfsc" [ "(" hfsc-opt [ [ "," ] hfsc-opt ] ")" ]
     cbq-opt        = ( "default" | "borrow" | "red" | "ecn" | "rio" )
     priq-opt       = ( "default" | "red" | "ecn" | "rio" )
     hfsc-opt       = ( "default" | "red" | "ecn" | "rio" |
                      linkshare-sc | realtime-sc | upperlimit-sc )
     linkshare-sc   = "linkshare" sc-spec
     realtime-sc    = "realtime" sc-spec
     upperlimit-sc  = "upperlimit" sc-spec
     sc-spec        = ( bandwidth-spec |
                      "(" bandwidth-spec number bandwidth-spec ")" )

FILES
     /etc/hosts      Host name database.
     /etc/pf.conf    Default location of the ruleset file.
     /etc/pf.os      Default location of OS fingerprints.
     /etc/protocols  Protocol name database.
     /etc/services   Service name database.
     /usr/share/pf   Example rulesets.

SEE ALSO
     icmp(4), icmp6(4), ip(4), ip6(4), pf(4), pfsync(4), tcp(4), udp(4),
     hosts(5), pf.os(5), protocols(5), services(5), ftp-proxy(8), pfctl(8),
     pflogd(8)

HISTORY
     The pf.conf file format first appeared in OpenBSD 3.0.

OpenBSD 3.5                    November 19, 2002                            29
