PF.CONF(5)                    File Formats Manual                   PF.CONF(5)


     pf.conf - packet filter configuration file


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

     This is an overview of the sections in this manual page:

     Packet Filtering
     Packet filtering, including network address translation (NAT).

     Global options tune the behaviour of the packet filtering engine.

     Queueing provides rule-based bandwidth control.

     Tables provide a method for dealing with large numbers of addresses.

     Anchors are containers for rules and tables.

     Stateful Filtering
     Stateful filtering tracks packets by state.

     Traffic Normalisation
     Including scrub, fragment handling, and blocking spoofed traffic.

     Operating System Fingerprinting
     A method for detecting a host's operating system.

     Some example rulesets.

     Complete BNF grammar reference.

     The current line can be extended over multiple lines using a backslash
     (`\').  Comments can be put anywhere in the file using a hash mark (`#'),
     and extend to the end of the current line.  Care should be taken when
     commenting out multi-line text: the comment is effective until the end of
     the entire block.

     Argument names not beginning with a letter, digit, or underscore must be

     Additional configuration files can be included with the include keyword,
     for example:

           include "/etc/pf/sub.filter.conf"

     Macros can be defined that will later be expanded in context.  Macro
     names must start with a letter, digit, or underscore, and may contain any
     of those characters.  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
           pass in  on $ext_if proto tcp from any to any port 25


     pf(4) has the ability to block, pass, and match packets based on
     attributes of their layer 3 and layer 4 headers.  Filter rules determine
     which of these actions are taken; filter parameters specify the packets
     to which a rule applies.

     For each packet processed by the packet filter, the filter rules are
     evaluated in sequential order, from first to last.  For block and pass,
     the last matching rule decides what action is taken; if no rule matches
     the packet, the default action is to pass the packet without creating a
     state.  For match, rules are evaluated every time they match; the
     pass/block state of a packet remains unchanged.

     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 pfctl(8) generates all needed rule

     By default pf(4) filters packets statefully: the first time a packet
     matches a pass rule, a state entry is created.  The packet filter
     examines each packet to see if it matches an existing state.  If it does,
     the packet is passed without evaluation of any rules.  After the
     connection is closed or times out, the state entry is automatically

     The following actions can be used in the filter:

           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           This causes a TCP RST to be returned for TCP
                            packets and an ICMP UNREACHABLE for other types of
           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
           return-rst       This applies only to TCP packets, and issues a TCP
                            RST which closes the connection.  An optional
                            parameter, ttl, may be given with a TTL value.

           Options returning ICMP packets currently have no effect if pf(4)
           operates on a bridge(4), as the code to support this feature has
           not yet been implemented.

           The simplest mechanism to block everything by default and only pass
           packets that match explicit rules is specify a first filter rule

                 block all

           The packet is matched.  This mechanism is used to provide fine
           grained filtering without altering the block/pass state of a
           packet.  match rules differ from block and pass rules in that
           parameters are set every time a packet matches the rule, not only
           on the last matching rule.  For the following parameters, this
           means that the parameter effectively becomes ``sticky'' until
           explicitly overridden: nat-to, binat-to, rdr-to, queue, rtable, and

           log is different still, in that the action happens every time a
           rule matches i.e. a single packet can get logged more than once.

     pass  The packet is passed; state is created unless the no state option
           is specified.

     The following parameters can be used in the filter:

     in or out
             A packet always comes in on, or goes out through, one interface.
             in and out apply to incoming and outgoing packets; if neither are
             specified, the rule will match packets in both directions.

     log (all | matches | to <interface> | user)
             In addition to any action specified, log the packet.  Only the
             packet that establishes the state is logged, unless the no state
             option is specified.  The logged packets are sent to a pflog(4)
             interface, by default pflog0; pflog0 is monitored by the
             pflogd(8) logging daemon which logs to the file /var/log/pflog in
             pcap(3) binary format.

             The keywords all, matches, to, and user are all optional, and can
             be combined using commas.

             Use all to force logging of all packets for a connection.  This
             is not necessary when no state is explicitly specified.

             If matches is specified, it logs the packet on all subsequent
             matching rules.  It is often combined with to <interface> to
             avoid adding noise to the default log file.

             The keyword user logs the UID and PID of the socket on the local
             host used to send or receive a packet, in addition to the normal

             To specify a logging interface other than pflog0, use the syntax
             to <interface>.

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

     on <interface>
             This rule applies only to packets coming in on, or going out
             through, this particular interface or interface group.  For more
             information on interface groups, see the group keyword in
             ifconfig(8).  any will match any existing interface except
             loopback ones.

     on rdomain <number>
             This rule applies only to packets coming in on, or going out
             through, this particular routing domain.

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

     proto <protocol>
             This rule applies only to packets of this protocol.  Common
             protocols are ICMP, ICMP6, TCP, and UDP.  For a list of all the
             protocol name to number mappings used by pfctl(8), see the file

     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, interface names or interface group names,
             or as any of the following keywords:

             any             Any address.
             no-route        Any address which is not currently routable.
             route <label>   Any address matching the given route(8) label.
             self            Expands to all addresses assigned to all
             <table>         Any address matching the given table.
             urpf-failed     Any source address that fails a unicast reverse
                             path forwarding (URPF) check, i.e. packets coming
                             in on an interface other than that which holds
                             the route back to the packet's source address.

             Ranges of addresses are specified using the `-' operator.  For
             instance: `` -'' means all addresses from
    to, hence addresses,, and

             Interface names, interface group names, and self can have
             modifiers appended:

             :0            Do not include interface aliases.
             :broadcast    Translates to the interface's broadcast
             :network      Translates to the network(s) attached to the
             :peer         Translates to the point-to-point interface's peer

             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.
             Surrounding 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 interface changes its address.  The ruleset does not
             need to be reloaded.  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 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
             following 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 port >= 1024 \
                         to ! port != ssh
                   pass in proto tcp from any os "OpenBSD"
                   pass in proto tcp from route "DTAG"

     The following additional parameters can be used in the filter:

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

             By default, IPv4 packets with IP options or IPv6 packets with
             routing extension headers are blocked.  When allow-opts is
             specified for a pass rule, packets that pass the filter based on
             that rule (last matching) do so even if they contain IP options
             or routing extension headers.  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.

     divert-packet port <port>
             Used to send matching packets to divert(4) sockets bound to port
             port.  If the default option of fragment reassembly is enabled,
             scrubbing with reassemble tcp is also enabled for divert-packet

             Used to receive replies for sockets that are bound to addresses
             which are not local to the machine.  See setsockopt(2) for
             information on how to bind these sockets.

     divert-to <host> port <port>
             Used to redirect packets to a local socket bound to host and
             port.  The packets will not be modified, so getsockname(2) on the
             socket will return the original destination address of the

     flags <a> /<b> | any
             This rule only applies to TCP packets that have the flags <a> set
             out of set <b>.  Flags not specified in <b> are ignored.  For
             stateful connections, the default is flags S/SA.  To indicate
             that flags should not be checked at all, specify flags any.  The
             flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and

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

             flags S/SA  This is the default setting for stateful connections.
                         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 example.

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

             Because flags S/SA is applied by default (unless no state is
             specified), only the initial SYN packet of a TCP handshake will
             create a state for a TCP connection.  It is possible to be less
             restrictive, and allow state creation from intermediate (non-SYN)
             packets, by specifying flags any.  This will cause pf(4) to
             synchronize to existing connections, for instance if one flushes
             the state table.  However, states created from such intermediate
             packets may be missing connection details such as the TCP window
             scaling factor.  States which modify the packet flow, such as
             those affected by af-to, modulate, nat-to, rdr-to, or synproxy
             state options, or scrubbed with reassemble tcp, will also not be
             recoverable from intermediate packets.  Such connections will
             stall and time out.

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

     icmp-type <type> code <code>
     icmp6-type <type> code <code>
             This rule only applies to ICMP or ICMP6 packets with the
             specified type and code.  Text names for ICMP types and codes are
             listed in icmp(4) and icmp6(4).  The protocol and the ICMP type
             indicator (icmp-type or icmp6-type) must match.

     label <string>
             Adds a label 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:

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

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

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

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

     once    Creates a one shot rule that will remove itself from an active
             ruleset after the first match.  In case this is the only rule in
             the anchor, the anchor will be destroyed automatically after the
             rule is matched.

     probability <number>
             A probability attribute can be attached to a rule, with a value
             set between 0 and 100%, in which case the rule is honoured using
             the given probability value.  For example, the following rule
             will drop 20% of incoming ICMP packets:

                   block in proto icmp probability 20%

     prio <number>
             Only match packets which have the given queueing priority

     received-on <interface>
             Only match packets which were received on the specified interface
             (or interface group).  any will match any existing interface
             except loopback ones.

     rtable <number>
             Used to select an alternate routing table for the routing lookup.
             Only effective before the route lookup happened, i.e. when
             filtering inbound.

     set prio <priority> | (<priority>, <priority>)
             Packets matching this rule will be assigned a specific queueing
             priority.  Priorities are assigned as integers 0 through 7, with
             a default priority of 3.  If the packet is transmitted on a
             vlan(4) interface, the queueing priority will also be written as
             the priority code point in the 802.1Q VLAN header.  If two
             priorities are given, packets which have a TOS of lowdelay and
             TCP ACKs with no data payload will be assigned to the second one.
             Packets with a higher priority number are processed first, and
             packets with the same priority are processed in the order in
             which they are received.

             For example:

                   pass in proto tcp to port 25 set prio 2
                   pass in proto tcp to port 22 set prio (2, 5)

             The interface priority queues accessed by the set prio keyword
             are always enabled and do not require any additional
             configuration, unlike the queues described below and in the
             QUEUEING section.

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

     set tos <string> | <number>
             Enforces a TOS for matching packets.  string may be one of
             critical, inetcontrol, lowdelay, netcontrol, throughput,
             reliability, or one of the DiffServ Code Points: ef, af11 ...
             af43, cs0 ... cs7; number may be either a hex or decimal number.

     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.  Tags take the
             same macros as labels (see above).

     tagged <string>
             Used with filter or translation 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.

     tos <string> | <number>
             This rule applies to packets with the specified TOS bits set.
             string may be one of critical, inetcontrol, lowdelay, netcontrol,
             throughput, reliability, or one of the DiffServ Code Points: ef,
             af11 ... af43, cs0 ... cs7; number may be either a hex or decimal

             For example, the following rules are identical:

                   pass all tos lowdelay
                   pass all tos 0x10
                   pass all tos 16

     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 destination port.

             When listening sockets are bound to the wildcard address, pf(4)
             cannot determine if a connection is destined for the firewall
             itself.  To avoid false matches on just the destination port,
             combine a user rule with source or destination address self.

             All packets, both outgoing and incoming, of one connection are
             associated with the same user and group.  Only TCP and UDP
             packets can be associated with users.

             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 creates 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 following
             example allows only selected users to open outgoing connections:

                   block out proto tcp all
                   pass  out proto tcp from self user { < 1000, dhartmei }

     Translation options modify either the source or destination address and
     port of the packets associated with a stateful connection.  pf(4)
     modifies the specified address and/or port in the packet and recalculates
     IP, TCP, and UDP checksums as necessary.

     Subsequent rules will see packets as they look after any addresses and
     ports have been translated.  These rules will therefore have to filter
     based on the translated address and port number.

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

     Different types of translation are possible with pf:

     af-to     Translation between different address families (NAT64) is
               handled using af-to rules.  Because address family translation
               overrides the routing table, it's only possible to use af-to on
               inbound rules, and a source address for the resulting
               translation must always be specified.

               The optional second argument is the host or subnet the original
               addresses are translated into for the destination.  The lowest
               bits of the original destination address form the host part of
               the new destination address according to the specified subnet.
               It is possible to embed a complete IPv4 address into an IPv6
               address using a network prefix of /96 or smaller.

               When a destination address is not specified it is assumed that
               the host part is 32-bit long.  For IPv6 to IPv4 translation
               this would mean using only the lower 32 bits of the original
               IPv6 destination address.  For IPv4 to IPv6 translation the
               destination subnet defaults to the subnet of the new IPv6
               source address with a prefix length of /96.  See RFC 6052
               Section 2.2 for details on how the prefix determines the
               destination address encoding.

               For example, the following rules are identical:

                     pass in inet af-to inet6 from 2001:db8::1 to 2001:db8::/96
                     pass in inet af-to inet6 from 2001:db8::1

               In the above example the matching IPv4 packets will be modified
               to have a source address of 2001:db8::1 and a destination
               address will get prefixed with 2001:db8::/96, e.g.
      will be translated to 2001:db8::c633:6464.

               In the reverse case the following rules are identical:

                     pass in inet6 af-to inet from to
                     pass in inet6 af-to inet from

               The destination IPv4 address is assumed to be embedded inside
               the original IPv6 destination address, e.g. 64:ff9b::c633:6464
               will be translated to

               The current implementation will only extract IPv4 addresses
               from the IPv6 addresses with a prefix length of /96 and

     binat-to  A binat-to rule specifies a bidirectional mapping between an
               external IP netblock and an internal IP netblock.  It expands
               to an outbound nat-to rule and an inbound rdr-to rule.

     nat-to    A nat-to option 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.  Those netblocks

            - (all of net 10, i.e. 10/8)
            - (i.e. 172.16/12)
            - (i.e. 192.168/16)

               nat-to is usually applied outbound.  If applied inbound, nat-to
               to a local IP address is not supported.

     rdr-to    The packet is redirected to another destination and possibly a
               different port.  rdr-to can optionally specify port ranges
               instead of single ports.  For instance:

               match in ... port 2000:2999 rdr-to ... port 4000
                       redirects ports 2000 to 2999 (inclusive) to port 4000.

               match in ... port 2000:2999 rdr-to ... port 4000:*
                       redirects port 2000 to 4000, port 2001 to 4001, ...,
                       port 2999 to 4999.

               rdr-to is usually applied inbound.  If applied outbound, rdr-to
               to a local IP address is not supported.

     In addition to modifying the address, some translation rules may modify
     source or destination ports for TCP or UDP connections; implicitly in the
     case of nat-to options and explicitly in the case of rdr-to ones.  Port
     numbers are never translated with a binat-to rule.

     Translation options 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.

     However packets may be redirected to hosts connected to the interface the
     packet arrived on by using redirection with NAT.  For example:

           pass in on $int_if proto tcp from $int_net to $ext_if port 80 \
                   rdr-to $server
           pass out on $int_if proto tcp to $server port 80 \
                   received-on $int_if nat-to $int_if

     Note that redirecting external incoming connections to the loopback
     address 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.  For example:

           pass in on egress proto tcp from any to any port smtp \
                   rdr-to port spamd

     Unless this effect is desired, any of the local non-loopback addresses
     should be used instead as the redirection target, which allows external
     connections only to daemons bound to this address or not bound to any

     For af-to, nat-to and rdr-to 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:

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

     least-states [sticky-address]
           The least-states option selects the address with the least active
           states from a given address pool and considers given weights
           associated with address(es).  Weights can be specified between 1
           and 65535.  Addresses with higher weights are selected more often.

           sticky-address can be specified to ensure that multiple connections
           from the same source are mapped to the same redirection address.
           Associations are destroyed as soon as there are no longer states
           which refer to them; in order to make the mappings last beyond the
           lifetime of the states, increase the global options with set
           timeout src.track.

     random [sticky-address]
           The random option selects an address at random within the defined
           block of addresses.  sticky-address is as described above.

     round-robin [sticky-address]
           The round-robin option loops through the redirection address(es)
           and considers given weights associated with address(es).  Weights
           can be specified between 1 and 65535.  Addresses with higher
           weights are selected more often.  sticky-address is as described

     source-hash [key]
           The source-hash option uses a hash of the source address to
           determine 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
           default pfctl(8) randomly generates a key for source-hash every
           time the ruleset is reloaded.

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

     When more than one redirection address or a table is specified, bitmask
     is not permitted as a pool type.

     If a packet matches a rule with one of the following route options 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.

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

           The reply-to option is similar to route-to, but routes packets that
           pass in the opposite direction (replies) to the specified
           interface.  Opposite direction is only defined in the context of a
           state entry, and reply-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 incoming connection arrived through (symmetric
           routing enforcement).

           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

     For the dup-to, reply-to, and route-to route 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), the methods
     least-states, random, round-robin, and source-hash, as described above,
     can be used.


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

     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.

     set debug
             Set the debug level, which limits the severity of log messages
             printed by pf(4).  This should be a keyword from the following
             ordered list (highest to lowest): emerg, alert, crit, err,
             warning, notice, info, and debug.  These keywords correspond to
             the similar (LOG_) values specified to the syslog(3) library

     set fingerprints
             Load fingerprints of known operating systems from the given
             filename.  By default fingerprints of known operating systems are
             automatically loaded from pf.os(5), 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.

     set hostid
             The 32-bit hostid identifies this firewall's state table entries
             to other firewalls in a pfsync(4) failover cluster.  By default
             the hostid is set to a pseudo-random value, however it may be
             desirable to manually configure it, for example to more easily
             identify the source of state table entries.  The hostid may be
             specified in either decimal or hexadecimal.

     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, to set the maximum number of entries in the memory
             pool used by state table entries (generated by pass rules which
             do not specify no state) to 20000:

                   set limit states 20000

             To set the maximum number of entries in the memory pool used for
             fragment reassembly to 2000:

                   set limit frags 2000

             This maximum may not exceed, and should be well below, the
             maximum number of mbuf clusters (sysctl kern.maxclusters) in the

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

                   set limit src-nodes 2000

             To set limits on the memory pools used by tables:

                   set limit tables 1000
                   set limit table-entries 100000

             The first limits the number of tables that can exist to 1000.
             The second limits the overall number of addresses that can be
             stored in tables to 100000.

             Various limits can be combined on a single line:

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

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

                   # pfctl -s info

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

                   set loginterface dc0

             One can disable the loginterface using:

                   set loginterface none

     set optimization
             Optimize state timeouts for one of the following network

                     Aggressively expire connections.  This can greatly reduce
                     the memory usage of the firewall at the cost of dropping
                     idle connections early.
                     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.
                     A high-latency environment (such as a satellite
             normal  A normal network environment.  Suitable for almost all
                     Alias for high-latency.

     set reassemble
             The reassemble option is used to enable or disable the reassembly
             of fragmented packets, and can be set to yes (the default) or no.
             If no-df is also specified, fragments with the dont-fragment bit
             set are reassembled too, instead of being dropped; the
             reassembled packet will have the dont-fragment bit cleared.

     set ruleset-optimization
             basic     Enable basic ruleset optimization.  This is the default
                       behaviour.  Basic ruleset optimization does four things
                       to improve the performance of ruleset evaluations:

                       1.   remove duplicate rules
                       2.   remove rules that are a subset of another rule
                       3.   combine multiple rules into a table when
                       4.   re-order the rules to improve evaluation
             none      Disable the ruleset optimizer.
             profile   Uses the currently loaded ruleset as a feedback profile
                       to tailor the ordering of quick rules to actual network

             It is important to note that the ruleset optimizer will modify
             the ruleset to improve performance.  A side effect of the ruleset
             modification is that per-rule accounting statistics will have
             different meanings than before.  If per-rule accounting is
             important for billing purposes or whatnot, either the ruleset
             optimizer should not be used or a label field should be added to
             all of the accounting rules to act as optimization barriers.

             Optimization can also be set as a command-line argument to
             pfctl(8), overriding the settings in pf.conf.

     set skip on <ifspec>
             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.  ifspec
             is only evaluated when the ruleset is loaded; interfaces created
             later will not be skipped.

     set state-defaults
             The state-defaults option sets the state options for states
             created from rules without an explicit keep state.  For example:

                   set state-defaults pflow, no-sync

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

             if-bound  States are bound to an interface.
             floating  States can match packets on any interfaces (the

     set timeout
             frag       Seconds before an unassembled fragment is expired.
             interval   Interval between purging expired states and fragments.
             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 protocol and
             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.

                     The state after one endpoint sends an RST.
                     The state after the first FIN has been sent.
                     The fully established state.
                     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 tcp.finwait (and possibly
                     tcp.closing) can prevent blocking of such packets.
                     The state after the first packet.
                     The state after the second packet but before both
                     endpoints have acknowledged the connection.

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

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

             Other protocols are handled similarly to UDP:


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

                     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).
                     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 timeouts are enabled by default, with an adaptive.start
             value equal to 60% of the state limit, and an adaptive.end value
             equal to 120% of the state limit.  They can be disabled by
             setting both adaptive.start and adaptive.end to 0.

             The adaptive timeout 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).


     Packets can be assigned to queues for the purpose of bandwidth control.
     At least one declaration is 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 passed packets will be queued, while for blocked packets it
     specifies where any resulting ICMP or TCP RST packets should be queued.
     If the referenced queue does not exist on the outgoing interface the
     default queue for that interface is used.  Queues attached to an
     interface build a tree, thus each queue can have further child queues.
     Only leaf queues, i.e. queues without children, can be used to assign
     packets to.  The root queue must specifically reference an interface, all
     other queues pick up the interface(s) they should be created on from
     their parent queues unless explicitly specified.

     In the following example, a queue named std is created on the interface
     em0, with 3 child queues ssh, mail and http.

           queue std on em0 bandwidth 100M
           queue ssh parent std bandwidth 10M
           queue mail parent std bandwidth 10M
           queue http parent std bandwidth 80M default

     The specified bandwidth is the target bandwidth, every queue can receive
     more bandwidth as long as the parent still has some available.  The
     maximum bandwidth that should be assigned to a given queue can be limited
     using the max keyword.  Similarily, a minimum (reserved) bandwidth can be

           queue ssh parent std bandwidth 10M, min 5M, max 25M

     For each of these 3 bandwidth specifications an additional burst
     bandwidth and time can be specified.

           queue ssh parent std bandwidth 10M burst 90M for 100ms

     All bandwidth values must be specified as an absolute value.  The
     suffixes K, M, and G are used to represent bits, kilobits, megabits, and
     gigabits per second, respectively.  The value must not exceed the
     interface bandwidth.

     In addition to the bandwidth specifications queues support the following

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

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

     parent <name>
           Defines which parent queue the queue should be attached to.
           Mandantory for all queues except root queues.  The parent queue
           must exist.

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

     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)
     sessions get a queue with a minimum bandwidth; scp(1) and sftp(1) bulk
     transfers go to a separate queue.  The queues are then referenced by
     filtering rules (see PACKET FILTERING, above).

         queue rootq on em0 bandwidth 100M max 100M
         queue http parent rootq bandwidth 60M burst 90M for 100ms
         queue  developers parent http bandwidth 45M
         queue  employees parent http bandwidth 15M
         queue mail parent rootq bandwidth 10M
         queue ssh parent rootq bandwidth 20M
         queue  ssh_interactive parent ssh bandwidth 10M min 5M
         queue  ssh_bulk parent ssh bandwidth 10M
         queue std parent rootq bandwidth 20M default

         block return out on em0 inet all set queue std
         pass out on em0 inet proto tcp from $developerhosts to any port 80 \
               set queue developers
         pass out on em0 inet proto tcp from $employeehosts to any port 80 \
               set queue employees
         pass out on em0 inet proto tcp from any to any port 22 \
               set queue(ssh_bulk, ssh_interactive)
         pass out on em0 inet proto tcp from any to any port 25 \
               set queue mail


     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

     Tables can be used as the source or destination of filter or translation
     rules.  They can also be used for the redirect address of nat-to and
     rdr-to and in the routing options of filter rules, but not for bitmask

     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
               addresses 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 attributes:

     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.

              The counters flag enables per-address packet and byte counters,
              which can be displayed with pfctl(8).

     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.

     This example 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:

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

     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 the following:

           # pfctl -t badhosts -Tadd

     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 interface name, a valid interface group, or the self
     keyword, in which case all addresses assigned to the interface(s) will be
     added to the table.


     Besides the main ruleset, pf.conf can specify anchor attachment points.
     An anchor is a container that can hold rules, address tables, and other
     anchors.  When evaluation of the main ruleset reaches an anchor rule,
     pf(4) will proceed to evaluate all rules specified in that anchor.

     The following example blocks all packets on the external interface by
     default, then evaluates all rules in the anchor named "spam", and finally
     passes all outgoing connections and incoming connections to port 25:

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

     Anchors can be manipulated through pfctl(8) without reloading the main
     ruleset or other anchors.  This loads a single rule into the anchor,
     which blocks all packets from a specific address:

           # echo "block in quick from to any" | pfctl -a spam -f -

     The anchor can also be populated by adding a load anchor rule after the
     anchor rule.  When pfctl(8) loads pf.conf, it will also load all the
     rules from the file /etc/pf-spam.conf into the anchor.

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

     Filter rule anchors can also be loaded inline in the ruleset within a
     brace-delimited block.  Brace delimited blocks may contain rules or other
     brace-delimited blocks.  When anchors are loaded this way the anchor name
     becomes optional.  Since the parser specification for anchor names is a
     string, double quote characters (`"') should be placed around the anchor

           anchor "external" on egress {
                   anchor out {
                           pass proto tcp from any to port { 25, 80, 443 }
                   pass in proto tcp to any port 22

     Anchor rules can also specify packet filtering parameters 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 anchors, like:

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

     The rules inside anchor "spam" are only evaluated for TCP packets with
     destination port 25.  Hence, the following will only block connections
     from to port 25:

           # echo "block in quick from to any" | pfctl -a spam -f -

     Matching filter and translation rules marked with the quick option are
     final and abort the evaluation of the rules in other anchors and the main
     ruleset.  If the anchor itself is marked with the quick option, ruleset
     evaluation will terminate when the anchor is exited if the packet is
     matched by any rule within the anchor.

     An anchor references other anchor attachment points using the following

     anchor <name>
           Evaluates the filter rules in the specified anchor.

     An anchor has a name which specifies the path where pfctl(8) can be used
     to access the anchor to perform operations on it, such as attaching child
     anchors to it or loading rules into it.  Anchors may be nested, with
     components separated by `/' characters, similar to how file system
     hierarchies are laid out.  The main ruleset is actually the default
     anchor, so filter and translation rules, for example, may also be
     contained in any anchor.

     Anchor rules are evaluated relative to the anchor in which they are
     contained.  For example, all anchor rules specified in the main ruleset
     will reference anchor attachment points underneath the main ruleset, and
     anchor rules specified in a file loaded from a load anchor rule will be
     attached under that anchor point.

     Anchors may end with the asterisk (`*') character, which signifies that
     all anchors attached at that point should be evaluated in the
     alphabetical ordering of their anchor name.  For example, the following
     will evaluate each rule in each anchor attached to the "spam" anchor:

           anchor "spam/*"

     Note that it will only evaluate anchors that are directly attached to the
     "spam" anchor, and will not descend to evaluate anchors recursively.

     Since anchors are evaluated relative to the anchor in which they are
     contained, there is a mechanism for accessing the parent and ancestor
     anchors of a given anchor.  Similar to file system path name resolution,
     if the sequence `..' appears as an anchor path component, the parent
     anchor of the current anchor in the path evaluation at that point will
     become the new current anchor.  As an example, consider the following:

           # printf 'anchor "spam/allowed"\n' | pfctl -f -
           # printf 'anchor "../banned"\npass\n' | pfctl -a spam/allowed -f -

     Evaluation of the main ruleset will lead into the spam/allowed anchor,
     which will evaluate the rules in the spam/banned anchor, if any, before
     finally evaluating the pass rule.


     pf(4) filters packets statefully, which has several advantages.  For TCP
     connections, comparing a packet to a state involves checking its sequence
     numbers, as well as TCP timestamps if a rule using the reassemble tcp
     parameter applies to the connection.  If these values 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.
     Similarly, pf(4) knows how to match ICMP replies to states.  For example,
     to allow echo requests (such as those created by ping(8)) out statefully
     and match incoming echo replies correctly to states:

           pass out inet proto icmp all icmp-type echoreq

     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

     Furthermore, correct handling of ICMP error messages is critical to many
     protocols, particularly TCP.  pf(4) matches ICMP error messages to the
     correct connection, checks them against connection parameters, and passes
     them if appropriate.  For example if an ICMP source quench message
     referring to a stateful TCP connection arrives, it will be matched to the
     state and get passed.

     Finally, state tracking is required for nat-to and rdr-to options, in
     order to track address and port translations and reverse the translation
     on returning packets.

     pf(4) will also create state for other protocols which are effectively
     stateless by nature.  UDP packets are matched to states using only host
     addresses and ports, and other protocols are matched to states using only
     the host addresses.

     If stateless filtering of individual packets is desired, the no state
     keyword can be used to specify that state will not be created if this is
     the last matching rule.  Note that packets which match neither block nor
     pass rules, and thus are passed by default, are effectively passed as if
     no state had been specified.

     A number of parameters can also be set to affect how pf(4) handles state
     tracking, as detailed below.

   State Modulation
     Much of the security derived from TCP is attributable to how well the
     initial sequence numbers (ISNs) are chosen.  Some popular stack
     implementations choose very poor ISNs and thus are normally susceptible
     to ISN prediction exploits.  By applying a modulate state rule to a TCP
     connection, 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/SFRA \
                 modulate state

     Note that modulated connections will not recover 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.  The
     default flags settings (or a more strict equivalent) should be used on
     modulate state rules to prevent ACK storms.

     Note that alternative methods are available to prevent loss of the state
     table and allow for firewall failover.  See carp(4) and pfsync(4) for
     further information.

   SYN Proxy
     By default, pf(4) passes packets that are part of a TCP handshake between
     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

     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
     connection from/to the other endpoint.  pf(4) chooses random initial
     sequence numbers for both handshakes.  Once the handshakes are completed,
     the sequence number modulators (see previous section) are used to
     translate further packets of the connection.  synproxy state includes
     modulate state.

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


           pass in proto tcp from any to any port www synproxy state

   Stateful Tracking Options
     A number of options related to stateful tracking can be applied on a per-
     rule basis.  One of keep state, modulate state, or synproxy state must be
     specified explicitly to apply these options to a rule.

           States can match packets on any interfaces (the opposite of
           if-bound).  This is the default.
           States are bound to an interface (the opposite of floating).
     max <number>
           Limits the number of concurrent states the rule may create.  When
           this limit is reached, further packets that would create state are
           dropped until existing states time out.
           Prevent state changes for states created by this rule from
           appearing on the pfsync(4) interface.
           States created by this rule are exported on the pflow(4) interface.
           Uses a sloppy TCP connection tracker that does not check sequence
           numbers at all, which makes insertion and ICMP teardown attacks way
           easier.  This is intended to be used in situations where one does
           not see all packets of a connection, e.g. in asymmetric routing
           situations.  It cannot be used with modulate or synproxy state.
     <timeout> <seconds>
           Changes the timeout values used for states created by 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 keep state \
                 (max 100, source-track rule, max-src-nodes 75, \
                 max-src-states 3, tcp.established 60, tcp.closing 5)

     When the source-track keyword is specified, the number of states per
     source IP is tracked.

     source-track global
           The number of states created by all rules that use this option is
           limited.  Each rule can specify different max-src-nodes and
           max-src-states options, however state entries created by any
           participating rule count towards each individual rule's limits.
     source-track rule
           The maximum number of states created by this rule is limited by the
           rule's max-src-nodes and max-src-states options.  Only state
           entries created by this particular rule count toward the rule's

     The following limits can be set:

     max-src-nodes <number>
           Limits the maximum number of source addresses which can
           simultaneously have state table entries.
     max-src-states <number>
           Limits the maximum number of simultaneous state entries that a
           single source address can create with this rule.

     For stateful TCP connections, limits on established connections
     (connections which have completed the TCP 3-way handshake) can also be
     enforced per source IP.

     max-src-conn <number>
           Limits the maximum number of simultaneous TCP connections which
           have completed the 3-way handshake that a single host can make.
     max-src-conn-rate <number> / <seconds>
           Limit the rate of new connections over a time interval.  The
           connection rate is an approximation calculated as a moving average.

     When one of these limits is reached, further packets that would create
     state are dropped until existing states time out.

     Because the 3-way handshake ensures that the source address is not being
     spoofed, more aggressive action can be taken based on these limits.  With
     the overload <table> state option, source IP addresses which hit either
     of the limits on established connections will be added to the named
     table.  This table can be used in the ruleset to block further activity
     from the offending host, redirect it to a tarpit process, or restrict its

     The optional flush keyword kills all states created by the matching rule
     which originate from the host which exceeds these limits.  The global
     modifier to the flush command kills all states originating from the
     offending host, regardless of which rule created the state.

     For example, the following rules will protect the webserver against hosts
     making more than 100 connections in 10 seconds.  Any host which connects
     faster than this rate will have its address added to the <bad_hosts>
     table and have all states originating from it flushed.  Any new packets
     arriving from this host will be dropped unconditionally by the block

           block quick from <bad_hosts>
           pass in on $ext_if proto tcp to $webserver port www keep state \
                 (max-src-conn-rate 100/10, overload <bad_hosts> flush global)


     Traffic normalisation is a broad umbrella term for aspects of the packet
     filter which deal with verifying packets, packet fragments, spoof
     traffic, and other irregularities.

     Scrub involves sanitising packet content in such a way that there are no
     ambiguities in packet interpretation on the receiving side.  It is
     invoked with the scrub option, added to regular rules.

     Parameters are specified enclosed in parentheses.  At least one of the
     following parameters must be specified:

     max-mss <number>
           Enforces a maximum segment size (MSS) for matching TCP packets.

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

           Clears the dont-fragment bit from a matching IPv4 packet.  Some
           operating systems have NFS implementations which are known to
           generate fragmented packets with the dont-fragment bit set.  pf(4)
           will drop such fragmented dont-fragment packets unless no-df is

           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 deleterious results if an upstream router later fragments the
           packet.  Using random-id is recommended in combination with no-df
           to ensure unique IP identifiers.

           Replaces the IPv4 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.

     reassemble tcp
           Statefully normalises TCP connections.  reassemble tcp performs the
           following normalisations:

           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.  reassemble tcp will raise the TTL of all packets
           back up to the highest value seen on the connection.

           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.  reassemble tcp will cause scrub
           to modulate the TCP timestamps with a random number.

           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.  reassemble tcp
           also makes sure the timestamp on the packet does not go forward
           more than the RFC allows.  By doing this, 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.

     For example:

           match in all scrub (no-df random-id max-mss 1440)

   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
     necessary 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
     subprotocol that allows pf(4) to filter on things such as TCP ports or to
     perform NAT.

     One alternative is to filter individual fragments with filter rules.  If
     packet reassembly is turned off, 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:

           pass in proto tcp from any to any port 80

     The rule above 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 impossible.

     In most cases, the benefits of reassembly outweigh the additional memory
     cost, so reassembly is on by default.

     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

     When forwarding reassembled IPv6 packets, pf refragments them with the
     original maximum fragment size.  This allows the sender to determine the
     optimal fragment size by path MTU discovery.

   Blocking Spoofed Traffic
     Spoofing is the faking of IP addresses, typically for malicious purposes.
     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

     For example:
           antispoof for lo0

     Expands to:
           block drop in on ! lo0 inet from 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 and a
     netmask of

           antispoof for wi0 inet

     Expands to:
           block drop in on ! wi0 inet from to any
           block drop in inet from to any

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


     Passive OS fingerprinting is a mechanism to inspect nuances of a TCP
     connection's initial SYN packet and guess at the host's operating system.
     Unfortunately these nuances are easily spoofed by an attacker so the
     fingerprint 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 vendor 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 as:

           "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
     normalised 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
     fingerprints may be listed by running:

           # pfctl -so

     Filter rules can enforce policy at any level of operating system
     specification 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.


           pass  out proto tcp from any os OpenBSD
           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"

     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.


     In this example, the external interface is kue0.  We use a macro for the
     interface name, so it can be changed easily.  All incoming traffic is
     "normalised", and everything is blocked and logged by default.

         ext_if = "kue0"
         match in all scrub (no-df max-mss 1440)
         block return log on $ext_if all

     Here we specifically block packets we don't want: anything coming from
     source we have no back routes for; packets whose ingress interface does
     not match the one in the route back to their source address; anything
     that does not have our address ( as source; broadcasts
     (cable modem noise); and anything from reserved address space or invalid

         block in from no-route to any
         block in from urpf-failed to any
         block out log quick on $ext_if from ! to any
         block in quick on $ext_if from any to
         block in log quick on $ext_if from {,, \
   , } to any

     For ICMP, pass out/in ping queries.  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

     For UDP, pass out all UDP connections.  DNS connections are passed in.

         pass out on $ext_if proto udp all
         pass in on $ext_if proto udp from any to any port domain

     For TCP, pass out all TCP connections and modulate state.  SSH, SMTP,
     DNS, and IDENT connections are passed in.  We do not allow Windows 9x
     SMTP connections since they are typically a viral worm.

         pass out on $ext_if proto tcp all modulate state
         pass in on $ext_if proto tcp from any to any \
             port { ssh, smtp, domain, auth }
         block in on $ext_if proto tcp from any \
             os { "Windows 95", "Windows 98" } to any port smtp

     Here we pass in/out all IPv6 traffic: note that we have to enable this in
     two different ways, on both our physical interface and our tunnel.

         pass quick on gif0 inet6
         pass quick on $ext_if proto ipv6

     This example illustrates packet tagging.  There are three interfaces:
     $int_if, $ext_if, and $wifi_if (wireless).  NAT is being done on $ext_if
     for all outgoing packets.  Packets in on $int_if are tagged and passed
     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
         pass in on $wifi_if from any to any

         block out on $ext_if from any to any
         pass out quick on $ext_if tagged INTNET
         pass out on $ext_if proto tcp from any to any port 80

     In this example, we tag incoming packets as they are redirected to
     spamd(8).  The tag is used to pass those packets through the packet

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

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

     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).

         match in on $ext_if proto tcp from any to any port 80 \
               rdr-to port 8080

     If a pass rule is used with the quick modifier, packets matching the
     translation rule are passed without inspecting subsequent filter rules.

         pass in quick on $ext_if proto tcp from any to any port 80 \
               rdr-to port 8080

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

         match out on ! vlan12 from to any nat-to

     In the example below, the machine sits between a fake internal
     144.19.74.* network, and a routable external IP of  The
     last rule excludes protocol AH from being translated.

         pass out on $ext_if from nat-to
         pass out on $ext_if proto ah from

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

         pass in on $int_if proto { tcp, udp } from any to any port 80 \
               rdr-to port 80
         pass in on $int_if proto { tcp, udp } from any to $server port 80
         pass in on $int_if proto { tcp, udp } from $sysadmins to any port 80

     This example maps 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.

         match out on $ext_if inet proto udp from any port isakmp to any \
             nat-to ($ext_if) port 500

     One more example uses rdr-to to redirect a TCP and UDP port to an
     internal machine.

         match in on $ext_if inet proto tcp from any to ($ext_if) port 8080 \
               rdr-to port 22
         match in on $ext_if inet proto udp from any to ($ext_if) port 8080 \
               rdr-to port 53

     In this example, a NAT gateway is set up to translate internal addresses
     using a pool of public addresses (  A given source address
     is always translated to the same pool address by using the source-hash
     keyword.  The gateway also translates incoming web server connections to
     a group of web servers on the internal network.

         match out on $ext_if inet from any to any nat-to \
         match in  on $ext_if proto tcp from any to any port 80 \
             rdr-to { weight 2, weight 1, \
             weight 8 } round-robin

     The bidirectional address translation example uses a single binat-to rule
     that expands to a nat-to and an rdr-to rule.

         pass on $ext_if from to any binat-to

     The previous example is identical to the following set of rules:

         pass out on $ext_if inet from to any \
               nat-to static-port
         pass in on $ext_if inet from any to rdr-to

     In the example below, a router handling both address families translates
     an internal IPv4 subnet to IPv6 using the well-known 64:ff9b::/96 prefix:

         pass in on $v4_if inet af-to inet6 from ($v6_if) to 64:ff9b::/96

     Paired with the example above, the example below can be used on another
     router handling both address families to translate back to IPv4:

         pass in on $v6_if inet6 to 64:ff9b::/96 af-to inet from ($v4_if)


     Syntax for pf.conf in BNF:

     line           = ( option | pf-rule |
                      antispoof-rule | queue-rule | anchor-rule |
                      anchor-close | load-anchor | table-rule | include )

     option         = "set" ( [ "timeout" ( timeout | "{" timeout-list "}" ) ] |
                      [ "ruleset-optimization" [ "none" | "basic" |
                      "profile" ] ] |
                      [ "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" | "floating" ) ]
                      [ "state-defaults" state-opts ]
                      [ "fingerprints" filename ] |
                      [ "skip on" ifspec ] |
                      [ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] |
                      [ "reassemble" ( "yes" | "no" ) [ "no-df" ] ] )

     pf-rule        = action [ ( "in" | "out" ) ]
                      [ "log" [ "(" logopts ")"] ] [ "quick" ]
                      [ "on" ( ifspec | "rdomain" number ) ] [ af ]
                      [ protospec ] hosts [ filteropts ]

     logopts        = logopt [ [ "," ] logopts ]
     logopt         = "all" | "matches" | "user" | "to" interface-name

     filteropts     = filteropt [ [ "," ] filteropts ]
     filteropt      = user | group | flags | icmp-type | icmp6-type |
                      "tos" tos |
                      ( "no" | "keep" | "modulate" | "synproxy" ) "state"
                      [ "(" state-opts ")" ] | "scrub" "(" scrubopts ")" |
                      "fragment" | "allow-opts" | "once" |
                      "divert-packet" "port" port | "divert-reply" |
                      "divert-to" host "port" port |
                      "label" string | "tag" string | [ ! ] "tagged" string |
                      "set prio" ( number | "(" number [ [ "," ] number ] ")" ) |
                      "set queue" ( string | "(" string [ [ "," ] string ] ")" ) |
                      "rtable" number | "probability" number"%" | "prio" number |
                      "af-to" af "from" ( redirhost | "{" redirhost-list "}" )
                      [ "to" ( redirhost | "{" redirhost-list "}" ) ] |
                      "binat-to" ( redirhost | "{" redirhost-list "}" )
                      [ portspec ] [ pooltype ] |
                      "rdr-to" ( redirhost | "{" redirhost-list "}" )
                      [ portspec ] [ pooltype ] |
                      "nat-to" ( redirhost | "{" redirhost-list "}" )
                      [ portspec ] [ pooltype ] [ "static-port" ] |
                      [ route ] | [ "set tos" tos ] |
                      [ [ "!" ] "received-on" ( interface-name | interface-group ) ]

     scrubopts      = scrubopt [ [ "," ] scrubopts ]
     scrubopt       = "no-df" | "min-ttl" number | "max-mss" number |
                      "reassemble tcp" | "random-id"

     antispoof-rule = "antispoof" [ "log" ] [ "quick" ]
                      "for" ifspec [ af ] [ "label" string ]

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

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

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

     anchor-close   = "}"

     load-anchor    = "load anchor" string "from" filename

     queueopts-list = queueopts-list queueopts | queueopts
     queueopts      = [ "bandwidth" bandwidth ] | [ "min" bandwidth ] |
                      [ "max" bandwidth ] | [ "parent" string ] |
                      [ "default" ] | [ "qlimit" number ]
     bandwidth      = bandwidth-spec [ "burst" bandwidth-spec "for" number "ms" ]
     bandwidth-spec = number ( "" | "K" | "M" | "G" )

     action         = "pass" | "match" | "block" [ return ]
     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-group ) ) |
                      "{" interface-list "}"
     interface-list = [ "!" ] ( interface-name | interface-group )
                      [ [ "," ] interface-list ]
     route          = ( "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" | "urpf-failed" | "self" |
                      host | "{" host-list "}" | "route" string ) [ port ]
                      [ os ]
                      "to"   ( "any" | "no-route" | "self" | host |
                      "{" host-list "}" | "route" string ) [ port ]

     ipspec         = "any" | host | "{" host-list "}"
     host           = [ "!" ] ( address [ "weight" number ] |
                      address [ "/" mask-bits ] [ "weight" number ] |
                      "<" string ">" )
     redirhost      = address [ "/" mask-bits ]
     routehost      = host | host "@" interface-name |
                      "(" interface-name [ address [ "/" mask-bits ] ] ")"
     address        = ( interface-name | interface-group |
                      "(" ( interface-name | interface-group ) ")" |
                      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 | "any" )
     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            = ( "lowdelay" | "throughput" | "reliability" |
                      [ "0x" ] number )

     state-opts     = state-opt [ [ "," ] state-opts ]
     state-opt      = ( "max" number | "no-sync" | timeout | "sloppy" |
                      "pflow" | "source-track" [ ( "rule" | "global" ) ] |
                      "max-src-nodes" number | "max-src-states" number |
                      "max-src-conn" number |
                      "max-src-conn-rate" number "/" number |
                      "overload" "<" string ">" [ "flush" [ "global" ] ] |
                      "if-bound" | "floating" )

     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" | "tables" |
                      "table-entries" ) number

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

     include        = "include" filename


     /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.


     pf(4), pflow(4), pfsync(4), pf.os(5), pfctl(8), pflogd(8)


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

OpenBSD 5.7                    February 16, 2015                   OpenBSD 5.7

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