OpenBSD manual page server

NAME

pf.conf — packet filter configuration file

DESCRIPTION

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

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

PACKET FILTERING

including network address translation (NAT).

OPTIONS

globally tune the behaviour of the packet filtering engine.

QUEUEING

provides rule-based bandwidth and traffic control.

TABLES

provide a method for dealing with large numbers of addresses.

ANCHORS

are containers for rules and tables.

STATEFUL FILTERING

tracks packets by state.

TRAFFIC NORMALISATION

includes scrub, fragment handling, and blocking spoofed traffic.

OPERATING SYSTEM FINGERPRINTING

is a method for detecting a host's operating system.

EXAMPLES

provides some example rulesets.

GRAMMAR

provides a 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 quoted.

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

PACKET FILTERING

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.

Each time a packet processed by the packet filter comes in on or goes out through an interface, 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. The matching for some parameters can be inverted with the ! operator. Certain parameters can be expressed as lists, in which case pfctl(8) generates all needed rule combinations.

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 removed.

The following actions can be used in the filter:

block

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

drop

The packet is silently dropped.

return

This causes a TCP RST to be returned for TCP packets and an ICMP UNREACHABLE for other types of packets.

return-icmp

 

return-icmp6

This causes ICMP messages to be returned for packets which match the rule. By default this is an ICMP UNREACHABLE message, however this can be overridden by specifying a message as a code or number.

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 of:

block all

match

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 scrub.

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 binary format.

The keywords all, matches, to, and user are optional and can be combined using commas, but must be enclosed in parentheses if given.

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 information.

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 | any

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.

inet | inet6

This rule applies only to packets of this address family.

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 /etc/protocols.

from source port source os source to dest port dest

This rule applies only to packets with the specified source and destination addresses and ports.

Addresses can be specified in CIDR notation (matching netblocks), as symbolic host names, 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 interfaces.

<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: “10.1.1.10 - 10.1.1.12” means all addresses from 10.1.1.10 to 10.1.1.12, hence addresses 10.1.1.10, 10.1.1.11, and 10.1.1.12.

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

:0

Do not include interface aliases.

:broadcast

Translates to the interface's broadcast address(es).

:network

Translates to the network(s) attached to the interface.

:peer

Translates to the point-to-point interface's peer address(es).

Host names may also have the :0 modifier 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 10.0.0.0/8 port >= 1024 \
      to ! 10.1.2.3 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’.

allow-opts

By default, packets with IPv4 options or IPv6 hop-by-hop or destination options header 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 options. For packets that match state, the rule that initially created the state is used. The implicit pass rule, that is used when a packet does not match any rules, does not allow IP options or option headers. Note that IPv6 packets with type 0 routing headers are always dropped.

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 rules.

divert-reply

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, preserving the original destination address for the application to access. SOCK_STREAM connections can access the original destination address using getsockname(2). SOCK_DGRAM sockets can be configured with the ip(4) IP_RECVDSTADDR and IP_RECVDSTPORT socket options when receiving IPv4 packets, or the ip6(4) IPV6_RECVPKTINFO and IPV6_RECVDSTPORT socket options when receiving IPv6 packets.

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 C(W)R.

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 state, 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.

ICMP responses are not permitted unless they either match an existing request, or unless no state or keep state (sloppy) is specified.

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

Expands to:

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

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

max-pkt-rate number/seconds

Measure the rate of packets matching the rule and states created by it. When the specified rate is exceeded, the rule stops matching. Only packets in the direction in which the state was created are considered, so that typically requests are counted and replies are not. For example, to pass up to 100 ICMP packets per 10 seconds:

block in proto icmp
pass in proto icmp max-pkt-rate 100/10

When the rate is exceeded, all ICMP is blocked until the rate falls below 100 per 10 seconds again.

once

Create a one shot rule. The first matching packet marks the rule as expired. Expired rules are skipped and hidden, unless pfctl(8) is used in debug or verbose mode.

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 assigned.

[!]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 delay milliseconds

Packets matching this rule will be delayed at the outbound interface by the given number of milliseconds.

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, TCP ACKs with no data payload and packets which have a TOS of lowdelay 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 string in order to match the rule.

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 number.

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.

The user and group arguments 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 }

The example below permits users with uid between 1000 and 1500 to open connections:

block out proto tcp all
pass  out proto tcp from self user { 999 >< 1501 }

The ‘:’ operator, which works for port number matching, does not work for user and group match.

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

pass in on egress proto tcp from any to any port smtp \
	rdr-to 127.0.0.1 port spamd

OPTIONS

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

set block-policy drop | return

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.

The default value is drop.

set debug level

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 routine. The default value is err.

set fingerprints filename

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. The default location for fingerprints is /etc/pf.os.

set hostid number

The 32-bit hostid number 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 limit-item number

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

Limits can be set on the following:

states

Set the maximum number of entries in the memory pool used by state table entries (those generated by pass rules which do not specify no state). The default is 100000.

src-nodes

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). The default is 10000.

frags

Set the maximum number of entries in the memory pool used for fragment reassembly. The maximum may not exceed, and should be well below, the maximum number of mbuf clusters (sysctl kern.maxclusters) in the system. The default is NMBCLUSTERS/32. NMBCLUSTERS defines the total number of packets which can exist in-system at any one time. Refer to <machine/param.h> for the platform-specific value.

tables

Set the number of tables that can exist. The default is 1000.

table-entries

Set the number of addresses that can be stored in tables. The default is 200000, or 100000 on machines with less than 100MB of physical memory.

pktdelay_pkts

Set the maximum number of packets that can be held in the delay queue. The default is 10000.

anchors

Set the number of anchors that can exist. The default is 512.

Multiple limits can be combined on a single line:

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

set loginterface interface | none

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 dc0:

set loginterface dc0

One can disable the loginterface using:

set loginterface none

The default value is none.

set optimization environment

Optimize state timeouts for one of the following network environments:

aggressive

Aggressively expire connections. This can greatly reduce the memory usage of the firewall at the cost of dropping idle connections early.

conservative

Extremely conservative settings. Avoid dropping legitimate connections at the expense of greater memory utilization (possibly much greater on a busy network) and slightly increased processor utilization.

high-latency

A high-latency environment (such as a satellite connection).

normal

A normal network environment. Suitable for almost all networks.

satellite

Alias for high-latency.

The default value is normal.

set reassemble yes | no [no-df]

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. The default value is yes.

set ruleset-optimization level

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 advantageous
4. reorder the rules to improve evaluation performance

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 traffic.

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. PF filters traffic on all interfaces by default.

set state-defaults state-option, ...

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 if-bound | floating

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 default).

set syncookies never | always | adaptive

When syncookies are active, pf will answer each and every incoming TCP SYN with a syncookie SYNACK, without allocating any resources. Upon reception of the client's ACK in response to the syncookie SYNACK, pf will evaluate the ruleset and create state if the ruleset permits it, complete the three way handshake with the target host, and continue the connection with synproxy in place. This allows pf to be resilient against large synflood attacks, which could otherwise exhaust the state table. Due to the blind answers to each and every SYN, syncookies share the caveats of synproxy: seemingly accepting connections that will be dropped later on.

never

pf will never send syncookie SYNACKs (the default).

always

pf will always send syncookie SYNACKs.

adaptive

pf will enable syncookie mode when a given percentage of the state table is used up by half-open TCP connections, such as those that saw the initial SYN but didn't finish the three way handshake. The thresholds for entering and leaving syncookie mode can be specified using:

set syncookies adaptive (start 25%, end 12%)

set timeout variable value

frag

Seconds before an unassembled fragment is expired (60 by default).

interval

Interval between purging expired states and fragments (10 seconds by default).

src.track

Length of time to retain a source tracking entry after the last state expires (0 by default, which means there is no global limit. The value is defined by the rule which creates the state.).

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. Alternatively, these values may be adjusted collectively in a manner suitable for a specific environment using set optimization (see above).

tcp.closed (90 seconds by default)

The state after one endpoint sends an RST.

tcp.closing (900 seconds by default)

The state after the first FIN has been sent.

tcp.established (24 hours by default)

The fully established state.

tcp.finwait (45 seconds by default)

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.

tcp.first (120 seconds by default)

The state after the first packet.

tcp.opening (30 seconds by default)

The state after the second packet but before both endpoints have acknowledged the connection.

tcp.tsdiff (30 seconds by default)

Maximum allowed time difference between RFC 1323 compliant packet timestamps.

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

icmp.error (10 seconds by default)

The state after an ICMP error came back in response to an ICMP packet.

icmp.first (20 seconds by default)

The state after the first packet.

udp.first (60 seconds by default)

The state after the first packet.

udp.multiple (60 seconds by default)

The state if both hosts have sent packets.

udp.single (30 seconds by default)

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:

other.first (60 seconds by default)

 

other.multiple (60 seconds by default)

 

other.single (30 seconds by default)

 

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

adaptive.start (60000 states by default)

When the number of state entries exceeds this value, adaptive scaling begins. All timeout values are scaled linearly with factor (adaptive.end - number of states) / (adaptive.end - adaptive.start).

adaptive.end (120000 states by default)

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).

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 60000, adaptive.end 120000 }
set limit states 100000

With 90000 state table entries, the timeout values are scaled to 50% (tcp.first 60, tcp.established 43200).

“pfctl -F Reset” restores default values for the following options: debug, all limit options, loginterface, reassemble, skip, syncookies, all timeouts.

QUEUEING

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. When filtering, 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 interfaces they should be created on from their parent queues.

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. If a limitation isn't imposed on the root queue, borrowing can result in saturating the bandwidth of the outgoing interface. Similarly, a minimum (reserved) bandwidth can be specified:

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

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

If multiple connections are assigned the same queue, they're not guaranteed to share the queue bandwidth fairly. An alternative flow queue manager can be used to achieve fair sharing by indicating how many simultaneous states are expected with a flows option, unless a minimum bandwidth has been specified as well.

When packets are classified by the stateful inspection engine, a flow identifier is assigned to all packets belonging to the state, thus limiting the number of individual flows that can be recognized by the resolution of a flow identifier. The current implementation is able to classify traffic into 32767 distinct flows. However, efficient fair sharing is observed even with a much smaller number of flows. For example on a 10Mbit/s DSL or a cable modem uplink, the following simple configuration can be used:

queue outq on em0 bandwidth 9M max 9M flows 1024 qlimit 1024 \
      default

It's important to specify the upper bound within 90-95% of the expected bandwidth and raise the default queue limit.

If a flows option appears without a bandwidth specification, the flow queue manager is selected as the queueing discipline for the corresponding interface acting as a default queue for all outgoing packets. In such a scenario, a queueing hierarchy is not supported.

In addition to the bandwidth and flow specifications, queues support the following options:

default

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. Mandatory for all queues except root queues. The parent queue must exist.

quantum size

Specifies the quantum of service for the flow queue manager. The lower the quantum size the more advantage is given to streams of smaller packets at the expense of bulk transfers. The default value is set to the configured Maximum Transmission Unit (MTU) of the specified interface.

qlimit limit

The maximum number of packets held in the queue. The default is 50.

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.

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

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 expansion).

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 pools.

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

manually

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

pf.conf

Table definitions can be placed directly in this file and loaded at the same time as other rules are loaded, atomically. Table definitions inside pf.conf use the table statement, and are especially useful to define non-persistent tables. The contents of a pre-existing table defined without a list of 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.

counters

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:

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.

ANCHORS

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 1.2.3.4 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"

An anchor rule can also contain a filter ruleset in a brace-delimited block. In that case, no separate loading of rules into the anchor is required. Brace delimited blocks may contain rules or other brace-delimited blocks. When an anchor is populated 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 name.

anchor "external" on egress {
	block
	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 1.2.3.4 to port 25:

# echo "block in quick from 1.2.3.4 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 syntax:

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.

STATEFUL FILTERING

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:

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

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.

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

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

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)

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

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.

pass in proto tcp from any to any port 80

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

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

OPERATING SYSTEM FINGERPRINTING

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:

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:

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:

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.

Examples:

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 packets to appear as any operating system; 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.

EXAMPLES

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 (157.161.48.183) as source; broadcasts (cable modem noise); and anything from reserved address space or invalid addresses.

block in from no-route to any
block in from urpf-failed to any
block out log quick on $ext_if from ! 157.161.48.183 to any
block in quick on $ext_if from any to 255.255.255.255
block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \
    192.168.0.0/16, 255.255.255.255/32 } to any

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 filter.

match in on $ext_if inet proto tcp from <spammers> to port smtp \
     tag SPAMD rdr-to 127.0.0.1 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 127.0.0.1 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 127.0.0.1 port 8080

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

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

In the example below, the machine sits between a fake internal 144.19.74.* network, and a routable external IP of 204.92.77.100. The last rule excludes protocol AH from being translated.

pass out on $ext_if from 144.19.74.0/24 nat-to 204.92.77.100
pass out on $ext_if proto ah from 144.19.74.0/24

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

pass in on $int_if proto { tcp, udp } from any to any port 80 \
      rdr-to 127.0.0.1 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 10.1.2.151 port 22
match in on $ext_if inet proto udp from any to ($ext_if) port 8080 \
      rdr-to 10.1.2.151 port 53

In this example, a NAT gateway is set up to translate internal addresses using a pool of public addresses (192.0.2.16/28). 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 192.0.2.16/28 \
    source-hash
match in  on $ext_if proto tcp from any to any port 80 \
    rdr-to { 10.1.2.155 weight 2, 10.1.2.160 weight 1, \
             10.1.2.161 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 10.1.2.120 to any binat-to 192.0.2.17

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

pass out on $ext_if inet from 10.1.2.120 to any \
      nat-to 192.0.2.17 static-port
pass in on $ext_if inet from any to 192.0.2.17 rdr-to 10.1.2.120

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)

GRAMMAR

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" ( "emerg" | "alert" | "crit" | "err" |
                 "warning" | "notice" | "info" | "debug" ) ] |
                 [ "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 |
                 "max-pkt-rate" number "/" seconds |
                 "set delay" number |
                 "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" ]) |
                 ([ "flows" number ] | [ "quantum" number ]) |
                 [ "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" )
                 ( redirhost | "{" redirhost-list "}" )
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 ]
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 ]

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" | "tcp.tsdiff" |
                 "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

FILES

/etc/hosts

Host name database.

/etc/pf.conf

Default location of the ruleset file.

/etc/examples/pf.conf

Example ruleset file.

/etc/pf.os

Default location of OS fingerprints.

/etc/protocols

Protocol name database.

/etc/services

Service name database.

SEE ALSO

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

HISTORY

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