path: root/share/man/man5/pf.conf.5

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.Dd November 19, 2002
.Dt PF.CONF 5
.Os
.Sh NAME
.Nm pf.conf
.Nd packet filter configuration file
.Sh DESCRIPTION
The
.Xr pf 4
packet filter modifies, drops or passes packets according to rules or
definitions specified in
.Nm pf.conf .
.Sh STATEMENT ORDER
There are seven types of statements in
.Nm pf.conf :
.Bl -tag -width xxxx
.It Cm Macros
User-defined variables may be defined and used later, simplifying
the configuration file.
Macros must be defined before they are referenced in
.Nm pf.conf .
.It Cm Tables
Tables provide a mechanism for increasing the performance and flexibility of
rules with large numbers of source or destination addresses.
.It Cm Options
Options tune the behaviour of the packet filtering engine.
.It Cm Traffic Normalization Li (e.g. Em scrub )
Traffic normalization protects internal machines against inconsistencies
in Internet protocols and implementations.
.It Cm Queueing
Queueing provides rule-based bandwidth control.
.It Cm Translation Li (Various forms of NAT)
Translation rules specify how addresses are to be mapped or redirected to
other addresses.
.It Cm Packet Filtering
Stateful and stateless packet filtering provides rule-based blocking or
passing of packets.
.El
.Pp
With the exception of
.Cm macros
and
.Cm tables ,
the types of statements should be grouped and appear in
.Nm pf.conf
in the order shown above, as this matches the operation of the underlying
packet filtering engine.
By default
.Xr pfctl 8
enforces this order (see
.Ar set require-order
below).
.Sh MACROS
Much like
.Xr cpp 1
or
.Xr m4 1 ,
macros can be defined that will later be expanded in context.
Macro names must start with a letter, and may contain letters, digits
and underscores.
Macro names may not be reserved words (for example
.Ar pass ,
.Ar in ,
.Ar out ) .
Macros are not expanded inside quotes.
.Pp
For example,
.Bd -literal -offset indent
ext_if = \&"kue0\&"
all_ifs = \&"{\&" $ext_if lo0 \&"}\&"
pass out on $ext_if from any to any keep state
pass in  on $ext_if proto tcp from any to any port 25 keep state
.Ed
.Sh TABLES
Tables are named structures which can hold a collection of addresses and
networks.
Lookups against tables in
.Xr pf 4
are relatively fast, making a single rule with tables much more efficient,
in terms of
processor usage and memory consumption, than a large number of rules which
differ only in IP address (either created explicitly or automatically by rule
expansion).
.Pp
Tables can be used as the source or destination of filter rules,
.Ar scrub
rules
or
translation rules such as
.Ar nat
or
.Ar rdr
(see below for details on the various rule types).
Tables cannot be used for things like the redirect address of
translation rules, nor can they be used in the routing options of
filter rules.
.Pp
Tables can be defined with any of the following
.Xr pfctl 8
mechanisms.
As with macros, reserved words may not be used as table names.
.Bl -tag -width "manually"
.It Ar manually
Persistent tables can be manually created with the
.Ar add
or
.Ar replace
option of
.Xr pfctl 8 ,
before or after the ruleset has been loaded.
.It Pa pf.conf
Table definitions can be placed directly in this file, and loaded at the
same time as other rules are loaded, atomically.
Table definitions inside
.Nm pf.conf
use the
.Ar table
statement, and are especially useful to define non-persistent tables.
The contents of a pre-existing table defined without a list of addresses
to initialize it is not altered when
.Nm pf.conf
is loaded.
A table initialized with the empty list,
.Li { } ,
will be cleared on load.
.El
.Pp
Tables may be defined with the following two attributes:
.Bl -tag -width persist
.It Ar persist
The
.Ar persist
flag forces the kernel to keep the table even when no rules refer to it.
If the flag is not set, the kernel will automatically remove the table
when the last rule referring to it is flushed.
.It Ar const
The
.Ar const
flag prevents the user from altering the contents of the table once it
has been created.
Without that flag,
.Xr pfctl 8
can be used to add or remove addresses from the table at any time, even
when running with
.Xr securelevel 7
= 2.
.El
.Pp
For example,
.Bd -literal -offset indent
table <private> const { 10/8, 172.16/12, 192.168/16 }
table <badhosts> persist
block on fxp0 from { <private>, <badhosts> } to any
.Ed
.Pp
creates a table called private, to hold RFC 1918 private network
blocks, and a table called badhosts, which is initially empty.
A filter rule is set up to block all traffic coming from addresses listed in
either table.
The private table cannot have its contents changed and the badhosts table
will exist even when no active filter rules reference it.
Addresses may later be added to the badhosts table, so that traffic from
these hosts can be blocked by using
.Bd -literal -offset indent
# pfctl -t badhosts -Tadd 204.92.77.111
.Ed
.Pp
A table can also be initialized with an address list specified in one or more
external files, using the following syntax:
.Bd -literal -offset indent
table <spam> persist file \&"/etc/spammers\&" file \&"/etc/openrelays\&"
block on fxp0 from <spam> to any
.Ed
.Pp
The files
.Pa /etc/spammers
and
.Pa /etc/openrelays
list IP addresses, one per line.
Any lines beginning with a # are treated as comments and ignored.
In addition to being specified by IP address, hosts may also be
specified by their hostname.
When the resolver is called to add a hostname to a table,
.Em all
resulting IPv4 and IPv6 addresses are placed into the table.
IP addresses can also be entered in a table by specifying a valid interface
name or the
.Em self
keyword, in which case all addresses assigned to the interface(s) will be
added to the table.
.Sh OPTIONS
.Xr pf 4
may be tuned for various situations using the
.Ar set
command.
.Bl -tag -width xxxx
.It Ar set timeout
.Pp
.Bl -tag -width interval -compact
.It Ar interval
Interval between purging expired states and fragments.
.It Ar frag
Seconds before an unassembled fragment is expired.
.El
.Pp
When a packet matches a stateful connection, the seconds to live for the
connection will be updated to that of the
.Ar proto.modifier
which corresponds to the connection state.
Each packet which matches this state will reset the TTL.
Tuning these values may improve the performance of the
firewall at the risk of dropping valid idle connections.
.Pp
.Bl -tag -width xxxx -compact
.It Ar tcp.first
The state after the first packet.
.It Ar tcp.opening
The state before the destination host ever sends a packet.
.It Ar tcp.established
The fully established state.
.It Ar tcp.closing
The state after the first FIN has been sent.
.It Ar tcp.finwait
The state after both FINs have been exchanged and the connection is closed.
Some hosts (notably web servers on Solaris) send TCP packets even after closing
the connection.
Increasing
.Ar tcp.finwait
(and possibly
.Ar tcp.closing )
can prevent blocking of such packets.
.It Ar tcp.closed
The state after one endpoint sends an RST.
.El
.Pp
ICMP and UDP are handled in a fashion similar to TCP, but with a much more
limited set of states:
.Pp
.Bl -tag -width xxxx -compact
.It Ar udp.first
The state after the first packet.
.It Ar udp.single
The state if the source host sends more than one packet but the destination
host has never sent one back.
.It Ar udp.multiple
The state if both hosts have sent packets.
.It Ar icmp.first
The state after the first packet.
.It Ar icmp.error
The state after an ICMP error came back in response to an ICMP packet.
.El
.Pp
Other protocols are handled similarly to UDP:
.Pp
.Bl -tag -width xxxx -compact
.It Ar other.first
.It Ar other.single
.It Ar other.multiple
.El
.Pp
Timeout values can be reduced adaptively as the number of state table
entries grows.
.Pp
.Bl -tag -width xxxx -compact
.It Ar adaptive.start
When the number of state entries exceeds this value, adaptive scaling
begins.
All timeout values are scaled linearly with factor
(adaptive.end - number of states) / (adaptive.end - adaptive.start).
.It Ar adaptive.end
When reaching this number of state entries, all timeout values become
zero, effectively purging all state entries immediately.
This value is used to define the scale factor, it should not actually
be reached (set a lower state limit, see below).
.El
.Pp
These values can be defined both globally and for each rule.
When used on a per-rule basis, the values relate to the number of
states created by the rule, otherwise to the total number of
states.
.Pp
For example:
.Bd -literal -offset indent
set timeout tcp.first 120
set timeout tcp.established 86400
set timeout { adaptive.start 6000, adaptive.end 12000 }
set limit states 10000
.Ed
.Pp
With 9000 state table entries, the timeout values are scaled to 50%
(tcp.first 60, tcp.established 43200).
.Pp
.It Ar set loginterface
Enable collection of packet and byte count statistics for the given interface.
These statistics can be viewed using
.Bd -literal -offset indent
# pfctl -s info
.Ed
.Pp
In this example
.Xr pf 4
collects statistics on the interface named dc0:
.Bd -literal -offset indent
set loginterface dc0
.Ed
.Pp
One can disable the loginterface using:
.Bd -literal -offset indent
set loginterface none
.Ed
.Pp
.It Ar set limit
Sets hard limits on the memory pools used by the packet filter.
See
.Xr pool 9
for an explanation of memory pools.
.Pp
For example,
.Bd -literal -offset indent
set limit states 20000
.Ed
.Pp
sets the maximum number of entries in the memory pool used by state table
entries (generated by
.Ar keep state
rules) to 20000.
Using
.Bd -literal -offset indent
set limit frags 20000
.Ed
.Pp
sets the maximum number of entries in the memory pool used for fragment
reassembly (generated by
.Ar scrub
rules) to 20000.
.Pp
These can be combined:
.Bd -literal -offset indent
set limit { states 20000, frags 20000 }
.Ed
.Pp
.It Ar set optimization
Optimize the engine for one of the following network environments:
.Pp
.Bl -tag -width xxxx -compact
.It Ar normal
A normal network environment.
Suitable for almost all networks.
.It Ar high-latency
A high-latency environment (such as a satellite connection).
.It Ar satellite
Alias for
.Ar high-latency .
.It Ar aggressive
Aggressively expire connections.
This can greatly reduce the memory usage of the firewall at the cost of
dropping idle connections early.
.It Ar conservative
Extremely conservative settings.
Avoid dropping legitimate connections at the
expense of greater memory utilization (possibly much greater on a busy
network) and slightly increased processor utilization.
.El
.Pp
For example:
.Bd -literal -offset indent
set optimization aggressive
.Ed
.Pp
.It Ar set block-policy
The
.Ar block-policy
option sets the default behaviour for the packet
.Ar block
action:
.Pp
.Bl -tag -width xxxxxxxx -compact
.It Ar drop
Packet is silently dropped.
.It Ar return
A TCP RST is returned for blocked TCP packets,
an ICMP UNREACHABLE is returned for blocked UDP packets,
and all other packets are silently dropped.
.El
.Pp
For example:
.Bd -literal -offset indent
set block-policy return
.Ed
.It Ar set require-order
By default
.Xr pfctl 8
enforces an ordering of the statement types in the ruleset to:
.Em options ,
.Em normalization ,
.Em queueing ,
.Em translation ,
.Em filtering .
Setting this option to
.Ar no
disables this enforcement.
There may be non-trivial and non-obvious implications to an out of
order ruleset.
Consider carefully before disabling the order enforcement.
.El
.Sh TRAFFIC NORMALIZATION
Traffic normalization is used to sanitize packet content in such
a way that there are no ambiguities in packet interpretation on
the receiving side.
The normalizer does IP fragment reassembly to prevent attacks
that confuse intrusion detection systems by sending overlapping
IP fragments.
Packet normalization is invoked with the
.Ar scrub
directive.
.Pp
.Ar scrub
has the following options:
.Bl -tag -width xxxx
.It Ar no-df
Clears the
.Ar dont-fragment
bit from a matching IP packet.
Some operating systems are known to generate fragmented packets with the
.Ar dont-fragment
bit set.
This is particularly true with NFS.
.Ar Scrub
will drop such fragmented
.Ar dont-fragment
packets unless
.Ar no-df
is specified.
.Pp
Unfortunately some operating systems also generate their
.Ar dont-fragment
packets with a zero IP identification field.
Clearing the
.Ar dont-fragment
bit on packets with a zero IP ID may cause deleterious results if an
upstream router later fragments the packet.
Using the
.Ar random-id
modifier (see below) is recommended in combination with the
.Ar no-df
modifier to ensure unique IP identifiers.
.It Ar min-ttl <number>
Enforces a minimum TTL for matching IP packets.
.It Ar max-mss <number>
Enforces a maximum MSS for matching TCP packets.
.It Ar random-id
Replaces the IP identification field with random values to compensate
for predictable values generated by many hosts.
This option only applies to outgoing packets that are not fragmented
after the optional fragment reassembly.
.It Ar fragment reassemble
Using
.Ar scrub
rules, fragments can be reassembled by normalization.
In this case, fragments are buffered until they form a complete
packet, and only the completed packet is passed on to the filter.
The advantage is that filter rules have to deal only with complete
packets, and can ignore fragments.
The drawback of caching fragments is the additional memory cost.
But the full reassembly method is the only method that currently works
with NAT.
This is the default behavior of a
.Ar scrub
rule if no fragmentation modifier is supplied.
.It Ar fragment crop
The default fragment reassembly method is expensive, hence the option
to crop is provided.
In this case,
.Xr pf 4
will track the fragments and cache a small range descriptor.
Duplicate fragments are dropped and overlaps are cropped.
Thus data will only occur once on the wire with ambiguities resolving to
the first occurrence.
Unlike the
.Ar fragment reassemble
modifier, fragments are not buffered, they are passed as soon as they
are received.
The
.Ar fragment crop
reassembly mechanism does not yet work with NAT.
.Pp
.It Ar fragment drop-ovl
This option is similar to the
.Ar fragment crop
modifier except that all overlapping or duplicate fragments will be
dropped, and all further corresponding fragments will be
dropped as well.
.It Ar reassemble tcp
Statefully normalizes TCP connections.
.Ar scrub reassemble tcp
rules may not have the direction (in/out) specified.
.Ar reassemble tcp
performs the following normalizations:
.Pp
.Bl -tag -width timeout -compact
.It ttl
Neither side of the connection is allowed to reduce their IP TTL.
An attacker may send a packet such that it reaches the firewall, affects
the firewall state, and expires before reaching the destination host.
.Ar reassemble tcp
will raise the TTL of all packets back up to the highest value seen on
the connection.
.It timeout modulation
Modern TCP stacks will send a timestamp on every TCP packet and echo
the other endpoint's timestamp back to them.
Many operating systems will merely start the timestamp at zero when
first booted, and increment it several times a second.
The uptime of the host can be deduced by reading the timestamp and multiplying
by a constant.
Also observing several different timestamps can be used to count hosts
behind a NAT device.
And spoofing TCP packets into a connection requires knowing or guessing
valid timestamps.
Timestamps merely need to be monotonically increasing and not derived off a
guessable base time.
.Ar reassemple tcp
will cause
.Ar scrub
to modulate the TCP timestamps with a random number.
.El
.El
.Pp
For example,
.Bd -literal -offset indent
scrub in on $ext_if all fragment reassemble
.Ed
.Sh QUEUEING
Packets can be assigned to queues for the purpose of bandwidth
control.
At least two declarations are required to configure queues, and later
any packet filtering rule can reference the defined queues by name.
During the filtering component of
.Nm pf.conf ,
the last referenced
.Ar queue
name is where any packets from
.Ar pass
rules will be queued, while for
.Ar block
rules it specifies where any resulting ICMP or TCP RST
packets should be queued.
The
.Ar scheduler
defines the algorithm used to decide which packets get delayed, dropped, or
sent out immediately.
There are three
.Ar schedulers
currently supported.
.Bl -tag -width xxxx
.It Ar cbq
Class Based Queueing.
.Ar Queues
attached to an interface build a tree, thus each
.Ar queue
can have further child
.Ar queues .
Each queue can have a
.Ar priority
and a
.Ar bandwidth
assigned.
.Ar Priority
mainly controls the time packets take to get sent out, while
.Ar bandwidth
has primarily effects on throughput.
.It Ar priq
Priority Queueing.
.Ar Queues
are flat attached to the interface, thus,
.Ar queues
cannot have further child
.Ar queues .
Each
.Ar queue
has a unique
.Ar priority
assigned, ranging from 0 to 15.
Packets in the
.Ar queue
with the highest
.Ar priority
are processed first.
.It Ar hfsc
Hierarchical Fair Service Curve.
.Ar Queues
attached to an interface build a tree, thus each
.Ar queue
can have further child
.Ar queues .
Each queue can have a
.Ar priority
and a
.Ar bandwidth
assigned.
.Ar Priority
mainly controls the time packets take to get sent out, while
.Ar bandwidth
has primarily effects on throughput.
.El
.Pp
The interfaces on which queueing should be activated are declared using
the
.Ar altq on
declaration.
.Ar altq on
has the following keywords:
.Bl -tag -width xxxx
.It Ar <interface>
Queueing is enabled on the named interface.
.It Ar <scheduler>
Specifies which queueing scheduler to use.
Currently supported values
are
.Ar cbq
for Class Based Queueing,
.Ar priq
for Priority Queueing and
.Ar. hfsc
for the Hierarchical Fair Service Curve scheduler.
.It Ar bandwidth <bw>
The maximum bitrate for all queues on an
interface may be specified using the
.Ar bandwidth
keyword.
The value can be specified as an absolute value or as a
percentage of the interface bandwidth.
When using an absolute value, the suffixes
.Ar b ,
.Ar Kb ,
.Ar Mb ,
and
.Ar Gb
are used to represent bits, kilobits, megabits, and
gigabits per second, respectively.
The value must not exceed the interface bandwidth.
If
.Ar bandwidth
is not specified, the interface bandwidth is used.
.It Ar qlimit <limit>
The maximum number of packets held in the queue.
The default is 50.
.It Ar tbrsize <size>
Adjusts the size, in bytes, of the token bucket regulator.
If not specified, heuristics based on the
interface bandwidth are used to determine the size.
.It Ar queue <list>
Defines a list of subqueues to create on an interface.
.El
.Pp
In the following example, the interface dc0
should queue up to 5 Mbit/s in four second-level queues using
Class Based Queueing.
Those four queues will be shown in a later example.
.Bd -literal -offset indent
altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh }
.Ed
.Pp
Once interfaces are activated for queueing using the
.Ar altq
directive, a sequence of
.Ar queue
directives may be defined.
The name associated with a
.Ar queue
must match a queue defined in the
.Ar altq
directive (e.g. mail), or, except for the
.Ar priq
.Ar scheduler ,
in a parent
.Ar queue
declaration.
The following keywords can be used:
.Bl -tag -width xxxx
.It Ar on <interface>
Specifies the interface the queue operates on.
If not given, it operates on all matching interfaces.
.It Ar bandwidth <bw>
Specifies the maximum bitrate to be processed by the queue.
This value must not exceed the value of the parent
.Ar queue
and can be specified as an absolute value or a percentage of the parent
queue's bandwidth.
The
.Ar priq
scheduler does not support bandwidth specification.
.It Ar priority <level>
Between queues a priority level can be set.
For
.Ar cbq
and
.Ar hfsc ,
the range is 0 to 7 and for
.Ar priq ,
the range is 0 to 15.
The default for all is 1.
.Ar Priq
queues with a higher priority are always served first.
.Ar Cbq
and
.Ar Hfsc
queues with a higher priority are preferred in the case of overload.
.It Ar qlimit <limit>
The maximum number of packets held in the queue.
The default is 50.
.El
.Pp
The
.Ar scheduler
can get additional parameters with
.Ar <scheduler> Ns Li (\& Ar <parameters> No ) .
Parameters are as follows:
.Pp
.Bl -tag -width Fl
.It Ar default
Packets not matched by another queue are assigned to this one.
Exactly one default queue is required.
.It Ar red
Enable RED (Random Early Detection) on this queue.
RED drops packets with a probability proportional to the average
queue length.
.It Ar rio
Enables RIO on this queue.
RIO is RED with IN/OUT, thus running
RED two times more than RIO would achieve the same effect.
RIO is currently not supported in the GENERIC kernel.
.It Ar ecn
Enables ECN (Explicit Congestion Notification) on this queue.
ECN implies RED.
.El
.Pp
The
.Ar cbq
.Ar scheduler
supports an additional option:
.Bl -tag -width Fl
.It Ar borrow
The queue can borrow bandwidth from the parent.
.El
.Pp
The
.Ar hfsc
.Ar scheduler
supports some additional options:
.Bl -tag -width Fl
.It Ar realtime <sc>
The minimum required bandwidth for the queue.
.It Ar upperlimit <sc>
The maximum allowed bandwidth for the queue.
.It Ar linkshare <sc>
The bandwidth share of a backlogged queue.
.El
.Pp
<sc> is an acronym for
.Ar service curve .
.Pp
The format for service curve specifications is
.Ar ( m1 , d , m2 ) .
.Ar m2
controls the bandwidth assigned to the queue.
.Ar m1
and
.Ar d
are optional and can be used to control the initial bandwidth assignment.
For the first
.Ar d
milliseconds the queue gets the bandwidth given as
.Ar m1 ,
afterwards the value given in
.Ar m2 .
.Pp
Furthermore, with
.Ar cbq
and
.Ar hfsc ,
child queues can be specified as in an
.Ar altq
declaration, thus building a tree of queues using a part of
their parent's bandwidth.
.Pp
Packets can be assigned to queues based on filter rules by using the
.Ar queue
keyword.
Normally only one
.Ar queue
is specified; when a second one is specified it will instead be used for
packets which have a
.Em TOS
of
.Em lowdelay
and for TCP ACKs with no data payload.
.Pp
To continue the previous example, the examples below would specify the
four referenced
queues, plus a few child queues.
Interactive
.Xr ssh 1
sessions get priority over bulk transfers like
.Xr scp 1
and
.Xr sftp 1 .
The queues may then be referenced by filtering rules (see
.Sx PACKET FILTERING
below).
.Bd -literal
queue std bandwidth 10% cbq(default)
queue http bandwidth 60% priority 2 cbq(borrow red) \e
      { employees, developers }
queue  developers bandwidth 75% cbq(borrow)
queue  employees bandwidth 15%
queue mail bandwidth 10% priority 0 cbq(borrow ecn)
queue ssh bandwidth 20% cbq(borrow) { ssh_interactive, ssh_bulk }
queue  ssh_interactive priority 7
queue  ssh_bulk priority 0

block return out on dc0 inet all queue std
pass out on dc0 inet proto tcp from $developerhosts to any port 80 \e
      keep state queue developers
pass out on dc0 inet proto tcp from $employeehosts to any port 80 \e
      keep state queue employees
pass out on dc0 inet proto tcp from any to any port 22 \e
      keep state queue(ssh_bulk, ssh_interactive)
pass out on dc0 inet proto tcp from any to any port 25 \e
      keep state queue mail
.Ed
.Sh TRANSLATION
Translation rules modify either the source or destination address of the
packets associated with a stateful connection.
A stateful connection is automatically created to track packets matching
such a rule as long as they are not blocked by the filtering section of
.Nm pf.conf .
The translation engine modifies the specified address and/or port in the
packet, recalculates IP, TCP and UDP checksums as necessary, and passes it to
the packet filter for evaluation.
Translation occurs before filtering.
.Pp
The state entry created permits
.Xr pf 4
to keep track of the original address for traffic associated with that state
and correctly direct return traffic for that connection.
.Pp
Various types of translation are possible with pf:
.Bl -tag -width xxxx
.It Ar binat
A
.Ar binat
rule specifies a bidirectional mapping between an external IP netblock
and an internal IP netblock.
.It Ar nat
A
.Ar nat
rule specifies that IP addresses are to be changed as the packet
traverses the given interface.
This technique allows one or more IP addresses
on the translating host to support network traffic for a larger range of
machines on an "inside" network.
Although in theory any IP address can be used on the inside, it is strongly
recommended that one of the address ranges defined by RFC 1918 be used.
These netblocks are:
.Bd -literal
10.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8)
172.16.0.0 - 172.31.255.255 (i.e., 172.16/12)
192.168.0.0 - 192.168.255.255 (i.e., 192.168/16)
.Ed
.It Pa rdr
The packet is redirected to another destination and possibly a
different port.
.Ar rdr
rules can optionally specify port ranges instead of single ports.
rdr ... port 2000:2999 -> ... port 4000
redirects ports 2000 to 2999 (inclusive) to port 4000.
rdr ... port 2000:2999 -> ... port 4000:*
redirects port 2000 to 4000, 2001 to 4001, ..., 2999 to 4999.
.El
.Pp
In addition to modifying the address, some translation rules may modify
source or destination ports for
.Xr tcp 4
or
.Xr udp 4
connections; implicitly in the case of
.Ar nat
rules and explicitly in the case of
.Ar rdr
rules.
Port numbers are never translated with a
.Ar binat
rule.
.Pp
For each packet processed by the translator, the translation rules are
evaluated in sequential order, from first to last.
The first matching rule decides what action is taken.
.Pp
The
.Ar no
option prefixed to a translation rule causes packets to remain untranslated,
much in the same way as
.Ar drop quick
works in the packet filter (see below).
.Pp
If no rule matches the packet, the packet is passed to the filter unmodified.
Translation occurs before the filter rules are applied;
therefore rules for redirected packets should specify the address and port
after translation.
.Pp
Translation rules apply only to packets that pass through
the specified interface, and if no interface is specified,
translation is applied to packets on all interfaces.
For instance, redirecting port 80 on an external interface to an internal
web server will only work for connections originating from the outside.
Connections to the address of the external interface from local hosts will
not be redirected, since such packets do not actually pass through the
external interface.
Redirections cannot reflect packets back through the interface they arrive
on, they can only be redirected to hosts connected to different interfaces
or to the firewall itself.
.Pp
Note that redirecting external incoming connections to the loopback
address, as in
.Bd -literal -offset indent
rdr on ne3 inet proto tcp to port 8025 -> 127.0.0.1 port 25
.Ed
.Pp
will effectively allow an external host to connect to daemons
bound solely to the loopback address, circumventing the traditional
blocking of such connections on a real interface.
Unless this effect is desired, any of the local non-loopback addresses
should be used as redirection target instead, which allows external
connections only to daemons bound to this address or not bound to
any address.
.Pp
See
.Sx TRANSLATION EXAMPLES
below.
.Sh PACKET FILTERING
.Xr pf 4
has the ability to
.Ar block
and
.Ar pass
packets based on attributes of their layer 3 (see
.Xr ip 4
and
.Xr ip6 4 )
and layer 4 (see
.Xr icmp 4 ,
.Xr icmp6 4 ,
.Xr tcp 4 ,
.Xr udp 4 )
headers.
In addition, packets may also be
assigned to queues for the purpose of bandwidth control.
.Pp
For each packet processed by the packet filter, the filter rules are
evaluated in sequential order, from first to last.
The last matching rule decides what action is taken.
.Pp
The following actions can be used in the filter:
.Pp
.Bl -tag -width xxxx
.It Ar block
The packet is blocked.
There are a number of ways in which a
.Ar block
rule can behave when blocking a packet.
The default behaviour is to
.Ar drop
packets silently, however this can be overridden or made
explicit either globally, by setting the
.Ar block-policy
option, or on a per-rule basis with one of the following options:
.Pp
.Bl -tag -width xxxx -compact
.It Ar drop
The packet is silently dropped.
.It Ar return-rst
This applies only to
.Xr tcp 4
packets, and issues a TCP RST which closes the
connection.
.It Ar return-icmp
.It Ar return-icmp6
This causes ICMP messages to be returned for packets which match the rule.
By default this is an ICMP UNREACHABLE message, however this
can be overridden by specifying a message as a code or number.
.It Ar return
This causes a TCP RST to be returned for
.Xr tcp 4
packets and an ICMP UNREACHABLE for UDP and other packets.
.El
.It Ar pass
The packet is passed.
.El
.Pp
If no rule matches the packet, the default action is
.Ar pass .
.Pp
To block everything by default and only pass packets
that match explicit rules, one uses
.Bd -literal -offset indent
block all
.Ed
.Pp
as the first filter rule.
.Pp
See
.Sx FILTER EXAMPLES
below.
.Sh PARAMETERS
The rule parameters specify the packets to which a rule applies.
A packet always comes in on, or goes out through, one interface.
Most parameters are optional.
If a parameter is specified, the rule only applies to packets with
matching attributes.
Certain parameters can be expressed as lists, in which case
.Xr pfctl 8
generates all needed rule combinations.
.Bl -tag -width xxxx
.It Ar in No or Ar out
This rule applies to incoming or outgoing packets.
If neither
.Ar in
nor
.Ar out
are specified, the rule will match packets in both directions.
.It Ar log
In addition to the action specified, a log message is generated.
All packets for that connection are logged, unless the
.Ar keep state
or
.Ar modulate state
options are specified, in which case only the
packet that establishes the state is logged.
(See
.Ar keep state
and
.Ar modulate state
below).
The logged packets are sent to the
.Xr pflog 4
interface.
This interface is monitored by the
.Xr pflogd 8
logging daemon, which dumps the logged packets to the file
.Pa /var/log/pflog
in
.Xr pcap 3
binary format.
.It Ar log-all
Used with
.Ar keep state
or
.Ar modulate state
rules to force logging of all packets for a connection.
As with
.Ar log ,
packets are logged to
.Xr pflog 4 .
.It Ar quick
If a packet matches a rule which has the
.Ar quick
option set, this rule
is considered the last matching rule, and evaluation of subsequent rules
is skipped.
.It Ar on <interface>
This rule applies only to packets coming in on, or going out through, this
particular interface.
.It Ar <af>
This rule applies only to packets of this address family.
Supported values are
.Ar inet
and
.Ar inet6 .
.It Ar proto <protocol>
This rule applies only to packets of this protocol.
Common protocols are
.Xr icmp 4 ,
.Xr icmp6 4 ,
.Xr tcp 4 ,
and
.Xr udp 4 .
For a list of all the protocol name to number mappings used by
.Xr pfctl 8 ,
see the file
.Em /etc/protocols .
.It Ar from <source> port <source> to <dest> port <dest>
This rule applies only to packets with the specified source and destination
addresses and ports.
.Pp
Addresses can be specified in CIDR notation (matching netblocks), as
symbolic host names or interface names, or as any of the following keywords:
.Pp
.Bl -tag -width xxxxxxxxxxxx -compact
.It Ar any
Any address.
.It Ar no-route
Any address which is not currently routable.
.It Ar <table>
Any address that matches the given table.
.El
.Pp
Interface names can have modifiers appended:
.Pp
.Bl -tag -width xxxxxxxxxxxx -compact
.It Ar :network
Translates to the network(s) attached to the interface.
.It Ar :broadcast
Translates to the interface's broadcast address(es).
.El
.Pp
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 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
.Ar nat .
.Pp
Ports can be specified either by number or by name.
For example, port 80 can be specified as
.Em www .
For a list of all port name to number mappings used by
.Xr pfctl 8 ,
see the file
.Pa /etc/services .
.Pp
Ports and ranges of ports are specified by using these operators:
.Bd -literal -offset indent
=	(equal)
!=	(unequal)
<	(less than)
<=	(less than or equal)
>	(greater than)
>=	(greater than or equal)
><	(range)
<>	(except range)
.Ed
.Pp
>< and <>
are binary operators (they take two arguments), and the range
does not include the limits.
For instance:
.Bl -tag -width Fl
.It Ar port 2000 >< 2004
means
.Sq all ports > 2000 and < 2004 ,
hence ports 2001, 2002 and 2003.
.It Ar port 2000 <> 2004
means
.Sq all ports < 2000 or > 2004 ,
hence ports 1-1999 and 2005-65535.
.El
.Pp
The host and port specifications are optional, as in the following examples:
.Bd -literal -offset indent
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 \e
      to ! 10.1.2.3 port != ssh
.Ed
.It Ar all
This is equivalent to "from any to any".
.It Ar group <group>
Similar to
.Ar user ,
this rule only applies to packets of sockets owned by the specified group.
.It Ar 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.
For forwarded connections, where the firewall is not a connection endpoint,
the user and group are
.Em unknown .
.Pp
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; for other protocols
these parameters are ignored.
.Pp
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.
.Pp
User and group IDs can be specified as either numbers or names.
The syntax is similar to the one for ports.
The value
.Em unknown
matches packets of forwarded connections.
.Em unknown
can only be used with the operators
.Cm =
and
.Cm != .
Other constructs like
.Cm user >= unknown
are invalid.
Forwarded packets with unknown user and group ID match only rules
that explicitly compare against
.Em unknown
with the operators
.Cm =
or
.Cm != .
For instance
.Cm user >= 0
does not match forwarded packets.
The following example allows only selected users to open outgoing
connections:
.Bd -literal -offset indent
block out proto { tcp, udp } all
pass  out proto { tcp, udp } all \e
      user { < 1000, dhartmei } keep state
.Ed
.It Ar flags <a>/<b> | /<b>
This rule only applies to TCP packets that have the flags
.Ar <a>
set out of set
.Ar <b> .
Flags not specified in
.Ar <b>
are ignored.
The flags are: (F)IN, (S)YN, (R)ST, (P)USH, (A)CK, (U)RG, (E)CE, and C(W)R.
.Bl -tag -width Fl
.It Ar flags S/S
Flag SYN is set.
The other flags are ignored.
.It Ar flags S/SA
Out of SYN and ACK, exactly SYN may be set.
SYN, SYN+PSH and SYN+RST match, but SYN+ACK, ACK and ACK+RST do not.
This is more restrictive than the previous example.
.It Ar flags /SFRA
If the first set is not specified, it defaults to none.
All of SYN, FIN, RST and ACK must be unset.
.El
.It Ar icmp-type <type> code <code>
.It Ar icmp6-type <type> code <code>
This rule only applies to ICMP or ICMPv6 packets with the specified type
and code.
This parameter is only valid for rules that cover protocols ICMP or
ICMP6.
The protocol and the ICMP type indicator (icmp-type or icmp6-type)
must match.
.It Ar allow-opts
By default, packets which contain IP options are blocked.
When
.Ar allow-opts
is specified for a
.Ar pass
rule, packets that pass the filter based on that rule (last matching)
do so even if they contain IP options.
For packets that match state, the rule that initially created the
state is used.
The implicit
.Ar pass
rule that is used when a packet does not match any rules does not
allow IP options.
.It Ar label <string>
Adds a label (name) to the rule, which can be used to identify the rule.
For instance,
pfctl -s labels
shows per-rule statistics for rules that have labels.
.Pp
The following macros can be used in labels:
.Pp
.Bl -tag -width $srcaddr -compact -offset indent
.It Ar $if
The interface.
.It Ar $srcaddr
The source IP address.
.It Ar $dstaddr
The destination IP address.
.It Ar $srcport
The source port specification.
.It Ar $dstport
The destination port specification.
.It Ar $proto
The protocol name.
.It Ar $nr
The rule number.
.El
.Pp
For example:
.Bd -literal -offset indent
ips = \&"{ 1.2.3.4, 1.2.3.5 }\&"
pass in proto tcp from any to $ips \e
      port > 1023 label \&"$dstaddr:$dstport\&"
.Ed
.Pp
expands to
.Bd -literal -offset indent
pass in inet proto tcp from any to 1.2.3.4 \e
      port > 1023 label \&"1.2.3.4:>1023\&"
pass in inet proto tcp from any to 1.2.3.5 \e
      port > 1023 label \&"1.2.3.5:>1023\&"
.Ed
.Pp
The macro expansion for the
.Ar label
directive occurs only at configuration file parse time, not during runtime.
.It Ar queue <queue> | ( <queue> , <queue> )
Packets matching this rule will be assigned to the specified queue.
If two queues are given, packets which have a
.Em tos
of
.Em lowdelay
and TCP ACKs with no data payload will be assigned to the second one.
See
.Sx QUEUE RULES
for setup details.
.Pp
For example:
.Bd -literal -offset indent
pass in proto tcp to port 25 queue mail
pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio)
.Ed
.It Ar tag <string>
A tag will be assigned to packets matching this rule.
Subsequent rules can match on that tag using the
.Ar tagged
keyword, even on another interface.
The tag is set on every matching rule, not just the last one.
There is one tag per packet, subsequent matches replace it.
.It Ar tagged <string>
This rule applies only to packets that have been tagged with the given
tag.
.El
.Sh ROUTING
If a packet matches a rule with a route option set, the packet filter will
route the packet according to the type of route option.
When such a rule creates state, the route option is also applied to all
packets matching the same connection.
.Bl -tag -width xxxx
.It Ar fastroute
The
.Ar fastroute
option does a normal route lookup to find the next hop for the packet.
.It Ar route-to
The
.Ar route-to
option routes the packet to the specified interface with an optional address
for the next hop.
When a
.Ar route-to
rule creates state, only packets that pass in the same direction as the
filter rule specifies will be routed in this way.
Packets passing in the opposite direction (replies) are not affected
and are routed normally.
.It Ar reply-to
The
.Ar reply-to
option is similar to
.Ar 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
.Ar route-to
is useful only in rules that create state.
It can be used on systems with multiple external connections to
route all outgoing packets of a connection through the interface
the incoming connection arrived through (symmetric routing enforcement).
.It Ar dup-to
The
.Ar dup-to
option creates a duplicate of the packet and routes it like
.Ar route-to .
The original packet gets routed as it normally would.
.El
.Sh POOL OPTIONS
For
.Ar nat
and
.Ar rdr
rules, (as well as for the
.Ar route-to ,
.Ar reply-to
and
.Ar dup-to
rule options) for which there is a single redirection address which has a
subnet mask smaller than 32 for IPv4 or 128 for IPv6 (more than one IP
address), a variety of different methods for assigning this address can be
used:
.Bl -tag -width xxxx
.It Ar bitmask
The
.Ar bitmask
option applies the network portion of the redirection address to the address
to be modified (source with
.Ar nat ,
destination with
.Ar rdr ) .
.It Ar random
The
.Ar random
option selects an address at random within the defined block of addresses.
.It Ar source-hash
The
.Ar 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
.Xr pfctl 8
randomly generates a key for source-hash every time the
ruleset is reloaded.
.It Ar round-robin
The
.Ar round-robin
option loops through the redirection address(es).
.Pp
When more than one redirection address is specified,
.Ar round-robin
is the only permitted pool type.
.It Ar static-port
With
.Ar nat
rules, the
.Ar static-port
option prevents
.Xr pf 4
from modifying the source port on TCP and UDP packets.
.El
.Sh STATEFUL INSPECTION
.Xr pf 4
is a stateful packet filter, which means it can track the state of
a connection.
Instead of passing all traffic to port 25, for instance, it is possible
to pass only the initial packet, and then begin to keep state.
Subsequent traffic will flow because the filter is aware of the connection.
.Pp
If a packet matches a
.Ar pass ... keep state
rule, the filter creates a state for this connection and automatically
lets pass all subsequent packets of that connection.
.Pp
Before any rules are evaluated, the filter checks whether the packet
matches any state.
If it does, the packet is passed without evaluation of any rules.
.Pp
States are removed after the connection is closed or has timed out.
.Pp
This has several advantages.
Comparing a packet to a state involves checking its sequence numbers.
If the sequence numbers are outside the narrow windows of expected
values, the packet is dropped.
This prevents spoofing attacks, such as when an attacker sends packets with
a fake source address/port but does not know the connection's sequence
numbers.
.Pp
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).
.Pp
For instance:
.Bd -literal -offset indent
block all
pass out proto tcp from any to any flags S/SA keep state
pass in  proto tcp from any to any port 25 flags S/SA keep state
.Ed
.Pp
This ruleset blocks everything by default.
Only outgoing connections and incoming connections to port 25 are allowed.
The initial packet of each connection has the SYN
flag set, will be passed and creates state.
All further packets of these connections are passed if they match a state.
.Pp
Specifying
.Ar flags S/SA
restricts state creation to the initial SYN
packet of the TCP handshake.
One can also be less restrictive, and allow state creation from
intermediate
.Pq non-SYN
packets.
This will cause
.Xr pf 4
to synchronize to existing connections, for instance
if one flushes the state table.
.Pp
For UDP, which is stateless by nature,
.Ar keep state
will create state as well.
UDP packets are matched to states using only host addresses and ports.
.Pp
ICMP messages fall into two categories: ICMP error messages, which always
refer to a TCP or UDP packet, are matched against the referred to connection.
If one keeps state on a TCP connection, and an ICMP source quench message
referring to this TCP connection arrives, it will be matched to the right
state and get passed.
.Pp
For ICMP queries,
.Ar keep state
creates an ICMP state, and
.Xr pf 4
knows how to match ICMP replies to states.
For example,
.Bd -literal -offset indent
pass out inet proto icmp all icmp-type echoreq keep state
.Ed
.Pp
allows echo requests (such as those created by
.Xr ping 8 )
out, creates state, and matches incoming echo replies correctly to states.
.Pp
Note:
.Ar nat , binat No and Ar rdr
rules implicitly create state for connections.
.Sh 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
.Em very
poor ISNs and thus are normally susceptible to ISN prediction exploits.
By applying a
.Ar modulate state
rule to a TCP connection,
.Xr pf 4
will create a high quality random sequence number for each connection
endpoint.
.Pp
The
.Ar modulate state
directive implicitly keeps state on the rule and is
only applicable to TCP connections.
.Pp
For instance:
.Bd -literal -offset indent
block all
pass out proto tcp from any to any modulate state
pass in  proto tcp from any to any port 25 flags S/SA modulate state
.Ed
.Pp
There are two caveats associated with state modulation:
A
.Ar modulate state
rule can not be applied to a pre-existing but unmodulated connection.
Such an application would desynchronize TCP's strict
sequencing between the two endpoints.
Instead,
.Xr pf 4
will treat the
.Ar modulate state
modifier as a
.Ar keep state
modifier and the pre-existing connection will be inferred without
the protection conferred by modulation.
.Pp
The other caveat affects currently modulated states when the state table
is lost (firewall reboot, flushing the state table, etc...).
.Xr 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.
Using a
.Ar flags S/SA
modifier on
.Ar modulate state
rules between fast networks is suggested to prevent ACK storms.
.Sh SYN PROXY
By default,
.Xr pf 4
passes packets that are part of a
.Xr tcp 4
handshake between the endpoints.
The
.Ar synproxy state
option can be used to cause
.Xr pf 4
itself to complete the handshake with the active endpoint, perform a handshake
with the passive endpoint, and then forward packets between the endpoints.
.Pp
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.
.Pp
The proxy is transparent to both endpoints, they each see a single
connection from/to the other endpoint.
.Xr pf 4
choses 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.
Hence,
.Ar synproxy state
includes
.Ar modulate state
and
.Ar keep state .
.Pp
Example:
.Bd -literal -offset indent
pass in proto tcp from any to any port www flags S/SA synproxy state
.Ed
.Sh STATEFUL TRACKING OPTIONS
Both
.Ar keep state
and
.Ar modulate state
support the following options:
.Pp
.Bl -tag -width xxxx -compact
.It Ar max <number>
Limits the number of concurrent states the rule may create.
When this limit is reached, further packets matching the rule that would
create state are dropped, until existing states time out.
.It Ar <timeout> <seconds>
Changes the timeout values used for states created by this rule.
For a list of all valid timeout names, see
.Sx OPTIONS
above.
.Pp
Multiple options can be specified, separated by commas:
.Bd -literal
pass in proto tcp from any to any \e
      port www flags S/SA keep state \e
      (max 100, tcp.established 60, tcp.closing 5)
.Ed
.El
.Sh BLOCKING SPOOFED TRAFFIC
"Spoofing" is the faking of IP addresses, typically for malicious
purposes.
The
.Ar antispoof
directive expands to a set of filter rules which will block all
traffic with a source IP from the network(s) directly connected
to the specified interface(s) from entering the system through
any other interface.
.Pp
For example, the line
.Bd -literal -offset indent
antispoof for lo0
.Ed
.Pp
expands to
.Bd -literal -offset indent
block drop in on ! lo0 inet from 127.0.0.1/8 to any
block drop in on ! lo0 inet6 from ::1 to any
.Ed
.Pp
For non-loopback interfaces, there are additional rules to block incoming
packets with a source IP address identical to the interface's IP(s).
For example, assuming the interface wi0 had an IP address of 10.0.0.1 and a
netmask of 255.255.255.0,
the line
.Bd -literal -offset indent
antispoof for wi0 inet
.Ed
.Pp
expands to
.Bd -literal -offset indent
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
.Ed
.Pp
Caveat: Rules created by the
.Ar antispoof
directive interfere with packets sent over loopback interfaces
to local addresses.
One should pass these explicitly.
.Sh FRAGMENT HANDLING
The size of IP datagrams (packets) can be significantly larger than the
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
.Xr pf 4
to filter on things such as TCP ports or to perform NAT.
.Pp
Besides the use of
.Ar scrub
rules as described in
.Sx TRAFFIC NORMALIZATION
above, there are three options for handling fragments in the packet filter.
.Pp
One alternative is to filter individual fragments with filter rules.
If no
.Ar scrub
rule applies to a fragment, it is passed to the filter.
Filter rules with matching IP header parameters decide whether the
fragment is passed or blocked, in the same way as complete packets
are filtered.
Without reassembly, fragments can only be filtered based on IP header
fields (source/destination address, protocol), since subprotocol header
fields are not available (TCP/UDP port numbers, ICMP code/type).
The
.Ar fragment
option can be used to restrict filter rules to apply only to
fragments, but not complete packets.
Filter rules without the
.Ar fragment
option still apply to fragments, if they only specify IP header fields.
For instance, the rule
.Bd -literal -offset indent
pass in proto tcp from any to any port 80
.Ed
.Pp
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.
.Pp
It's also possible to reassemble only certain fragments by specifying
source or destination addresses or protocols as parameters in
.Ar scrub
rules.
.Pp
In most cases, the benefits of reassembly outweigh the additional
memory cost, and it's recommended to use
.Ar scrub
rules to reassemble
all fragments via the
.Ar fragment reassemble
modifier.
.Pp
The memory allocated for fragment caching can be limited using
.Xr 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 adjusted.
.Pp
Currently, only IPv4 fragments are supported and IPv6 fragments
are blocked unconditionally.
.Sh ANCHORS AND NAMED RULESETS
Besides the main ruleset,
.Xr pfctl 8
can load named rulesets into
.Ar anchor
attachment points.
An
.Ar anchor
contains a list of named rulesets.
An
.Ar anchor
has a name which specifies where
.Xr pfctl 8
can be used to attach sub-rulesets.
A named ruleset contains filter and translation rules, like the
main ruleset.
The main ruleset can reference
.Ar anchor
attachment points
using the following kinds
of rules:
.Bl -tag -width xxxx
.It Ar nat-anchor <name>
Evaluates the
.Ar nat
rules of all named rulesets in the specified
.Ar anchor .
.It Ar rdr-anchor <name>
Evaluates the
.Ar rdr
rules of all named rulesets in the specified
.Ar anchor .
.It Ar binat-anchor <name>
Evaluates the
.Ar binat
rules of all named rulesets in the specified
.Ar anchor .
.It Ar anchor <name>
Evaluates the filter rules of all named rulesets in the specified
.Ar anchor .
.El
.Pp
When evaluation of the main ruleset reaches an
.Ar anchor
rule,
.Xr pf 4
will proceed to evaluate all rules specified in the
named rulesets attached to that
.Ar anchor .
.Pp
Matching filter rules in named rulesets with the
.Ar quick
option and matching translation rules are final and abort the
evaluation of both the rules in the
.Ar anchor
and the main ruleset.
.Pp
Only the main ruleset can contain
.Ar anchor
rules.
.Pp
When an
.Ar anchor
contains more than one named ruleset, they are evaluated
in the alphabetical order of their names.
.Pp
Rules may contain
.Ar anchor
attachment points which do not contain any rules when the main ruleset
is loaded, and later such named rulesets can be manipulated through
.Xr pfctl 8
without reloading the main ruleset.
For example,
.Bd -literal -offset indent
ext_if = \&"kue0\&"
block on $ext_if all
anchor spam
pass out on $ext_if all keep state
pass in on $ext_if proto tcp from any \e
      to $ext_if port smtp keep state
.Ed
.Pp
blocks all packets on the external interface by default, then evaluates
all rulesets in the
.Ar anchor
named "spam", and finally passes all outgoing connections and
incoming connections to port 25.
.Bd -literal -offset indent
# echo \&"block in quick from 1.2.3.4 to any\&" \&| \e
      pfctl -a spam:manual -f -
.Ed
.Pp
loads a single ruleset containing a single rule into the
.Ar anchor ,
which blocks all packets from a specific address.
.Pp
Optionally,
.Ar anchor
rules can specify the parameter's
direction, interface, address family, protocol and source/destination
address/port
using the same syntax as filter rules.
When parameters are used, the
.Ar anchor
rule is only evaluated for matching packets.
This allows conditional evaluation of named rulesets, like:
.Bd -literal -offset indent
block on $ext_if all
anchor spam proto tcp from any to any port smtp
pass out on $ext_if all keep state
pass in on $ext_if proto tcp from any to $ext_if port smtp keep state
.Ed
.Pp
The rules inside
.Ar anchor
spam are only evaluated for
.Ar tcp
packets with destination port 25.
Hence,
.Bd -literal -offset indent
# echo \&"block in quick from 1.2.3.4 to any" \&| \e
      pfctl -a spam:manual -f -
.Ed
.Pp
will only block connections from 1.2.3.4 to port 25.
.Sh TRANSLATION EXAMPLES
This example maps incoming requests on port 80 to port 8080, on
which a daemon is running (because, for example, it is not run as root,
and therefore lacks permission to bind to port 80).
.Bd -literal
# map daemon on 8080 to appear to be on 80
rdr on ne3 proto tcp from any to any port 80 -> 127.0.0.1 port 8080
.Ed
.Pp
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.)
.Bd -literal
nat on ! vlan12 from 192.168.168.0/24 to any -> 204.92.77.111
.Ed
.Pp
In the example below, fxp1 is the outside interface; the machine sits between a
fake internal 144.19.74.* network, and a routable external IP of 204.92.77.100.
The
.Ar no nat
rule excludes protocol AH from being translated.
.Bd -literal
# NO NAT
no nat on fxp1 proto ah from 144.19.74.0/24 to any
nat on fxp1 from 144.19.74.0/24 to any -> 204.92.77.100
.Ed
.Pp
In the example below, fxp0 is the internal interface.
Packets bound
for one specific server, as well as those generated by the sysadmins
are not proxied; all other connections are.
.Bd -literal
# NO RDR
no rdr on fxp0 proto { tcp, udp } from any to $server port 80
no rdr on fxp0 proto { tcp, udp } from $sysadmins to any port 80
rdr on fxp0 proto { tcp, udp } from any to any port 80 -> 127.0.0.1 port 80
.Ed
.Pp
This longer example uses both a NAT and a redirection.
Interface kue0 is the outside interface, and its external address is
157.161.48.183.
Interface fxp0 is the inside interface, and we are running
.Xr ftp-proxy 8 ,
listening for outbound ftp sessions captured to port 8021.
.Bd -literal
# NAT
# translate outgoing packets' source addresses (any protocol)
# in this case, any address but the gateway's external address is mapped
nat on kue0 inet from ! (kue0) to any -> (kue0)

# NAT PROXYING
# map outgoing packets' source port to an assigned proxy port instead of
# an arbitrary port
# in this case, proxy outgoing isakmp with port 500 on the gateway
nat on kue0 inet proto udp from any port = isakmp to any -> (kue0) \e
      port 500

# BINAT
# translate outgoing packets' source address (any protocol)
# translate incoming packets' destination address to an internal machine
# (bidirectional)
binat on kue0 from 10.1.2.150 to any -> (kue0)

# RDR
# translate incoming packets' destination addresses
# as an example, redirect a TCP and UDP port to an internal machine
rdr on kue0 inet proto tcp from any to (kue0) port 8080 -> 10.1.2.151 \e
      port 22
rdr on kue0 inet proto udp from any to (kue0) port 8080 -> 10.1.2.151 \e
      port 53

# RDR
# translate outgoing ftp control connections to send them to localhost
# for proxying with ftp-proxy(8) running on port 8021
rdr on fxp0 proto tcp from any to any port 21 -> 127.0.0.1 port 8021

In this example, a NAT gateway is set up to translate internal addresses
using a pool of public addresses (192.0.2.16/28) and to redirect
incoming web server connections to a group of web servers on the internal
network.
Interface fxp0 is the external interface.

# NAT LOAD BALANCE
# translate outgoing packets' source addresses using an address pool.  A
# given source address is always translated to the same pool address by
# using the source-hash keyword.
nat on fxp0 inet from any to any -> 192.0.2.16/28 source-hash

# RDR ROUND ROBIN
# translate incoming web server connections to a group of web servers on
# the internal network
rdr on fxp0 proto tcp from any to any port 80 \e
      -> { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin
.Ed
.Sh FILTER EXAMPLES
.Bd -literal
# The external interface is kue0
# (157.161.48.183, the only routable address)
# and the private network is 10.0.0.0/8, for which we are doing NAT.

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

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

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

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

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

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

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

# ICMP

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

# UDP

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

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

# TCP

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

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

# pass in data mode connections for ftp-proxy running on this host.
# (see ftp-proxy(8) for details)
pass in on $ext_if proto tcp from any to 157.161.48.183 port >= 49152 \e
      flags S/SA keep state
.Ed
.Sh GRAMMAR
Syntax for
.Nm
in BNF:
.Bd -literal
line           = ( OPTION | PF-RULE | NAT-RULE | BINAT-RULE | RDR-RULE
                 | ANTISPOOF-RULE | ALTQ-RULE | QUEUE-RULE | ANCHOR-RULE
                 | TRANS-ANCHORS | LOAD-ANCHORS )

option         = set ( [ TIMEOUT ( TIMEOUT | '{' TIMEOUT-LIST '}' ) ] |
                 [ optimization [ default | normal
                 | high-latency | satellite
                 | aggressive | conservative ] ]
                 [ limit LIMIT-LIST ] |
                 [ loginterface ( INTERFACE-NAME | none ) ] |
                 [ block-policy ( drop | return ) ] |
                 [ require-order ( yes | no ) ] )

pf-rule        = ACTION [ ( in | out ) ]
                 [ log | log-all ] [ quick ]
                 [ on IFSPEC ] [ ROUTE ] [ AF ] [ PROTOSPEC ]
                 HOSTS [ FILTEROPT-LIST ]

filteropt-list = FILTEROPT-LIST FILTEROPT | FILTEROPT
filteropt      = USER | GROUP | FLAGS | ICMP-TYPE | ICMP6-TYPE | TOS |
                 ( keep | modulate ) state [ '(' STATE-OPTS ')' ] |
                 fragment | no-df | min-ttl NUMBER | max-mss NUMBER |
                 random-id | reassemble tcp | FRAGMENTATION | allow-opts |
                 label STRING | tag STRING | tagged STRING
		 queue '(' STRING | ( STRING [ [ ',' ] STRING ] ) ')'

nat-rule       = [ no ] nat [ on IFSPEC ] [ AF ] [ PROTOSPEC ]
                 HOSTS [ '->' ( REDIRHOST | '{' REDIRHOST-LIST '}' )
                 [ PORTSPEC ] [ POOLTYPE ] [ static-port ] ]

binat-rule     = [ no ] binat [ on INTERFACE-NAME ] [ AF ]
                 [ proto ( PROTO-NAME | PROTO-NUMBER ) ]
                 from ADDRESS [ '/' MASK-BITS ] to IPSPEC
                 [ '->' ADDRESS [ '/' MASK-BITS ] ]

rdr-rule       = [ no ] rdr [ on IFSPEC ] [ AF ] [ PROTOSPEC ]
                 HOSTS [ '->' ( REDIRHOST | '{' REDIRHOST-LIST '}' )
                 [ PORTSPEC ] [ POOLTYPE ] ]

antispoof-rule = antispoof [ log ] [ quick ]
                 for ( INTERFACE-NAME | '{' INTERFACE-LIST '}' )
                 [ AF ] [ label STRING ]

table-rule     = table '<' STRING '>' [ TABLEOPTS-LIST ]
tableopts-list = TABLEOPTS-LIST TABLEOPTS | TABLEOPTS
tableopts      = persist | const | file STRING | '{' [ TABLEADDR-LIST ] '}'
tableaddr-list = TABLEADDR-LIST [ ',' ] TABLEADDR-SPEC | TABLEADDR-SPEC
tableaddr-spec = [ '!' ] TABLEADDR [ '/' MASK-BITS ]
tableaddr      = HOSTNAME | IPV4-DOTTED-QUAD | IPV6-COLONED-HEX |
                 INTERFACE-NAME | self

altq-rule      = altq on INTERFACE-NAME QUEUEOPTS-LIST
                 queue QUEUE-LIST
queue-rule     = queue STRING [ on INTERFACE-NAME ] QUEUEOPTS-LIST
                 QUEUE-LIST

anchor-rule    = anchor STRING [ ( in | out ) ] [ on IFSPEC ] [ AF ]
                 [ proto ] [ PROTOSPEC ] [ HOSTS ]

trans-anchors  = ( nat-anchor | rdr-anchor | binat-anchor ) STRING
                 [ on IFSPEC ] [ AF ] [ proto ] [ PROTOSPEC ] [ HOSTS ]

load-anchor    = load anchorname:rulesetname from filename

queueopts-list = QUEUEOPTS-LIST QUEUEOPTS | QUEUEOPTS
queueopts      = [ bandwidth BANDWIDTH-SPEC ] |
                 [ qlimit NUMBER ] | [ tbrsize NUMBER ] |
                 [ priority NUMBER ] | [ SCHEDULERS ] |
                 [ qlimit NUMBER ]
schedulers     = ( CBQ-DEF | PRIQ-DEF | HFSC-DEF )
bandwidth-spec = number ( b | Kb | Mb | Gb | '%' )

action         = pass | block [ return ] | scrub
return         = drop | return | return-rst [ '(' ttl NUMBER ')' ]
                 | return-icmp [ '(' ICMPCODE [',' ICMP6CODE ] ')' ]
                 | return-icmp6 [ '(' ICMP6CODE ')' ]
icmpcode       = ( ICMP-CODE-NAME | ICMP-CODE-NUMBER )
icmp6code      = ( ICMP6-CODE-NAME | ICMP6-CODE-NUMBER )

ifspec         = ( [ '!' ] INTERFACE-NAME ) | '{' INTERFACE-LIST '}'
interface-list = [ '!' ] INTERFACE-NAME [ [ ',' ] INTERFACE-LIST ]
route          = fastroute |
                 ( route-to | reply-to | dup-to )
                 ( ROUTEHOST | '{' ROUTEHOST-LIST '}' )
                 [ POOLTYPE ]
af             = inet | inet6

protospec      = proto ( PROTO-NAME | PROTO-NUMBER |
                 '{' PROTO-LIST '}' )
proto-list     = ( PROTO-NAME | PROTO-NUMBER ) [ [ ',' ] PROTO-LIST ]

hosts          = all |
                 from ( any | no-route | self | HOST |
                 '{' HOST-LIST '}' ) [ PORT ]
                 to   ( any | no-route | self | HOST |
                 '{' HOST-LIST '}' ) [ PORT ]

ipspec         = any | HOST | '{' HOST-LIST '}'
host           = [ '!' ] ( ADDRESS [ '/' MASK-BITS ] | '<' STRING '>' )
redirhost      = ADDRESS [ '/' MASK-BITS ]
routehost      = ( INTERFACE-NAME [ ADDRESS [ '/' MASK-BITS ] ] )
address        = ( INTERFACE-NAME | '(' INTERFACE-NAME ')' | HOSTNAME
                 | IPV4-DOTTED-QUAD | IPV6-COLONED-HEX )
host-list      = HOST [ [ ',' ] HOST-LIST ]
redirhost-list = REDIRHOST [ [ ',' ] REDIRHOST-LIST ]
routehost-list = ROUTEHOST [ [ ',' ] ROUTEHOST-LIST ]

port           = port ( UNARY-OP | BINARY-OP | '{' OP-LIST '}' )
portspec       = port ( NUMBER | NAME ) [ ':' ( '*' | NUMBER | NAME ) ]
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 ]

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

icmp-type      = icmp-type ( ICMP-TYPE-CODE | '{' ICMP-LIST '}' )
icmp6-type     = icmp6-type ( ICMP-TYPE-CODE | '{' ICMP-LIST '}')
icmp-type-code = ( ICMP-TYPE-NAME | ICMP-TYPE-NUMBER )
                 [ code ( ICMP-CODE-NAME | ICMP-CODE-NUMBER ) ]
icmp-list      = ICMP-TYPE-CODE [ [ ',' ] ICMP-LIST ]

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

state-opts     = STATE-OPT [ [ ',' ] STATE-OPTS ]
state-opt      = ( max NUMBER ) | ( timeout SECONDS )

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

timeout-list   = TIMEOUT [ [ ',' ] TIMEOUT-LIST ]
timeout        = ( tcp.first | tcp.opening | tcp.established
                 | tcp.closing | tcp.finwait | tcp.closed
                 | udp.first | udp.single | udp.multiple
                 | icmp.first | icmp.error
                 | other.first | other.single | other.multiple )
                 SECONDS
seconds        = NUMBER

limit-list     = LIMIT-ITEM [ [ ',' ] LIMIT-LIST ]
limit-item     = ( states | frags ) NUMBER

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

subqueue       = STRING | '{' QUEUE-LIST '}'
queue-list     = STRING [ [ ',' ] STRING ]
cbq-def        = cbq [ '(' CBQ-OPT [ [ ',' ] CBQ-OPT ] ')' ]
priq-def       = priq [ '(' PRIQ-OPT [ [ ',' ] PRIQ-OPT ] ')' ]
hfsc-def       = hfsc [ '(' HFSC-OPT [ [ ',' ] HFSC-OPT ] ')' ]
cbq-opt        = ( default | borrow | red | ecn | rio )
priq-opt       = ( default | red | ecn | rio )
hfsc-opt       = ( default | red | ecn | rio
                 | LINKSHARE-SC | REALTIME-SC | UPPERLIMIT-SC )
linkshare-sc   = linkshare SC-SPEC
realtime-sc    = realtime SC-SPEC
upperlimit-sc  = upperlimit SC-SPEC
sc-spec        = ( BANDWIDTH-SPEC
                 | '(' BANDWIDTH-SPEC NUMBER BANDWIDTH-SPEC ')' )
.Ed
.Sh FILES
.Bl -tag -width "/etc/protocols" -compact
.It Pa /etc/hosts
Host name database.
.It Pa /etc/pf.conf
Default location of the ruleset file.
.It Pa /etc/protocols
Protocol name database.
.It Pa /etc/services
Service name database.
.It Pa /usr/share/pf
Example rulesets.
.El
.Sh SEE ALSO
.Xr icmp 4 ,
.Xr icmp6 4 ,
.Xr ip 4 ,
.Xr ip6 4 ,
.Xr pf 4 ,
.Xr tcp 4 ,
.Xr udp 4 ,
.Xr hosts 5 ,
.Xr protocols 5 ,
.Xr services 5 ,
.Xr ftp-proxy 8 ,
.Xr pfctl 8 ,
.Xr pflogd 8
.Sh HISTORY
The
.Nm
file format first appeared in
.Ox 3.0 .