NAME¶
pf.conf —
packet filter configuration
file
DESCRIPTION¶
The
pf(4) packet filter modifies, drops or passes packets
according to rules or definitions specified in
pf.conf.
STATEMENT ORDER¶
There are seven types of statements in
pf.conf:
- Macros
- User-defined variables may be defined and used later,
simplifying the configuration file. Macros must be defined before they are
referenced in pf.conf.
- Tables
- Tables provide a mechanism for increasing the performance
and flexibility of rules with large numbers of source or destination
addresses.
- Options
- Options tune the behaviour of the packet filtering
engine.
- Traffic
Normalization
(e.g.
scrub)
- Traffic normalization protects internal machines against
inconsistencies in Internet protocols and implementations.
- Queueing
- Queueing provides rule-based bandwidth control.
- Translation
(Various forms of NAT)
- Translation rules specify how addresses are to be mapped or
redirected to other addresses.
- Packet
Filtering
- Packet filtering provides rule-based blocking or passing of
packets.
With the exception of
macros and
tables, the
types of statements should be grouped and appear in
pf.conf
in the order shown above, as this matches the operation of the underlying
packet filtering engine. By default
pfctl(8) enforces this
order (see
set require-order below).
Comments can be put anywhere in the file using a hash mark (‘#’),
and extend to the end of the current line.
Additional configuration files can be included with the
include keyword, for example:
include "/etc/pf/sub.filter.conf"
MACROS¶
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
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
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 rules,
scrub rules or translation rules such as
nat or
rdr (see below for details
on the various rule types). Tables can also be used for the redirect address
of
nat and
rdr rules and in the
routing options of filter rules, but only for
round-robin pools.
Tables can be defined with any of the following
pfctl(8)
mechanisms. As with macros, reserved words may not be used as table names.
- manually
- Persistent tables can be manually created with the
add or replace option of
pfctl(8), before or after the ruleset has been
loaded.
- pf.conf
- Table definitions can be placed directly in this file, and
loaded at the same time as other rules are loaded, atomically. Table
definitions inside pf.conf use the
table statement, and are especially useful to define
non-persistent tables. The contents of a pre-existing table defined
without a list of 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:
- persist
- The persist flag forces the kernel to
keep the table even when no rules refer to it. If the flag is not set, the
kernel will automatically remove the table when the last rule referring to
it is flushed.
- const
- The const flag prevents the user from
altering the contents of the table once it has been created. Without that
flag, pfctl(8) can be used to add or remove addresses
from the table at any time, even when running with
securelevel(7) = 2.
- counters
- The counters flag enables per-address
packet and byte counters which can be displayed with
pfctl(8).
For example,
table <private> const { 10/8, 172.16/12, 192.168/16 }
table <badhosts> persist
block on fxp0 from { <private>, <badhosts> } to any
creates a table called private, to hold RFC 1918 private network blocks, and a
table called badhosts, which is initially empty. A filter rule is set up to
block all traffic coming from addresses listed in either table. The private
table cannot have its contents changed and the badhosts table will exist even
when no active filter rules reference it. Addresses may later be added to the
badhosts table, so that traffic from these hosts can be blocked by using
# pfctl -t badhosts -Tadd 204.92.77.111
A table can also be initialized with an address list specified in one or more
external files, using the following syntax:
table <spam> persist file "/etc/spammers" file "/etc/openrelays"
block on fxp0 from <spam> to any
The files
/etc/spammers and
/etc/openrelays
list IP addresses, one per line. Any lines beginning with a # are treated as
comments and ignored. In addition to being specified by IP address, hosts may
also be specified by their hostname. When the resolver is called to add a
hostname to a table,
all resulting IPv4 and IPv6 addresses
are placed into the table. IP addresses can also be entered in a table by
specifying a valid 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.
OPTIONS¶
pf(4) may be tuned for various situations using the
set command.
- set
timeout
-
- interval
- Interval between purging expired states and
fragments.
- frag
- Seconds before an unassembled fragment is expired.
- src.track
- Length of time to retain a source tracking entry after
the last state expires.
When a packet matches a stateful connection, the seconds to live for the
connection will be updated to that of the
proto.modifier which corresponds to the connection
state. Each packet which matches this state will reset the TTL. Tuning
these values may improve the performance of the firewall at the risk of
dropping valid idle connections.
- tcp.first
- The state after the first packet.
- tcp.opening
- The state before the destination host ever sends a
packet.
- tcp.established
- The fully established state.
- tcp.closing
- The state after the first FIN has been sent.
- tcp.finwait
- The state after both FINs have been exchanged and the
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.closed
- The state after one endpoint sends an RST.
ICMP and UDP are handled in a fashion similar to TCP, but with a much more
limited set of states:
- udp.first
- The state after the first packet.
- udp.single
- The state if the source host sends more than one packet
but the destination host has never sent one back.
- udp.multiple
- The state if both hosts have sent packets.
- icmp.first
- The state after the first packet.
- icmp.error
- The state after an ICMP error came back in response to
an ICMP packet.
Other protocols are handled similarly to UDP:
- other.first
-
- other.single
-
- other.multiple
-
Timeout values can be reduced adaptively as the number of state table
entries grows.
- adaptive.start
- When the number of state entries exceeds this value,
adaptive scaling begins. All timeout values are scaled linearly with
factor (adaptive.end - number of states) / (adaptive.end -
adaptive.start).
- adaptive.end
- When reaching this number of state entries, all timeout
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 6000, adaptive.end 12000 }
set limit states 10000
With 9000 state table entries, the timeout values are scaled to 50%
(tcp.first 60, tcp.established 43200).
- set
loginterface
- Enable collection of packet and byte count statistics for
the given interface or interface group. These statistics can be viewed
using
In this example pf(4) collects statistics on the interface
named dc0:
One can disable the loginterface using:
- set
limit
- Sets hard limits on the memory pools used by the packet
filter. See zone(9) for an explanation of memory pools.
For example,
sets the maximum number of entries in the memory pool used by state table
entries (generated by pass rules which do not
specify no state) to 20000. Using
sets the maximum number of entries in the memory pool used for fragment
reassembly (generated by scrub rules) to 20000.
Using
sets the maximum number of entries in the memory pool used for tracking
source IP addresses (generated by the sticky-address
and src.track options) to 2000. Using
set limit tables 1000
set limit table-entries 100000
sets limits on the memory pools used by tables. The first limits the number
of tables that can exist to 1000. The second limits the overall number of
addresses that can be stored in tables to 100000.
Various limits can be combined on a single line:
set limit { states 20000, frags 20000, src-nodes 2000 }
- set
ruleset-optimization
-
- none
- Disable the ruleset optimizer.
- basic
- Enable basic ruleset optimization. This is the default
behaviour. Basic ruleset optimization does four things to improve the
performance of ruleset evaluations:
- remove duplicate
rules
- remove rules that are
a subset of another rule
- combine multiple rules
into a table when advantageous
- re-order the rules to
improve evaluation performance
- 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
optimization
- Optimize state timeouts for one of the following network
environments:
- normal
- A normal network environment. Suitable for almost all
networks.
- high-latency
- A high-latency environment (such as a satellite
connection).
- satellite
- Alias for high-latency.
- aggressive
- Aggressively expire connections. This can greatly
reduce the memory usage of the firewall at the cost of dropping idle
connections early.
- conservative
- Extremely conservative settings. Avoid dropping
legitimate connections at the expense of greater memory utilization
(possibly much greater on a busy network) and slightly increased
processor utilization.
For example:
set optimization aggressive
- set
block-policy
- The block-policy option sets the
default behaviour for the packet block action:
- drop
- Packet is silently dropped.
- return
- A TCP RST is returned for blocked TCP packets, an ICMP
UNREACHABLE is returned for blocked UDP packets, and all other packets
are silently dropped.
For example:
- set
state-policy
- The state-policy option sets the
default behaviour for states:
- if-bound
- States are bound to interface.
- floating
- States can match packets on any interfaces (the
default).
For example:
set state-policy if-bound
- set
state-defaults
- The state-defaults option sets the
state options for states created from rules without an explicit
keep state. For example:
set state-defaults pflow, no-sync
- set
hostid
- The 32-bit hostid identifies this
firewall's state table entries to other firewalls in a
pfsync(4) failover cluster. By default the hostid is set
to a pseudo-random value, however it may be desirable to manually
configure it, for example to more easily identify the source of state
table entries.
The hostid may be specified in either decimal or hexadecimal.
- set
require-order
- By default pfctl(8) enforces an ordering
of the statement types in the ruleset to: options,
normalization, queueing,
translation, filtering. Setting this
option to no disables this enforcement. There may be
non-trivial and non-obvious implications to an out of order ruleset.
Consider carefully before disabling the order enforcement.
- set
fingerprints
- Load fingerprints of known operating systems from the given
filename. By default fingerprints of known operating systems are
automatically loaded from pf.os(5) in
/etc but can be overridden via this option. Setting this
option may leave a small period of time where the fingerprints referenced
by the currently active ruleset are inconsistent until the new ruleset
finishes loading.
For example:
set fingerprints
"/etc/pf.os.devel"
- set 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. For example:
set skip on lo0
- set
debug
- Set the debug level to one of the
following:
- none
- Don't generate debug messages.
- urgent
- Generate debug messages only for serious errors.
- misc
- Generate debug messages for various errors.
- loud
- Generate debug messages for common conditions.
TRAFFIC NORMALIZATION¶
Traffic normalization is used to sanitize packet content in such a way that
there are no ambiguities in packet interpretation on the receiving side. The
normalizer does IP fragment reassembly to prevent attacks that confuse
intrusion detection systems by sending overlapping IP fragments. Packet
normalization is invoked with the
scrub directive.
scrub has the following options:
- no-df
- Clears the dont-fragment bit from a
matching IP packet. Some operating systems are known to generate
fragmented packets with the dont-fragment bit set.
This is particularly true with NFS. Scrub will drop
such fragmented dont-fragment packets unless
no-df is specified.
Unfortunately some operating systems also generate their
dont-fragment packets with a zero IP identification
field. Clearing the dont-fragment bit on packets
with a zero IP ID may cause deleterious results if an upstream router
later fragments the packet. Using the random-id
modifier (see below) is recommended in combination with the
no-df modifier to ensure unique IP identifiers.
- min-ttl
⟨number⟩
- Enforces a minimum TTL for matching IP packets.
- max-mss
⟨number⟩
- Enforces a maximum MSS for matching TCP packets.
- set-tos
⟨string⟩ |
⟨number⟩
- Enforces a TOS for matching IP packets.
TOS may be given as one of
lowdelay, throughput,
reliability, or as either hex or decimal.
- random-id
- Replaces the IP identification field with random values to
compensate for predictable values generated by many hosts. This option
only applies to packets that are not fragmented after the optional
fragment reassembly.
- fragment
reassemble
- Using scrub rules, fragments can be
reassembled by normalization. In this case, fragments are buffered until
they form a complete packet, and only the completed packet is passed on to
the filter. The advantage is that filter rules have to deal only with
complete packets, and can ignore fragments. The drawback of caching
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 scrub rule if no fragmentation
modifier is supplied.
- fragment
crop
- The default fragment reassembly method is expensive, hence
the option to crop is provided. In this case, 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 fragment reassemble modifier, fragments
are not buffered, they are passed as soon as they are received. The
fragment crop reassembly mechanism does not yet work
with NAT.
- fragment
drop-ovl
- This option is similar to the fragment
crop modifier except that all overlapping or duplicate fragments
will be dropped, and all further corresponding fragments will be dropped
as well.
- reassemble
tcp
- Statefully normalizes TCP connections.
scrub reassemble tcp rules may not have the
direction (in/out) specified. reassemble tcp
performs the following normalizations:
- ttl
- Neither side of the connection is allowed to reduce
their IP TTL. An attacker may send a packet such that it reaches the
firewall, affects the firewall state, and expires before reaching the
destination host. reassemble tcp will raise the
TTL of all packets back up to the highest value seen on the
connection.
- timestamp modulation
- Modern TCP stacks will send a timestamp on every TCP
packet and echo the other endpoint's timestamp back to them. Many
operating systems will merely start the timestamp at zero when first
booted, and increment it several times a second. The uptime of the
host can be deduced by reading the timestamp and multiplying by a
constant. Also observing several different timestamps can be used to
count hosts behind a NAT device. And spoofing TCP packets into a
connection requires knowing or guessing valid timestamps. Timestamps
merely need to be monotonically increasing and not derived off a
guessable base time. reassemble tcp will cause
scrub to modulate the TCP timestamps with a
random number.
- extended PAWS checks
- There is a problem with TCP on long fat pipes, in that
a packet might get delayed for longer than it takes the connection to
wrap its 32-bit sequence space. In such an occurrence, the old packet
would be indistinguishable from a new packet and would be accepted as
such. The solution to this is called PAWS: Protection Against Wrapped
Sequence numbers. It protects against it by making sure the timestamp
on each packet does not go backwards. reassemble
tcp also makes sure the timestamp on the packet does not go
forward more than the RFC allows. By doing this,
pf(4) artificially extends the security of TCP
sequence numbers by 10 to 18 bits when the host uses appropriately
randomized timestamps, since a blind attacker would have to guess the
timestamp as well.
For example,
scrub in on $ext_if all fragment reassemble
The
no option prefixed to a scrub rule causes matching
packets to remain unscrubbed, much in the same way as
drop
quick works in the packet filter (see below). This mechanism should be
used when it is necessary to exclude specific packets from broader scrub
rules.
QUEUEING¶
The ALTQ system is currently not available in the GENERIC kernel nor as loadable
modules. In order to use the herein after called queueing options one has to
use a custom built kernel. Please refer to
altq(4) to learn
about the related kernel options.
Packets can be assigned to queues for the purpose of bandwidth control. At least
two declarations are required to configure queues, and later any packet
filtering rule can reference the defined queues by name. During the filtering
component of
pf.conf, the last referenced
queue name is where any packets from
pass rules will be queued, while for
block rules it specifies where any resulting ICMP or TCP
RST packets should be queued. The
scheduler defines the
algorithm used to decide which packets get delayed, dropped, or sent out
immediately. There are three
schedulers currently
supported.
- cbq
- Class Based Queueing. Queues attached
to an interface build a tree, thus each queue can
have further child queues. Each queue can have a
priority and a bandwidth
assigned. Priority mainly controls the time packets
take to get sent out, while bandwidth has primarily
effects on throughput. cbq achieves both
partitioning and sharing of link bandwidth by hierarchically structured
classes. Each class has its own queue and is
assigned its share of bandwidth. A child class can
borrow bandwidth from its parent class as long as excess bandwidth is
available (see the option borrow, below).
- priq
- Priority Queueing. Queues are flat
attached to the interface, thus, queues cannot have
further child queues. Each
queue has a unique priority
assigned, ranging from 0 to 15. Packets in the queue
with the highest priority are processed first.
- hfsc
- Hierarchical Fair Service Curve.
Queues attached to an interface build a tree, thus
each queue can have further child
queues. Each queue can have a
priority and a bandwidth
assigned. Priority mainly controls the time packets
take to get sent out, while bandwidth primarily
affects throughput. hfsc supports both link-sharing
and guaranteed real-time services. It employs a service curve based QoS
model, and its unique feature is an ability to decouple
delay and bandwidth
allocation.
The interfaces on which queueing should be activated are declared using the
altq on declaration.
altq on has
the following keywords:
- ⟨interface⟩
- Queueing is enabled on the named interface.
- ⟨scheduler⟩
- Specifies which queueing scheduler to use. Currently
supported values are cbq for Class Based Queueing,
priq for Priority Queueing and
hfsc for the Hierarchical Fair Service Curve
scheduler.
- bandwidth
⟨bw⟩
- The maximum bitrate for all queues on an interface may be
specified using the bandwidth keyword. The value can
be specified as an absolute value or as a percentage of the interface
bandwidth. When using an absolute value, the suffixes
b, Kb,
Mb, and Gb are used to
represent bits, kilobits, megabits, and gigabits per second, respectively.
The value must not exceed the interface bandwidth. If
bandwidth is not specified, the interface bandwidth
is used (but take note that some interfaces do not know their bandwidth,
or can adapt their bandwidth rates).
- qlimit
⟨limit⟩
- The maximum number of packets held in the queue. The
default is 50.
- tbrsize
⟨size⟩
- Adjusts the size, in bytes, of the token bucket regulator.
If not specified, heuristics based on the interface bandwidth are used to
determine the size.
- queue
⟨list⟩
- Defines a list of subqueues to create on an interface.
In the following example, the interface dc0 should queue up to 5Mbps in four
second-level queues using Class Based Queueing. Those four queues will be
shown in a later example.
altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh }
Once interfaces are activated for queueing using the
altq
directive, a sequence of
queue directives may be
defined. The name associated with a
queue must match a
queue defined in the
altq directive (e.g. mail), or,
except for the
priq scheduler, in
a parent
queue declaration. The following keywords can
be used:
- on
⟨interface⟩
- Specifies the interface the queue operates on. If not
given, it operates on all matching interfaces.
- bandwidth
⟨bw⟩
- Specifies the maximum bitrate to be processed by the queue.
This value must not exceed the value of the parent
queue and can be specified as an absolute value or a
percentage of the parent queue's bandwidth. If not specified, defaults to
100% of the parent queue's bandwidth. The priq
scheduler does not support bandwidth specification.
- priority
⟨level⟩
- Between queues a priority level can be set. For
cbq and hfsc, the range is 0
to 7 and for priq, the range is 0 to 15. The default
for all is 1. Priq queues with a higher priority are
always served first. Cbq and
Hfsc queues with a higher priority are preferred in
the case of overload.
- qlimit
⟨limit⟩
- The maximum number of packets held in the queue. The
default is 50.
The
scheduler can get additional parameters with
⟨
scheduler⟩
(⟨
parameters⟩). Parameters are as follows:
- default
- Packets not matched by another queue are assigned to this
one. Exactly one default queue is required.
- red
- Enable RED (Random Early Detection) on this queue. RED
drops packets with a probability proportional to the average queue
length.
- rio
- Enables RIO on this queue. RIO is RED with IN/OUT, thus
running RED two times more than RIO would achieve the same effect. RIO is
currently not supported in the GENERIC kernel.
- ecn
- Enables ECN (Explicit Congestion Notification) on this
queue. ECN implies RED.
The
cbq scheduler supports an
additional option:
- borrow
- The queue can borrow bandwidth from the parent.
The
hfsc scheduler supports some
additional options:
- realtime
⟨sc⟩
- The minimum required bandwidth for the queue.
- upperlimit
⟨sc⟩
- The maximum allowed bandwidth for the queue.
- linkshare
⟨sc⟩
- The bandwidth share of a backlogged queue.
⟨
sc⟩ is an acronym for
service curve.
The format for service curve specifications is (
m1,
d,
m2).
m2
controls the bandwidth assigned to the queue.
m1 and
d are optional and can be used to control the initial
bandwidth assignment. For the first
d milliseconds the
queue gets the bandwidth given as
m1, afterwards the
value given in
m2.
Furthermore, with
cbq and
hfsc,
child queues can be specified as in an
altq declaration,
thus building a tree of queues using a part of their parent's bandwidth.
Packets can be assigned to queues based on filter rules by using the
queue keyword. Normally only one
queue is specified; when a second one is specified it
will instead be used for packets which have a
TOS of
lowdelay and for TCP ACKs with no data payload.
To continue the previous example, the examples below would specify the four
referenced queues, plus a few child queues. Interactive
ssh(1) sessions get priority over bulk transfers like
scp(1) and
sftp(1). The queues may then be
referenced by filtering rules (see
PACKET FILTERING below).
queue std bandwidth 10% cbq(default)
queue http bandwidth 60% priority 2 cbq(borrow red) \
{ employees, developers }
queue developers bandwidth 75% cbq(borrow)
queue employees bandwidth 15%
queue mail bandwidth 10% priority 0 cbq(borrow ecn)
queue ssh bandwidth 20% cbq(borrow) { ssh_interactive, ssh_bulk }
queue ssh_interactive bandwidth 50% priority 7 cbq(borrow)
queue ssh_bulk bandwidth 50% priority 0 cbq(borrow)
block return out on dc0 inet all queue std
pass out on dc0 inet proto tcp from $developerhosts to any port 80 \
queue developers
pass out on dc0 inet proto tcp from $employeehosts to any port 80 \
queue employees
pass out on dc0 inet proto tcp from any to any port 22 \
queue(ssh_bulk, ssh_interactive)
pass out on dc0 inet proto tcp from any to any port 25 \
queue mail
TRANSLATION¶
Translation rules modify either the source or destination address of the packets
associated with a stateful connection. A stateful connection is automatically
created to track packets matching such a rule as long as they are not blocked
by the filtering section of
pf.conf. The 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.
Since translation occurs before filtering the filter engine will see packets as
they look after any addresses and ports have been translated. Filter rules
will therefore have to filter based on the translated address and port number.
Packets that match a translation rule are only automatically passed if the
pass modifier is given, otherwise they are still subject
to
block and
pass rules.
The state entry created permits
pf(4) to keep track of the
original address for traffic associated with that state and correctly direct
return traffic for that connection.
Various types of translation are possible with pf:
- binat
- A binat rule specifies a
bidirectional mapping between an external IP netblock and an internal IP
netblock.
- nat
- A nat rule specifies that IP
addresses are to be changed as the packet traverses the given interface.
This technique allows one or more IP addresses on the translating host to
support network 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:
10.0.0.0 - 10.255.255.255 (all of net 10, i.e., 10/8)
172.16.0.0 - 172.31.255.255 (i.e., 172.16/12)
192.168.0.0 - 192.168.255.255 (i.e., 192.168/16)
- rdr
- The packet is redirected to another destination and
possibly a different port. rdr rules can optionally
specify port ranges instead of single ports. rdr ... port 2000:2999 ->
... port 4000 redirects ports 2000 to 2999 (inclusive) to port 4000. rdr
... port 2000:2999 -> ... port 4000:* redirects port 2000 to 4000, 2001
to 4001, ..., 2999 to 4999.
In addition to modifying the address, some translation rules may modify source
or destination ports for
tcp(4) or
udp(4)
connections; implicitly in the case of
nat rules and
explicitly in the case of
rdr rules. Port numbers are
never translated with a
binat rule.
Evaluation order of the translation rules is dependent on the type of the
translation rules and of the direction of a packet.
binat rules are always evaluated first. Then either the
rdr rules are evaluated on an inbound packet or the
nat rules on an outbound packet. Rules of the same type
are evaluated in the same order in which they appear in the ruleset. The first
matching rule decides what action is taken.
The
no option prefixed to a translation rule causes
packets to remain untranslated, much in the same way as
drop
quick works in the packet filter (see below). If no rule matches the
packet it is passed to the filter engine unmodified.
Translation rules apply only to packets that pass through the specified
interface, and if no interface is specified, translation is applied to packets
on all interfaces. For instance, redirecting port 80 on an 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.
Note that redirecting external incoming connections to the loopback address, as
in
rdr on ne3 inet proto tcp to port smtp -> 127.0.0.1 port spamd
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.
See
TRANSLATION EXAMPLES below.
PACKET FILTERING¶
pf(4) has the ability to
block and
pass packets based on attributes of their layer 3 (see
ip(4) and
ip6(4)) and layer 4 (see
icmp(4),
icmp6(4),
tcp(4),
udp(4)) headers. In addition,
packets may also be assigned to queues for the purpose of bandwidth control.
For each packet processed by the packet filter, the filter rules are evaluated
in sequential order, from first to last. The last matching rule decides what
action is taken. If no rule matches the packet, the default action is to pass
the packet.
The following actions can be used in the filter:
- block
- The packet is blocked. There are a number of ways in which
a block rule can behave when blocking a packet. The
default behaviour is to drop packets silently,
however this can be overridden or made explicit either globally, by
setting the block-policy option, or on a per-rule
basis with one of the following options:
- drop
- The packet is silently dropped.
- return-rst
- This applies only to tcp(4) packets,
and issues a TCP RST which closes the connection.
- return-icmp
-
- return-icmp6
- This causes ICMP messages to be returned for packets
which match the rule. By default this is an ICMP UNREACHABLE message,
however this can be overridden by specifying a message as a code or
number.
- return
- This causes a TCP RST to be returned for
tcp(4) packets and an ICMP UNREACHABLE for UDP and
other packets.
Options returning ICMP packets currently have no effect if
pf(4) operates on a if_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:
- pass
- The packet is passed; state is created unless the
no state option is specified.
By default
pf(4) filters packets statefully; the first time a
packet matches a
pass rule, a state entry is created;
for subsequent packets the filter checks whether the packet matches any 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.
This has several advantages. For TCP connections, comparing a packet to a state
involves checking its sequence numbers, as well as TCP timestamps if a
scrub reassemble tcp rule 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,
pass out inet proto icmp all icmp-type echoreq
allows echo requests (such as those created by
ping(8)) out
statefully, and matches 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,
binat and
rdr rules, 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. A number of parameters can also be set to
affect how
pf(4) handles state tracking. See
STATEFUL TRACKING OPTIONS
below for further details.
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
pfctl(8) generates all needed rule combinations.
- in
or out
- This rule applies to incoming or outgoing packets. If
neither in nor out are
specified, the rule will match packets in both directions.
- log
- In addition to the action specified, a log message is
generated. 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. This interface is monitored by the
pflogd(8) logging daemon, which dumps the logged packets
to the file /var/log/pflog in pcap(3)
binary format.
- log
(all)
- Used to force logging of all packets for a connection. This
is not necessary when no state is explicitly
specified. As with log, packets are logged to
pflog(4).
- log
(user)
- Logs the UNIX user ID of the user
that owns the socket and the PID of the process that has the socket open
where the packet is sourced from or destined to (depending on which socket
is local). This is in addition to the normal information logged.
Due to the problems described in the BUGS section only the first packet
logged via log (all, user) will have the user
credentials logged when using stateful matching.
- log (to
⟨interface⟩)
- Send logs to the specified pflog(4)
interface instead of pflog0.
- quick
- If a packet matches a rule which has the
quick option set, this rule is considered the last
matching rule, and evaluation of subsequent rules is skipped.
- on
⟨interface⟩
- This rule applies only to packets coming in on, or going
out through, this particular interface or interface group. For more
information on interface groups, see the group keyword
in ifconfig(8).
- ⟨af⟩
- This rule applies only to packets of this address family.
Supported values are inet and
inet6.
- proto
⟨protocol⟩
- This rule applies only to packets of this protocol. Common
protocols are icmp(4), icmp6(4),
tcp(4), and udp(4). For a list of all
the protocol name to number mappings used by pfctl(8),
see the file /etc/protocols.
- from
⟨source⟩ port
⟨source⟩ os
⟨source⟩ to
⟨dest⟩ port
⟨dest⟩
- This rule applies only to packets with the specified source
and destination addresses and ports.
Addresses can be specified in CIDR notation (matching netblocks), as
symbolic host names, interface names or interface group names, or as any
of the following keywords:
- any
- Any address.
- route
⟨label⟩
- Any address whose associated route has label
⟨label⟩. See
route(4) and route(8).
- no-route
- Any address which is not currently routable.
- 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.
- ⟨table⟩
- Any address that matches the given table.
Ranges of addresses are specified by 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 and interface group names can have modifiers appended:
- :network
- Translates to the network(s) attached to the
interface.
- :broadcast
- Translates to the interface's broadcast
address(es).
- :peer
- Translates to the point-to-point interface's peer
address(es).
- :0
- Do not include interface aliases.
Host names may also have the :0 option appended to
restrict the name resolution to the first of each v4 and v6 address found.
Host name resolution and interface to address translation are done at
ruleset load-time. When the address of an interface (or host name) changes
(under DHCP or PPP, for instance), the ruleset must be reloaded for the
change to be reflected in the kernel. 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 by using these operators:
= (equal)
!= (unequal)
< (less than)
≤ (less than or equal)
> (greater than)
≥ (greater than or equal)
: (range including boundaries)
>< (range excluding boundaries)
<> (except range)
‘><’, ‘<>’ and ‘:’ are
binary operators (they take two arguments). For instance:
- port
2000:2004
- means ‘all ports ≥ 2000 and ≤
2004’, hence ports 2000, 2001, 2002, 2003 and 2004.
- port
2000 >< 2004
- means ‘all ports > 2000 and < 2004’,
hence ports 2001, 2002 and 2003.
- port
2000 <> 2004
- means ‘all ports < 2000 or > 2004’,
hence ports 1-1999 and 2005-65535.
The operating system of the source host can be specified in the case of TCP
rules with the OS modifier. See the
OPERATING SYSTEM
FINGERPRINTING section for more information.
The host, port and OS specifications are optional, as in the 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"
- all
- This is equivalent to "from any to any".
- group
⟨group⟩
- Similar to user, this rule only
applies to packets of sockets owned by the specified group.
- user
⟨user⟩
- This rule only applies to packets of sockets owned by the
specified user. For outgoing connections initiated from the firewall, this
is the user that opened the connection. For incoming connections to the
firewall itself, this is the user that listens on the destination port.
For forwarded connections, where the firewall is not a connection
endpoint, the user and group are unknown.
All packets, both outgoing and incoming, of one connection are associated
with the same user and group. Only TCP and UDP packets can be associated
with users; for other protocols these parameters are ignored.
User and group refer to the effective (as opposed to the real) IDs, in case
the socket is created by a setuid/setgid process. User and group IDs are
stored when a socket is created; when a process 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 value unknown
matches packets of forwarded connections. unknown can
only be used with the operators = and
!=. Other constructs like user ≥
unknown are invalid. Forwarded packets with unknown user and group ID
match only rules that explicitly compare against unknown
with the operators = or !=. For
instance user ≥ 0 does not match forwarded
packets. The following example allows only selected users to open outgoing
connections:
block out proto { tcp, udp } all
pass out proto { tcp, udp } all user { < 1000, dhartmei }
- flags
⟨a⟩
/⟨b⟩ |
/⟨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
nat, binat
or rdr rules,
modulate or
synproxy state options, or scrubbed with
reassemble tcp will also not be recoverable from
intermediate packets. Such connections will stall and time out.
- icmp-type
⟨type⟩ code
⟨code⟩
-
- icmp6-type
⟨type⟩ code
⟨code⟩
- This rule only applies to ICMP or ICMPv6 packets with the
specified type and code. Text names for ICMP types and codes are listed in
icmp(4) and icmp6(4). 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.
- tos
⟨string⟩ |
⟨number⟩
- This rule applies to packets with the specified
TOS bits set. TOS may be given as one
of lowdelay, throughput,
reliability, or as either hex or decimal.
For example, the following rules are identical:
pass all tos lowdelay
pass all tos 0x10
pass all tos 16
- allow-opts
- By default, IPv4 packets with IP options or IPv6 packets
with routing extension headers are blocked. When
allow-opts is specified for a
pass rule, packets that pass the filter based on
that rule (last matching) do so even if they contain IP options or routing
extension headers. For packets that match state, the rule that initially
created the state is used. The implicit pass rule
that is used when a packet does not match any rules does not allow IP
options.
- label
⟨string⟩
- Adds a label (name) to the rule, which can be used to
identify the rule. For instance, pfctl -s labels shows per-rule statistics
for rules that have labels.
The following macros can be used in labels:
- $if
- The interface.
- $srcaddr
- The source IP address.
- $dstaddr
- The destination IP address.
- $srcport
- The source port specification.
- $dstport
- The destination port specification.
- $proto
- The protocol name.
- $nr
- The rule number.
For example:
ips = "{ 1.2.3.4, 1.2.3.5 }"
pass in proto tcp from any to $ips \
port > 1023 label "$dstaddr:$dstport"
expands to
pass in inet proto tcp from any to 1.2.3.4 \
port > 1023 label "1.2.3.4:>1023"
pass in inet proto tcp from any to 1.2.3.5 \
port > 1023 label "1.2.3.5:>1023"
The macro expansion for the label directive occurs
only at configuration file parse time, not during runtime.
- queue
⟨queue⟩ |
(⟨queue⟩,
⟨queue⟩)
- Packets matching this rule will be assigned to the
specified queue. If two queues are given, packets which have a
TOS of lowdelay and TCP ACKs with no
data payload will be assigned to the second one. See
QUEUEING for setup details.
For example:
pass in proto tcp to port 25 queue mail
pass in proto tcp to port 22 queue(ssh_bulk, ssh_prio)
- tag
⟨string⟩
- Packets matching this rule will be tagged with the
specified string. The tag acts as an internal marker that can be used to
identify these packets later on. This can be used, for example, to provide
trust between interfaces and to determine if packets have been processed
by translation rules. Tags are “sticky”, meaning that the
packet will be tagged even if the rule is not the last matching rule.
Further matching rules can replace the tag with a new one but will not
remove a previously applied tag. A packet is only ever assigned one tag at
a time. Packet tagging can be done during nat,
rdr, or binat rules in
addition to filter rules. Tags take the same macros as labels (see
above).
- tagged
⟨string⟩
- Used with filter, translation or scrub rules to specify
that packets must already be tagged with the given tag in order to match
the rule. Inverse tag matching can also be done by specifying the
! operator before the tagged
keyword.
- 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.
- divert-to
⟨host⟩ port
⟨port⟩
- Used to redirect packets to a local socket bound to
host and port. The packets
will not be modified, so getsockname(2) on the socket
will return the original destination address of the packet.
- 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.
- probability
⟨number⟩
- A probability attribute can be attached to a rule, with a
value set between 0 and 1, bounds not included. In that case, the rule
will be honoured using the given probability value only. For example, the
following rule will drop 20% of incoming ICMP packets:
block in proto icmp probability 20%
ROUTING¶
If a packet matches a rule with a route option set, the packet filter will route
the packet according to the type of route option. When such a rule creates
state, the route option is also applied to all packets matching the same
connection.
- fastroute
- The fastroute option does a normal
route lookup to find the next hop for the packet.
- route-to
- The route-to option routes the packet
to the specified interface with an optional address for the next hop. When
a route-to rule creates state, only packets that
pass in the same direction as the filter rule specifies will be routed in
this way. Packets passing in the opposite direction (replies) are not
affected and are routed normally.
- reply-to
- The reply-to option is similar to
route-to, but routes packets that pass in the
opposite direction (replies) to the specified interface. Opposite
direction is only defined in the context of a state entry, and
reply-to is useful only in rules that create state.
It can be used on systems with multiple external connections to route all
outgoing packets of a connection through the interface the incoming
connection arrived through (symmetric routing enforcement).
- dup-to
- The dup-to option creates a duplicate
of the packet and routes it like route-to. The
original packet gets routed as it normally would.
POOL OPTIONS¶
For
nat and
rdr rules, (as well as
for the
route-to,
reply-to and
dup-to rule options) for which there is a single
redirection address which has a subnet mask smaller than 32 for IPv4 or 128
for IPv6 (more than one IP address), a variety of different methods for
assigning this address can be used:
- bitmask
- The bitmask option applies the
network portion of the redirection address to the address to be modified
(source with nat, destination with
rdr).
- random
- The random option selects an address
at random within the defined block of addresses.
- source-hash
- The source-hash option uses a hash of
the source address to determine the redirection address, ensuring that the
redirection address is always the same for a given source. An optional key
can be specified after this keyword either in hex or as a string; by
default pfctl(8) randomly generates a key for
source-hash every time the ruleset is reloaded.
- round-robin
- The round-robin option loops through
the redirection address(es).
When more than one redirection address is specified,
round-robin is the only permitted pool type.
- static-port
- With nat rules, the
static-port option prevents pf(4)
from modifying the source port on TCP and UDP packets.
Additionally, the
sticky-address option can be specified
to help ensure that multiple connections from the same source are mapped to
the same redirection address. This option can be used with the
random and
round-robin pool
options. Note that by default these associations are destroyed as soon as
there are no longer states which refer to them; in order to make the mappings
last beyond the lifetime of the states, increase the global options with
set timeout src.track. See
STATEFUL TRACKING OPTIONS
for more ways to control the source tracking.
STATE MODULATION¶
Much of the security derived from TCP is attributable to how well the initial
sequence numbers (ISNs) are chosen. Some popular stack implementations choose
very poor ISNs and thus are normally susceptible to ISN
prediction exploits. By applying a
modulate state rule
to a TCP connection,
pf(4) will create a high quality random
sequence number for each connection endpoint.
The
modulate state directive implicitly keeps state on the
rule and is only applicable to TCP connections.
For instance:
block all
pass out proto tcp from any to any modulate state
pass in proto tcp from any to any port 25 flags S/SFRA modulate state
Note that modulated connections will not recover when the state table is lost
(firewall reboot, flushing the state table, etc...).
pf(4)
will not be able to infer a connection again after the state table flushes the
connection's modulator. When the state is lost, the connection may be left
dangling until the respective endpoints time out the connection. It is
possible on a fast local network for the endpoints to start an ACK storm while
trying to resynchronize after the loss of the modulator. The default
flags settings (or a more strict equivalent) should be
used on
modulate state rules to prevent ACK storms.
Note that alternative methods are available to prevent loss of the state table
and allow for firewall failover. See
carp(4) and
pfsync(4) for further information.
SYN PROXY¶
By default,
pf(4) passes packets that are part of a
tcp(4) handshake between the endpoints. The
synproxy state option can be used to cause
pf(4) itself to complete the handshake with the active
endpoint, perform a handshake with the passive endpoint, and then forward
packets between the endpoints.
No packets are sent to the passive endpoint before the active endpoint has
completed the handshake, hence so-called SYN floods with spoofed source
addresses will not reach the passive endpoint, as the sender can't complete
the handshake.
The proxy is transparent to both endpoints, they each see a single connection
from/to the other endpoint.
pf(4) chooses random initial
sequence numbers for both handshakes. Once the handshakes are completed, the
sequence number modulators (see previous section) are used to translate
further packets of the connection.
synproxy state
includes
modulate state.
Rules with
synproxy will not work if
pf(4) operates on a
bridge(4).
Example:
pass in proto tcp from any to any port www synproxy state
STATEFUL TRACKING OPTIONS¶
A number of options related to stateful tracking can be applied on a per-rule
basis.
keep state,
modulate state
and
synproxy state support these options, and
keep state must be specified explicitly to apply options
to a rule.
- max
⟨number⟩
- Limits the number of concurrent states the rule may create.
When this limit is reached, further packets that would create state will
not match this rule until existing states time out.
- no-sync
- Prevent state changes for states created by this rule from
appearing on the pfsync(4) interface.
- ⟨timeout⟩
⟨seconds⟩
- Changes the timeout values used for states created by this
rule. For a list of all valid timeout names, see
OPTIONS above.
- sloppy
- Uses a sloppy TCP connection tracker that does not check
sequence numbers at all, which makes insertion and ICMP teardown attacks
way easier. This is intended to be used in situations where one does not
see all packets of a connection, e.g. in asymmetric routing situations.
Cannot be used with modulate or synproxy state.
- pflow
- States created by this rule are exported on the
pflow(4) interface.
Multiple options can be specified, separated by commas:
pass in proto tcp from any to any \
port www keep state \
(max 100, source-track rule, max-src-nodes 75, \
max-src-states 3, tcp.established 60, tcp.closing 5)
When the
source-track keyword is specified, the number of
states per source IP is tracked.
- source-track
rule
- The maximum number of states created by this rule is
limited by the rule's max-src-nodes and
max-src-states options. Only state entries created
by this particular rule count toward the rule's limits.
- source-track
global
- The number of states created by all rules that use this
option is limited. Each rule can specify different
max-src-nodes and
max-src-states options, however state entries
created by any participating rule count towards each individual rule's
limits.
The following limits can be set:
- max-src-nodes
⟨number⟩
- Limits the maximum number of source addresses which can
simultaneously have state table entries.
- max-src-states
⟨number⟩
- Limits the maximum number of simultaneous state entries
that a single source address can create with this rule.
For stateful TCP connections, limits on established connections (connections
which have completed the TCP 3-way handshake) can also be enforced per source
IP.
- max-src-conn
⟨number⟩
- Limits the maximum number of simultaneous TCP connections
which have completed the 3-way handshake that a single host can make.
- max-src-conn-rate
⟨number⟩ /
⟨seconds⟩
- Limit the rate of new connections over a time interval. The
connection rate is an approximation calculated as a moving average.
Because the 3-way handshake ensures that the source address is not being
spoofed, more aggressive action can be taken based on these limits. With the
overload ⟨
table⟩
state option, source IP addresses which hit either of the limits on
established connections will be added to the named table. This table can be
used in the ruleset to block further activity from the offending host,
redirect it to a tarpit process, or restrict its bandwidth.
The optional
flush keyword kills all states created by the
matching rule which originate from the host which exceeds these limits. The
global modifier to the flush command kills all states
originating from the offending host, regardless of which rule created the
state.
For example, the following rules will protect the webserver against hosts making
more than 100 connections in 10 seconds. Any host which connects faster than
this rate will have its address added to the ⟨bad_hosts⟩ table
and have all states originating from it flushed. Any new packets arriving from
this host will be dropped unconditionally by the block rule.
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)
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
"OpenBSD 2.6"
The subtype of an operating system is typically used to describe the patchlevel
if that patch led to changes in the TCP stack behavior. In the case of
OpenBSD, the only subtype is for a fingerprint that
was normalized by the
no-df scrub option and would be
specified as
"OpenBSD 3.3 no-df"
Fingerprints for most popular operating systems are provided by
pf.os(5). Once
pf(4) is running, a
complete list of known operating system fingerprints may be listed by running:
# pfctl -so
Filter rules can enforce policy at any level of operating system specification
assuming a fingerprint is present. Policy could limit traffic to approved
operating systems or even ban traffic from hosts that aren't at the latest
service pack.
The
unknown class can also be used as the fingerprint
which will match packets for which no operating system fingerprint is known.
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 his packets to appear as any
operating system he chooses; an operating system patch could change the stack
behavior and no fingerprints will match it until the database is updated; and
multiple operating systems may have the same fingerprint.
BLOCKING SPOOFED TRAFFIC¶
"Spoofing" is the faking of IP addresses, typically for malicious
purposes. The
antispoof directive expands to a set of
filter rules which will block all traffic with a source IP from the network(s)
directly connected to the specified interface(s) from entering the system
through any other interface.
For example, the line
expands to
block drop in on ! lo0 inet from 127.0.0.1/8 to any
block drop in on ! lo0 inet6 from ::1 to any
For non-loopback interfaces, there are additional rules to block incoming
packets with a source IP address identical to the interface's IP(s). For
example, assuming the interface wi0 had an IP address of 10.0.0.1 and a
netmask of 255.255.255.0, the line
expands to
block drop in on ! wi0 inet from 10.0.0.0/24 to any
block drop in inet from 10.0.0.1 to any
Caveat: Rules created by the
antispoof directive interfere
with packets sent over loopback interfaces to local addresses. One should pass
these explicitly.
FRAGMENT HANDLING¶
The size of IP datagrams (packets) can be significantly larger than the maximum
transmission unit (MTU) of the network. In cases when it is necessary or more
efficient to send such large packets, the large packet will be fragmented into
many smaller packets that will each fit onto the wire. Unfortunately for a
firewalling device, only the first logical fragment will contain the necessary
header information for the subprotocol that allows
pf(4) to
filter on things such as TCP ports or to perform NAT.
Besides the use of
scrub rules as described in
TRAFFIC NORMALIZATION above,
there are three options for handling fragments in the packet filter.
One alternative is to filter individual fragments with filter rules. If no
scrub rule applies to a fragment, it is passed to the
filter. Filter rules with matching IP header parameters decide whether the
fragment is passed or blocked, in the same way as complete packets are
filtered. Without reassembly, fragments can only be filtered based on IP
header fields (source/destination address, protocol), since subprotocol header
fields are not available (TCP/UDP port numbers, ICMP code/type). The
fragment option can be used to restrict filter rules to
apply only to fragments, but not complete packets. Filter rules without the
fragment option still apply to fragments, if they only
specify IP header fields. For instance, the rule
pass in proto tcp from any to any port 80
never applies to a fragment, even if the fragment is part of a TCP packet with
destination port 80, because without reassembly this information is not
available for each fragment. This also means that fragments cannot create new
or match existing state table entries, which makes stateful filtering and
address translation (NAT, redirection) for fragments impossible.
It's also possible to reassemble only certain fragments by specifying source or
destination addresses or protocols as parameters in
scrub rules.
In most cases, the benefits of reassembly outweigh the additional memory cost,
and it's recommended to use
scrub rules to reassemble
all fragments via the
fragment reassemble modifier.
The memory allocated for fragment caching can be limited using
pfctl(8). Once this limit is reached, fragments that would
have to be cached are dropped until other entries time out. The timeout value
can also be adjusted.
Currently, only IPv4 fragments are supported and IPv6 fragments are blocked
unconditionally.
ANCHORS¶
Besides the main ruleset,
pfctl(8) can load rulesets into
anchor attachment points. An
anchor is a container that can hold rules, address
tables, and other anchors.
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.
An anchor can reference another
anchor attachment point
using the following kinds of rules:
- nat-anchor
⟨name⟩
- Evaluates the nat rules in the
specified anchor.
- rdr-anchor
⟨name⟩
- Evaluates the rdr rules in the
specified anchor.
- binat-anchor
⟨name⟩
- Evaluates the binat rules in the
specified anchor.
- anchor
⟨name⟩
- Evaluates the filter rules in the specified
anchor.
- load
anchor ⟨name⟩
from ⟨file⟩
- Loads the rules from the specified file into the anchor
name.
When evaluation of the main ruleset reaches an
anchor
rule,
pf(4) will proceed to evaluate all rules specified in
that anchor.
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.
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.
Rules may be contained in
anchor attachment points which
do not contain any rules when the main ruleset is loaded, and later such
anchors can be manipulated through
pfctl(8) without
reloading the main ruleset or other anchors. For example,
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
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.
# echo "block in quick from 1.2.3.4 to any" | \
pfctl -a spam -f -
This loads a single rule into the
anchor, which blocks all
packets from a specific address.
The anchor can also be populated by adding a
load anchor
rule after the
anchor rule:
anchor spam
load anchor spam from "/etc/pf-spam.conf"
When
pfctl(8) loads
pf.conf, it will also
load all the rules from the file
/etc/pf-spam.conf into the
anchor.
Optionally,
anchor rules can 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,
# echo "block in quick from 1.2.3.4 to any" | \
pfctl -a spam -f -
will only block connections from 1.2.3.4 to port 25.
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,
will evaluate each rule in each anchor attached to the
spam
anchor. 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:
# echo ' anchor "spam/allowed" ' | pfctl -f -
# echo -e ' anchor "../banned" \n pass' | \
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.
Filter rule
anchors can also be loaded inline in the
ruleset within a brace ('{' '}') delimited block. Brace delimited blocks may
contain rules or other brace-delimited blocks. When anchors are loaded this
way the anchor name becomes optional.
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
}
Since the parser specification for anchor names is a string, any reference to an
anchor name containing ‘/’ characters will require double quote
(‘"’) characters around the anchor name.
TRANSLATION EXAMPLES¶
This example maps incoming requests on port 80 to port 8080, on which a daemon
is running (because, for example, it is not run as root, and therefore lacks
permission to bind to port 80).
# use a macro for the interface name, so it can be changed easily
ext_if = "ne3"
# map daemon on 8080 to appear to be on 80
rdr on $ext_if proto tcp from any to any port 80 -> 127.0.0.1 port 8080
If the
pass modifier is given, packets matching the
translation rule are passed without inspecting the filter rules:
rdr pass on $ext_if proto tcp from any to any port 80 -> 127.0.0.1 \
port 8080
In the example below, vlan12 is configured as 192.168.168.1; the machine
translates all packets coming from 192.168.168.0/24 to 204.92.77.111 when they
are going out any interface except vlan12. This has the net effect of making
traffic from the 192.168.168.0/24 network appear as though it is the Internet
routable address 204.92.77.111 to nodes behind any 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.)
nat on ! vlan12 from 192.168.168.0/24 to any -> 204.92.77.111
In the example below, the machine sits between a fake internal 144.19.74.*
network, and a routable external IP of 204.92.77.100. The
no
nat rule excludes protocol AH from being translated.
# NO NAT
no nat on $ext_if proto ah from 144.19.74.0/24 to any
nat on $ext_if from 144.19.74.0/24 to any -> 204.92.77.100
In the example below, packets bound for one specific server, as well as those
generated by the sysadmins are not proxied; all other connections are.
# NO RDR
no rdr on $int_if proto { tcp, udp } from any to $server port 80
no rdr on $int_if proto { tcp, udp } from $sysadmins to any port 80
rdr on $int_if proto { tcp, udp } from any to any port 80 -> 127.0.0.1 \
port 80
This longer example uses both a NAT and a redirection. The external interface
has the address 157.161.48.183. On localhost, we are running
ftp-proxy(8), waiting for FTP sessions to be redirected to
it. The three mandatory anchors for
ftp-proxy(8) are omitted
from this example; see the
ftp-proxy(8) manpage.
# NAT
# Translate outgoing packets' source addresses (any protocol).
# In this case, any address but the gateway's external address is mapped.
nat on $ext_if inet from ! ($ext_if) to any -> ($ext_if)
# NAT PROXYING
# Map outgoing packets' source port to an assigned proxy port instead of
# an arbitrary port.
# In this case, proxy outgoing isakmp with port 500 on the gateway.
nat on $ext_if inet proto udp from any port = isakmp to any -> ($ext_if) \
port 500
# BINAT
# Translate outgoing packets' source address (any protocol).
# Translate incoming packets' destination address to an internal machine
# (bidirectional).
binat on $ext_if from 10.1.2.150 to any -> $ext_if
# RDR
# Translate incoming packets' destination addresses.
# As an example, redirect a TCP and UDP port to an internal machine.
rdr on $ext_if inet proto tcp from any to ($ext_if) port 8080 \
-> 10.1.2.151 port 22
rdr on $ext_if inet proto udp from any to ($ext_if) port 8080 \
-> 10.1.2.151 port 53
# RDR
# Translate outgoing ftp control connections to send them to localhost
# for proxying with ftp-proxy(8) running on port 8021.
rdr on $int_if proto tcp from any to any port 21 -> 127.0.0.1 port 8021
In this example, a NAT gateway is set up to translate internal addresses using a
pool of public addresses (192.0.2.16/28) and to redirect incoming web server
connections to a group of web servers on the internal network.
# NAT LOAD BALANCE
# Translate outgoing packets' source addresses using an address pool.
# A given source address is always translated to the same pool address by
# using the source-hash keyword.
nat on $ext_if inet from any to any -> 192.0.2.16/28 source-hash
# RDR ROUND ROBIN
# Translate incoming web server connections to a group of web servers on
# the internal network.
rdr on $ext_if proto tcp from any to any port 80 \
-> { 10.1.2.155, 10.1.2.160, 10.1.2.161 } round-robin
FILTER EXAMPLES¶
# The external interface is kue0
# (157.161.48.183, the only routable address)
# and the private network is 10.0.0.0/8, for which we are doing NAT.
# use a macro for the interface name, so it can be changed easily
ext_if = "kue0"
# normalize all incoming traffic
scrub in on $ext_if all fragment reassemble
# block and log everything by default
block return log on $ext_if all
# block anything coming from source we have no back routes for
block in from no-route to any
# block packets whose ingress interface does not match the one in
# the route back to their source address
block in from urpf-failed to any
# block and log outgoing packets that do not have our address as source,
# they are either spoofed or something is misconfigured (NAT disabled,
# for instance), we want to be nice and do not send out garbage.
block out log quick on $ext_if from ! 157.161.48.183 to any
# silently drop broadcasts (cable modem noise)
block in quick on $ext_if from any to 255.255.255.255
# block and log incoming packets from reserved address space and invalid
# addresses, they are either spoofed or misconfigured, we cannot reply to
# them anyway (hence, no return-rst).
block in log quick on $ext_if from { 10.0.0.0/8, 172.16.0.0/12, \
192.168.0.0/16, 255.255.255.255/32 } to any
# ICMP
# pass out/in certain ICMP queries and keep state (ping)
# state matching is done on host addresses and ICMP id (not type/code),
# so replies (like 0/0 for 8/0) will match queries
# ICMP error messages (which always refer to a TCP/UDP packet) are
# handled by the TCP/UDP states
pass on $ext_if inet proto icmp all icmp-type 8 code 0
# UDP
# pass out all UDP connections and keep state
pass out on $ext_if proto udp all
# pass in certain UDP connections and keep state (DNS)
pass in on $ext_if proto udp from any to any port domain
# TCP
# pass out all TCP connections and modulate state
pass out on $ext_if proto tcp all modulate state
# pass in certain TCP connections and keep state (SSH, SMTP, DNS, IDENT)
pass in on $ext_if proto tcp from any to any port { ssh, smtp, domain, \
auth }
# Do not allow Windows 9x SMTP connections since they are typically
# a viral worm. Alternately we could limit these OSes to 1 connection each.
block in on $ext_if proto tcp from any os {"Windows 95", "Windows 98"} \
to any port smtp
# IPv6
# 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
# Packet Tagging
# three interfaces: $int_if, $ext_if, and $wifi_if (wireless). NAT is
# being done on $ext_if for all outgoing packets. tag packets in on
# $int_if and pass those tagged packets out on $ext_if. all other
# outgoing packets (i.e., packets from the wireless network) are only
# permitted to access port 80.
pass in on $int_if from any to any tag INTNET
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
# tag incoming packets as they are redirected to spamd(8). use the tag
# to pass those packets through the packet filter.
rdr on $ext_if inet proto tcp from <spammers> to port smtp \
tag SPAMD -> 127.0.0.1 port spamd
block in on $ext_if
pass in on $ext_if inet proto tcp tagged SPAMD
GRAMMAR¶
Syntax for
pf.conf in BNF:
line = ( option | pf-rule | nat-rule | binat-rule | rdr-rule |
antispoof-rule | altq-rule | queue-rule | trans-anchors |
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 ]
[ "require-order" ( "yes" | "no" ) ]
[ "fingerprints" filename ] |
[ "skip on" ifspec ] |
[ "debug" ( "none" | "urgent" | "misc" | "loud" ) ] )
pf-rule = action [ ( "in" | "out" ) ]
[ "log" [ "(" logopts ")"] ] [ "quick" ]
[ "on" ifspec ] [ "fastroute" | route ] [ af ] [ protospec ]
hosts [ filteropt-list ]
logopts = logopt [ "," logopts ]
logopt = "all" | "user" | "to" interface-name
filteropt-list = filteropt-list filteropt | filteropt
filteropt = user | group | flags | icmp-type | icmp6-type | "tos" tos |
( "no" | "keep" | "modulate" | "synproxy" ) "state"
[ "(" state-opts ")" ] |
"fragment" | "no-df" | "min-ttl" number | "set-tos" tos |
"max-mss" number | "random-id" | "reassemble tcp" |
fragmentation | "allow-opts" |
"label" string | "tag" string | [ ! ] "tagged" string |
"queue" ( string | "(" string [ [ "," ] string ] ")" ) |
"rtable" number | "probability" number"%"
nat-rule = [ "no" ] "nat" [ "pass" [ "log" [ "(" logopts ")" ] ] ]
[ "on" ifspec ] [ af ]
[ protospec ] hosts [ "tag" string ] [ "tagged" string ]
[ "->" ( redirhost | "{" redirhost-list "}" )
[ portspec ] [ pooltype ] [ "static-port" ] ]
binat-rule = [ "no" ] "binat" [ "pass" [ "log" [ "(" logopts ")" ] ] ]
[ "on" interface-name ] [ af ]
[ "proto" ( proto-name | proto-number ) ]
"from" address [ "/" mask-bits ] "to" ipspec
[ "tag" string ] [ "tagged" string ]
[ "->" address [ "/" mask-bits ] ]
rdr-rule = [ "no" ] "rdr" [ "pass" [ "log" [ "(" logopts ")" ] ] ]
[ "on" ifspec ] [ af ]
[ protospec ] hosts [ "tag" string ] [ "tagged" string ]
[ "->" ( redirhost | "{" redirhost-list "}" )
[ portspec ] [ pooltype ] ]
antispoof-rule = "antispoof" [ "log" ] [ "quick" ]
"for" ifspec [ af ] [ "label" string ]
table-rule = "table" "<" string ">" [ tableopts-list ]
tableopts-list = tableopts-list tableopts | tableopts
tableopts = "persist" | "const" | "counters" | "file" string |
"{" [ tableaddr-list ] "}"
tableaddr-list = tableaddr-list [ "," ] tableaddr-spec | tableaddr-spec
tableaddr-spec = [ "!" ] tableaddr [ "/" mask-bits ]
tableaddr = hostname | ifspec | "self" |
ipv4-dotted-quad | ipv6-coloned-hex
altq-rule = "altq on" interface-name queueopts-list
"queue" subqueue
queue-rule = "queue" string [ "on" interface-name ] queueopts-list
subqueue
anchor-rule = "anchor" [ string ] [ ( "in" | "out" ) ] [ "on" ifspec ]
[ af ] [ protospec ] [ hosts ] [ filteropt-list ] [ "{" ]
anchor-close = "}"
trans-anchors = ( "nat-anchor" | "rdr-anchor" | "binat-anchor" ) string
[ "on" ifspec ] [ af ] [ "proto" ] [ protospec ] [ hosts ]
load-anchor = "load anchor" string "from" filename
queueopts-list = queueopts-list queueopts | queueopts
queueopts = [ "bandwidth" bandwidth-spec ] |
[ "qlimit" number ] | [ "tbrsize" number ] |
[ "priority" number ] | [ schedulers ]
schedulers = ( cbq-def | priq-def | hfsc-def )
bandwidth-spec = "number" ( "b" | "Kb" | "Mb" | "Gb" | "%" )
action = "pass" | "block" [ return ] | [ "no" ] "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-group ) ) |
"{" interface-list "}"
interface-list = [ "!" ] ( interface-name | interface-group )
[ [ "," ] interface-list ]
route = ( "route-to" | "reply-to" | "dup-to" )
( routehost | "{" routehost-list "}" )
[ pooltype ]
af = "inet" | "inet6"
protospec = "proto" ( proto-name | proto-number |
"{" proto-list "}" )
proto-list = ( proto-name | proto-number ) [ [ "," ] proto-list ]
hosts = "all" |
"from" ( "any" | "no-route" | "urpf-failed" | "self" | host |
"{" host-list "}" | "route" string ) [ port ] [ os ]
"to" ( "any" | "no-route" | "self" | host |
"{" host-list "}" | "route" string ) [ port ]
ipspec = "any" | host | "{" host-list "}"
host = [ "!" ] ( address [ "/" mask-bits ] | "<" string ">" )
redirhost = address [ "/" mask-bits ]
routehost = "(" interface-name [ address [ "/" mask-bits ] ] ")"
address = ( interface-name | interface-group |
"(" ( interface-name | interface-group ) ")" |
hostname | ipv4-dotted-quad | ipv6-coloned-hex )
host-list = host [ [ "," ] host-list ]
redirhost-list = redirhost [ [ "," ] redirhost-list ]
routehost-list = routehost [ [ "," ] routehost-list ]
port = "port" ( unary-op | binary-op | "{" op-list "}" )
portspec = "port" ( number | name ) [ ":" ( "*" | number | name ) ]
os = "os" ( os-name | "{" os-list "}" )
user = "user" ( unary-op | binary-op | "{" op-list "}" )
group = "group" ( unary-op | binary-op | "{" op-list "}" )
unary-op = [ "=" | "!=" | "<" | "≤" | ">" | "≥" ]
( name | number )
binary-op = number ( "<>" | "><" | ":" ) number
op-list = ( unary-op | binary-op ) [ [ "," ] op-list ]
os-name = operating-system-name
os-list = os-name [ [ "," ] os-list ]
flags = "flags" ( [ flag-set ] "/" flag-set | "any" )
flag-set = [ "F" ] [ "S" ] [ "R" ] [ "P" ] [ "A" ] [ "U" ] [ "E" ]
[ "W" ]
icmp-type = "icmp-type" ( icmp-type-code | "{" icmp-list "}" )
icmp6-type = "icmp6-type" ( icmp-type-code | "{" icmp-list "}" )
icmp-type-code = ( icmp-type-name | icmp-type-number )
[ "code" ( icmp-code-name | icmp-code-number ) ]
icmp-list = icmp-type-code [ [ "," ] icmp-list ]
tos = ( "lowdelay" | "throughput" | "reliability" |
[ "0x" ] number )
state-opts = state-opt [ [ "," ] state-opts ]
state-opt = ( "max" number | "no-sync" | timeout | "sloppy" | "pflow" |
"source-track" [ ( "rule" | "global" ) ] |
"max-src-nodes" number | "max-src-states" number |
"max-src-conn" number |
"max-src-conn-rate" number "/" number |
"overload" "<" string ">" [ "flush" ] |
"if-bound" | "floating" )
fragmentation = [ "fragment reassemble" | "fragment crop" |
"fragment drop-ovl" ]
timeout-list = timeout [ [ "," ] timeout-list ]
timeout = ( "tcp.first" | "tcp.opening" | "tcp.established" |
"tcp.closing" | "tcp.finwait" | "tcp.closed" |
"udp.first" | "udp.single" | "udp.multiple" |
"icmp.first" | "icmp.error" |
"other.first" | "other.single" | "other.multiple" |
"frag" | "interval" | "src.track" |
"adaptive.start" | "adaptive.end" ) number
limit-list = limit-item [ [ "," ] limit-list ]
limit-item = ( "states" | "frags" | "src-nodes" ) number
pooltype = ( "bitmask" | "random" |
"source-hash" [ ( hex-key | string-key ) ] |
"round-robin" ) [ sticky-address ]
subqueue = string | "{" queue-list "}"
queue-list = string [ [ "," ] string ]
cbq-def = "cbq" [ "(" cbq-opt [ [ "," ] cbq-opt ] ")" ]
priq-def = "priq" [ "(" priq-opt [ [ "," ] priq-opt ] ")" ]
hfsc-def = "hfsc" [ "(" hfsc-opt [ [ "," ] hfsc-opt ] ")" ]
cbq-opt = ( "default" | "borrow" | "red" | "ecn" | "rio" )
priq-opt = ( "default" | "red" | "ecn" | "rio" )
hfsc-opt = ( "default" | "red" | "ecn" | "rio" |
linkshare-sc | realtime-sc | upperlimit-sc )
linkshare-sc = "linkshare" sc-spec
realtime-sc = "realtime" sc-spec
upperlimit-sc = "upperlimit" sc-spec
sc-spec = ( bandwidth-spec |
"(" bandwidth-spec number bandwidth-spec ")" )
include = "include" filename
FILES¶
- /etc/hosts
- Host name database.
- /etc/pf.conf
- Default location of the ruleset file.
- /etc/pf.os
- Default location of OS fingerprints.
- /etc/protocols
- Protocol name database.
- /etc/services
- Service name database.
BUGS¶
Due to a lock order reversal (LOR) with the socket layer, the use of the
group and
user filter parameter in
conjuction with a Giant-free netstack can result in a deadlock. A workaround
is available under the
debug.pfugidhack sysctl which is
automatically enabled when a
user /
group rule is added or
log (user)
is specified.
Route labels are not supported by the
FreeBSD
route(4) system. Rules with a route label do not match any
traffic.
SEE ALSO¶
altq(4),
carp(4),
icmp(4),
icmp6(4),
ip(4),
ip6(4),
pf(4),
pflow(4),
pfsync(4),
route(4),
tcp(4),
udp(4),
hosts(5),
pf.os(5),
protocols(5),
services(5),
ftp-proxy(8),
pfctl(8),
pflogd(8),
route(8)
HISTORY¶
The
pf.conf file format first appeared in
OpenBSD 3.0.