CONTENTS

DESCRIPTION

STATEMENT ORDER

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.

Tables may be defined with the following two attributes:

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

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.

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

Other protocols are handled similarly to UDP:

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

These values can be defined both globally and for each rule. When used on a per-rule basis, the values relate to the number of states created by the rule, otherwise to the total number of states.

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

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

For example:
set optimization aggressive

For example:
set block-policy return

For example:
set state-policy if-bound

TRAFFIC NORMALIZATION

scrub has the following options:

For example,
scrub in on $ext_if all fragment reassemble

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.

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

In the following example, the interface dc0 should queue up to 5 Mbit/s in four second-level queues using Class Based Queueing. Those four queues will be shown in a later example.
altq on dc0 cbq bandwidth 5Mb queue { std, http, mail, ssh }

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

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

The cbq scheduler supports an additional option:

The hfsc scheduler supports some additional options:

<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.

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:

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

For each packet processed by the translator, the translation rules are evaluated in sequential order, from first to last. The first matching rule decides what action is taken.

The no option prefixed to a translation rule causes packets to remain 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 8025 -> 127.0.0.1 port 25

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.

For each packet processed by the packet filter, the filter rules are evaluated in sequential order, from first to last. The last matching rule decides what action is taken.

The following actions can be used in the filter:

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

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

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

as the first filter rule.

Interface names can have modifiers appended:

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:

ROUTING

POOL OPTIONS

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

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

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

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

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

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

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

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

The default policy is specified by the state-policy global option, but this can be adjusted on a per-rule basis by adding one of the if-bound, group-bound or floating keywords to the keep state option. For example, if a rule is defined as:
pass out on ppp from any to 10.12/16 keep state (group-bound)

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

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

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

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

ICMP messages fall into two categories: ICMP error messages, which always refer to a TCP or UDP packet, are matched against the referred to 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.

For ICMP queries, keep state creates an ICMP state, and pf(4) knows how to match ICMP replies to states. For example,
pass out inet proto icmp all icmp-type echoreq keep state

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

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

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

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

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. Hence, synproxy state includes modulate state and keep state.

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

Multiple options can be specified, separated by commas:
pass in proto tcp from any to any \
port www flags S/SA keep state \
(max 100, source-track rule, max-src-nodes 75, \
max-src-states 3, tcp.established 60, tcp.closing 5)

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

The following limits can be set:

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

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.

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

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

For example, the line
antispoof for lo0

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

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

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

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:

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 in anchors with the quick option are final and abort the evaluation of the rules in other anchors and the main ruleset.

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 keep state
pass in on $ext_if proto tcp from any \
to $ext_if port smtp keep state

blocks all packets on the external interface by default, then evaluates all 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 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 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 keep state
pass in on $ext_if proto tcp from any to $ext_if port smtp keep state

The rules inside anchor spam are only evaluated for tcp packets with 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,
anchor "spam/*"

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.

# 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 the internal interface, we are running ftp-proxy(8), listening for outbound ftp sessions captured to port 8021.
# NAT
# Translate outgoing packets’ source addresses (any protocol).
# In this case, any address but the gateway’s external address is mapped.
nat on $ext_if inet from ! ($ext_if) to any -> ($ext_if)

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

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

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

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

In this example, a NAT gateway is set up to translate internal addresses using a pool of public addresses (192.0.2.16/28) and to redirect incoming web server connections to a group of web servers on the internal network.
# NAT LOAD BALANCE
# Translate outgoing packets’ source addresses using an address pool.
# A given source address is always translated to the same pool address by
# using the source-hash keyword.
nat on $ext_if inet from any to any -> 192.0.2.16/28 source-hash

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

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

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

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

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

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

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

# ICMP

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

# UDP

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

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

# TCP

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

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

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

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

# Packet Tagging

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

load-anchor = "load anchor" 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-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 "}" | "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-name ")" | hostname |
ipv4-dotted-quad | ipv6-coloned-hex )
host-list = host [ [ "," ] host-list ]
redirhost-list = redirhost [ [ "," ] redirhost-list ]
routehost-list = routehost [ [ "," ] routehost-list ]

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

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

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

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

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

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

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

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

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

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

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

BUGS

SEE ALSO

HISTORY