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ipfw.8
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.\"
.\" $FreeBSD: src/sbin/ipfw/ipfw.8,v 1.63.2.33 2003/02/04 01:36:02 brueffer Exp $
.\" $DragonFly: src/sbin/ipfw/ipfw.8,v 1.20 2008/11/23 21:55:52 swildner Exp $
.\"
.Dd October 3, 2008
.Dt IPFW 8
.Os
.Sh NAME
.Nm ipfw
.Nd IP firewall and traffic shaper control program
.Sh SYNOPSIS
.Nm
.Op Fl cq
.Cm add
.Ar rule
.Nm
.Op Fl acdeftNS
.Brq Cm list | show
.Op Ar number ...
.Nm
.Op Fl f | q
.Cm flush
.Nm
.Op Fl q
.Brq Cm delete | zero | resetlog
.Op Cm set
.Op Ar number ...
.Nm
.Cm enable
.Brq Cm firewall | one_pass | debug | verbose | dyn_keepalive
.Nm
.Cm disable
.Brq Cm firewall | one_pass | debug | verbose | dyn_keepalive
.Pp
.Nm
.Cm set Oo Cm disable Ar number ... Oc Op Cm enable Ar number ...
.Nm
.Cm set move
.Op Cm rule
.Ar number Cm to Ar number
.Nm
.Cm set swap Ar number number
.Nm
.Cm set show
.Pp
.Nm
.Brq Cm pipe | queue
.Ar number
.Cm config
.Ar config-options
.Nm
.Op Fl s Op Ar field
.Brq Cm pipe | queue
.Brq Cm delete | list | show
.Op Ar number ...
.Pp
.Nm
.Op Fl q
.Oo
.Fl p Ar preproc
.Oo Fl D
.Ar macro Ns Op = Ns Ar value
.Oc
.Op Fl U Ar macro
.Oc
.Ar pathname
.Sh DESCRIPTION
The
.Nm
utility is the user interface for controlling the
.Xr ipfw 4
firewall and the
.Xr dummynet 4
traffic shaper in
.Dx .
.Bd -ragged -offset XXXX
.Em NOTE:
this manual page documents the newer version of
.Nm
introduced in
.Fx
CURRENT in July 2002, also known as
.Nm ipfw2 .
.Nm ipfw2
is a superset of the old firewall,
.Nm ipfw1 .
The differences between the two are listed in Section
.Sx IPFW2 ENHANCEMENTS ,
which you are encouraged to read to revise older rulesets and possibly
write them more efficiently.
.Ed
.Pp
An
.Nm
configuration, or
.Em ruleset ,
is made of a list of
.Em rules
numbered from 1 to 65535.
Packets are passed to
.Nm
from a number of different places in the protocol stack
(depending on the source and destination of the packet,
it is possible that
.Nm
is invoked multiple times on the same packet).
The packet passed to the firewall is compared
against each of the rules in the firewall
.Em ruleset .
When a match is found, the action corresponding to the
matching rule is performed.
.Pp
Depending on the action and certain system settings, packets
can be reinjected into the firewall at some rule after the
matching one for further processing.
.Pp
An
.Nm
ruleset always includes a
.Em default
rule (numbered 65535) which cannot be modified,
and matches all packets.
The action associated with the
.Em default
rule can be either
.Cm deny
or
.Cm allow
depending on how the kernel is configured.
.Pp
If the ruleset includes one or more rules with the
.Cm keep-state
or
.Cm limit
option, then
.Nm
assumes a
.Em stateful
behaviour, i.e. upon a match it will create dynamic rules matching
the exact parameters (addresses and ports) of the matching packet.
.Pp
These dynamic rules, which have a limited lifetime, are checked
at the first occurrence of a
.Cm check-state ,
.Cm keep-state
or
.Cm limit
rule, and are typically used to open the firewall on-demand to
legitimate traffic only.
See the
.Sx STATEFUL FIREWALL
and
.Sx EXAMPLES
Sections below for more information on the stateful behaviour of
.Nm .
.Pp
All rules (including dynamic ones) have a few associated counters:
a packet count, a byte count, a log count and a timestamp
indicating the time of the last match.
Counters can be displayed or reset with
.Nm
commands.
.Pp
Rules can be added with the
.Cm add
command; deleted individually or in groups with the
.Cm delete
command, and globally with the
.Cm flush
command; displayed, optionally with the content of the
counters, using the
.Cm show
and
.Cm list
commands.
Finally, counters can be reset with the
.Cm zero
and
.Cm resetlog
commands.
.Pp
Also, each rule belongs to one of 32 different
.Em sets
, and there are
.Nm
commands to atomically manipulate sets, such as enable,
disable, swap sets, move all rules in a set to another
one, delete all rules in a set. These can be useful to
install temporary configurations, or to test them.
See Section
.Sx SETS OF RULES
for more information on
.Em sets .
.Pp
The following options are available:
.Bl -tag -width indent
.It Fl a
While listing, show counter values.
The
.Cm show
command just implies this option.
.It Fl c
When entering or showing rules, print them in compact form,
i.e. without the optional "ip from any to any" string
when this does not carry any additional information.
.It Fl d
While listing, show dynamic rules in addition to static ones.
.It Fl e
While listing, if the
.Fl d
option was specified, also show expired dynamic rules.
.It Fl f
Don't ask for confirmation for commands that can cause problems
if misused,
.No i.e. Cm flush .
If there is no tty associated with the process, this is implied.
.It Fl N
Try to resolve addresses and service names in output.
.It Fl q
While
.Cm add Ns ing ,
.Cm zero Ns ing ,
.Cm resetlog Ns ging
or
.Cm flush Ns ing ,
be quiet about actions
(implies
.Fl f ) .
This is useful for adjusting rules by executing multiple
.Nm
commands in a script
(e.g.,
.Ql sh\ /etc/rc.firewall ) ,
or by processing a file of many
.Nm
rules across a remote login session.
If a
.Cm flush
is performed in normal (verbose) mode (with the default kernel
configuration), it prints a message.
Because all rules are flushed, the message might not be delivered
to the login session, causing the remote login session to be closed
and the remainder of the ruleset to not be processed.
Access to the console would then be required to recover.
.It Fl S
While listing rules, show the
.Em set
each rule belongs to.
If this flag is not specified, disabled rules will not be
listed.
.It Fl s Op Ar field
While listing pipes, sort according to one of the four
counters (total or current packets or bytes).
.It Fl t
While listing, show last match timestamp.
.El
.Pp
To ease configuration, rules can be put into a file which is
processed using
.Nm
as shown in the last synopsis line.
An absolute
.Ar pathname
must be used.
The file will be read line by line and applied as arguments to the
.Nm
utility.
.Pp
Optionally, a preprocessor can be specified using
.Fl p Ar preproc
where
.Ar pathname
is to be piped through.
Useful preprocessors include
.Xr cpp 1
and
.Xr m4 1 .
If
.Ar preproc
doesn't start with a slash
.Pq Ql /
as its first character, the usual
.Ev PATH
name search is performed.
Care should be taken with this in environments where not all
file systems are mounted (yet) by the time
.Nm
is being run (e.g. when they are mounted over NFS).
Once
.Fl p
has been specified, optional
.Fl D
and
.Fl U
specifications can follow and will be passed on to the preprocessor.
This allows for flexible configuration files (like conditionalizing
them on the local hostname) and the use of macros to centralize
frequently required arguments like IP addresses.
.Pp
The
.Nm
.Cm pipe
and
.Cm queue
commands are used to configure the traffic shaper, as shown in the
.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
Section below.
.Pp
If the world and the kernel get out of sync the
.Nm
ABI may break, preventing you from being able to add any rules. This can
adversely affect the booting process. You can use
.Nm
.Cm disable
.Cm firewall
to temporarily disable the firewall to regain access to the network,
allowing you to fix the problem.
.Sh PACKET FLOW
A packet is checked against the active ruleset in multiple places
in the protocol stack, under control of several sysctl variables.
These places and variables are shown below, and it is important to
have this picture in mind in order to design a correct ruleset.
.Bd -literal -offset indent
^ to upper layers V
| |
+------------>------------+
^ V
[ip_input] [ip_output] net.inet.ip.fw.enable=1
| |
^ V
[ether_demux_oncpu] [ether_output_frame] net.link.ether.ipfw=1
^ V
| to devices |
.Ed
.Pp
As can be noted from the above picture, the number of
times the same packet goes through the firewall can
vary between 0 and 4 depending on packet source and
destination, and system configuration.
.Pp
Note that as packets flow through the stack, headers can be
stripped or added to it, and so they may or may not be available
for inspection.
E.g., incoming packets will include the MAC header when
.Nm
is invoked from
.Fn ether_demux_oncpu ,
but the same packets will have the MAC header stripped off when
.Nm
is invoked from
.Fn ip_input .
.Pp
Also note that each packet is always checked against the complete ruleset,
irrespective of the place where the check occurs, or the source of the packet.
If a rule contains some match patterns or actions which are not valid
for the place of invocation (e.g. trying to match a MAC header within
.Fn ip_input ) ,
the match pattern will not match, but a
.Cm not
operator in front of such patterns
.Em will
cause the pattern to
.Em always
match on those packets.
It is thus the responsibility of
the programmer, if necessary, to write a suitable ruleset to
differentiate among the possible places.
.Cm skipto
rules can be useful here, as an example:
.Bd -literal -offset indent
# packets from ether_demux_oncpu
ipfw add 10 skipto 1000 all from any to any layer2 in
# packets from ip_input
ipfw add 10 skipto 2000 all from any to any not layer2 in
# packets from ip_output
ipfw add 10 skipto 3000 all from any to any not layer2 out
# packets from ether_output_frame
ipfw add 10 skipto 4000 all from any to any layer2 out
.Ed
.Sh RULE FORMAT
The format of
.Nm
rules is the following:
.Bd -ragged -offset indent
.Op Ar rule_number
.Op Cm set Ar set_number
.Op Cm prob Ar match_probability
.br
.Ar " " action
.Op Cm log Op Cm logamount Ar number
.Ar body
.Ed
.Pp
where the body of the rule specifies which information is used
for filtering packets, among the following:
.Pp
.Bl -tag -width "Source and dest. addresses and ports" -offset XXX -compact
.It Layer-2 header fields
When available
.It IPv4 Protocol
TCP, UDP, ICMP, etc.
.It Source and dest. addresses and ports
.It Direction
See Section
.Sx PACKET FLOW
.It Transmit and receive interface
By name or address
.It Misc. IP header fields
Version, type of service, datagram length, identification,
fragment flag (non-zero IP offset),
Time To Live
.It IP options
.It Misc. TCP header fields
TCP flags (SYN, FIN, ACK, RST, etc.),
sequence number, acknowledgment number,
window
.It TCP options
.It ICMP types
for ICMP packets
.It User/group ID
When the packet can be associated with a local socket.
.El
.Pp
Note that some of the above information, e.g. source MAC or IP addresses and
TCP/UDP ports, could easily be spoofed, so filtering on those fields
alone might not guarantee the desired results.
.Bl -tag -width indent
.It Ar rule_number
Each rule is associated with a
.Ar rule_number
in the range 1..65535, with the latter reserved for the
.Em default
rule.
Rules are checked sequentially by rule number.
Multiple rules can have the same number, in which case they are
checked (and listed) according to the order in which they have
been added.
If a rule is entered without specifying a number, the kernel will
assign one in such a way that the rule becomes the last one
before the
.Em default
rule.
Automatic rule numbers are assigned by incrementing the last
non-default rule number by the value of the sysctl variable
.Ar net.inet.ip.fw.autoinc_step
which defaults to 100.
If this is not possible (e.g. because we would go beyond the
maximum allowed rule number), the number of the last
non-default value is used instead.
.It Cm set Ar set_number
Each rule is associated with a
.Ar set_number
in the range 0..31, with the latter reserved for the
.Em default
rule.
Sets can be individually disabled and enabled, so this parameter
is of fundamental importance for atomic ruleset manipulation.
It can be also used to simplify deletion of groups of rules.
If a rule is entered without specifying a set number,
set 0 will be used.
.It Cm prob Ar match_probability
A match is only declared with the specified probability
(floating point number between 0 and 1).
This can be useful for a number of applications such as
random packet drop or
(in conjunction with
.Xr dummynet 4 )
to simulate the effect of multiple paths leading to out-of-order
packet delivery.
.It Cm log Op Cm logamount Ar number
When a packet matches a rule with the
.Cm log
keyword, a message will be
logged to
.Xr syslogd 8
with a
.Dv LOG_SECURITY
facility.
The logging only occurs if the sysctl variable
.Em net.inet.ip.fw.verbose
is set to 1
(which is the default when the kernel is compiled with
.Dv IPFIREWALL_VERBOSE )
and the number of packets logged so far for that
particular rule does not exceed the
.Cm logamount
parameter.
If no
.Cm logamount
is specified, the limit is taken from the sysctl variable
.Em net.inet.ip.fw.verbose_limit .
In both cases, a value of 0 removes the logging limit.
.Pp
Once the limit is reached, logging can be re-enabled by
clearing the logging counter or the packet counter for that entry, see the
.Cm resetlog
command.
.El
.Ss RULE ACTIONS
A rule can be associated with one of the following actions, which
will be executed when the packet matches the body of the rule.
.Bl -tag -width indent
.It Cm allow | accept | pass | permit
Allow packets that match rule.
The search terminates.
.It Cm check-state
Checks the packet against the dynamic ruleset.
If a match is found, execute the action associated with
the rule which generated this dynamic rule, otherwise
move to the next rule.
.br
.Cm Check-state
rules do not have a body.
If no
.Cm check-state
rule is found, the dynamic ruleset is checked at the first
.Cm keep-state
or
.Cm limit
rule.
.It Cm count
Update counters for all packets that match rule.
The search continues with the next rule.
.It Cm deny | drop
Discard packets that match this rule.
The search terminates.
.It Cm divert Ar port
Divert packets that match this rule to the
.Xr divert 4
socket bound to port
.Ar port .
The search terminates.
.It Cm fwd | forward Ar ipaddr Ns Op , Ns Ar port
Change the next-hop on matching packets to
.Ar ipaddr ,
which can be an IP address in dotted quad format or a host name.
The search terminates if this rule matches.
.Pp
If
.Ar ipaddr
is a local address, then matching packets will be forwarded to
.Ar port
(or the port number in the packet if one is not specified in the rule)
on the local machine.
.br
If
.Ar ipaddr
is not a local address, then the port number
(if specified) is ignored, and the packet will be
forwarded to the remote address, using the route as found in
the local routing table for that IP.
.br
A
.Ar fwd
rule will not match layer-2 packets (those received
on
.Fn ether_input
or
.Fn ether_output ) .
.br
The
.Cm fwd
action does not change the contents of the packet at all.
In particular, the destination address remains unmodified, so
packets forwarded to another system will usually be rejected by that system
unless there is a matching rule on that system to capture them.
For packets forwarded locally,
the local address of the socket will be
set to the original destination address of the packet.
This makes the
.Xr netstat 1
entry look rather weird but is intended for
use with transparent proxy servers.
.It Cm pipe Ar pipe_nr
Pass packet to a
.Xr dummynet 4
.Dq pipe
(for bandwidth limitation, delay, etc.).
See the
.Sx TRAFFIC SHAPER (DUMMYNET) CONFIGURATION
Section for further information.
The search terminates; however, on exit from the pipe and if
the
.Xr sysctl 8
variable
.Em net.inet.ip.fw.one_pass
is not set, the packet is passed again to the firewall code
starting from the next rule.
.It Cm queue Ar queue_nr
Pass packet to a
.Xr dummynet 4
.Dq queue
(for bandwidth limitation using WF2Q+).
.It Cm reject
(Deprecated).
Synonym for
.Cm unreach host .
.It Cm reset
Discard packets that match this rule, and if the
packet is a TCP packet, try to send a TCP reset (RST) notice.
The search terminates.
.It Cm skipto Ar number
Skip all subsequent rules numbered less than
.Ar number .
The search continues with the first rule numbered
.Ar number
or higher.
.It Cm tee Ar port
Send a copy of packets matching this rule to the
.Xr divert 4
socket bound to port
.Ar port .
The search terminates and the original packet is accepted
(but see Section
.Sx BUGS
below).
.It Cm unreach Ar code
Discard packets that match this rule, and try to send an ICMP
unreachable notice with code
.Ar code ,
where
.Ar code
is a number from 0 to 255, or one of these aliases:
.Cm net , host , protocol , port ,
.Cm needfrag , srcfail , net-unknown , host-unknown ,
.Cm isolated , net-prohib , host-prohib , tosnet ,
.Cm toshost , filter-prohib , host-precedence
or
.Cm precedence-cutoff .
The search terminates.
.El
.Ss RULE BODY
The body of a rule contains zero or more patterns (such as
specific source and destination addresses or ports,
protocol options, incoming or outgoing interfaces, etc.)
that the packet must match in order to be recognised.
In general, the patterns are connected by (implicit)
.Cm and
operators -- i.e. all must match in order for the
rule to match.
Individual patterns can be prefixed by the
.Cm not
operator to reverse the result of the match, as in
.Pp
.Dl "ipfw add 100 allow ip from not 1.2.3.4 to any"
.Pp
Additionally, sets of alternative match patterns
.Em ( or-blocks )
can be constructed by putting the patterns in
lists enclosed between parentheses ( ) or braces { }, and
using the
.Cm or
operator as follows:
.Pp
.Dl "ipfw add 100 allow ip from { x or not y or z } to any"
.Pp
Only one level of parentheses is allowed.
Beware that most shells have special meanings for parentheses
or braces, so it is advisable to put a backslash \\ in front of them
to prevent such interpretations.
.Pp
The body of a rule must in general include a source and destination
address specifier.
The keyword
.Ar any
can be used in various places to specify that the content of
a required field is irrelevant.
.Pp
The rule body has the following format:
.Bd -ragged -offset indent
.Op Ar proto Cm from Ar src Cm to Ar dst
.Op Ar options
.Ed
.Pp
The first part (protocol from src to dst) is for backward
compatibility with
.Nm ipfw1 .
In
.Nm ipfw2
any match pattern (including MAC headers, IPv4 protocols,
addresses and ports) can be specified in the
.Ar options
section.
.Pp
Rule fields have the following meaning:
.Bl -tag -width indent
.It Ar proto : protocol | Cm { Ar protocol Cm or ... }
An IPv4 protocol (or an
.Em or-block
with multiple protocols) specified by number or name
(for a complete list see
.Pa /etc/protocols ) .
The
.Cm ip
or
.Cm all
keywords mean any protocol will match.
.It Ar src No and Ar dst : ip-address | Cm { Ar ip-address Cm or ... } Op Ar ports
A single
.Ar ip-address
, or an
.Em or-block
containing one or more of them,
optionally followed by
.Ar ports
specifiers.
.It Ar ip-address :
An address (or set of addresses) specified in one of the following
ways, optionally preceded by a
.Cm not
operator:
.Bl -tag -width indent
.It Cm any
matches any IP address.
.It Cm me
matches any IP address configured on an interface in the system.
The address list is evaluated at the time the packet is
analysed.
.It Ar numeric-ip | hostname
Matches a single IPv4 address, specified as dotted-quad or a hostname.
Hostnames are resolved at the time the rule is added to the firewall list.
.It Ar addr Ns / Ns Ar masklen
Matches all addresses with base
.Ar addr
(specified as a dotted quad or a hostname)
and mask width of
.Cm masklen
bits.
As an example, 1.2.3.4/25 will match
all IP numbers from 1.2.3.0 to 1.2.3.127 .
.It Ar addr Ns / Ns Ar masklen Ns Cm { Ns Ar num,num,... Ns Cm }
Matches all addresses with base address
.Ar addr
(specified as a dotted quad or a hostname)
and whose last byte is in the list between braces { } .
Note that there must be no spaces between braces, commas and
numbers.
The
.Ar masklen
field is used to limit the size of the set of addresses,
and can have any value between 24 and 32.
.br
As an example, an address specified as 1.2.3.4/24{128,35,55,89}
will match the following IP addresses:
.br
1.2.3.128 1.2.3.35 1.2.3.55 1.2.3.89 .
.br
This format is particularly useful to handle sparse address sets
within a single rule. Because the matching occurs using a
bitmask, it takes constant time and dramatically reduces
the complexity of rulesets.
.It Ar addr Ns : Ns Ar mask
Matches all addresses with base
.Ar addr
(specified as a dotted quad or a hostname)
and the mask of
.Ar mask ,
specified as a dotted quad.
As an example, 1.2.3.4/255.0.255.0 will match
1.*.3.*.
We suggest to use this form only for non-contiguous
masks, and resort to the
.Ar addr Ns / Ns Ar masklen
format for contiguous masks, which is more compact and less
error-prone.
.El
.It Ar ports : Oo Cm not Oc Bro Ar port | port Ns \&- Ns Ar port Ns Brc Op , Ns Ar ...
For protocols which support port numbers (such as TCP and UDP), optional
.Cm ports
may be specified as one or more ports or port ranges, separated
by commas but no spaces, and an optional
.Cm not
operator.
The
.Ql \&-
notation specifies a range of ports (including boundaries).
.Pp
Service names (from
.Pa /etc/services )
may be used instead of numeric port values.
The length of the port list is limited to 30 ports or ranges,
though one can specify larger ranges by using an
.Em or-block
in the
.Cm options
section of the rule.
.Pp
A backslash
.Pq Ql \e
can be used to escape the dash
.Pq Ql -
character in a service name (from a shell, the backslash must be
typed twice to avoid the shell itself interpreting it as an escape
character).
.Pp
.Dl "ipfw add count tcp from any ftp\e\e-data-ftp to any"
.Pp
Fragmented packets which have a non-zero offset (i.e. not the first
fragment) will never match a rule which has one or more port
specifications.
See the
.Cm frag
option for details on matching fragmented packets.
.El
.Ss RULE OPTIONS (MATCH PATTERNS)
Additional match patterns can be used within
rules. Zero or more of these so-called
.Em options
can be present in a rule, optionally prefixed by the
.Cm not
operand, and possibly grouped into
.Em or-blocks .
.Pp
The following match patterns can be used (listed in alphabetical order):
.Bl -tag -width indent
.It Cm dst-ip Ar ip address
Matches IP packets whose destination IP is one of the address(es)
specified as argument.
.It Cm dst-port Ar source ports
Matches IP packets whose destination port is one of the port(s)
specified as argument.
.It Cm established
Matches TCP packets that have the RST or ACK bits set.
.It Cm frag
Matches packets that are fragments and not the first
fragment of an IP datagram. Note that these packets will not have
the next protocol header (e.g. TCP, UDP) so options that look into
these headers cannot match.
.It Cm gid Ar group
Matches all TCP or UDP packets sent by or received for a
.Ar group .
A
.Ar group
may be specified by name or number.
.It Cm icmptypes Ar types
Matches ICMP packets whose ICMP type is in the list
.Ar types .
The list may be specified as any combination of ranges or
individual types separated by commas.
The supported ICMP types are:
.Pp
echo reply
.Pq Cm 0 ,
destination unreachable
.Pq Cm 3 ,
source quench
.Pq Cm 4 ,
redirect
.Pq Cm 5 ,
echo request
.Pq Cm 8 ,
router advertisement
.Pq Cm 9 ,
router solicitation
.Pq Cm 10 ,
time-to-live exceeded
.Pq Cm 11 ,
IP header bad
.Pq Cm 12 ,
timestamp request
.Pq Cm 13 ,
timestamp reply
.Pq Cm 14 ,
information request
.Pq Cm 15 ,
information reply
.Pq Cm 16 ,
address mask request
.Pq Cm 17
and address mask reply
.Pq Cm 18 .
.It Cm in | out
Matches incoming or outgoing packets, respectively.
.Cm in
and
.Cm out
are mutually exclusive (in fact,
.Cm out
is implemented as
.Cm not in Ns No ).
.It Cm ipid Ar id
Matches IP packets whose
.Cm ip_id
field has value
.Ar id .
.It Cm iplen Ar len
Matches IP packets whose total length, including header and data, is
.Ar len
bytes.
.It Cm ipoptions Ar spec
Matches packets whose IP header contains the comma separated list of
options specified in
.Ar spec .
The supported IP options are:
.Pp
.Cm ssrr
(strict source route),
.Cm lsrr
(loose source route),
.Cm rr
(record packet route) and
.Cm ts
(timestamp).
The absence of a particular option may be denoted
with a
.Ql \&! .
.It Cm ipprecedence Ar precedence
Matches IP packets whose precedence field is equal to
.Ar precedence .
.It Cm iptos Ar spec
Matches IP packets whose
.Cm tos
field contains the comma separated list of
service types specified in
.Ar spec .
The supported IP types of service are:
.Pp
.Cm lowdelay
.Pq Dv IPTOS_LOWDELAY ,
.Cm throughput
.Pq Dv IPTOS_THROUGHPUT ,
.Cm reliability
.Pq Dv IPTOS_RELIABILITY ,
.Cm mincost
.Pq Dv IPTOS_MINCOST ,
.Cm congestion
.Pq Dv IPTOS_CE .
The absence of a particular type may be denoted
with a
.Ql \&! .
.It Cm ipttl Ar ttl
Matches IP packets whose time to live is
.Ar ttl .
.It Cm ipversion Ar ver
Matches IP packets whose IP version field is
.Ar ver .
.It Cm keep-state
Upon a match, the firewall will create a dynamic rule, whose
default behaviour is to match bidirectional traffic between
source and destination IP/port using the same protocol.
The rule has a limited lifetime (controlled by a set of
.Xr sysctl 8
variables), and the lifetime is refreshed every time a matching
packet is found.
.It Cm layer2
Matches only layer2 packets, i.e. those passed to
.Nm
from
.Fn ether_demux_oncpu
and
.Fn ether_output_frame .
.It Cm limit Bro Cm src-addr | src-port | dst-addr | dst-port Brc Ar N
The firewall will only allow
.Ar N
connections with the same
set of parameters as specified in the rule.
One or more
of source and destination addresses and ports can be
specified.
.It Cm { MAC | mac } Ar dst-mac src-mac
Match packets with a given
.Ar dst-mac
and
.Ar src-mac
addresses, specified as the
.Cm any
keyword (matching any MAC address), or six groups of hex digits
separated by colons,
and optionally followed by a mask indicating how many bits are
significant, as in
.Pp
.Dl "MAC 10:20:30:40:50:60/33 any"
.Pp
Note that the order of MAC addresses (destination first,
source second) is
the same as on the wire, but the opposite of the one used for
IP addresses.
.It Cm mac-type Ar mac-type
Matches packets whose Ethernet Type field
corresponds to one of those specified as argument.
.Ar mac-type
is specified in the same way as
.Cm port numbers
(i.e. one or more comma-separated single values or ranges).
You can use symbolic names for known values such as
.Em vlan , ipv4, ipv6 .
Values can be entered as decimal or hexadecimal (if prefixed by 0x),
and they are always printed as hexadecimal (unless the
.Cm -N
option is used, in which case symbolic resolution will be attempted).
.It Cm proto Ar protocol
Matches packets with the corresponding IPv4 protocol.
.It Cm recv | xmit | via Brq Ar ifX | Ar if Ns Cm * | Ar ipno | Ar any
Matches packets received, transmitted or going through,
respectively, the interface specified by exact name
.Ns No ( Ar ifX Ns No ),
by device name
.Ns No ( Ar if Ns Ar * Ns No ),
by IP address, or through some interface.
.Pp