| ipfw, dnctl(8) | User interface for firewall, traffic shaper, packet scheduler, in-kernel NAT. |
| dnctl, ipfw(8) | User interface for firewall, traffic shaper, packet scheduler, in-kernel NAT. |
| IPFW(8) | MidnightBSD System Manager's Manual | IPFW(8) |
ipfw, dnctl
— User interface for firewall, traffic shaper,
packet scheduler, in-kernel NAT.
ipfw |
[-cq] add
rule |
ipfw |
[-acdefnNStT] [set
N] {list |
show} [rule |
first-last ...] |
ipfw |
[-f | -q]
[set N]
flush |
ipfw |
[-q] [set
N] {delete |
zero | resetlog}
[number ...] |
ipfw |
set [disable
number ...] [enable
number ...] |
ipfw |
set move [rule]
number to
number |
ipfw |
set swap number
number |
ipfw |
set show |
ipfw |
enable {firewall |
altq | one_pass |
debug | verbose |
dyn_keepalive} |
ipfw |
disable {firewall |
altq | one_pass |
debug | verbose |
dyn_keepalive} |
ipfw |
[set N]
table name
create create-options |
ipfw |
[set N]
table {name |
all} destroy |
ipfw |
[set N]
table name
modify modify-options |
ipfw |
[set N]
table name
swap name |
ipfw |
[set N]
table name
add table-key
[value] |
ipfw |
[set N]
table name
add [table-key
value ...] |
ipfw |
[set N]
table name
atomic add [table-key
value ...] |
ipfw |
[set N]
table name
delete [table-key ...] |
ipfw |
[set N]
table name
lookup addr |
ipfw |
[set N]
table name
lock |
ipfw |
[set N]
table name
unlock |
ipfw |
[set N]
table {name |
all} list |
ipfw |
[set N]
table {name |
all} info |
ipfw |
[set N]
table {name |
all} detail |
ipfw |
[set N]
table {name |
all} flush |
dnctl |
{pipe | queue |
sched} number
config config-options |
dnctl |
[-s [field]]
{pipe | queue |
sched} {delete |
list | show}
[number ...] |
ipfw |
[-q] nat
number config
config-options |
ipfw |
nat number
show {config |
log} |
ipfw |
[set N]
nat64lsn name
create create-options |
ipfw |
[set N]
nat64lsn name
config config-options |
ipfw |
[set N]
nat64lsn {name |
all} {list |
show} [states] |
ipfw |
[set N]
nat64lsn {name |
all} destroy |
ipfw |
[set N]
nat64lsn name
stats [reset] |
ipfw |
[set N]
nat64stl name
create create-options |
ipfw |
[set N]
nat64stl name
config config-options |
ipfw |
[set N]
nat64stl {name |
all} {list |
show} |
ipfw |
[set N]
nat64stl {name |
all} destroy |
ipfw |
[set N]
nat64stl name
stats [reset] |
ipfw |
[set N]
nat64clat name
create create-options |
ipfw |
[set N]
nat64clat name
config config-options |
ipfw |
[set N]
nat64clat {name |
all} {list |
show} |
ipfw |
[set N]
nat64clat {name |
all} destroy |
ipfw |
[set N]
nat64clat name
stats [reset] |
ipfw |
[set N]
nptv6 name
create create-options |
ipfw |
[set N]
nptv6 {name |
all} {list |
show} |
ipfw |
[set N]
nptv6 {name |
all} destroy |
ipfw |
[set N]
nptv6 name
stats [reset] |
ipfw |
internal iflist |
ipfw |
internal talist |
ipfw |
internal vlist |
ipfw |
[-cfnNqS] [-p
preproc [preproc-flags]]
pathname |
The ipfw utility is the user interface for
controlling the ipfw(4)
firewall, the
dummynet(4) traffic
shaper/packet scheduler, and the in-kernel NAT services.
A firewall configuration, or ruleset, is made of a list of rules numbered from 1 to 65535. Packets are passed to the firewall from a number of different places in the protocol stack (depending on the source and destination of the packet, it is possible for the firewall to be invoked multiple times on the same packet). The packet passed to the firewall is compared against each of the rules in the ruleset, in rule-number order (multiple rules with the same number are permitted, in which case they are processed in order of insertion). When a match is found, the action corresponding to the matching rule is performed.
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.
A ruleset always includes a default rule
(numbered 65535) which cannot be modified or deleted, and matches all
packets. The action associated with the default rule can
be either deny or allow
depending on how the kernel is configured.
If the ruleset includes one or more rules with the
keep-state, record-state,
limit or set-limit option,
the firewall will have a
stateful
behaviour, i.e., upon a match it will create dynamic
rules, i.e., rules that match packets with the same 5-tuple (protocol,
source and destination addresses and ports) as the packet which caused their
creation. Dynamic rules, which have a limited lifetime, are checked at the
first occurrence of a check-state,
keep-state or limit rule,
and are typically used to open the firewall on-demand to legitimate traffic
only. Please note, that keep-state and
limit imply implicit
check-state for all packets (not only these matched
by the rule) but record-state and
set-limit have no implicit
check-state. See the
STATEFUL FIREWALL and
EXAMPLES Sections below for more
information on the stateful behaviour of ipfw.
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
ipfw commands.
Each rule belongs to one of 32 different sets ,
and there are ipfw 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
SETS OF RULES for more information
on sets.
Rules can be added with the add command;
deleted individually or in groups with the delete
command, and globally (except those in set 31) with the
flush command; displayed, optionally with the
content of the counters, using the show and
list commands. Finally, counters can be reset with
the zero and resetlog
commands.
The following general options are available when invoking
ipfw:
-ashow
command implies this option.-b-c.-c-d-D-fflush. If there is no
tty associated with the process, this is implied. The
delete command with this flag ignores possible
errors, i.e., nonexistent rule number. And for batched commands execution
continues with the next command.-i-n-N-qadd,
nat, zero,
resetlog or flush
commands; (implies -f). This is useful when
updating rulesets by executing multiple ipfw
commands in a script (e.g.,
‘sh /etc/rc.firewall’), or by
processing a file with many ipfw rules across a
remote login session. It also stops a table add or delete from failing if
the entry already exists or is not present.
The reason why this option may be important is that for some
of these actions, ipfw may print a message; if
the action results in blocking the traffic to the remote client, the
remote login session will be closed and the rest of the ruleset will not
be processed. Access to the console would then be required to
recover.
-S-s
[field]-tctime().-TTo ease configuration, rules can be put into a file which is
processed using ipfw as shown in the last synopsis
line. An absolute pathname must be used. The file will
be read line by line and applied as arguments to the
ipfw utility.
Optionally, a preprocessor can be specified using
-p preproc where
pathname is to be piped through. Useful preprocessors
include cpp(1) and
m4(1). If
preproc does not start with a slash
(‘/’) as its first character, the
usual PATH name search is performed. Care should be
taken with this in environments where not all file systems are mounted (yet)
by the time ipfw is being run (e.g. when they are
mounted over NFS). Once -p has been specified, any
additional arguments are passed on to the preprocessor for interpretation.
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.
The dnctl pipe,
queue and sched commands are
used to configure the traffic shaper and packet scheduler. See the
TRAFFIC SHAPER
(DUMMYNET) CONFIGURATION Section below for details.
If the world and the kernel get out of sync the
ipfw ABI may break, preventing you from being able
to add any rules. This can adversely affect the booting process. You can use
ipfw disable
firewall to temporarily disable the firewall to
regain access to the network, allowing you to fix the problem.
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.
^ to upper layers V
| |
+----------->-----------+
^ V
[ip(6)_input] [ip(6)_output] net.inet(6).ip(6).fw.enable=1
| |
^ V
[ether_demux] [ether_output_frame] net.link.ether.ipfw=1
| |
+-->--[bdg_forward]-->--+ net.link.bridge.ipfw=1
^ V
| to devices |
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.
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
ipfw is invoked from
ether_demux(), but the same packets will have the
MAC header stripped off when ipfw is invoked from
ip_input() or
ip6_input().
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 ip_input or ip6_input
), the match pattern will not match, but a
not operator in front of such patterns
will cause the
pattern to
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. skipto rules can be useful here, as an
example:
# packets from ether_demux or bdg_forward 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
(yes, at the moment there is no way to differentiate between ether_demux and bdg_forward).
Also note that only actions allow,
deny, netgraph,
ngtee and related to
dummynet are processed for
layer2 frames and all other actions act as if they
were allow for such frames. Full set of actions is
supported for IP packets without layer2 headers
only. For example, divert action does not divert
layer2 frames.
In general, each keyword or argument must be provided as a separate command line argument, with no leading or trailing spaces. Keywords are case-sensitive, whereas arguments may or may not be case-sensitive depending on their nature (e.g. uid's are, hostnames are not).
Some arguments (e.g., port or address lists) are comma-separated lists of values. In this case, spaces after commas ',' are allowed to make the line more readable. You can also put the entire command (including flags) into a single argument. E.g., the following forms are equivalent:
ipfw -q add deny src-ip 10.0.0.0/24,127.0.0.1/8 ipfw -q add deny src-ip 10.0.0.0/24, 127.0.0.1/8 ipfw "-q add deny src-ip 10.0.0.0/24, 127.0.0.1/8"
The format of firewall rules is the following:
set set_number]
[prob match_probability] action
[log [logamount number]]
[altq queue]
[{tag
| untag} number] bodywhere the body of the rule specifies which information is used for filtering packets, among the following:
Note that some of the above information, e.g. source MAC or IP addresses and TCP/UDP ports, can be easily spoofed, so filtering on those fields alone might not guarantee the desired results.
set
set_numberipfw flush command (but you can
delete them with the ipfw delete set 31 command).
Set 31 is also used for the default rule.prob
match_probabilitydummynet) to simulate the effect of multiple paths
leading to out-of-order packet delivery.
Note: this condition is checked before any other condition,
including ones such as keep-state or
check-state which might have side effects.
log
[logamount number]log keyword will
be made available for logging in two ways: if the sysctl variable
net.inet.ip.fw.verbose is set to 0 (default), one
can use bpf(4) attached to
the ipfw0 pseudo interface. This pseudo interface
can be created manually after a system boot by using the following
command:
# ifconfig ipfw0 create
Or, automatically at boot time by adding the following line to the rc.conf(5) file:
firewall_logif="YES"
There is zero overhead when no bpf(4) is attached to the pseudo interface.
If net.inet.ip.fw.verbose is set to 1,
packets will be logged to
syslogd(8) with a
LOG_SECURITY facility up to a maximum of
logamount packets. If no
logamount is specified, the limit is taken from
the sysctl variable net.inet.ip.fw.verbose_limit.
In both cases, a value of 0 means unlimited logging.
Once the limit is reached, logging can be re-enabled by
clearing the logging counter or the packet counter for that entry, see
the resetlog command.
Note: logging is done after all other packet matching conditions have been successfully verified, and before performing the final action (accept, deny, etc.) on the packet.
tag
numbertag keyword,
the numeric tag for the given number in the range
1..65534 will be attached to the packet. The tag acts as an internal
marker (it is not sent out over the wire) that can be used to identify
these packets later on. This can be used, for example, to provide trust
between interfaces and to start doing policy-based filtering. A packet can
have multiple tags at the same time. Tags are "sticky", meaning
once a tag is applied to a packet by a matching rule it exists until
explicit removal. Tags are kept with the packet everywhere within the
kernel, but are lost when packet leaves the kernel, for example, on
transmitting packet out to the network or sending packet to a
divert(4) socket.
To check for previously applied tags, use the
tagged rule option. To delete previously applied
tag, use the untag keyword.
Note: since tags are kept with the packet everywhere in
kernelspace, they can be set and unset anywhere in the kernel network
subsystem (using the
mbuf_tags(9)
facility), not only by means of the
ipfw(4)
tag and untag keywords.
For example, there can be a specialized
netgraph(4) node
doing traffic analyzing and tagging for later inspecting in
firewall.
untag
numberuntag
keyword, the tag with the number number is searched
among the tags attached to this packet and, if found, removed from it.
Other tags bound to packet, if present, are left untouched.altq
queuealtq
keyword, the ALTQ identifier for the given queue
(see altq(4)) will be
attached. Note that this ALTQ tag is only meaningful for packets going
"out" of IPFW, and not being rejected or going to divert
sockets. Note that if there is insufficient memory at the time the packet
is processed, it will not be tagged, so it is wise to make your ALTQ
"default" queue policy account for this. If multiple
altq rules match a single packet, only the first
one adds the ALTQ classification tag. In doing so, traffic may be shaped
by using count altq
queue rules for classification early in the ruleset,
then later applying the filtering decision. For example,
check-state and keep-state
rules may come later and provide the actual filtering decisions in
addition to the fallback ALTQ tag.
You must run pfctl(8) to set up the queues before IPFW will be able to look them up by name, and if the ALTQ disciplines are rearranged, the rules in containing the queue identifiers in the kernel will likely have gone stale and need to be reloaded. Stale queue identifiers will probably result in misclassification.
All system ALTQ processing can be turned on or off via
ipfw enable
altq and ipfw
disable altq. The usage of
net.inet.ip.fw.one_pass is irrelevant to ALTQ
traffic shaping, as the actual rule action is followed always after
adding an ALTQ tag.
A rule can be associated with one of the following actions, which will be executed when the packet matches the body of the rule.
allow
|
accept
|
pass
|
permitcheck-state
[:flowname | :any]Check-state rules do not have a body. If no
check-state rule is found, the dynamic ruleset is
checked at the first keep-state or
limit rule. The :flowname is
symbolic name assigned to dynamic rule by
keep-state opcode. The special flowname
:any can be used to ignore states flowname when
matching. The :default keyword is special name
used for compatibility with old rulesets.countdeny
|
dropdivert
portfwd
|
forward
ipaddr |
tablearg[,port]tablearg keyword instead of an explicit address.
The search terminates if this rule matches.
If ipaddr is a local address, then
matching packets will be forwarded to port (or the
port number in the packet if one is not specified in the rule) on the
local machine.
If 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.
A fwd rule will not match layer2 packets (those
received on ether_input, ether_output, or bridged).
The 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
netstat(1) entry
look rather weird but is intended for use with transparent proxy
servers.
nat
nat_nr | global |
tableargnat64lsn
namenat64stl
namenat64clat
namenptv6
namepipe
pipe_nrdummynet “pipe”
(for bandwidth limitation, delay, etc.). See the
TRAFFIC
SHAPER (DUMMYNET) CONFIGURATION Section for further information. The
search terminates; however, on exit from the pipe and if the
sysctl(8) variable
net.inet.ip.fw.one_pass is not set, the packet is
passed again to the firewall code starting from the next rule.queue
queue_nrdummynet “queue”
(for bandwidth limitation using WF2Q+).rejectunreach host.resetreset6skipto
number | tableargtablearg keyword with a skipto for a
computed
skipto. Skipto may work either in O(log(N)) or in O(1) depending on amount
of memory and/or sysctl variables. See the
SYSCTL VARIABLES section for
more details.call
number | tableargreturn action is encountered, the processing
returns to the first rule with number of this call
rule plus one or higher (the same behaviour as with packets returning from
divert(4) socket after
a divert action). This could be used to make
somewhat like an assembly language “subroutine” calls to
rules with common checks for different interfaces, etc.
Rule with any number could be called, not just forward jumps
as with skipto. So, to prevent endless loops in
case of mistakes, both call and
return actions don't do any jumps and simply go
to the next rule if memory cannot be allocated or stack
overflowed/underflowed.
Internally stack for rule numbers is implemented using
mbuf_tags(9)
facility and currently has size of 16 entries. As mbuf tags are lost
when packet leaves the kernel, divert should not
be used in subroutines to avoid endless loops and other undesired
effects.
returncall action and returns ruleset processing to the
first rule with number greater than number of corresponding
call rule. See description of the
call action for more details.
Note that return rules usually end a
“subroutine” and thus are unconditional, but
ipfw command-line utility currently requires
every action except check-state to have body.
While it is sometimes useful to return only on some packets, usually you
want to print just “return” for readability. A workaround
for this is to use new syntax and -c switch:
# Add a rule without actual body ipfw add 2999 return via any # List rules without "from any to any" part ipfw -c list
This cosmetic annoyance may be fixed in future releases.
tee
portunreach
codenet, host,
protocol, port,
needfrag, srcfail,
net-unknown, host-unknown,
isolated, net-prohib,
host-prohib, tosnet,
toshost, filter-prohib,
host-precedence or
precedence-cutoff. The search terminates.unreach6
codeno-route, admin-prohib, address or
port. The search terminates.netgraph
cookiengtee
cookienetgraph and
ngtee actions.setfib
fibnum | tableargtablearg keyword with setfib. If the tablearg
value is not within the compiled range of fibs, the packet's fib is set to
0.setdscp
DSCP | number |
tableargcs0 (000000),
cs1 (001000),
cs2 (010000),
cs3 (011000),
cs4 (100000),
cs5 (101000),
cs6 (110000),
cs7 (111000),
af11 (001010),
af12 (001100),
af13 (001110),
af21 (010010),
af22 (010100),
af23 (010110),
af31 (011010),
af32 (011100),
af33 (011110),
af41 (100010),
af42 (100100),
af43 (100110),
ef (101110),
be (000000).
Additionally, DSCP value can be specified by number (0..63). It is also
possible to use the tablearg keyword with
setdscp. If the tablearg value is not within the 0..63 range, lower 6
bits of supplied value are used.
tcp-setmss
mssipfw_pmod should be loaded or kernel should have
options IPFIREWALL_PMOD to be able use this
action. This command does not change a packet if original MSS value is
lower than specified value. Both TCP over IPv4 and over IPv6 are
supported. Regardless of matched a packet or not by the
tcp-setmss rule, the search continues with the
next rule.reassFragment handling can be tuned via net.inet.ip.maxfragpackets and net.inet.ip.maxfragsperpacket which limit, respectively, the maximum number of processable fragments (default: 800) and the maximum number of fragments per packet (default: 16).
NOTA BENE: since fragments do not contain port numbers, they
should be avoided with the reass rule.
Alternatively, direction-based (like in /
out ) and source-based (like
via ) match patterns can be used to select
fragments.
Usually a simple rule like:
# reassemble incoming fragments ipfw add reass all from any to any in
is all you need at the beginning of your ruleset.
abortabort6The 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)
and operators -- i.e., all must match in order for
the rule to match. Individual patterns can be prefixed by the
not operator to reverse the result of the match, as
in
ipfw add 100 allow ip from not
1.2.3.4 to anyAdditionally, sets of alternative match patterns
(or-blocks) can be constructed by putting the patterns in
lists enclosed between parentheses ( ) or braces { }, and using the
or operator as follows:
ipfw add 100 allow ip from { x or not
y or z } to anyOnly 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.
The body of a rule must in general include a source and destination address specifier. The keyword any can be used in various places to specify that the content of a required field is irrelevant.
The rule body has the following format:
from src
to dst]
[options]The first part (proto from src to dst) is for backward compatibility with earlier versions of FreeBSD. In modern FreeBSD any match pattern (including MAC headers, IP protocols, addresses and ports) can be specified in the options section.
Rule fields have the following meaning:
{
protocol or ... }not]
protocol-name |
protocol-numberThe ipv6 in
proto option will be treated as inner protocol.
And, the ipv4 is not available in
proto option.
The { protocol
or ... } format (an or-block)
is provided for convenience only but its use is deprecated.
addr |
{ addr or ...
}} [[not] ports]The second format (or-block with multiple addresses) is provided for convenience only and its use is discouraged.
not]
{any | me |
me6 |
table(name[,value])
| addr-list | addr-set}anymeme6table(name[,value])masklen bits. As an example, 1.2.3.4/25 or
1.2.3.0/25 will match all IP numbers from 1.2.3.0 to 1.2.3.127 .{list}masklen
bits.No support for sets of IPv6 addresses is provided because IPv6 addresses are typically random past the initial prefix.
ports may be specified as one or more
ports or port ranges, separated by commas but no spaces, and an optional
not operator. The
‘-’ notation specifies a range of
ports (including boundaries).
Service names (from /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 or-block in the
options section of the rule.
A backslash (‘\’) can be
used to escape the dash (‘-’)
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).
ipfw add count tcp from any
ftp\\-data-ftp to anyFragmented 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 frag option for details
on matching fragmented packets.
Additional match patterns can be used within rules. Zero or more
of these so-called
options
can be present in a rule, optionally prefixed by the
not operand, and possibly grouped into
or-blocks.
The following match patterns can be used (listed in alphabetical order):
// this is a
comment.count action followed by the comment.bridgedlayer2.defer-immediate-action
|
defer-actionrecord-state or
keep-state as the dynamic rule, created but
ignored on match, will work as intended. Rules with both
record-state and
defer-immediate-action create a dynamic rule and
continue with the next rule without actually performing the action part of
this rule. When the rule is later activated via the state table, the
action is performed as usual.diverteddiverted-loopbackdiverted-outputdst-ip
ip-addressdst-ip6 | dst-ipv6}
ip6-addressdst-port
portsestablishedext6hdr
headerFragment, (frag), Hop-to-hop options
(hopopt), any type of Routing Header
(route), Source routing Routing Header Type 0
(rthdr0), Mobile IPv6 Routing Header Type 2
(rthdr2), Destination options
(dstopt), IPSec authentication headers
(ah), and IPsec encapsulated security payload
headers (esp).
fib
fibnumflow
table(name[,value])tablearg is set to the value extracted from the
table.
This option can be useful to quickly dispatch traffic based on certain packet fields. See the LOOKUP TABLES section below for more information on lookup tables.
flow-id
labelsfrag
specip_off field contains
the comma separated list of IPv4 fragmentation options specified in
spec. The recognized options are:
df (don't fragment),
mf (more fragments),
rf (reserved fragment bit)
offset (non-zero fragment
offset). The absence of a particular options may be denoted with a
‘!’.
Empty list of options defaults to matching on non-zero fragment offset. Such rule would match all not the first fragment datagrams, both IPv4 and IPv6. This is a backward compatibility with older rulesets.
gid
groupjail
jailicmptypes
typesecho reply (0), destination
unreachable (3), source quench
(4), redirect (5), echo
request (8), router advertisement
(9), router solicitation
(10), time-to-live exceeded
(11), IP header bad
(12), timestamp request
(13), timestamp reply
(14), information request
(15), information reply
(16), address mask request
(17) and address mask reply
(18).
icmp6types
typesin |
outin and out are mutually
exclusive (in fact, out is implemented as
not in).ipid
id-listip_id field has value
included in id-list, which is either a single value
or a list of values or ranges specified in the same way as
ports.iplen
len-listipoptions
specssrr (strict source route),
lsrr (loose source route),
rr (record packet route) and
ts (timestamp). The absence of a particular
option may be denoted with a
‘!’.
ipprecedence
precedenceipsecNote that specifying ipsec is
different from specifying proto
ipsec as the latter will only look at the specific
IP protocol field, irrespective of IPSEC kernel support and the validity
of the IPSEC data.
Further note that this flag is silently ignored in kernels
without IPSEC support. It does not affect rule processing when given and
the rules are handled as if with no ipsec
flag.
iptos
spectos field contains the
comma separated list of service types specified in
spec. The supported IP types of service are:
lowdelay
(IPTOS_LOWDELAY),
throughput
(IPTOS_THROUGHPUT),
reliability
(IPTOS_RELIABILITY),
mincost (IPTOS_MINCOST),
congestion
(IPTOS_ECN_CE). The absence of a particular type
may be denoted with a ‘!’.
dscp
spec[,spec]DS field value is
contained in spec mask. Multiple values can be
specified via the comma separated list. Value can be one of keywords used
in setdscp action or exact number.ipttl
ttl-listipversion
verkeep-state
[:flowname]check-state rule. The
:default keyword is special name used for
compatibility with old rulesets.layer2ipfw from
ether_demux()
and
ether_output_frame().limit
{src-addr | src-port |
dst-addr | dst-port}
N [:flowname]lookup
{dst-ip | dst-port |
src-ip | src-port |
uid | jail}
nametablearg is set to the
value extracted from the table.
This option can be useful to quickly dispatch traffic based on certain packet fields. See the LOOKUP TABLES section below for more information on lookup tables.
{
MAC |
mac }
dst-mac src-macany keyword (matching any MAC address), or six
groups of hex digits separated by colons, and optionally followed by a
mask indicating the significant bits. The mask may be specified using
either of the following methods:
MAC 10:20:30:40:50:60/33
anyMAC
10:20:30:40:50:60&00:00:00:00:ff:ff anyNote that the ampersand character has a special meaning in many shells and should generally be escaped.
mac-type
mac-typeport numbers (i.e., one or more
comma-separated single values or ranges). You can use symbolic names for
known values such as
vlan,
ipv4,
ipv6. Values can be entered as decimal or hexadecimal (if prefixed
by 0x), and they are always printed as hexadecimal (unless the
-N option is used, in which case symbolic
resolution will be attempted).proto
protocolrecord-statekeep-state was specified. However, this option
doesn't imply an implicit check-state in contrast
to keep-state.recv
|
xmit
| via
{ifX | ifmask |
table(name[,value])
| ipno | any}Interface name may be matched against ifmask with fnmatch(3) according to the rules used by the shell (f.e. tun*). See also the EXAMPLES section.
Table name may be used to match interface by its kernel ifindex. See the LOOKUP TABLES section below for more information on lookup tables.
The via keyword causes the interface
to always be checked. If recv or
xmit is used instead of
via, then only the receive or transmit interface
(respectively) is checked. By specifying both, it is possible to match
packets based on both receive and transmit interface, e.g.:
ipfw add deny ip from any to any
out recv ed0 xmit ed1The recv interface can be tested on
either incoming or outgoing packets, while the
xmit interface can only be tested on outgoing
packets. So out is required (and
in is invalid) whenever
xmit is used.
A packet might not have a receive or transmit interface: packets originating from the local host have no receive interface, while packets destined for the local host have no transmit interface.
set-limit
{src-addr | src-port |
dst-addr | dst-port}
Nlimit but does not have an implicit
check-state attached to it.setuptcpflags syn,!ack”.sockargtablearg value, which in turn can be used as
skipto or pipe
number.src-ip
ip-addresssrc-ip6
ip6-addresssrc-port
portstagged
tag-listtag rule action parameter (see it's
description for details on tags).tcpack
acktcpdatalen
tcpdatalen-listtcpflags
specfin, syn,
rst, psh,
ack and urg. The absence
of a particular flag may be denoted with a
‘!’. A rule which contains a
tcpflags specification can never match a
fragmented packet which has a non-zero offset. See the
frag option for details on matching fragmented
packets.
tcpmss
tcpmss-listtcpseq
seqtcpwin
tcpwin-listtcpoptions
specmss (maximum segment size),
window (tcp window advertisement),
sack (selective ack), ts
(rfc1323 timestamp) and cc (rfc1644 t/tcp
connection count). The absence of a particular option may be denoted
with a ‘!’.
uid
userverrevpathThe name and functionality of the option is intentionally similar to the Cisco IOS command:
ip verify unicast
reverse-pathThis option can be used to make anti-spoofing rules to reject
all packets with source addresses not from this interface. See also the
option antispoof.
versrcreachThe name and functionality of the option is intentionally similar to the Cisco IOS command:
ip verify unicast source
reachable-via anyThis option can be used to make anti-spoofing rules to reject all packets whose source address is unreachable.
antispoofThis option can be used to make anti-spoofing rules to reject
all packets that pretend to be from a directly connected network but do
not come in through that interface. This option is similar to but more
restricted than verrevpath because it engages
only on packets with source addresses of directly connected networks
instead of all source addresses.
Lookup tables are useful to handle large sparse sets of addresses or other search keys (e.g., ports, jail IDs, interface names). In the rest of this section we will use the term ``key''. Table name needs to match the following spec: table-name. Tables with the same name can be created in different sets. However, rule links to the tables in set 0 by default. This behavior can be controlled by net.inet.ip.fw.tables_sets variable. See the SETS OF RULES section for more information. There may be up to 65535 different lookup tables.
The following table types are supported:
addrifacenumberflowTables require explicit creation via
create before use.
The following creation options are supported:
type table-type |
valtype
value-mask |
algo
algo-desc |limit
number |
locked
|
missing
|
or-flushtypevaltypealgolimitlockedmissingor-flushmissing so existing table must be compatible with
new one.Some of these options may be modified later via
modify keyword. The following options can be
changed:
limit
numberlimitAdditionally, table can be locked or unlocked using
lock or unlock commands.
Tables of the same type can be swapped with
each other using swap name
command. Swap may fail if tables limits are set and data exchange would
result in limits hit. Operation is performed atomically.
One or more entries can be added to a table at once using
add command. Addition of all items are performed
atomically. By default, error in addition of one entry does not influence
addition of other entries. However, non-zero error code is returned in that
case. Special atomic keyword may be specified before
add to indicate all-or-none add request.
One or more entries can be removed from a table at once using
delete command. By default, error in removal of one
entry does not influence removing of other entries. However, non-zero error
code is returned in that case.
It may be possible to check what entry will be found on particular
table-key using lookup
table-key command. This functionality is optional and
may be unsupported in some algorithms.
The following operations can be performed on
one or all tables:
listflushinfodetailThe following lookup algorithms are supported:
addr:
radixaddr:hashaddr:hash
masks=/v4,/v6 algorithm creation options. Assume /32 and /128 masks
by default. Search removes host bits (according to mask) from supplied
address and checks resulting key in appropriate hash. Mostly optimized for
/64 and byte-ranged IPv6 masks.iface:arraynumber:arrayflow:hashThe tablearg feature provides the ability
to use a value, looked up in the table, as the argument for a rule action,
action parameter or rule option. This can significantly reduce number of
rules in some configurations. If two tables are used in a rule, the result
of the second (destination) is used.
Each record may hold one or more values according to
value-mask. This mask is set on table creation via
valtype option. The following value types are
supported:
skiptopipefibnatdscptagdivertnetgraphlimitipv4ipv6The tablearg argument can be used with the
following actions: nat, pipe, queue, divert, tee, netgraph,
ngtee, fwd, skipto, setfib, action parameters: tag,
untag, rule options: limit, tagged.
When used with the skipto action, the user
should be aware that the code will walk the ruleset up to a rule equal to,
or past, the given number.
See the EXAMPLES Section for example usage of tables and the tablearg keyword.
Each rule or table belongs to one of 32 different sets , numbered 0 to 31. Set 31 is reserved for the default rule.
By default, rules or tables are put in set 0, unless you use the
set N attribute when adding a new rule or table.
Sets can be individually and atomically enabled or disabled, so this
mechanism permits an easy way to store multiple configurations of the
firewall and quickly (and atomically) switch between them.
By default, tables from set 0 are referenced when adding rule with table opcodes regardless of rule set. This behavior can be changed by setting net.inet.ip.fw.tables_sets variable to 1. Rule's set will then be used for table references.
The command to enable/disable sets is
ipfw
set [disable
number ...] [enable
number ...]where multiple enable or
disable sections can be specified. Command execution
is atomic on all the sets specified in the command. By default, all sets are
enabled.
When you disable a set, its rules behave as if they do not exist in the firewall configuration, with only one exception:
The set number of rules can be changed with the command
ipfw set
move {rule rule-number |
old-set} to
new-setAlso, you can atomically swap two rulesets with the command
ipfw set
swap first-set second-setSee the EXAMPLES Section on some possible uses of sets of rules.
Stateful operation is a way for the firewall to dynamically create
rules for specific flows when packets that match a given pattern are
detected. Support for stateful operation comes through the
check-state, keep-state,
record-state, limit and
set-limit options of
rules.
Dynamic rules are created when a packet matches a
keep-state, record-state,
limit or set-limit rule,
causing the creation of a dynamic rule which will match
all and only packets with a given
protocol between
a
src-ip/src-port
dst-ip/dst-port pair of addresses
(src and
dst are used
here only to denote the initial match addresses, but they are completely
equivalent afterwards). Rules created by keep-state
option also have a :flowname taken from it. This name
is used in matching together with addresses, ports and protocol. Dynamic
rules will be checked at the first check-state,
keep-state or limit occurrence, and the
action performed upon a match will be the same as in the parent rule.
Note that no additional attributes other than protocol and IP addresses and ports and :flowname are checked on dynamic rules.
The typical use of dynamic rules is to keep a closed firewall configuration, but let the first TCP SYN packet from the inside network install a dynamic rule for the flow so that packets belonging to that session will be allowed through the firewall:
ipfw add check-state
:OUTBOUNDipfw add allow tcp from my-subnet to
any setup keep-state :OUTBOUNDipfw add deny tcp from any to
anyA similar approach can be used for UDP, where an UDP packet coming from the inside will install a dynamic rule to let the response through the firewall:
ipfw add check-state
:OUTBOUNDipfw add allow udp from my-subnet to
any keep-state :OUTBOUNDipfw add deny udp from any to
anyDynamic rules expire after some time, which depends on the status
of the flow and the setting of some sysctl
variables. See Section SYSCTL
VARIABLES for more details. For TCP sessions, dynamic rules can be
instructed to periodically send keepalive packets to refresh the state of
the rule when it is about to expire.
See Section EXAMPLES for more examples on how to use dynamic rules.
ipfw is also the user interface for the
dummynet traffic shaper, packet scheduler and
network emulator, a subsystem that can artificially queue, delay or drop
packets emulating the behaviour of certain network links or queueing
systems.
dummynet operates by first using the
firewall to select packets using any match pattern that can be used in
ipfw rules. Matching packets are then passed to
either of two different objects, which implement the traffic regulation:
ipfw, and then transferred in FIFO order to the
link at the desired rate.In practice, pipes can be used to set hard limits to the bandwidth that a flow can use, whereas queues can be used to determine how different flows share the available bandwidth.
A graphical representation of the binding of queues, flows, schedulers and links is below.
(flow_mask|sched_mask) sched_mask
+---------+ weight Wx +-------------+
| |->-[flow]-->--| |-+
-->--| QUEUE x | ... | | |
| |->-[flow]-->--| SCHEDuler N | |
+---------+ | | |
... | +--[LINK N]-->--
+---------+ weight Wy | | +--[LINK N]-->--
| |->-[flow]-->--| | |
-->--| QUEUE y | ... | | |
| |->-[flow]-->--| | |
+---------+ +-------------+ |
+-------------+
ipfw sched N config mask SCHED_MASK
...ipfw queue X config mask FLOW_MASK
...The SCHED_MASK is used to assign flows to one or more scheduler instances, one for each value of the packet's 5-tuple after applying SCHED_MASK. As an example, using ``src-ip 0xffffff00'' creates one instance for each /24 destination subnet.
The FLOW_MASK, together with the SCHED_MASK, is used to split packets into flows. As an example, using ``src-ip 0x000000ff'' together with the previous SCHED_MASK makes a flow for each individual source address. In turn, flows for each /24 subnet will be sent to the same scheduler instance.
The above diagram holds even for the pipe case,
with the only restriction that a pipe only supports a
SCHED_MASK, and forces the use of a FIFO scheduler (these are for backward
compatibility reasons; in fact, internally, a
dummynet's pipe is implemented exactly as
above).
There are two modes of dummynet operation:
“normal” and “fast”. The “normal”
mode tries to emulate a real link: the dummynet
scheduler ensures that the packet will not leave the pipe faster than it
would on the real link with a given bandwidth. The “fast” mode
allows certain packets to bypass the dummynet
scheduler (if packet flow does not exceed pipe's bandwidth). This is the
reason why the “fast” mode requires less CPU cycles per packet
(on average) and packet latency can be significantly lower in comparison to
a real link with the same bandwidth. The default mode is
“normal”. The “fast” mode can be enabled by
setting the net.inet.ip.dummynet.io_fast
sysctl(8) variable to a
non-zero value.
The pipe, queue and scheduler configuration commands are the following:
pipe
number config
pipe-configuration
queue number
config queue-configuration
sched number
config sched-configuration
The following parameters can be configured for a pipe:
bw
bandwidth | deviceK|M|G]{bit/s|Byte/s}.
A value of 0 (default) means unlimited bandwidth. The unit must immediately follow the number, as in
dnctl pipe 1 config bw
300Kbit/sIf a device name is specified instead of a numeric value, as in
dnctl pipe 1 config bw
tun0then the transmit clock is supplied by the specified device. At the moment only the tun(4) device supports this functionality, for use in conjunction with ppp(8).
delay
ms-delayburst
sizedummynet scheduler, and will
be sent as fast as the physical link allows. Any additional data will be
transmitted at the rate specified by the pipe
bandwidth. The burst size depends on how long the pipe has been idle; the
effective burst size is calculated as follows: MAX(
size , bw * pipe_idle_time).
profile
filenameSome link types introduce extra delays in the transmission of a packet, e.g., because of MAC level framing, contention on the use of the channel, MAC level retransmissions and so on. From our point of view, the channel is effectively unavailable for this extra time, which is constant or variable depending on the link type. Additionally, packets may be dropped after this time (e.g., on a wireless link after too many retransmissions). We can model the additional delay with an empirical curve that represents its distribution.
cumulative probability
1.0 ^
|
L +-- loss-level x
| ******
| *
| *****
| *
| **
| *
+-------*------------------->
delay
The file format is the following, with whitespace acting as a separator and '#' indicating the beginning a comment:
name
identifierbw
valueloss-level
Lsamples
Ndelay prob | prob
delayipfw utility
will sort and interpolate the curve as needed.Example of a profile file:
name bla_bla_bla samples 100 loss-level 0.86 prob delay 0 200 # minimum overhead is 200ms 0.5 200 0.5 300 0.8 1000 0.9 1300 1 1300 #configuration file end
The following parameters can be configured for a queue:
pipe
pipe_nrweight
weightThe following case-insensitive parameters can be configured for a scheduler:
type
{fifo | wf2q+ |
rr | qfq |
fq_codel | fq_pie}fifowf2q+rrqfqfq_codelfq_piefq_codel but uses per sub-queue PIE
AQM instance to control the queue delay.fq_codel inherits AQM parameters and
options from codel (see below), and
fq_pie inherits AQM parameters and options from
pie (see below). Additionally, both of
fq_codel and fq_pie have
shared scheduler parameters which are:
quantumlimitflowsNote that any token after fq_codel or
fq_pie is considered a parameter for
fq_{codel/pie}. So, ensure all scheduler configuration options not
related to fq_{codel/pie} are written before
fq_codel/fq_pie tokens.
In addition to the type, all parameters allowed for a pipe can also be specified for a scheduler.
Finally, the following parameters can be configured for both pipes and queues:
buckets
hash-table-sizemask
mask-specifieripfw
rule can be further classified into multiple flows, each of which is then
sent to a different dynamic pipe or queue. A flow
identifier is constructed by masking the IP addresses, ports and protocol
types as specified with the mask options in the
configuration of the pipe or queue. For each different flow identifier, a
new pipe or queue is created with the same parameters as the original
object, and matching packets are sent to it.
Thus, when dynamic pipes are used, each flow
will get the same bandwidth as defined by the pipe, whereas when
dynamic queues are used, each flow will share the
parent's pipe bandwidth evenly with other flows generated by the same
queue (note that other queues with different weights might be connected
to the same pipe).
Available mask specifiers are a combination of one or more of the
following:
dst-ip mask,
dst-ip6 mask,
src-ip mask,
src-ip6 mask,
dst-port mask,
src-port mask,
flow-id mask,
proto mask or
all,
where the latter means all bits in all fields are significant.
noerrordummynet queue or
pipe, the error is normally reported to the caller routine in the kernel,
in the same way as it happens when a device queue fills up. Setting this
option reports the packet as successfully delivered, which can be needed
for some experimental setups where you want to simulate loss or congestion
at a remote router.
plr
packet-loss-ratequeue
{slots |
sizeKbytes}KBytes. Default value is 50 slots, which is the
typical queue size for Ethernet devices. Note that for slow speed links
you should keep the queue size short or your traffic might be affected by
a significant queueing delay. E.g., 50 max-sized Ethernet packets (1500
bytes) mean 600Kbit or 20s of queue on a 30Kbit/s pipe. Even worse effects
can result if you get packets from an interface with a much larger MTU,
e.g. the loopback interface with its 16KB packets. The
sysctl(8) variables
net.inet.ip.dummynet.pipe_byte_limit and
net.inet.ip.dummynet.pipe_slot_limit control the maximum
lengths that can be specified.
red
|
gred
w_q/min_th/max_th/max_pdummynet also supports the gentle RED variant
(gred) and ECN (Explicit Congestion Notification) as optional. Three
sysctl(8) variables can
be used to control the RED behaviour:
codel
[target time]
[interval time]
[ecn | noecn]target
time (5ms by default) is the minimum acceptable
persistent queue delay that CoDel allows. CoDel does not drop packets
directly after packets sojourn time becomes higher than
target time but waits for
interval time (100ms
default) before dropping. interval
time should be set to maximum RTT for all expected
connections. ecn enables (disabled by default)
packet marking (instead of dropping) for ECN-enabled TCP flows when queue
delay becomes high.
Note that any token after codel is
considered a parameter for CoDel. So, ensure all pipe/queue
configuration options are written before codel
token.
The sysctl(8) variables net.inet.ip.dummynet.codel.target and net.inet.ip.dummynet.codel.interval can be used to set CoDel default parameters.
pie
[target time]
[tupdate time]
[alpha n]
[beta n]
[max_burst time]
[max_ecnth n]
[ecn | noecn]
[capdrop | nocapdrop]
[drand | nodrand]
[onoff] [dre |
ts]tupdate time (15ms by
default) a background process (re)calculates the probability based on
queue delay deviations from target
time (15ms by default) and queue delay trends. PIE
approximates current queue delay by using a departure rate estimation
method, or (optionally) by using a packet timestamp method similar to
CoDel. time is interpreted as milliseconds by
default but seconds (s), milliseconds (ms) or microseconds (us) can be
specified instead. The other PIE parameters and options are as follows:
alpha
nbeta
nmax_burst
timemax_ecnth
nmax_ecnth n , the
default is 0.1 (i.e 10%) and 1 is the maximum value.ecn
|
noecncapdrop
|
nocapdropdrand
|
nodrandonoffdre
|
tsdre or timestamps ts.
dre is used by default.Note that any token after pie is
considered a parameter for PIE. So ensure all pipe/queue the
configuration options are written before pie
token. sysctl(8)
variables can be used to control the pie default
parameters. See the SYSCTL
VARIABLES section for more details.
When used with IPv6 data, dummynet
currently has several limitations. Information necessary to route link-local
packets to an interface is not available after processing by
dummynet so those packets are dropped in the output
path. Care should be taken to ensure that link-local packets are not passed
to dummynet.
Here are some important points to consider when designing your rules:
in and
out. Most connections need packets going in both
directions.ipfw is probably not as straightforward as you
would think. The following command line is recommended:
kldload ipfw && \ ipfw add 32000 allow ip from any to any
Along the same lines, doing an
ipfw flush
in similar surroundings is also a bad idea.
ipfw filter list may not be modified if the
system security level is set to 3 or higher (see
init(8) for information
on system security levels).A divert(4) socket bound to the specified port will receive all packets diverted to that port. If no socket is bound to the destination port, or if the divert module is not loaded, or if the kernel was not compiled with divert socket support, the packets are dropped.
ipfw support in-kernel NAT using the
kernel version of
libalias(3). The kernel
module ipfw_nat should be loaded or kernel should
have options IPFIREWALL_NAT to be able use NAT.
The nat configuration command is the following:
nat
nat_number config
nat-configurationThe following parameters can be configured:
ip
ip_addressif
niclogdeny_insame_portsunreg_onlyunreg_cgnresetreverseproxy_onlyskip_globalport_range
lower-upperSome special values can be supplied instead of nat_number in nat rule actions:
globaltableargTo let the packet continue after being (de)aliased, set the sysctl variable net.inet.ip.fw.one_pass to 0. For more information about aliasing modes, refer to libalias(3). See Section EXAMPLES for some examples of nat usage.
Redirect and LSNAT support follow closely the syntax used in natd(8). See Section EXAMPLES for some examples on how to do redirect and lsnat.
SCTP nat can be configured in a similar manner to TCP through the
ipfw command line tool. The main difference is that
sctp nat does not do port translation. Since the
local and global side ports will be the same, there is no need to specify
both. Ports are redirected as follows:
nat
nat_number config
if nic redirect_port
sctp ip_address
[,addr_list] {[port | port-port] [,ports]}Most sctp nat configuration can be done in
real-time through the
sysctl(8) interface. All
may be changed dynamically, though the hash_table size will only change for
new nat instances. See
SYSCTL VARIABLES for more
info.
ipfw supports in-kernel IPv6/IPv4 network
address and protocol translation. Stateful NAT64 translation allows
IPv6-only clients to contact IPv4 servers using unicast TCP, UDP or ICMP
protocols. One or more IPv4 addresses assigned to a stateful NAT64
translator are shared among several IPv6-only clients. When stateful NAT64
is used in conjunction with DNS64, no changes are usually required in the
IPv6 client or the IPv4 server. The kernel module
ipfw_nat64 should be loaded or kernel should have
options IPFIREWALL_NAT64 to be able use stateful
NAT64 translator.
Stateful NAT64 uses a bunch of memory for several types of objects. When IPv6 client initiates connection, NAT64 translator creates a host entry in the states table. Each host entry uses preallocated IPv4 alias entry. Each alias entry has a number of ports group entries allocated on demand. Ports group entries contains connection state entries. There are several options to control limits and lifetime for these objects.
NAT64 translator follows RFC7915 when does ICMPv6/ICMP translation, unsupported message types will be silently dropped. IPv6 needs several ICMPv6 message types to be explicitly allowed for correct operation. Make sure that ND6 neighbor solicitation (ICMPv6 type 135) and neighbor advertisement (ICMPv6 type 136) messages will not be handled by translation rules.
After translation NAT64 translator by default sends packets
through corresponding netisr queue. Thus translator host should be
configured as IPv4 and IPv6 router. Also this means, that a packet is
handled by firewall twice. First time an original packet is handled and
consumed by translator, and then it is handled again as translated packet.
This behavior can be changed by sysctl variable
net.inet.ip.fw.nat64_direct_output. Also translated
packet can be tagged using tag rule action, and then
matched by tagged opcode to avoid loops and extra
overhead.
The stateful NAT64 configuration command is the following:
nat64lsn
name create
create-optionsThe following parameters can be configured:
prefix4
ipv4_prefix/plenprefix6
ipv6_prefix/lengthstates_chunks
numberhost_del_age
secondspg_del_age
secondstcp_syn_age
secondstcp_est_age
secondstcp_close_age
secondsudp_age
secondsicmp_age
secondslogifconfig command. Note that it has different
purpose than ipfw0 interface. Translators sends to
BPF an additional information with each packet. With
tcpdump you are able to see each handled packet
before and after translation.-logallow_private-allow_privatenat64
instance.To inspect a states table of stateful NAT64 the following command can be used:
nat64lsn
name show
statesStateless NAT64 translator doesn't use a states table for translation and converts IPv4 addresses to IPv6 and vice versa solely based on the mappings taken from configured lookup tables. Since a states table doesn't used by stateless translator, it can be configured to pass IPv4 clients to IPv6-only servers.
The stateless NAT64 configuration command is the following:
nat64stl
name create
create-optionsThe following parameters can be configured:
prefix6
ipv6_prefix/lengthtable4
table46table6
table64log-logallow_private-allow_privatenat64
instance.Note that the behavior of stateless translator with respect to not matched packets differs from stateful translator. If corresponding addresses was not found in the lookup tables, the packet will not be dropped and the search continues.
XLAT464 CLAT NAT64 translator implements client-side stateless translation as defined in RFC6877 and is very similar to statless NAT64 translator explained above. Instead of lookup tables it uses one-to-one mapping between IPv4 and IPv6 addresses using configured prefixes. This mode can be used as a replacement of DNS64 service for applications that are not using it (e.g. VoIP) allowing them to access IPv4-only Internet over IPv6-only networks with help of remote NAT64 translator.
The CLAT NAT64 configuration command is the following:
nat64clat
name create
create-optionsThe following parameters can be configured:
clat_prefix
ipv6_prefix/lengthplat_prefix
ipv6_prefix/lengthlog-logallow_privatenat64clat instance will not process IPv4 packets
with destination address from private ranges as defined in RFC1918.-allow_privatenat64clat
instance.Note that the behavior of CLAT translator with respect to not matched packets differs from stateful translator. If corresponding addresses were not matched against prefixes configured, the packet will not be dropped and the search continues.
ipfw supports in-kernel IPv6-to-IPv6
network prefix translation as described in RFC6296. The kernel module
ipfw_nptv6 should be loaded or kernel should has
options IPFIREWALL_NPTV6 to be able use NPTv6
translator.
The NPTv6 configuration command is the following:
nptv6
name create
create-optionsThe following parameters can be configured:
int_prefix
ipv6_prefixext_prefix
ipv6_prefixext_if
nicext_prefix and ext_if
options are mutually exclusive.prefixlen
lengthNote that the prefix translation rules are silently ignored when IPv6 packet forwarding is disabled. To enable the packet forwarding, set the sysctl variable net.inet6.ip6.forwarding to 1.
To let the packet continue after being translated, set the sysctl variable net.inet.ip.fw.one_pass to 0.
Tunables can be set in loader(8) prompt, loader.conf(5) or kenv(1) before ipfw module gets loaded.
options IPFW_DEFAULT_TO_(ACCEPT|DENY) from kernel
configuration file.A set of
sysctl(8) variables
controls the behaviour of the firewall and associated modules
(dummynet, bridge,
sctp nat). These are shown below together with their
default value (but always check with the
sysctl(8) command what
value is actually in use) and meaning:
nat responds to receipt of global
OOTB ASCONF-AddIP:
01nat will accept and process all OOTB global
AddIP messages.Option 1 should never be selected as this forms a security risk. An attacker can establish multiple fake associations by sending AddIP messages.
net.inet.ip.alias.sctp.initialising_chunk_proc_limit.
A high value is a DoS risk yet setting too low a value may result in
important control chunks in the packet not being located and parsed.nat responds to any
Out-of-the-Blue (OOTB) packets with ErrorM packets. An OOTB packet is a
packet that arrives with no existing association registered in the
nat and is not an INIT or ASCONF-AddIP packet:
012nat is tracking global IP addresses.3At the moment the default is 0, since the ErrorM packet is not
yet supported by most SCTP stacks. When it is supported, and if not
tracking global addresses, we recommend setting this value to 1 to allow
multi-homed local hosts to function with the
nat. To track global addresses, we recommend
setting this value to 2 to allow global hosts to be informed when they
need to (re)send an ASCONF-AddIP. Value 3 should never be chosen (except
for debugging) as the nat will respond to all
OOTB global packets (a DoS risk).
nat lookups (100 <
prime_number > 1000001). This value sets the hash
table size for any future created nat
instance and therefore must be set prior to creating a
nat instance. The table sizes may be changed to
suit specific needs. If there will be few concurrent associations, and
memory is scarce, you may make these smaller. If there will be many
thousands (or millions) of concurrent associations, you should make these
larger. A prime number is best for the table size. The sysctl update
function will adjust your input value to the next highest prime
number.nat and places an upper limit on the number of
addresses tracked for each association:
0>1This variable is fully dynamic, the new value will be adopted
for all newly arriving associations, existing associations are treated
as they were previously. Global tracking will decrease the number of
collisions within the nat at a cost of increased
processing load, memory usage, complexity, and possible
nat state problems in complex networks with
multiple nats. We recommend not tracking global
IP addresses, this will still result in a fully functional
nat.
codel AQM interval in microseconds. The
value must be in the range 1..5000000.codel AQM target delay time in
microseconds (the minimum acceptable persistent queue delay). The value
must be in the range 1..5000000.fq_codel creates and manages. The value must be in
the range 1..65536.fq_codel scheduler/AQM interval in
microseconds. The value must be in the range 1..5000000.fq_codel scheduler. The value
must be in the range 1..20480.fq_codel in
unit of byte. The value must be in the range 1..9000.fq_codel scheduler/AQM target delay time
in microseconds (the minimum acceptable persistent queue delay). The value
must be in the range 1..5000000.fq_pie scheduler/AQM. The value must be in the
range 1..7000.fq_pie scheduler/AQM. The value must be in the
range 1..7000.fq_pie creates and manages. The value must be in
the range 1..65536.fq_pie scheduler. The value
must be in the range 1..20480.fq_pie scheduler/AQM does not drop/mark packets.
The value must be in the range 1..10000000.fq_pie scheduler/AQM. The value must be in the
range 1..7000.fq_pie in unit
of byte. The value must be in the range 1..9000.target delay of the
fq_pie in unit of microsecond. The value must be
in the range 1..5000000.tupdate of the
fq_pie in unit of microsecond. The value must be
in the range 1..5000000.buckets option is specified when
configuring a pipe/queue.dummynet operation (see above) is enabled.dummynet.dummynet.dummynet
scheduler.max_chain_len*hash_size is used to
determine the threshold over which empty pipes/queues will be expired even
when net.inet.ip.dummynet.expire=0.pie AQM. The value must be in the range
1..7000.pie AQM. The value must be in the range
1..7000.pie AQM does not drop/mark packets. The value must
be in the range 1..10000000.pie AQM. The value must be in the range
1..7000.target delay of
pie AQM in unit of microsecond. The value must be
in the range 1..5000000.tupdate of pie
AQM in unit of microsecond. The value must be in the range
1..5000000.ipfw.ipfw, the default rule is the last one, so its
number can also serve as the highest number allowed for a rule.flush command
to make sure that the hash table is resized.keep-state rules on TCP sessions. A keepalive is
generated to both sides of the connection every 5 seconds for the last 20
seconds of the lifetime of the rule.dummynet
pipe or from
ng_ipfw(4) node is not
passed though the firewall again. Otherwise, after an action, the packet
is reinjected into the firewall at the next rule.ipfw. Default is no.ipfw. Default is no.ipfw_nat64
module.ipfw_nat64
module:
0ipfw twice. First time
an original packet is handled by ipfw and
consumed by ipfw_nat64 translator. Then
translated packet is queued via netisr to input processing again.1ipfw only once, and
after translation it will be pushed directly to outgoing
interface.There are some commands that may be useful to understand current state of certain subsystems inside kernel module. These commands provide debugging output which may change without notice.
Currently the following commands are available as
internal sub-options:
There are far too many possible uses of
ipfw so this Section will only give a small set of
examples.
This command adds an entry which denies all tcp packets from cracker.evil.org to the telnet port of wolf.tambov.su from being forwarded by the host:
ipfw add deny tcp from
cracker.evil.org to wolf.tambov.su telnetThis one disallows any connection from the entire cracker's network to my host:
ipfw add deny ip from 123.45.67.0/24
to my.host.orgA first and efficient way to limit access (not using dynamic rules) is the use of the following rules:
ipfw add allow tcp from any to any
establishedipfw add allow tcp from net1
portlist1 to net2 portlist2 setupipfw add allow tcp from net3
portlist3 to net3 portlist3 setup...ipfw add deny tcp from any to
anyThe first rule will be a quick match for normal TCP packets, but
it will not match the initial SYN packet, which will be matched by the
setup rules only for selected source/destination
pairs. All other SYN packets will be rejected by the final
deny rule.
If you administer one or more subnets, you can take advantage of the address sets and or-blocks and write extremely compact rulesets which selectively enable services to blocks of clients, as below:
goodguys="{
10.1.2.0/24{20,35,66,18} or 10.2.3.0/28{6,3,11} }"badguys="10.1.2.0/24{8,38,60}"ipfw add allow ip from ${goodguys} to
anyipfw add deny ip from ${badguys} to
any... normal policies ...Allow any transit packets coming from single vlan 10 and going out to vlans 100-1000:
ipfw add 10 allow out recv vlan10
\{ xmit vlan1000 or xmit
"vlan[1-9]??" }The verrevpath option could be used to do
automated anti-spoofing by adding the following to the top of a ruleset:
ipfw add deny ip from any to any not
verrevpath inThis rule drops all incoming packets that appear to be coming to the system on the wrong interface. For example, a packet with a source address belonging to a host on a protected internal network would be dropped if it tried to enter the system from an external interface.
The antispoof option could be used to do
similar but more restricted anti-spoofing by adding the following to the top
of a ruleset:
ipfw add deny ip from any to any not
antispoof inThis rule drops all incoming packets that appear to be coming from
another directly connected system but on the wrong interface. For example, a
packet with a source address of 192.168.0.0/24,
configured on fxp0, but coming in on
fxp1 would be dropped.
The setdscp option could be used to
(re)mark user traffic, by adding the following to the appropriate place in
ruleset:
ipfw add setdscp be ip from any to
any dscp af11,af21If your network has network traffic analyzer connected to your host directly via dedicated interface or remotely via RSPAN vlan, you can selectively mirror some Ethernet layer2 frames to the analyzer.
First, make sure your firewall is already configured and runs. Then, enable layer2 processing if not already enabled:
sysctl
net.link.ether.ipfw=1Next, load needed additional kernel modules:
kldload ng_ether ng_ipfwOptionally, make system load these modules automatically at startup:
sysrc kld_list+="ng_ether
ng_ipfw"Next, configure ng_ipfw(4) kernel module to transmit mirrored copies of layer2 frames out via vlan900 interface:
ngctl connect ipfw: vlan900: 1
lowerThink of "1" here as of "mirroring instance index" and vlan900 is its destination. You can have arbitrary number of instances. Refer to ng_ipfw(4) for details.
At last, actually start mirroring of selected frames using "instance 1". For frames incoming from em0 interface:
ipfw add ngtee 1 ip from any to
192.168.0.1 layer2 in recv em0For frames outgoing to em0 interface:
ipfw add ngtee 1 ip from any to
192.168.0.1 layer2 out xmit em0For both incoming and outgoing frames while flowing through em0:
ipfw add ngtee 1 ip from any to
192.168.0.1 layer2 via em0Make sure you do not perform mirroring for already duplicated frames or kernel may hang as there is no safety net.
In order to protect a site from flood attacks involving fake TCP packets, it is safer to use dynamic rules:
ipfw add check-stateipfw add deny tcp from any to any
establishedipfw add allow tcp from my-net to any
setup keep-stateThis will let the firewall install dynamic rules only for those
connection which start with a regular SYN packet coming from the inside of
our network. Dynamic rules are checked when encountering the first
occurrence of a check-state,
keep-state or limit rule. A
check-state rule should usually be placed near the
beginning of the ruleset to minimize the amount of work scanning the
ruleset. Your mileage may vary.
For more complex scenarios with dynamic rules
record-state and
defer-action can be used to precisely control
creation and checking of dynamic rules. Example of usage of these options
are provided in
NETWORK ADDRESS
TRANSLATION (NAT) Section.
To limit the number of connections a user can open you can use the following type of rules:
ipfw add allow tcp from my-net/24 to
any setup limit src-addr 10ipfw add allow tcp from any to me
setup limit src-addr 4The former (assuming it runs on a gateway) will allow each host on a /24 network to open at most 10 TCP connections. The latter can be placed on a server to make sure that a single client does not use more than 4 simultaneous connections.
BEWARE: stateful rules can be subject to denial-of-service attacks by a SYN-flood which opens a huge number of dynamic rules. The effects of such attacks can be partially limited by acting on a set of sysctl(8) variables which control the operation of the firewall.
Here is a good usage of the list command
to see accounting records and timestamp information:
ipfw -at listor in short form without timestamps:
ipfw -a listwhich is equivalent to:
ipfw showNext rule diverts all incoming packets from 192.168.2.0/24 to divert port 5000:
ipfw divert 5000 ip from
192.168.2.0/24 to any inThe following rules show some of the applications of
ipfw and dummynet for
simulations and the like.
This rule drops random incoming packets with a probability of 5%:
ipfw add prob 0.05 deny ip from any
to any inA similar effect can be achieved making use of
dummynet pipes:
dnctl add pipe 10 ip from any to
anydnctl pipe 10 config plr
0.05We can use pipes to artificially limit bandwidth, e.g. on a machine acting as a router, if we want to limit traffic from local clients on 192.168.2.0/24 we do:
ipfw add pipe 1 ip from
192.168.2.0/24 to any outdnctl pipe 1 config bw 300Kbit/s
queue 50KBytesnote that we use the out modifier so that
the rule is not used twice. Remember in fact that
ipfw rules are checked both on incoming and outgoing
packets.
Should we want to simulate a bidirectional link with bandwidth limitations, the correct way is the following:
ipfw add pipe 1 ip from any to any
outipfw add pipe 2 ip from any to any
indnctl pipe 1 config bw 64Kbit/s queue
10Kbytesdnctl pipe 2 config bw 64Kbit/s queue
10KbytesThe above can be very useful, e.g. if you want to see how your fancy Web page will look for a residential user who is connected only through a slow link. You should not use only one pipe for both directions, unless you want to simulate a half-duplex medium (e.g. AppleTalk, Ethernet, IRDA). It is not necessary that both pipes have the same configuration, so we can also simulate asymmetric links.
Should we want to verify network performance with the RED queue management algorithm:
ipfw add pipe 1 ip from any to
anydnctl pipe 1 config bw 500Kbit/s
queue 100 red 0.002/30/80/0.1Another typical application of the traffic shaper is to introduce some delay in the communication. This can significantly affect applications which do a lot of Remote Procedure Calls, and where the round-trip-time of the connection often becomes a limiting factor much more than bandwidth:
ipfw add pipe 1 ip from any to any
outipfw add pipe 2 ip from any to any
indnctl pipe 1 config delay 250ms bw
1Mbit/sdnctl pipe 2 config delay 250ms bw
1Mbit/sPer-flow queueing can be useful for a variety of purposes. A very simple one is counting traffic:
ipfw add pipe 1 tcp from any to
anyipfw add pipe 1 udp from any to
anyipfw add pipe 1 ip from any to
anydnctl pipe 1 config mask
allThe above set of rules will create queues (and collect statistics)
for all traffic. Because the pipes have no limitations, the only effect is
collecting statistics. Note that we need 3 rules, not just the last one,
because when ipfw tries to match IP packets it will
not consider ports, so we would not see connections on separate ports as
different ones.
A more sophisticated example is limiting the outbound traffic on a net with per-host limits, rather than per-network limits:
ipfw add pipe 1 ip from
192.168.2.0/24 to any outipfw add pipe 2 ip from any to
192.168.2.0/24 indnctl pipe 1 config mask src-ip
0x000000ff bw 200Kbit/s queue 20Kbytesdnctl pipe 2 config mask dst-ip
0x000000ff bw 200Kbit/s queue 20KbytesIn the following example, we need to create several traffic bandwidth classes and we need different hosts/networks to fall into different classes. We create one pipe for each class and configure them accordingly. Then we create a single table and fill it with IP subnets and addresses. For each subnet/host we set the argument equal to the number of the pipe that it should use. Then we classify traffic using a single rule:
dnctl pipe 1 config bw
1000Kbyte/sdnctl pipe 4 config bw
4000Kbyte/s...ipfw table T1 create type
addripfw table T1 add 192.168.2.0/24
1ipfw table T1 add 192.168.0.0/27
4ipfw table T1 add 192.168.0.2
1...ipfw add pipe tablearg ip from
'table(T1)' to anyUsing the fwd action, the table entries
may include hostnames and IP addresses.
ipfw table T2 create type addr
valtype ipv4ipfw table T2 add 192.168.2.0/24
10.23.2.1ipfw table T2 add 192.168.0.0/27
router1.dmz...ipfw add 100 fwd tablearg ip from any
to 'table(T2)'In the following example per-interface firewall is created:
ipfw table IN create type iface
valtype skipto,fibipfw table IN add vlan20
12000,12ipfw table IN add vlan30
13000,13ipfw table OUT create type iface
valtype skiptoipfw table OUT add vlan20
22000ipfw table OUT add vlan30
23000..ipfw add 100 setfib tablearg ip from
any to any recv 'table(IN)' inipfw add 200 skipto tablearg ip from
any to any recv 'table(IN)' inipfw add 300 skipto tablearg ip from
any to any xmit 'table(OUT)' outThe following example illustrate usage of flow tables:
ipfw table fl create type
flow:src-ip,proto,dst-ip,dst-portipfw table fl add
2a02:6b8:77::88,tcp,2a02:6b8:77::99,80 11ipfw table fl add
10.0.0.1,udp,10.0.0.2,53 12..ipfw add 100 allow ip from any to any
flow 'table(fl,11)' recv ix0To add a set of rules atomically, e.g. set 18:
ipfw set disable 18ipfw add NN set 18 ... # repeat as
neededipfw set enable 18To delete a set of rules atomically the command is simply:
ipfw delete set 18To test a ruleset and disable it and regain control if something goes wrong:
ipfw set disable 18ipfw add NN set 18 ... # repeat as
neededipfw set enable 18; echo done; sleep
30 && ipfw set disable 18Here if everything goes well, you press control-C before the "sleep" terminates, and your ruleset will be left active. Otherwise, e.g. if you cannot access your box, the ruleset will be disabled after the sleep terminates thus restoring the previous situation.
To show rules of the specific set:
ipfw set 18 showTo show rules of the disabled set:
ipfw -S set 18 showTo clear a specific rule counters of the specific set:
ipfw set 18 zero NNTo delete a specific rule of the specific set:
ipfw set 18 delete NNFirst redirect all the traffic to nat instance 123:
ipfw add nat 123 all from any to
anyThen to configure nat instance 123 to alias all the outgoing traffic with ip 192.168.0.123, blocking all incoming connections, trying to keep same ports on both sides, clearing aliasing table on address change and keeping a log of traffic/link statistics:
ipfw nat 123 config ip 192.168.0.123
log deny_in reset same_portsOr to change address of instance 123, aliasing table will be cleared (see reset option):
ipfw nat 123 config ip
10.0.0.1To see configuration of nat instance 123:
ipfw nat 123 show configTo show logs of all the instances in range 111-999:
ipfw nat 111-999 showTo see configurations of all instances:
ipfw nat show configOr a redirect rule with mixed modes could looks like:
ipfw nat 123 config redirect_addr 10.0.0.1 10.0.0.66 redirect_port tcp 192.168.0.1:80 500 redirect_proto udp 192.168.1.43 192.168.1.1 redirect_addr 192.168.0.10,192.168.0.11 10.0.0.100 # LSNAT redirect_port tcp 192.168.0.1:80,192.168.0.10:22 500 # LSNAT
or it could be split in:
ipfw nat 1 config redirect_addr 10.0.0.1 10.0.0.66 ipfw nat 2 config redirect_port tcp 192.168.0.1:80 500 ipfw nat 3 config redirect_proto udp 192.168.1.43 192.168.1.1 ipfw nat 4 config redirect_addr 192.168.0.10,192.168.0.11,192.168.0.12 10.0.0.100 ipfw nat 5 config redirect_port tcp 192.168.0.1:80,192.168.0.10:22,192.168.0.20:25 500
Sometimes you may want to mix NAT and dynamic rules. It could be
achieved with record-state and
defer-action options. Problem is, you need to create
dynamic rule before NAT and check it after NAT actions (or vice versa) to
have consistent addresses and ports. Rule with
keep-state option will trigger activation of
existing dynamic state, and action of such rule will be performed as soon as
rule is matched. In case of NAT and allow rule
packet need to be passed to NAT, not allowed as soon is possible.
There is example of set of rules to achieve this. Bear in mind that this is example only and it is not very useful by itself.
On way out, after all checks place this rules:
ipfw add allow record-state
skip-actionipfw add nat 1And on way in there should be something like this:
ipfw add nat 1ipfw add check-statePlease note, that first rule on way out doesn't allow packet and
doesn't execute existing dynamic rules. All it does, create new dynamic rule
with allow action, if it is not created yet. Later,
this dynamic rule is used on way in by check-state
rule.
codel and pie AQM
can be configured for dummynet
pipe or queue.
To configure a pipe with
codel AQM using default configuration for traffic
from 192.168.0.0/24 and 1Mbits/s rate limit, we do:
dnctl pipe 1 config bw 1mbits/s
codelipfw add 100 pipe 1 ip from
192.168.0.0/24 to anyTo configure a queue with
codel AQM using different configurations parameters
for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:
dnctl pipe 1 config bw
1mbits/sdnctl queue 1 config pipe 1 codel
target 8ms interval 160ms ecnipfw add 100 queue 1 ip from
192.168.0.0/24 to anyTo configure a pipe with
pie AQM using default configuration for traffic from
192.168.0.0/24 and 1Mbits/s rate limit, we do:
dnctl pipe 1 config bw 1mbits/s
pieipfw add 100 pipe 1 ip from
192.168.0.0/24 to anyTo configure a queue with
pie AQM using different configuration parameters for
traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we do:
dnctl pipe 1 config bw
1mbits/sdnctl queue 1 config pipe 1 pie
target 20ms tupdate 30ms ecnipfw add 100 queue 1 ip from
192.168.0.0/24 to anyfq_codel and
fq_pie AQM can be configured for
dummynet schedulers.
To configure fq_codel scheduler using
different configurations parameters for traffic from 192.168.0.0/24 and
1Mbits/s rate limit, we do:
dnctl pipe 1 config bw
1mbits/sdnctl sched 1 config pipe 1 type
fq_codeldnctl queue 1 config sched
1ipfw add 100 queue 1 ip from
192.168.0.0/24 to anyTo change fq_codel default configuration
for a sched such as disable ECN and change the
target to 10ms, we do:
dnctl sched 1 config pipe 1 type
fq_codel target 10ms noecnSimilar to fq_codel, to configure
fq_pie scheduler using different configurations
parameters for traffic from 192.168.0.0/24 and 1Mbits/s rate limit, we
do:
dnctl pipe 1 config bw
1mbits/sdnctl sched 1 config pipe 1 type
fq_piednctl queue 1 config sched
1ipfw add 100 queue 1 ip from
192.168.0.0/24 to anyThe configurations of fq_pie
sched can be changed in a similar way as for
fq_codel
cpp(1), m4(1), fnmatch(3), altq(4), divert(4), dummynet(4), if_bridge(4), ip(4), ipfirewall(4), ng_ether(4), ng_ipfw(4), protocols(5), services(5), init(8), kldload(8), reboot(8), sysctl(8), syslogd(8), sysrc(8)
The ipfw utility first appeared in
FreeBSD 2.0. dummynet was
introduced in FreeBSD 2.2.8. Stateful extensions
were introduced in FreeBSD 4.0.
ipfw2 was introduced in Summer 2002.
Ugen J. S. Antsilevich,
Poul-Henning Kamp,
Alex Nash,
Archie Cobbs,
Luigi Rizzo,
Rasool Al-Saadi.
API based upon code written by Daniel Boulet for BSDI.
Dummynet has been introduced by Luigi Rizzo in 1997-1998.
Some early work (1999-2000) on the
dummynet traffic shaper supported by Akamba
Corp.
The ipfw core (ipfw2) has been completely redesigned and reimplemented by Luigi Rizzo in summer 2002. Further actions and options have been added by various developers over the years.
In-kernel NAT support written by Paolo Pisati <piso@FreeBSD.org> as part of a Summer of Code 2005 project.
SCTP nat support has been developed by
The Centre for Advanced Internet Architectures
(CAIA) ⟨http://www.caia.swin.edu.au⟩. The primary
developers and maintainers are David Hayes and Jason But. For further
information visit:
⟨http://www.caia.swin.edu.au/urp/SONATA⟩
Delay profiles have been developed by Alessandro Cerri and Luigi Rizzo, supported by the European Commission within Projects Onelab and Onelab2.
CoDel, PIE, FQ-CoDel and FQ-PIE AQM for Dummynet have been implemented by The Centre for Advanced Internet Architectures (CAIA) in 2016, supported by The Comcast Innovation Fund. The primary developer is Rasool Al-Saadi.
The syntax has grown over the years and sometimes it might be confusing. Unfortunately, backward compatibility prevents cleaning up mistakes made in the definition of the syntax.
Misconfiguring the firewall can put your computer in an unusable state, possibly shutting down network services and requiring console access to regain control of it.
Incoming packet fragments diverted by
divert are reassembled before delivery to the
socket. The action used on those packet is the one from the rule which
matches the first fragment of the packet.
Packets diverted to userland, and then reinserted by a userland
process may lose various packet attributes. The packet source interface name
will be preserved if it is shorter than 8 bytes and the userland process
saves and reuses the sockaddr_in (as does
natd(8)); otherwise, it may
be lost. If a packet is reinserted in this manner, later rules may be
incorrectly applied, making the order of divert
rules in the rule sequence very important.
Dummynet drops all packets with IPv6 link-local addresses.
Rules using uid or
gid may not behave as expected. In particular,
incoming SYN packets may have no uid or gid associated with them since they
do not yet belong to a TCP connection, and the uid/gid associated with a
packet may not be as expected if the associated process calls
setuid(2) or similar
system calls.
Rule syntax is subject to the command line environment and some patterns may need to be escaped with the backslash character or quoted appropriately.
Due to the architecture of libalias(3), ipfw nat is not compatible with the TCP segmentation offloading (TSO). Thus, to reliably nat your network traffic, please disable TSO on your NICs using ifconfig(8).
ICMP error messages are not implicitly matched by dynamic rules for the respective conversations. To avoid failures of network error detection and path MTU discovery, ICMP error messages may need to be allowed explicitly through static rules.
Rules using call and
return actions may lead to confusing behaviour if
ruleset has mistakes, and/or interaction with other subsystems (netgraph,
dummynet, etc.) is used. One possible case for this is packet leaving
ipfw in subroutine on the input pass, while later on
output encountering unpaired return first. As the
call stack is kept intact after input pass, packet will suddenly return to
the rule number used on input pass, not on output one. Order of processing
should be checked carefully to avoid such mistakes.
| April 25, 2023 | midnightbsd-3.1 |