IP6FW(8) BSD System Manager's Manual IP6FW(8)NAMEip6fw — controlling utility for IPv6 firewall
SYNOPSISip6fw [-q] [-p preproc [-D macro[=value]] [-U macro]] pathname
ip6fw [-f | -q] flush
ip6fw [-q] zero [number ...]
ip6fw delete number ...
ip6fw [-aftN] list [number ...]
ip6fw [-ftN] show [number ...]
ip6fw [-q] add [number] action [log] proto from src to dst
[via name | ipv6no] [options]
To ease configuration, rules can be put into a file which is processed
using ip6fw as shown in the first synopsis line. An absolute pathname
must be used. The file will be read line by line and applied as argu‐
ments to the ip6fw 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 doesn't start with a slash (‘/’) as its first charac‐
ter, 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 ip6fw is being run (e.g. when they are mounted over NFS). Once -p
has been specified, optional -D and -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.
The ip6fw code works by going through the rule-list for each packet,
until a match is found. All rules have two associated counters, a packet
count and a byte count. These counters are updated when a packet matches
The rules are ordered by a “line-number” from 1 to 65534 that is used to
order and delete rules. Rules are tried in increasing order, and the
first rule that matches a packet applies. Multiple rules may share the
same number and apply in the order in which they were added.
If a rule is added without a number, it is numbered 100 higher than the
previous rule. If the highest defined rule number is greater than 65434,
new rules are appended to the last rule.
The delete operation deletes the first rule with number number, if any.
The list command prints out the current rule set.
The show command is equivalent to `ip6fw -a list'.
The zero operation zeroes the counters associated with rule number
The flush operation removes all rules.
Any command beginning with a ‘#’, or being all blank, is ignored.
One rule is always present:
65535 deny all from any to any
This rule is the default policy, i.e., don't allow anything at all. Your
job in setting up rules is to modify this policy to match your needs.
The following options are available:
-a While listing, show counter values. See also “show” command.
-f Don't ask for confirmation for commands that can cause problems if
misused (ie; flush). Note, if there is no tty associated with the
process, this is implied.
-q While adding, zeroing or flushing, be quiet about actions (implies
'-f'). This is useful for adjusting rules by executing multiple
ip6fw commands in a script (e.g. sh /etc/rc.firewall), or by pro‐
cessing a file of many ip6fw rules, across a remote login session.
If a flush is performed in normal (verbose) mode, it prints a mes‐
sage. Because all rules are flushed, the message cannot be deliv‐
ered to the login session, the login session is closed and the
remainder of the ruleset is not processed. Access to the console
is required to recover.
-t While listing, show last match timestamp.
-N Try to resolve addresses and service names in output.
allow Allow packets that match rule. The search termi‐
nates. Aliases are pass, permit, and accept.
deny Discard packets that match this rule. The search
terminates. Drop is an alias for deny.
reject (Deprecated.) Discard packets that match this rule,
and try to send an ICMPv6 host unreachable notice.
The search terminates.
unreach code Discard packets that match this rule, and try to
send an ICMPv6 unreachable notice with code code,
where code is a number from zero to 255, or one of
these aliases: noroute, admin, notneighbor, addr,
or noport, The search terminates.
reset TCP packets only. Discard packets that match this
rule, and try to send a TCP reset (RST) notice.
The search terminates (not working yet).
count Update counters for all packets that match rule.
The search continues with the next rule.
skipto number Skip all subsequent rules numbered less than
number. The search continues with the first rule
numbered number or higher.
If the kernel was compiled with IPV6FIREWALL_VERBOSE, then when a packet
matches a rule with the “log” keyword or a clear/resetlog is performed, a
message will be logged to syslogd(8), or, if that fails, to the console.
If the kernel was compiled with the IPV6FIREWALL_VERBOSE_LIMIT option,
then logging will cease after the number of packets specified by the
option are received for that particular chain entry. When this limit is
reached, the limit and rule number will be logged. Logging may then be
re-enabled by clearing the packet counter for that entry.
The syslogd(8) logging and the default log limit are adjustable dynami‐
cally through the sysctl(8) interface.
ipv6 All packets match. The alias all has the same
tcp Only TCP packets match.
udp Only UDP packets match.
ipv6-icmp Only ICMPv6 packets match.
<number|name> Only packets for the specified protocol matches
(see /etc/protocols for a complete list).
src and dst:
The <address/prefixlen> may be specified as:
ipv6no An ipv6number of the form fec0::1:2:3:4.
ipv6no/prefixlen An ipv6number with a prefix length of the form
The sense of the match can be inverted by preceding an address with the
“not” modifier, causing all other addresses to be matched instead. This
does not affect the selection of port numbers.
With the TCP and UDP protocols, optional ports may be specified as:
Service names (from /etc/services) may be used instead of numeric port
values. A range may only be specified as the first value, and the length
of the port list is limited to IPV6_FW_MAX_PORTS (as defined in
Fragmented packets which have a non-zero offset (i.e. not the first frag‐
ment) will never match a rule which has one or more port specifications.
See the frag option for details on matching fragmented packets.
Rules can apply to packets when they are incoming, or outgoing, or both.
The in keyword indicates the rule should only match incoming packets.
The out keyword indicates the rule should only match outgoing packets.
To match packets going through a certain interface, specify the interface
via ifX Packet must be going through interface ifX.
via if* Packet must be going through interface ifX, where X
is any unit number.
via any Packet must be going through some interface.
via ipv6no Packet must be going through the interface having
IPv6 address ipv6no.
The via keyword causes the interface to always be checked. If recv or
xmit is used instead of via, then the only 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.:
ip6fw add 100 deny ip from any to any out recv ed0 xmit ed1
The 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 invalid) whenever xmit is used. Specifying via
together with xmit or recv is invalid.
A packet may not have a receive or transmit interface: packets originat‐
ing from the local host have no receive interface. while packets destined
for the local host have no transmit interface.
frag Matches if the packet is a fragment and this is not
the first fragment of the datagram. frag may not
be used in conjunction with either tcpflags or
TCP/UDP port specifications.
in Matches if this packet was on the way in.
out Matches if this packet was on the way out.
ipv6options spec Matches if the IPv6 header contains the comma sepa‐
rated list of options specified in spec. The sup‐
ported IPv6 options are: hopopt (hop-by-hop options
header), route (routing header), frag (fragment
header), esp (encapsulating security payload), ah
(authentication header), nonxt (no next header),
and opts (destination options header). The absence
of a particular option may be denoted with a “!”
(not working yet).
established Matches packets that have the RST or ACK bits set.
TCP packets only.
setup Matches packets that have the SYN bit set but no
ACK bit. TCP packets only.
tcpflags spec Matches if the TCP header contains the comma sepa‐
rated list of flags specified in spec. The sup‐
ported TCP flags are: fin, 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.
icmptypes types Matches if the ICMPv6 type is in the list types.
The list may be specified as any combination of
ranges or individual types separated by commas.
Here are some important points to consider when designing your rules:
· Remember that you filter both packets going in and out. Most
connections need packets going in both directions.
· Remember to test very carefully. It is a good idea to be near
the console when doing this.
· Don't forget the loopback interface.
There is one kind of packet that the firewall will always discard, that
is an IPv6 fragment with a fragment offset of one. This is a valid
packet, but it only has one use, to try to circumvent firewalls.
If you are logged in over a network, loading the KLD version of ip6fw is
probably not as straightforward as you would think (not supported). I
recommend this command line:
kldload /modules/ip6fw_mod.o && \
ip6fw add 32000 allow all from any to any
Along the same lines, doing an
in similar surroundings is also a bad idea.
This command adds an entry which denies all tcp packets from
hacker.evil.org to the telnet port of wolf.tambov.su from being forwarded
by the host:
ip6fw add deny tcp from hacker.evil.org to wolf.tambov.su 23
This one disallows any connection from the entire hackers network to my
ip6fw add deny all from fec0::123:45:67:0/112 to my.host.org
Here is a good usage of the list command to see accounting records and
or in short form without timestamps:
SEE ALSOip(4), ipfirewall(4), protocols(5), services(5), reboot(8), sysctl(8),
This program can put your computer in rather unusable state. When using
it for the first time, work on the console of the computer, and do NOT do
anything you don't understand.
When manipulating/adding chain entries, service and protocol names are
Ugen J. S. Antsilevich,
API based upon code written by Daniel Boulet for BSDI.
A ip6fw utility first appeared in FreeBSD 4.0.
BSD March 13, 2000 BSD