ip6fw(8)

NAME

ip6fw - controlling utility for IPv6 firewall

SYNOPSIS

ip6fw [-nq]  [-p  preproc  [-D  macro[=value]]  [-U  macro]]
pathname
ip6fw [-n] [-f | -q] flush
ip6fw [-nq] zero [number ...]
ip6fw [-n] delete number ...
ip6fw [-aftN] list [number ...]
ip6fw [-ftN] show [number ...]
ip6fw [-nq] add [number] action [log] proto from src to dst
      [via name | ipv6no] [options]

DESCRIPTION

To ease configuration, rules can be put into a file which is

processed
using ip6fw as shown in the first synopsis line. An abso

lute pathname
must be used. The file will be read line by line and ap

plied as arguments to the ip6fw utility.

Optionally, a preprocessor can be specified using -p preproc

where
pathname is to be piped through. Useful preprocessors in

clude 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 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 coun

ters, a packet
count and a byte count. These counters are updated when a

packet matches
the rule.

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
number.

The flush operation removes all rules.

Any command beginning with a `#', or being all blank, is ig

nored.

One rule is always present:

65535 deny all from any to any

This rule is the default policy, i.e., do not 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 Do not ask for confirmation for commands that can

cause problems if

misused (ie; flush). Note, if there is no tty associ

ated with the
process, this is implied.

-n Only check syntax of the command strings, without ac

tually passing

them into the kernel.

-q While adding, zeroing or flushing, be quiet about ac

tions (implies

'-f'). This is useful for adjusting rules by execut

ing multiple
ip6fw commands in a script (e.g. sh /etc/rc.firewall),

or by processing a file of many ip6fw rules, across a remote

login session.
If a flush is performed in normal (verbose) mode, it

prints a message. Because all rules are flushed, the message can

not be delivered 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.

action:

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

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_VER

BOSE_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. Log

ging may then
be re-enabled by clearing the packet counter for that entry.

The syslogd(8) logging and the default log limit are ad

justable dynamically through the sysctl(8) interface.

proto:

ipv6 All packets match. The alias all has

the same

effect.

tcp Only TCP packets match.

udp Only UDP packets match.

ipv6-icmp Only ICMPv6 packets match.

<number|name> Only packets for the specified proto

col matches

(see /etc/protocols for a complete

list).

src and dst:

<address/prefixlen> [ports]

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

fec0::1:2:3:4/112.

The sense of the match can be inverted by preceding an ad

dress 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 speci

fied as:

{port|port-port}[,port[,...]]

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 ports.

Fragmented packets which have a non-zero offset (i.e., not

the first
fragment) will never match a rule which has one or more port

specifications. See the frag option for details on matching frag

mented packets.

Rules can apply to packets when they are incoming, or outgo

ing, or both.
The in keyword indicates the rule should only match incoming

packets.
The out keyword indicates the rule should only match outgo

ing packets.

To match packets going through a certain interface, specify

the interface
using via:

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 in

terface.

via ipv6no Packet must be going through the in

terface 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 trans

mit interface
(respectively) is checked. By specifying both, it is possi

ble 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 out

going packets,
while the xmit interface can only be tested on outgoing

packets. So out
is required (and in invalid) whenever xmit is used. Speci

fying via
together with xmit or recv is invalid.

A packet may not have a receive or transmit interface: pack

ets originating from the local host have no receive interface, while

packets destined
for the local host have no transmit interface.

Additional options:

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 supported 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 supported 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 frag

mented packets.

icmptypes types Matches if the ICMPv6 type is in the

list types.

The list may be specified as any com

bination of
ranges or individual types separated

by commas.

CHECKLIST

Here are some important points to consider when designing

your rules:

+o Remember that you filter both packets going in and

out. Most

connections need packets going in both directions.

+o Remember to test very carefully. It is a good idea

to be near

the console when doing this.

+o Do not forget the loopback interface.

FINE POINTS

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 fire

walls.

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 ip6fw &&

ip6fw add 32000 allow all from any to any

Along the same lines, doing an

ip6fw flush

in similar surroundings is also a bad idea.

PACKET DIVERSION

not supported.

EXAMPLES

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.tam

bov.su 23

This one disallows any connection from the entire hackers

network to my
host:

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
timestamp information:

ip6fw -at l

or in short form without timestamps:

ip6fw -a l

SEE ALSO

ip(4), ipfirewall(4), protocols(5), services(5), reboot(8),

sysctl(8),
syslogd(8)

HISTORY

A ip6fw utility first appeared in FreeBSD 4.0.

AUTHORS

Ugen J. S. Antsilevich,
Poul-Henning Kamp,
Alex Nash,
Archie Cobbs.

API based upon code written by Daniel Boulet for BSDI.

BUGS

WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!

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 do not understand.

When manipulating/adding chain entries, service and protocol

names are
not accepted.

BSD March 13, 2000

BSD