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NAME

ip6fw — controlling utility for IPv6 firewall

SYNOPSIS

DESCRIPTION

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 arguments 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 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 counters, 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 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 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 cannot 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 terminates. 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 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 protocol 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 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:

{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 <net/ip6fw/ip6_fw.h>) 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 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 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 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.:

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 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 separated 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 separated 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 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.

CHECKLIST

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.

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 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 /boot/modules/ip6fw_mod.o && \
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:

This one disallows any connection from the entire hackers network to my host:

Here is a good usage of the list command to see accounting records and timestamp information:

or in short form without timestamps:

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 don't understand.

When manipulating/adding chain entries, service and protocol names are not accepted.