IPChains(3)

NAME
IPChains - Create and Manipulate ipchains via Perl

SYNOPSIS
use IPChains;

$fw = IPChains->new(-option => value, ... ); $fw->append('chain');

DESCRIPTION
This module acts as an interface to the ipchains(8) userspace utility by Paul "Rusty" Russell (http://www.rustcorp.com/linux/ipchains/). It attempts to include all the functionality of the original code with a simplified user interface via Perl. In addition, plans for log parsing facilities, an integrated interface to ipmasqadm, and possibly traffic shaping are slated for up and coming versions.

The new() and attribute() methods support the following options: Specifies origination address of packet. Appending hostmask to this address using a / is OK, as well as specifying it separately (see SourceMask). Hostmask for origination address. Can either be in 24 or 255.255.255.0 style. Specific port or port range (use xxx:xxx to denote range), requires specific protocol specification. Specifies destination address of packet. Appending hostmask to this address using a / is OK, as well as specifying it separately (see DestMask) Destination address, (see SourceMask). Destination Port, (see SourcePort). Protocol. Can be tcp, udp, icmp, or all. Required for specifying specific port(s). ICMP Name/Code (in place of port when ICMP is specified as protocol).

Here is a small table of some of the most common ICMP packets:

       Number  Name                     Required by
       0       echo-reply               ping
       3       destination-unreachable  Any TCP/UDP traffic.
       5       redirect                 routing if not running
                                        routing daemon
       8       echo-request             ping
       11      time-exceeded            traceroute
Target. Can be ACCEPT, DENY, REJECT, MASQ, REDIRECT, RETURN, or a user-defined chain. Note: This is case sensitive. Specify a specify interface as part of the criteria (ie, eth0, ppp0, etc.). Rule only refers to second and further fragments of fragmented packets (1 or 0). Makes criteria effective in both directions (1 or 0). Set verbose option for setting rules or list() (1 or 0). Show output from list() in numeric format. No DNS lookups, etc.. (1 or 0). Enable kernel logging (via syslog, kern.info) of matched packets (1 or 0). Copy matching packets to the userspace device (advanced). Mark matching packets with specified number (advanced). Used for modifying the TOS field in the IP header. Takes 2 args, AND and XOR masks, (ie, (TOS => ["0x01", "0x10"])). This feature is highly untested.

The first mask is ANDed with the packet's current TOS, and the second mask is XORed with it. Use the following table for reference:

       TOS Name                Value           Typical Uses
       Minimum Delay           0x01 0x10       ftp, telnet
       Maximum Throughput      0x01 0x08       ftp-data
       Maximum Reliability     0x01 0x04       snmp
       Minimum Cost            0x01 0x02       nntp

Display exact numbers in byte counters instead of numbers rounded in K's, M's, or G's (1 or 0). Only match TCP packets with the SYN bit set and the ACK and FIN bits cleared (1 or 0).

METHODS
The following methods are available to you: $fw = IPChains->new(option => value, ...) create new fw object with options $fw->attribute(option, value) to set option to value, OR $value = $obj->attribute(option) to get current value of option. $fw->clopts() clears all option settings (do this before calling methods like list(), flush(), delete(), etc. that take only a few specific options). $fw->append(chain) appends current rule to end of chain $fw->insert(chain, rulenum) inserts rule at position rulenum in chain. If rulenum is omitted 1 is assumed. $fw->replace(chain, rulenum) replace rule at rulenum in chain with current rule. $fw->delete(chain, rulenum) deletes rule rulenum from chain. $fw->check(chain) check given packet against chain for testing. $fw->flush(chain) deletes all rules from chain. $fw->list(chain) lists all rules defined for chain. $fw->zero(chain) zero's all packet counters for chain. Cannot zero counters for chain policy. $fw->masq() lists current masqueraded connections. $fw->new_chain(chain) creates new user defined chain. $fw->del_chain(chain) delete user defined chain. $fw->set_policy(chain) set default policy for chain. Takes Rule option only.

EXAMPLES
To set the default policy for the "forward" chain to DENY:

 use IPChains;
 $fw = IPChains->new(Rule => "DENY");
 $fw->set_policy("forward");
To list current rules in "input" chain to stdout (without parsing through /proc/net/ip_fw*):

 use IPChains;
 $fw = IPChains->new(Verbose => 1);
 $fw->list("input");
To create a rule that would allow all traffic on an internal lan, and deny all tcp traffic from external hosts on relevant ports, and log it,you could use something like:

 use IPChains;
 $internal = IPChains->new(Source    => "192.168.100.0/24",
                           Rule      => "ACCEPT",
                           Interface => "eth0");
 $external = IPChains->new(Interface => "ppp0",
                           Prot      => "tcp",
                           DestPort  => "0:1024",
                           Log       => 1);
 $internal->append("input");
 $external->append("input");
You could also create one object, set up the attributes, append() it, then use clopts() to clear it's options, then use attribute() to individually specify it's next set of options, then append() it again with the new rule. See the examples/ subdirectory in the IPChains.pm source for more examples.

BUGS
Much of this is highly untested. Masquerading timeout setting and negative attributes (!) aren't yet implemented. Much of what's planned to be done hasn't been yet. This is to be considered nothing more than an early beta to work out bugs in the basic code, and get feedback on usefulness and improvements that could be made.

AUTHOR
Jessica Hutchison (j@splatlabs.com). Please feel free to email me with feedback, questions, or comments (or indeed patches/additions).

COPYRIGHT
This package is free software; you can redistribute it and/or modify it under the same terms as Perl itself, with the exception of the libipfwc.c, ipchains.c, and the files in include/ which have separate terms derived from those of the original ipchains sources. See COPYING for details of this license. Please see README.ipchains for the README that was included with the original source code for ipchains and contains copyrights and credits for such.