IPChains - Create and Manipulate ipchains via Perl
$fw = IPChains->new(-option => value, ... ); $fw->append('chain');
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).
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->list_chains() returns array with the names of all user-defined chains or undef if none exist.
$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.
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.
To forward all tcp traffic destined to port 80 to port 3000 instead (this is useful for transparently forwarding traffic to a cache):
use IPChains; $fw = IPChains->new(Source => "0.0.0.0/0", Destination => "0.0.0.0/0", DestPort => "80", Interface => "eth0", Rule => "REDIRECT", RedirectPort => "3000" ); $fw->append("input");
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.
Jessica Hutchison (firstname.lastname@example.org). Please feel free to email me with feedback, questions, or comments (or indeed patches/additions).
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.