IPChains3pm

Usage

Overview

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:

Source

Specifies origination address of packet. Appending hostmask to this address using a / is OK, as well as specifying it separately (see SourceMask).

SourceMask

Hostmask for origination address. Can either be in 24 or 255.255.255.0 style.

SourcePort

Specific port or port range (use xxx:xxx to denote range), requires specific protocol specification.

Dest

Specifies destination address of packet. Appending hostmask to this address using a / is OK, as well as specifying it separately (see DestMask)

DestMask

Destination address, (see SourceMask).

DestPort

Destination Port, (see SourcePort).

Prot

Protocol. Can be tcp, udp, icmp, or all. Required for specifying specific port(s).

ICMP

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

Rule

Target. Can be ACCEPT, DENY, REJECT, MASQ, REDIRECT, RETURN, or a user-defined chain. Note: This is case sensitive.

Interface

Specify a specify interface as part of the criteria (ie, eth0, ppp0, etc.).

Fragment

Rule only refers to second and further fragments of fragmented packets (1 or 0).

Bidir

Makes criteria effective in both directions (1 or 0).

Verbose

Set verbose option for setting rules or list() (1 or 0).

Numeric

Show output from list() in numeric format. No DNS lookups, etc.. (1 or 0).

Log

Enable kernel logging (via syslog, kern.info) of matched packets (1 or 0).

Output

Copy matching packets to the userspace device (advanced).

Mark

Mark matching packets with specified number (advanced).

TOS

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

Exact

Display exact numbers in byte counters instead of numbers rounded in K's, M's, or G's (1 or 0).

SYN

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:

new()

$fw = IPChains->new(option => value, ...) create new fw object with options

attribute()

$fw->attribute(option, value) to set option to value, OR $value = $obj->attribute(option) to get current value of option.

clopts()

$fw->clopts() clears all option settings (do this before calling methods like list(), flush(), delete(), etc. that take only a few specific options).

append()

$fw->append(chain) appends current rule to end of chain

insert()

$fw->insert(chain, rulenum) inserts rule at position rulenum in chain. If rulenum is omitted 1 is assumed.

replace()

$fw->replace(chain, rulenum) replace rule at rulenum in chain with current rule.

delete()

$fw->delete(chain, rulenum) deletes rule rulenum from chain.

check()

$fw->check(chain) check given packet against chain for testing.

flush()

$fw->flush(chain) deletes all rules from chain.

list()

$fw->list(chain) lists all rules defined for chain.

list_chains()

$fw->list_chains() returns array with the names of all user-defined chains or undef if none exist.

zero()

$fw->zero(chain) zero's all packet counters for chain. Cannot zero counters for chain policy.

masq()

$fw->masq() lists current masqueraded connections.

new_chain()

$fw->new_chain(chain) creates new user defined chain.

del_chain()

$fw->del_chain(chain) delete user defined chain.

set_policy()

$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.