Information Technology Grimoire

Version .0.0.1

IT Notes from various projects because I forget, and hopefully they help you too.

Use Perl to Match IP to Subnets

In the case that you have many IP addresses in your logs and don’t know what networks they belong to, you can easily map them using Perl.

  • You must have a database of networks to match against
  • You must have a list of IP to search in the database of networks
  • use NetAddr::IP module to help you do the heavy lifting
  • Term::ANSIcolor and Win32::Console::ANSI colorize stuff
  • Create a subroutine to convert between dotted dash format and decimal (for sorting)
  • Then loop over all of your ips and see where they fit!

Custom Perl Programming can solve tedious work like this in seconds without the risk of errors. This particular snippet was written to parse millions of IP addresses against a few thousand known networks. What will you use our Perl script that matches IP to subnets script for? Please comment if it’s helped you.

Here is the script that uses Perl to match IP addresses to subnets:

{% raw %} #!/usr/bin/perl

use warnings;
use strict;
use NetAddr::IP;

# Term::ANSIColor doesn't work on windows without Win32 Console
if( $^O eq 'MSWin32' ){{
  eval { require Win32::Console::ANSI; } or last;
use Term::ANSIColor;			# I like colors
use Benchmark;					# in case we need to optimize

# start timer
my $t0 = new Benchmark;

# the database of networks we know of
my %nets = (
'' => 'CORP WAN',
'' => 'VLAN 388 - DMZ Servers',
'' => 'VLAN 400 - Guest Wireless',

my %data;		# will contain deduped ips
my %unknowns;	# if we want to see the unknown IP, deduped
my $unknowns	= 0;	# contains unknown Ips
my $lines 		= 0;	# just a counter

# this sub converts a decimal IP to a dotted IP
sub dec2ip ($) { join '.', unpack 'C4', pack 'N', shift; }

# this sub converts a dotted IP to a decimal IP
sub ip2dec ($) { unpack N => pack CCCC => split /\./ => shift; }

	# build unique list from __DATA__
	while (<data>) {

		# tested: finds multiple (all on each line)
		if (m/([0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}[\/-][0-9]{1,2}|[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})/g) {
			my $ip = $1;
			chomp $ip;
			$ip = ip2dec($ip);

print color ('yellow'), "
 IP to Net Mapper
Mapping $lines IP to Known Networks...

GIVEN IP\tFITS IN THIS NETWORK\n", color("reset");

	# build  network only map from input side.
	foreach my $ips (sort keys %data){
		my $found = 0;

		# build ip object
		my $ip = NetAddr::IP->new($ips);
		$ips = dec2ip($ips);

		# loop over data hash and check every key to see where it fits
		# FIXME: what happens if it fits in an overlap?
		foreach my $cidr (keys %nets) {

			# define net object
			my $network  = NetAddr::IP->new($cidr);
			if ($ip->within($network)) {

				print color ('green'),"$ips\t$cidr ($nets{$cidr})\n", color('reset');

		# these ips were not found, so... handle
		unless ($found) {
			#print "$ips\tUNKNOWN NETWORK\n";

# we want a list to munge and parse later, give it to us
my $unique_ip = keys %data;
	if ($unknowns) {
		foreach my $unknown (sort keys %unknowns) {
		print color('red'),"$unknown\t0.0.0.0 (UNKNOWN)\n", color('reset');

# print stats:
print color ('yellow'),"
     INPUT: $lines
 UNIQUE IP: $unique_ip
UNKNOWN IP: $unknowns

my $t1 = new Benchmark; my $td = timediff($t1,$t0);
print "\ntook '",timestr($td), "' seconds\n", color("reset");

# sample data

{% endraw %}

Last updated on 9 Oct 2018
Published on 9 Oct 2018