Ttyjfyk

I have a log file that lists whitelisted IP ranges in this manner:

"217.29.0.0-217.29.255.255",
"204.12.0.0-204.12.255.255",
"198.54.223.0-198.54.223.255",

I am also working on a bash script which, amongst other things, needs to check this logfile and determine if a specified IP is whitelisted.

In the case of IP 204.12.5.10, for instance, how would I use the log file with the specified ranges to determine whether that IP is part of a range in that file?

The useful thing to remember with IP addresses is that they're actually just representations of a 32bit number.

So you can convert them to a decimal by multiplying the octets as base 256.

E.g.:

217.29.0.0 == 216 * 256 ^ 3 + 29 * 256 ^2 + 0 * 256 ^1 + 0 * 256 ^ 0
 == 3640655872

So given a range like the above - first convert them both, such that you've got a start and end. Then compare any incoming IPs to see if they 'fit'.

So something like this (illustrating algorithm):

#!/usr/bin/env perl
use strict;
use warnings;

my $ip_to_check = "204.12.5.10";
my $dword = 0;
for ( split( '.', $ip_to_check ) ) $dword *= 256; $dword += $_ 
print "Checking $dwordn";

while (<DATA>) 
 my ( $start, $finish ) = m/([d.]+)/g;
 my $start_dword = 0;
 for ( split '.', $start ) $start_dword *= 256; $start_dword += $_ 
 my $end_dword = 0;
 for ( split '.', $finish ) $end_dword *= 256; $end_dword += $_ 
 print "Range:n";
 print "t$start t=> $start_dwordn";
 print "t$finish t=> $end_dwordn";

 print "$ip_to_check is in $_n" if $dword >= $start_dword and $dword <= $end_dword;


__DATA__
"217.29.0.0-217.29.255.255",
"204.12.0.0-204.12.255.255",
"198.54.223.0-198.54.223.255",

Could quite easily do that as a 'check script' - by reading a file (rather than DATA) and getting $ip_to_check from STDIN).

(note - as pure perl could be turned into a one liner fairly easily, or a script to call. Or re-written - I daresay you could do this with expr easily enough).

Here's an awk version:

want=204.12.77.5
awk -v want=$want -F- '
function canon(ip)
 split(" "ip,x,/[^0-9]+/)
 return sprintf("%03d%03d%03d%03d",x[2],x[3],x[4],x[5])

BEGIN val = canon(want) 
 low = canon($1); high = canon($2);
 if(val>=low && val<=high)print "in range " $0
' mylogfile

The function canon takes an ip address, splits out the number fields,
then extends each to 3 digits and returns the string.
It is called for the 2 values on each line, and these are
compared with the wanted ip address (set at the start), which
has also been "canonified".