Re^2: Generating a List of numbers

You are not chomping $OuterData. Therefore, it contains a newline at the end which prevents it from matching in the regular expression.
Update: Looping over the file several times makes your algorithm very slow if the file is big. Using a hash, you can avoid this problem:

#!/usr/bin/perl

use warnings;
use strict;

my $tmpipaccountingfile    = "tmpipaccountingfile";
my $DestDevice = "Box";

my %data;

open my $TMPIPACCOUNTINGFILE, "<", "$tmpipaccountingfile" or die "$!";
while (<$TMPIPACCOUNTINGFILE>) {
    next if (/^(?:$|sh|\s*Source|^$DestDevice|Accounting)/);
    my @fields = split;
    push @{ $data{$fields[1]} }, [ @fields[0,2,3] ];
}
close $TMPIPACCOUNTINGFILE;

while (<DATA>) {
    print;
    chomp;
    for my $match (@{ $data{$_} }) {
        print join "\t", $match->[0], $_, @{$match}[1,2];
        print "\n";
    }
}

__DATA__
10.2.9.2
10.2.9.3
10.2.9.6
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