use Data::Dumper;
$Data::Dumper::Useqq = 1;

print Dumper $var;
print Dumper \@allServers;
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You might have some non-printable characters either in the server list or in $var that prevent you from getting matches.

Surprise surprise,

 
print Dumper \@allServers;
print Dumper \@bigArray;
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prints nothing; just  $VAR1 = []  print Dumper $var; correctly prints the IP present in the incoming SNMP trap. So my reading from file part is going wrong?! How? Its fairly straight forward and I have even tested it by writing  exit(0); after the read from config (populates @allServers) and write into @bigArray (<ip,server>) format. Help... :(

The easist explanation is that your open call fails. Since you don't check the return value, it does that silently.

open my $fh, '<', $configFile
   or die "Can't open '$configFile' for reading: $!";

my @allServers;

while (<$fh>) {
    push (@allServers, $_) if /^\w/;
}
close $fh or warn "Error while closing file: $!";
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Perl 6 - links to (nearly) everything that is Perl 6.

The code I gave in my last reply with hard-coded values for IP addresses, works.

truptivk: what follows is intended not as a rebuke, but for future reference. When moritz asked for example code to run, the implicit assumption was that the code would demonstrate the problem, not that it would run just fine. I may not have been the only monk who spent time trying to figure out what (nothing) was wrong with the code. (Well, maybe just a little bit of a rebuke:)

I understand, and I'm extremely sorry for taking some/many monks' time. I should've found a way to provide code that demonstrated my problem, rather than hard-code values which made it run correctly. Not to make an excuse, but I'm overwhelmed at work with lots to do, and I did the mistake. I sincerely apologise once again. Meanwhile, I'm still trying to figure out what's wrong with my code.

It might help if you posted a copy of your log file.