Update : as this looks like homework, change my solution to be more cryptic, and from which I'm quite sure the OP will be able to learn from :

As you say in your title, you must use a hash:

m!([\S]+)\t(\d+)(?{$hash{$1} +=$2})! while (<DATA>);
print "$_ -> $hash{$_}\n" foreach (keys %hash);
__DATA__
192.168.1    23
192.168.1    14
192.168.4    8
192.168.3    13
192.168.3    12
[download]

However, you question looks like a homework. I would be better if you provided your work so that we give you direction or better code if needed.

PS : anyone interested into a obfuscated context on this request ?