I would do something like (untested):

use autodie;
my %byte_count;
open my $fh1, "<", "TmpLookingForIPFile";
while (<$fh1>) {
    chomp;
    $byte_count{$_} = 0;
}
open my $fh2, "<", "TmpIPFile";
while (<$fh2>) {
    next if /^sh|^\s*Source|^$DestDevice|^Accounting|^^M|^$/;  # Do NO
+T end with |/ here, as it then will always match
    chomp;
    my ($dest, $bytes) = (split)[1, 3];
    $byte_count{$dest} += $bytes if exists $byte_count{$dest};
}
while (my ($ip, $bytes) = each %byte_count) {
    my_sub($ip, $bytes);
}

sub my_sub {
    ... something that uses the ip and the byte count
}
[download]