Assuming the the IP_Address:size blocks are the hash values (say, you were keying off of a connection ID, or something), then you could do something like:

my %counts;
my %sizes;
for (values %inhash) {
  my ($ip, $size) = split /:/;
  next unless defined $ip;
  $counts{$ip}++; 
  $sizes($ip)+= $size;
}

for $ip (keys $counts) {
  my ($count, $size) = ($counts{$ip},$sizes{$ip};
  print "IP Address $ip appeared $count times, for a total size of $si
+ze\n";
}
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