This would be the simpler, less memory-intensive way:

# Scan for source/dest pairs and count hits on each dest:

$ipregex = qr/(?:\d{1,3}\.){3}\d{1,3}/;

open(CAP, "$file");

while(<CAP>)
{
  if ( /\s+($ipregex)\s+->($ipregex)\s+/ )
  {
    $dest{$2}++;
  }
}
close CAP;
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(I think your original post had a problem in the second part of your regex match. I took the easier way on that too.)