code: def _check_len(self, pkt):
          
          if len(pkt) % 2:
              last_chr = pkt[-1]
              if last_chr <= b'\x80':
                  return pkt[:-1] + b'\x00' + last_chr
              else:
                  return pkt[:-1] + b'\xff' + chb(orb(last_chr) - 1)
          else:
              return pkt
docs: Check for odd packet length and pad according to Cisco spec.
          This padding is only used for checksum computation.  The original
          packet should not be altered.