code: function normalize (mac) {
    let m = CISCO_MAC_ADDRESS_RE.exec(mac)
    if (m) {
      const halfwords = m.slice(1)
      mac = halfwords.map((halfword) => {
        return zeroFill(4, halfword)
      }).join('')
      return chunk(mac, 2).join(':').toUpperCase()
    }
  
    m = MAC_ADDRESS_RE.exec(mac)
    if (m) {
      const bytes = m.slice(1)
      return bytes
        .map(byte => zeroFill(2, byte))
        .join(':')
        .toUpperCase()
    }
  }
docs: Takes a MAC address in various formats:
  
  - 00:00:00:00:00:00,
  - 00-00-00-00-00-00,
  - 0000.0000.0000
  
  ... and returns it in the format 00:00:00:00:00:00.
  
  @param  {string} mac
  @return {string}