def _discover_mac(self):
mac = None<EOL>mac_reversed = None<EOL>cmd = MAGIC + DISCOVERY<EOL>resp = self._udp_transact(cmd, self._discovery_resp,<EOL>broadcast=True,<EOL>timeout=DISCOVERY_TIMEOUT)<EOL>if resp:<EOL><INDENT>(mac, mac_reversed) = resp<EOL><DEDENT>if mac is None:<EOL><INDENT>raise S20Exception("<STR_LIT>".format(self.host))<EOL><DEDENT>return (mac, mac_reversed)<EOL>
Discovers MAC address of device.

        Discovery is done by sending a UDP broadcast.
        All configured devices reply. The response contains
        the MAC address in both needed formats.

        Discovery of multiple switches must be done synchronously.

        :returns: Tuple of MAC address and reversed MAC address.