def _mac_to_oid(mac):
    """Converts a six-byte hex form MAC address to six-byte decimal form.

    For example:
        00:1A:2B:3C:4D:5E converts to 0.26.43.60.77.94

    Returns:
        str, six-byte decimal form used in SNMP OIDs.
    """
    fields = mac.split(':')
    oid_fields = [str(int(v, 16)) for v in fields]
    oid = '.'.join(oid_fields)
    return oid