1-3An LLDPDU can carry up 28 types of TLVs, of which the chassis ID TLV, port ID TLV, TTL TLV, and endof LLDPDU TLV (end TLV in the figure) are mandatory TLVs that must be carried and other TLVs areoptional.TLVsTLVs are type, length, and value sequences that carry information elements, where the type fieldidentifies the type of information, the length field indicates the length of the information field in octets,and the value field contains the information itself.LLDPDU TLVs fall into these categories: basic management TLVs, organizationally (IEEE 802.1 andIEEE 802.3) specific TLVs, and LLDP-MED (media endpoint discovery) TLVs. Basic management TLVsare essential to device management. Organizationally specific TLVs and LLDP-MED TLVs are used forenhanced device management; they are defined by standardization or other organizations and thus areoptional to LLDPDUs.1) Basic management TLVsTable 1-3 lists the basic management TLV types currently in use. Some of them are mandatory toLLDPDUs, that is, must be included in every LLDPDU.Table 1-3 Basic LLDP TLVsType Description RemarksChassis ID Bridge MAC address of the sending device.Port IDID of the sending port.If MED TLVs are included in the LLDPDU, the portID TLV carries the MAC address of the sending portor the bridge MAC in case the port does not have aMAC address. If no MED TLVs are included, theport ID TLV carries the port name.Time To Live Life of the transmitted information on the receivingdevice.End of LLDPDU Marks the end of the TLV sequence in the LLDPDU.MandatoryPort Description Port description of the sending port.System Name Assigned name of the sending device.System Description Description of the sending device.System CapabilitiesIdentifies the primary functions of the sendingdevice and the primary functions that have beenenabled.Management AddressManagement address used to reach higher levelentities to assist discovery by networkmanagement, and the interface number and OID(object identifier) associated with the address.Optional2) IEEE 802.1 organizationally specific TLVsTable 1-4 IEEE 802.1 organizationally specific TLVsType DescriptionPort VLAN ID PVID of the sending portPort And Protocol VLAN ID Port and protocol VLAN IDs
