Information is exchanged using specific units of data known as LLDP Data Units (LLDPDU). These data unit consists of TLVs ( Type-Length-Values), and each TLV field corresponds to a certain type and has a certain length.
In accordance with the LLDP standard IEEE 802.1AB three TLVs are mandatory at the beginning of an LLDPU in the following order:
- Type 1 = Chassis ID
- Type 2 = Chassis ID
- Type 3 = Time to live
Following these mandatory TLVs, an LLDPDU can include additional, optional TLVs:
- Type 4 = Port description
- Type 5 = System name
- Type 6 = System description
- Type 7 = System capabilities
- Type 8 = Management address
At the end of an LLDPDU the following TLV is mandatory:
- Type 0 = End of LLDPDU
Tabular overview of the TLVs
| TLV | Usage | Name | Example | Function |
|---|---|---|---|---|
| Type 1 | Mandatory | Chassis ID | 0018.2fa6.b28c | Identifies the device |
| Type 2 | Mandatory | Port ID | Fi-0/12 | Identifies the port |
| Type 3 | Mandatory | Time to live | 60 sec | Signals to the receiving device how long the received information should remain valid |
| Type 4 | Optional | Port description | GigabitEthernet0/12 | Displays details about the port such as the hardware version |
| Type 5 | Optional | System name | PN-I/O 3 | Displays the name given to the device by the administrator |
| Type 6 | Optional | System description | LCOS software, version 8.9.1 SE | Displays details about the device such as the version of the networking software |
| Type 7 | Optional | System capabilities | Router | Displays the primary function and capabilities of the device. |
| Type 8 | Optional | Management address | 192,168.0.1 | Shows the IP or MAC address of the device |
| Type 0 | Mandatory | End of LLDPDU | ------------- | Signals the end of the data unit |
