Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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Protocol Data Units

Configuration information is exchanged in the form of type, length, value (TLV) segments. The below figure shows the chassis ID TLV.

Type — Indicates the type of field that a part of the message represents.
Length — Indicates the size of the value field (in byte).
Value — Indicates the data for this part of the message.

Figure 1. Type, Length, Value (TLV) Segment TLV Segment

TLV Segment

TLVs are encapsulated in a frame called an LLDP data unit (LLDPDU), which is transmitted from one LLDP-enabled device to its LLDP-enabled neighbors. LLDP is a one-way protocol. LLDP-enabled devices (LLDP agents) can transmit and/or receive advertisements, but they cannot solicit and do not respond to advertisements.

There are five types of TLVs (as shown in the below table). All types are mandatory in the construction of an LLDPDU except Optional TLVs. You can configure the inclusion of individual Optional TLVs.

Table 1. Type, Length, Value (TLV) Types
Type	TLV	Description
0	End of LLDPDU	Marks the end of an LLDPDU.
1	Chassis ID	The Chassis ID TLV is a mandatory TLV that identifies the chassis containing the IEEE 802 LAN station associated with the transmitting LLDP agent.
2	Port ID	The Port ID TLV is a mandatory TLV that identifies the port component of the MSAP identifier associated with the transmitting LLDP agent.
3	Time to Live	The Time To Live TLV indicates the number of seconds that the recipient LLDP agent considers the information associated with this MSAP identifier to be valid.
—	Optional	Includes sub-types of TLVs that advertise specific configuration information. These sub-types are Management TLVs, IEEE 802.1, IEEE 802.3, and TIA-1057 Organizationally Specific TLVs.

Figure 2. LLDPDU Frame

LLDPDU Frame