642 | Link Layer Discovery Protocol (LLDP)
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Figure 30-1. Type, Length, Value (TLV) Segment
TLVs are encapsulated in a frame called an LLDP Data Unit (LLDPDU) (Figure 30-2), 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. All types are mandatory in the construction of an LLDPDU except Optional
TLVs. The inclusion of individual Optional TLVs is user configurable.
Table 30-1. Type, Length, Value (TLV) Types
Type TLV Description
0 End of LLDPDU Marks the end of an LLDPDU
1 Chassis ID An administratively assigned name that identifies the LLDP agent
2 Port ID An administratively assigned name that identifies a port through which TLVs are sent
and received
3 Time to Live A value that tells the receiving agent how long the information contained in the TLV
Value field is 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.
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