Link Layer Discovery Protocol (LLDP)
Page 30 7210 SAS M, T, X, R6, R12, Mxp Interface Configu-
ration Guide
LLDP Protocol Features
The IEEE 802.1ab Link Layer Discovery Protocol (LLDP) is a uni-directional protocol that uses
the MAC layer to transmit specific information related to the capabilities and status of the local
device. The LLDP can send as well as receive information from a remote device stored in the
related MIB(s).
The LLDP does not contain a mechanism to solicit information received from other LLDP agents.
The protocol also does not provide means to confirm the receipt of information. LLDP provides
the flexibility of enabling a transmitter and receiver separately, therefore the following LLDP
configurations are allowed:
• An LLDP agent can only transmit information.
• An LLDP agent can only receive information.
• An LLDP agent can transmit and receive information.
The information fields in each LLDP frame are contained in an LLDP Data Unit (LLDPDU) as a
sequence of variable length information elements. Each information element includes Type,
Length, and Value fields (TLVs).
• Type indicates the nature of information being transmitted.
• Length indicates the length of the information string in octets.
• Value is the actual information that is transmitted. (For example, a binary bit map or an
alphanumeric string that can contain one or more fields).
Each LLDPDU contains four mandatory TLVs and optional TLVs selected by the Network
Management. Below is the format of a LLDPDU:
• Chassis ID TLV
•Port ID TLV
• Time To Live TLV
• Zero or more optional TLVs, depending on the maximum size of the LLDPDU allowed.
• End Of LLDPDU TLV
An LLDP agent or port is identified by a concatenated string formed by the Chassis ID TLV and
the Port ID TLV. This string is used by a recipient to identify an LLDP port or agent. The
combination of the Port ID and Chassis ID TLVs remains unchanged until the port or agent is
operational.
The TTL (Time To Live) field of an Time-To-Live TLV can be either zero or a non-zero value. A
zero value in the TTL field notifies the receiving LLDP agent to immediately discard all
information related to the sending LLDP agent. A non-zero value in the TTL field indicates the
time duration for which the receiving LLDP agent should retain the sending LLDP agent’s
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