Reference Guide
Link layer discovery protocol
LLDP enables a LAN device to advertise its conguration and receive conguration information from adjacent LLDP-enabled LAN devices.
• LLDP is enabled by default.
• LLDP supports a maximum of 250 total neighbors per system. If the number of interfaces multiplied by eight exceeds the maximum,
the system does not congure more than 250.
• OS10 devices receive and periodically transmit link layer discovery protocol data units (LLDPDUs). The default transmission interval is
30 seconds.
• LLDPDU information received from a neighbor expires after the default time to live (TTL) value (120 seconds).
• Spanning-tree blocked ports allow LLDPDUs.
• 802.1X-controlled ports do not allow LLDPDUs until the connected device is authenticated.
• Link layer discovery protocol-media endpoint discovery (LLDP-MED) is enabled on all interfaces by default.
Protocol data units
LLDP devices exchange conguration information represented as type, length, and value (TLV) segments:
Type Information included in the TLV.
Length Value (in bytes) of the TLV after the Length eld.
Value Conguration information the agent is advertising.
TLVs are encapsulated in a frame called an LLDPDU, transmitted from one LLDP-enabled device to its LLDP-enabled neighbors. LLDP is a
one-way protocol and LLDP-enabled devices (LLDP agents) transmit and/or receive advertisements but they cannot solicit and do not
respond to advertisements.
There are three mandatory TLVs followed by zero or more optional TLVs and the end of the LLDPDU TLV. The three mandatory TLVs must
be located at the beginning of the LLDPDU in the following order:
• Node ID TLV
• Port ID TLV
• Time-to-live TLV
0 — End of
LLDPDU
Marks the end of an LLDPDU.
1 — Node ID Identies the LLDP agent.
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