OS10 Enterprise Edition User Guide Release 10.4.0E(R3)

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Link layer discovery protocol

LLDP enables a LAN device to advertise its system and receive system information from adjacent LAN devices.

  • LLDP is enabled by default on OS10 interfaces.
  • An LLDP-enabled interface can support up to eight neighbors. An OS10 switch supports a maximum of 250 total neighbors per system.
  • OS10 devices receive and periodically transmit link layer discovery protocol data units (LLDPDUs), which are data packets. 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 system 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 field.
Value
System information the agent is advertising.

tlv segment

LAN devices transmit LLDPDUs, which encapsulate TLVs, to neighboring LAN devices. LLDP is a one-way protocol and LAN 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:
  • Chassis ID TLV
  • Port ID TLV
  • Time-to-live TLV
0 — End of LLDPDU
Marks the end of an LLDPDU.
1 — Chassis ID
Identifies the LAN agent.
2 — Port ID
Identifies a port through which the LAN device transmits LLDPDUs.
3 — Time-to-live
Number of seconds that the recipient LLDP agent considers the information associated with this MAP 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 organization-specific TLVs.

lldp pdu frame


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