LLDP Configuration
Chapter 1 Link Layer-2 Discovery Protocol (LLDP)
1.1 LLDP Overview
802.1ABThe link layer discovery protocol (LLDP) at 802.1AB helps to detect
network troubles easily and maintain the network topology. It enables the neighboring
device to sending out notice of its own state information to other devices and each port
of all devices stores information of defining themselves. If necessary, they can also
sending update information to the neighboring devices and the neighboring devices
will store the information in standard SNMP MIBs. The network management system
can inquire the connection of current layer-2 from MIB. LLDPcan neither configure
nor control the network element or traffic. It only reports configuration of layer-2.
Simply, LLDP is a neighbor discovery protocol. It sets a standard method for the
Ethernet network device, such as switches, routers and WAPs. It enables the Ethernet
device notify its existence to other nodes and save the discovery information of
neighboring devices. For instance, all information including the device configuration
and the device identification can be notified through the protocol. Specifically, LLDP
defines a universal notification information set, a transmission notification protocol and
a method of storing all notification information. The device need to notify the
notification information can transmit many notifications in a LAN data packet. The
transmission type is TLV.
TLV has three compulsory types: Chassis ID TLV, Port ID TLV and Time To Live
TLV; five optional types: Port Description, System Name, System Description, System
Capabilities and Management Address; and three extension TLVs: DOT1 (Port Vlan
ID, Protocol Vlan ID, Vlan Name, Protocol Identity); DOT3 (MAC/PHY
Configuration/Status, Power Via MDI, Link Aggregation, Max Frame Size); MED (MED
Capability, Network Policy, Location Identification, Extended Power-via-MDI, Inventory
(Hardware Revision, Firmware Revision, Software Revision, Serial Number,
Manufacturer Name, Mode Name, Assert ID).
LLDP is a unidirectional protocol. One LLDP agent transmits its state information
and functions through its connected MSAP, or receives the current state information or
function information about the neighbor. However, the LLDP agent cannot request any
information from the peer through the protocol. During message exchange, message
transmission and reception do not affect each other. You can configure only message
transmission or reception or both.
1.1.1 Initializing the Protocol
LLDP can work under three modes: transmit-only, receive-only and
transmit-and-receive. The default mode is transmit-and-receive.
1.1.2 Initializing LLDP Transmit Mode
Set LLDP to transmit-only in the interface mode. In transmit-only mode, the
interface transmits LLDP packets when the state or value of one or more information
elements (management object) of the local system change or the transmission timer is
timeout. The interface will not transmit LLDP packets when disabling the function.
