User's Manual

11-1
Chapter 11 LLDP Function Operation
Configuration
11.1 Introduction to LLDP Function
Link Layer Discovery Protocol (LLDP) is a new protocol defined in 802.1ab. It enables neighbor devices to
send notices of their own state to other devices, and enables all ports of every device to store information
about them. If necessary, the ports can also send update information to the neighbor devices directly
connected to them, and those neighbor devices will store the information in standard SNMP MIBs. The
network management system can check the layer-two connection state from MIB. LLDP won’t configure or
control network elements or flows, but only report the configuration of layer-two. Another content of 802.1ab is
to utilizing the information provided by LLDP to find the conflicts in layer-two. IEEE now uses the existing
physical topology, interfaces and Entity MIBs of IETF.
To simplify, LLDP is a neighbor discovery protocol. It defines a standard method for Ethernet devices, such as
switches, routers and WLAN access points, to enable them to notify their existence to other nodes in the
network and store the discovery information of all neighbor devices. For example, the detail information of the
device configuration and discovery can both use this protocol to advertise.
In specific, LLDP defines a general advertisement information set, a transportation advertisement protocol
and a method to store the received advertisement information. The device to advertise its own information
can put multiple pieces of advertisement information in one LAN data packet to transport. The type of
transportation is the type length value (TLV) field. All devices supporting LLDP have to support device ID
and port ID advertisement, but it is assumed that, most devices should also support system name, system
description and system performance advertisement. System name and system description advertisement can
also provide useful information for collecting network flow data. System description advertisement can include
data such as the full name of the advertising device, hardware type of system, the version information of
software operation system and so on.
802.1AB Link Layer Discovery Protocol will make searching the problems in an enterprise network an easier
process and can strengthen the ability of network management tools to discover and maintain accurate
network topology structure.
Many kinds of network management software use “Automated Discovery” function to trace the change and
condition of topology, but most of them can reach layer-three and classify the devices into all IP subnets at
best. This kind of data are very primitive, only referring to basic events like the adding and removing of relative
devices instead of details about where and how these devices operate with the network.
Layer 2 discovery covers information like which devices have which ports, which switches connect to other
devices and so on, it can also display the routs between clients, switches, routers, application servers and
network servers. Such details will be very meaningful for schedule and investigate the source of network
failure.
LLDP will be a very useful management tool, providing accurate information about network mirroring, flow
data and searching network problems.