Manual

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Москва, Новозаводская ул., 18, стр. 1
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Chapter 5 LLDP Function Operation
Configuration
5.1 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