Background: Know: Link Layer Discovery, prereq - multicast, Ethertype, TTL; TLV coding Recognize: system group, VLAN

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LLDP messagesEdit

This slide describes the working procedure of Link Layer Discovery Protocol (LLDP). To determine the devices connected to the network, to have information about the ports and links which leads to the corresponding device and for other link layer management issues, LLDP lays down the solution. LLD protocol is a vendor-independent IEEE standard, known as IEEE802.1AB link layer discovery protocol.

How LLDP works?

Link Layer Discovery Protocol (LLDP) is used to discover and determine the devices exist on a network, the information of LLDP could be found in Link Layer Discovery.

Without a centralized server, which will control the devices and their memberships in the network, it is very difficult to manage the network. However, LLDP enabled devices send out their information in !@!URL must be fixed to be a link to the corresponding wiki page rather than to PDF!@! TLV} format periodically in every minute to the multicast address 01-80-c2-00-00-0e and with ethertype 0x88CC. This information is heard by all the multicast members of the group and they can update their ARP tables according to the information.
In the announcement, a device provides a list of descriptive objects, which are of two types : the mandatory objects and the optional objects.

Mandatory Objects

The mandatory objects in the list are Chassis ID, Port ID, TTL and End.

Chasis ID – identifies the device. Typically it is the MAC address of the device, as it is unique of identify the device in a network.

Port ID – is the identification of the port from which the LLDP message is sent. For instance, if the device is a switch, it may have several ports which can be identified by Port ID. The receiving device combines the chasis ID and the port ID to represent the device connected to the port from which it has received the frame. If the port is of a repeater, then this TLV is optional.

TTL – is the number of seconds the information in the LLDP message is valid for the receiving devices. This filed has a valid range of values from 0 to 65535.

End – indicated the end of mandatory objects, after which optional objects can be added.

Optional Objects

The optional objects can be basic management information, 802.1, 802.3 and extension for media end point discovery.

Basic Management – information can be sent by the device which can be the IEEE defined system !@!URL must be fixed to be a link to the corresponding wiki page rather than to PDF!@! MIB} group which will let other devices learn about it and can be stored in their local MIB database which can be accessed by SNMP.

802.1 – describes the VLAN attribute, which contains Port VLAN ID, VLAN Name, Protocol Identity and Port & Protocol VLAN ID.

802.3 – describes various capabilities associated with the 802.3 LAN interface, namely type of channel (e.g. duplex or half-duplex), rate (e.g. 100Mbps/1Gbps port) and power capabilities like power over Ethernet (PoE) or Power-via-MDI.

Media Endpint Discovery – is an enhancement of LLDP, it is also known as LLDP-MED. It provides auto-discovery of LAN policies, resembling, VLAN, layer 2 priority and Differentiated Services (Diffserv) which enables plug & play networking. It also provides device location discovery, automated power management and inventory management for network administrator by providing the facility of tracking of the networking devices.

See alsoEdit

tools such as Fluke LinkRunner use protocols such as LLDP