3Com 2928 User Guide - Page 252

1 LLDP Overview Background In a heterogeneous network, it is important that different types of network devices from different vendors can discover one other and exchange configuration for interoperability and management sake. This calls for a standard configuration exchange platform. To address the needs, the IETF drafted the Link Layer Discovery Protocol (LLDP) in IEEE 802.1AB. The protocol operates on the data link layer to exchange device information between directly connected devices. With LLDP, a device sends local device information as TLV (type, length, and value) triplets in LLDPDUs to the directly connected devices, and at the same time, stores the device information received in LLDPDUs sent from the LLDP neighbors in a standard management information base (MIB). It allows a network management system to fast detect Layer-2 network topology change and identify what the change is. Basic Concepts LLDPDUs LLDP sends device information in LLDP data units (LLDPDUs). LLDPDUs are encapsulated in Ethernet II or SNAP frames. 1) LLDPDUs encapsulated in Ethernet II Figure 1-1 LLDPDU encapsulated in Ethernet II The fields in the frame are described in Table 1-1: Table 1-1 Description of the fields in an Ethernet II encapsulated LLDPDU Field Description Destination MAC address The MAC address to which the LLDPDU is advertised. It is fixed to 0x0180-C200-000E, a multicast MAC address. 1-1