Link Layer Discovery Protocol (Lldp) - Allied Telesis SwitchBlade x3100 Series Manual

Introduction

7.4 Link Layer Discovery Protocol (LLDP)

7.4.1 Introduction
A network topology is defined as a set of Network Elements (NEs) and the network links that interconnect
them.
The IEEE (Institute of Electrical and Electronic Engineers) defined Link Layer Discovery Protocol (LLDP) stan-
dard 802.1ab is an application protocol that runs directly over layer 2 in network elements (NEs) to facilitate a
centrally located network manger to derive the physical network topology the NEs are part of.
The LLDP runs over network links, and not over links that connect the NE to the customer endpoint.
Note:
This is covered by another protocol, LLDP Media Endpoint Discovery, or LLDP-MED, which is not part
of this feature.
7.4.1.1 LLDP Protocol Elements
To assist in the discovery of the network topology, LLDP has two components:
Transmitting - This transmits or advertises the local NE discovery-related data on a per link basis to the
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remote NE at the other end of the link. Since a network link is spanned by two physical ports on each of the
two NEs (local and remote), the NEs are advertising their local network port related discovery data to each
other.
Receiving - This collects the advertised data received over the network link from the transmitting NE,
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resulting in both the local NE and the remote NE having the port discovery data at each end of the network
link.
Using both LLDP protocol components allows the NE to posses discovery-related data for each of the network
links between itself and the neighboring NE. This data can then be used to deduce the physical topology of the
network which the NEs and the network (port) links are part of.
Note that the responsibility of the LLDP protocol lies in only with providing the protocol message formats, the
type of discovery data to be advertised, and the procedures required to send and receive the above mentioned
data on a per link basis. The transmission of the data (collected via the LLDP protocol) to a central location like
a Network Management System (NMS), and how it uses the data to deduce the network topology, is outside of
the scope of the LLDP protocol. The LLDP does not favor one method over another in the method of transmit-
ting the data to the NMS, although Simple Network Management Protocol (SNMP) is the most common.
An SNMP based interaction between an NMS and the network agent in the NE is shown in the following figure.
Software Reference for SwitchBlade x3100 Series Switches (Network Management)
Introduction
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