Link Layer Discovery Protocol (LLDP) - Extreme Networks

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How LLDP Works LLDP is essentially a neighbor discovery protocol that defines a method for network access devices using Ethernet connectivity to advertise information about them to peer devices on the same physical LAN and store information about the network. It allows a device to learn higher layer management reachability and connection endpoint information from adjacent devices. LLDP has been fully implemented in Extreme Networks switches and is accessible from the EPICenter ® management system. Using LLDP, an Extreme Networks device is able to advertise its own identification information, its capabilities and media-specific configuration information, as well as learn the same information from the devices connected to it. LLDP advertises this information over Logical Link-Layer Control frames and the information received from other agents in IEEE-defined Management Information Bases (MIB) modules. Figure 1 shows this relationship. Port Device Info A13 Switch xxxx C2 D2 F3 Discovery MIB IP Phone PC IP-PBX xxxx xxxx xxxx BlackDiamond ® 10808 BlackDiamond 8810 Intellegent Core PSTN LLDP—How it Works The IEEE 802.1ab Link Layer Discovery Protocol defines a standard way for Ethernet devices to advertise information about themselves to their network neighbors and store information they discover from other device. 1. 2. 3. Figure 1: LLDP Peer Discovery LAN switch and router advertise chassis/port ids and system descriptions to each other. The devices store the information they learn about each other in local MIB databases accessible via SNMP. A network management system (Extreme Networks EPICenter) retrieves the data stored by each device that builds a network topology map. OSI Reference Model Layers Application Presentation Session Transport Network Data Link Physical IEEE 802 Model Layer Higher Protocol Layers MAC Client {Bridge Relay Entity, LLC, etc.} Link Aggregation Sublayer (Optional) LLDP MAC Control (Optional) MAC Extreme Networks Technical Brief LLDP significantly aids in the deployment of any network device that supports the protocol. As a media independent protocol intended to be run on all IEEE 802 devices, LLDP may be used to discover routers, bridges, repeaters, WLAN APs, IP telephones, network camera or any LLDP-enabled device, regardless of manufacturer. Since LLDP runs over the data-link layer only, an Extreme Networks switch running one network layer protocol can discover and learn about an access device running a different network layer protocol. LLDP Architecture LLDP is a data-link layer protocol, operating above the MAC service layer and, as a result, can be used in any networking device that implements a MAC service. Figure 2 shows where LLDP resides in the IEEE 802 Model Layers. LLDP LLDP MAC Control (Optional) MAC Control (Optional) MAC MAC Physical Physical Physical BlackDiamond 8810 © 2006 Extreme Networks, Inc. All rights reserved. Link Layer Discovery Protocol—Page 2 Router MIB Network Management System ` Figure 2: LLDP Architecture 3 2 1 LAN Switch MIB IP Phone
LLDP will advertise and store messages and will not solicit information or keep state between devices. Each Extreme Networks switch configured with an active LLDP agent will send and receive messages on all physical interfaces enabled for LLDP transmission. These messages are sent periodically and are typically configured for short time intervals to ensure that accurate information is always available. These messages are then stored for a configurable period of time, determined by the time-to-live (TTL) value set by a user and contained within the received packet. The message information expires and is discarded when the TTL value is met. There is a default recommended time value for the TTL of 120 seconds. The only other time an advertisement would be sent is when a relevant change takes place in the switch. If information values change for any reason, the LLDP agent will be notified and will send out and update the new values. Basic LLDP functionality is represented in Figure 3. STACK NO STACK NO LLDP Summit X450 Advertisements Summit X450 11 22 3 44 55 66 77 88 99 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 11 22 33 44 55 66 77 88 99 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 CONSOLE CONSOLE CONSOLE CONSOLE MIB MIB SNMP Advertisements In this example LLDP advertisements are exchanged between participating network devices and stored in the MIB. As a result, EPICenter is able to gain access to that information using SNMP and build a complete topology and detailed inventory of network devices. These is true even if some network devices, such as IP phones, only advertise messages and are not able to store peer information. Protocol Data Unit Format ` A single LLDP Protocol Data Unit (LLDP PDU) is transmitted in a single 802.3 Ethernet frame. The basic LLDP PDU consists of a header, followed by a variable number of information elements known as TLVs that each includes fields for Type, Length, and Value. ‘Type’ identifies what kind of information is being sent. ‘Length’ indicates the length of the information string. ‘Value’ is the actual information sent. Each LLDP PDU includes three mandatory TLVs followed by optional TLVs. The three mandatory TLVs are Chassis ID, Port ID and TTL. Other TLVs are optional to advertise. For STACK NO STACK NO 1 22 33 44 55 66 77 88 99 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 11 2 3 4 5 66 7 8 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18 19 19 20 20 21 21 22 22 23 23 24 24 EPICenter Network Management Figure 3: Basic LLDP Functionality CONSOLE CONSOLE CONSOLE CONSOLE Extreme Networks Technical Brief Extreme Networks switch ports enabled with basic LLDP, the information shown in Table 1 can be transmitted and stored using LLDP. Chassis ID © 2006 Extreme Networks, Inc. All rights reserved. Link Layer Discovery Protocol—Page 3 Port ID TLV Time-to-live (TTL) Port description System name System description System capabilities Management address Organizationally specific End of LLDP PDU DESCRIPTION Represents the chassis identification for the device that transmitted the LLDP frame. The receiving LLDP agent combines the Chassis ID and Port ID to represent the entity connected to the port where the frame was received. Represents the identification of the specific port that transmitted the LLDP frame. The receiving LLDP agent combines the Chassis ID and Port to represent the entity connected to the port where the frame was received. Represents the length of time that information contained in the receive LLDP frame shall be valid. If a value of zero is sent it can also identify a device that has shut down or is no longer transmitting, prompting deletion of the record from the local database. Identifies information about the interface. This will include the name of the manufacturer, the product name and the version of the interface hardware/software (per RFC2863). Identifies the administratively-assigned name for the device (per RFC3418). A textual description of the device. This value typically includes the full name and version identification of the system’s hardware type, software operating-system, and networking software (per RFC3418). Identifies the capabilities of the device and its primary function. (e.g. Repeater, Bridge, WLAN Access Point, Router, Telephone, DOCSIS cable device, Station only, etc.). Identifies the IP address or MAC address of the device. The IEEE has further enhanced the value of the LLDP protocol by making it possible for other standards organizations and vendors to create custom advertisement messages for other types of endpoints. For Extreme Networks switches, the following TLV based information is maintained: - 802.1 VLAN extensions - 802.3 LAN interface extensions - LLDP-MED extensions Marks the end of data. No further processing of TLVs after this is necessary. This is a mandatory TLV and must therefore be present at the end of the data stream. Table 1: Basic TLVs supported by Extreme Networks
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Link Layer Discovery Protocol (LLDP) - Extreme Networks

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