Link Layer Discovery Protocol (LLDP)

Extreme Networks Technical Brief

If there is any certainty in the access layer of a network, it is that the number and the complexity of devices that reside in this layer will continue to experience rapid growth. Ethernet access ports are expected to more than triple from 2004 to 2007 (IDC Research, 2004). This exponential growth in the number of devices requiring LAN connectivity is due largely to the proliferation of new applications such as IP Telephony and wireless access.

From a network management perspective, there are direct implications that come from these changes. In the past, many network equipment vendors have developed propri-etary discovery methods in order to incorporate new access devices that they develop. In addition, key infrastructure vendors have developed proprietary discovery protocols, storing the data in an enterprise extension of the Manage-ment Information Base (MIB) used with Simple Network Management Protocol (SNMP). Today’s network manage-ment solutions are required to add expanded functionality and, at the same time, reduce complexity. Deployment, configuration, monitoring and other management disciplines must accommodate new technologies and network changes that are necessary to support new applications. Further, management systems must incorporate features that meet or exceed existing TDM voice solutions while providing advanced functionality to take advantage of the data infrastructure.

Extreme Networks® simplifies today’s expanding network environment and management challenges by improving intelligence and automation throughout the network. Extreme Networks now incorporates the recently finalized LLDP—IEEE standard, 802.1AB into its infrastructure products. LLDP was recently accepted as the standard open protocol for discovering network topologies and information concerning devices on the network.

LLDP promises to simplify troubleshooting of enterprise networks and enhance the ability of network management tools to discover and maintain accurate network topologies in multi-vendor environments. It serves to reduce the complexities and expenses involved with convergence driven network changes by greatly simplifying management and connectivity issues. The new standard sets the stage for convergence applications by allowing enterprises to add new access devices in a non-disruptive Plug-and-Play fashion. Voice and wireless services can be easily imple-mented without major network upgrades..

Today’s networks must incorporate best-of-breed solutions at every layer of the network, regardless of which vendor you choose. LLDP allows enterprises to build a best-of-breed open converged network that can easily accommo-date new applications, such as voice, while achieving five 9’s availability. The open nature of LLDP forms a foundation for co-development of new add-on discovery features that will help enable new Ethernet-based applications and services in the future.

Extreme Networks employs LLDP not only as a means tosimplify deployment of access devices, but also as a troubleshooting and firmware management tool and eventually as a way to legitimize new data services. For instance, in the future, Extreme Networks plans to provide much-needed E911 emergency call services in Voice-over-IP (VoIP) applications and enable new applications such as Voice over WLAN (VoWLAN).

Benefits

The business level benefits that can be realized from deploying LLDP in an Extreme Networks device are far-reaching.

Lower Operating Costs

Increases in automation achieved through LLDP can directly contribute to lower operating costs. Management and network maintenance are greatly simplified as a result of management tool consolidation and automation of diagnostic and consistency checking procedures. Automated discovery of access devices also reduce general setup costs of new equipment. LLDP simplifies management and network deployment, and as a result, lessens the number and complexity of processes and reduces headcount.

Improved Choice and Flexibility in Network Design

LLDP helps create an open market and customer choice so that a business can choose the best vendor for a particular network application. LLDP helps eliminate the barriers to creating a multi-vendor best-of-breed solution, thus allowing for a more advanced network and reduced capitalexpenditures due to competitive bidding and increasedbargaining power. Open standards benefit the end customer as a result of vendors co-developing technology. This coordination simultaneously advances development cycles on new technology and increases price competition.

Link Layer Discovery Protocol (LLDP)A New Standard for Discovering and Managing Converged Network Devices

© 2006 Extreme Networks, Inc. All rights reserved. Link Layer Discovery Protocol—Page 1

Application

OSI ReferenceModel Layers

IEEE 802 Model Layer

Presentation

Session

Transport

Network

Data Link

Physical

Higher Protocol Layers

MAC Client {Bridge Relay Entity, LLC, etc.}

Link Aggregation Sublayer (Optional)

LLDPMAC Control(Optional)

MAC Control(Optional)

MAC Control(Optional)

MAC

Physical Physical Physical

MAC MAC

LLDP LLDP


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 informa-tion from adjacent devices. LLDP has been fully implement-ed 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.

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.


BlackDiamond 8810

BlackDiamond® 10808

Port Device InfoA13

C2

D2

F3

Switch

IP Phone

PC

IP-PBX

xxxx

xxxx

xxxx

xxxx

Discovery MIB

Intellegent Core

PSTN

LLDP—How it WorksThe 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.

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.

1.

2.

3.

BlackDiamond 8810

Router

MIB

NetworkManagement

System

LAN Switch

MIB

IP Phone

1

2

3

`

Figure 2: LLDP Architecture

Figure 1: LLDP Peer Discovery


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 advertise-ment 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.

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

Extreme Networks switch ports enabled with basic LLDP, the information shown in Table 1 can be transmitted and stored using LLDP.


CONSOLECONSOLE

STACK NO

11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424

CONSOLECONSOLE

STACK NO

11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424

CONSOLECONSOLE

STACK NO

11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424

CONSOLECONSOLE

STACK NO

11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424

MIB MIB

Summit X450 Summit X450LLDP

Advertisements

SNMPAdvertisements

EPICenterNetwork Management`

Chassis ID

Port ID

Time-to-live (TTL)

Port description

System name

System description

System capabilities

Management address

Organizationally specific

End of LLDP PDU

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 IDand 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 valuetypically 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.

DESCRIPTIONTLV

Figure 3: Basic LLDP Functionality

Table 1: Basic TLVs supported by Extreme Networks


Organizationally-Specific TLVs

Extreme Networks implementation of organizationally-specific TLVs represent a commitment to fully enabling the network for converged applications and provide level of functionality beyond that of most equipment vendors. Organizationally-specific TLV extensions simplify the integration of multi-vendor access networks by assisting in the detection and configuration of IEEE 802.1 and IEEE 802.3 information. Additionally, standards organizations as well as vendors such as Extreme Networks will help to drive new functionality in LLDP extensions. New standards, such as LLDP-Media Endpoint Discovery (MED), will provide extensibility to fully standardized solutions to other reason-ably predictable needs in this area, as well as allowing for vendor-specific extensions.

802.1 Extensions IEEE 802.1 extensions deal primarily with describing VLAN attributes. They will also be supported in the first release of LLDP support on Extreme Networks switches. Supported 802.1 extensions are the TLVs shown in Table 2.

802.3 ExtensionsThe IEEE 802.3 TLV extensions describe various attributes associates with the operation of an 802.3 LAN interface. The defined TLVs supported in the first implementation of LLDP are shown in Table 3.

LLDP-MED

LLDP-MED is a new set of standards enhancing the basic LLDP protocol, which applies to increased discovery of endpoint devices. In the future, Extreme Networks will imple-ment many of the new LLDP-MED standards under develop-ment by the Telecommunications Industry Association (TIA).

Management Components

EPICenter Management

LLDP provides detailed Layer 2 network information for connected access devices, exposing the entire LAN to theEPICenter management system. Layer 2 discovery drills down to the port that access devices are connected to and gives a complete understanding of connectivity and device properties. This granularity of detail is necessary to configure and maintain end-to-end networks from a network manage-ment system—“End-to-end,” meaning that network adminis-trators should not have to manually audit a network to discover third-party vendor devices. Instead, LLDP allows for centralized management and automated discovery of all wired and wireless devices. This is achieved through flexible management views, with options that can be selected per device, user, action, time or location.

Using LLDP in Extreme Networks devices, EPICenter manager is able to build a complete topology of the network and make automation a reality. Because LLDP messages are stored in the MIB of an Extreme Networks switch, EPICenter is able to obtain complete access to the information through SNMP advertisements. Having this control and information availability through EPICenter allows centralized access to accurate and timely network data, enabling simplified device management and troubleshooting. For example, it becomes possible for EPICenter management to discover configuration inconsistencies or malfunctions that can result in impaired communication at higher layers. Most importantly, EPICenter can obtain this information from all network devices, not just Extreme Networks devices.

Command Line Interface (CLI)CLI is an optional method of configuration for LLDP. CLI can send configuration information per port to Extreme Networks switches via SNMP. CLI can also be used to maintain a list of LLDP enabled ports and the port mode (i.e. transmit only, receive only or transmit and receive).


DESCRIPTIONTLV

Port VLAN ID

Port & Protocol VLAN ID

VLAN Name

Protocol Identity

Identifies the VLAN identifier associated with an untagged VLAN. Only one Port VLAN ID can exist in an LLDP PDU.

Allows the port to advertise if it supports port/protocol based VLANs, and there associated VLAN ID.

Allows a device to advertise the textual name of any VLAN with which it is configured.

Provides the protocols that are accessible through the LLDP port.

DESCRIPTIONTLV

MAC/PHY Configuration and Status

Power-via-MDI

Link Aggregation

Maximum Frame Size

Determines more about the auto negotiation settings of the port, as well as the type of physical interface used.

Advertises the power-via-MDI implementa-tions supported by the port. Power Informa-tion allows for improved power management for endpoints utilizing IEEE 802.3af Power over Ethernet (PoE).

Allows the port to send information about its configured link aggregation (whether the link is capable of being aggregated, whether it is currently in an aggregation and if in an ag--gregation, the port of the aggregation).

Reports the maximum supported frame size for the port.

Table 2: LLDP 802.1 Extensions

Table 3: LLDP 802.3 Extensions


Applications

Diagnostics/Troubleshooting

LLDP is a natural diagnostic tool because of its inherent ability to discover and maintain accurate and up-to-date network topologies. The TLV information exposes network mapping, inventory data and network troubleshooting information that may otherwise be unavailable. Network administrators can use this information to identify outdated hardware and software, speed and duplex mismatches and improperly configured devices. For example, using TTL values, LLDP can be used to locate ports that are no longer sending LLDP advertisements to determine endpoint devices that have gone out of service.

Voice

VoIP continues to demand availability standards and advanced functionality from data networks that will help put it on par with TDM systems. LLDP takes another step forward in achieving this goal by facilitating multi-vendor IP Telephony networks and enabling these networks to achieve dial-tone reliability. VoIP networks have been relatively slow to adopt voice-class features and have lacked complete integration with existing network management systems. IP telephones typically lack support of management protocols such as SNMP, prohibiting NMS systems from a complete network view. LLDP now brings discovery of VoIP topology information to Extreme Networks Management System. LLDP allows an IP phone to be dynamically and fully recognized by an Extreme Networks device. The Extreme Networks device is then able to adapt to the network according to the needs of the IP telephone and MIB informa-tion becomes accessible to EPICenter.

Extreme Networks acts as an industry innovator byincorporating early-standards LLDP-MED functions and by making significant headway in building Plug-and-Play IP Telephony networks.

Extreme Networks LLDP Implementation vs. Other Discovery Protocols

Many network equipment vendors have developed discovery protocols to operate in homogeneous networks comprised of their own equipment. Cisco Systems has Cisco Discovery

Protocol (CDP); Enterasys Networks, Cabletron Discovery Protocol (CDP); and Nortel Networks, Nortel Discovery Protocol (NDP).

However, many network architects building out enterprise and carrier VoIP networks would like a standard means of discovery allowing them to mix best-of-breed equipment from multiple ven-dors. Most network designs are moving to a best-of-breed strategy where individual components in the network are chosen for their unique ability to handle an application. A standards-based discovery protocol readies a network for convergence applications without major dependencies concerning the manufacturer of network equipment. See Figure 4 for a compari-son between discovery protocols.

www.extremenetworks.com email: [email protected]

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© 2006 Extreme Networks, Inc. All rights reserved. Extreme Networks, the Extreme Networks Logo, BlackDiamond and EPICenter, are either registered trademarks or trademarks of Extreme Networks, Inc. in the United States and/or other countries. Specifications are subject to change without notice.

1061_01 11/06 Link Layer Discovery Protocol Technology Brief

Industry Standards Based

Multi-Vendor Network Support

Chassis & Port ID

Port Description

System Name

System Description

System Capabilities

Management Address

VLAN ID

Voice VLANs

Network Policy

Auto Negotiation Requirements

Power Information (PoE Capable)

Frame Size Requirements

Location Advertisements (E911 capable)

YY YYN

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Y

Y

NN N N

N N NNNN

YYYYY

YY Y Y

YY Y

YY

Y

Y

YYY

YYY

Y

Y N NNN NN

LLD

P-M

ED

Cis

co C

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Nor

tel N

DP

Ente

rasy

s C

DP

Figure 4: Competitive Discovery Methods

Documents

Link Layer Discovery Protocol (LLDP)