Link Layer Discovery Protocol
Encyclopedia
The Link Layer Discovery Protocol (LLDP) is a vendor-neutral Link Layer
protocol in the Internet Protocol Suite
used by network devices for advertising their identity, capabilities, and neighbors on a IEEE 802
local area network, principally wired Ethernet
. The protocol is formally referred to by the IEEE as Station and Media Access Control Connectivity Discovery specified in standards document IEEE 802.1AB.
LLDP performs functions similar to several proprietary protocol
s, such as Cisco Discovery Protocol
, Extreme Discovery Protocol from Extreme Networks
, Nortel Discovery Protocol
(also known as SONMP), and Microsoft
's Link Layer Topology Discovery
(LLTD).
(TLV) structures.
The Ethernet frame used in LLDP has its destination MAC address
typically set to a special multicast address
that 802.1D-compliant bridges do not forwardIEEE 802.1AB-2009 suggests three such addresses, 01:80:c2:00:00:0e, 01:80:c2:00:00:03 and 01:80:c2:00:00:00. other multicast and unicast destination addresses are permitted. The EtherType
field is set to 0x88cc.
Each LLDP frame starts with the following mandatory TLVs: Chassis ID, Port ID, and Time-to-Live. The mandatory TLVs are followed by any number of optional TLVs. The frame ends with a special TLV, named end of LLDPDU in which both the type and length fields are 0.
Accordingly, an Ethernet frame containing an LLDPDU has the following structure:
Each of the TLV components has the following basic structure:
Custom TLVs,Termed Organizationally Specific TLVs by IEEE 802.1AB are supported via a TLV type 127. The value of a custom TLV starts with a 24-bit organizationally unique identifier and a 1 byte organizationally specific subtype followed by data. The basic format for an organizationally specific TLV is show below:
According to IEEE Std 802.1AB 9.6.1.3 "The Organizationally Unique Identifier shall contain the organization's OUI as defined in IEEE Std 802-2001." Each organization is responsible for managing their subtypes.
(MIB) and can be queried with the Simple Network Management Protocol
(SNMP) as specified in RFC 2922. The topology of an LLDP-enabled network can be discovered by crawling the hosts and querying this database. Information that may be retrieved include:
The LLDP-MED protocol extension was formally approved and published as the standard ANSI/TIA-1057 by the Telecommunications Industry Association
(TIA) in April 2006.
requirements.
The (DCBX) is a discovery and capability exchange protocol that is used for conveying capabilities and configuration of the above features between neighbors to ensure consistent configuration across the network.
Link Layer
In computer networking, the link layer is the lowest layer in the Internet Protocol Suite , the networking architecture of the Internet . It is the group of methods or protocols that only operate on a host's link...
protocol in the Internet Protocol Suite
Internet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...
used by network devices for advertising their identity, capabilities, and neighbors on a IEEE 802
IEEE 802
IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks.More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. IEEE 802 refers to a family of IEEE standards dealing with local area networks and...
local area network, principally wired Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
. The protocol is formally referred to by the IEEE as Station and Media Access Control Connectivity Discovery specified in standards document IEEE 802.1AB.
LLDP performs functions similar to several proprietary protocol
Proprietary protocol
In telecommunications, a proprietary protocol is a communications protocol owned by a single organization or individual.-Enforcement:Proprietors may enforce restrictions through patents and by keeping the protocol specification a trade secret...
s, such as Cisco Discovery Protocol
Cisco Discovery Protocol
The Cisco Discovery Protocol is a proprietary Data Link Layer network protocol developed by Cisco Systems. It is used to share information about other directly connected Cisco equipment, such as the operating system version and IP address...
, Extreme Discovery Protocol from Extreme Networks
Extreme Networks
Extreme Networks, founded in 1996, is a publicly listed company that designs, builds, and installs Ethernet network solutions for enterprise and Carrier Class networks.-Corporate History:Extreme Networks is located in Santa Clara, California...
, Nortel Discovery Protocol
Nortel Discovery Protocol
The Nortel Discovery Protocol is a Data Link Layer network protocol for discovery of Nortel devices...
(also known as SONMP), and Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's Link Layer Topology Discovery
Link Layer Topology Discovery
Link Layer Topology Discovery is a proprietary Link Layer protocol for network topology discovery and quality of service diagnostics. Microsoft developed it as part of the Windows Rally set of technologies...
(LLTD).
Frame structure
LLDP information is sent by devices from each of their interfaces at a fixed interval, in the form of an Ethernet frame. Each frame contains one Link Layer Discovery Protocol Data Unit (LLDPDU). Each LLDPDU is a sequence of type-length-valueType-length-value
Within data communication protocols, optional information may be encoded as a type-length-value or TLV element inside of the protocol. TLV is also known as tag-length value....
(TLV) structures.
The Ethernet frame used in LLDP has its destination MAC address
MAC address
A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...
typically set to a special multicast address
Multicast address
A multicast address is a logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be multicast for a designated network service...
that 802.1D-compliant bridges do not forwardIEEE 802.1AB-2009 suggests three such addresses, 01:80:c2:00:00:0e, 01:80:c2:00:00:03 and 01:80:c2:00:00:00. other multicast and unicast destination addresses are permitted. The EtherType
EtherType
EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the PayLoad of an Ethernet Frame. This field was first defined by the Ethernet II framing networking standard, and later adapted for the IEEE 802.3 Ethernet networking standard.EtherType...
field is set to 0x88cc.
Each LLDP frame starts with the following mandatory TLVs: Chassis ID, Port ID, and Time-to-Live. The mandatory TLVs are followed by any number of optional TLVs. The frame ends with a special TLV, named end of LLDPDU in which both the type and length fields are 0.
Accordingly, an Ethernet frame containing an LLDPDU has the following structure:
| Preamble | Destination MAC | Source MAC | Ethertype EtherType EtherType is a two-octet field in an Ethernet frame. It is used to indicate which protocol is encapsulated in the PayLoad of an Ethernet Frame. This field was first defined by the Ethernet II framing networking standard, and later adapted for the IEEE 802.3 Ethernet networking standard.EtherType... |
Chassis ID TLV | Port ID TLV | Time to live TLV | Optional TLVs | End of LLDPDU TLV | Frame check sequence Frame Check Sequence A frame check sequence refers to the extra checksum characters added to a frame in a communication protocol for error detection and correction. Frames are used to send upper-layer data and ultimately the user application data from a source to a destination. The data package includes the message... |
|---|---|---|---|---|---|---|---|---|---|
| 01:80:c2:00:00:0e, 01:80:c2:00:00:03 or 01:80:c2:00:00:00 | Station's address | 0x88CC | Type=1 | Type=2 | Type=3 | Zero or more complete TLVs | Type=0, Length=0 |
Each of the TLV components has the following basic structure:
| Type | Length | Value |
|---|---|---|
| 7 bits | 9 bits | 0-510 octets |
Custom TLVs,Termed Organizationally Specific TLVs by IEEE 802.1AB are supported via a TLV type 127. The value of a custom TLV starts with a 24-bit organizationally unique identifier and a 1 byte organizationally specific subtype followed by data. The basic format for an organizationally specific TLV is show below:
| Type | Length | Organizationally unique identifier (OUI) | Organizationally defined subtype | Organizationally defined information string |
|---|---|---|---|---|
| 7 bits—127 | 9 bits | 24 bits | 8 bits | 0-507 octets |
According to IEEE Std 802.1AB 9.6.1.3 "The Organizationally Unique Identifier shall contain the organization's OUI as defined in IEEE Std 802-2001." Each organization is responsible for managing their subtypes.
Information gathered
Information gathered with LLDP is stored in the device as a management information databaseManagement information base
A management information base is a virtual database used for managing the entities in a communications network. Most often associated with the Simple Network Management Protocol , the term is also used more generically in contexts such as in OSI/ISO Network management model...
(MIB) and can be queried with the Simple Network Management Protocol
Simple Network Management Protocol
Simple Network Management Protocol is an "Internet-standard protocol for managing devices on IP networks. Devices that typically support SNMP include routers, switches, servers, workstations, printers, modem racks, and more." It is used mostly in network management systems to monitor...
(SNMP) as specified in RFC 2922. The topology of an LLDP-enabled network can be discovered by crawling the hosts and querying this database. Information that may be retrieved include:
- System name and description
- Port name and description
- VLAN name
- IP management address
- System capabilities (switching, routing, etc.)
- MAC/PHY information
- MDI powerPower over EthernetPower over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling. The IEEE standard for PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable for low power levels...
- Link aggregation
Media endpoint discovery extension
Media Endpoint Discovery is an enhancement of LLDP, known as LLDP-MED, that provides the following facilities:- Auto-discovery of LAN policies (such as VLAN, Layer 2 Priority and Differentiated servicesDifferentiated servicesDifferentiated Services or DiffServ is a computer networking architecture that specifies a simple, scalable and coarse-grained mechanism for classifying and managing network traffic and providing Quality of Service on modern IP networks...
(Diffserv) settings) enabling plug and play networking. - Device location discovery to allow creation of location databases and, in the case of Voice over Internet Protocol (VoIP), Enhanced 911Enhanced 911Enhanced 911, E-911 or E911 in North America is one example of the modern evolution of telecommunications based system meant as an easy way to link people experiencing an emergency with the public resources that can help. The dial-three-digits concept first originated in the United Kingdom in 1937....
services. - Extended and automated power management of Power over EthernetPower over EthernetPower over Ethernet or PoE technology describes a system to pass electrical power safely, along with data, on Ethernet cabling. The IEEE standard for PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable for low power levels...
(PoE) end points. - Inventory management, allowing network administrators to track their network devices, and determine their characteristics (manufacturer, software and hardware versions, serial or asset number).
The LLDP-MED protocol extension was formally approved and published as the standard ANSI/TIA-1057 by the Telecommunications Industry Association
Telecommunications Industry Association
The Telecommunications Industry Association is accredited by the American National Standards Institute to develop voluntary, consensus-based industry standards for a wide variety of ICT products, and currently represents nearly 400 companies...
(TIA) in April 2006.
Applications
The Link Layer Discovery Protocol may be used as a component in network management and monitoring applications. One such example is its use in data center bridgingData center bridging
Data center bridging refers to a set of enhancements to Ethernet local area networks for use in data center environments. Specifically, DCB goals are, for selected traffic, to eliminate loss due to queue overflow and to be able to allocate bandwidth on links. Essentially, DCB enables, to some...
requirements.
The (DCBX) is a discovery and capability exchange protocol that is used for conveying capabilities and configuration of the above features between neighbors to ensure consistent configuration across the network.