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LLDP in Networking - Link Layer Discovery Protocol

LLDP in Networking - Link Layer Discovery Protocol (LLDP) is Media End Point Discovery (LLDP-MED), which is an extension of Link Layer Discovery Protocol (LLDP) that works between endpoint devices such as “IP” phones to provide support for VoIP applications (VoIP), where “LLDP-MED” endpoints determine the capabilities of the connected device and whether those capabilities are enabled.


LLDP in Networking - Link Layer Discovery Protocol


What is Link Layer Discovery Protocol (LLDP) in Networking


Link Layer Discovery Protocol (LLDP) is a vendor-neutral link layer protocol, used by network devices to announce device attributes. For hardware transfers, details such as configuration information, device capabilities, and device identity can also be announced by this protocol.


Knowing that “MSS TLVs” support the following properties: port description, system name, system description, system capabilities, and management address, where you can configure the frequency of LLDP updates, the amount of time to keep information before it is discarded, and the initialization delay time, where you can also specify “ “LLDP TLVs” to be sent and received, where “LLDP” stands for Link Layer Discovery Protocol, as it is an open “layer 2” protocol with the “IEEE (802.1AB) standard. LLDP is an open-source alternative to the Cisco Discovery Protocol.


It is also a device discovery protocol that works on Layer 2 which is the data link layer only on devices manufactured by “Cisco”, from routers, bridges, access servers, and switches. The Link Layer Discovery Protocol (LLDP) operates through the data link layer that allows two different devices to collect hardware and protocol information About Neighbors that are useful for network troubleshooting, and they support a specific set of attributes that they use to discover Neighbors and are referred to as “TLVs” and are as follows:


  • T: type.
  • L: length.
  • V: value descriptions.
  • “LLDP” is an acronym for “Link Layer Discovery Protocol”.


1. Send Link Layer Discovery Protocol (LLDP) information in networks


LLDP information is sent or received by neighboring devices through each of its LLDP-enabled interfaces in a specified period of time in the form of an Ethernet frame, where each Ethernet frame contains a data unit. (LLDPDU), that is a series of “TLV” structures, where the LLDP Ethernet frame starts with forced “TLVs” through the topology identifier, port identifier, and time-to-live (TTL).


Note that devices that run the Link Layer Discovery Protocol “LLDP” on one of its interfaces use “TLVs”, to receive information and send it to their neighbors, as these devices store the information of neighboring devices in a local table that can be accessed using “SNMP” which is the network management protocol Simple, where information stored by devices includes the following:


  • System name and description.
  • Port name and description.
  • IP address management.
  • VLAN.
  • neighboring device capabilities.
  • MAC address.
  • MDI power.
  • Link aggregation.


 2. Uses of the Link Layer Discovery Protocol “LLDP”


The Link Layer Discovery Protocol (LLDP) is used in data center bridging requirements, as it is used to advertise Power over Ethernet (PoE), knowing that it can work on both Cisco and non-Cisco devices as it is an open standard protocol recommended by CISCO as well. And that the Link Layer Discovery Protocol “LLDP” is an extension of “MED” as it gives an advantage over “CDP”.


Link Layer Discovery Protocol (LLDP) is a Layer 2 Neighbor Discovery protocol that allows devices to advertise device information to their directly connected peers or neighbors. A best practice is to enable LLDP globally, to standardize the network topology across all devices if you have A multi-vendor network, and the commonly used Layer 2 discovery protocols are often vendor-owned, for example, “Cisco’s CDP”, “Foundry’s FDP”, “Extreme’s EDP” and “Nortel’s NDP”, this makes Layer 2 discovery difficult in a non-Vendor environment. To counter this, the IETF introduced a vendor-neutral configuration exchange protocol.


Using Link Layer Discovery Protocol “LLDP” device information such as topology identification, port ID, port description, system name and description, device capability such as router, switch, hub, “IP/MAC” address, etc. is transmitted to neighboring devices where this information is also stored in databases Local Management Information (MIBs), and can be queried using Simple Network Management Protocol (SNMP). Devices that support LLDP have an LLDP proxy installed in them, which sends advertisements from all physical interfaces either directly or indirectly. periodically or when changes occur.


Network monitoring software such as WhatsUp Gold uses SNMP queries to scan the device's MIB to retrieve neighborhood information. “ARP Cache Discovery” as well as other “layer 2/3” protocols, to navigate through interconnected devices and retrieve information to build a detailed topology map; This is because LLDP works only at the data link layer, as WhatsUp Gold will detect devices that do not have recent IP traffic as well as devices in a blocked state.


3. Link Layer Discovery Protocol (LLDP) Advantages


  • Simplifies the use of network management tools in a multi-vendor environment.
  • Accurate discovery of physical network topology that simplifies troubleshooting within enterprise networks.
  • Enables the discovery of stations in multi-vendor environments.
  • Provides device capability and supports system name, an optional description, and management address.
  • Provides information that can be used to detect duplex and speed mismatches.
  • Discover devices with misconfigured or inaccessible IP addresses.


4. Using LLDP Link Layer Discovery Protocol with PROFINET


You can set up your PROFINET system including the controller and hardware, during startup the devices will start exchanging LLDP information, and structure information can be read from the devices by the engineering tool PROFINET, where it can now be saved This topology is set as “baseline” and downloaded into the “PROFINET IO” console If any changes to the chassis are detected, the console will receive an alert from the affected station, For example, the port has been switched from the neighborhood of the station in the downstream device is not connected to the network and the cable is disconnected, using The mechanisms in PROFINET, this is like a 'neighborhood watch' added to our system.