LLDP

Link Layer Discovery Protocol (LLDP) (also known as 802.1ab) is an industry-standard protocol designed to supplant proprietary Link-Layer protocols such as Extreme's Discovery Protocol (EDP) and Cisco Discovery Protocol (CDP). The goal of LLDP is to provide an inter-vendor-compatible mechanism to deliver Link-Layer notifications to adjacent network devices.

An LLDP device advertises itself to adjacent (neighbor) devices by transmitting LLDP data packets on all interfaces on which outbound LLDP is enabled and reading LLDP advertisements from neighbor devices on ports on which inbound LLDP is enabled. Inbound packets from neighbor devices are stored in a LLDP Management Information Base (MIB). This information can then be queried by other devices through SNMP.

 

LLDP information is used by network management tools to create accurate physical network topologies by determining which devices are neighbors and through which interfaces they connect. LLDP operates at layer 2 and requires an LLDP agent to be active on each interface that sends and receives LLDP advertisements. LLDP advertisements can contain a variable number of TLV (type, length, value) information elements. Each TLV describes a single attribute of a device such as: system capabilities, management IP address, device ID, port ID. LLDP is useful in obtaining information about an external power device, such as a Wireless Access Point (WAP). 

WAPs are treated as external devices that are configured using the LLDP profile to set up inventory information, (e.g., manufacturer’s name) and LLDP-MED Power extensions, if the device fully supports those extensions, which will designate peak power required by the device.

Moreover, LLDP also supports Time-To-Live (TTL) mechanism which helps prevent loops in redundant networks by limiting the number of hops a packet can travel before being discarded. This ensures efficient use of network resources while improving overall network stability. 

LLDP supports a defined set of attributes that it uses to discover neighbor devices and are referred to as TLVs which are as follows:

• Type = Chassis Id, Port Id, Mgt Address, Vendor Specific 
• Length = Length of value field in octets (not including pads)  
• Value = Binary list of octets + pads for alignment 

Devices running LLDP, on one of their interfaces, uses TLVs to receive and send information to their neighbors. These devices store the information of neighboring devices in a local table that can be accessed using Simple Network Management Protocol (SNMP). Information stored by the devices includes:

• System name & description
• Port name & description
• IP management address
• VLAN
• Capabilities of the neighbor device
• MAC address
• MDI power

LLDP-MED

LLDP-MED (ANSI/TIA-1057/D6) extends the LLDP (IEEE 802.1AB) industry standard to support advanced features on the network edge for Voice Over IP (VoIP) endpoint devices with specialized capabilities and LLDP-MED standards-based functionality. LLDP-MED in the switches uses the standard LLDP commands described earlier in this section, with some extensions, and also introduces new commands unique to LLDP-MED operation. The show commands described elsewhere in this section are applicable to both LLDP and LLDP-MED operation. LLDP-MED enables:

• Configure Voice VLAN and advertise it to connected MED endpoint devices.
• Power over Ethernet (PoE) status and troubleshooting support via SNMP.
• LLDP-MED capabilities TLV
• Network policy TLV
• Power management TLV
• Inventory management TLV
• Location TLV

LLDP Frame Format

In 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 LLDP Data Unit (LLDPDU). Each LLDPDU is a sequence of type-length-value (TLV) structures.

• The Ether Type field is set to 0x88cc.
• Each LLDP frame starts with the following mandatory TLVs and must intact in LLDP implementations.
  • Chassis ID
  • Port ID, and
  • Time-to-Live (TTL).
• Any number of optional TLVs are followed by mandatory TLVs.
• The frame ends with a special TLV named end of LLDPDU in which both the type and length fields are 0.
• The LLDP specification allows for various organizations to define and encode their own TLVs. These are called Organizationally Specific TLVs. All Organizationally Specific TLVs start with an LLDP TLV Type value of 127.

LLDP Profile Attributes

The following LLDP profile attributes are available for user creation and editing.

Admin State

Standard Type-Length-Value Activation

• Chassis ID - 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. 
• Time To Live (TTL) - 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. 
• Port ID - 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. 
• System Name - Identifies the administratively-assigned name for the device (per RFC3418). 
• System Capabilities - 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.). 
• Port Description - 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). 
• System Description - 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). 
• Management Address - Identifies the IP address or MAC address of the device. 

Standard Parameters

• Chassis ID Source - Select from:
  • ONT User label (TID)/Chassis (1)
  • Port User Label/(ifAlias (2)
  • ONT User Label/Port (3)
  • MAC Address (4)
  • IP/Network Address (5)
  • Port AID/ifName( 6)

• Port ID Source - Select from:
  • Port User Label/ifAlias (1)
  • ONT User label/Port (2)
  • MAC Address (3)
  • IP/Network Address (4)
  • Port AID/ifName (5)
  • CID/Agent Circuit (6)
  • Template/Local (7)

• Port ID Template - Supports the following variables: 
  • %TID%,%SLOT%,%PON%,%ONT%,%PORT%,%AID%,%PORT-LABEL%,%ONT-LABEL%,%PON -LABEL%
  • Meaning: TID, Slot Number, PON Number, ONT Number, Port Number, Port AID, Port User Label, ONT User Label, and PON User Label, correspondingly.

IEEE 802.1 Type-Length-Values Activation (TLV)

• Port VLAN ID (PVID) - Identifies the VLAN identifier associated with an untagged VLAN. Only one Port VLAN ID can exist in an LLDP PDU. 
• VLAN Name - Allows a device to advertise the textual name of any VLAN with which it is configured. 
• Port & Protocol VLAN ID (PPVID) - Allows the port to advertise if it supports port/protocol based VLANs, and their associated VLAN ID. 
• Protocol Identity - Provides the protocols that are accessible through the LLDP port.

IEEE 802.3 Type-Length-Values Activation

• MAC/PHY Config/Status - Determines more about the auto negotiation settings of the port, as well as the type of physical interface used. 
• Link Aggregation - 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 aggregation, the port of the aggregation). 
• Power via MDI - Advertises the power-via-MDI implementations supported by the port. Power Information allows for improved power management for endpoints utilizing IEEE 802.3af Power over Ethernet (PoE). 
• Maximum Frame Size (MTU) - Reports the maximum supported frame size for the port. 

LLDP-MED Type-Length-Values Activation

• Capabilities - Selecting capabilities enables the LLDP-Med extensions, of which Network Policy is the only extension available at this time. If Capabilities is selected, the remaining options in this TLV are enabled. 
• Location - Location information for the LLDP MED interface. 
• Extended Power via MDI (PD) - Advertises the power source equipment type, power source, power priority, and power value of the port. It is the responsibility of the PSE device (network connectivity device) to advertise the power priority on a port. 
• Network Policy - Allows both network connectivity devices and endpoints to advertise VLAN configurations and associated Layer-2 and Layer-3 attributes for specific applications on that port. For example, the switch can notify a phone of the VLAN number that it should use. The phone can connect into any switch, contain its VLAN number, and then start communication with the configured call control. 
• Extended Power via MDI (PSE) - Advertises the power source equipment type, power source, power priority, and power value of the port. It is the responsibility of the PSE device (network connectivity device) to advertise the power priority on a port. 
• Inventory - Advertises inventory information about itself to the switch to which it is attached. 

LLDP-MED Parameters

• MED Fast Start Repeat Count - Enables a device to initially advertise itself at a faster rate for a limited time when an LLDP-MED Endpoint has been newly detected or connected to the network. Default is 4. 
• Location Source - Select from Port AID, User Label, Port LLDP MED Location, or Template
  • Note 1: If Port LLDP_MED Location is selected, Location Type allows selection of Civic Address or ECS ELIN. 
  • Note 2: If Template is selected, the Location Type allows the selection of ECS ELIN.
• Location Type - If Location Source of Port LLDP-MED or Template is selected, select from Civic Address or ECS ELIN. 
• Location Template - Template for the Civic or ECS ELIN Location Type. 

Notification Activation

• Port Config Notifications - Advertises Port Configuration notifications. 
• LLDP-MED Notifications - Advertises LLDP_MED SNMP notifications. 

VLAN Assignment for VoIP Phone

• Delay Untagged VLAN Access - Select from Disable, Enable (default) 
  • LLDP VLAN Assignment Delay - LLDP VLAN Assignment delay in seconds. Default is 60.