LLDP, LLDP-MED, and Wired Location Service Overview
LLDP
The Cisco Discovery Protocol (CDP) is a device discovery protocol that runs over Layer 2 (the data link layer) on all Cisco-manufactured devices (routers, bridges, access servers, switches, and controllers). CDP allows network management applications to automatically discover and learn about other Cisco devices connected to the network.
To support non-Cisco devices and to allow for interoperability between other devices, the switch supports the IEEE 802.1AB Link Layer Discovery Protocol (LLDP). LLDP is a neighbor discovery protocol that is used for network devices to advertise information about themselves to other devices on the network. This protocol runs over the data-link layer, which allows two systems running different network layer protocols to learn about each other.
LLDP Supported TLVs
LLDP supports a set of attributes that it uses to discover neighbor devices. These attributes contain type, length, and value descriptions and are referred to as TLVs. LLDP supported devices can use TLVs to receive and send information to their neighbors. This protocol can advertise details such as configuration information, device capabilities, and device identity.
The switch supports these basic management TLVs. These are mandatory LLDP TLVs.
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Port description TLV
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System name TLV
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System description TLV
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System capabilities TLV
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Management address TLV
These organizationally specific LLDP TLVs are also advertised to support LLDP-MED.
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Port VLAN ID TLV (IEEE 802.1 organizationally specific TLVs)
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MAC/PHY configuration/status TLV (IEEE 802.3 organizationally specific TLVs)
LLDP and Cisco Switch Stacks
A switch stack appears as a single switch in the network. Therefore, LLDP discovers the switch stack, not the individual stack members.
LLDP and Cisco Medianet
When you configure LLDP or CDP location information on a per-port basis, remote devices can send Cisco Medianet location information to the switch. For information, go to http://www.cisco.com/en/US/docs/ios/netmgmt/configuration/guide/nm_cdp_discover.html.
LLDP-MED
LLDP for Media Endpoint Devices (LLDP-MED) is an extension to LLDP that operates between endpoint devices such as IP phones and network devices such as switches. It specifically provides support for voice over IP (VoIP) applications and provides additional TLVs for capabilities discovery, network policy, Power over Ethernet, inventory management and location information. By default, all LLDP-MED TLVs are enabled.
LLDP-MED Supported TLVs
LLDP-MED supports these TLVs:
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LLDP-MED capabilities TLV
Allows LLDP-MED endpoints to determine the capabilities that the connected device supports and has enabled.
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Network policy TLV
Allows both network connectivity devices and endpoints to advertise VLAN configurations and associated Layer 2 and Layer 3 attributes for the specific application on that port. For example, the switch can notify a phone of the VLAN number that it should use. The phone can connect to any switch, obtain its VLAN number, and then start communicating with the call control.
By defining a network-policy profile TLV, you can create a profile for voice and voice-signaling by specifying the values for VLAN, class of service (CoS), differentiated services code point (DSCP), and tagging mode. These profile attributes are then maintained centrally on the switch and propagated to the phone.
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Power management TLV
Enables advanced power management between LLDP-MED endpoint and network connectivity devices. Allows switches and phones to convey power information, such as how the device is powered, power priority, and how much power the device needs.
LLDP-MED also supports an extended power TLV to advertise fine-grained power requirements, end-point power priority, and end-point and network connectivity-device power status. LLDP is enabled and power is applied to a port, the power TLV determines the actual power requirement of the endpoint device so that the system power budget can be adjusted accordingly. The switch processes the requests and either grants or denies power based on the current power budget. If the request is granted, the switch updates the power budget. If the request is denied, the switch turns off power to the port, generates a syslog message, and updates the power budget. If LLDP-MED is disabled or if the endpoint does not support the LLDP-MED power TLV, the initial allocation value is used throughout the duration of the connection.
You can change power settings by entering the power inline {auto [max max-wattage] | never | static [max max-wattage]} interface configuration command. By default the PoE interface is in auto mode; If no value is specified, the maximum is allowed (30 W).
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Inventory management TLV
Allows an endpoint to send detailed inventory information about itself to the switch, including information hardware revision, firmware version, software version, serial number, manufacturer name, model name, and asset ID TLV.
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Location TLV
Provides location information from the switch to the endpoint device. The location TLV can send this information:
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Civic location information
Provides the civic address information and postal information. Examples of civic location information are street address, road name, and postal community name information.
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ELIN location information
Provides the location information of a caller. The location is determined by the Emergency location identifier number (ELIN), which is a phone number that routes an emergency call to the local public safety answering point (PSAP) and which the PSAP can use to call back the emergency caller.
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Wired Location Service
The switch uses the location service feature to send location and attachment tracking information for its connected devices to a Cisco Mobility Services Engine (MSE). The tracked device can be a wireless endpoint, a wired endpoint, or a wired switch or controller. The switch notifies the MSE of device link up and link down events through the Network Mobility Services Protocol (NMSP) location and attachment notifications.
The MSE starts the NMSP connection to the switch, which opens a server port. When the MSE connects to the switch there are a set of message exchanges to establish version compatibility and service exchange information followed by location information synchronization. After connection, the switch periodically sends location and attachment notifications to the MSE. Any link up or link down events detected during an interval are aggregated and sent at the end of the interval.
When the switch determines the presence or absence of a device on a link-up or link-down event, it obtains the client-specific information such as the MAC address, IP address, and username. If the client is LLDP-MED- or CDP-capable, the switch obtains the serial number and UDI through the LLDP-MED location TLV or CDP.
Depending on the device capabilities, the switch obtains this client information at link up:
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Slot and port specified in port connection
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MAC address specified in the client MAC address
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IP address specified in port connection
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802.1X username if applicable
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Device category is specified as a wired station
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State is specified as new
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Serial number, UDI
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Model number
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Time in seconds since the switch detected the association
Depending on the device capabilities, the switch obtains this client information at link down:
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Slot and port that was disconnected
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MAC address
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IP address
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802.1X username if applicable
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Device category is specified as a wired station
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State is specified as delete
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Serial number, UDI
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Time in seconds since the switch detected the disassociation
When the switch shuts down, it sends an attachment notification with the state delete and the IP address before closing the NMSP connection to the MSE. The MSE interprets this notification as disassociation for all the wired clients associated with the switch.
If you change a location address on the switch, the switch sends an NMSP location notification message that identifies the affected ports and the changed address information.
Default LLDP Configuration
Feature |
Default Setting |
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LLDP global state |
Disabled |
LLDP holdtime (before discarding) |
120 seconds |
LLDP timer (packet update frequency) |
30 seconds |
LLDP reinitialization delay |
2 seconds |
LLDP tlv-select |
Disabled to send and receive all TLVs |
LLDP interface state |
Disabled |
LLDP receive |
Disabled |
LLDP transmit |
Disabled |
LLDP med-tlv-select |
Disabled to send all LLDP-MED TLVs. When LLDP is globally enabled, LLDP-MED-TLV is also enabled. |
Restrictions for LLDP
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If the interface is configured as a tunnel port, LLDP is automatically disabled.
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If you first configure a network-policy profile on an interface, you cannot apply the switchport voice vlan command on the interface. If the switchport voice vlan vlan-id is already configured on an interface, you can apply a network-policy profile on the interface. This way the interface has the voice or voice-signaling VLAN network-policy profile applied on the interface.
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You cannot configure static secure MAC addresses on an interface that has a network-policy profile.
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When Cisco Discovery Protocol and LLDP are both in use within the same switch, it is necessary to disable LLDP on interfaces where Cisco Discover Protocol is in use for power negotiation. LLDP can be disabled at interface level with the commands no lldp tlv-select power-management or no lldp transmit / no lldp receive .