Understanding LLDP
The Link Layer Discovery Protocol (LLDP) is a vendor-neutral data-link layer protocol, used by network devices for advertising their identity, capabilities, and neighbors on an IEEE 802 local area network, principally wired Ethernet.
As protocol runs over the data-link layer, it allows two systems running different network layer protocols to learn about each other. Therefore the protocol allows interoperability between Cisco devices and non-Cisco devices.
LLDP supports a set of attributes that it uses to discover neighboring devices. These attributes contain type, length, and value descriptions and are referred to as type-length-value (TLV) structures. LLDP supported devices can use TLVs to receive and send information to their neighbors. Details such as configuration information, device capabilities, and device identity can be advertised using this protocol.
Configuring LLDP
You can configure LLDP only through the CLI.
The following commands are to be executed in global configuration mode.
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lldp run |
To enable LLDP |
ap(config) # lldp run |
lldp holdtime seconds |
To specify the amount of time a receiving device should hold the information sent by your device before discarding it. |
ap(config) # lldp holdtime 120 |
lldp reinit seconds |
To set the delay (in sec) for LLDP initialization on any interface. |
ap(config)# lldp reinit 60 |
lldp timer seconds |
To specify the rate at which LLDP packets are sent (in sec) |
ap(config)# lldp timer 50 |
lldp tlv-select tlv_name |
To specify the TLVs to send and receive LLDP packets. The available TLVs are dcbxp, management-address, port-description, port-vlan, system-capabilities, system-description, and system-name. All available TLVs are enabled by default. |
ap(config)# lldp tlv-select system-name |
Default LLDP Configuration
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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 |
Enabled to send and receive all TLVs. |
LLDP interface state |
Enabled |
LLDP receive |
Enabled |
LLDP transmit |
Enabled |
Disabling and Re-Enabling LLDP on Gigabit Ethernet Interfaces
To disable LLDP on a Gigabit Ethernet (GbE) interface, perform the following steps.
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Step 1 |
configure terminal |
Enters global configuration mode. |
Step 2 |
interface interface-id |
Specifies the interface on which you are disabling LLDP, and enters interface configuration mode. |
Step 3 |
no lldp transmit |
Disallows sending LLDP packets on the interface. |
Step 4 |
no lldp receive |
Disallows receiving LLDP packets on the interface. |
Step 5 |
end |
Returns to privileged EXEC mode. |
Step 6 |
copy running-config startup-config |
Saves your entries in the configuration file. |
To re-enable LLDP on a GbE interface, perform the following steps.
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Step 1 |
configure terminal |
Enters global configuration mode. |
Step 2 |
interface interface-id |
Specifies the interface on which you are disabling LLDP, and enters interface configuration mode. |
Step 3 |
lldp transmit |
Allows sending LLDP packets on the interface. |
Step 4 |
lldp receive |
Allows receiving LLDP packets on the interface. |
Step 5 |
end |
Returns to privileged EXEC mode. |
Step 6 |
copy running-config startup-config |
Saves your entries in the configuration file. |
Viewing and Deleting LLDP Information
The following commands are to be executed in privileged EXEC mode.
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show lldp |
Displays global information, such as frequency of transmissions, the holdtime for packets being sent, and the delay time for LLDP, to initialize on an interface. |
show lldp entry entry-name |
Displays information about a specific neighbor. You can enter an asterisk (*) to display all neighbors, or you can enter the name of the neighbor about which you want information. |
show lldp errors |
Displays LLDP computational errors and overflows. |
show lldp interface |
Displays information about interfaces where LLDP is enabled. You can limit the display to the interface about which you want information. |
show lldp neighbors [interface-id] [detail] |
Displays information about neighbors, including device type, interface type and number, holdtime settings, capabilities, and port ID. You can limit the display to neighbors of a specific interface or expand the display to provide more detailed information. |
show lldp traffic |
Displays LLDP counters, including the number of packets sent and received, number of packets discarded, and number of unrecognized TLVs. |
clear lldp counters |
Resets the traffic and error counters to zero. |
clear lldp table |
Deletes the LLDP table of information about neighbors. |