Configuring LLDP

This chapter describes how to configure the Link Layer Discovery Protocol (LLDP) on the Catalyst 2960 switch.

Note For complete syntax and usage information for the commands used in this chapter, see the command reference for this release and the "System Management Commands" section in the Cisco IOS Configuration Fundamentals Command Reference, Release 12.2.

This chapter consists of these sections:

•Understanding LLDP

•Configuring LLDP

•Monitoring and Maintaining LLDP

Understanding 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, and switches). 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 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. Details such as configuration information, device capabilities, and device identity can be advertised using this protocol.

The switch supports these basic management TLVs. These are mandatory LLDP TLVs.

•Port description TLV

•System name TLV

•System description

•System capabilities TLV

• Management address TLV

•Port VLAN ID TLV ((IEEE 802.1 organizationally specific TLVs)

•MAC/PHY configuration/status TLV(IEEE 802.3 organizationally specific TLVs)

Note A switch stack appears as a single switch in the network. Therefore, LLDP discovers the switch stack, not the individual stack members.

Configuring LLDP

This section contains this configuration information:

•Default LLDP Configuration

•Configuring LLDP Characteristics

•Disabling and Enabling LLDP Globally

•Disabling and Enabling LLDP on an Interface

•Monitoring and Maintaining LLDP

Default LLDP Configuration

Table 21-1 shows the default LLDP configuration. To change the default settings, use the LLDP global configuration and LLDP interface configuration commands.

Table 21-1 Default LLDP Configuration

Feature
Default Setting

LLDP global state

Enabled

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


Configuring LLDP Characteristics

You can configure the frequency of LLDP updates, the amount of time to hold the information before discarding it, and the initialization delay time. You can also select the LLDP TLVs to be sent and received.

Beginning in privileged EXEC mode, follow these steps to configure these characteristics:

Note Steps 2 through 5 are all optional and can be performed in any order.

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

lldp holdtime seconds

(Optional) Specify the amount of time a receiving device should hold the information sent by your device before discarding it.

The range is 0 to 65535 seconds; the default is 120 seconds.

Step 3 

lldp reinit

(Optional) Specify the delay time in seconds for LLDP to initialize on any interface.

The range is 2 to 5 seconds; the default is 2 seconds.

Step 4 

lldp timer seconds

(Optional) Set the transmission frequency of LLDP updates in seconds.

The range is 5 to 65534 seconds; the default is 30 seconds.

Step 5 ll

lldp tlv-select

(Optional) Specify the LLDP TLVs to send or receive.

Step 6 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Use the no form of each of the LLDP commands to return to the default setting.

This example shows how to configure LLDP characteristics. 

Switch# configure terminal

Switch(config)# lldp holdtime 120

Switch(config)# lldp reinit 2

Switch(config)# lldp timer 30

Switch(config)# end

For additional LLDP show commands, see the "Monitoring and Maintaining LLDP" section.

Disabling and Enabling LLDP Globally

LLDP is enabled by default.

Beginning in privileged EXEC mode, follow these steps to disable LLDP:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

no lldp run

Disable LLDP.

Step 3 

end

Return to privileged EXEC mode.

Beginning in privileged EXEC mode, follow these steps to enable LLDP when it has been disabled:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

lldp run

Enable LLDP.

Step 3 

end

Return to privileged EXEC mode.

This example shows how to disable LLDP. 

Switch# configure terminal

Switch(config)# no lldp run

Switch(config)# end

This example shows how to enable LLDP. 

Switch# configure terminal

Switch(config)# lldp run

Switch(config)# end

Disabling and Enabling LLDP on an Interface

LLDP is enabled by default on all supported interfaces to send and to receive LLDP information.

Note If the interface is configured as a tunnel port, LLDP is automatically disabled.

Beginning in privileged EXEC mode, follow these steps to disable LLDP on an interface.

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface interface-id

Specify the interface on which you are disabling LLDP, and enter interface configuration mode.

Step 3 

no lldp transmit

No LLDP packets are sent on the interface.

Step 4 

no lldp receive

No LLDP packets are received on the interface.

Step 5 

end

Return to privileged EXEC mode.

Step 6 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

Beginning in privileged EXEC mode, follow these steps to enable LLDP on an interface when it has been disabled:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface interface-id

Specify the interface on which you are enabling LLDP, and enter interface configuration mode.

Step 3 

lldp transmit

LLDP packets are sent on the interface.

Step 4 

lldp receive

LLDP packets are received on the interface.

Step 5 

end

Return to privileged EXEC mode.

Step 6 

copy running-config startup-config

(Optional) Save your entries in the configuration file.

This example shows how to enable LLDP on an interface. 

Switch# configure terminal

Switch(config)# interface GigabitEthernet0/1

Switch(config-if)# lldp transmit

Switch(config-if)# lldp receive

Switch(config-if)# end

Monitoring and Maintaining LLDP

To monitor and maintain LLDP on your device, perform one or more of these tasks, beginning in privileged EXEC mode.

Command
Description

clear lldp counters

Reset the traffic counters to zero.

clear lldp table

Delete the LLDP table of information about neighbors.

show lldp

Display 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

Display 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 interface [interface-id]

Display 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]

Display 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

Display LLDP counters, including the number of packets sent and received, number of packets discarded, and number of unrecognized TLVs.