Using Link Layer Discovery Protocol in Multivendor Networks

Link Layer Discovery Protocol (LLDP), standardized by the IEEE as part of 802.1ab, enables standardized discovery of nodes, which in turn facilitates future applications of standard management tools such as Simple Network Management Protocol (SNMP) in multivendor networks. Using standard management tools makes physical topology information available and helps network administrators detect and correct network malfunctions and inconsistencies in configuration.

The Cisco implementation of LLDP is based on the IEEE 802.1ab standard.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Information About Using Link Layer Discovery Protocol in Multivendor Networks

IEEE 802.1ab LLDP

IEEE 802.1ab Link Layer Discovery Protocol (LLDP) is an optional link layer protocol for network topology discovery in multivendor networks. Discovery information includes device identifiers, port identifiers, versions, and other details. As a protocol that aids network management, LLDP provides accurate network mapping, inventory data, and network troubleshooting information.

LLDP is unidirectional, operating only in an advertising mode. LLDP does not solicit information or monitor state changes between LLDP nodes. LLDP periodically sends advertisements to a constrained multicast address. Devices supporting LLDP can send information about themselves while they receive and record information about their neighbors. Additionally, devices can choose to turn off the send or receive functions independently. Advertisements are sent out and received on every active and enabled interface, allowing any device in a network to learn about all devices to which it is connected. Applications that use this information include network topology discovery, inventory management, emergency services, VLAN assignment, and inline power supply.


Note

LLDP and Cisco Discovery Protocol can operate on the same interface.

The figure below shows a high-level view of LLDP operating in a network node.

When you configure LLDP or Cisco Discovery Protocol location information on a per-port basis, remote devices can send Cisco medianet location information to the switch. For more information, see the Using Cisco Discovery Protocol module.

Benefits of LLDP

  • Follows IEEE 802.1ab standard.

  • Enables interoperability among multivendor devices.

  • Facilitates troubleshooting of enterprise networks and uses standard network management tools.

  • Provides extension for applications such as VoIP.

How to Configure Link Layer Discovery Protocol in Multivendor Networks

Enabling and Disabling LLDP Globally

LLDP is disabled globally by default. This section describes the tasks for enabling and disabling LLDP globally.

Enabling LLDP Globally

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. lldp {hold time seconds | reinit delay | run | timer rate | tlv-select tlv }
  4. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

lldp {hold time seconds | reinit delay | run | timer rate | tlv-select tlv }

Example:

Device(config)# lldp run

Enables LLDP globally.

Step 4

end

Example:

Device(config)# end

Returns to privileged EXEC mode.

Disabling and Enabling LLDP on a Supported Interface

LLDP is enabled by default on all supported interfaces. This section describes the tasks for disabling and enabling LLDP on a supported interface.

Disabling LLDP on a Supported Interface

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number
  4. no lldp {tlv-select tlv | receive | transmit }
  5. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

interface type number

Example:

Device(config)# interface ethernet 0/1

Specifies the interface type and number and enters interface configuration mode.

Step 4

no lldp {tlv-select tlv | receive | transmit }

Example:

Device(config-if)# no lldp receive

Disables an LLDP TLV or LLDP packet reception on a supported interface.

Step 5

end

Example:

Device(config-if)# end

Returns to privileged EXEC mode.

Setting LLDP Packet Hold Time

Hold time is the duration that a receiving device should maintain LLDP neighbor information before aging it. Perform this task to define a hold time for an LLDP-enabled device.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. lldp holdtime seconds
  4. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

lldp holdtime seconds

Example:


Device(config)# lldp holdtime 100

Specifies the hold time.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Setting LLDP Packet Frequency

Perform this task to specify an interval at which the Cisco software sends LLDP updates to neighboring devices.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. lldp timer rate
  4. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

lldp timer rate

Example:


Device(config)# lldp timer 75

Specifies the rate at which LLDP packets are sent every second.

Step 4

end

Example:


Device(config)# end

Returns to privileged EXEC mode.

Monitoring and Maintaining LLDP in Multivendor Networks

Perform this task to monitor and maintain LLDP in multivendor networks. This task is optional, and Steps 2 and 3 can be performed in any sequence.

SUMMARY STEPS

  1. enable
  2. show lldp [entry {* | word } | errors | interface [ethernet number ] | neighbors [ethernet number | detail ] | traffic ]
  3. clear lldp {counters | table }
  4. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

show lldp [entry {* | word } | errors | interface [ethernet number ] | neighbors [ethernet number | detail ] | traffic ]

Example:


Device# show lldp entry *

Displays summarized and detailed LLDP information.

Note 

When the show lldp neighbors command is issued, if the device ID has more than 20 characters, the ID is truncated to 20 characters in command output because of display constraints.

Step 3

clear lldp {counters | table }

Example:


Device# clear lldp counters

Resets LLDP traffic counters and tables to zero.

Step 4

end

Example:


Device# end

Returns to user EXEC mode.

Enabling and Disabling LLDP TLVs

LLDP TLV support is enabled by default if LLDP is enabled globally and locally on a supported interface. Specific TLVs, however, can be enabled and suppressed.

Feature Information for Link Layer Discovery Protocol in Multivendor Networks

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1. Feature Information for Using Link Layer Discovery Protocol in Multivendor Networks

Feature Name

Releases

Feature Information

IEEE 802.1ab LLDP (Link Layer Discovery Protocol)

Cisco IOS XE Release 3.8S

Cisco IOS XE Release 3.9S

LLDP, standardized by the IEEE as part of 802.1ab, enables standardized discovery of nodes, which in turn facilitates future applications of standard management tools such as SNMP in multivendor networks.

In Cisco IOS XE Release 3.9S, support was added for the Cisco 903 Series Aggregation Services Routers.

The following commands were introduced or modified: clear lldp , lldp , and show lldp .