Configure LACP on an MLT

Configure an MLT with LACP to use the dynamic link aggregation function.

About this task

Important

Important

Attach ports to an aggregator only if their system priorities are the same; otherwise, they are considered to be operating in two different switches. You can attach ports to an aggregator only if their keys are the same.

When you add a VLAN to a dynamic MLT, only the active ports of the MLT are added as port members of the VLAN. Ports configured with the same aggregation key, but not active, are not added to the VLAN. If these inactive ports become active later, the system does not automatically add them to the VLAN port member list.

You must add all inactive ports to the VLAN. If you do not add the inactive ports to the VLAN, when they become active later, hashing can result in choosing a newly active port for traffic forwarding. Because the port is not a port member of the VLAN, traffic will be dropped. When you add the VLAN to the MLT, also add the inactive aggregation ports to the VLAN. You may need to disable LACP on the inactive ports before you can add them to the VLAN. Because the ports are inactive, disabling LACP does not cause a traffic interruption.

Similarly when you remove a VLAN from a dynamic MLT, all active ports of the MLT are removed from the VLAN port member list but the inactive members are not removed. You must remove the inactive aggregation members from the VLAN.

If you later configure a port for the same aggregation, you must add this port to all VLANs that are members of the MLT.

Procedure

  1. Enter MLT Interface Configuration mode:

    enable

    configure terminal

    interface mlt <1-512>

  2. Configure LACP on an MLT:

    lacp enable [key <0-512>] [system-priority <0-65535>]

Example

Enable LACP and configure the LACP key on MLT 3:

Switch:1(config)# interface mlt 3 
Switch:1(config-mlt)# lacp enable key 1281

Variable definitions

Use the data in the following table to use the lacp command.

Variable

Value

enable

Enables LACP on the MLT interface.

key <0-512>

Configures the LACP aggregator key for a specific MLT.

  • 0-512 is the LACP actor admin key.

system-priority <0-65535>

Configures the LACP system priority for a specific MLT.

  • 0-65535 is the system priority.