Configuring Link Aggregation Control Protocol (LACP)


Link Aggregation Control Protocol (LACP) is part of the IEEE specification 802.3ad that allows you to bundle several physical ports to form a single logical channel. When you change the number of active bundled ports on a port channel, traffic patterns reflect the rebalanced state of the port channel.


LACP supports the automatic creation of Gigabit Ethernet port trunks by exchanging LACP packets between ports. It learns the capabilities of port groups and informs the other ports. Once LACP identifies correctly matched Ethernet links, it facilitates grouping the links into Gigabit Ethernet port trunks.


LACP performs the following functions on the switch:


  • Maintains configuration information to control aggregation.
  • Exchanges configuration information with other peer devices.
  • Attaches or detaches ports from the LAG based on the exchanged configuration information.


LACP packets are exchanged between ports in these modes:


  • Active — Places a port into an active negotiating state, and the port initiates negotiations by sending LACP packets.
  • Passive — Places a port into a passive negotiating state where the port responds to LACP packets it receives but does not initiate LACP negotiation. In this mode, the port channel group attaches the interface to the bundle.
  • Off — LACP is not enabled on the switch port or trunk.


Active and passive modes allow LACP to negotiate between ports to determine if they can form a port channel based on criteria such as port speed and trunking state.


To enable or disable LACP, or change the system priority, use the following command:


CLI (network-admin@switch) > lacp-modify enable system-priority 35000


The default system priority value is 32768 with a range from 0 to 65535.


Understanding LACP Priority


LACP port priority is configured on each port using LACP. You can use the default value, 32768, or configure a specific value from 0 to 65535. LACP uses the port priority with the port number to form the port identifier. The port priority determines which ports should be in standby mode when there is a hardware limitation that prevents all compatible ports from aggregating.


LACP system priority can be configured automatically or using the CLI. LACP uses the system priority with the device MAC address to form the system ID and also during negotiations with other systems. The range of LACP system priority is from 0 to 65535. The default value is 32768.


To create a trunk with LACP, use the following command:


CLI (network-admin@switch) > trunk-create name trunk23 port 20-36 lacp-mode active


To modify a trunk with LACP, use the following command:


CLI (network-admin@switch) > trunk-modify name trunk23 lacp-mode passive


To modify a port configuration and add LACP priority to the port, use the following command:


CLI (network-admin@switch) > port-config-modify port 33 lacp-priority 34