Trunk group operation using LACP

The switch can automatically configure a dynamic LACP trunk group, or you can manually configure a static LACP trunk group.


LACP requires full-duplex (FDx) links of the same media type (10/100Base-T, 100FX, and so on) and the same speed and enforces speed and duplex conformance across a trunk group. For most installations, it is recommended that you leave the port mode settings at Auto (the default). LACP also operates with Auto-10, Auto-100, and Auto-1000 (if negotiation selects FDx), and 10FDx, 100FDx, and 1000FDx settings.

LACP trunk status commands include:

Trunk display method

Static LACP trunk

Dynamic LACP trunk

CLI show lacp command

Included in listing.

Included in listing.

CLI show trunk command

Included in listing.

Not included.

Thus, to display a listing of dynamic LACP trunk ports, you must use the show lacp command.

In most cases, trunks configured for LACP on the switches operate as described in the following table.

Table 11: LACP trunk types

LACP port trunk configuration


Dynamic LACP

This option automatically establishes an 802.3ad-compliant trunk group, with LACP for the port Type parameter and DynX for the port Group name, where X is an automatically assigned value from 1 to 60, depending on how many dynamic and static trunks are currently on the switch. (The switch allows a maximum of 60 trunk groups in any combination of static and dynamic trunks.)

Dynamic LACP trunks operate only in the default VLAN (unless GVRP is enabled and Forbid is used to prevent the trunked ports from joining the default VLAN). Thus, if an LACP dynamic port forms using ports that are not in the default VLAN, the trunk automatically moves to the default VLAN unless GVRP operation is configured to prevent this from occurring. In some cases, this can create a traffic loop in your network. For more information on this topic, see VLANs and dynamic LACP .

Under the following conditions, the switch automatically establishes a dynamic LACP port trunk group and assigns a port Group name:
  • The ports on both ends of each link have compatible mode settings (speed and duplex).

  • The port on one end of each link must be configured for LACP Active and the port on the other end of the same link must be configured for either LACP Passive or LACP Active. For Example:
Either of the above link configurations allows a dynamic LACP trunk link.

Backup Links: A maximum of eight operating links are allowed in the trunk, but, with dynamic LACP, you can configure one or more additional (backup) links that the switch automatically activates if a primary link fails. To configure a link as a standby for an existing eight-port dynamic LACP trunk, ensure that the ports in the standby link are configured as either active-to-active or active-to-passive between switches.

Displaying dynamic LACP trunk data: To list the configuration and status for a dynamic LACP trunk, use the CLI show lacp command.

The dynamic trunk is automatically created by the switch and is not listed in the static trunk listings available in the menu interface or in the CLI show trunk listing.

Static LACP

Provides a manually configured, static LACP trunk to accommodate these conditions:
  • The port on the other end of the trunk link is configured for a static LACP trunk.

  • You want to configure non-default Spanning Tree or IGMP parameters on an LACP trunk group.

  • You want an LACP trunk group to operate in a VLAN other than the default VLAN and GVRP is disabled. (See VLANs and dynamic LACP.)

  • You want to use a monitor port on the switch to monitor an LACP trunk.

The trunk operates if the trunk group on the opposite device is running one of the following trunking protocols:
  • Active LACP

  • Passive LACP

  • Trunk

This option uses LACP for the port Type parameter and TrkX for the port Group parameter, where X is an automatically assigned value in a range corresponding to the maximum number of trunks the switch allows. (See Port trunk features and operation for the maximum number of trunk groups allowed on the switches.)

Displaying static LACP trunk data : To list the configuration and status for a static LACP trunk, use the CLI show lacp command. To list a static LACP trunk with its assigned ports, use the CLI show trunk command or display the menu interface Port/Trunk Settings screen.Static LACP does not allow standby ports.