Troubleshooting LAGs

To troubleshoot problems with static and dynamic LAG configuration, use the following troubleshooting tips.

When a link has problem, the show port-channel command displays the following message:

Mux machine state: Deskew not OK.

Troubleshooting static LAGs

If a link is not able to join a static LAG:

Make sure that the mode is "on."
Make sure that the port-channel interface is in the administrative "up" state by ensuring that the no shutdown command was entered on the interface on both ends of the link.

If a link is not able to join dynamic (LACP) LAG:

Make sure that both ends of the link are not configured for passive mode. They must be configured as active /active, active /passive, or passive /active.
Make sure that the port-channel interface is in the administrative "up" state by ensuring that the no shutdown command was entered on the interface on both ends of the link.
Make sure that the links that are part of the LAG are connected to the same neighboring switch.
Make sure that the system ID of the switches connected by the link is unique. You can verify this by entering the show lacp sys-id command on both switches.
Make sure that LACP PDUs are being received and transmitted on both ends of the link and that there are no error PDUs. You can verify this by entering the show lacp counters number command and looking at the receive mode (rx) and transmit mode (tx) statistics. The statistics should be incrementing and should not be at zero or a fixed value. If the PDU rx count is not incrementing, check the interface for possible CRC errors by entering the show interface link-name command on the neighboring switch. If the PDU tx count is not incrementing, check the operational status of the link by entering the show interface link-name command and verifying that the interface status is "up."