Tips For Troubleshooting When 802.3ad Link Aggregation Activation Remains in Negotiating State

Summary

On AIX, if 802.3ad Link Aggregation negotiation fails during configuration, the failure can be due to LACPDU packets not being received from the switch. Packets can fail to be received from the switch for one of the following reasons:
- Incorrect switch configuration.
- A faulty switch.
- A bad cable between the ethernet adapter port and the switch.
- A malfunctioning port on the ethernet adapter.
- A complete failure of the ethernet adapter containing the 802.3ad Link Aggregation port.

When this issue is seen, symptoms are:
- "ECH_PORT_OUT_OF_SYN" reported in the error log.
- Output from "entstat -d [802.3ad_device]" reports "OUT_OF_SYNC".
- A network trace shows 802.3ad LACP packets being sent to negotiate the connection from the IEEE 802.3ad Link Aggregation port that is in negotiating state; but no 802.3ad LACP packets being received from the switch.

Resolution steps:
- Check the cable and that it is connected properly. Replace the cable if necessary.
- Check the adapter. Replace it if necessary.
- Check the switch configuration.

Tips for checking the switch configuration:
In order for the switch port to transmit and receive LACP packets, configure the switch port as a member of a port channel group and set the switch port to either active or passive mode. When the switch port is configured in this way and the EtherChannel mode on AIX is set to "8023ad", the associated IEEE 802.3ad Link Aggregation port synchronizes with the switch port without issue. However, if switch port channel members are changed to either "regular access" or the trunk ports are set to "channel group on" (no LACP), the 802.3ad synchronization expires as designed.

If the channel group mode on the switch is changed to "channel group on" (no LACP), regular access, or trunk ports, then set the AIX EtherChannel mode to "standard" to establish a successful EtherChannel connection without LACP. When the switch is configured this way, if the AIX EtherChannel is configured for "8023ad" mode, or continues to be set to "8023ad" mode from a previous environment, then the negotiation to establish a IEEE 802.3ad Link Aggregation connection fails, remaining in "negotiating" state on AIX, continuing to transmit LACP packets containing the previous Partner_Port and Partner_Key. Since the switch is not configured for LACP, it does not respond to these packets. In order to update the Partner_Port and Partner_Key in LACP packets transmitted by the IEEE 802.3ad Link Aggregation port on AIX, it is necessary to first receive the new Partner_Port and Partner_Key in LACP packets from the switch.