Symptom

The connection is flapping over both devices. The frequency of this behavior is constantly; the interface goes down and up, and then down and so on.

Conditions

Both devices have the same configuration in the ports: interface TenGigabitEthernet3/0/8 switchport mode trunk cts manual no propagate sgt sap pmk 0000000000000000000000000000000000000000000000000000001234567890 mode-list gcm-encrypt end interface TwentyFiveGigE1/1/0/24 switchport mode trunk cts manual no propagate sgt sap pmk 0000000000000000000000000000000000000000000000000000001234567890 mode-list gcm-encrypt end C9400 version: Cisco IOS XE Software, Version 17.06.05 C9600 version: Cisco IOS XE Software, Version 17.06.02

Workaround

Disable TrustSec. Use the no cts manual command Or disable the encryption. no sap pmk 0000000000000000000000000000000000000000000000000000001234567890 mode-list gcm-encrypt

Further Problem Description