Description |
This article describes steps to take when the MCLAG-ICL interface shows a 'discarding' STP state. |
Scope | Managed FortiSwitch version 7.2.x and above. |
Solution |
Refer to the following topology:
Both the core1 and core2 MCLAG-ICL FortiSwitches should act as root bridge. Execute the following command on both Core FortiSwitches to identify if both core FortiSwitches are acting as root bridge:
diag stp instance list
Instance ID 0 (CST) Root MAC xxxxxc6, Priority 20480, Path Cost 0, Remaining Hops 20 Regional Root MAC xxxxxc6, Priority 20480, Path Cost 0
Instance ID 15
The root MAC address will be the MCLAG mac address:
diagnose switch mclag icl
But if only one of the core FortiSwitches acts as a root Bridge, then the MCLAG-ICL interface will show the STP discarding state on both Core FortiSwitches. For example:
diagnose stp instance list
_FlInK1_ICL0_ 200G 1 128 DESIGNATED LEARNING 2 EN ED
Solution:
Refer to the article and change STP priority to 4096 on both Core FortiSwitches MSTP instance 0 and 15. In this way both Core FortiSwitches will act as root Bridge and MCLAG-ICL interface STP state will change to forwarding. See this article. |