This article explains the limitation for dual tagged frames passing in MC-LAG setup through interchassis link (ICL). The limitation causes the dual tagged frames to be dropped on the ICL link.

Unable to pass Dual Tag Frames on ICL link of MC-LAG

Dual tag frames are used on different designs such:  QinQ (802.1Q) or VXLAN.

The dual-tag over ICL link is not supported. This is a limitation in MC-LAG environment for dual tag frames over ICL link.

 For more information on MC-LAG settings please review the below links:

Multichassis link aggregation (MC-LAG) Platforms

Multichassis link aggregation (MC-LAG) features ​​​​​​​

Understanding Multichassis Link Aggregation Groups


Note: Multichassis link aggregation groups (MC-LAGs) are not supported with VXLAN.

VXLAN Constraints on EX Series, QFX Series and PTX Series Devices