Re: A QinQ problem with QFX5100

Try this:

set interfaces ae31 flexible-vlan-tagging 
set interfaces ae31 mtu 9216 
set interfaces ae31 encapsulation extended-vlan-bridge
set interfaces ae31 unit 3174 vlan-tags outer 3174
set interfaces ae31 unit 3174 vlan-tags inner-range 21-22
set interfaces ae31 unit 3174 input-vlan-map push
set interfaces ae31 unit 3174 output-vlan-map pop

Question: Why do you need to create vlan 21? Either QinQ or single-tag in your case.