This post enquires whether eNSP supports the QinQ tunnel feature.
Via S3300 simulation, I have configured:
interface GigabitEthernet0/0/1
port link-type dot1q-tunnel
port default vlan 100
#
interface GigabitEthernet0/0/2
port link-type trunk
port trunk allow-pass vlan 100
Then I started sending single-tagged frames (arp broadcast frames) to g0/0/1. In debugging mode, I could see arp broadcast frames being received on g0/0/1, but I never saw any frames being sent on g0/0/2.
I tried both 1.2.00 B350 and 1.2.00 B360.