Lately I’ve been playing around with some Arista Networks switches (nice switches, not a fan of the Cisco-style CLI) and was having issues with the configuration of Q-in-Q for VLANs (802.1ad or double tagging). There is an interesting little gotcha for the port configuration on those puppies:
interface Ethernet1
switchport access vlan 500
switchport mode dot1q-tunnel
This will tag the packet with an outer VLAN tag of 500, while leaving the inner tag untouched.
