Juniper QinQ

A very simple topology for this one. 3 vMX devices, 2 Arista vEOS acting as the CE devices (you can use other devices if prefer) and 2vPC’s to confirm IP connectivity. 55 is the C-Tag, 110 the S-Tag

EVE-NG import file

vMX1

set interfaces ge-0/0/0 unit 0 family bridge interface-mode access
set interfaces ge-0/0/0 unit 0 family bridge vlan-id 110
set interfaces ge-0/0/1 unit 0 family bridge interface-mode trunk
set interfaces ge-0/0/1 unit 0 family bridge vlan-id 110
set bridge-domains customer1 vlan-id 110

vMX2

set interfaces ge-0/0/0 flexible-vlan-tagging
set interfaces ge-0/0/0 encapsulation flexible-ethernet-services
set interfaces ge-0/0/0 unit 0 family bridge interface-mode trunk
set interfaces ge-0/0/0 unit 0 family bridge vlan-id 110
set interfaces ge-0/0/1 flexible-vlan-tagging
set interfaces ge-0/0/1 encapsulation flexible-ethernet-services
set interfaces ge-0/0/1 unit 0 family bridge interface-mode trunk
set interfaces ge-0/0/1 unit 0 family bridge vlan-id 110
set bridge-domains customer1 vlan-id 110

vMX3

set interfaces ge-0/0/0 unit 0 family bridge interface-mode access
set interfaces ge-0/0/0 unit 0 family bridge vlan-id 110
set interfaces ge-0/0/1 unit 0 family bridge interface-mode trunk
set interfaces ge-0/0/1 unit 0 family bridge vlan-id 110
set bridge-domains customer1 vlan-id 110

Configure IP addresses from the same subnet on both of the vPC’s and they should be able to ping each other. The below image of a Wireguard capture shows the double VLAN tags when ping is sent.