Have you taken a look at Chapter 49 (Service Provider Bridging) that begins on page 855 of the Dell "Configuration Guide for the S4048-ON System 188.8.131.52" where it covers the topic of "Service provider bridging provides the ability to add a second VLAN ID tag in an Ethernet frame and is referred to as VLAN stacking in the Dell EMC Networking OS.?
The document can be found at the following link:
It is called VLAN stacking on these switches. Page 1711 shows the command, see if it does what you need. http://downloads.dell.com/manuals/all-products/esuprt_ser_stor_net/esuprt_networking/esuprt_net_fxd_...
It is a bit vague, I must admit even from looking through the manuals.
Selective qinq can identify the inner VLAN tag of the packets according to the MAC address, IP protocol, source IP address and VLAN tag, then determine which tag should be added. - This is what I want to do - cannot see an example or reference to it.