QinQ

QinQ — allows multiple VLAN tags to be inserted into a single frame.

QinQ can be used to tunnel vlans in a vlan.

vif-s and vif-c stand for the ethertype tags that get set:
The inner tag is the tag which is closest to the payload portion of the frame; it is officially called C-TAG (Customer tag, with ethertype 0x8100).
The outer tag is the one closer/closest to the Ethernet header; its name is S-TAG (Service tag, ethertype 0x88a8). Ethertype for service tag might be redefined by cli command.

Example:

vyos@vyos-rtr:~$ configure
vyos@vyos-rtr#set interfaces ethernet eth0 vif-s 333
vyos@vyos-rtr#set interfaces ethernet eth0 vif-s 333 address 192.0.2.10/32
vyos@vyos-rtr#set interfaces ethernet eth0 vif-s 333 vif-c 777
vyos@vyos-rtr#set interfaces ethernet eth0 vif-s 333 vif-c 777 address 10.10.10.10/24

Configuration commands:

interfaces
    ethernet 
        address 
        address 
        description 
        disable
        ip
            
        ipv6
            
        vif-s <[0-4096]>
            address 
            address 
            description 
            disable
            ip
                
            ipv6
                
            vif-c <[0-4096]>
                address 
                address 
                description 
                disable
                ip
                    
                ipv6