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IEEE 802.1ad was an Ethernet networking standard informally known as QinQ as an amendment to IEEE standard VLAN (802.1q). 802.1ad was incorporated into the base 802.1q standard in 2011. The technique is also known as provider bridging, Stacked VLANs, or simply QinQ or Q-in-Q. “Q-in-Q” can for supported devices apply to C-tag stacking on C-tag (Ethernet Type = 0x8100).
The original 802.1q specification allows a single Virtual Local Area Network (VLAN) header to be inserted into an Ethernet frame. QinQ allows multiple VLAN tags to be inserted into a single frame, an essential capability for implementing Metro Ethernet network topologies. Just as QinQ extends 802.1Q, QinQ itself is extended by other Metro Ethernet protocols.
In a multiple VLAN header context, out of convenience the term “VLAN tag” or just “tag” for short is often used in place of “802.1Q VLAN header”. QinQ allows multiple VLAN tags in an Ethernet frame; together these tags constitute a tag stack. When used in the context of an Ethernet frame, a QinQ frame is a frame that has 2 VLAN 802.1Q headers (double-tagged).
In VyOS the terms vif-s and vif-c stand for the ethertype tags that are used:
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 with ethertype 0x88a8).
interfaces ethernet <eth[0-999]> address <ipv4> address <ipv6> description <txt> disable ip <usual IP options> ipv6 <usual IPv6 options> vif-s <[0-4096]> address <ipv4> address <ipv6> description <txt> disable ip <usual IP options> ipv6 <usual IPv6 options> vif-c <[0-4096]> address <ipv4> address <ipv6> description <txt> disable ip <usual IP options> ipv6 <usual IPv6 options>
set interfaces ethernet eth0 vif-s 333 set interfaces ethernet eth0 vif-s 333 address 192.0.2.10/32 set interfaces ethernet eth0 vif-s 333 vif-c 777 set interfaces ethernet eth0 vif-s 333 vif-c 777 address 10.10.10.10/24