Can the Xilinx Ethernet MAC IP cores support Double VLAN applications?
Double VLAN is specified in IEEE 802.1ad.
The frame is like the following:
DA-SA-81 00-V1V2-88 a8-V3V4-L/T-DATA-
Our Ethernet MAC IP cores can support it with VLAN and Jumbo frames enabled. With Jumbo frames enabled, the MAC is still able to mark the Double VLAN frames received as the good frames. These cores include the LogiCORE Tri-Mode Ethernet MAC, Gigabit Ethernet MAC, 10-Gigabit Ethernet MAC, and VIrtex-4/Virtex-5 Embedded Tri-Mode Ethernet MAC Wrapper.
If the length/type field is 8100, then the MAC will recognize the frame as a 'type'. It will not check the later VLAN length/type to check the actual length of the frame versus the length reported in the frame, but it will still check the frame length against min/max ethernet frame lengths as is done with all 'type' frames. Since VLAN allows for extra bytes, you will need to enable VLAN to not have max size frames marked as bad frames (because it is oversized for non VLAN frames). For double VLAN, you will need to enable jumbo frames to have max size frames not marked as bad.