Why are the padding bits not stripped out when the frame is configured to include VLAN support?
If the VLAN enable bits are set, does that mean all packets must have a VLAN tag?
The Gigabit and 10 Gigabit Ethernet MAC cores handle VLAN tagged frames by passing them through; the MAC allows the extra 4 bytes without marking the frames as BAD.
VLAN frames are treated internally as normal "Type" frames, so the Length/Type field is not checked.
It is not necessary for all packets to have a VLAN tag if the VLAN Enable bit is set; the MAC is always capable of transmitting and receiving normal packets at the same time.