VLAN Identifier is the 12-bit VLAN number (maximum possible decimal value is 4,096) assigned to a frame during the ingress process. A frame's VID, used in conjunction with ingress and egress rules as defined by the VLAN administrator, dictates whether individual ports are permitted to handle the frame. It is useful to think of 802.1q as 802.1d, but with a few added restrictions that tend to reduce the communication possibilities.