Ingress Process

Each port is capable of passing tagged or untagged frames. Ingress process identifies if the incoming frames contain tag, and classifies the incoming frames belonging to a VLANi. Each port has its own Ingress rule. If ingress rule accept tagged frames only, the switch port will drop all incoming non-tagged frames. If ingress rule accept all frame type, the switch port simultaneously allow the incoming tagged and untagged frames:

  • When a tagged frame is received on a port, it carries a tag header that has an explicit VIDi. Ingress process directly passes the tagged frame to forwarding process.

  • An untagged frame doesn't carry any VID to which it belongs. When an untagged frame is received, ingress process insert a tag contained the PVIDi into the untagged frame. Each physical port has a default VID called PVID (Port VID). PVID is assigned to untagged frames or priority tagged frames (frames with null (0) VID) received on this port.

Figure 6-2: Ingress process.

After ingress process, all frames have 4-bytes tag and VID information, and then go to forwarding process.