ZyXEL Communications ES-4024A - Manual (Page 43)

ES-4024A Series Switch Support Notes
All contents copyright (c) 2006 ZyXEL Communications Corporation.
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• How 802.1Q VLAN works
According to the VID information in the tag, the switch forward and filter the
frames among ports. These ports with same VID can communicate with each
other. IEEE 802.1Q VLAN function contains the following three tasks, Ingress
Process, Forwarding Process and Egress Process.
1. 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 VLAN . 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 a
explicit VID. Ingress Process directly pass the tagged frame to Forwarding
Process.
• An untagged frame doesn't carry any VID to which it belongs. When a