ZyXEL Communications ES-4024A manual How 802.1Q Vlan works, Ingress Process

ES-4024A Series Switch Support Notes

•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

43

All contents copyright (c) 2006 ZyXEL Communications Corporation.