ZyXEL GS1500-24P User Guide - Page 68
Forwarding Tagged and Untagged Frames, Common IEEE 802.1Q VLAN terminology
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Chapter 8 VLAN frame with VID (VLAN Identifier) of null (0) is called a priority frame, meaning that only the priority level is significant and the default VID of the ingress port is given as the VID of the frame. Of the 4096 possible VIDs, a VID of 0 is used to identify priority frames and value 4095 (FFF) is reserved, so the maximum possible VLAN configurations are 4,094. TPID User Priority 2 Bytes 3 Bits CFI VLAN ID 1 Bit 12 bits 8.3.2 Forwarding Tagged and Untagged Frames Each port on the Switch is capable of passing tagged or untagged frames. To forward a frame from an 802.1Q VLAN-aware switch to an 802.1Q VLAN-unaware switch, the Switch first decides where to forward the frame and then strips off the VLAN tag. To forward a frame from an 802.1Q VLAN-unaware switch to an 802.1Q VLAN-aware switch, the Switch first decides where to forward the frame, and then inserts a VLAN tag reflecting the ingress port's default VID. The default PVID is VLAN 1 for all ports, but this can be changed. A broadcast frame (or a multicast frame for a multicast group that is known by the system) is duplicated only on ports that are members of the VID (except the ingress port itself), thus confining the broadcast to a specific domain. 8.3.3 Common IEEE 802.1Q VLAN terminology Please refer to the following table. Table 13 IEEE 802.1Q VLAN Terminology VLAN PARAMETER TERM DESCRIPTION VLAN Type Permanent VLAN This is a static VLAN created manually. VLAN Administrative Control VLAN Tag Control Dynamic VLAN This is a VLAN configured by a GVRP registration/ deregistration process. Registration Fixed Fixed registration ports are permanent VLAN members. Registration Forbidden Ports with registration forbidden are forbidden to join the specified VLAN. Normal Registration Ports dynamically join a VLAN using GVRP. Tagged Ports belonging to the specified VLAN tag all outgoing frames transmitted. Untagged Ports belonging to the specified VLAN don't tag all outgoing frames transmitted. 68 GS1500-24P User's Guide