Adding and Removing VLAN Tags
Ethernet data frames are tagged or untagged based on the interface type and default VLAN. The following describes how access, trunk, and hybrid interfaces process data frames.
Access Interface
Figure 4-4 and Figure 4-5 show how an access interface adds and removes VLAN tags.
Trunk Interface
Figure 4-6 and Figure 4-7 show how a trunk interface adds and removes VLAN tags.
Hybrid Interface
Figure 4-8 and Figure 4-9 show how a hybrid interface adds and removes VLAN tags.
Frame Processing on Different Interfaces
Port Type |
Untagged Frame Processing |
Tagged Frame Processing |
Frame Transmission |
|---|---|---|---|
Access port |
Accepts any untagged frame and adds a tag with the default VLAN ID to the frame. |
|
Removes the PVID tag and transmits the frame. |
Trunk port |
|
|
|
Hybrid port |
|
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If the frame's VLAN ID is permitted by the port, the frame is transmitted. The port can be configured whether to transmit frames with tags. |
- Access, trunk, and hybrid interfaces add VLAN tags to received untagged frames. Trunk and hybrid interfaces determine whether to accept untagged frames depending on whether VLANs specified by the VLAN IDs in the frames are allowed, whereas an access interface accepts the untagged frames unconditionally.
- Access, trunk, and hybrid interfaces determine whether to accept tagged frames depending on whether VLANs specified by the VLAN IDs in the frames are allowed (the VLAN ID allowed by an access interface is the default VLAN ID).
Interfaces send frames as follows:
- An access interface directly removes VLAN tags from frames before sending the frames.
- A trunk interface removes VLAN tags from frames only when their VLAN IDs are the same as the PVID on the interface.
- A hybrid interface determines whether to remove VLAN tags from frames based on the interface configuration.
Frames sent by an access interface are all untagged. On a trunk interface, only frames of one VLAN are sent without tags, and frames of other VLANs are sent with tags. On a hybrid interface, you can specify the VLANs of which frames are sent with or without tags.