3Com 2928 User Guide - Page 165
Introduction to Port-Based VLAN, Port link type, Default VLAN (PVID)
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Because the Web interface is available only for port-based VLANs, this chapter introduces only port-based VLANs. Introduction to Port-Based VLAN Port-based VLANs group VLAN members by port. A port forwards traffic for a VLAN only after it is assigned to the VLAN. Port link type Depending on the tag handling mode, the link type of a port can be one of the following three: z Access. An access port belongs to only one VLAN and usually connects to a user device. z Trunk. A trunk port can join multiple VLANs to receive and send traffic for them. It usually connects to a network device. z Hybrid. A hybrid port can join multiple VLANs to receive and send traffic for them. It can connect either a user device or a network device. A hybrid port is different from a trunk port in that: z A hybrid port allows traffic of multiple VLANs to pass through untagged. z A trunk port allows only traffic of the default VLAN to pass through untagged. Default VLAN (PVID) By default, VLAN 1 is the default VLAN for all ports. However, you can change the default VLAN for a port as required. When doing this, follow these guidelines: z Because an access port can join only one VLAN, its default VLAN is the VLAN to which it belongs and cannot be configured. z Because a trunk or hybrid port can join multiple VLANs, you can configure a default VLAN for the port. A port configured with a default VLAN handles a frame as follows: Port type Access Trunk Hybrid Actions (in the inbound direction) Untagged frame Tagged frame Actions (in the outbound direction) Tag the frame with the default VLAN tag. z Receive the frame if its VLAN ID is the same as the default VLAN ID. Remove the default VLAN tag and z Drop the frame if its send the frame. VLAN ID is different from the default VLAN ID. z Remove the tag and send the frame if the frame carries the Check whether the default VLAN tag and the port default VLAN is carried on the port: z Receive the frame if its VLAN is carried belongs to the default VLAN. z Send the frame without removing z If yes, tag the on the port. the tag if its VLAN is carried on z frame with the default VLAN tag. If not, drop the frame. z Drop the frame if its VLAN is not carried on the port. the port but is different from the default one. Send the frame if its VLAN is carried on the port. The frame is sent with the VLAN tag removed or intact depending on your configuration. 1-3