LevelOne GSW-2600TXM Forwarding Tagged / Untagged Frames, Port Overlapping, Port-based VLANs

4.3.1.2.Port Overlapping

Port overlapping can be used to allow access to commonly shared network resources among different VLAN groups, such as file servers or printers. Note that if you implement VLANs which do not overlap, but still need to communicate, you can connect them by setting this switch to multilayer mode, and assigning an IP interface address to the different VLANs. (See “Connecting VLAN Groups” on chapter 4.)

4.3.1.3.Port-based VLANs

Port-based (or static) VLANs are manually tied to specific ports. The switch’s forwarding decision is based on the destination MAC address and its associated port. Therefore, to make valid forwarding or flooding decisions, the switch must learn the relationship of the MAC address to its related port—and thus to the VLAN—at run-time. However, when GVRP is enabled, this process can be fully automatic.

4.3.1.4.Automatic VLAN Registration (GVRP)

GVRP defines a system whereby the switch can automatically learn the VLANs to which each endstation should be assigned. If an endstation (or its network adapter) supports the IEEE 802.1Q VLAN protocol, it can be configured to broadcast a message to your network indicating the VLAN groups it wants to join. When this switch receives these messages, it will automatically place the receiving port in the specified VLANs, and then forward the message to all other ports. When the message arrives at another switch that supports GVRP, it will also place the receiving port in the specified VLANs, and pass the message on to all other ports. VLAN requirements are propagated in this way throughout the network. This allows GVRP-compliant devices to be automatically configured for VLAN groups based solely on endstation requests.

4.3.2.Forwarding Tagged / Untagged Frames

Ports can be assigned to multiple tagged or untagged VLANs. Each port on the switch is therefore capable of passing tagged or untagged frames. To forward a frame from a VLAN-aware device to a VLAN-unaware device, the switch first decides where to forward the frame, and then strips off the VLAN tag. However, to forward a frame from a VLAN-unaware device to a VLAN-aware device, the switch first decides where to forward the frame, and then inserts a VLAN tag reflecting this port’s default VID. The default PVID is VLAN 1 for all ports, but this can be changed (see chapter 2 “VLAN Port Configuration” or chapter 3 “VLAN Port Configuration”).

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