D-Link 3312SR - Switch Spécifications télécharger pdf (Page 96)

DGS-3212SR Stackable Gigabit Layer 2 Switch

VLANs

The Switch Web Manager’s VLANs sub-folder is divided into two main windows, 802.1Q Static VLANs and 802.1Q

Port Settings. Each is described after a short overview of VLANs.

Understanding 802.1Q VLANs

This review of 802.1Q VLANs presents some basic background about how VLANs work according to the IEEE 802.1Q

standard. VLANs operate according to the same rules regardless of whether the Switching environment is Layer 2 or Layer

3. The difference is primarily that in a Layer 3 Switch there is an added capability of unique association between a VLAN

and an IP interface or subnet group.

A VLAN is a collection of end nodes grouped by logic rather than physical location. End nodes that frequently

communicate with each other are assigned to the same VLAN, regardless of where they are located physically on the

network. Logically, a VLAN can be equated to a broadcast domain, because broadcast packets are forwarded only to

members of the VLAN on which the broadcast was initiated

IEEE 802.1Q VLANs

Some relevant terms:

• Tagging - The act of putting 802.1Q VLAN information into the header of a packet.

• Untagging - The act of stripping 802.1Q VLAN information out of the packet header.

• Ingress port - A port on a Switch where packets are flowing into the Switch and VLAN decisions must be made.

• Egress port - A port on a Switch where packets are flowing out of the Switch, either to another Switch or to an

end station, and tagging decisions must be made.

IEEE 802.1Q (tagged) VLANs are implemented on the DGS-3212SR Switch. 802.1Q VLANs require tagging, which

enables the VLANs to span an entire network (assuming all Switches on the network are IEEE 802.1Q-compliant).

Any port can be configured as either tagging or untagging. The untagging feature of IEEE 802.1Q VLANs allow VLANs

to work with legacy Switches that don’t recognize VLAN tags in packet headers. The tagging feature allows VLANs to

span multiple 802.1Q VLAN compliant Switches through a single physical connection and allows Spanning Tree to be

enabled on all ports and work normally.

802.1Q VLAN Packet Forwarding

Packet forwarding decisions are made based upon the following three types of rules:

• Ingress rules – rules relevant to the classification of received frames belonging to a VLAN.

• Forwarding rules between ports – decides filter or forward the packet

• Egress rules – determines if the packet must be sent tagged or untagged.

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D-Link 3312SR - Switch Spécifications Page 96