Enterasys Networks VH-8G manual Appendix B. Virtual Lans Vlans, VLANs and Frame Tagging

APPENDIX B. VIRTUAL LANS (VLANS)

VLANs and Frame Tagging

The VH-8G switch supports IEEE 802.1Q-compliant virtual LANs (VLANs). This capability provides a highly efficient architecture for establishing VLANs within a network and for controlling broadcast/ multicast traffic between workgroups. Central to this capability is an explicit frame tagging approach for carrying VLAN information between interconnected network devices.

With frame tagging, a four byte data tag field is appended to frames that cross the network. The tag identifies which VLAN the frame belongs to. The tag may be added to the frame by the end station itself or by a network device, such as a switch. In addition to VLAN information, the relative priority of the frame in the network can specified by the tag (see Appendix C, “Class of Service”).

VLANs provide greater network efficiency by reducing broadcast traffic, but also allow you to make network changes without having to update IP addresses or IP subnets. VLANs inherently provide a high level of network security, since traffic must pass through a Layer 3 switch or a router to reach a different VLAN.

This switch supports the following VLAN features:

•Up to 256 VLANs based on the IEEE 802.1Q standard

•Distributed VLAN learning across multiple switches using explicit or implicit tagging and GARP/GVRP protocol

•Port overlapping, allowing a port to participate in multiple VLANs

•End stations can belong to multiple VLANs

•Passing traffic between VLAN-aware and VLAN-unaware devices

•Two-level priority tagging

•Port trunking with VLANs

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