APPENDIX A

VIRTUAL LANS (VLANS)

A.1 VLANS AND FRAME TAGGING

The ELS10-27TX 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 the example in Figure A-1 below, the workstations attached to the top switch are members of the same two VLANs as the workstations attached to the bottom switch. The 802.1Q tags are used to carry VLAN information in the frames traveling between the two switches.

VLAN X

 

 

 

 

VLAN Y

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

EPIM100

ETHERNET SWITCH

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PORT STATUS MODE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ELS10-27TX

 

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1

802.1Q tag added by Incoming port*

2

802.1Q tag carries

VLAN Identifier

ETHERNET SWITCH

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3

802.1Q used by

switch to determine VLAN, then stripped by forwarding port*

VLAN XVLAN Y

* Note

1

is true if it does not have a tag and is a hybrid port, or the port is an

access port.

* Note

3

is only stripped, if the hybrid port and the tag in the packet matches the

PVID or is an access port.

Figure A-1. Two-Switch VLAN Configuration

A-1

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Enterasys Networks ELS10-27TX manual Appendix a Virtual Lans Vlans Vlans and Frame Tagging, Vlan Vlan Y