Two Rings Connected by One Switch

The following figure shows how a data VLAN can span two rings interconnected by a common switch—a figure eight topology.

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Two Rings Interconnected by One Switch
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A data VLAN that spans multiple physical rings or EAPS (Extreme Automatic Protection Switching) domains and is protected by EAPS is called an overlapping VLAN. An overlapping VLAN requires loop protection for each EAPS domain to which it belongs.

In the following figure, there is an EAPS domain with its own control VLAN running on ring 1 and another EAPS domain with its own control VLAN running on ring 2. A data VLAN that spans both rings is added as a protected VLAN to both EAPS domains to create an overlapping VLAN. Switch S5 has two instances of EAPS domains running on it, one for each ring.