Bridge Domain Restrictions with STP in Ethernet Virtual Circuit Environment

C.

In an Ethernet Virtual Circuit (EVC) environment, bridge domains are used to group together a set of interfaces that share the same forwarding behavior. The Spanning Tree Protocol (STP) is a protocol that runs on bridges and switches to prevent loops in the network topology. STP operates by selectively blocking some links in the network to prevent loops, and by dynamically changing the topology when links fail or are restored.

When STP is running, bridge domains have a restriction in that they must be mapped to a different VLAN. This is because STP operates on a per-VLAN basis, and different VLANs can have different topologies and forwarding behavior. By mapping bridge domains to different VLANs, it is possible to apply STP independently to each VLAN.

Option A states that the STP mode must be RSTP or PVST+. RSTP (Rapid Spanning Tree Protocol) is an evolution of the original STP protocol that provides faster convergence and more efficient use of network resources. PVST+ (Per-VLAN Spanning Tree Protocol) is a Cisco proprietary protocol that enables STP to be run on a per-VLAN basis. However, neither of these options is a restriction for bridge domains when STP is running.

Option C states that the STP mode must be MSTP (Multiple Spanning Tree Protocol). MSTP is a protocol that enables multiple instances of STP to be run on a single switch, with each instance having its own set of VLANs. However, this option is not a restriction for bridge domains when STP is running.

Option D states that bridge domains must belong to different MST (Multiple Spanning Tree) instances. This option is also not a restriction for bridge domains when STP is running, as MSTP allows multiple instances of STP to be run on a single switch, with each instance having its own set of VLANs.

Therefore, the correct answer to the question is B: bridge domains must be mapped to a different VLAN when STP is running in an EVC environment.