300-515 · Question #26
300-515 Question #26: Real Exam Question with Answer & Explanation
The correct answer is C. The STP mode must be MSTP. In an EVC (Ethernet Virtual Circuit) environment, bridge domains require MSTP (Multiple Spanning Tree Protocol) because MSTP's instance-based model aligns with how bridge domains logically partition the network - each MST instance can be mapped to one or more bridge domains, enab
Question
Options
- AThe STP mode must be RSTP or PVST+
- BBridge domains must be mapped to a different VLAN.
- CThe STP mode must be MSTP
- DBridge domains must belong to different MST instances.
Explanation
In an EVC (Ethernet Virtual Circuit) environment, bridge domains require MSTP (Multiple Spanning Tree Protocol) because MSTP's instance-based model aligns with how bridge domains logically partition the network - each MST instance can be mapped to one or more bridge domains, enabling proper loop prevention across the EVC fabric. Option A is wrong because RSTP runs a single spanning-tree instance for the entire network (no per-domain control), and PVST+ is VLAN-centric and not applicable to the bridge domain model used in EVC. Option B is wrong because bridge domains in EVC are explicitly designed to be independent of traditional 802.1Q VLAN mappings - forcing a VLAN mapping would negate their purpose. Option D is a near-miss trap: while MSTP is required, bridge domains are not restricted to different MST instances - multiple bridge domains can share one MST instance.
Memory tip: Associate "EVC Bridge Domains → MSTP" by thinking of it as "Match the M's" - the Multiple-instance nature of MSTP is the only STP flavor flexible enough to serve Multiple bridge domains in an EVC design.
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