Advanced Spanning Tree Protocols (MSTP/VSTP) JN0-650 Practice Questions (Page 3)

Questions 11–15

1. 11application · medium

   A network engineer is deploying MSTP across two campus buildings connected by a single trunk link. Building A has switches configured with region name 'CAMPUS', revision 1, and VLANs 10-20 mapped to instance 1. Building B has switches configured with region name 'CAMPUS', revision 2, and VLANs 10-20 mapped to instance 1. The engineer notices that VLAN 10 traffic is being blocked on the trunk link even though the link is healthy. What is the most likely cause?

   • AThe region name must be unique per building; using the same name 'CAMPUS' causes a conflict that forces both switches to run RSTP instead of MSTP.
   • BThe revision number mismatch prevents the switches from forming a common region, causing them to treat each other as separate regions and block VLAN 10 on the IST.
   • CThe VLAN-to-instance mapping is identical, so the switches form a region correctly, but the trunk link is blocked because MSTP defaults to blocking all VLANs on inter-switch links.
   • DThe revision number must be set to 0 for MSTP to operate; any non-zero value disables the protocol and causes all VLANs to be blocked.
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2. 12foundation · easy

   What is a key advantage of running VSTP in a network with multiple VLANs?

   • AIt eliminates the need for VLAN tagging on trunk links.
   • BIt simplifies configuration by using a single instance for all VLANs.
   • CIt reduces the number of spanning tree instances, lowering CPU usage.
   • DIt allows each VLAN to have its own active topology, enabling load balancing across links.
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4. 13application · medium

   A company runs a network with 50 VLANs and wants to use VSTP to provide per-VLAN load balancing across two redundant links. The network also has a few legacy switches that only support RSTP. What is the primary limitation the engineer must consider before deploying VSTP?

   • AVSTP only supports a maximum of 16 VLANs, so the network would need to be redesigned.
   • BVSTP runs a separate spanning tree instance per VLAN, which increases CPU and memory usage on switches, especially with many VLANs.
   • CVSTP cannot interoperate with RSTP switches, so the legacy switches must be upgraded or replaced.
   • DVSTP requires all switches to be in the same MSTP region, which is not possible with legacy switches.
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5. 14application · medium

   An engineer configures VSTP on a Junos switch with 'set protocols vstp vlan 10,20,30'. The switch is connected to a switch running MSTP. The engineer notices that VLAN 10 traffic is not being forwarded on the link. What is the most likely reason?

   • AVSTP requires the MSTP switch to be configured with the same VLAN-to-instance mappings.
   • BThe VSTP configuration is missing the 'all' keyword, so VLAN 10 is not included.
   • CVSTP and MSTP are incompatible, and the link is blocked because neither protocol can understand the other's BPDUs.
   • DThe MSTP switch is blocking the port because it detects a loop, and VSTP cannot override this.
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6. 15application · medium

   A network engineer is planning to deploy MSTP in a network with 30 VLANs. The engineer wants to minimize the number of spanning tree instances while still providing some load-balancing capability. What is the most efficient configuration?

   • AUse VSTP instead of MSTP to provide per-VLAN load balancing.
   • BMap each VLAN to a separate instance to maximize load balancing.
   • CMap all 30 VLANs to a single instance, instance 1, to minimize overhead.
   • DMap VLANs 1-15 to instance 1 and VLANs 16-30 to instance 2, providing two instances for load balancing.
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