Virtual Spanning Tree Protocol (VSTP)

A

If you use VLANs, we recommend that you enable MSTP unless your network requires the device compatibility provided by VSTP. Switches configured to run

VSTP automatically assign each VLAN to one spanning-tree instance that runs RSTP. While this approach is useful to optimize network usage in small networks with a limited number of VLANs, a VSTP configuration in a network with several hundred VLANs can overload switch CPUs.

VSTP (Virtual Switch Redundancy Protocol) is a protocol used for providing redundancy in a network by allowing multiple switches to act as a single virtual switch. It is an enhancement to the standard Spanning Tree Protocol (STP) and is supported on Juniper Networks switches.

Out of the given options, the statement that is true about VSTP is:

B. It supports 4093 spanning-tree topologies.

Explanation:

A. Adding VLANs to VSTP consumes more CPU resources. This statement is false. Adding VLANs to VSTP does not consume more CPU resources. Instead, VSTP reduces the number of STP instances needed to support a large number of VLANs, thereby reducing the CPU utilization.

B. It supports 4093 spanning-tree topologies. This statement is true. VSTP supports up to 4093 spanning-tree topologies, which is the maximum number of VLANs supported by IEEE 802.1Q.

C. It is compatible with PVST+, but not with PVST. This statement is false. VSTP is not compatible with PVST+ or PVST. Instead, VSTP is a proprietary protocol developed by Juniper Networks and is compatible with MSTP (Multiple Spanning Tree Protocol) as well as other VSTP-enabled switches.

D. Different VLANs must use different spanning-tree topologies. This statement is false. VSTP allows multiple VLANs to share a single spanning-tree topology, unlike the standard STP, which creates a separate spanning-tree instance for each VLAN.

In summary, option B is the correct answer as VSTP supports 4093 spanning-tree topologies.