VSTP (VLAN Spanning Tree Protocol) is designed for interoperability with environments running Cisco’s Per-VLAN Spanning Tree Plus (PVST+).
Per-VLAN Instances (Option E):The core function of VSTP is to maintain aseparate spanning tree instancefor every VLAN configured on the switch. This allows for different root bridges and different topologies per VLAN, enabling traffic load-balancing across various physical links.
BPDU Generation (Option A):Because each VLAN has its own instance, VSTP must sendseparate BPDUsfor each VLAN. These BPDUs are tagged with the respective VLAN ID to ensure the receiving switch can process them for the correct instance.
Instance Limits (Option D):On many Juniper platforms, VSTP is limited to supporting a maximum of253 unique spanning tree topologies(instances). If the number of VLANs exceeds this limit, additional VLANs will not have spanning tree protection unless migrated to a different protocol like MSTP.
Incorrect Statements:Option Bis incorrect because VSTP is compatible with RSTP; it actually uses RSTP algorithms (Rapid-VSTP) by default in modern Junos versions to provide fast convergence.Option Cis incorrect because STP or RSTP is usually the default spanning tree protocol on EX Series switches, not VSTP.
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