Interactive Spanning Tree Protocol (PVST+) Simulator

Explore Root Bridge election, Path Cost, and Port ID tie-breakers across VLANs.

Simulation Control

Select Active VLAN (1-4094)

Set priorities, link cost, and VLAN, then click "Rerun STP".

Switch Base Priority (Multiple of 4096)

Link & Port Tie-Breakers

S2 ↔ S3 Link Speed (Cost)

S2-P2 Port Priority (0-255)

S3-P2 Port Priority (0-255)

Learning Point: Per-VLAN STP (PVST+) and Tie-Breakers

STP runs per VLAN. The final blocking decision is made using four tie-breakers in order:

**Lowest Root Bridge ID** (Priority + VLAN ID + MAC).
**Lowest Root Path Cost** (Determined by link speeds, e.g., 100M=19, 1G=4).
**Lowest Sending Bridge ID** (MAC).
**Lowest Port ID** (Port Priority + Port Number/Index).

Network Topology - Loop Analysis for VLAN 1

STP Election Logic for VLAN 1