Spanning-Tree Protocol prevents Layer 2 loops by detecting redundant paths and putting one in a blocking state. Rapid-PVST (Rapid Per-VLAN Spanning Tree) is the modern Cisco variant - per-VLAN STP, but using RSTP convergence times (sub-second instead of 30-50 seconds). This lab is your hands-on with the three-switch triangle that has SW1 explicitly configured as root and SW2 as backup.
What you will learn
- The structure of a spanning-tree decision: bridge ID, root bridge election, root port selection, designated port selection
- How priority + sys-id-ext combine to form the Bridge ID
- The four port states in Rapid-PVST (Discarding, Learning, Forwarding, plus Disabled)
- The four port roles (Root, Designated, Alternate, Backup)
- How to read
show spanning-treeoutput and identify each role - How to manually set root bridge priority (and why)
What this lab does NOT cover
- PortFast, BPDU Guard, Root Guard - those are na-09 and na-10
- MST (Multiple Spanning Tree)
- STP attacks and detailed mitigations beyond the per-VLAN structure
Topology
Download the STP+VLAN Reference Lab .yaml
Three IOSvL2 switches in a triangle with VLANs 10/20/99, dot1q trunks, rapid-PVST root election (SW1 root, SW2 backup), and an LACP EtherChannel between SW1 and SW2.
