Spanning Tree Configuration (3.3) > STP

Overview

• This chapter focuses on the configuration of PVST+ and Rapid PVST+ in a switched LAN environment.
• PVST+ allows for Per-VLAN Spanning Tree instances, providing redundancy and load balancing without loops.

PVST+ Configuration (3.3.1)

Catalyst 2960 Default Configuration (3.3.1.1)

• Default spanning-tree mode: PVST+
• Default switch priority: 32768
• Spanning-tree port and VLAN priorities: 128
• Spanning-tree cost for different speeds:
  • 1000 Mbps: 4
  • 100 Mbps: 19
  • 10 Mbps: 100

Configuring and Verifying the Bridge ID (3.3.1.2)

• Can lower the bridge priority to make a switch the root bridge:
  • spanning-tree vlan [vlan-id] root primary
  • spanning-tree vlan [vlan-id] root secondary for alternate root bridge
• Verify using show spanning-tree command.

PortFast and BPDU Guard (3.3.1.3)

• PortFast: Immediately transitions ports from blocking to forwarding state.
• BPDU Guard: Puts ports in error-disabled state if BPDU is received, preventing loops.
• PortFast is typically used on access ports.

PVST+ Load Balancing (3.3.1.4)

• Configure root bridge for specific VLANs to manage load balancing across VLANs.
• Use spanning-tree vlan [number] root {primary | secondary} command.

Rapid PVST+ Configuration (3.3.2)

Spanning Tree Mode (3.3.2.1)

• Rapid PVST+ is an enhancement, supporting RSTP per VLAN.
• Enable using spanning-tree mode rapid-pvst.
• Verify configuration with show spanning-tree vlan [vlan-id] command.

STP Configuration Issues (3.3.3)

Analyzing the STP Topology (3.3.3.1)

• Steps to analyze include discovering Layer 2 topology and determining expected Layer 2 paths.
• Ensure switches are functioning as root bridges where needed.

Expected vs. Actual Topology (3.3.3.2)

• Importance of comparing network design to actual STP topology to spot configuration issues.

Spanning Tree Failure Consequences (3.3.3.4)

• Failures can lead to loops, infinite frame forwarding, and network congestion.

Repairing Spanning Tree Problems (3.3.3.5)

• Eliminate redundant links to break loops and restore normal operations.

Switch Stacking and Chassis Aggregation (3.3.4)

Switch Stacking Concepts (3.3.4.1)

• A stack consists of up to 9 switches with a single IP management point.
• Benefits include simplified management and reduced STP diameter.

Spanning Tree and Switch Stacks (3.3.4.2)

• Stacking maintains or reduces STP diameter since all switches in a stack use the same bridge ID.

Activities and Labs

• Packet Tracer and lab activities included for hands-on learning of PVST+ and Rapid PVST+ configurations.