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CCNA lab 12 of 46

Rapid PVST+: choosing root bridges and sharing the load

Read a spanning tree that elected itself, upgrade three switches from PVST+ to Rapid PVST+, place the root bridge for each VLAN on purpose so both uplinks carry traffic, and watch an alternate port take over in a second.

Run this lab

It needs Lite: its 5 nodes are set to 5 vCPU and 5,120 MB in total. That fits the free demo too.

In your workspace: Shared, then CCNA 200-301 guided labs, then 12 - Rapid PVST plus - choosing root bridges and sharing the load

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Level
Intermediate
Time
About 55 minutes
Nodes need
5 vCPU, 5,120 MB
Smallest plan
Lite

The scenario

Hollin Hall School's three core switches form a triangle so that any one link can fail. Spanning tree stops that triangle from looping, but nobody ever configured it: the root bridge is whichever switch has the lowest MAC address, both VLANs use the same links, and a failure takes up to 50 seconds to recover. You'll read the tree as it is, move to Rapid PVST+ and design it on purpose.

DevicePortsAddresses
S1Gi0/0 to S2, Gi0/1 to S3 (trunks)VLAN 10 10.12.10.1, VLAN 20 10.12.20.1
S2Gi0/0 to S1, Gi0/1 to S3 (trunks)VLAN 10 10.12.10.2, VLAN 20 10.12.20.2
S3Gi0/0 to S1, Gi0/1 to S2 (trunks); Gi1/0 PC1 (VLAN 10); Gi1/1 PC2 (VLAN 20)VLAN 10 10.12.10.3, VLAN 20 10.12.20.3
PC1S3 Gi1/010.12.10.10/24
PC2S3 Gi1/110.12.20.10/24

Design goal: S1 is root for VLAN 10 (backup S2), S2 is root for VLAN 20 (backup S1), so S3 sends VLAN 10 up one uplink and VLAN 20 up the other.

What you’ll practise

  • Explain the root bridge, root port, designated port and alternate port elections
  • Read show spanning-tree output: bridge ID, cost, port roles and states
  • Migrate from PVST+ to Rapid PVST+ and compare port states and roles
  • Use root primary and root secondary to share load between VLANs
  • Predict the effect of a port cost change and observe rapid convergence

The tasks

  1. Read the tree that elected itself
  2. Move to Rapid PVST+
  3. Place the root bridges on purpose
  4. Predict S3's alternate ports
  5. Change a port cost
  6. Watch rapid convergence

The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.

Topology and devices

The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.

Topology of Rapid PVST plus - choosing root bridges and sharing the load5 nodes, 5 links. Every link is listed as text below the diagram.S1S2S3PC1PC2Gi1/0eth0Gi1/1eth0Gi0/1Gi0/0Gi0/1Gi0/1Gi0/0Gi0/0
5 nodes, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • S1 Gi0/0 to S2 Gi0/0
  • S1 Gi0/1 to S3 Gi0/0
  • S2 Gi0/1 to S3 Gi0/1
  • S3 Gi1/0 to PC1 eth0
  • S3 Gi1/1 to PC2 eth0
Nodes in Rapid PVST+: choosing root bridges and sharing the load, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
S1Cisco IOSvL2viosl2-adventerprisek9-m.ssa.high_iron_202009291 vCPU, 1,024 MB
S2Cisco IOSvL2viosl2-adventerprisek9-m.ssa.high_iron_202009291 vCPU, 1,024 MB
S3Cisco IOSvL2viosl2-adventerprisek9-m.ssa.high_iron_202009291 vCPU, 1,024 MB
PC1VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB
PC2VPCS hostBuilt in to EVE-NGCounted as 1 vCPU, 1,024 MB

How to open this lab

  1. Sign in to your workspace at lab.cloudlabbox.com.

  2. In File Manager, open Shared, then the folder CCNA 200-301 guided labs.

  3. Open 12 - Rapid PVST plus - choosing root bridges and sharing the load and start its nodes, then open Lab Tasks for the scenario and the steps.

The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.

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CloudLabBox is independent of Cisco. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.