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Spanning tree ring 56 — root SW-D, backup SW-B
Enterprise Advanced 4 devices 4 checked tasks 100 points Plan lab
Scenario — four switches in Warangal are cabled in a ring (A–B–C–D–A) and the oldest MAC, an old access switch, has become the root. Make SW-D the root bridge (priority 4096) and SW-B, the switch across the ring, the standby root (priority 8192), so a failure of the root moves the tree to a distribution-class switch rather than a random one. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This lab is part of the full simulator: open it free for 7 days with a new account, then with a plan. It needs an account, which keeps your progress.
The scenario
four switches in Warangal are cabled in a ring (A–B–C–D–A) and the oldest MAC, an old access switch, has become the root. Make SW-D the root bridge (priority 4096) and SW-B, the switch across the ring, the standby root (priority 8192), so a failure of the root moves the tree to a distribution-class switch rather than a random one.
Your role: a network engineer on the enterprise team. Level: Advanced Done when: all 4 goals show as passed (100 points).
Network status
Devices: 4 switchs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. SW-A, SW-B, SW-C, SW-D start with an empty configuration. Known problems
None: nothing is misconfigured. The network is simply not finished: what the goals list is what you have to build or secure. Goals
SW-D has priority 4096 for VLAN 1 (25 pts) SW-D is the root bridge (35 pts) SW-B is configured as the standby root (priority 8192 or lower) (25 pts) The other two switches are not the root (15 pts) The activity, in order
SW-D has priority 4096 for VLAN 1 Why: The lowest priority wins the root election; the MAC address only breaks ties. Verify with: show spanning-tree SW-D is the root bridge Why: The root decides which links forward and which block. Leave it to chance and the slowest switch can win. Verify with: show spanning-tree SW-B is configured as the standby root (priority 8192 or lower) Why: The lowest priority wins the root election; the MAC address only breaks ties. Verify with: show spanning-tree The other two switches are not the root Why: Reading a show command is the core skill of troubleshooting: the output is the truth, not your configuration. Verify with: show spanning-tree Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: Setting a priority that is not a multiple of 4096 Common mistake: Configuring only the root and leaving the backup to chance Common mistake: Making an access switch the root Why this matters
With no priority set, the switch with the lowest MAC address becomes the root — usually the oldest, slowest box. A designed network picks a root and a backup root deliberately, one hop apart across the ring.
What you will be able to do
Choose a root and a backup root
Set priority in multiples of 4096
Verify the election
The network
Catalyst 2960-24TT — 4 devices in all, already cabled.
Gi0/1 Gi0/1 Gi0/2 Gi0/1 Gi0/2 Gi0/1 Gi0/2 Gi0/2 SW-A SW-B SW-C SW-D Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
SW-A Catalyst 2960-24TT configure it SW-B Catalyst 2960-24TT configure it SW-C Catalyst 2960-24TT configure it SW-D Catalyst 2960-24TT configure it
Cabling
SW-A Gi0/1 ↔ SW-B Gi0/1 SW-B Gi0/2 ↔ SW-C Gi0/1 SW-C Gi0/2 ↔ SW-D Gi0/1 SW-D Gi0/2 ↔ SW-A Gi0/2
What is configured at the start
Nothing is configured to start with beyond the addresses above: you build the configuration from a clean start.
Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 SW-D has priority 4096 for VLAN 1 25 Checked automatically against the device’s live state (stpPriority). 2 SW-D is the root bridge 35 On SW-D: show spanning-tree says This bridge is the root . 3 SW-B is configured as the standby root (priority 8192 or lower) 25 Checked automatically against the device’s live state (stpPriority). 4 The other two switches are not the root 15 On SW-A: show spanning-tree output matches This bridge is the root — it must not . and On SW-B: show spanning-tree output matches This bridge is the root — it must not . and On SW-C: show spanning-tree output matches This bridge is the root — it must not .
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
Setting a priority that is not a multiple of 4096
Configuring only the root and leaving the backup to chance
Making an access switch the root
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
SW-D spanning-tree vlan 1 priority 4096 SW-B spanning-tree vlan 1 priority 8192 Where this is examined
CCNA 2.0 STP; CCNP ENCOR Layer 2.
This lab practises these topics in the zNetLaB certification courses:
Spanning Tree (RSTP/PVST+) — CCNA · Network Access Trunking, EtherChannel, RSTP and MST — CCNP Enterprise · ENCOR · Infrastructure Switched campus: VTPv3, MST, EtherChannel, UDLD, loop guard — CCIE Enterprise Infrastructure · Network Infrastructure VLANs, trunking, STP, EtherChannel, VTP — CompTIA Network+ · Network Implementation Spanning tree: choosing the root — Switching and VLAN Mastery · Loop prevention and bundling
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