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IntermediatePublished 2026-07-02

STP 5: PortFast on Access Ports (VLAN 50 Triangle)

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Configure PortFast correctly on access ports in a triangle switch loop while maintaining normal STP protection on inter-switch trunks. Force SW1 as the root for VLAN 50 and verify that only edge ports are fast-tracked. Observe the difference in host convergence with and without PortFast.

Track
Est. time
45 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Cabling and VLAN 50 across a triangle of L2 switches (SW1–SW2–SW3) with a real loop present
  • Deterministically force the STP root bridge for VLAN 50 using bridge priority (SW1 at 4096)
  • Apply PortFast on host-facing access ports only and confirm it is not present on trunks
  • Verify STP operation and PortFast status with show spanning-tree commands
  • Validate that end hosts in VLAN 50 can communicate immediately after link-up without STP timer delays

Troubleshooting focus

  • If hosts cannot communicate, confirm VLAN 50 exists on all switches and is allowed on all trunks
  • If a trunk port shows PortFast, remove it immediately; PortFast belongs only on host-facing access ports
  • If SW1 is not the root for VLAN 50, verify the configured bridge priority is lower than the others
  • If ports flap between states, check for native VLAN mismatches or incorrect access assignments

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How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
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