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BeginnerPublished 2026-07-04

DHCP Snooping Trust Boundary

Free preview — the first lab of Layer 2 Security Hardening

Harden the Layer-2 access edge by enabling DHCP Snooping on a single access switch and placing the trust boundary only toward the legitimate DHCP server/gateway. Validate with show commands and end-host connectivity.

Track
Est. time
30 minutes
Difficulty
Beginner
Topics

Learning objectives

  • Explain the purpose of DHCP Snooping and the trust boundary on an access switch
  • Enable DHCP Snooping globally and for a specific VLAN
  • Trust only the uplink interface toward the legitimate DHCP server
  • Verify DHCP Snooping operational status and bindings

Troubleshooting focus

  • DHCP Snooping enabled globally but not for the correct VLAN
  • Trust configured on the wrong interface (host-facing port) causing a security gap
  • Uplink not trusted, dropping legitimate DHCP replies from the server
  • Using the wrong VLAN number for snooping leading to no bindings

Topology

Lab topology diagram

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Grade your work

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.
  • Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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