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IntermediatePublished 2026-07-04

Dynamic ARP Inspection

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Harden the Layer-2 access edge by enabling Dynamic ARP Inspection (DAI) on a single access switch. DHCP Snooping is already in place and the uplink toward the DHCP server/gateway is trusted. Your job: enable DAI for VLAN 10 and trust the uplink so ARP on host-facing ports is validated against the DHCP Snooping bindings.

Track
Est. time
35 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Explain how DAI uses the DHCP Snooping binding table to validate ARP
  • Enable DAI for a specific VLAN while preserving a correct trust boundary
  • Trust the uplink toward the DHCP server/gateway and leave host-facing ports untrusted
  • Verify DAI state and port roles using show commands

Troubleshooting focus

  • Forgetting to trust the uplink for DAI causes legitimate upstream ARP to be inspected and can drop traffic
  • Enabling DAI on the wrong VLAN yields no protection on the target VLAN
  • If DHCP Snooping is not enabled for the VLAN, DAI has no bindings and will drop ARP from untrusted ports
  • Mismatched access VLAN assignments on host ports prevent DHCP from working, so no bindings are learned

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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.
  • 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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