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IntermediatePublished 2026-07-04

DHCP Snooping Rate Limiting

Bundle lab

Harden the Layer-2 access edge by rate-limiting DHCP messages on untrusted ports. SW1 already has DHCP snooping enabled for VLAN 10 with the uplink trusted. Your task is to apply a per-interface rate limit on the host-facing access ports to blunt DHCP starvation attacks while leaving the trusted uplink unlimited.

Track
Est. time
30 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Identify the DHCP snooping trust boundary on an access switch
  • Apply deterministic DHCP rate limiting to untrusted access ports only
  • Avoid rate-limiting the trusted uplink toward the legitimate DHCP server
  • Verify configuration with show ip dhcp snooping and per-interface settings
  • Explain how exceeding the limit triggers errdisable and how to observe it

Troubleshooting focus

  • If hosts fail to obtain an address, confirm the uplink is trusted and not rate-limited
  • If a port goes down unexpectedly, check for errdisable due to dhcp-rate-limit
  • If show output does not list a rate on the access ports, the limit was not applied at interface scope
  • If the DHCP server stops working, ensure the rate limit was not configured on the uplink

Topology

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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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