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IntermediatePublished 2026-07-02

Lab 4: DHCP Relay with ip helper-address

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Configure a centralized DHCP server on an IOS-XE router and relay DHCP from a remote branch LAN using ip helper-address on a branch router. Verify leases, helper configuration, and end-host reachability across a routed path.

Track
Est. time
40 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Configure an IOS-XE router as a DHCP server with pool options and exclusions
  • Relay DHCP using ip helper-address on a remote router interface
  • Verify DHCP operation using show ip dhcp binding and client-side Linux tools
  • Understand return-path routing requirements for centralized DHCP

Troubleshooting focus

  • A missing or incorrect ip helper-address prevents broadcast DISCOVER from reaching the DHCP server
  • Pool network/mask does not match the client subnet, so the server refuses or misconfigures leases
  • Default-router option refers to the wrong gateway, breaking connectivity even with a lease
  • Excluded-address range removes all usable addresses, so no leases are assigned
  • Return path missing on the DHCP server, so OFFER/ACK cannot reach the clients

Topology

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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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