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IntermediatePublished 2026-07-02

Lab 3: Full DHCP Pool — Gateway, DNS, Domain, Lease

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Configure an IOS-XE router as a DHCP server delivering a complete, production-grade option set (gateway, DNS servers, domain suffix, explicit 8-hour lease) to two Alpine Linux clients over a pure L2 access switch. Validate that clients obtain dynamic addresses in-scope and that /etc/resolv.conf reflects the delivered DNS and domain options. The graded outcome is the deterministic router DHCP configuration — not the clients’ dynamic addresses.

Track
Est. time
40 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Build a correctly scoped IOS DHCP pool for a /24 LAN with network/mask
  • Set default-router, dns-server (two IPs), domain-name, and an explicit 8-hour lease
  • Protect the gateway address using ip dhcp excluded-address
  • Verify leases and options via show ip dhcp binding and show running-config
  • Confirm Alpine clients receive IP/DNS/domain via udhcpc and /etc/resolv.conf

Troubleshooting focus

  • Pool network/mask must match the client LAN exactly; a mismatch prevents leases
  • default-router must be the router’s real LAN IP; otherwise clients lose reachability
  • Lease options (DNS, domain) appear in resolv.conf only if udhcpc completes successfully
  • If no client leases appear, confirm the switch is pure L2 and the LAN interface is up/up
  • Avoid excluding the entire usable range; only exclude the gateway as specified

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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