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IntermediatePublished 2026-08-27

CCNA Break/Fix: The DHCP Request That Goes Nowhere

Archive lab

A branch LAN’s clients can’t obtain IP addresses even though the DHCP server at the hub is up and reachable. Diagnose where the broadcast-to-unicast relay path breaks and restore end-to-end DHCP lease delivery while preserving the rest of the clean, working design.

Track
Est. time
55 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Trace a DHCP request from a remote client to an off-subnet DHCP server and back
  • Verify and repair DHCP relay on a router LAN interface
  • Identify and fix missing return reachability that prevents DHCP offers from arriving
  • Use show commands to validate bindings, routing tables, and interface roles
  • Confirm resolution by testing from the endpoints and reviewing server bindings

Troubleshooting focus

  • When a client receives no lease, verify the client interface state and whether it is actually sending DHCP discover messages.
  • On the relay router, confirm the client-facing interface has a relay target that matches the documented DHCP server address and that basic IP connectivity to that target exists.
  • On the DHCP server’s router, confirm there is return routing for the client subnet so DHCPOFFER/ACK replies have a path back.
  • Use show ip dhcp binding and packet counters to distinguish server inactivity from routing failures.
  • Test end-to-end after each suspected fix; if one issue is corrected but leases still fail, continue tracing the return path.

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.
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