IntermediatePublished 2026-07-21
CCNA Foundations: DHCP Relay — ip helper-address Across Subnets
Archive lab
CCNA exam domain: IP Services
Deploy a centralized DHCP service across subnets using DHCP relay (ip helper-address). A branch client on a switched LAN requests an address from a DHCP server that resides at HQ. You will configure the relay on the branch gateway, create a DHCP pool for the remote subnet on the HQ router, verify the client lease and default gateway, and test end-to-end connectivity.
Learning objectives
- Configure DHCP relay (ip helper-address) on a branch gateway for an off-subnet server.
- Build a DHCP pool on a central IOS router for a remote subnet with a correct default-router.
- Verify DHCP bindings and statistics on the server and observe the client lease.
- Validate end-to-end IP connectivity from a DHCP client to an HQ resource across routed hops.
- Troubleshoot common DHCP relay faults: wrong helper IP, missing route, incorrect pool network/mask.
Troubleshooting focus
- Client fails to obtain an IP: confirm the relay helper-address points to the reachable DHCP server IP.
- No DHCP bindings on the server: confirm the pool network/mask matches the remote client subnet and does not overlap an excluded range.
- Client gets an address but cannot reach HQ: confirm static routes between branch and HQ exist and are correct.
- Intermittent DHCP: check for mismatched subnets on the client-facing interface or unconfigured switch access VLAN mapping.
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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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