Lab 9: Centralized DHCP for Two Departments via Relay

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Build a central DHCP service on an IOS-XE router and service two branch departments across a routed hop via DHCP relay. Configure two DHCP pools (SALES and SUPPORT) with proper options and excluded ranges on the HQ server, and enable ip helper-address on both branch LAN interfaces so clients obtain leases from the correct pool. Verify leases and bindings using Linux and IOS show commands, and confirm return-path reachability with prebuilt static routes.

Learning objectives

• Design two DHCP pools on a centralized IOS-XE router with correct scope, default-gateway, DNS, domain-name, lease, and excluded addresses
• Enable and verify DHCP relay (ip helper-address) on multiple branch interfaces toward the central server
• Confirm dynamic leases on Linux clients without relying on hard-coded host addresses
• Use IOS show commands to validate pools and bindings and ensure the return path via static routes
• Troubleshoot common relay and scoping mistakes (missing helper, wrong pool network, over-excluded ranges, bad default-router)

Troubleshooting focus

• If a client has no IP, check the correct ip helper-address on the branch interface and the routing path to 10.70.0.1.
• If the client gets an IP but cannot reach the server, review the static routes on DHCP-SRV back to 10.71.10.0/24 and 10.71.20.0/24.
• If a client pulls an unexpected network, verify the pool network masks match the actual LAN subnets.
• If no leases are issued, ensure pools are not fully excluded and that service dhcp is enabled.