IntermediatePublished 2026-09-19
CCNA Break/Fix: The Renumbering That Left Two Floors Offline
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Lab 5 of 13 in CCNA Break/Fix II: Read the Symptom · ← Previous · Next →
Daily CCNA troubleshooting repair: two branch floors were renumbered and now users report DHCP failures and no Internet access. Work end-to-end from each floor’s client to the WAN: trace DHCP pool-to-interface bindings, validate NAT policy per floor, and restore both floors so leases are issued from the new plan and both can reach the provider loopback.
Learning objectives
- Diagnose why a client fails to obtain a DHCP lease by tracing the pool’s network statement against the serving interface subnet
- Trace host-to-outside flows to distinguish DHCP success from upstream NAT egress failures
- Isolate which source subnets receive NAT overload versus which do not by comparing ACLs to translation rules
- Verify end-to-end reachability from the client perspective, confirming both the lease parameters and the translated egress path
- Compare observed DHCP bindings and NAT translations against the intended addressing plan and egress policy
Troubleshooting focus
- Observe client symptoms first: does the host have an address, and is the default gateway present from DHCP?
- Correlate each DHCP pool’s network/mask with the actual gateway interface address on the same device
- Check whether all intended inside subnets are included in dynamic PAT rules and reference the correct ACLs
- Confirm inside/outside NAT roles on the correct interfaces and that the default route points toward the provider
- Validate results from the endpoint: a successful lease followed by outside reachability to the ISP loopback
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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.
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