EIGRP Troubleshooting Capstone

Bundle lab

Advanced EIGRP capstone, run as a fault hunt. The branch LAN has disappeared from the network, one router sees only half its neighbours, and the routing process looks healthy on every device. Nothing was recorded. You get symptoms and the required end state — no fault list. Faults span all three routers, and two of them leave EIGRP running perfectly while doing nothing useful.

Learning objectives

• Diagnose EIGRP from operational state alone, with no list of what was changed
• Separate 'no adjacency' from 'adjacency up but the prefix is missing' — they need different evidence
• Recognise passive-interface as a cause of a missing neighbour on a link that is otherwise fine
• Know why two routers in different autonomous systems never become neighbours
• Repair faults across three routers rather than assuming the router reporting the problem owns it

Troubleshooting focus

• If a neighbor is missing, verify EIGRP runs on the correct interface subnets and that domain parameters match.
• Use show ip protocols to confirm the AS number and which interfaces EIGRP is enabled on.
• Check for control-plane mismatches (AS/K-values/auth) before assuming data-plane or cabling issues.
• Compare EIGRP interfaces against actual interface addressing to catch missing or incorrect network wildcards.
• Validate route tables end-to-end: an advertised loopback should appear as an internal EIGRP route on remote routers.