EIGRP Interview Questions and Answers
EIGRP questions test whether you understand its fast-convergence machinery — DUAL, successors, feasibility. Interviewers use these to gauge routing depth for Cisco-centric roles. Anchor the concepts in our EIGRP guide.
How to prepare
The core of an EIGRP interview is the DUAL algorithm and loop-free backups. Be able to define successor vs feasible successor, state the feasibility condition, and explain why EIGRP converges so fast. Knowing what "stuck in active" means signals hands-on experience.
Frequently asked questions
What algorithm does EIGRP use?
DUAL — the Diffusing Update Algorithm — which maintains a loop-free topology and precomputed backup paths for rapid convergence.
What is a successor in EIGRP?
The best (lowest-metric) loop-free route to a destination — the one installed in the routing table.
What is a feasible successor?
A precomputed backup route that is guaranteed loop-free (meets the feasibility condition) and can be installed instantly if the successor fails — no recalculation needed.
What is the feasibility condition?
A neighbour's reported distance to the destination must be less than the current successor's feasible distance — this guarantees the backup won't create a loop.
What metrics does EIGRP use by default?
Bandwidth and delay (K1 and K3). Reliability, load and MTU are available but off by default.
What must match for EIGRP neighbours to form?
The autonomous-system number and the K-value settings must match; mismatches prevent the adjacency.
What does 'stuck in active' (SIA) mean?
EIGRP marked a route active (recomputing) and didn't receive query replies from all neighbours in time — often due to a slow, congested or unresponsive neighbour.
How does EIGRP compare to OSPF for convergence?
EIGRP often converges faster because feasible successors provide instant, precomputed backups, whereas OSPF must rerun the SPF calculation.
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