Configure EIGRP on Cisco IOS: Metrics, DUAL, Stub, and Authentication
Working reference for EIGRP on Cisco IOS. The composite metric (bandwidth + delay, with K-values), DUAL and the feasibility condition (Successor and Feasible Successor for sub-second convergence), basic configuration with no auto-summary and explicit router-id, passive-interface default + selective unpassive pattern, per-interface summarization, EIGRP stub for branch routers (bounding query scope and avoiding Stuck-In-Active), MD5 authentication via key-chain, the five verification commands, and the pitfalls (auto-summary trap, K-value mismatches, SIA, AS-number agreement).