Routing reliability is essential for maintaining service continuity in enterprise IP networks, particularly under failure conditions. Among interior gateway protocols, Open Shortest Path First (OSPF) and Enhanced Interior Gateway Routing Protocol (EIGRP) are widely adopted due to their scalability and adaptability to dynamic environments. This paper presents a systematic evaluation of OSPF and EIGRP under diverse network failure scenarios using a hierarchical enterprise topology. The considered scenarios include single link failures, core router failures, edge router failures, sequential failures, and recovery processes. Performance is assessed using key metrics, including convergence time, packet loss ratio, end-to-end delay, throughput degradation, and routing control overhead. Results show that EIGRP achieves significantly faster convergence (300-600 ms) compared to OSPF (900-1,500 ms), along with lower packet loss (1-3% versus 6-10%). In addition, EIGRP generates substantially less control overhead, reducing delay and improving recovery performance under dynamic conditions. Conversely, OSPF exhibits greater routing stability and more consistent behavior in large-scale, multi-area deployments. These findings reveal a fundamental trade-off between convergence speed and structural stability, providing practical guidance for routing protocol selection in fault-tolerant enterprise network design.