Cisco Certified Network Associate (CCNA) Practice Exam

What feature allows EIGRP to quickly converge in the event of a route failure?

1. Link Layer Switching

2. Rapid Update Protocol

3. DUAL algorithm

4. Adaptive Load Balancing

The correct answer is: DUAL algorithm

The capability of EIGRP (Enhanced Interior Gateway Routing Protocol) to quickly converge after a route failure is primarily due to the DUAL (Diffusing Update Algorithm) algorithm. DUAL ensures that EIGRP routers keep track of both the best route to a destination as well as feasible successors—backup routes that can be used if the primary route fails. When a route goes down, DUAL allows the routers to quickly reroute traffic to a feasible successor without needing to wait for the entire routing table to update, which would take significantly longer. This mechanism minimizes downtime and maintains network stability. In contrast, other features mentioned do not provide this same level of rapid convergence in the face of route failure. For example, Link Layer Switching pertains to a different layer of the network model and does not specifically address routing protocols or convergence. The Rapid Update Protocol is not associated with EIGRP convergence. Adaptive Load Balancing focuses more on distributing traffic efficiently across multiple links but does not relate to the mechanism EIGRP employs for route recomputation and failure handling.