Which routing protocol has an administrative distance (AD) of 115?

The routing protocol that has an administrative distance (AD) of 115 is EIGRP when it is operating in a non-automated manner.

Administrative distance is used by routers to determine the trustworthiness of routing information received from different sources. Each routing protocol is assigned a specific administrative distance, which helps the router decide which protocol's route to prefer when multiple paths to a destination exist. For EIGRP, if it's configured for non-autonomous systems or not using the automatic summarization feature, it will indeed have an AD of 115.

In contrast, RIP has a lower administrative distance of 120, making it less preferred than EIGRP in scenarios where both protocols present routing information. OSPF, which is a link-state protocol, has an AD of 110, thereby being preferred over both RIP and EIGRP's non-autonomous routes. IS-IS has an AD of 115 as well, but it operates differently and isn't as commonly associated with Cisco environments compared to EIGRP. Recognizing the distinctions in administrative distances is critical for understanding how routers prioritize routes, ensuring optimal routing paths in a network.