Routing Protocol with Default Administrative Distance of 90

C

The administrative distance (AD) is a measure of the trustworthiness of a routing protocol. It is a value assigned to a routing protocol to reflect its reliability or trustworthiness. The lower the administrative distance value, the more trusted the protocol is.

To answer the question, we need to identify the routing protocol with a default administrative distance of 90.

A. S: S stands for Static routes, which are manually configured routes. The default administrative distance for static routes is either 1 or 0, depending on the platform.

B. E: E stands for EIGRP (Enhanced Interior Gateway Routing Protocol), which is a Cisco proprietary routing protocol. The default administrative distance for EIGRP is 90.

C. D: D stands for EIGRP external routes redistributed into OSPF (Open Shortest Path First). The default administrative distance for EIGRP external routes is 170.

D. R: R stands for RIP (Routing Information Protocol), which is a distance-vector routing protocol. The default administrative distance for RIP is 120.

E. O: O stands for OSPF (Open Shortest Path First), which is a link-state routing protocol. The default administrative distance for OSPF is 110.

Therefore, the correct answer is B. E, which represents EIGRP with a default administrative distance of 90.