300-440 Question 10
Single answerA network engineer has configured a router that is connected to two upstream routers. OSPF is running on one link, while EIGRP is running on the other. Both routing protocols advertise the same destination prefix (10.1.1.0/24) to the local router. The local router is using its default administrative distances. However, the network engineer realizes that traffic is being forwarded over the EIGRP path instead of the OSPF path. What could be the reason?
- A
EIGRP has a lower administrative distance than OSPF by default.
- B
OSPF routes are preferred due to their lower metric.
- C
The router is misconfigured and not learning the OSPF route.
- D
EIGRP supports unequal-cost load balancing, which OSPF does not.
Show answer and explanation
Correct answer: A
Explanation
When multiple routing protocols advertise the same destination prefix to a router, the router uses administrative distance to determine which route to install in the routing table. EIGRP has a default administrative distance of 90, which is lower than OSPF's default administrative distance of 110. Therefore, the router prefers the EIGRP route, even if OSPF has a better metric.
- A. Correct.
EIGRP has a lower administrative distance (90) compared to OSPF (110) by default. Administrative distance determines the trustworthiness of the route, so the router prefers the EIGRP route.
- B. Incorrect.
While OSPF may have a lower metric depending on the topology, administrative distance takes precedence when routes to the same prefix are learned from different routing protocols.
- C. Incorrect.
The scenario does not indicate any misconfiguration or absence of the OSPF route. The route is being learned, but it is not chosen because of the higher administrative distance.
- D. Incorrect.
Unequal-cost load balancing is a feature of EIGRP, but it is unrelated to the selection of a single best route when multiple protocols advertise the same prefix.