Cisco Certified Support Technician (CCST) NetworkingIP ConnectivityMedium
A network technician observes that a router's routing table contains multiple paths to the same destination network learned via different routing protocols. For example, OSPF has a path with a cost of 20, and EIGRP has a path with a composite metric of 256000. Which path will the router choose to forward traffic, assuming default administrative distances?
- AThe EIGRP path, because its composite metric is higher.
- BThe OSPF path, because its cost is lower.
- CThe OSPF path, because OSPF has a lower administrative distance than EIGRP.
- DThe EIGRP path, because EIGRP has a lower administrative distance than OSPF.
Show answer & explanationAnswer & explanation
Correct answer: D. The EIGRP path, because EIGRP has a lower administrative distance than OSPF.
When a router learns multiple paths to the same destination via different routing protocols, it uses Administrative Distance (AD) to determine which protocol's route is preferred. EIGRP (internal) has a default AD of 90, while OSPF has a default AD of 110. A lower AD is preferred.
Why the other options are wrong
- A. Higher metrics are generally worse; EIGRP's metric is not directly comparable to OSPF's cost without AD consideration.
- B. Metric comparison is only used when comparing routes from the same routing protocol; AD is used for different protocols.
- C. OSPF has an AD of 110, which is higher (less preferred) than EIGRP's AD of 90.
Administrative Distance (AD)
Administrative Distance (AD) is a value used by Cisco routers to rank the trustworthiness of routing information sources, with lower values indicating higher preference.
- Used when multiple routing protocols offer paths to the same destination.
- Compares protocols, not metrics within a protocol.
- Static routes (1) and connected interfaces (0) have the lowest ADs.
Memory trick: Always Determine Every Router's Decision.