Cisco Certified Support Technician (CCST) NetworkingIP ConnectivityMedium
A network administrator is reviewing the routing table of a Cisco router. They notice multiple routes to the same destination network, learned from different routing sources. The router uses a specific value to determine which route is the most preferred to install in the routing table. What is this value called?
- ACost
- BPreference
- CAdministrative Distance
- DMetric
Show answer & explanationAnswer & explanation
Correct answer: C. Administrative Distance
Administrative distance (AD) is a value used by Cisco routers to rank the trustworthiness of routing information sources. When a router learns about the same destination from multiple routing protocols or static configurations, the route with the lowest administrative distance is preferred and installed in the routing table.
Why the other options are wrong
- A. Cost is a term often synonymous with metric, especially in OSPF, but it's not used for inter-protocol comparison.
- B. Preference is a general term for route selection, but 'administrative distance' is the specific technical term used by Cisco for this purpose.
- D. Metric is used by a routing protocol to determine the best path *within* that specific protocol, not between different protocols.
Administrative Distance (AD)
A value used by Cisco routers to rate the trustworthiness of routing information sources. When multiple routes to the same destination exist, the route with the lowest AD is preferred and installed in the routing table.
- Lower AD is more preferred.
- Static routes typically have an AD of 1.
- EIGRP has an AD of 90, OSPF 110, RIP 120.
Memory trick: AD: The lower the score, the higher the rank.