A router has learned three possible routes that could be used to reach a destination network. One route is from EIGRP and has a composite metric of 20584570. Another route is from OSPF with a metric of 842. The last is from RIPv2 and has a metric of 3. Which route or routes will the router install in the routing table?
- RIPv2
- none of the above
- EIGRP route
- OSPF route
- all three routes
Explanation: When a router learns multiple paths to the same destination from different routing protocols, it uses a value called Administrative Distance (AD) to decide which route to install in the IP routing table. Administrative distance is a measure of the "trustworthiness" of the source protocol; the lower the AD, the more trusted the protocol is.
The router's decision-making process is as follows:
- AD before Metric: The router first compares the administrative distance of the protocols. Metrics (such as RIP's hop count, OSPF's cost, or EIGRP's composite value) are only compared if multiple paths are learned from the same protocol.
- Protocol Hierarchy: According to the sources, EIGRP has a lower administrative distance than OSPF, meaning EIGRP routes are preferred over OSPF routes regardless of the metric values. While OSPF has a default distance of 110, EIGRP is more trusted. RIPv2, as an older distance-vector protocol, typically has an even higher (less trusted) administrative distance than both EIGRP and OSPF.
In this scenario, even though the EIGRP metric is much larger than the others, the router will install the EIGRP route because its administrative distance makes it the most trustworthy source among the three.
Related exam: Modules 8 – 13: Checkpoint Exam: Network Routing Answers (CCNP ENCOR v9)
