Cisco CCNA (200-301)IP ConnectivityMedium
A network administrator issues the 'show ip route' command on a router and observes the following entry: O E2 10.10.10.0/24 [110/20] via 192.168.1.1, 00:01:30, GigabitEthernet0/0 What does the value '20' represent in this routing table entry?
- AThe number of hops to the destination network.
- BThe OSPF metric (cost) to reach the 10.10.10.0/24 network.
- CThe external metric (cost) advertised for this E2 route.
- DThe administrative distance of the OSPF route.
Show answer & explanationAnswer & explanation
Correct answer: C. The external metric (cost) advertised for this E2 route.
In an OSPF E2 route entry, the first number in the brackets (110) is the administrative distance, and the second number (20) is the external metric, which remains constant regardless of the internal cost to the ASBR.
Why the other options are wrong
- A. OSPF uses cost (bandwidth-based metric), not hop count, as its metric.
- B. This is an E2 route; the 'cost' shown is the external metric, not the cumulative OSPF cost.
- D. The administrative distance is 110 for OSPF, which is the first value in the brackets.
OSPF E2 Route Metric
For OSPF External Type 2 (E2) routes, the metric displayed in the routing table (after the administrative distance) is the external cost advertised by the ASBR, which remains constant.
- E2 routes are external routes.
- The metric is the external cost from the ASBR.
- Internal cost to ASBR is not added for E2 routes.
Memory trick: OSPF's journey: Internal cost accumulates, E1 adds, E2 keeps it fixed.