Cisco CCNA (200-301)IP ConnectivityMedium
A technician examines an OSPF-enabled Ethernet segment with four routers and notices that one router is configured with 'ip ospf priority 0' on its interface facing the segment. What effect does this have?
- AThe router will always become the DR regardless of other priorities
- BThe router will not form any OSPF neighbor adjacencies on that interface
- CThe router's OSPF cost on that interface becomes zero
- DThe router is excluded from DR/BDR election and will remain a DROTHER
Show answer & explanationAnswer & explanation
Correct answer: D. The router is excluded from DR/BDR election and will remain a DROTHER
An OSPF interface priority of 0 makes the router ineligible to be elected DR or BDR on that multi-access segment; it will still form adjacencies and participate as a DROTHER.
Why the other options are wrong
- A. A priority of 0 excludes the router from DR election entirely, the opposite of guaranteeing DR status.
- B. The router still forms full adjacencies with the DR and BDR; only the election role changes.
- C. Interface priority does not affect OSPF cost, which is based on bandwidth.
OSPF DR/BDR Election
On multi-access networks, OSPF elects a Designated Router (DR) and Backup DR (BDR) to reduce the number of adjacencies; election is based on highest interface priority, then highest router ID.
- Default priority is 1; range is 0-255
- Priority 0 makes a router ineligible to be DR/BDR (DROTHER)
- Election is non-preemptive once DR/BDR are chosen
Memory trick: Priority 0 means 'I refuse the crown.'