OSPF Router ID selection without a loopback interface If multiple routers in one area share the same OSPF priority and a router has no loopback interface configured, which address is chosen as the OSPF Router ID on that device?

Introduction / Context:
OSPF requires a 32-bit Router ID (RID) to uniquely identify each router within the OSPF domain. Understanding OSPF RID selection rules helps predict neighbor relationships, LSA origination, and troubleshooting outcomes when loopbacks are absent or misconfigured.

Given Data / Assumptions:

• No loopback interface is configured on the router.
• Multiple routers use the same OSPF priority (not directly relevant to RID selection but common in exams).
• OSPF will select a RID automatically if not manually set.

Concept / Approach:
OSPF selects the Router ID using a deterministic order: (1) the manually configured RID if present; else (2) the highest IP address on any loopback interface; else (3) the highest IP address on any active physical interface. Because the problem specifies no loopback, rule (3) applies. Priority values affect DR/BDR elections on multiaccess segments, not the RID selection process itself.

Step-by-Step Solution:
Confirm there is no configured RID and no loopback interfaces.Enumerate active physical interfaces and note their IPs.Choose the numerically highest IP address among those physical interfaces.That address becomes the OSPF Router ID until changed or the process restarts with different interface IPs.

Verification / Alternative check:
Use the command to view RID: show ip ospf; it will display the chosen RID. Adding a loopback with a higher IP and restarting OSPF will change the RID unless statically set.

Why Other Options Are Wrong:

• A/C/D: OSPF selects the highest IP, and loopback takes precedence over physical, but loopbacks are absent in this scenario.
• E: The startup-config order does not influence RID selection.

Common Pitfalls:
Assuming the lowest IP is chosen, or confusing DR/BDR priority with RID rules. RID is independent and persists until the OSPF process is cleared or the device reloads.

Final Answer:
The highest IP address of any physical interface