Which of the following best describes the OSPF router ID selection process?

The OSPF router ID (RID) is a 32-bit number that uniquely identifies a router in the OSPF domain. The selection follows a specific hierarchy. The highest priority is a manually configured RID. If not manually configured, the router automatically selects an ID. The preferred automatic method is to use the highest IP address assigned to any loopback interface. This is favored because loopback interfaces are virtual and always active, providing a stable RID even if physical interfaces go down. If no loopback is configured, the highest IP on a physical interface is used.

A. The router ID is manually configured by the network administrator: While this is the most recommended method and has the highest priority, it is not the only method. The question asks for the best description of the process, which includes automatic selection.

B. The lowest IP address on a physical interface is selected as the router ID: The selection process uses the highest IP address, not the lowest.

D. The router ID is randomly selected at the time of OSPF router startup: The selection is deterministic, based on configured IP addresses, not random.

1. Moy

J. (1998). RFC 2328: OSPF Version 2. The Internet Society. Appendix C.2

"Router ID". The RFC states the RID can be configured

and if not

"a good choice for Router ID is the largest IP address of any of the router's interfaces." Vendor implementations commonly prioritize loopback interfaces for this selection.

2. Juniper Networks Documentation. (2023). Understanding OSPF Router ID. "If the router ID is not explicitly configured... Junos OS uses the primary IP address configured on the loopback interface (lo0). If no address is configured on lo0

the software uses the primary IP address of the primary interface." While Junos uses the "primary" address

the industry-standard behavior tested is the "highest" IP on a loopback.