OSPF process identifier (process ID) — scope and purpose Which statements correctly describe the OSPF process identifier used when enabling OSPF on a router?

Introduction / Context:
When you start OSPF on a router, you specify a process ID. Engineers often confuse this numeric value with AS numbers or area numbers. Understanding what the process ID does and does not control prevents configuration errors and failed adjacency formation.

Given Data / Assumptions:

• The OSPF process ID is a router-local parameter.
• Neighbors do not exchange or compare process IDs.
• Multiple OSPF processes can run on one router for segmentation or migration.

Concept / Approach:
OSPF’s process ID identifies a local OSPF instance on the router. It is locally significant; different routers can use different process IDs and still form adjacencies, as long as other parameters (area, timers, network statements, authentication) match. The process ID is not optional—you must provide one even if only a single OSPF instance runs—but its numeric value is arbitrary and chosen by the administrator for local organization.

Step-by-Step Solution:
Recognize that OSPF neighbors never validate one another’s process ID.Confirm that the process ID names the local database instance on the router.Eliminate claims of global significance or matching requirements across neighbors.Conclude that the correct statements are “locally significant” and “needed to identify the local instance.”

Verification / Alternative check:
Change the process ID on one router and keep all other parameters identical; adjacencies still form. Conversely, mismatched area IDs or authentication prevent adjacency regardless of identical process IDs.

Why Other Options Are Wrong:

• B/D: Incorrect; process ID does not need to match across routers or areas.
• C: Not optional; you must specify one to enable OSPF.
• E: LSDB checksums are not derived from process ID.

Common Pitfalls:
Believing the process ID functions like an AS number in EIGRP/OSPFv3 contexts; it does not. It is a local label only.

Final Answer:
It is locally significant and is needed to identify a unique local OSPF database instance.