Question: In a certificate lifecycle management framework for Network Functions (NFs), how might an NF Repository Function (NRF) verify the validity of an NF producer instance's certificate during discovery, to prevent unnecessary signaling?
Option 1: By periodically polling the NF producer instance directly for its current certificate status.
Option 2: Through locally stored information about the NF producer instances' certificates or by querying external entities like OCSP (Online Certificate Status Protocol) / CRL (Certificate Revocation List) servers.
Option 3: Automatically, as the NRF is always synchronized with the latest certificate revocation lists without needing to query external sources.
Option 4: By relying on the NF consumer to report any invalid certificates encountered during NF discovery.
Explanation: This option is correct because it aligns with the described approach in the context of certificate lifecycle management, where the NRF can utilize either its own stored data or query other network entities (like OCSP/CRL servers) to check the validity of certificates. This method prevents the inclusion of non-valid certificates in the discovery response, thus avoiding unnecessary signaling. The other options either introduce inefficiencies (Option 1), assume an unrealistic level of automation without external checks (Option 3), or shift responsibility away from the NRF (Option 4).