Determine protocol and scope
Identify whether the issue affects SMB, NFS, or both; one client or many; one share/export or the entire NAS service. Record the client, NAS interface, path, time, and exact error.
Validate network and name resolution
Confirm the client reaches the intended NAS IP, routes correctly, and resolves names as expected. DNS problems can look like authentication or service problems, especially after migrations or IP changes.
Separate authentication from authorization
For SMB, distinguish domain/authentication failures from share and filesystem permissions. For NFS, distinguish network/export access from UID/GID mapping and filesystem permissions. The layer returning the error determines the next test.
Check NAS service health and dependencies
Review data interfaces, SMB/NFS service state, directory services, DNS, time synchronization, and storage resource health. Recent changes to AD, LDAP, DNS, certificates, interfaces, or exports are especially relevant.
Test with a controlled client
Use a known client and a simple path to isolate the issue. Avoid changing permissions broadly just to make access work; that can create a security problem while hiding the actual cause.
This article is a general troubleshooting framework. Validate commands and procedures against your platform version, vendor documentation, support requirements, and change-control process before making production changes.