NCM SSH Backups - NCM SSH Backups not showing configuration line changes

Products

• Network Observability

Issue/Introduction

We have started to notice that many of our Cisco devices are no longer showing when configuration lines have changed. The capture only updates the 'Last Verified Time' and no longer shows changes for the past few months.

Environment

• Software Version: 24.3, 25.4

• Protocol: SSH

• Feature: Network Configuration Manager (NCM)

Cause

Improperly configured Regex Mask that was matching on the differences and marking them 

Jan 20, 2026 13:37:14.866 (grpc-default-executor-50437) - ###.###.###.###:  getDiff entering 1st while loop. Jan 20, 2026 13:37:14.866 (grpc-default-executor-50437) - ###.###.###.###:  getDiff finished 1st, entering 2nd while loop. Jan 20, 2026 13:37:14.871 (grpc-default-executor-50437) - ###.###.###.###:  Differing deleted line:  snmp-server contact 000-000-0000 |  NETWORK Ops Jan 20, 2026 13:37:14.875 (grpc-default-executor-50437) - ###.###.###.###:    check diff against maskList[0]:  [!#] Jan 20, 2026 13:37:14.875 (grpc-default-executor-50437) - ###.###.###.###:    check diff against maskList[1]:  [^username.admin] Jan 20, 2026 13:37:14.875 (grpc-default-executor-50437) - ###.###.###.###:      matched mask, uninteresting diff Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:  Differing added line:  snmp-server contact 000-000-0000 | TESTING-BACKUP Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:    check diff against maskList[0]:  [!#] Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:    check diff against maskList[1]:  [^username.admin] Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:      matched mask, uninteresting diff Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - getDiffResults going to release permit, now permits: 1 Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:    the diff was uninteresting:

Resolution

PREREQUISITES:

• Administrative access to DX NetOps Spectrum/NCM

• Access to NCM Mask Configuration settings

   

STEPS:

1. ENABLE NCM DEBUGGING: Enable debugging in config.xml to capture the getDiff process and verify mask behavior
   
       <debugging type="java.lang.String">max</debugging> 

   EXPECTED: NCMSERV.OUT and debug.log.xxxxxxxxxxxxxxxxxxxx record the comparison process
   
   
   

2. IDENTIFY IMPROPER REGEX MASK: Review debug logs for "matched mask, uninteresting diff" entries to identify which mask is triggering on valid changes
   
   
   

   Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:  Differing added line:  snmp-server contact 000-000-0000 | TESTING-BACKUP Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:    check diff against maskList[0]:  [!#] Jan 20, 2026 13:37:14.876 (grpc-default-executor-50437) - ###.###.###.###:    check diff against maskList[1]:  [^username.admin]

    

   NOTE: An improperly formatted mask like [^username.admin] may match on unintended characters, causing valid diffs to be ignored

    

3. REMOVE CONFLICTING MASK: Access the Mask Configuration for the affected device families and remove the improperly developed RegEx entry

    

   Path: NCM > Mask Configuration Action: Delete the entry: [^username.admin]

    

4. PERFORM TEST CAPTURE: Make an inconsequential change on a test device and perform a manual capture

    

   EXPECTED: NCM should now identify the difference and update the 'Last Capture Time'

    
    

Additional Information

ROOT CAUSE: The issue was caused by an improperly formatted RegEx Mask entry [^username.admin]. This mask matched unintended characters in the configuration lines, leading NCM to mark valid differences as "uninteresting" and ignore them.