Cisco C9500-48Y4C blanks out model number during Discovery, repeatedly

[HeyMarkWarmack]

Annoying issue/mystery that I have been able to solve, I am hoping someone has found a fix.

Situation:  I have ONE Cisco IP Switch, Cisco Systems, Inc. Catalyst 9500 Series Switches C9500-48Y4C. 

I set the Manufacturer and Model ID manually and Discovery blanks out the Model ID repeatedly for the last year.  Left alone, and Discovery does not update the model.

Widget path: CMDB Data Foundations dashboard > Data Management Practices tab > Managed CIs Missing Model Entries widget

Things I have tried/checked:

* Checked the CI Class Manager for IP Switch

* It's STACKED partner unit does not do this, just this one.  Even is Master or Slave.  See pics.

* Hardware Model is only one model and is normalized.

* Set the Manufacturer and Model ID manually dozens of times, only to have Discovery blank it out and make my widget back off 100%.

Has someone seen this before?  Have a fix for it?

[AJ-TechTrek]

Hi @HeyMarkWarmack ,

As per my understanding Why this is happening:


What you’re seeing is a classic case where:

* Discovery (or its probe/pattern) runs → doesn’t get the model value back from the target (via SNMP, SSH, etc.)
* Discovery writes blank → which overwrites your manually populated value
* The data source (target switch) isn’t returning the expected model in SNMP sysObjectID, sysDescr, or the OIDs your discovery pattern expects
This is why it’s only happening on one switch, while its stacked partner keeps the model value.

Root causes to verify first:
1. SNMP configuration
* Confirm SNMP community / version is the same on both master & partner switches

2. sysObjectID & sysDescr values
* Use SNMPwalk or snmpget on the problematic switch
snmpget -v2c -c <community> <ip> sysObjectID.0
* Compare output to the healthy switch

3. Discovery behavior:
* By default, Discovery will clear the model field if no value is returned in SNMP

Possible solution options can be :-

Option A – Fix at the data source (Recommended)

* Check and fix SNMP config so this switch correctly returns:
* sysObjectID that maps to the correct model in SNMP OID to model mapping
* sysDescr that includes the model string
* If the switch is running older firmware: upgrade it — Cisco sometimes fixes MIB/OID inconsistencies

Option B – Fix in ServiceNow (if data source cannot be fixed)

1. Adjust identification rule / CI Classifier:
* For IP Switch class, check the classifier using sysObjectID to map to model
* Update classifier to map the actual sysObjectID returned by this switch → to the correct model
2. Prevent overwriting:
* Update discovery behavior so if the model value is blank in discovery, do not overwrite existing model
* This can be done by:
* Modifying the pattern (skip update if no value)
* Or using Reclassification Exclusion Rules (in CI Class Manager) to ignore reclassification when model is missing
* Or customizing the identification rule: in Identification Rule → data source priority → give manual entries higher priority over discovery

Option C – Hardcode / normalize

* Use Hardware Model Normalization (Normalization Rules) to map blank or specific values to your model
* Downside: if the device truly changes, it won't reflect automatically

Widget issue:
Your widget flags it missing because the model field is empty.
Once Discovery stops blanking it out (via one of the fixes above), the widget will stop reporting the CI as missing model.

steps to troubleshooting :-
1. Run SNMPwalk on the problem switch:
snmpwalk -v2c -c <community> <ip> sysDescr
snmpwalk -v2c -c <community> <ip> sysObjectID

2. Compare to partner switch → see what's different.
3. In CI Classifier (for IP Switch):
* Add the returned sysObjectID → map it to the correct model.
4. In Identification Rule → set “Skip if source value is empty” for Model attribute
(or in pattern step: add logic: if value != null then update).
5. Test: run discovery again → confirm Model ID is not blanked out.

My understanding's:

* It happens because Discovery updates CI with blank if it can’t get data
* Fix by:
* Fixing SNMP data returned by the device
* Adjusting classifier / pattern to handle special case
* Setting “don’t overwrite if empty” rules in the Identification Rule
* Finally, confirm the fix by testing Discovery and checking the dashboard widget

Please appreciate the efforts of community contributors by marking appropriate response as Mark my Answer Helpful or Accept Solution this may help other community users to follow correct solution in future.
 
Thank You
AJ - TechTrek with AJ
LinkedIn:- https://www.linkedin.com/in/ajay-kumar-66a91385/
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ServiceNow Community MVP 2025