One OID needs to be shared across two classes

[ViniY]

Hi Team,

I have two classes—[Cisco Firewalls and Intrusion Detection Systems]—that share the same OID. How can I use two classifiers for one OID?

I'm looking for guidance on setting up the classifiers.

Regards,

Vini.

[AJ-TechTrek]

Hi @ViniY ,

As per my Understanding the Problem recap is -

* You have two CMDB classes (e.g., cmdb_ci_firewall and cmdb_ci_ids).
* Both device types share the same SNMP OID.
* Discovery Classifiers normally use OID to identify the class.
* You cannot just have two classifiers with the same OID because the system won’t know which to use.

Solution Overview:
To distinguish between them, you need to:
* Use additional conditions in the classifiers beyond the shared OID.
* Or, in the associated Identification and Connection Sections or Patterns, further refine classification based on other device attributes.

Step-by-step guidance:
1.Create two classifiers (one for each class):
* Go to:
Discovery Definition → Classifiers.
* Create classifier A:
* Class: Cisco Firewall
* Condition: sysObjectID = shared OID
* Create classifier B:
* Class: Intrusion Detection System
* Condition: sysObjectID = same shared OID

2. Add differentiating criteria
Since OID alone isn’t enough, add additional distinguishing attributes:
* For example:
* sysName contains “FW” vs. “IDS”
* description field contains unique keywords
* Another SNMP attribute that differs between firewall & IDS (like a product name, vendor string, software version, etc.)
Check what data is returned in SNMP by doing an SNMP walk on each device and look for differences.

3.Use classifier priorities:
* ServiceNow uses classifier order to decide which to evaluate first.
* Set higher priority (lower order number) for the more specific classifier.
* Example:
* Classifier for Firewall: order = 100
* Classifier for IDS: order = 110

4. Validate classifiers:
* Use the “Validate” feature in Classifiers:
* Enter test data to see which classifier will match.
* Adjust until each classifier correctly identifies only its own device type.

5. (Optional): Use Patterns
If devices cannot be distinguished reliably in the classifier:
* Use a single classifier (e.g., “Generic Cisco Device”).
* In the associated Discovery Pattern, use conditions to decide the class dynamically.
* Example: In the Identification section, add branching logic:
* “If sysName contains FW → classify as Firewall”
* “If sysName contains IDS → classify as IDS”

Step and What to do
Create -classifiers Both use same OID
Add conditions- Use unique data like sysName, description, etc.
Set order -Prioritize more specific classifier
Validate -Confirm classifier behavior
Use patterns- Add dynamic classification if classifier isn't enough

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Thank You
AJ - TechTrek with AJ
LinkedIn:- https://www.linkedin.com/in/ajay-kumar-66a91385/
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ServiceNow Community MVP 2025