CIS-DF--Day11- IRE - Identification Rule - Types

Описание: 1. Overview of the IRE (Identification & Reconciliation Engine)
IRE determines whether to update an existing CI or create a new one by checking fields like:

Serial Number
Name
MAC Address
Other identifiers (based on class)

If no match is found → a new CI is created.

2. Types of CI Classes
Every CI class in ServiceNow falls into either:

Hardware
Application

Each class inherits default identification rules from its parent (hardware/app).

3. Identification Rules
Identification rules ensure:

Data integrity
Avoidance of duplicate CIs
Consistency
Improved data quality

They define how a CI is uniquely identified.
Two Types of Identification Rules


Independent

Identifies CI only using its own attributes
Faster and recommended



Dependent

Identification depends on another CI and its relationship
Slower; not recommended



Example analogy:
Independent = travelling alone
Dependent = waiting for someone else before travelling

4. Creating a Custom CI Class
Steps covered:

Add child class under cmdb_ci_computer
Add attributes (fields)
Set identification rule
Choose rule type (independent/dependent)
Configure lookup tables if needed

Lookup Tables
Used when CI info needs to be verified from another table (e.g., Asset table).
Still independent, just referencing other data.

5. Duplicate CI vs Overloaded CI
Duplicate CI
Same CI represented multiple times in CMDB.
Occurs when identification rules are weak.
Overloaded CI
Multiple different CIs being treated as one CI.
Example: All fruits identified as “Lemon”.
Occurs due to bad rules or multi‑source mismatches.

6. Multi‑Source Discovery
Why do we need multiple sources (e.g., SCCM, Intune, Discovery, Monitoring tools)?

Some tools don’t discover all device types
User devices often not discovered by ServiceNow Discovery
Network devices monitored via specialized tools
Multiple sources bring different data attributes
To get full infrastructure coverage


7. Reconciliation Rules (Brief Introduction)
Reconciliation determines:

Which source’s data should be trusted
Which attribute values override others when conflicts occur

Example:
One source reports RAM = 16GB, another says 32GB → reconciliation rule decides which wins.
Full topic to be covered in the next session.

8. Key Takeaways

Independent rules are preferred.
CI classes rarely need to be created; ServiceNow provides 900+ classes.
Lookup helps reference other tables but keeps the rule independent.
Upgrade impact is minimal for custom classes unless ServiceNow introduces the same class.
Multi-source always demands reconciliation rules.
IRE is available even without Discovery plugin, but multi-source property may need enabling.