Big Picture (one‑liner)

👉Identification & Reconciliation rules answer two different questions:

 

Answered by
|
|
“Is this CI already existing or is it new?”
|
Identification Rules
|
|
“If multiple sources update the same CI, whose data should I trust?”
|
Reconciliation Rules
|

 

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1️⃣Identification Rules (IR)

 

🔹What are Identification Rules?

Identification Rules decide HOW ServiceNow recognizes a CI.

In simple words:

This rule tells ServiceNow how to uniquely identify a CI record.

---

🧠 Think of it like Aadhaar / PAN Card

• Aadhaar number uniquely identifies you
• PAN card also identifies you
• Same person → not two people

Similarly:

• Serial Number
• IP Address
• Host name

These help identify one unique CI

---

✅ What happens without Identification Rules?

If identification is weak:

• Same server gets created multiple times
• CMDB becomes dirty
• Reports & dependency maps break

---

🔧 Where are Identification Rules used?

Mostly during:

• Discovery
• Service Mapping
• Import Sets
• Integrations (SCCM, Azure, AWS, etc.)

---

📘 Simple Example – Server CI

CI Class: cmdb_ci_server

Why
|
|
serial_number
|
Hardware-level unique
|
|
(OR) name + IP address
|
Logical identification
|

 

Rule:

IF serial_number matches → SAME CI
ELSE create NEW CI

✅Result:

• Discovery runs daily
• Same server updates
• No duplicates created

---

📘Example – Network Device

| Attribute | Used for Identification |
| MAC Address |  Primary |
| IP Address | Can change |

 

👉Identification Rule:

Use MAC Address to identify network device

---

🔑 Key Takeaway for Identification Rules

✅ Identification decides CREATE vs UPDATE

“Is this CI already there or not?”

---

2️⃣Reconciliation Rules (RR)

 

🔹 What are Reconciliation Rules?

Reconciliation rules decide WHO wins when multiple sources update the same CI attribute.

In simple words:

This rule decides which source’s data is trusted more.

---

🧠 Think of it like conflicting information

Suppose:

• Your passport says DOB = 1 Jan 1990
• Your driving license says DOB = 2 Jan 1990

❓Which one should be trusted?

👉You decide a priority Same concept here.

---

✅ Why Reconciliation Rules are needed

In CMDB:

• Multiple tools update the same CI
  • Discovery
  • SCCM
  • Cloud integrations
  • Manual updates

Without rules:

• Data keeps flipping
• CMDB becomes unreliable

---

🔧 Where are Reconciliation Rules applied?

• Attribute level
• CI level
• Source-based priority

---

📘 Simple Example – Server OS Version

CI: Server-01

| Source | OS Version |
| Discovery | Windows 2019 |
| SCCM | Windows 2016 |
| Manual Update | Windows 2022 |

 

✅Reconciliation Rule (Priority-based)

Discovery → Priority 1
SCCM → Priority 2
Manual → Priority 3

✅Final value saved:

OS Version = Windows 2019
(from Discovery)

---

📘 Example – IP Address Conflict

| Source | IP |
| Discovery | 10.10.1.5 |
| Import Set | 10.10.1.7 |

 

Rule:

Discovery has higher priority → wins

✅CMDB keeps 10.10.1.5

---

🔑 Key Takeaway for Reconciliation Rules

✅ Reconciliation decides SOURCE PRIORITY

“If multiple sources update the same CI, whose data should I trust?”

---

3️⃣ Identification vs Reconciliation – Side-by-Side

| Aspect | Identification Rules | Reconciliation Rules |
| Main Question | Is this CI new or existing? | Which source wins? |
| Used When | CI creation / matching | CI update conflicts |
| Works On | CI identity | CI attributes |
| Prevents | Duplicate CIs | Data overwrites |
| Example | Serial Number | Discovery vs SCCM |

4️⃣End-to-End Example (Very Important)

🔄 Discovery Flow

1. Discovery runs

2. Identification Rule

   • Serial Number matches → ✅ update existing CI

3. Reconciliation Rule

   • Discovery beats SCCM → ✅ Discovery values kept

4. ✅CMDB stays clean and trusted

---

🧠 One-line Memory Trick (for exams & interviews)

Identification = “Who are you?”

Reconciliation = “Whose data do I believe?”

---

👉 Identification Rules are evaluated first

👉 Reconciliation Rules apply only after a CI is identified

👉If conflicts occur, ServiceNow follows a strict order of precedence , not “random behavior”

 

_ Lets Discuss Conflicts in details below: _

 

1️⃣Conflict Type 1: Identification Rules Conflict

 

❓What does this mean?

More than one CI matches the same incoming data during identification.

---

📘Example

Incoming data from Discovery:

Serial Number = ABC123
IP Address = 10.10.1.5

Existing CIs:

| CI | Serial Number | IP |
| CI‑1 | ABC123 | 10.10.1.4 |
| CI‑2 | ABC124 | 10.10.1.5 |

 

👉One rule matches CI‑1

👉Another rule matches CI‑2

❗ Conflict detected

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✅ What ServiceNow Does

ServiceNow will NOT guess

It will:

• ❌ Fail identification
• ❌ NOT update any CI
• ✅Log an IRE (Identification Engine) error
• ✅Mark record as “Ambiguous match”

📍Result:

CI NOT updated
No duplicate created
Admin must fix identification rules or CMDB data

---

🔑 Key Rule

If Identification is ambiguous, CMDB refuses to process

This is by design to protect data integrity.

---

2️⃣ Conflict Type 2: Multiple Identification Rules Apply

 

❓ What does this mean?

More than one valid identification rule exists for the same CI class.

---

✅ How ServiceNow resolves it

Identification Rules are processed in this order:

1. Class hierarchy

2. Rule priority (Order field)

3. Attribute strength

✅The first successful rule wins

---

📘Example

Rules for cmdb_ci_server:

| Rule | Attributes | Order |
| Rule‑1 | Serial Number | 100 |
| Rule‑2 | Name + IP | 200 |

✅If Serial Number matches → Rule‑1 used

✅Rule‑2 is ignored

---

3️⃣ Conflict Type 3: Reconciliation Rules Conflict

 

❓What does this mean?

Two or more data sources try to update the same attribute.

---

📘Example

CI Attribute: Operating System

Source Value Priority

| Source | Value | Priority |
| Discovery | Windows 2019 | 1 |
| SCCM | Windows 2022 | 2 |
| Manual | Windows 2016 | 3 |

---

✅ What ServiceNow Does

ServiceNow uses Source Priority (lower number = higher priority)

✅Final value:

Windows 2019
(Source = Discovery)

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🔑Important Rule

Only ONE source wins per attribute

There is no merging logic unless custom logic is built.

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4️⃣ Conflict Between Identification & Reconciliation

 

This is a very common misunderstanding.

❓Does reconciliation apply if identification fails?

❌ NO

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✅ Actual Processing Order

1️⃣ Identification
   ├─ If CI is NOT uniquely identified → STOP
2️⃣ Reconciliation
   ├─ Happens ONLY if identification succeeds
3️⃣ Update CI

👉If identification fails:

• ❌No reconciliation
• ❌No update
• ❌No create

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5️⃣ Conflict Type 4: Same Priority Sources

 

📘Example

Two sources both have priority 1:

• Discovery
• Cloud Integration

✅What ServiceNow Does

ServiceNow uses:

• Last Updated timestamp
• Source precedence order
• In some cases → non-deterministic result

⚠️This is considered bad design

---

✅Best Practice

Always:

• Avoid equal priorities
• Clearly define single system of record per attribute

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6️⃣ How You Detect These Conflicts

 

🔍Tools & Logs

• Identification Engine Logs
• cmdb_ire_log
• Discovery Error Logs
• CI Audit History

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7️⃣ Summary Table — What Happens When Rules Conflict

| Conflict Type | Outcome ❌ |
| Multiple CI match in Identification | ❌No update, error logged |
| Multiple Identification rules valid | ✅Higher priority rule wins |
| Multiple data sources updating same field | ✅Higher priority source wins |
| Identification fails | ❌Reconciliation never runs |
| Same source priority | ⚠️Unpredictable, avoid |

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🧠 Exam / Interview One‑Liners

✅“Identification conflicts stop CMDB updates to prevent corruption.”

✅“Reconciliation applies only after a CI is uniquely identified.”

✅“Source priority decides reconciliation conflicts.”

 

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Regards,

Anubhav Ritolia

Community Rising Star 2023, 2024

Organizer of Pune Developer Meetup

Technical Architect at LTIMindtree

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