Sunday, May 3, 2026

IP Requirements for 3-Node Oracle RAC Database

 

🎯 Objective

This SOP explains the IP addressing requirements for a 3-node Oracle Real Application Clusters (RAC) environment, including:

  • Public IPs

  • Private Interconnect IPs

  • Virtual IPs (VIPs)

  • SCAN IPs

  • DNS / Hosts configuration

  • Best practices

🏗️ 1. Oracle RAC Network Architecture Overview

A RAC cluster requires multiple network interfaces for:

  • Client connectivity

  • Cluster communication

  • Failover handling

  • SCAN-based load balancing

📊 2. IP Types Required in 3-Node RAC

IP TypePurposeQuantity Required
Public IPNode communication & client access3
Private IPInterconnect / Cache Fusion3
VIP (Virtual IP)Fast failover handling3
SCAN IPClient load balancing3
DNS EntryName resolutionRequired

🧠 3. Understanding Each IP Type

🌐 A. Public IP

Purpose

  • Normal communication

  • SSH access

  • Node hostname resolution

Requirement

One public IP per node.

Example

NodeHostnamePublic IP
Node1rac1192.168.1.101
Node2rac2192.168.1.102
Node3rac3192.168.1.103

🔒 B. Private IP (Interconnect)

Purpose

Used for:

  • Cache Fusion

  • Cluster heartbeat

  • Internode communication

Important

This network must be:

  • Private

  • Low latency

  • High speed

Example

NodePrivate HostnamePrivate IP
Node1rac1-priv10.10.10.101
Node2rac2-priv10.10.10.102
Node3rac3-priv10.10.10.103

⚡ C. VIP (Virtual IP)

Purpose

Fast client failover.

If a node fails:

  • VIP relocates to another node

  • Client gets immediate TCP reset

  • Faster reconnection

Requirement

One VIP per node.

Example

NodeVIP HostnameVIP IP
Node1rac1-vip192.168.1.111
Node2rac2-vip192.168.1.112
Node3rac3-vip192.168.1.113

🔄 D. SCAN IP (Single Client Access Name)

Purpose

Provides:

  • Load balancing

  • Simplified client connection

  • Transparent node addition/removal

Requirement

Minimum 3 SCAN IPs recommended by Oracle.

Example

SCAN NameSCAN IPs
rac-scan192.168.1.120
rac-scan192.168.1.121
rac-scan192.168.1.122

🧾 4. Total IP Requirement Summary

For 3-Node RAC

TypeCount
Public IP3
Private IP3
VIP3
SCAN IP3
Total12 IPs

📁 5. Sample /etc/hosts Configuration

# Public IPs
192.168.1.101   rac1
192.168.1.102   rac2
192.168.1.103   rac3

# VIPs
192.168.1.111   rac1-vip
192.168.1.112   rac2-vip
192.168.1.113   rac3-vip

# Private IPs
10.10.10.101    rac1-priv
10.10.10.102    rac2-priv
10.10.10.103    rac3-priv

# SCAN
192.168.1.120   rac-scan
192.168.1.121   rac-scan
192.168.1.122   rac-scan

🌐 6. DNS Requirements

Oracle strongly recommends:

  • DNS configuration
    OR

  • GNS (Grid Naming Service)

✅ DNS Checks

nslookup rac-scan

ping rac1-vip

⚙️ 7. Network Interface Example

InterfacePurpose
eth0Public
eth1Private Interconnect

🚨 8. Important Best Practices

✅ Public Network

  • Use bonded NICs if possible

  • Ensure low packet loss

✅ Private Interconnect

  • Dedicated network only

  • Jumbo frames recommended

  • No public traffic

✅ VIP

  • Must be unused IPs

  • Same subnet as public IP

✅ SCAN

  • Must resolve to 3 IPs

  • Round-robin DNS recommended

🔍 9. Pre-Installation Validation Commands

Verify Interconnect

oifcfg getif

Verify Cluster Network

cluvfy comp nodecon -n rac1,rac2,rac3 -verbose

Verify SCAN

nslookup rac-scan

🧪 10. Oracle RAC Connection Flow

Client
   ↓
SCAN Listener
   ↓
Node Listener
   ↓
RAC Instance

⚠️ 11. Common Issues

IssueCause
Node evictionPrivate interconnect failure
Slow failoverVIP misconfiguration
Connection issueSCAN DNS issue
Split brainInterconnect latency

🔥 12. Interview Questions & Answers

Q1: Why are VIPs used in RAC?

Answer:

VIPs provide faster client failover by immediately rejecting failed TCP connections instead of waiting for timeout.

Q2: Why 3 SCAN IPs?

Answer:

Oracle recommends 3 SCAN IPs for high availability and load balancing.

Q3: Can SCAN IPs be on different subnet?

Answer:

No, SCAN IPs should typically be on same public subnet.

🏁 13. Final Checklist Before RAC Installation

CheckStatus
Public IP configured✅
Private IP configured✅
VIP available✅
SCAN resolves correctly✅
DNS working✅
Interconnect tested✅

🚀 14. Recommended Enterprise Design

Production Environment

  • Bonded NICs

  • Redundant switches

  • Dedicated interconnect VLAN

  • DNS-managed SCAN


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