RAC#2 Network & GNS in Oracle Clusterware

 RAC#2 Network & GNS in Oracle Clusterware

🟢 Step 1: Basic Question

👉 What do we need before installing Clusterware?

✅ Answer: Network setup is very IMPORTANT

🟢 Step 2: Minimum Network Requirement

👉 Each node must have:

✅ At least 2 Network Adapters (NICs)

AdapterPurpose
1️⃣ Public NetworkClient connections
2️⃣ Private Network (Interconnect)Node-to-node communication

🔹 Example (3-node cluster):

Each node has:

  • eth0 → Public
  • eth1 → Private

✅ Important Rule: 👉 Interface names must be same on all nodes

🟢 Step 3: Why Two Networks?

👉 Think like this:

  • Public = “Outside world” 🌍
  • Private = “Internal discussion” 🔒

✅ Separation gives:

  • Better performance
  • Security
  • Stability

🟢 Step 4: Important Network Rules

❌ Do NOT:

  • Use cross-cables
  • Directly connect nodes

✅ Always:

  • Use a network switch

👉 Why?

  • Ensures proper communication
  • Avoids failures

🟢 Step 5: IP Address Configuration

You have 2 options:

🔹 Option 1: Static IP (Common ✅)

  • Manually assign IPs
  • Used in typical installation

🔹 Option 2: GNS (Grid Naming Service)

  • Automatic IP assignment
  • Uses DNS + DHCP

🟢 Step 6: Protocol Requirements

NetworkProtocol
PublicTCP/IP
PrivateUDP / RDS / TCP (Windows)

👉 Private network uses:

  • Grid Interprocess Communication (IPC)

🟢 Step 7: IPv4 vs IPv6 (Important Rule)

✅ Supported:

  • IPv4
  • IPv6

❌ Not Allowed:

  • Mixing IPv4 & IPv6 during installation

👉 Example:

  • Node1 = IPv4
  • Node2 = IPv6 ❌ (Not allowed)

✅ After install:

  • You can add IPv6 to IPv4 cluster (or vice versa)

🟢 Step 8: Best Practice

👉 Remember this line:

👉 “Do NOT mix IP versions during installation.”

🟢 Step 9: What is GNS?

👉 GNS = Grid Naming Service

📌 Think of it as: 👉 “Automatic DNS inside cluster”

✅ What GNS does:

  • Resolves hostnames
  • Assigns IP addresses
  • Reduces manual configuration

🟢 Step 10: GNS Requirements

Before using GNS:

✅ You need:

  • DNS configured
  • Domain delegation
  • DHCP server

🔹 Key Point:

  • Only 1 static IP needed → GNS VIP

🟢 Step 11: How GNS Works

👉 Flow:

  1. Client sends request
  2. Goes to GNS VIP
  3. GNS resolves using internal mDNS
  4. Sends response

✅ Extra Tip: 👉 Disable any third-party mDNS tools

🟢 Step 12: GNS Modes

🔹 Automatic Mode

  • Uses DHCP
  • Auto IP assignment

🔹 Static Mode

  • DNS manually configured
  • SCAN IPs fixed

🟢 Step 13: New Feature — Shared GNS

👉 Earlier:

  • One GNS per cluster

👉 Now:

  • One GNS for multiple clusters ✅

✅ Benefits:

  • Centralized naming
  • Less admin work
  • Better cloud integration

🟢 Step 14: Highly Available GNS

👉 GNS supports HA (High Availability)

Structure:

RoleFunction
Primary GNSMain server
Secondary GNSBackup

✅ If primary fails:

👉 Secondary becomes primary

Data Sync Methods:

  • Full transfer
  • Incremental transfer

🟢 Step 15: SCAN (Very Important)

👉 SCAN = Single Client Access Name

📌 Think of it as: 👉 “One entry point for the cluster”

✅ Key Features:

  • Clients connect using SCAN
  • No need to know node details

🔹 SCAN Properties:

  • Fully qualified name (hostname + domain)
  • Maps to 3 IP addresses

✅ Why 3 IPs?

👉 For:

  • Load balancing
  • High availability

🟢 Step 16: SCAN Working

👉 Process:

  1. Client connects to SCAN
  2. SCAN listener receives request
  3. Redirects to least loaded node

✅ Advantage: 👉 No config change when nodes added/removed

🟢 Step 17: Quick Visualization

Client → SCAN → Any Node → Database

🟢 Step 18: Installation Checklist

Before install:

✅ Same OS on all nodes
✅ Two NICs per node
✅ Proper DNS or GNS setup
✅ Static IPs or DHCP
✅ Switch (not cross-cable)

🧠 Easy Memory Summary

👉 Remember this line:

👉 “2 networks, 2 IP types, 1 SCAN, optional GNS.”

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