OCI - Networking

 

All these are part of Oracle Corporation Cloud Infrastructure (OCI) networking.

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1️⃣ What is VCN? (Virtual Cloud Network)

In your screenshot:
Training_VCN

🔹 VCN (Virtual Cloud Network)

A VCN is your private network inside OCI Cloud.

It is similar to:

• A Virtual Data Center network

• Like your company LAN, but in cloud

Example:

Training_VCN
CIDR: 10.0.0.0/16 (example)

Inside a VCN you create:

• Subnets

• Route Tables

• Gateways

• Security Lists

• DRG etc.

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2️⃣ What is CIDR Block?

Example from your screenshot:

• Public Subnet → 10.0.0.0/24

• Private Subnet → 10.0.1.0/24

🔹 CIDR (Classless Inter-Domain Routing)

It defines IP address range.

Example:

10.0.0.0/24

Means:

• Total 256 IP addresses

• 10.0.0.0 – 10.0.0.255

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3️⃣ What is Subnet?

From your screenshots:

• Training_Public_Subnet → 10.0.0.0/24

• Training_Private_Subnet → 10.0.1.0/24

🔹 Subnet

A subnet is a smaller network inside VCN.

Think like:

VCN = Big Apartment Building
Subnet = One Floor
VM = One Flat

🔹 Types of Subnets

✅ Public Subnet

• Has route to Internet Gateway

• VMs can have Public IP

• Used for:

  • Bastion server

  • Web server

✅ Private Subnet

• No direct internet access

• Used for:

  • Database

  • Application server

  • Internal systems

Your screenshot shows:

Subnet Access:
- Public Subnet
- Private Subnet

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4️⃣ What is Internet Gateway (IGW)?

From your screenshot:

Training-IGW

🔹 Internet Gateway

It allows traffic between:

VCN  <---->  Internet

If a subnet has route:

0.0.0.0/0 → Internet Gateway

Then that subnet becomes PUBLIC.

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5️⃣ What is Route Table?

From your screenshot:

Default Route Table for Training_VCN
Private_route_table

🔹 Route Table

It tells traffic:
👉 “Where should I go?”

Example Route Rule:

Destination: 0.0.0.0/0
Target: Internet Gateway

Meaning:
“All internet traffic go via IGW”

Your Private Route Table shows:

No items to display

Meaning:

• No internet access

• Only internal VCN traffic allowed

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6️⃣ What is Route Rule?

Inside Route Table → Route Rules

Each rule contains:

• Destination CIDR

• Target Type

• Target

Example:

Destination: 0.0.0.0/0
Target Type: Internet Gateway
Target: Training-IGW

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7️⃣ What is DRG? (Dynamic Routing Gateway)

In your screenshot:

No items to display
Create DRG Attachment

🔹 DRG

Used to connect:

• OCI VCN ↔ On-Premise Data Center

• OCI ↔ OCI (different regions)

• OCI ↔ FastConnect / IPSec VPN

If you want Hybrid Cloud → DRG required.

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8️⃣ What is DHCP Option?

From screenshot:

Default DHCP Options for Training_VCN

🔹 DHCP

Automatically gives:

• IP address

• DNS server

• Gateway

When VM starts → DHCP assigns networking details.

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9️⃣ What is Security List? (Not shown but important)

Security List works like:
👉 Firewall

Controls:

• Ingress (Inbound)

• Egress (Outbound)

Example:
Allow:

• Port 22 (SSH)

• Port 1521 (Oracle DB)

• Port 80/443 (Web)

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🔟 What is DNS Domain Name?

From screenshot:

trainingsubnet.trainingvcn.oraclevcn.com

Used for:

• Internal hostname resolution

Private subnet shows:

DNS isn’t enabled

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1️⃣1️⃣ Regional Subnet

Your subnet type:

Regional

Means:

• Available across all Availability Domains in region

Example region in screenshot:
Frankfurt (eu-frankfurt-1)

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1️⃣2️⃣ Full Architecture from Your Screenshot

Your design currently:

Training_VCN
│
├── Public Subnet (10.0.0.0/24)
│     └── Internet Gateway attached
│
├── Private Subnet (10.0.1.0/24)
│     └── Private Route Table (No Internet)
│
└── Internet Gateway (Training-IGW)

This is a standard 2-tier architecture.

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🔥 Simple Real-Time Example (For Oracle DBA)

If you deploy:

Component	Subnet
Bastion Host	Public Subnet
App Server	Private Subnet
Database	Private Subnet

Flow:

Your Laptop → Public IP → Bastion
Bastion → Private IP → DB

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🚀 What is VPC / VCN Difference?

In AWS:

• It is called VPC

In OCI:

• It is called VCN

Both mean same:
Virtual private cloud network.

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🎯 Summary Table

Component	Purpose
VCN	Entire virtual network
Subnet	Smaller network inside VCN
CIDR	IP range
Route Table	Traffic direction rules
Route Rule	Single routing entry
Internet Gateway	Connect to Internet
DRG	Connect to On-prem
DHCP	Auto IP configuration
Security List	Firewall

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