All these are part of Oracle Corporation Cloud Infrastructure (OCI) networking.
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.
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
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
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.
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
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
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.
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.
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)
🔟 What is DNS Domain Name?
From screenshot:
trainingsubnet.trainingvcn.oraclevcn.com
Used for:
-
Internal hostname resolution
Private subnet shows:
DNS isn’t enabled
1️⃣1️⃣ Regional Subnet
Your subnet type:
Regional
Means:
-
Available across all Availability Domains in region
Example region in screenshot:
Frankfurt (eu-frankfurt-1)
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.
🔥 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
🚀 What is VPC / VCN Difference?
In AWS:
-
It is called VPC
In OCI:
-
It is called VCN
Both mean same:
Virtual private cloud network.
🎯 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 |
