Virtual Server Configuration and NAT vs Bridge Summary

🧩 Background

This post summarizes what I learned while observing virtual server implementation at work.
The provided operating system was Windows OS

⚙️ Process

Using virtualization software (VMware) on Windows, a total of 3 virtual machines (VMs) were created:

Application server
DB server
Other server (I don’t remember the exact purpose)

When creating VMs, network configuration is required, and you typically choose between two main methods: NAT and Bridge
These two methods differ significantly in how virtual machines communicate with external or internal networks

🌐 NAT vs Bridge – Differences Summary

Category	NAT(Network Address Translation)	Bridge(Bridge Network)
IP Assignment	Host OS acts as DHCP server and assigns internal IP	Direct IP allocation from actual physical network (DHCP server or router)
External Communication	VM can communicate externally but direct access from outside is not possible	Direct access from outside is possible
Structure	External → Host OS → VM (via host)	External → Direct VM access
Security	Relatively secure (feels like internal network)	Can be exposed externally, security configuration needed
Use Case	Suitable for development/test environments	Production service environments, when communication between multiple devices is needed
Related Concept	Similar to Jump Host structure (e.g., SSH connection using `ProxyCommand`)	Uses independent IP like regular server

What is ProxyCommand?

An option that defines a command to create a tunnel through an intermediate server before SSH connects to the final destination server
[My Computer] – SSH –> [Jump Host] – SSH –> [Destination Server]
```
ssh -o "ProxyCommand ssh user@jump.example.com nc private.server.local 22" user@private.server.local
```
1) Access jump.example.com server via SSH 2) Connect to private.server.local:22 through intermediate nc command 3) Complete SSH connection to final server through tunnel

💡 Additional Explanation (Analogy)

NAT
→ Similar to using a router (Wi-Fi) at home VM has a private IP (e.g., 192.168.x.x) and communicates externally through the host
External parties cannot directly access this VM

Bridge
→ VM operates like a regular PC directly connected via LAN cable Receives public IP or private IP directly from router, enabling equal communication with other devices on the same network

✅ Summary

NAT method is suitable for individual developer testing,
Bridge method is useful when configuring like an actual server It’s important to choose the appropriate method based on security, accessibility, and network policies