What is it?
A VPN (Virtual Private Network) creates an encrypted tunnel across an untrusted network (usually the internet) so traffic stays confidential and cannot be read or tampered with in transit. There are two main types: Site-to-Site VPN, which permanently connects two networks (e.g. Head Office and Branch Office), and Remote Access VPN, which connects an individual user’s device to the company network on demand.
Why should I learn it?
VPNs are the default way companies protect traffic across the internet, and “site-to-site vs remote access” is one of the first questions in almost every VPN interview.
How it works
Site-to-Site: two VPN gateways (routers/firewalls) build a permanent tunnel between them → traffic from any device on Network A to Network B is automatically encrypted and routed through the tunnel → no end-user configuration needed. Remote Access: a user runs VPN client software → authenticates (often with AAA/MFA) → a temporary tunnel is built from their device to the company gateway → only that user’s traffic uses the tunnel.
Real-world example
A company connects its Mumbai and Bangalore offices with a permanent site-to-site VPN so both offices share resources transparently. A remote employee working from home uses a remote access VPN client to securely reach the same internal resources.
Troubleshooting mindset
If VPN connectivity fails, first identify which type is involved — a site-to-site issue usually points to the gateway configuration, while a remote access issue usually points to client authentication or the user’s local network.
Common mistake
Do not memorise the definition without connecting it to packet flow, device state and verification. Ask: what should happen, what actually happened, and which command or capture can prove the difference?
Quick recap
- Understand the job of the protocol or feature.
- Know where it sits in the traffic path.
- Verify behaviour instead of guessing.
- Connect the topic to the next networking layer.
Interview connection
Explain the concept in simple words first. Then give one practical example or troubleshooting check. That is stronger than repeating a textbook definition.
References & Further Reading
- AddySec original content — written for the Network Security track to build practical, interview-ready understanding.
Apni Bhasha mein samjho
Site-to-site VPN do offices ko permanently connect karta hai. Remote access VPN ek user ko temporarily company network se connect karta hai — jaise WFH.
Kaise padho?
Concept ko pehle flow ke saath samjho. Phir English note ke technical terms, commands aur tables dekho — technical terminology same rahegi.