VPNs & Proxies - Virtual Private Networks

Businesses have many reasons to maintain secure networks, which include:
- Protecting proprietary information.
- Ensuring that network services are accessible only to employees.
- Implementing technologies to restrict access to resources.
Common security technologies include:
- Firewalls: Control the incoming and outgoing network traffic.
- NAT (Network Address Translation): Masks internal IP addresses.
- Non-routable address space: Prevents external access to internal networks.

Definition: A technology that allows the extension of a private or local network to hosts not physically connected to it.
Primary Use: Enables employees to access business networks remotely when they're not in the office (e.g., working from home).
Functionality:
- Establishes a VPN tunnel: A secure connection that enables remote access to the organization's network.
- Provides a virtual interface on the employee's computer with an IP address matching the company's network.
- Allows data to be sent and received as if the employee's device was physically connected to the internal network.

VPN Tunneling Protocol:
- Works primarily at the transport layer to carry an encrypted payload containing the original data packets.
- The encrypted payload passes through the VPN's endpoint where it's decrypted and stripped of its non-essential layers, then repackaged and sent out with the appropriate data link layer information.
Bidirectional Process:
- The process above happens in reverse for incoming data from the VPN server back to the remote user.

Authentication Procedures:
- VPNs require strict protocols for authentication to prevent unauthorized access.
- Commonly incorporate two-factor authentication (2FA):
- Beyond a username and password, it involves a secondary verification step, usually a time-sensitive numerical token generated by hardware or software.

VPNs can also facilitate site-to-site connections:
- Similar in concept to remote employee connectivity but involves routers or specific VPN devices from separate networks establishing a tunnel between them.
- Enables collaboration as if the separate offices are on a single network.

General Technology, Not a Protocol: VPNs are versatile concepts with various implementations, differing in technical details but fundamentally serving to create encrypted tunnels for secure remote access.
Key Takeaway: VPNs enable remote computers or networks to behave as if they are part of a different network, enhancing security and accessibility for businesses.