What is Site-to-Site VPN? Complete Guide

All companies nowadays have operations from various locations, branch offices in different cities, remote data centers, or partner networks that need to be interconnected in a secure manner. For uninterrupted and safe communication among these geographically disparate sites, companies establish a site-to-site VPN.

Site-to-site VPN links two or more networks to each other by the establishment of an encrypted “tunnel” through which they are able to send data to each other as if they were part of a shared local network. Unlike a regular remote-access VPN, which connects individual users, a site-to-site VPN links networks and hence is best suited to business institutions that have branches or widespread affiliations.

In this guide, you’ll learn how site-to-site VPNs work, their key benefits, setup steps, best practices, and why they remain one of the most secure and cost-effective ways to connect distributed networks.

What is Site-to-Site VPN

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A site-to-site VPN securely links two or more separate networks over the Internet. It acts like a private, encrypted highway between offices, allowing devices at each location to share information as if they were on the same local network.

While a remote-access VPN connects an individual user to a network, site-to-site connects both the relevant LANs (Local Area Networks) at each location.

Example:

If the head office is in New York, the branch office is in London, Site-to-Site VPN securely connects both office LANs – so employees have the same access to send/receive files and internal applications, and work together in harmony.

Types of Site-to-Site VPNs

Site-to-site VPNs mainly fall into two categories, depending on who you’re connecting with:

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1. Intranet-based site-to-site VPNs

• Site-to-site VPN services connect several offices, branches, or data centers of one organization to create one single private network.
• All locations that are attached to the VPN can exchange their internal resources privately as if they were located in the same Local Area Network (LAN).

Example:

The business has headquarters in New York and offices for a region in London and Tokyo. A VPN with intranet use securely connects all these offices such that any employee, irrespective of where they are, can easily access common servers, programs, and documents.

Best for:

• Large enterprises with multiple offices across various locations globally.
• Companies often have employees needing to access resources from one central location.

Extranet-based Site-to-Site VPN

• A VPN links a firm’s network to that of a vendor, partner, or customer.
• Not an intranet VPN, however, such a link provides restricted access either direction where internal private resources are not revealed.

Example:

A manufacturer can link its network with that of its supply firm, for instance, to provide current inventory levels. The manufacturer would provide some data, i.e., status of orders, but factory production quantities would be under key.

Best For:

• Characteristics of a business relationship or contract with limited access.
• Firms seeking to offer assurance of the transfer of chosen resources with outside stakeholders.

Read Also: Proxy vs VPN: A Detailed Comparison

How Does a Site-to-Site VPN Work?

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A site-to-site VPN works by establishing a safe, encrypted tunnel between two or more networks over the internet. Here is how it works step by step:

• Two Networks Are Merged: Every site has a local network (LAN) of its own. A site-to-site VPN merges these LANs in a manner that they become a giant private network.

• VPN Gateways Encrypt and Decrypt Traffic: Every site contains a VPN gateway (typically a router or firewall) that encrypts all outgoing traffic and decrypts incoming traffic.

• Encrypted Tunnel Through Internet: Rather than sending information in the open over the internet, the VPN creates an encrypted tunnel through which all data becomes encrypted and cannot be accessed by intruders.

• Automatic Communication: The VPN provides automatic connection of the sites after they have been set up, without users Log in.

• Secure Remote Access: Office workers can view a server or file in a remote office as if local, but securely.

In simple words, a site-to-site VPN is a virtual bridge between networks across which secure and continuous communication takes place.

Advantages of Site-to-Site VPNs

• Cost-efficient: Prevents the use of costly leased lines between offices.

• Secure transmission: Protects data while in transit across the public internet.

• Easy scaling: Easy addition of new offices or partner networks.

• Increased productivity: Stability of work performed by teams in remote locations.

• Simple middle level network administration: Simpler observation and administration of all the sites connected together.

Limitations of site-to-site VPN

Tough Setup & Administration

• Requires technical knowledge to set up and administer, particularly in large companies. 
• Misconfigurations can cause security compromises.

Hardware failure & Infrastructure Dependency

• Require compatible VPN hardware or firewalls at both ends with additional expense.
• Hardware breakdown will bring down the entire connection.

Less Flexible

• Best for fixed location sites and not for individual distant users.
• Scaling or relocating network locations might be problematic.

Bandwidth & Performance Problems

• Network performance is minimized with VPN encryption.
• Heavy traffic might demand more sophisticated equipment.

Security Dangers if Not Upgraded

• Insecurely obtained or hacked VPN software or settings can be hacked into by intruders.

Common Use of a site-to-site VPN

• Connecting Remote Office Locations to Head Office: Secures various office locations in order to link and exchange internal resources such as files, databases, and email servers.

• Business Mergers or Partnerships: Unites two separate organizations to exchange information securely and communicate without opening networks to the external public.

• Access to Centralized Resources: The remote office users have access to company applications, intranet, or storage centers remotely as if they were in the headquarters.

• Secure Data Transfer Across Data Centers: Allows encrypted data transfer between heterogeneous data centers or cloud environments.

• Cost-Effective Interoffice Interconnection Solution: Offers a cost-effective solution for interconnecting offices versus dedicated private circuits.

Best Practices for using a Site-to-Site VPN: Securely & Efficiently

• Utilize Strong Encryption Algorithms: Always leverage VPN tunnels with strong encryption such as AES-256, and secure protocols such as IPsec.

• Keep VPN Devices Up-to-Date: Update firewall, router, or VPN gateway firmware to close security vulnerabilities.

• Use Strong Authentication: Use certificates or multi-factor authentication instead of simple pre-shared keys.

• Segregate Network Traffic: Limit which internal networks are accessible via the VPN to minimize exposure if breached.

• Facilitate Logging and Monitoring: Continuous monitoring of VPN traffic for suspicious behavior and keeping in-depth logs for audit purposes.

• Test VPN Connections Regularly: Validate tunnel stability, latency, and performance on a regular interval to prevent catastrophic downtime.

• Backup Configurations: Backup VPN gateway configuration securely to enable easy recovery in case of failure.

Recommended Read: How to Turn Off VPN on Android? Step by Step

Final Thoughts

A site to site VPN is one of the most secure and most reliable available technologies to link multiple office networks, data centers, or partner systems. It establishes encrypted tunnels that encrypt the communications between locations as if these locations were local.

Although it needs to be properly configured, hardware that is compatible with it, and timely updates, its benefits of secure data transmission, cost-savings, and enhanced collaboration make it an ideal choice for today’s organizations. By following best practices such as secure encryption, frequent updates, and network segmentation, organizations can manage their site-to-site VPN efficiently without exposure to cyber attacks.

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