What is Site-to-Site VPN?

Site-to-Site Virtual Private Networks (VPNs) allow network infrastructures to securely connect the Local Area Network (LAN) of multiple business locations via public internet. Often referred to as a ‘tunnel’, VPNs allow for an encrypted connection between networks so that they appear to be a single entity. This allows sharing of common resources, applications and data, as if the separated networks were one singular larger private network.

VPN connectivity encrypts transmitted data, providing a secure link between each network join. This allows geographically separated networks to seamlessly communicate and share resources. Site-to-Site VPNs can be considered a cost-effective way to provide private Wide Area Network (WAN) links.

As dedicated communication lines are expensive, VPNs utilise affordable public internet. This significantly reduces the cost to organisations whilst the aforementioned encryption implemented by the VPN means that traffic is still secured over the public internet. This means that the resources are only accessible over the VPN and simplifies security as all devices are considered to be on the same network, meaning only one set of security policies are required. By using public internet, this enables site-to-site VPNs to be scalable, as adding new sites simply requires adding a single endpoint to the VPN network, further reducing the complexity of the overall network architecture.

Key Components

Site-to-Site VPN use several components to allow for shared access between sites:

To ensure security, site-to-site VPNs use encryption protocols (such as AES-256) in order to protect traffic from unauthorised access. Multi-factor authentication (MFA) can be implemented in order to verify identity based on confirmation of several identifiers, further preventing unauthorised access. In the event of a breach, site-to-site VPNs can also provide segmentation to prevent any lateral movement between systems within the network, thus reducing the attack plane.

Site-to-Site VPN solutions can improve ease of use by providing user-friendly systems. These implementations can come in the form of a web-based interface (or similar) and provide network administrators an easy method of managing the VPN over different sites.

Site-to-Site VPNs can also be hosted in the cloud. By utilising the cloud, this offers network administrators remote access from any location. Due to residing in the cloud, this enables seamless VPN connections between different devices.

Another component is that Site-to-Site VPNs are enabling the ability to automate the creation and deployment of new sites, which minimises human error and the need for individual appliances, as through cloud, these new sites can all be managed through a single dashboard. This makes Site-to-Site VPNs able to dynamically scale without re-design, improving the entire network scalability.

For failover, redundant gateways can be created with Site-to-Site VPNs. The distribution of traffic across multiple ISPs provides the network with better resilience and creates more stable connectivity.

Site-to-Site VPN and SD-WAN

When comparing Site-to-Site VPN with Software Defined Wide Area Network (SD-WAN) solutions, SD-WAN provides the benefit of being able to leverage multiple network transport links such as broadband, LTE and MPLS to provide optimal bandwidth utilisation and therefore improve the performance of applications. This improves on Site-to-Site VPN solutions as these only use a single transport link, tunnelling over broadband internet connections.

For some Site-to-Site VPN solutions, a separated management system is required for multiple VPN tunnels running across different sites, creating complexity and increasing workload for network administrators. Unlike Site-to-Site VPN, SD-WAN provides a single controller interface which remotely manages all of the network via infrastructure-wide policies. This therefore reduces the workload on network administrators by minimising complexity, improving on Site-to-Site VPN offerings.

Site-to-Site VPN can be integrated alongside SD-WAN. By integrating the two technologies together, the application-aware routing that SD-WAN provides can be utilised to steer application data over the most secure and reliable connection, therefore steering over site-to-site VPN when this offers the most secure and reliable link, benefitting overall performance.

By integrating Site-to-Site VPN into SD-WAN, this ensures that there is no compromise on security, as SD-WAN can use internet broadband over VPN as a communication link, gaining the privatised network security benefit that Site-to-Site VPN has to offer.

Furthermore, should a network be using multiple Site-to-Site VPN links (via different ISPs), SD-WAN can increase the reliability of the network by switching traffic over these VPN connections when a single VPN link is down or to optimise overall performance of the network.

The Limitations of Traditional VPNs and the Rise of SASE

As more and more businesses shift to cloud, leveraging models such as Software-as-a-Service (SaaS), the limitations of traditional VPNs have been emphasised. The emergence of the SASE framework as a cloud-native networking solution offers increased scalability, security and management over traditional VPNs.

Traditional VPN solutions are not designed to scale to cater for massive scales of remote users or devices, increasing the complexity to manage these systems. SASE improves on this by being designed with a large, distributed workforce in mind, there improving the scalability of the network.

With traditional VPN, there are no inherent additional security components besides encryption, MFA and segmentation. This limits the security of the network without adding further appliances. SASE is designed with Cloud Access Security Broker (CASB), Secure Web Gateway (SWG), Zero Trust Network Access (ZTNA) and Firewall-as-a-Service (FWaaS) in order to provide more layers of security to a network.

When connecting to a cloud service via traditional VPN, data would be required to be backhauled via a central data centre before accessing the cloud. SASE eliminates this as the framework uses Points of Presence (PoPs) to provide direct access to the cloud, closer to users and devices. This reduces latency and improves overall network performance.

Cloud Implementations

Cloud implementations of Site-to-Site VPN solutions differ between cloud providers.

For Amazon Web Services (AWS), initially a Virtual Private Cloud (VPC) must be configured. To allow connections, a Virtual Private Gateway (VGW) must be attached to the VPC. Then a device or piece of software must be deployed on-premises to act as the customer gateway, enabling a connection between the VGW and customer gateway. This connection is the VPN tunnel, either through two IPsec tunnels, or static/dynamic BGP routing.

For Microsoft Azure cloud, a Virtual network gateway must be deployed within the gateway subnet of Azure net. Using an on-premises local network gateway enables connections by defining connection type (such as IPsec) and entering the shared key.

Despite differences in implementations, leveraging cloud implementations for Site-to-Site VPN solutions can have multiple benefits. As cloud implementations allow Site-to-Site VPNs to be deployed quickly, this enables rapid scaling of the network infrastructure. Cloud providers offer many endpoints, with tunnels across large geographical regions, creating high availability to the network. The integration with other cloud networking services, such as transit gateways, accelerators and traffic mirroring improve network performance and reliability. Cloud implementations of Site-to-Site VPN solutions offer monitoring and logging of traffic telemetry throughout the entirety of communicates and, cloud providers manage all underlying infrastructure and endpoints, ensuring less complexity and cost to businesses to maintain these links.

Vendor-Specific Solutions

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