Secure Socket Tunneling Protocol (SSTP) is a virtual private network (VPN) protocol that confines traffic over HyperText Transfer Protocol Secure (HTTPS). This definition may sound very complicated, but in essence, SSTP enables VPN traffic to pass through most firewalls.
Firewalls and web proxies usually block VPN protocols, so employees in some industries can’t access corporate networks remotely. With the SSTP VPN protocol, traffic passes through an encrypted tunnel using the same security protocols and ports that establish HTTPS connections. As a result, connecting to a firewalled network becomes possible.
Other interesting terms…
Read More about the “Secure Socket Tunneling Protocol (SSTP)”
SSTP was developed by Microsoft and introduced when the company released Windows Vista. Windows versions after Vista continue to offer native support for SSTP.
Microsoft developed the VPN protocol specifically for businesses that don’t allow other types of VPN traffic. For example, hotels usually block Point-to-Point Tunneling Protocol (PPTP) and Layer Two Tunneling Protocol/Internet Protocol Security (L2TP/IPsec) traffic. These two VPN protocols are used by most service providers. Some Internet service providers (ISPs) also don’t allow specific ports used in PPTP, adding to the difficulty of establishing remote connections.
With these roadblocks associated with older VPN protocols, Microsoft developed a newer tunneling protocol that can bypass firewalls and allow employees to access corporate networks remotely.
How Does the Secure Socket Tunneling Protocol Work?
To better understand how SSTP works, we need to learn some key terms first, including the following:
- SSL/TLS protocol: SSL/TLS refers to Secure Sockets Layer (SSL) and its newer version Transport Layer Security. This protocol encrypts traffic.
- Transmission Control Protocol (TCP) connection: A TCP connection acts as a bridge between a traffic source and a destination. HTTPS connections use TCP port 443.
- SSL/TLS handshake: This is the authentication process where the source and destination agree on what secret key to use to communicate. An SSL/TLS handshake happens over a TCP connection.
When a VPN user connects to a VPN using SSTP, it first establishes a TCP connection to the SSTP server. The TCP port used is port 443, the same port used in HTTPS connections. After a successful SSL/TLS handshake, the VPN user’s device sends an HTTP request. The SSPT server sends back an HTTP response that okays the HTTPS connection. The diagram below may make things easier to grasp.
PPTP, L2TP, and SSTP: What Are Their Key Differences?
Aside from being a newer VPN protocol, SSPT differs from other VPN protocols in various ways. We present these significant differences in the table below.
| PPTP | L2TP | SSTP | |
| Platforms supported | macOS, iOS, Android, and Windows | macOS, iOS, Android, and Windows | Windows (native support) |
| Encryption | Basic | IPsec | SSL 3.0 |
| Port | TCP port 1723 | UDP port 500 | TCP port 443 |
| Firewall bypass | Easy to block | Easy to block | Difficult to block |
SSTP versus OpenVPN
SSTP is often compared to OpenVPN since both VPN protocols use SSL/TLS for encryption. Both protocols can also bypass most firewalls since their traffic is similar to HTTPS connections.
However, OpenVPN is open-source, which means that it is not owned by a company, unlike SSTP. OpenVPN configuration is highly customizable, and anyone can inspect its source code. SSTP, on the other hand, is most suitable for VPN users that are not very tech-savvy and want a straightforward setup process.
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SSTP is arguably one of the most secure VPN protocols. Still, some privacy advocates are hesitant to use it since it is owned and developed by a single company, and there’s no way to inspect the technology and its code. Windows users do not mind this, though, as they find SSTP VPN easy to set up. It also provides high-level security.
