Which TCP port must be open for remote access VPN using SSTP?

SSTP, or Secure Socket Tunneling Protocol, is designed to provide a secure, encrypted connection for VPN users over the internet. It specifically utilizes the HTTPS protocol, which operates over TCP port 443. This makes SSTP especially advantageous because port 443 is commonly open on firewalls and network devices since it is used for standard secure web traffic.

When establishing a remote access VPN through SSTP, ensuring that TCP port 443 is open is crucial for successful communication between the client and the server. This allows the establishment of a secure tunnel over an existing HTTPS connection, effectively bypassing many common firewall restrictions that might block other VPN protocols requiring different ports.

The other options represent ports that are used by different VPN protocols or services. For example, port 500 is primarily used for IKE (Internet Key Exchange) in IPsec VPN, port 1723 is used for PPTP (Point-to-Point Tunneling Protocol), and port 1812 is typically associated with RADIUS authentication services, not with SSTP.