SSTP
Microsoft's SSL tunnel, native to Windows.
How widely is it used?
Still around, but being replacedWindows-only and fading, but still handy where only HTTPS is allowed out.
How it works
PPP frames are carried inside an HTTPS session on TCP 443, which is why SSTP survives networks that block every UDP VPN port.
Connects
Windows device → VPN gateway
Protocols
SSTP, TLS, PPP
Typical users
Windows-centric organisations
Main use case
Remote access from networks that only allow HTTPS.
Advantages
- Built into Windows
- Passes almost any firewall
Limitations
- Effectively Windows-only
- TCP-in-TCP performance penalty