Why I cannot connect over https from inside a docker container when using vpn?

Question

i need to use a VPN to connect to some ressources my container needs. Therefore I use the integrated openconnect client in my Ubuntu network manager. When I am connected to the VPN, from inside the Docker container I

• can access normal http sites
• can access http sites only availble in my VPN
• cannot access any https sites in VPN or internet (I even don't get timeout)

From inside my host terminal I can access any site http and https. I tested this with curl because my VPN blocks Ping outside my local network.

When I disconnect from VPN, from inside my docker container I

• can access normal http sites
• cannot access any sites only available in my VPN (obviously)
• can access normal https sites

So I could narrow my problem down being dependent on my VPN connection, but also only occuring inside Docker container.

Why is this happening and how can I reach HTTPS sites in my VPN from inside the Docker container?

Answer 1

I had the same issue on Ubuntu 17.10, and resolved it by using the openconnect commandline utility with DTLS disabled instead of Ubuntu's NetworkManager to connect to my VPN.

openconnect VPNURL --user=USER --interface=tun0 --no-dtls