Connection timeout to single IP I have a strange problem and I am not sure how to debug this.

My Android phone (OnePlus One, Android 5.1) is connected to my WiFi (FritzBox 7490) at home. Everything works fine except connections to my own server which is used for ownCloud, e-mails, and other services. Every connection attempt results in a timeout, regardless of the service used (HTTP, HTTPS, IMAPS).

The first attempt to find the cause for this was to try other devices in the same WiFi network. And yes, every one of them is able to establish the connections. However, if I try to connect with my OnePlus One using another WiFi or mobile data, connections are also possible.

So now I am in a bad position. The manufacturer of my WiFi router says "Other devices are working, it must be the fault of your phone.". And I already hear CM developers say "Other WiFi APs or mobile data works, it has to be your WiFi router".

My last attempt was to reset both the phone and the router to factory settings, without any luck.

Does anyone has a clue about how to debug this kind of problem?
Okay, I found it. According to this serverfault question, TCP timestamps cause the error. I disabled the option on the server with

sysctl -w net.ipv4.tcp_timestamps=0