Can not reach some web sites

[A.J. Bonnema]

Hallo,

I have been experiencing a problem with reaching some websites. Example: 
I can not reach http://en.wikipedia.org.
In my network I have 2 workstations, one gaming (windows) and one work 
(fedora). When accessing the same sites from the gaming machine all is 
reachable. When using Fedora I cannot reach en.wikipedia.org. In all 
cases I get a time out from my browsers.

What I have done to find the problem:

1. I have checked my Firefox addons by disabling them. That did not help.
2. I checked other browsers (epiphany and elinks). Neither can reach the 
site.
3. I stopped the firewall and disabled it.  Same result.
4. I checked that I do not have any anti-virus program running.
5. I checked google to find causes and remedies, but nothing outside 
what I already did.

I am running Fedora 20 on an X86-64

Does anyone have a idea what steps to follow in order to isolate the 
problem? Maybe someone has a useful link?
I have exhausted all that I know and subscribed to this mailinglist to 
hopefully find some advice from people more experienced than me.

Kind regards, Guus.