I know this probably sounds like a silly question, and it sort of is. But just bear with me for a moment.
My girlfriend recently purchased an apartment in Downtown Budapest, and it came with a cable internet connection from Digikabel.hu.
When she's trying to connect to her gmail, hotmail, and most other sites that require that you POST data to the server, the internet connection slows to a crawl. When trying to login to her GMail account, she simply gets a timeout. Hotmail works after a while (+- 5 minutes to login).
She has reported that some other sites are extremely slow loading also. Google.hu works perfectly (very fast), the same counts for google.no. When she's accessing google.com or facebook.com, the wait is also up to five minutes. GTalk and MSN Messenger works halfway – she can receive messages but no-one else receives the messages she sends out. Skype works, though..
She's tried with three different computers (2*MacBook Pro, 1 MacBook), in both Windows 7 and OS X Leopard, so it's not a software problem from her side. I've talked to the ISP several times, and they claim it can't have anything to do with the modem, and stick with the story that the problem isn't theirs. I've also asked the customer service reps. to try the websites in question from their computers, and they are successful.
I'm absolutely certain that the problem is theirs, as she has no problem surfing at coffee shops or anywhere else.
And yes, I've tried clearing the browser cache, DNS cache and changing the DNS servers to OpenDNS.
Any ideas on what might cause this experience?