Bug#482279: Same thing happens with python-pycurl

[Simon Josefsson]

I just realized I wasn't clear what the likely cause of your problem is.
The problem may be caused by the server you are talking to.  Can you
access the servers that your clients use from your location?  Then
running 'gnutls-cli -d 4711' against that host may give enough details
to resolve it.

Earlier bug reports of this kind suggests that the server is buggy
(which can be worked around), but it may also be that the Cisco box is
filtering out the traffic if you are only seeing the problem behind
those boxes.

/Simon