Cannot update packages

[Bas]

Hi,

I'm having trouble connecting to the Ubuntu servers; when I try to
update my package lists about half of the downloads fail with:

Error reading from server - read (104 connection reset by peer)

If I retry it gives download errors for different files but sometimes I
can get all downloads to succeed (after many retries).

Downloading the packages themselves is even worse: about 95% will fail
with a connection reset or the occasional time-out. The strange thing is
that the connection only resets when the download is allmost done e.g. a
small file will fail immediately but downloading a 10.4 MB file will
fail at 10.3 MB.

So does anybody know what's going on and how to fix this?
Is it possible that my university's NAT has something to do with this?

Thanks,
Bastiaan