Large file upload/download using IIS - Paul Baker [MVP, Windows - SDK]

I have a Windows client application that needs to be able to transparently
upload and download large files to and from our server.

What are the limitations on file sizes when using IIS HTTP and can they be
worked around? I think the problem may only be with requests, not responses.
For requests, I believe I read the limit is configurable up to 1GB on IIS6
and 2GB on IIS7, but what is the underlying cause of this limit? Does it
read the entire request into memory before proceeding and, if so, is it IIS
that is doing it or the ISAPI handler (like ASP) that is doing that? It
seems like you should be able to read the request as it becomes available
and dump it to a file with minimal resource usage.

Some background information:

Currently, we use the FTP protocol with a Serv-U server. We always use the
PASV command (passive FTP), but despitre that we have a significant and
ever-growing number of repeat customers who experience routine connectivity
problems, most of which can probably be explained by firewalls or other
security intervention.

We have not been able to successfully troubleshoot the cause and resolve it,
probably by adding a firewall exception, in any of these cases except a
couple where the customer finally realised it on their own. This is due to a
lack of expert support technicians who are capable of dealing with it.

I am considering, as one possible solution, using the HTTP or HTTPS
protocol, which should be more firewall friendly. However, these files are
large. They are often hundreds of MB and I would like to be able to support
multiple GB, as the revenue for processing the file is approximately
proportional to the size of the file and I don't want to do something that
would exclude those large customers.

Thanks,

Paul