Hi, I am running Windows Server 2016 / IIS 10, and really hoping someone can help me with an ongoing problem.
We are having sporadic but persistent problems downloading large files over HTTPS (not HTTP). Here is what I've learned so far:
1. The problem only happens when downloading files - there are no problems with browsing web pages.
2. While some downloads work perfectly, others go for a while - usually several MB (sometimes say 20-30MB or more) - but then just stop. I've captured the traffic to the browser, and the data just stops coming from the server with no HTTP error. The browser
eventually times out. After it stops, I can resume the download which usually works for another few seconds and then fails again.
3. This is sporadic and seemingly random: some large downloads work fine, but it's still happening frequently enough to be a problem. Sometimes I can download a large file OK, but then a re-download fails part way through, for no apparent reason.
4. There are no relevant events in the Event Log. ASP.NET throws a "remote host closed the connection" error, as it does if the user closed their browser. I've confirmed (through traffic capture) that the browsers certainly are not 'disconnecting'. But to the server, it looks as if the browser has disconnected.
5. The same behavior happens whether serving a static file via IIS or via ASP.NET (using Response.TransmitFile) so I am sure it isn't an ASP.NET issue.
6. A key thing: it only applies to HTTPS downloads. I've confirmed this by testing. I have tested downloading a file over HTTPS and it fails repeatedly. I then immediately download the same file using HTTP and it works perfectly. I immediately try again via
HTTPS and it fails again. I've even had an HTTP download running perfectly while simultaneously seeing HTTPS downloads fail. I've confirmed the SSL certificate is valid, and the HTTPS downloads often do work, so I doubt anything wrong with the cert. Plus,
I tried with a self-signed cert and got the same result.
7. Large downloads over FTP and RDP work fine (like HTTP) - it's only HTTPS downloads that fail sporadically.
8. I doubt it is a network card error, because everything works perfectly over HTTP (and other protocols) at same time as an HTTPS download is failing repeatedly.
9. Have tried with firewall disabled, and get the same result.
I'm really out of ideas for this, so any suggestions will be gratefully received.
Thank you!
