IIS 7 and Above
Known Issues and Workarounds
More than 2 paralel file download using https in Windows Server 2016...
Last post Nov 23, 2017 10:36 PM by kohepu
Nov 17, 2017 01:43 PM|Antxon|LINK
Hi to all,
I have found problems downloading files from IIS and Windows Server 2016 using HTTPS.
I found the problem trying to install a file sharing web application in a Windows 20016 Servers for our employees. At the beginning, I though the problem was related to the web application but after several tests It seems to be a Windows Server 2016 problem.
Doing some tests with the web application I've found that if I try to download more than a file at a time, the second file download is very slow. If I try a third download the third download doesn't' start until one of the others is finished. Even more,
If I try to navigate in the web application while 2 files are being downloaded the web server didn't respond.
To try to find which is the root cause I've installed a new windows 2016 server in a test enviroment:
- Window Server 2016, virtual machine. Fresh Windows installation and IIS installed with default settings.
- Add https support with a self signed certificate to IIS default web site.
- In the default Web site root folder copy 3 files. This files are mp4 videos compressed in zip archives.
- Test client computer used to download files is a Windows 10 dell computer. The test client computer and the server are connected to a Gigabit ethernet LAN network.
- To simulate a slower network environment, I forced the network adapter in the test client computer to 10Mbps full. This is done trough the network adapter setting option in control panel.
To do the test I try to download 3 zip files from the server to the test client computer using HTTPS. The first file download starts OK. the second file donwload starts fine too, but the download in this case is much slower. When I try to download the third
file, the download doesn't start. It starts only after finshing or stoppping one of the other downloads. Even worst, If I try to browse the server using HTTPS while two files are being downloaded I get a server not responding error.
While files are being downloaded I run a netstat and I see only one HTTPS TCP connection between the client and the server.
I have done the same test using HTTP instead of HTTPS. With HTTP I dont' have any problem. I can download 3 files simultaneously and browse the web server at a time without problems. Using netsat I see that in this case, there is a HTTP TCP connection per each
file beeing downloaded.
I have done the same test with different web browsers, firefox, Chrome, Internet Explorer, having the same result with all of them.
The problem is in some way related to the network bandwidth available between the server and the client. Because if I change the client computer network adapter link settings to auto-negotiation. I can download 3 files at a time using HTTPS without any problem.
To check if the problem is related just to Windows Server 2016 y have set up another server with Windows server 2012 R2. With exactly the same settings as the Windows 2016 Server. In this case otherwise, all the test go fine. I can download 3 or 4 files in
parallel using HTTPS without problems.
I have tested to with Windows 2008 Servers and I didn't have any problems either.
So it seems something like a bug in Windows 2016. I have tried to found somebody in the internet having similar problems but found nothing, so I'm a bit lost. This behaviour is weird for me.
¿Any idea about this?
Nov 17, 2017 07:02 PM|lextm|LINK
Very likely you hit a TCP/IP related change in Windows Server 2016 default settings, which is not quite clear yet.
Never an easy task to locate the culprit in such cases, unless you capture enough network packets (starting from the downloads so as to capture TLS handshakes) and are capable of analyze them yourself.
If possible, open a support case via http://support.microsoft.com and let Microsoft support team take a look of the setup.
Nov 23, 2017 10:36 PM|kohepu|LINK
This sounds very similar to the issues reported at:
https://forums.iis.net/t/1235830.aspx?minBytesPerSecond+webLimit+setting+not+taking+effect [see later replies]
Hopefully someone from MS IIS team can look at this.