1. Problem

The server was having problems installing MS updates and that led to the discovery of poor performance when trying to install the updates manually.

Running internet speed tests showed our download was just around 2MB and oddly 9MB upload. Any other workstation would be getting 50MB download and 9MB upload.

2. The cause

So, there is a feature within the Windows Server OS called “Explicit Congestion Notification (ECN)” This feature which sits in the IP Stack helps stop the loss of data packets. But it relies on the network equipment also running this “ECN”.

So if your hardware doesn’t support “ECN”  it slows down your outbound connections, because packets need to be re-transmitted. As re-transmission intervals increase, it may take up to 10 seconds before a connection is made.  So there is the reason, lucky it is optional to use “ECN” so off it must go!

3. Find out if ECN is Enabled 

You will need administrator access to do this.

1. Open command prompt with Administrator access
2. Now type this at the prompt: netsh int tcp show global
3. If you see an entry highlighted in Yellow as Enabled

5. How to Disable ECN

To turn this feature off. You will need administrator access to do this.

1. Open command prompt with Administrator access
2. Now type this at the prompt:

netsh interface tcp set global ecncapability=disabled

That’s all there is to it.