Windows 2012 R2 unstable internet connection

I had 2x HP DL 380 G6 servers with Windows 2012 R2 whit the same problem. When I start a download (I try a lot of different sites) the download drops and fluctuate. When I connect my laptop or another server on the same cable the download is stable. So my conclusion was the onboard nic.

What I tried:

  • Update latest HP SSP (2014_2)
  • Update firmware NIC
  • Update driver NIC
  • Update Windows (patches)
  • change all the default nic settings like disable tcp offload for example
  • Try another switch

Bandwidth during download:

hp ethernet

I thought the problem must be the NIC so I added an intel pro to my server with the same result 🙁

Then I found the command netsh interface tcp show global

Output:

C:\Windows\system32>netsh interface tcp show global
Querying active state...

TCP Global Parameters
----------------------------------------------
Receive-Side Scaling State          : enabled
Chimney Offload State               : disabled
NetDMA State                        : disabled
Direct Cache Access (DCA)           : disabled
Receive Window Auto-Tuning Level    : enabled
Add-On Congestion Control Provider  : none
ECN Capability                      : enabled
RFC 1323 Timestamps                 : disabled
Initial RTO                         : 3000
Receive Segment Coalescing State    : enabled
Non Sack Rtt Resiliency             : disabled
Max SYN Retransmissions             : 2

I dived in to these settings and I found the “Receive Window Auto-Tuning Level on enabled”. So I disabled the setting with:

netsh int tcp set global autotuninglevel=disabled

After that setting the network connection to the internet was stable 🙂

fixed

I found an article on the net that Cisco PIX IOS 8.0 doesn’t support “TCP Window Scaling”. Source: http://www.cisco.com/c/en/us/support/docs/security/ios-firewall/71613-iosfw-tcp-scaling-ts.html

So I use the workaround to disable the Automatic Windows Scaling in Windows because I can’t update our old PIX.

Problem solved 😀

 

Author: Thomas Faddegon

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