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:
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 🙂
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 😀