The AWS Linux instance in question has the following kernel settings applied in nf: _max = 16777216 I've read lots of guides on auto-tuning, but these are typically about disabling scaling altogether to work around bad terrible home networking kit.Ĭan anyone tell me what's happening here and give me a way of fixing it? (Preferably something I can stick in to the registry via GPO.) Notes

This can't be something in the intervening hops or our local switches/routers and seems to affect Windows 7 and 8 clients alike. Without any forcing, it scales as expected. The TCP handshakes use the same starting points in each case, but the forced one scalesĬonversely, from a Linux client on the same network a straight, iperf -c (using the system default 85kb) gives me: local 10.169.40.14 port 5001 connected with 1.2.3.4 port 33263 iperf -c -w1M Windows SYN - Windows 64kb, Scale 1 - Linux SYN, ACK: Window 14kb, Scale: 9Ĭlearly the link can sustain this high throughput, but I have to explicity set the window size to make any use of it, which most real world applications won't let me do.iperf -c Windows SYN - Window 64kb, Scale 1 - Linux SYN, ACK: Window 14kb, Scale: 9 (*512).The latter figure can vary significantly on subsequent tests, (Vagaries of AWS) but is usually between 70 and 130Mbit/s which is more than enough for our needs. I broke out iperf -s on a an AWS instance and then from a Windows client in the office: This bore out in testing and from multiple locations clients were seeing stable 2-5Mbit/s to the host from their Windows systems. The initial report was that uploads to a new server instance were much slower than they could be. We have 1Gbit/s synchronous bandwidth at the office and the servers are either AWS instances or physically hosted in US DCs. Scenario: We have a number of Windows clients regularly uploading large files (FTP/SVN/HTTP PUT/SCP) to Linux servers that are ~100-160ms away.

Windows afd service