Slow LAN connection (especially receiving) on Windows 8

Question

I was diagnosing my SMB performance issues when I noticed my whole network speed was off. These are my benchmarking results between my desktop and my Linux server:

Both are connected using CAT6 and have gigabit networking.

~$ iperf -c 192.168.2.10 -r
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------
------------------------------------------------------------
Client connecting to 192.168.2.10, TCP port 5001
TCP window size:  110 KByte (default)
------------------------------------------------------------
[  5] local 192.168.2.2 port 54320 connected with 192.168.2.10 port 5001
[ ID] Interval       Transfer     Bandwidth
[  5]  0.0-10.0 sec   114 MBytes  95.2 Mbits/sec
[  4] local 192.168.2.2 port 5001 connected with 192.168.2.10 port 49719
[  4]  0.0-10.0 sec   532 MBytes   446 Mbits/sec

So, that's 446 Mb/s from my desktop to my server, and no more than 95 Mb/s from my server to my desktop, where both values should be (close to) 1000 Mb/s.

I recall getting >900 Mb/s in both directions when I was still running Windows 7.

I already tried all sorts of things, like turning off different offloading features in the NIC driver, manually downloading the latest NIC driver from Realtek and disabling autotuning using netsh interface tcp set global autotuning=disabled.

EDIT:

I did some extensive testing with iperf between the switches and such in the way between my Linux server (LARS-ILLIUM) and my desktop (LARS-VIGIL). LARS-FEROS and LARS-RANNOCH are both switches, and the connection is as follows:

LARS-ILLIUM <---> LARS-FEROS <---> LARS-RANNOCH <---> LARS-VIGIL

Of course there are other devices connected to the switches, but this is the path between LARS-ILLIUM and LARS-VIGIL.

I made table of iperf results: http://prntscr.com/39r0eh I guess the table is fairly self-explainatory, but the first three rows are test results from left to right, and the bottom three rows are the other way around. All tests were UDP btw. Complete command: iperf -c 192.168.2.x -u -b 1000M

Now I know that the problem isn't limited to my desktop LARS-VIGIL, but happens in the rest of my LAN as well. Still haven't a single clue what's happening though...

Answer 1

I figured it out. The reason for the weird iperf results, was that every system I tested on has different default TCP window and UDP buffer sizes. After setting those manually with the -w option I get consistent results:

C:\Users\Lars Veldscholte\Downloads\iperf>iperf -c 192.168.2.2 -w 416k -r
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  416 KByte
------------------------------------------------------------
------------------------------------------------------------
Client connecting to 192.168.2.2, TCP port 5001
TCP window size:  416 KByte
------------------------------------------------------------
[  4] local 192.168.2.10 port 55803 connected with 192.168.2.2 port 5001
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  1003 MBytes   841 Mbits/sec
[  4] local 192.168.2.10 port 5001 connected with 192.168.2.2 port 45938
[  4]  0.0-10.0 sec   863 MBytes   724 Mbits/sec

At least, between my server (LARS-ILLIUM) and my desktop (LARS-VIGIL). Testing on the switches in between still yields weird results:

C:\Users\Lars Veldscholte\Downloads\iperf>iperf -c 192.168.2.1 -w 320k -r
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  320 KByte
------------------------------------------------------------
------------------------------------------------------------
Client connecting to 192.168.2.1, TCP port 5001
TCP window size:  320 KByte
------------------------------------------------------------
[  4] local 192.168.2.10 port 55833 connected with 192.168.2.1 port 5001
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.3 sec  9.12 MBytes  7.43 Mbits/sec
[  4] local 192.168.2.10 port 5001 connected with 192.168.2.1 port 55335
[  4]  0.0-10.4 sec  5.00 MBytes  4.01 Mbits/sec

I don't know what's up with that.