Tuning TCP parameters to maximise throughput - Windows 2003 and 2008

Got 3 servers, A (Win 2008), B (Win 2003), and C (Win 2003) with network timeout issues between them.

Been testing with iperf and using various tcp window sizes.

A to B - works fine -high speed.
A to C - worksfine - high speed.
B to C - very slow. Increase in TCP windows size in iperf makes difference (But still not as fast as previous 2).

B to A - very very slow. Increase in TCP window size in iperf makes big difference.
C to A - same.
C to B - same.

I can sort of understand why B to C is slow (both are Windows 2003). These have not had TCP parameters tuned at all which I understand is possible on Windows 2003. My plan was to try increasing the TCP window size on these servers.

But B to A is from 2003 to destination of Windows 2008. I thought TCP was all sorted in 2008 and there was nothing to tune?

Ah. Would this by why? 2003 to 2008......


Ah. Would this by why? 2003 to 2008......


Is it too much to ask to just ditch Windows 2003? It's been around a long time and the end of support is very near. Not exactly a solution, but it's getting time to say goodbye. Networking in the later versions of Windows is greatly improved. I can actually push 1 GBs with the newer versions of Windows.

Is this over a WAN ,or LAN?

hi paul,
we need some more details ...

first - same network segment or routed
second - the question from pgm554: WAN or LAN connections
what do you mean with "works fine -high speed" and "very very slow"

i would suggest to not use iperf at the first steps.
copy a big file from one server to the other and look to the taskmanagers network-load. copy the file from the other server back to your server and look to the taskmanagers throughput.
post the results please.
if the difference from one direction to the other is really big (>50%) you have other problems than windows size. If one direction is OK, i think WS is not your problem. Changing WS is an option to optimize the throughput at WAN links but not the local LAN. Good description and calculation at http://bradhedlund.com/2008/12/19/how-to-calculate-tcp-throughput-for-long-distance-links/

We can search and find these errors if you provide us with many details as possible.

Here's my goto on tuning older versions of Windows:

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