That TCP Windowing fault

Here is the smoking gun, let me show you it (new window).

That's an entire TCP segment. Packet 339 there is the end of the TCP window as far as the NetWare side is concerned. Packet 340 is a delayed ACK, which is a normal TCP timeout. Then follows a somewhat confusing series of packets and the big delay in packet 345.

That pattern, the 200ms delay, and 5 packets later a delay measurable in full seconds, is common throughout the capture. They seem to happen on boundaries between TCP windows. Not all windows, but some windows. Looking through the captures, it seems to happen when the window has an odd number of packets in it. The Windows server is ACKing after every two packets, which is expected. It's when it has to throw a Delayed ACK into the mix, such as the odd packet at the end of a 27 packet window, is when we get our unstable state.

The same thing happened on a different server (NW65SP8) before I turned off "Receive Window Auto Tuning" on the Server 2008 server. After I turned that off, the SP8 server stopped doing that and started streaming at expectedly high data-rates. The rates still aren't as good as they were when doing the same backup to the Server 2003 server, but at least it's a lot closer. 28 hours for this one backup versus 21, instead of over 5 days before I made the change.

The packets you see are for an NW65 SP5 server after the update to the Windows server. Clearly there are some TCP/IP updates in the later NetWare service-packs that help it talk to Server 2008's TCP/IP stack.


I may look into this on why some of our Netware SP7 move like snails. Some of my media servers are Linux, some are Windows... would explain the seemingly random differences.

I want to quote your post in my blog. It can?And you et an account on Twitter?