Windows Vista and terminal service
July 11, 2007 – 6:54 pmI actually stumbled across this a few days ago at work. While trying to remote desktop into our terminal server, I kept experiencing some odd slowdowns as if the connection was intermittently working. The odd thing, is I had no issues while typing in my password or typing in a window when I turned up the command prompt. After doing a bit of searching I came across some sites that explained what was going on.
With Windows Vista a new technology referred to as autotuning was introduced. This feature enables the system to adjust the size of tcp packets beyond 64kb. To do this, a SYN packet to negotiate a larger packet size is sent to the client. This is all fine and dandy except that some routers think this is something else and strip the acknowledgment packet so the server starts running with the new packet size, and the client sits dumbfounded.
To make a long story short, I disabled autotuning with the following command:
netsh interface tcp set global autotuning=disabled
After which, I was able to remote desktop to my hearts content. The reason this only occured with our 2003 server was that our 2000 servers don’t support autotuning. Go figure.
2 Responses to “Windows Vista and terminal service”
Why in the whole wide world of muffins would the auto-tuning in Vista start using larger packets without an ACK. Don’t get me wrong, optimizing TCP throughput is an awesome idea, and, in Microsoft’s defense (whoa, that sounds weird), there *is* an established RFC for it, but you have to have the error checking around it. I mean, it’s software. It doesn’t take every manufacturer having to change a standard. Unless, I guess, a false ACK comes back from the unsupported router. I guess I’ll have to read more about it. Damn you. But, hell, odds are even then the false ACK could be predictably detected.
ehrm, yeah.
[/nerd]
..damn your technie corner too.
By Brandon on Jul 13, 2007
Hm, okay, so I read a bit about it. It seems like it could be an actual software problem: Windows or its RDP client not receiving the larger packets fast enough, or it could be any router’s problem: implementing QoS because of the large bursts of data.
I didn’t see anything about routers stripping ACKs, but I didn’t read too much. Is it just a certain brand?
But if it’s the software problem, they’ll probably fix it in an upcoming patch, and if that’s the case, I’d suggest re-enabling the autotuning. If it works right, it supposed to be much much better.
By Brandon on Jul 13, 2007