Hi I don´t know if this the right forum, but I´m facing an interesting problem with UDP datagrams and Windows 2008 TCP/IP stack Well, we have a scenario where a machine can´t receive over 30 mbits of UDP data on a local gigabit ethernet, and to make it worse, the whole windows TCP/IP stack becomes unstable, and I mean that because if we use ping 127.0.0.1 –t we see strange delays as 30ms, even 800ms! After a lot of researching on the problem, we found that some video equipments that we are receiving video from (RTP over UDP), sends each packet of video from a different source port! The source port is always incremented for each packet the equipment sends, and there are about 50 equipments sending about 170 packets per second, giving a total of 2mbits of data per second per equipment (About 100mbits total). I made a little program to test such behaviour, I opened a server on a machine, listening on 50 UDP ports and a client on 4 different machines sending datagrams to this server. if I send the UDP packets all from the same source port (Same “connection/bind”) I can receive over 200mbits of data easily, but if I change the client to send 1 packet per source port then, the server will not be able to receive more than 30mbits and ping 127.0.0.1 –t from the server will start delaying to 5~10ms. I believe that this is something related to windows 7/2008 IP stack implementation, does anybody have an idea on why does this happens? Maybe the overhead of managing packets from different source ports is too high! Thanks

Hi, Thanks for posting here. I suspect that this situation may relate with TCP Chimney Offload feature on Windows server 2008 host, could you verify if it is working with following the introduction in the article below and test with disable it to see how is going : Information about the TCP Chimney Offload, Receive Side Scaling, and Network Direct Memory Access features in Windows Server 2008 http://support.microsoft.com/kb/951037 Thanks. Tiger LiPlease remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Dear Tiger Li, In this particular system we have a broadcom gigabit ethernet card that supports offload, we tried turning it on and off but nothing, we got the same results We found that Windows XP doesn´t suffer from this behaviour, but I know many things have changed in the TCP/IP stack, so, I believe that it is related to something new that was implemented after Windows XP Do you have any other idea?