Hi all, I have been doing some monitoring on my lan as there are various complaints of slowness, my software is telling me there is a number of slow tcp responses from servers, and also excessive udp restransmissions, Does udp retransmit? I thought that was only tcp.
UDP itself doesn't retransmit, but the application using it can. E.g. tftp.
One of the biggest peformance killers is a high packet drop rate. The two most common causes I've seen have been either a duplex error along the path, or a highly congested interface. (Busy shared Ethenet can be a problem too, but I'm assuming you're running in a switched environment.)
Since you did mention UDP, something you have to sometimes watch for, someone brings in a "special" high speed transfer application "much faster and better than TCP", which uses it own custom protocol. There are reasons why TCP works as it does, some of which concern sharing bandwidth. Some of these "special" applications can really impact everyone else on a shared path.
A zero sized received window would block a TCP sender from tranmission to that receiver. However, what Robert might have in mind is the TCP "silly window syndrome", see this wiki, http://en.wikipedia.org/wiki/Silly_window_syndrome, for a brief description.
Window 0 indicates the receiver does not have any memory buffer to queue packet prior to send off to application. When this occurs, it is basically telling all senders to stop transmitting until window size increases.
Typically you would expect to see a window size of 64K for server and 32K - 64K for client machines.
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