Randomized Ports

That behavior does not make much sense. When your source port setting is set to change, we will potentially change the source port - but when the connection is finished, it should be properly torn down between LTM and the CAS server.... Like Hoolio said, would be helpful to know versions of F5 gear and Windows systems in use - but sounds like a collision with TIME_WAIT state on the servers... This SOL has more info on best settings to accommodate for it - unfortunately, no matter what we do with our proxy settings, we can't control how long the server will keep the closed TCP connection in the TIME_WAIT state, and if you have a lot of traffic and port reuse, you could have collisions - so in SNAT situations, it's best to set it to Change for both Virtual and SNAT - is that what your current settings are?