Solaris

Before you even try to use ndd to modify system parameter, I think you should use netstat -i 3 while you ftp a file of at least 200MB.

Look at the error column. If there is collision and dropped pkts, go talk to the networkers and work with them.

In a confrontation, both sides lose. Work together as a team

no harm to try find out, but if it is a network problem I think it will also tell the same story on the wintel boxes which could be using the same network.

And if I was the comms guy that's what I will generally say in defence if a unix guy approached me and told me he suspected it's a network problem, I would say "the wintel guys don't have this problem, how come only you guys have it"

most likely the wintel boxes are themselves tuned and have their tcp RWIN values set higher than the unix boxes hence performing a lot better.

It could be an MTU Problem, but i dont know where is this parameter in Sun Solaris, also as what sparcguy said, why you dont just pay some respect to the Windows Admins who seems did there work better than you ?