I can't figure out why the slow upload speed on windows 2003?

Question

Computer networks

Hello!
there is a terminal server based on windows server 2003 SP2 enterprise edition.
Mother: HA65M-UD3H-B3, i3-2120, 16Gb RAM, and 3 HDDs.
and Internet with a channel width of about 70Mbps in both directions. (from MTS)
Behind this server it was noticed that it has a very low upload speed. loading is higher but also does not hold out.
It's definitely not the network card, before the server worked through the network card built into the mother. Today I put another one (built-in turned off).
Internet speed on the jump is from 30 to 40Mbps,
but the upload speed does not rise above 16Mbps
Speed ​​is measured by SpeedTest and Yandex.ru\internet
The speed over LAN is normal. return of the order of 8-9 MB per second. that is, for 100Mbit it is quite normal.
The Internet is cut.
Other servers (windows 2008r2 and windows 2012r2) connected to the same switch (Cisco Catalyst 2960) as the problem server show a normal speed of 50-70Mbps in both directions.
Everything is fine with the port on the cat to which the server is connected. I checked it by connecting a laptop to the port (in which the server was connected) and running the same speed tests.
Guys, please help me understand what the problem is and what cuts the return.
thanks in advance!

Answer 1

Look at the router. As an option, connect to another port of the router (or subinterface) of the client and drive with iperf.

Answer 2

the situation is the same to other port was connected.