I recently ran into this issue in which transferring files through a Cisco ASA Firewall was extremely slow only in one direction. The transfer would run between 10-15 MB/s one way and between 100-500 KB/s the other way. The servers were both Windows 2008 R2 in which this issue would occur. I could transfer files from the server inside the DMZ to a Windows 2003 server without experiencing the same issue. I was able to duplicate this scenario for any other given Windows 2008 R2 to Windows 2008 R2 server doing the same testing. So obviously the issue was Windows 2008 R2 specific in this case. So after some investigation and testing I was able to come up with the following TCP setting changes that corrected the issue and the transfers were the same either way after the reboot which was 10-15 MB/s either way. In my scenario I only needed to make the change on the server inside the DMZ. I also did this same test using a PFSense firewall with the exact same firewall rules in place and this issue was not present.
These are the issues you may experience.
•Slow data transfer
Changes made to server inside DMZ.
netsh int tcp set global RSS=Disable netsh int tcp set global chimney=Disabled netsh int tcp set global autotuninglevel=Disabled netsh int tcp set global congestionprovider=None netsh int tcp set global ecncapability=Disabled netsh int ip set global taskoffload=disabled netsh int tcp set global timestamps=Disabled
To revert changes back to default.
netsh int tcp set global RSS=Enabled netsh int tcp set global chimney=Enabled netsh int tcp set global autotuninglevel=normal netsh int tcp set global congestionprovider=ctcp netsh int tcp set global ecncapability=Enabled netsh int ip set global taskoffload=Enabled netsh int tcp set global timestamps=Enabled