Configuring rfc1323 in IBM i:

How to turn off/on TCP window Scaling on IBM i

To change the settings use the following steps:

1. Login using QSECOFR user profile
2. Run STRSST and enter the service tools username and password
3. Select option 1 (Start a service tool)
4. Select option 4 (Display/Alter/Dump)
5. Select option 1 (Display/Alter storage)
6. Select option 2 (Licensed Internal Code (LIC) data)
7. Select option 14 (Advanced Analysis)
8. Select option 1 and type IPCONFIG on the first command line and press enter
9. Specify option -DISPLAY to display configuration options command line and press enter

There will be two IPCONFIG options for RFC1323 on the last page, where you can view the current status:

To enable or disable the TCP Timestamps or Windows Scaling follow the below steps:

1. Press F12 to exit the Display menu
2. Enter -rfc1323TcpTimestamps:<on> or -rfc1323TcpTimestamps:<off>
3. Enter -rfc1323TcpWindowScaling:<on> or -rfc1323TcpWindowScaling:<off> 

Note: When TCP RCVBUF is higher than 64K and window scaling is off, 64K will be used. TCP takes the minimum of RCVBUF and calculated window size using window size scaling factor.