If your SSH Session disconnect even if you enabled “Sending of null packets to keep session active” and “Enable TCP keepalives (SO_KEEPALIVE option)” you might want to try this:
From the Putty FAQ:
On Windows NT, 2000, or XP, the registry key to create or change is
and it must be of type DWORD. (See MS Knowledge Base articles 120642 and 314053 for more information.)
Set the key’s value to something like 10. This will cause Windows to try harder to keep connections alive instead of abandoning them.
Description of the registry key:
Value Type: REG_DWORD – Number
Valid Range: 0 – 0xFFFFFFFF
Default: 3 (in Windows NT)
Default: 2 (in Windows 2000)
Description: This parameter determines the number of times TCP will retransmit a connect request (SYN) before aborting the attempt. The retransmission timeout is doubled with each successive retransmission in a given connect attempt. The initial timeout value is three seconds.
If this does not work for you, you could start for example top (top –d 2, delay 2s) which should have more or less the same result.