When using Putty for SSH connections via command line, sessions often timeout after periods of inactivity. This happens because:

• Network devices (routers/firewalls) drop idle TCP connections
• Default Putty configuration doesn't send keepalive packets
• SSH servers may terminate inactive sessions

To enable keepalive directly in your Putty command line:

putty.exe -ssh user@192.11.11.11 -pw mypassword -serial -keepalive 60

Key parameters:

• -keepalive 60: Sends keepalive packet every 60 seconds (adjust as needed)
• -serial: Required for keepalive to work with command line connections

Saved Session Configuration

For frequently used connections:

1. Launch Putty GUI
2. Configure keepalive under Connection → Seconds between keepalives
3. Save session
4. Call from command line:

   putty.exe -load "SavedSessionName" -ssh user@host -pw password
   

Registry Modification

For permanent system-wide settings:

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\Software\SimonTatham\PuTTY\Sessions\Default%20Settings]
"Keepalive"="60"
"PingIntervalSecs"="60"
"PingInterval"="60"

• If keepalive isn't working, try decreasing the interval (e.g., 30 seconds)
• Some corporate networks may block ICMP packets - try TCP keepalive instead
• Combine with server-side configuration (ClientAliveInterval in sshd_config)

For a production-ready command with all options:

putty.exe -ssh admin@prod-server.example.com -pw S3cur3P@ss 
-serial -keepalive 30 -no-antispoof -ssh-connection-timeout 0

When using Putty from command line with basic authentication:

putty.exe -ssh user@192.11.11.11 -pw mypassword

The connection may timeout after a few minutes of inactivity, especially when working through firewalls or NAT devices that drop stale connections.

Putty supports two complementary approaches to maintain connection persistence:

putty.exe -ssh user@host -pw password -serial 60 -keepalive 30

Where:

• -serial: Sets the keepalive packet interval in seconds (default 0 = disabled)
• -keepalive: Configures TCP keepalive packets (SO_KEEPALIVE)

For enterprise environments with strict firewall policies, consider these additional parameters:

putty.exe -ssh user@host -pw password \
   -serial 45 \
   -keepalive 15 \
   -no-antispoof \
   -ssh -serial-log=keepalive.log

For Windows systems where you want persistent settings across sessions:

reg add "HKCU\Software\SimonTatham\PuTTY\Sessions\Default%20Settings" \
   /v "PingInterval" /t REG_DWORD /d 60 /f
reg add "HKCU\Software\SimonTatham\PuTTY\Sessions\Default%20Settings" \
   /v "PingIntervalSecs" /t REG_DWORD /d 30 /f

If keepalives aren't working, test your network path with:

ping -t host
tcping host 22

Check for intermediate devices that might be dropping packets:

tracert host
pathping host