4.14.3 ‘Enable TCP keepalives’

NOTE: TCP keepalives should not be confused with the application-level keepalives described in section 4.14.1. If in doubt, you probably want application-level keepalives; TCP keepalives are provided for completeness.

The idea of TCP keepalives is similar to application-level keepalives, and the same caveats apply. The main differences are:

• TCP keepalives are available on all network connection types, including Raw, Rlogin, and SUPDUP.
• The interval between TCP keepalives is usually much longer, typically two hours; this is set by the operating system, and cannot be configured within PuTTY.
• If the operating system does not receive a response to a keepalive, it may send out more in quick succession and terminate the connection if no response is received.

TCP keepalives may be more useful for ensuring that half-open connections are terminated than for keeping a connection alive.

TCP keepalives are disabled by default.