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Add a configuration option for TCP keepalives (SO_KEEPALIVE), default off.

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No very good reason, but I've occasionally wanted to frob it to see if it
makes any difference to problems I'm having, and it was easy.

Tested that it does actually cause keepalives on Windows (with tcpdump);
should also work on Unix. Not implemented on Mac (does nothing), but then
neither is TCP_NODELAY.

Quite a big checkin, much of which is adding `keepalive' alongside `nodelay'
in network function calls.

[originally from svn r4309]
This commit is contained in:
Jacob Nevins
2004-06-20 17:07:38 +00:00
parent 6bcac21e36
commit 20f433efac
29 changed files with 109 additions and 51 deletions
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33
doc/config.but
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@ -1,4 +1,4 @@
\versionid $Id: config.but,v 1.83 2004/06/15 11:31:30 jacob Exp $
\versionid $Id: config.but,v 1.84 2004/06/20 17:07:36 jacob Exp $
\C{config} Configuring PuTTY
@ -1506,7 +1506,8 @@ what \e{kind} of network problems you have between you and the
server.
Keepalives are only supported in Telnet and SSH; the Rlogin and Raw
protocols offer no way of implementing them.
protocols offer no way of implementing them. (For an alternative, see
\k{config-tcp-keepalives}.)
Note that if you are using SSH1 and the server has a bug that makes
it unable to deal with SSH1 ignore messages (see
@ -1525,6 +1526,34 @@ types of server.
The Nagle algorithm is disabled by default.
\S{config-tcp-keepalives} \q{Enable TCP keepalives}
\cfg{winhelp-topic}{connection.tcpkeepalive}
\e{NOTE:} TCP keepalives should not be confused with the
application-level keepalives described in \k{config-keepalive}. 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:
\b TCP keepalives are available on \e{all} connection types, including
Raw and Rlogin.
\b 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.
\b If the operating system does not receive a response to a keepalive,
it may send out more in quick succession and if terminate the connection
if no response is received.
TCP keepalives may be useful for ensuring that half-open connections
are terminated than for keeping a connection alive.
TCP keepalives are disabled by default.
\H{config-proxy} The Proxy panel
\cfg{winhelp-topic}{proxy.main}