+The Nagle algorithm is disabled by default for \i{interactive connections}.
+
+\S{config-tcp-keepalives} \q{Enable \i{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 terminate the connection
+if no response is received.
+
+TCP keepalives may be more useful for ensuring that \i{half-open connections}
+are terminated than for keeping a connection alive.
+
+TCP keepalives are disabled by default.
+
+\S{config-address-family} \I{Internet protocol version}\q{Internet protocol}
+
+\cfg{winhelp-topic}{connection.ipversion}
+
+This option allows the user to select between the old and new
+Internet protocols and addressing schemes (\i{IPv4} and \i{IPv6}).
+The selected protocol will be used for most outgoing network
+connections (including connections to \I{proxy}proxies); however,
+tunnels have their own configuration, for which see
+\k{config-ssh-portfwd-address-family}.
+
+The default setting is \q{Auto}, which means PuTTY will do something
+sensible and try to guess which protocol you wanted. (If you specify
+a literal \i{Internet address}, it will use whichever protocol that
+address implies. If you provide a \i{hostname}, it will see what kinds
+of address exist for that hostname; it will use IPv6 if there is an
+IPv6 address available, and fall back to IPv4 if not.)
+
+If you need to force PuTTY to use a particular protocol, you can
+explicitly set this to \q{IPv4} or \q{IPv6}.
+
+\S{config-loghost} \I{logical host name}\q{Logical name of remote host}
+
+\cfg{winhelp-topic}{connection.loghost}
+
+This allows you to tell PuTTY that the host it will really end up
+connecting to is different from where it thinks it is making a
+network connection.
+
+You might use this, for instance, if you had set up an SSH port
+forwarding in one PuTTY session so that connections to some
+arbitrary port (say, \cw{localhost} port 10022) were forwarded to a
+second machine's SSH port (say, \cw{foovax} port 22), and then
+started a second PuTTY connecting to the forwarded port.
+
+In normal usage, the second PuTTY will access the host key cache
+under the host name and port it actually connected to (i.e.
+\cw{localhost} port 10022 in this example). Using the logical host
+name option, however, you can configure the second PuTTY to cache
+the host key under the name of the host \e{you} know that it's
+\e{really} going to end up talking to (here \c{foovax}).
+
+This can be useful if you expect to connect to the same actual
+server through many different channels (perhaps because your port
+forwarding arrangements keep changing): by consistently setting the
+logical host name, you can arrange that PuTTY will not keep asking
+you to reconfirm its host key. Conversely, if you expect to use the
+same local port number for port forwardings to lots of different
+servers, you probably didn't want any particular server's host key
+cached under that local port number.
+
+If you just enter a host name for this option, PuTTY will cache the
+SSH host key under the default SSH port for that host, irrespective
+of the port you really connected to (since the typical scenario is
+like the above example: you connect to a silly real port number and
+your connection ends up forwarded to the normal port-22 SSH server
+of some other machine). To override this, you can append a port
+number to the logical host name, separated by a colon. E.g. entering
+\cq{foovax:2200} as the logical host name will cause the host key to
+be cached as if you had connected to port 2200 of \c{foovax}.
+
+If you provide a host name using this option, it is also displayed
+in other locations which contain the remote host name, such as the
+default window title and the default SSH password prompt. This
+reflects the fact that this is the host you're \e{really} connecting
+to, which is more important than the mere means you happen to be
+using to contact that host. (This applies even if you're using a
+protocol other than SSH.)
+
+\H{config-data} The Data panel
+
+The Data panel allows you to configure various pieces of data which
+can be sent to the server to affect your connection at the far end.
+
+Each option on this panel applies to more than one protocol.
+Options which apply to only one protocol appear on that protocol's
+configuration panels.
+
+\S{config-username} \q{\ii{Auto-login username}}
+
+\cfg{winhelp-topic}{connection.username}
+
+All three of the SSH, Telnet and Rlogin protocols allow you to
+specify what user name you want to log in as, without having to type
+it explicitly every time. (Some Telnet servers don't support this.)
+
+In this box you can type that user name.
+
+\S{config-username-from-env} Use of system username
+
+\cfg{winhelp-topic}{connection.usernamefromenv}
+
+When the previous box (\k{config-username}) is left blank, by default,
+PuTTY will prompt for a username at the time you make a connection.
+
+In some environments, such as the networks of large organisations
+implementing \i{single sign-on}, a more sensible default may be to use
+the name of the user logged in to the local operating system (if any);
+this is particularly likely to be useful with \i{GSSAPI} authentication
+(see \k{config-ssh-auth-gssapi}). This control allows you to change
+the default behaviour.
+
+The current system username is displayed in the dialog as a
+convenience. It is not saved in the configuration; if a saved session
+is later used by a different user, that user's name will be used.
+
+\S{config-termtype} \q{\ii{Terminal-type} string}
+
+\cfg{winhelp-topic}{connection.termtype}
+
+Most servers you might connect to with PuTTY are designed to be
+connected to from lots of different types of terminal. In order to
+send the right \i{control sequence}s to each one, the server will need
+to know what type of terminal it is dealing with. Therefore, each of
+the SSH, Telnet and Rlogin protocols allow a text string to be sent
+down the connection describing the terminal. On a \i{Unix} server,
+this selects an entry from the \i\c{termcap} or \i\c{terminfo} database
+that tells applications what \i{control sequences} to send to the
+terminal, and what character sequences to expect the \i{keyboard}
+to generate.
+
+PuTTY attempts to emulate the Unix \i\c{xterm} program, and by default
+it reflects this by sending \c{xterm} as a terminal-type string. If
+you find this is not doing what you want - perhaps the remote
+system reports \q{Unknown terminal type} - you could try setting
+this to something different, such as \i\c{vt220}.
+
+If you're not sure whether a problem is due to the terminal type
+setting or not, you probably need to consult the manual for your
+application or your server.
+
+\S{config-termspeed} \q{\ii{Terminal speed}s}
+
+\cfg{winhelp-topic}{connection.termspeed}
+
+The Telnet, Rlogin, and SSH protocols allow the client to specify
+terminal speeds to the server.
+
+This parameter does \e{not} affect the actual speed of the connection,
+which is always \q{as fast as possible}; it is just a hint that is
+sometimes used by server software to modify its behaviour. For
+instance, if a slow speed is indicated, the server may switch to a
+less \i{bandwidth}-hungry display mode.
+
+The value is usually meaningless in a network environment, but
+PuTTY lets you configure it, in case you find the server is reacting
+badly to the default value.
+
+The format is a pair of numbers separated by a comma, for instance,
+\c{38400,38400}. The first number represents the output speed
+(\e{from} the server) in bits per second, and the second is the input
+speed (\e{to} the server). (Only the first is used in the Rlogin
+protocol.)
+
+This option has no effect on Raw connections.
+
+\S{config-environ} Setting \i{environment variables} on the server
+
+\cfg{winhelp-topic}{telnet.environ}
+
+The Telnet protocol provides a means for the client to pass
+environment variables to the server. Many Telnet servers have
+stopped supporting this feature due to security flaws, but PuTTY
+still supports it for the benefit of any servers which have found
+other ways around the security problems than just disabling the
+whole mechanism.
+
+Version 2 of the SSH protocol also provides a similar mechanism,
+which is easier to implement without security flaws. Newer \i{SSH-2}
+servers are more likely to support it than older ones.
+
+This configuration data is not used in the SSH-1, rlogin or raw
+protocols.
+
+To add an environment variable to the list transmitted down the
+connection, you enter the variable name in the \q{Variable} box,
+enter its value in the \q{Value} box, and press the \q{Add} button.
+To remove one from the list, select it in the list box and press
+\q{Remove}.