+If your X display is somewhere unusual, you will need to enter its
+location in the \q{X display location} box; if this is left blank,
+PuTTY will try to find a sensible default in the environment, or use the
+primary local display (\c{:0}) if that fails.
+
+See \k{using-x-forwarding} for more information about X11
+forwarding.
+
+\S{config-ssh-x11auth} Remote \i{X11 authentication}
+
+\cfg{winhelp-topic}{ssh.tunnels.x11auth}
+
+If you are using X11 forwarding, the virtual X server created on the
+SSH server machine will be protected by authorisation data. This
+data is invented, and checked, by PuTTY.
+
+The usual authorisation method used for this is called
+\i\cw{MIT-MAGIC-COOKIE-1}. This is a simple password-style protocol:
+the X client sends some cookie data to the server, and the server
+checks that it matches the real cookie. The cookie data is sent over
+an unencrypted X11 connection; so if you allow a client on a third
+machine to access the virtual X server, then the cookie will be sent
+in the clear.
+
+PuTTY offers the alternative protocol \i\cw{XDM-AUTHORIZATION-1}. This
+is a cryptographically authenticated protocol: the data sent by the
+X client is different every time, and it depends on the IP address
+and port of the client's end of the connection and is also stamped
+with the current time. So an eavesdropper who captures an
+\cw{XDM-AUTHORIZATION-1} string cannot immediately re-use it for
+their own X connection.
+
+PuTTY's support for \cw{XDM-AUTHORIZATION-1} is a somewhat
+experimental feature, and may encounter several problems:
+
+\b Some X clients probably do not even support
+\cw{XDM-AUTHORIZATION-1}, so they will not know what to do with the
+data PuTTY has provided.
+
+\b This authentication mechanism will only work in SSH-2. In SSH-1,
+the SSH server does not tell the client the source address of
+a forwarded connection in a machine-readable format, so it's
+impossible to verify the \cw{XDM-AUTHORIZATION-1} data.
+
+\b You may find this feature causes problems with some SSH servers,
+which will not clean up \cw{XDM-AUTHORIZATION-1} data after a
+session, so that if you then connect to the same server using
+a client which only does \cw{MIT-MAGIC-COOKIE-1} and are allocated
+the same remote display number, you might find that out-of-date
+authentication data is still present on your server and your X
+connections fail.
+
+PuTTY's default is \cw{MIT-MAGIC-COOKIE-1}. If you change it, you
+should be sure you know what you're doing.
+
+\S{config-ssh-xauthority} X authority file for local display
+
+\cfg{winhelp-topic}{ssh.tunnels.xauthority}
+
+If you are using X11 forwarding, the local X server to which your
+forwarded connections are eventually directed may itself require
+authorisation.
+
+Some Windows X servers do not require this: they do authorisation by
+simpler means, such as accepting any connection from the local
+machine but not from anywhere else. However, if your X server does
+require authorisation, then PuTTY needs to know what authorisation
+is required.
+
+One way in which this data might be made available is for the X
+server to store it somewhere in a file which has the same format
+as the Unix \c{.Xauthority} file. If this is how your Windows X
+server works, then you can tell PuTTY where to find this file by
+configuring this option. By default, PuTTY will not attempt to find
+any authorisation for your local display.
+
+\H{config-ssh-portfwd} \I{port forwarding}The Tunnels panel
+
+\cfg{winhelp-topic}{ssh.tunnels.portfwd}
+
+The Tunnels panel allows you to configure tunnelling of arbitrary
+connection types through an SSH connection.
+
+Port forwarding allows you to tunnel other types of \i{network
+connection} down an SSH session. See \k{using-port-forwarding} for a
+general discussion of port forwarding and how it works.
+
+The port forwarding section in the Tunnels panel shows a list of all
+the port forwardings that PuTTY will try to set up when it connects
+to the server. By default no port forwardings are set up, so this
+list is empty.
+
+To add a port forwarding:
+
+\b Set one of the \q{Local} or \q{Remote} radio buttons, depending
+on whether you want to \I{local port forwarding}forward a local port
+to a remote destination (\q{Local}) or \I{remote port forwarding}forward
+a remote port to a local destination (\q{Remote}). Alternatively,
+select \q{Dynamic} if you want PuTTY to \I{dynamic port forwarding}provide
+a local SOCKS 4/4A/5 proxy on a local port (note that this proxy only
+supports TCP connections; the SSH protocol does not support forwarding
+\i{UDP}).
+
+\b Enter a source \i{port number} into the \q{Source port} box. For
+local forwardings, PuTTY will listen on this port of your PC. For
+remote forwardings, your SSH server will listen on this port of the
+remote machine. Note that most servers will not allow you to listen
+on \I{privileged port}port numbers less than 1024.
+
+\b If you have selected \q{Local} or \q{Remote} (this step is not
+needed with \q{Dynamic}), enter a hostname and port number separated
+by a colon, in the \q{Destination} box. Connections received on the
+source port will be directed to this destination. For example, to
+connect to a POP-3 server, you might enter
+\c{popserver.example.com:110}.
+
+\b Click the \q{Add} button. Your forwarding details should appear
+in the list box.
+
+To remove a port forwarding, simply select its details in the list
+box, and click the \q{Remove} button.
+
+In the \q{Source port} box, you can also optionally enter an \I{listen
+address}IP address to listen on, by specifying (for instance)
+\c{127.0.0.5:79}.
+See \k{using-port-forwarding} for more information on how this
+works and its restrictions.
+
+In place of port numbers, you can enter \i{service names}, if they are
+known to the local system. For instance, in the \q{Destination} box,
+you could enter \c{popserver.example.com:pop3}.
+
+You can \I{port forwarding, changing mid-session}modify the currently
+active set of port forwardings in mid-session using \q{Change
+Settings} (see \k{using-changesettings}). If you delete a local or
+dynamic port forwarding in mid-session, PuTTY will stop listening for
+connections on that port, so it can be re-used by another program. If
+you delete a remote port forwarding, note that:
+
+\b The SSH-1 protocol contains no mechanism for asking the server to
+stop listening on a remote port.
+
+\b The SSH-2 protocol does contain such a mechanism, but not all SSH
+servers support it. (In particular, \i{OpenSSH} does not support it in
+any version earlier than 3.9.)
+
+If you ask to delete a remote port forwarding and PuTTY cannot make
+the server actually stop listening on the port, it will instead just
+start refusing incoming connections on that port. Therefore,
+although the port cannot be reused by another program, you can at
+least be reasonably sure that server-side programs can no longer
+access the service at your end of the port forwarding.
+
+If you delete a forwarding, any existing connections established using
+that forwarding remain open. Similarly, changes to global settings
+such as \q{Local ports accept connections from other hosts} only take
+effect on new forwardings.
+
+If the connection you are forwarding over SSH is itself a second SSH
+connection made by another copy of PuTTY, you might find the
+\q{logical host name} configuration option useful to warn PuTTY of
+which host key it should be expecting. See \k{config-loghost} for
+details of this.
+
+\S{config-ssh-portfwd-localhost} Controlling the visibility of
+forwarded ports
+
+\cfg{winhelp-topic}{ssh.tunnels.portfwd.localhost}
+
+The source port for a forwarded connection usually does not accept
+connections from any machine except the \I{localhost}SSH client or
+server machine itself (for local and remote forwardings respectively).
+There are controls in the Tunnels panel to change this:
+
+\b The \q{Local ports accept connections from other hosts} option
+allows you to set up local-to-remote port forwardings in such a way
+that machines other than your client PC can connect to the forwarded
+port. (This also applies to dynamic SOCKS forwarding.)
+
+\b The \q{Remote ports do the same} option does the same thing for
+remote-to-local port forwardings (so that machines other than the
+SSH server machine can connect to the forwarded port.) Note that
+this feature is only available in the SSH-2 protocol, and not all
+SSH-2 servers support it (\i{OpenSSH} 3.0 does not, for example).
+
+\S{config-ssh-portfwd-address-family} Selecting \i{Internet protocol
+version} for forwarded ports
+
+\cfg{winhelp-topic}{ssh.tunnels.portfwd.ipversion}
+
+This switch allows you to select a specific Internet protocol (\i{IPv4}
+or \i{IPv6}) for the local end of a forwarded port. By default, it is
+set on \q{Auto}, which means that:
+
+\b for a local-to-remote port forwarding, PuTTY will listen for
+incoming connections in both IPv4 and (if available) IPv6
+
+\b for a remote-to-local port forwarding, PuTTY will choose a
+sensible protocol for the outgoing connection.
+
+This overrides the general Internet protocol version preference
+on the Connection panel (see \k{config-address-family}).
+
+Note that some operating systems may listen for incoming connections
+in IPv4 even if you specifically asked for IPv6, because their IPv4
+and IPv6 protocol stacks are linked together. Apparently \i{Linux} does
+this, and Windows does not. So if you're running PuTTY on Windows
+and you tick \q{IPv6} for a local or dynamic port forwarding, it
+will \e{only} be usable by connecting to it using IPv6; whereas if
+you do the same on Linux, you can also use it with IPv4. However,
+ticking \q{Auto} should always give you a port which you can connect
+to using either protocol.
+
+\H{config-ssh-bugs} \I{SSH server bugs}The Bugs panel
+
+Not all SSH servers work properly. Various existing servers have
+bugs in them, which can make it impossible for a client to talk to
+them unless it knows about the bug and works around it.
+
+Since most servers announce their software version number at the
+beginning of the SSH connection, PuTTY will attempt to detect which
+bugs it can expect to see in the server and automatically enable
+workarounds. However, sometimes it will make mistakes; if the server
+has been deliberately configured to conceal its version number, or
+if the server is a version which PuTTY's bug database does not know
+about, then PuTTY will not know what bugs to expect.
+
+The Bugs panel allows you to manually configure the bugs PuTTY
+expects to see in the server. Each bug can be configured in three
+states:
+
+\b \q{Off}: PuTTY will assume the server does not have the bug.
+
+\b \q{On}: PuTTY will assume the server \e{does} have the bug.
+
+\b \q{Auto}: PuTTY will use the server's version number announcement
+to try to guess whether or not the server has the bug.
+
+\S{config-ssh-bug-ignore1} \q{Chokes on SSH-1 \i{ignore message}s}
+
+\cfg{winhelp-topic}{ssh.bugs.ignore1}
+
+An ignore message (SSH_MSG_IGNORE) is a message in the SSH protocol
+which can be sent from the client to the server, or from the server
+to the client, at any time. Either side is required to ignore the
+message whenever it receives it. PuTTY uses ignore messages to
+\I{password camouflage}hide the password packet in SSH-1, so that
+a listener cannot tell the length of the user's password; it also
+uses ignore messages for connection \i{keepalives} (see
+\k{config-keepalive}).
+
+If this bug is detected, PuTTY will stop using ignore messages. This
+means that keepalives will stop working, and PuTTY will have to fall
+back to a secondary defence against SSH-1 password-length
+eavesdropping. See \k{config-ssh-bug-plainpw1}. If this bug is
+enabled when talking to a correct server, the session will succeed,
+but keepalives will not work and the session might be more
+vulnerable to eavesdroppers than it could be.
+
+\S{config-ssh-bug-plainpw1} \q{Refuses all SSH-1 \i{password camouflage}}
+
+\cfg{winhelp-topic}{ssh.bugs.plainpw1}
+
+When talking to an SSH-1 server which cannot deal with ignore
+messages (see \k{config-ssh-bug-ignore1}), PuTTY will attempt to
+disguise the length of the user's password by sending additional
+padding \e{within} the password packet. This is technically a
+violation of the SSH-1 specification, and so PuTTY will only do it
+when it cannot use standards-compliant ignore messages as
+camouflage. In this sense, for a server to refuse to accept a padded
+password packet is not really a bug, but it does make life
+inconvenient if the server can also not handle ignore messages.
+
+If this \q{bug} is detected, PuTTY will assume that neither ignore
+messages nor padding are acceptable, and that it thus has no choice
+but to send the user's password with no form of camouflage, so that
+an eavesdropping user will be easily able to find out the exact length
+of the password. If this bug is enabled when talking to a correct
+server, the session will succeed, but will be more vulnerable to
+eavesdroppers than it could be.
+
+This is an SSH-1-specific bug. SSH-2 is secure against this type of
+attack.
+
+\S{config-ssh-bug-rsa1} \q{Chokes on SSH-1 \i{RSA} authentication}
+
+\cfg{winhelp-topic}{ssh.bugs.rsa1}
+
+Some SSH-1 servers cannot deal with RSA authentication messages at
+all. If \i{Pageant} is running and contains any SSH-1 keys, PuTTY will
+normally automatically try RSA authentication before falling back to
+passwords, so these servers will crash when they see the RSA attempt.
+
+If this bug is detected, PuTTY will go straight to password
+authentication. If this bug is enabled when talking to a correct
+server, the session will succeed, but of course RSA authentication
+will be impossible.
+
+This is an SSH-1-specific bug.
+
+\S{config-ssh-bug-ignore2} \q{Chokes on SSH-2 \i{ignore message}s}
+
+\cfg{winhelp-topic}{ssh.bugs.ignore2}
+
+An ignore message (SSH_MSG_IGNORE) is a message in the SSH protocol
+which can be sent from the client to the server, or from the server
+to the client, at any time. Either side is required to ignore the
+message whenever it receives it. PuTTY uses ignore messages in SSH-2
+to confuse the encrypted data stream and make it harder to
+cryptanalyse. It also uses ignore messages for connection
+\i{keepalives} (see \k{config-keepalive}).
+
+If it believes the server to have this bug, PuTTY will stop using
+ignore messages. If this bug is enabled when talking to a correct
+server, the session will succeed, but keepalives will not work and
+the session might be less cryptographically secure than it could be.
+
+\S{config-ssh-bug-hmac2} \q{Miscomputes SSH-2 HMAC keys}
+
+\cfg{winhelp-topic}{ssh.bugs.hmac2}
+
+Versions 2.3.0 and below of the SSH server software from
+\cw{ssh.com} compute the keys for their \i{HMAC} \i{message authentication
+code}s incorrectly. A typical symptom of this problem is that PuTTY
+dies unexpectedly at the beginning of the session, saying
+\q{Incorrect MAC received on packet}.
+
+If this bug is detected, PuTTY will compute its HMAC keys in the
+same way as the buggy server, so that communication will still be
+possible. If this bug is enabled when talking to a correct server,
+communication will fail.
+
+This is an SSH-2-specific bug.
+
+\S{config-ssh-bug-derivekey2} \q{Miscomputes SSH-2 \i{encryption} keys}
+
+\cfg{winhelp-topic}{ssh.bugs.derivekey2}
+
+Versions below 2.0.11 of the SSH server software from \i\cw{ssh.com}
+compute the keys for the session encryption incorrectly. This
+problem can cause various error messages, such as \q{Incoming packet
+was garbled on decryption}, or possibly even \q{Out of memory}.
+
+If this bug is detected, PuTTY will compute its encryption keys in
+the same way as the buggy server, so that communication will still
+be possible. If this bug is enabled when talking to a correct
+server, communication will fail.
+
+This is an SSH-2-specific bug.
+
+\S{config-ssh-bug-sig} \q{Requires padding on SSH-2 \i{RSA} \i{signatures}}
+
+\cfg{winhelp-topic}{ssh.bugs.rsapad2}
+
+Versions below 3.3 of \i{OpenSSH} require SSH-2 RSA signatures to be
+padded with zero bytes to the same length as the RSA key modulus.
+The SSH-2 specification says that an unpadded signature MUST be
+accepted, so this is a bug. A typical symptom of this problem is
+that PuTTY mysteriously fails RSA authentication once in every few
+hundred attempts, and falls back to passwords.
+
+If this bug is detected, PuTTY will pad its signatures in the way
+OpenSSH expects. If this bug is enabled when talking to a correct
+server, it is likely that no damage will be done, since correct
+servers usually still accept padded signatures because they're used
+to talking to OpenSSH.
+
+This is an SSH-2-specific bug.
+
+\S{config-ssh-bug-pksessid2} \q{Misuses the \i{session ID} in SSH-2 PK auth}
+
+\cfg{winhelp-topic}{ssh.bugs.pksessid2}
+
+Versions below 2.3 of \i{OpenSSH} require SSH-2 \i{public-key authentication}
+to be done slightly differently: the data to be signed by the client
+contains the session ID formatted in a different way. If public-key
+authentication mysteriously does not work but the Event Log (see
+\k{using-eventlog}) thinks it has successfully sent a signature, it
+might be worth enabling the workaround for this bug to see if it
+helps.
+
+If this bug is detected, PuTTY will sign data in the way OpenSSH
+expects. If this bug is enabled when talking to a correct server,
+SSH-2 public-key authentication will fail.
+
+This is an SSH-2-specific bug.
+
+\S{config-ssh-bug-rekey} \q{Handles SSH-2 key re-exchange badly}
+
+\cfg{winhelp-topic}{ssh.bugs.rekey2}
+
+Some SSH servers cannot cope with \i{repeat key exchange} at
+all, and will ignore attempts by the client to start one. Since
+PuTTY pauses the session while performing a repeat key exchange, the
+effect of this would be to cause the session to hang after an hour
+(unless you have your rekey timeout set differently; see
+\k{config-ssh-kex-rekey} for more about rekeys).
+Other, very old, SSH servers handle repeat key exchange even more
+badly, and disconnect upon receiving a repeat key exchange request.
+
+If this bug is detected, PuTTY will never initiate a repeat key
+exchange. If this bug is enabled when talking to a correct server,
+the session should still function, but may be less secure than you
+would expect.
+
+This is an SSH-2-specific bug.
+
+\S{config-ssh-bug-maxpkt2} \q{Ignores SSH-2 \i{maximum packet size}}
+
+\cfg{winhelp-topic}{ssh.bugs.maxpkt2}
+
+When an SSH-2 channel is set up, each end announces the maximum size
+of data packet that it is willing to receive for that channel. Some
+servers ignore PuTTY's announcement and send packets larger than PuTTY
+is willing to accept, causing it to report \q{Incoming packet was
+garbled on decryption}.
+
+If this bug is detected, PuTTY never allows the channel's
+\i{flow-control window} to grow large enough to allow the server to
+send an over-sized packet. If this bug is enabled when talking to a
+correct server, the session will work correctly, but download
+performance will be less than it could be.
+
+\S{config-ssh-bug-winadj} \q{Chokes on PuTTY's SSH-2 \cq{winadj} requests}
+
+\cfg{winhelp-topic}{ssh.bugs.winadj}
+
+PuTTY sometimes sends a special request to SSH servers in the middle
+of channel data, with the name \cw{winadj@putty.projects.tartarus.org}
+(see \k{sshnames-channel}). The purpose of this request is to measure
+the round-trip time to the server, which PuTTY uses to tune its flow
+control. The server does not actually have to \e{understand} the
+message; it is expected to send back a \cw{SSH_MSG_CHANNEL_FAILURE}
+message indicating that it didn't understand it. (All PuTTY needs for
+its timing calculations is \e{some} kind of response.)
+
+It has been known for some SSH servers to get confused by this message
+in one way or another \dash because it has a long name, or because
+they can't cope with unrecognised request names even to the extent of
+sending back the correct failure response, or because they handle it
+sensibly but fill up the server's log file with pointless spam, or
+whatever. PuTTY therefore supports this bug-compatibility flag: if it
+believes the server has this bug, it will never send its
+\cq{winadj@putty.projects.tartarus.org} request, and will make do
+without its timing data.
+
+\H{config-serial} The Serial panel
+
+The \i{Serial} panel allows you to configure options that only apply
+when PuTTY is connecting to a local \I{serial port}\i{serial line}.
+
+\S{config-serial-line} Selecting a serial line to connect to
+
+\cfg{winhelp-topic}{serial.line}
+
+The \q{Serial line to connect to} box allows you to choose which
+serial line you want PuTTY to talk to, if your computer has more
+than one serial port.
+
+On Windows, the first serial line is called \i\cw{COM1}, and if there
+is a second it is called \cw{COM2}, and so on.
+
+This configuration setting is also visible on the Session panel,
+where it replaces the \q{Host Name} box (see \k{config-hostname}) if
+the connection type is set to \q{Serial}.
+
+\S{config-serial-speed} Selecting the speed of your serial line
+
+\cfg{winhelp-topic}{serial.speed}
+
+The \q{Speed} box allows you to choose the speed (or \q{baud rate})
+at which to talk to the serial line. Typical values might be 9600,
+19200, 38400 or 57600. Which one you need will depend on the device
+at the other end of the serial cable; consult the manual for that
+device if you are in doubt.
+
+This configuration setting is also visible on the Session panel,
+where it replaces the \q{Port} box (see \k{config-hostname}) if the
+connection type is set to \q{Serial}.
+
+\S{config-serial-databits} Selecting the number of data bits
+
+\cfg{winhelp-topic}{serial.databits}
+
+The \q{Data bits} box allows you to choose how many data bits are
+transmitted in each byte sent or received through the serial line.
+Typical values are 7 or 8.
+
+\S{config-serial-stopbits} Selecting the number of stop bits
+
+\cfg{winhelp-topic}{serial.stopbits}
+
+The \q{Stop bits} box allows you to choose how many stop bits are
+used in the serial line protocol. Typical values are 1, 1.5 or 2.
+
+\S{config-serial-parity} Selecting the serial parity checking scheme
+
+\cfg{winhelp-topic}{serial.parity}
+
+The \q{Parity} box allows you to choose what type of parity checking
+is used on the serial line. The settings are:
+
+\b \q{None}: no parity bit is sent at all.
+
+\b \q{Odd}: an extra parity bit is sent alongside each byte, and
+arranged so that the total number of 1 bits is odd.
+
+\b \q{Even}: an extra parity bit is sent alongside each byte, and
+arranged so that the total number of 1 bits is even.
+
+\b \q{Mark}: an extra parity bit is sent alongside each byte, and
+always set to 1.
+
+\b \q{Space}: an extra parity bit is sent alongside each byte, and
+always set to 0.
+
+\S{config-serial-flow} Selecting the serial flow control scheme
+
+\cfg{winhelp-topic}{serial.flow}
+
+The \q{Flow control} box allows you to choose what type of flow
+control checking is used on the serial line. The settings are:
+
+\b \q{None}: no flow control is done. Data may be lost if either
+side attempts to send faster than the serial line permits.
+
+\b \q{XON/XOFF}: flow control is done by sending XON and XOFF
+characters within the data stream.
+
+\b \q{RTS/CTS}: flow control is done using the RTS and CTS wires on
+the serial line.
+
+\b \q{DSR/DTR}: flow control is done using the DSR and DTR wires on
+the serial line.
+
+\H{config-file} \ii{Storing configuration in a file}