XPAMethod - XPA Communication Methods
XPA supports both inet and unix (local) socket communication.
XPA uses sockets for communication between processes. It supports three methods
of socket communication: inet, localhost, and unix. In general, the same
method should be employed for all XPA processes in a session and the global
environment variable XPA_METHOD should be used to set up the desired method.
By default, the preferred method is "inet", which is appropriate for
most users. You can set up a different method by typing something like:
setenv XPA_METHOD local # unix csh
XPA_METHOD=local; export XPA_METHOD # unix sh, bash, windows/cygwin
set XPA_METHOD=localhost # dos/windows
The options for XPA_METHOD are: inet
. On Unix machines, this environment setup command can be
placed in your shell init file (.cshrc, .profile, .bashrc, etc.) On Windows
platforms, it can be placed in your AUTOEXEC.BAT file (I think!).
By default, inet
sockets are used by XPA. These are the standard Internet
sockets that are used by programs such as Netscape, ftp. etc. Inet sockets
utilize the IP address of the given machine and a (usually random) port number
to communicate between processes on the same machine or between different
machines on the Internet. (Note that XPA has an Access Control mechanism to
prevent unauthorized access of XPA access points by other computers on the
Net). For users connected to the Internet, this usually is the appropriate
communication method. For more information about setting up XPA communication
between machines, see Communication Between Machines.
In you are using XPA on a machine without an Internet connection, then inet
sockets are not appropriate. In fact, an XPA process often will hang for many
seconds while waiting for a response from the Domain Name Service (DNS) when
using inet sockets. Instead of inet sockets, users on Unix platforms can also
sockets (also known as local sockets). These sockets are based
on the local file system and do not make use of the DNS. They generally are
considered to be faster than inet sockets, but they are not implemented under
Windows. Use local sockets as a first resort if you are on a Unix machine that
is not connected to the Internet.
Users not connected to the Internet also can use localhost
are also inet-type sockets but the IP address used for the local machine is
address, 0x7F000001, instead of the real IP of the
machine. Depending on how sockets are set up for a given platform,
communication with the DNS usually is not required in this case (though of
course, XPA cannot interact with other machines). The localhost method will
generally work on both Unix and Windows platforms, but whether the DNS is
required or not is subject to individual configurations.
A final warning/reminder: if your XPA-enabled server hangs at startup time and
your XPA_METHOD is inet
, the problem probably is related to an
incorrect Internet configuration. This can be confirmed by using the
method or (usually) the localhost
method. You can use these
alternate methods if other hosts do not need access to the XPA server.
See xpa(7) for a list of XPA help pages