393 lines
18 KiB
Groff
393 lines
18 KiB
Groff
.\" $Xorg: xfwp.man,v 1.4 2001/02/09 02:05:46 xorgcvs Exp $
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.\" Copyright 1996, 1998 The Open Group
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.\"
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.\" Permission to use, copy, modify, distribute, and sell this software and its
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.\" documentation for any purpose is hereby granted without fee, provided that
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.\" the above copyright notice appear in all copies and that both that
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.\" copyright notice and this permission notice appear in supporting
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.\" documentation.
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.\"
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.\" The above copyright notice and this permission notice shall be included
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.\" in all copies or substantial portions of the Software.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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.\" OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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.\" IN NO EVENT SHALL THE OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR
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.\" OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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.\" ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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.\" OTHER DEALINGS IN THE SOFTWARE.
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.\"
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.\" Except as contained in this notice, the name of The Open Group shall
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.\" not be used in advertising or otherwise to promote the sale, use or
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.\" other dealings in this Software without prior written authorization
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.\" from The Open Group.
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.\"
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.\"
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.\" $XFree86: xc/programs/xfwp/xfwp.man,v 1.7 2001/02/07 22:35:23 tsi Exp $
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.\"
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.nh
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.TH XFWP 1 __xorgversion__
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.SH NAME
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xfwp - X firewall proxy
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.SH SYNOPSIS
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.B xfwp
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[option ...]
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.PP
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.SH COMMAND LINE OPTIONS
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The command line options that can be specified are:
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.PP
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.TP 8
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.B \-cdt \fInum_secs\fP
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Used to override the default time-to-close (604800 seconds) for xfwp client
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data connections on which there is no activity (connections over which
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X protocol is already being relayed by xfwp)
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.PP
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.TP 8
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.B \-clt \fInum_secs\fP
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Used to override the default time-to-close (86400 seconds) for xfwp client
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listen ports (ports on xfwp to which X clients first connect when trying to
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reach an X server)
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.PP
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.TP 8
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.B \-pdt \fInum_secs\fP
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Used to override the default time-to-close (3600 seconds) for Proxy Manager
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connections on which there is no activity
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.PP
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.TP 8
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.B \-config \fIfile_name\fP
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Used to specify the configuration the name of the configuration file
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.PP
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.TP 8
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.B \-pmport \fIport_number\fP
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Used to override the default port address (4444) for proxy manager connections
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.PP
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.TP 8
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.B \-verify
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Used to display the configuration file rule that was actually matched for
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each service request
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.PP
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.TP 8
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.B \-logfile \fIfile_name\fP
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Used to specify the name of a file where audit information should be logged.
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The format of a logged entry is: time of day; event code; source IP address;
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destination IP address; and configuration rule number. The event codes
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are: "0" for a successful connection; "1" if a connection is denied because of
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a configuration rule; and "2" if a connection is denied because of an
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authorization failure. If the event code is "1", and a configuration file
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is used, the configuration rule number is the line number of the
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configuration file where the match was made (see the section
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CONFIGURATION FILE for more information). If the event code is not "1",
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or if no configuration file is used, the configuration rule number is "-1".
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.PP
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.TP 8
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.B \-loglevel \fI{0,1}\fP
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Used to specify the amount of audit detail that should be logged. If "0",
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all connections are logged. If "1", only unsuccessful connections are logged.
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.PP
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.TP 8
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.B \-max_pm_conns \fInum_connections\fP
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Used to specify the maximum number of Proxy Manager connections. The
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default is 10.
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.PP
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.TP 8
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.B \-max_pm_conns \fInum_connections\fP
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Used to specify the maximum number of X server connections. The
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default is 100.
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.PP
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.SH DESCRIPTION
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The X firewall proxy (xfwp) is an application layer gateway proxy
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that may be run on a network firewall host to forward X traffic
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across the firewall. Used in conjunction with the X server Security
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extension and authorization checking, xfwp constitutes a safe, simple,
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and reliable mechanism both to hide the addresses of X servers located
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on the Intranet and to enforce a server connection policy. Xfwp cannot
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protect against mischief originating on the Intranet; however, when
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properly configured it can guarantee that only trusted clients originating
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on authorized external Internet hosts will be allowed inbound access to
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local X servers.
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To use xfwp there must be an X proxy manager running in the local environment
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which has been configured at start-up to know the location of the xfwp.
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[NOTE: There may be more than one xfwp running in a local environment;
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see notes below on load balancing for further discussion.] Using the
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xfindproxy utility (which relays its requests through the proxy manager)
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a user asks xfwp to allocate a client listen port for a particular X server,
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which is internally associated with all future connection requests for that
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server. This client listen port address is returned by the proxy manager
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through xfindproxy. The xfwp hostname and port number is then passed
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out-of-band (i.e., via a Web browser) to some remote X client, which will
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subsequently connect to xfwp instead of to the target X server.
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When an X client connection request appears on one of xfwp's listen ports,
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xfwp connects to the X server associated with this listen port and performs
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authorization checks against the server as well as against its own configurable
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access control list for requesting clients. If these checks fail, or if
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the requested server does not support the X Security Extension, the client
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connection is refused. Otherwise, the connection is accepted and all ensuing
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data between client and server is relayed by xfwp until the client terminates
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the connection or, in the case of an inactive client, until a configured
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timeout period is exceeded. Xfwp is designed to block while waiting for
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activity on its connections, thereby minimizing demand for system cycles.
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If xfwp is run without a configuration file and thus no sitepolicy is
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defined, if xfwp is using an X server where xhost + has been run to turn
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off host-based authorization checks, when a client tries to connect to
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this X server via xfwp, the X server will deny the connection. If xfwp
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does not define a sitepolicy, host-based authorization must be turned on
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for clients to connect to an X server via the xfwp.
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.PP
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.SH INTEROPERATION WITH IP PACKET-FILTERING ROUTERS
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The whole purpose of the xfwp is to provide reliable control over access
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to Intranet X servers by clients originating outside the firewall. At
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the present time, such access control is typically achieved by firewall
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configurations incorporating IP packet-filtering routers. Frequently,
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the rules for such filters deny access to X server ports (range 6000 -
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6xxx) for all Intranet host machines.
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In order for xfwp to do its job, restrictions on access for ports 6001 - 6xxx
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must be removed from the rule-base of the IP packet-filtering router. [NOTE:
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xfwp only assigns ports in the range beginning with 6001; access to port
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6000 on all Intranet hosts may continue to be denied.] This does not
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mean the Intranet firewall will be opened for indiscriminate entry by X
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clients. Instead, xfwp supports a fully configurable rule-based access
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control system, similar to that of the IP packet-filter router itself.
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Xfwp in effect adds another level of packet-filtering control which is
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fully configurable and applies specifically to X traffic. See section
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entitled CONFIGURATION FILE, below, for further details.
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.PP
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.SH INSTALLATION, SETUP AND TROUBLESHOOTING
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Xfwp is typically run as a background process on the Intranet firewall host.
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It can be launched using any of the command-line options described above.
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As noted above, xfwp works only in conjunction with proxy manager and the
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xfindproxy utility. It can also be configured to support a user-defined
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X server site security policy, in which the X server is required to indicate
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to xfwp whether or not it supports the particular policy. Consult the
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X server man pages for further information on these components. Xfwp
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diagnostics can be turned on by compiling with the -DDEBUG switch.
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Connection status can be recorded by using the -logfile and -loglevel
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command line options.
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.PP
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.SH PERFORMANCE, LOAD BALANCING AND RESOURCE MANAGEMENT
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Xfwp manages four different kinds of connections: proxy manager (PM) data,
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X client listen, X client data, and X server. The sysadmin employing xfwp
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must understand how the resources for each of these connection types are
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allocated and reclaimed by xfwp in order to optimize the availability of
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xfwp service.
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Each connection-type has a default number of allocation slots and
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a default timeout. The number of allocation slots for PM connections
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and X server connections is configurable via command line options.
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Connection timeouts are also configurable via command line options.
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Each connection timeout represents the period the connection
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will be allowed to remain open in the absence of any activity on that
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connection. Whenever there is activity on a connection, the time-to-close
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is automatically reset. The default distribution of total process connection
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slots across the four connection types, as well as the choice of default
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timeouts for the connection types, is governed by a number of assumptions
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embedded in the xfwp use model.
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The default number of PM connections is 10 and the
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default duration for PM connections is 3,600
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seconds (1 hour) for each connection after time of last activity.
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At start-up, xfwp listens for PM connection requests on any non-reserved
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port (default of 4444 if not specified on the xfwp command-line). The PM
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normally connects to xfwp only when a call is made to the PM with xfindproxy.
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Thereafter, the PM remains connected to xfwp, even after the messaging between
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them has been completed, for the default connection duration period. In some
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cases this may result in depletion of available PM connection slots.
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If the sysadmin expects connections to a single xfwp from many PM's,
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xfwp should be started using the -pdt command line option, with a timeout
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value reflecting the desired duration that inactive connections will be
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permitted to remain open.
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Xfwp client listeners are set up by a call to xfindproxy and continue to
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listen for X client connection requests for a default duration of 86,400
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seconds (24 hours) from the point of last activity. After this time they
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are automatically closed and their fd's recovered for future allocation.
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In addressing the question of how to choose some alternative timeout
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value which will guarantee the availability of client listen ports,
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sysadmins should take into consideration the expected delay between
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the time when the listener was allocated (using xfindproxy) and the time
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when a client actually attempts to connect to xfwp, as well the likelihood
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that client listeners will be re-used after the initial client data
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connection is closed.
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Each client connection is allocated a default lifetime of 604,800
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seconds (7 * 24 hours)
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from the point when it last saw activity. After this time it is
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automatically closed and its fd's recovered for future allocation.
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Because server connections are not actually established until a connection
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request from a remote X client arrives at one of the xfwp's client listen
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ports, the client data timeout applies both to client-xfwp connections as well
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as to xfwp-server connections. If the system administrator expects many
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client data connections through xfwp, an overriding of the default timeout
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should be considered.
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.PP
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.SH CONFIGURATION FILE
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The xfwp configuration file resides on the xfwp host machine and is
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used to determine whether X client data connection requests will be
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permitted or denied. The path to the file is specified at start-up
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time. If no configuration file is specified, all X client data
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connection requests routed through xfwp will be by default permitted,
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assuming that other X server authorization checks are successful. If
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a configuration file is supplied but none of its entries matches the
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connection request then the connection is by default denied.
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If a line in the configuration file begins with the '#' character
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or a new-line character, the line is ignored and the evaluator will
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skip the line.
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The configuration file supports two entirely independent authorization
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checks: one which is performed by xfwp itself, and a second which is the
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result of xfwp's querying the target X server. For the first of these,
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the configuration file employs a syntax and semantic similar to that of IP
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packet-filtering routers. It contains zero or more source-destination
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rules of the following form:
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.PP
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{permit | deny} <src> <src mask> [<dest> <dest mask> [<operator> <service>]]
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.sp
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.IP permit/deny 12
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the keywords ``permit'' or ``deny'' indicate whether the
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rule will enable or disable access, respectively
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.IP src 12
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the IP address against the host who originated the
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connection request will be matched, expressed in IP
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format (x.x.x.x)
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.IP "src mask" 12
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a subnet mask, also in IP format, for further qualifying
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the source mask. Bits set in the mask indicate bits of the
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incoming address to be \fIignored\fP when comparing to the specified src
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.IP dest 12
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the IP address against which the destination of the
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incoming connection request (i.e. the host IP of the
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X server to which the incoming client is attempting to
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connect) will be matched
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.IP "dest mask" 12
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a subnet mask, also in IP format, for further qualifying
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the destination mask. Bits set in the mask indicate bits of the
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destination address to be \fIignored\fP when comparing to the specified dest
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.IP operator 12
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always ``eq'' (if the service field is not NULL)
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.IP service 12
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one of the following three strings: ``pm'', ``fp'', or
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``cd'', corresponding to proxy manager, xfindproxy, or
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client data, respectively
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.PP
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For the second type of authorization check, the configuration file contains
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zero or more site policy rules of the following form:
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.PP
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{require | disallow} sitepolicy <site_policy>
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.sp
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.IP require 12
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specifies that the X server \fImust\fP be configured with \fIat least one\fP
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of the corresponding site policies, else it must refuse the connection.
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.IP disallow 12
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specifies that the X server \fImust not\fP be configured with \fIany\fP of
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the corresponding site policies, else it must refuse the connection.
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.IP sitepolicy 12
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a required keyword
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.IP "<site_policy>" 12
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specifies the policy string. The string may contain any
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combination of alphanumeric characters subject
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only to interpretation by the target X server
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.PP
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.SH RULES FOR EVALUATING THE XFWP CONFIGURATION FILE ENTRIES
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For the first type of configurable authorization checking, access
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can be permitted or denied for each connection type based upon
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source and, optionally, destination and service. Each file entry must
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at a minimum specify the keyword ``permit'' or ``deny'' and the two
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source fields. The
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destination and service fields can be used to provide finer-grained
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access control if desired.
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.PP
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The algorithm for rule-matching is as follows:
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.PP
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.RS 3
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while (more entries to check)
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{
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if ((<originator IP> AND (NOT <src mask>)) == src)
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[if ((<dest X server IP> AND (NOT <dest mask>)) == dest)]
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[if (service fields present and matching)]
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do either permit or deny connection depending on keyword
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else
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continue
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}
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if (no rule matches)
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deny connection
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.RE
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.PP
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If a permit or deny rule does not specify a service and operation, then
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the rule applies to all services. If a configuration file is specified
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and it contains at least one valid deny or permit rule, then a host
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that is not explicitly permitted will be denied a connection.
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.PP
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Site policy configuration checking constitutes a separate (and X server
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only) authorization check on incoming connection requests. Any number of
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require or disallow rules may be specified, but all rules must be of the
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same type; that is, a single rule file cannot have both ``require'' and
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``disallow'' keywords. The algorithm for this check is as follows:
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.PP
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.RS 3
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if (X server recognizes any of the site policy strings)
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if (keyword == require)
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permit connection
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else
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deny connection
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else
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if (keyword == require)
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deny connection
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else
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permit connection
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.RE
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.PP
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The site policy check is performed by xfwp only if the source-destination
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rules permit the connection.
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.PP
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.SH
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EXAMPLES
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.PP
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.sp
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\fC
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.nf
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\&# if and only if server supports one of these policies then authorize
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\&# connections, but still subject to applicable rule matches
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\&#
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require sitepolicy policy1
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require sitepolicy policy2
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\&#
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\&# deny pm connections originating on 8.7.6.5 [NOTE: If pm service
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\&# is explicitly qualified, line must include destination fields as
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\&# shown.]
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\&#
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deny 8.7.6.5 0.0.0.0 0.0.0.0 255.255.255.255 eq pm
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\&#
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\&# permit xfindproxy X server connects to anywhere [NOTE: If
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\&# fp service is explicitly qualified, line must include source fields
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\&# as shown.]
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\&#
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permit 0.0.0.0 255.255.255.255 0.0.0.0 255.255.255.255 eq fp
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\&#
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\&# permit all connection types originating from the 192.0.0.0
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\&# IP domain only
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\&#
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permit 192.0.0.0 0.255.255.255
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.fi
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\fP
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.PP
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Care should be taken that source-destination rules are written in the correct
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order, as the first matching rule will be applied. In addition to parser
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syntax checking, a special command-line switch (-verify) has been provided
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to assist the sysadmin in determining which rule was actually matched.
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.PP
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.SH BUGS
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.PP
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Xfwp should check server site policy and security extension before
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allocating a listen port.
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.PP
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.SH SEE ALSO
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xfindproxy (1), Proxy Management Protocol spec V1.0, proxymngr(1), Xserver(1)
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.SH AUTHOR
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Reed Augliere, consulting to X Consortium, Inc.
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