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XFWP(1) 										  XFWP(1)

       xfwp - X firewall proxy

       xfwp [option ...]

       The command line options that can be specified are:

       -cdt num_secs
	       Used  to  override the default time-to-close (604800 seconds) for xfwp client data
	       connections on which there is no activity (connections over which  X  protocol  is
	       already being relayed by xfwp)

       -clt num_secs
	       Used  to override the default time-to-close (86400 seconds) for xfwp client listen
	       ports (ports on xfwp to which X clients first connect when trying to  reach  an	X

       -pdt num_secs
	       Used  to  override the default time-to-close (3600 seconds) for Proxy Manager con-
	       nections on which there is no activity

       -config file_name
	       Used to specify the configuration the name of the configuration file

       -pmport port_number
	       Used to override the default port address (4444) for proxy manager connections

       -verify Used to display the configuration file rule that was  actually  matched	for  each
	       service request

       -logfile file_name
	       Used  to specify the name of a file where audit information should be logged.  The
	       format of a logged entry is: time of day; event code; source IP address;  destina-
	       tion  IP  address;  and configuration rule number.  The event codes are: "0" for a
	       successful connection; "1" if a connection is denied because  of  a  configuration
	       rule;  and  "2" if a connection is denied because of an authorization failure.  If
	       the event code is "1", and a configuration file is used,  the  configuration  rule
	       number  is the line number of the configuration file where the match was made (see
	       the section CONFIGURATION FILE for more information).  If the event  code  is  not
	       "1", or if no configuration file is used, the configuration rule number is "-1".

       -loglevel {0,1}
	       Used  to  specify  the  amount of audit detail that should be logged.  If "0", all
	       connections are logged.	If "1", only unsuccessful connections are logged.

       -max_pm_conns num_connections
	       Used to specify the maximum number of Proxy Manager connections.  The  default  is

       -max_pm_conns num_connections
	       Used to specify the maximum number of X server connections.  The default is 100.

       The  X  firewall  proxy	(xfwp) is an application layer gateway proxy that may be run on a
       network firewall host to forward X traffic across the firewall.	Used in conjunction  with
       the  X server Security extension and authorization checking, xfwp constitutes a safe, sim-
       ple, and reliable mechanism both to hide  the  addresses  of  X	servers  located  on  the
       Intranet  and to enforce a server connection policy.  Xfwp cannot protect against mischief
       originating on the Intranet; however, when properly configured it can guarantee that  only
       trusted	clients originating on authorized external Internet hosts will be allowed inbound
       access to local X servers.

       To use xfwp there must be an X proxy manager running in the local  environment  which  has
       been  configured  at start-up to know the location of the xfwp.	[NOTE:	There may be more
       than one xfwp running in a local environment; see notes below on load balancing	for  fur-
       ther  discussion.]   Using  the	xfindproxy utility (which relays its requests through the
       proxy manager) a user asks xfwp to allocate a  client  listen  port  for  a  particular	X
       server,	which  is  internally  associated  with  all  future connection requests for that
       server.	This client listen port address is returned by the proxy manager  through  xfind-
       proxy.	The  xfwp  hostname  and  port number is then passed out-of-band (i.e., via a Web
       browser) to some remote X client, which will subsequently connect to xfwp  instead  of  to
       the target X server.

       When  an  X client connection request appears on one of xfwp's listen ports, xfwp connects
       to the X server associated with this listen port and performs authorization checks against
       the  server  as	well  as  against its own configurable access control list for requesting
       clients.  If these checks fail, or if the requested server does not support the X Security
       Extension,  the	client	connection is refused.	Otherwise, the connection is accepted and
       all ensuing data between client and server is relayed by xfwp until the client  terminates
       the connection or, in the case of an inactive client, until a configured timeout period is
       exceeded.  Xfwp is designed to block  while  waiting  for  activity  on	its  connections,
       thereby minimizing demand for system cycles.

       If  xfwp is run without a configuration file and thus no sitepolicy is defined, if xfwp is
       using an X server where xhost + has been run to turn off host-based authorization  checks,
       when  a client tries to connect to this X server via xfwp, the X server will deny the con-
       nection.  If xfwp does not define a sitepolicy, host-based authorization must be turned on
       for clients to connect to an X server via the xfwp.

       The  whole  purpose  of	the xfwp is to provide reliable control over access to Intranet X
       servers by clients originating outside the firewall.  At the  present  time,  such  access
       control is typically achieved by firewall configurations incorporating IP packet-filtering
       routers.  Frequently, the rules for such filters deny access to X server ports (range 6000
       - 6xxx) for all Intranet host machines.

       In  order  for  xfwp  to  do its job, restrictions on access for ports 6001 - 6xxx must be
       removed from the rule-base of the IP packet-filtering router.  [NOTE:  xfwp  only  assigns
       ports in the range beginning with 6001; access to port 6000 on all Intranet hosts may con-
       tinue to be denied.]  This does not mean the Intranet firewall will be opened  for  indis-
       criminate  entry  by  X	clients.   Instead, xfwp supports a fully configurable rule-based
       access control system, similar to that of the IP packet-filter  router  itself.	 Xfwp  in
       effect  adds  another  level  of  packet-filtering control which is fully configurable and
       applies specifically to X traffic.  See section entitled CONFIGURATION  FILE,  below,  for
       further details.

       Xfwp  is  typically  run as a background process on the Intranet firewall host.	It can be
       launched using any of the command-line options described  above.   As  noted  above,  xfwp
       works  only  in conjunction with proxy manager and the xfindproxy utility.  It can also be
       configured to support a user-defined X server site security policy, in which the X  server
       is required to indicate to xfwp whether or not it supports the particular policy.  Consult
       the X server man pages for further information on these components.  Xfwp diagnostics  can
       be  turned  on by compiling with the -DDEBUG switch.  Connection status can be recorded by
       using the -logfile and -loglevel command line options.

       Xfwp manages four different kinds of connections:  proxy manager (PM) data, X client  lis-
       ten,  X	client	data,  and X server.  The sysadmin employing xfwp must understand how the
       resources for each of these connection types are allocated and reclaimed by xfwp in  order
       to optimize the availability of xfwp service.

       Each  connection-type has a default number of allocation slots and a default timeout.  The
       number of allocation slots for PM connections and X server connections is configurable via
       command line options.  Connection timeouts are also configurable via command line options.
       Each connection timeout represents the period the connection will  be  allowed  to  remain
       open  in  the absence of any activity on that connection.  Whenever there is activity on a
       connection, the time-to-close is automatically reset.  The default distribution	of  total
       process	connection  slots  across  the	four  connection  types, as well as the choice of
       default timeouts for the connection types, is governed by a number of assumptions embedded
       in the xfwp use model.

       The  default number of PM connections is 10 and the default duration for PM connections is
       3,600 seconds (1 hour) for each connection after time of last activity.	At start-up, xfwp
       listens for PM connection requests on any non-reserved port (default of 4444 if not speci-
       fied on the xfwp command-line).	The PM normally connects to xfwp only when a call is made
       to  the	PM with xfindproxy.  Thereafter, the PM remains connected to xfwp, even after the
       messaging between them has been completed, for the default connection duration period.  In
       some cases this may result in depletion of available PM connection slots.  If the sysadmin
       expects connections to a single xfwp from many PM's, xfwp should be started using the -pdt
       command	line  option,  with a timeout value reflecting the desired duration that inactive
       connections will be permitted to remain open.

       Xfwp client listeners are set up by a call to xfindproxy and  continue  to  listen  for	X
       client  connection  requests  for a default duration of 86,400 seconds (24 hours) from the
       point of last activity.	After this time they are  automatically  closed  and  their  fd's
       recovered  for future allocation.  In addressing the question of how to choose some alter-
       native timeout value which will guarantee the availability of client listen ports,  sysad-
       mins  should take into consideration the expected delay between the time when the listener
       was allocated (using xfindproxy) and the time when a client actually attempts  to  connect
       to  xfwp,  as  well the likelihood that client listeners will be re-used after the initial
       client data connection is closed.

       Each client connection is allocated a default lifetime of 604,800 seconds (7 *  24  hours)
       from  the point when it last saw activity.  After this time it is automatically closed and
       its fd's recovered for future allocation.  Because server  connections  are  not  actually
       established until a connection request from a remote X client arrives at one of the xfwp's
       client listen ports, the client data timeout applies both to  client-xfwp  connections  as
       well  as to xfwp-server connections.  If the system administrator expects many client data
       connections through xfwp, an overriding of the default timeout should be considered.

       The xfwp configuration file resides on the xfwp host machine  and  is  used  to	determine
       whether	X  client  data connection requests will be permitted or denied.  The path to the
       file is specified at start-up time.  If no configuration file is specified, all	X  client
       data  connection  requests routed through xfwp will be by default permitted, assuming that
       other X server authorization checks are successful.  If a configuration file  is  supplied
       but  none  of its entries matches the connection request then the connection is by default

       If a line in the configuration file begins with the '#' character or a new-line character,
       the line is ignored and the evaluator will skip the line.

       The  configuration file supports two entirely independent authorization checks:	one which
       is performed by xfwp itself, and a second which is the result of xfwp's querying the  tar-
       get  X server.  For the first of these, the configuration file employs a syntax and seman-
       tic similar to that of IP packet-filtering routers.  It contains zero or more  source-des-
       tination rules of the following form:

       {permit | deny} <src> <src mask> [<dest> <dest mask> [<operator> <service>]]

       permit/deny the	keywords  ``permit'' or ``deny'' indicate whether the rule will enable or
		   disable access, respectively

       src	   the IP address against the host who originated the connection request will  be
		   matched, expressed in IP format (x.x.x.x)

       src mask    a  subnet  mask,  also  in  IP format, for further qualifying the source mask.
		   Bits set in the mask indicate bits of the incoming address to be ignored  when
		   comparing to the specified src

       dest	   the	IP  address  against  which  the  destination  of the incoming connection
		   request (i.e. the host IP of the X server to  which	the  incoming  client  is
		   attempting to connect) will be matched

       dest mask   a subnet mask, also in IP format, for further qualifying the destination mask.
		   Bits set in the mask indicate bits of the destination address  to  be  ignored
		   when comparing to the specified dest

       operator    always ``eq'' (if the service field is not NULL)

       service	   one	of the following three strings:  ``pm'', ``fp'', or ``cd'', corresponding
		   to proxy manager, xfindproxy, or client data, respectively

       For the second type of authorization check, the configuration file contains zero  or  more
       site policy rules of the following form:

       {require | disallow} sitepolicy <site_policy>

       require	   specifies that the X server must be configured with at least one of the corre-
		   sponding site policies, else it must refuse the connection.

       disallow    specifies that the X server must not be configured with any of the correspond-
		   ing site policies, else it must refuse the connection.

       sitepolicy  a required keyword

		   specifies  the  policy  string.   The  string  may  contain any combination of
		   alphanumeric characters subject only to interpretation by the target X server

       For the first type of configurable authorization checking,  access  can	be  permitted  or
       denied  for  each  connection type based upon source and, optionally, destination and ser-
       vice.  Each file entry must at a minimum specify the keyword ``permit''	or  ``deny''  and
       the  two  source fields.  The destination and service fields can be used to provide finer-
       grained access control if desired.

       The algorithm for rule-matching is as follows:

	    while (more entries to check)
	      if ((<originator IP> AND (NOT <src mask>)) == src)
		[if ((<dest X server IP> AND (NOT <dest mask>)) == dest)]
		  [if (service fields present and matching)]
		    do either permit or deny connection depending on keyword
	    if (no rule matches)
	      deny connection

       If a permit or deny rule does not specify a service and operation, then the  rule  applies
       to  all services.  If a configuration file is specified and it contains at least one valid
       deny or permit rule, then a host that is not explicitly permitted will be denied a connec-

       Site  policy  configuration checking constitutes a separate (and X server only) authoriza-
       tion check on incoming connection requests.  Any number of require or disallow  rules  may
       be  specified,  but all rules must be of the same type; that is, a single rule file cannot
       have both ``require'' and ``disallow'' keywords.  The algorithm for this check is as  fol-

	    if (X server recognizes any of the site policy strings)
	      if (keyword == require)
		permit connection
		deny connection
	      if (keyword == require)
		deny connection
		permit connection

       The site policy check is performed by xfwp only if the source-destination rules permit the


       # if and only if server supports one of these policies then authorize
       # connections, but still subject to applicable rule matches
       require sitepolicy policy1
       require sitepolicy policy2
       # deny pm connections originating on [NOTE:  If pm service
       # is explicitly qualified, line must include destination fields as
       # shown.]
       deny  eq  pm
       # permit xfindproxy X server connects to anywhere [NOTE:  If
       # fp service is explicitly qualified, line must include source fields
       # as shown.]
       permit  eq	fp
       # permit all connection types originating from the
       # IP domain only

       Care should be taken that source-destination rules are written in the  correct  order,  as
       the first matching rule will be applied.  In addition to parser syntax checking, a special
       command-line switch (-verify) has been provided to  assist  the	sysadmin  in  determining
       which rule was actually matched.

       Xfwp  should  check  server  site policy and security extension before allocating a listen

       xfindproxy (1), Proxy Management Protocol spec V1.0, proxymngr(1), Xserver(1)

       Reed Augliere, consulting to X Consortium, Inc.

X Version 11				    xfwp 1.0.1					  XFWP(1)
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