# 2.11BSD#431 - /usr/man/cat8/tcpd.0

    TCPD(8)             UNIX Programmer's Manual		  TCPD(8)

    NAME
         tcpd - access control facility for internet services

    DESCRIPTION
         The tcpd program can be set up to monitor incoming requests
         for telnet, finger, ftp, exec, rsh, rlogin, tftp, talk, com-
         sat and other services that have a one-to-one mapping onto
         executable files.

         The program supports both 4.3BSD-style sockets and System
         V.4-style TLI.  Functionality may be limited when the proto-
         col underneath TLI is not an internet protocol.

         Operation is as follows: whenever a request for service
         arrives, the inetd daemon is tricked into running the tcpd
         program instead of the desired server. tcpd logs the request
         and does some additional checks. When all is well, tcpd runs
         the appropriate server program and goes away.

         Optional features are: pattern-based access control, client
         username lookups with the RFC 931 etc. protocol, protection
         against hosts that pretend to have someone elses host name,
         and protection against hosts that pretend to have someone
         elses network address.

    LOGGING
         Connections that are monitored by tcpd are reported through
         the syslog(3) facility. Each record contains a time stamp,
         the client host name and the name of the requested service.
         The information can be useful to detect unwanted activities,
         especially when logfile information from several hosts is
         merged.

         In order to find out where your logs are going, examine the
         syslog configuration file, usually /etc/syslog.conf.

    ACCESS CONTROL
         Optionally, tcpd supports a simple form of access control
         that is based on pattern matching.  The access-control
         software provides hooks for the execution of shell commands
         when a pattern fires.  For details, see the hosts_access(5)
         manual page.

    HOST NAME VERIFICATION
         The authentication scheme of some protocols (rlogin, rsh)
         relies on host names. Some implementations believe the host
         name that they get from any random name server; other imple-
         mentations are more careful but use a flawed algorithm.

         tcpd verifies the client host name that is returned by the
         address->name DNS server by looking at the host name and
         address that are returned by the name->address DNS server.

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    TCPD(8)             UNIX Programmer's Manual		  TCPD(8)

         If any discrepancy is detected, tcpd concludes that it is
         dealing with a host that pretends to have someone elses host
         name.

         If the sources are compiled with -DPARANOID, tcpd will drop
         the connection in case of a host name/address mismatch.
         Otherwise, the hostname can be matched with the PARANOID
         wildcard, after which suitable action can be taken.

    HOST ADDRESS SPOOFING
         Optionally, tcpd disables source-routing socket options on
         every connection that it deals with. This will take care of
         most attacks from hosts that pretend to have an address that
         belongs to someone elses network. UDP services do not bene-
         fit from this protection. This feature must be turned on at
         compile time.

    RFC 931
         When RFC 931 etc. lookups are enabled (compile-time option)
         tcpd will attempt to establish the name of the client user.
         This will succeed only if the client host runs an RFC 931-
         compliant daemon.	Client user name lookups will not work
         for datagram-oriented connections, and may cause noticeable
         delays in the case of connections from PCs.

    EXAMPLES
         The details of using tcpd depend on pathname information
         that was compiled into the program.

    EXAMPLE 1
         This example applies when tcpd expects that the original
         network daemons will be moved to an "other" place.

         In order to monitor access to the finger service, move the
         original finger daemon to the "other" place and install tcpd
         in the place of the original finger daemon. No changes are
         required to configuration files.

    	  # mkdir /other/place
    	  # mv /usr/etc/in.fingerd /other/place
    	  # cp tcpd /usr/etc/in.fingerd

         The example assumes that the network daemons live in
         /usr/etc. On some systems, network daemons live in /usr/sbin
         or in /usr/libexec, or have no `in.' prefix to their name.

    EXAMPLE 2
         This example applies when tcpd expects that the network dae-
         mons are left in their original place.

         In order to monitor access to the finger service, perform
         the following edits on the inetd configuration file (usually

    Printed 11/24/99						2

    TCPD(8)             UNIX Programmer's Manual		  TCPD(8)

         /etc/inetd.conf or /etc/inet/inetd.conf):

    	  finger  stream  tcp  nowait  nobody  /usr/etc/in.fingerd  in.fingerd

         becomes:

    	  finger  stream  tcp  nowait  nobody  /some/where/tcpd     in.fingerd

         The example assumes that the network daemons live in
         /usr/etc. On some systems, network daemons live in /usr/sbin
         or in /usr/libexec, the daemons have no `in.' prefix to
         their name, or there is no userid field in the inetd confi-
         guration file.

         Similar changes will be needed for the other services that
         are to be covered by tcpd.  Send a `kill -HUP' to the
         inetd(8) process to make the changes effective.

    EXAMPLE 3
         In the case of daemons that do not live in a common direc-
         tory ("secret" or otherwise), edit the inetd configuration
         file so that it specifies an absolute path name for the pro-
         cess name field. For example:

    	 ntalk	dgram  udp  wait  root	/some/where/tcpd  /usr/local/lib/ntalkd

         Only the last component (ntalkd) of the pathname will be
         used for access control and logging.

    BUGS
         Some UDP (and RPC) daemons linger around for a while after
         they have finished their work, in case another request comes
         in.  In the inetd configuration file these services are
         registered with the wait option. Only the request that
         started such a daemon will be logged.

         The program does not work with RPC services over TCP. These
         services are registered as rpc/tcp in the inetd configura-
         tion file. The only non-trivial service that is affected by
         this limitation is rexd, which is used by the on(1) command.
         This is no great loss.  On most systems, rexd is less secure
         than a wildcard in /etc/hosts.equiv.

         RPC broadcast requests (for example: rwall, rup, rusers)
         always appear to come from the responding host. What happens
         is that the client broadcasts the request to all portmap
         daemons on its network; each portmap daemon forwards the
         request to a local daemon. As far as the rwall etc.  daemons
         know, the request comes from the local host.

    Printed 11/24/99						3

    TCPD(8)             UNIX Programmer's Manual		  TCPD(8)

    FILES
         The default locations of the host access control tables are:

         /etc/hosts.allow
         /etc/hosts.deny

    SEE ALSO
         hosts_access(5), format of the tcpd access control tables.
         syslog.conf(5), format of the syslogd control file.
         inetd.conf(5), format of the inetd control file.

    AUTHORS
         Wietse Venema (wietse@wzv.win.tue.nl),
         Department of Mathematics and Computing Science,
         Eindhoven University of Technology
         Den Dolech 2, P.O. Box 513,
         5600 MB Eindhoven, The Netherlands

    Printed 11/24/99						4

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