'\" t
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.\" Modified for Solaris to to add the Solaris stability classification,
.\" and to add a note about source availability.
.\"
.TH TCPD 8 "Sep 15, 2011"
.SH NAME
tcpd \- access control facility for internet services
.SH DESCRIPTION
.PP
The \fItcpd\fR program can be set up to monitor incoming requests for
\fItelnet\fR, \fIfinger\fR, \fIftp\fR, \fIexec\fR, \fIrsh\fR,
\fIrlogin\fR, \fItftp\fR, \fItalk\fR, \fIcomsat\fR and other services
that have a one-to-one mapping onto executable files.
.PP
The program supports both 4.3BSD-style sockets and System V.4-style
TLI.  Functionality may be limited when the protocol underneath TLI is
not an internet protocol.
.PP
Operation is as follows: whenever a request for service arrives, the
\fIinetd\fP daemon is tricked into running the \fItcpd\fP program
instead of the desired server. \fItcpd\fP logs the request and does
some additional checks. When all is well, \fItcpd\fP runs the
appropriate server program and goes away.
.PP
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.
.SH LIBWRAP INTERFACE
The same monitoring and access control functionality provided by the
tcpd standalone program is also available through the libwrap shared
library interface. Some programs, including the Solaris inetd daemon,
have been modified  to use the libwrap interface and thus do not
require replacing the real server programs with tcpd. The libwrap
interface is also more efficient and can be used for inetd internal
services. See
.BR inetd (8)
for more information.
.SH LOGGING
Connections that are monitored by
.I tcpd
are reported through the \fIsyslog\fR(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.
.PP
In order to find out where your logs are going, examine the syslog
configuration file, usually /etc/syslog.conf.
.SH ACCESS CONTROL
Optionally,
.I 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
\fIhosts_access\fR(5) manual page.
.SH HOST NAME VERIFICATION
The authentication scheme of some protocols (\fIrlogin, rsh\fR) relies
on host names. Some implementations believe the host name that they get
from any random name server; other implementations are more careful but
use a flawed algorithm.
.PP
.I 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.  If any discrepancy is detected,
.I tcpd
concludes that it is dealing with a host that pretends to have someone
elses host name.
.PP
If the sources are compiled with -DPARANOID,
.I tcpd
will drop the connection in case of a host name/address mismatch.
Otherwise, the hostname can be matched with the \fIPARANOID\fR wildcard,
after which suitable action can be taken.
.SH HOST ADDRESS SPOOFING
Optionally,
.I 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 benefit from this protection. This feature must be turned on
at compile time.
.SH RFC 931
When RFC 931 etc. lookups are enabled (compile-time option) \fItcpd\fR
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.
.PP
Warning: If the local system runs an RFC 931 server it is important
that it be configured NOT to use TCP Wrappers, or that TCP Wrappers
be configured to avoid RFC 931-based access control for this service.
If you use usernames in the access control files, make sure that you
have a hosts.allow entry that allows the RFC 931 service (often called
"identd" or "auth") without any username restrictions. Failure to heed
this warning can result in two hosts getting in an endless loop of
consulting each other's identd services.
.SH EXAMPLES
.\" Begin Sun update
.SH ATTRIBUTES
See
.BR attributes (7)
for descriptions of the following attributes:
.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
=
Interface Stability	Committed
.TE
.\" End Sun update