This manual provides an introductory overview of TCP/IP networking and
internets, and describes OpenVMS DCL support for TCP/IP capabilities.
Revision/Update Information:
This manual supersedes TCP/IP Networking on OpenVMS Systems, Version 6.2.
Software Version:
OpenVMS Alpha Version 7.1 OpenVMS VAX Version 7.1
Digital Equipment Corporation Maynard, Massachusetts
November 1996
Digital Equipment Corporation makes no representations that the use of
its products in the manner described in this publication will not
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contained in this publication imply the granting of licenses to make,
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Possession, use, or copying of the software described in this
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The following are trademarks of Digital Equipment Corporation: Alpha,
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VMS, VT100, VT300, and the DIGITAL logo.
The following are third-party trademarks:
AppleTalk and Macintosh are registered trademarks of Apple Computer,
Inc.
BSD is a trademark of the University of California, Berkeley, CA.
IBM is a registered trademark of International Business Machines, Inc.
MultiNet is a registered trademark of TGV, Inc.
NetWare is a registered trademark of Novell, Inc.
NFS is a registered trademark of Sun Microsystems, Inc.
PathWay is a trademark of The Wollongong Group, Inc.
TCPware is a registered trademark of Process Software Corporation.
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All other trademarks and registered trademarks are the property of
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ZK6436
The OpenVMS documentation set is available on CD-ROM.
This document was prepared using VAX DOCUMENT, Version V3.2m.
This manual is intended for anyone who is interested in using TCP/IP
networking on either the OpenVMS Alpha or the OpenVMS VAX operating
system.
Readers may be new to networking or may be familiar with the
traditional DECnet networking interface on OpenVMS systems.
Document Structure
This manual contains the following chapters:
Chapter 1 introduces TCP/IP networking, internetworking, and the
Internet.
Chapter 2 summarizes TCP/IP networking architecture, layers,
protocols, and addressing.
Chapter 3 describes common TCP/IP applications that perform
general network operations. The chapter also describes Internet
information retrieval tools.
Chapter 4 discusses mapping UNIX identification codes to OpenVMS
user names in TCP/IP applications.
Chapter 5 specifies the reference format of OpenVMS DCL commands
that can be used to invoke TCP/IP capabilities provided by layered
product software running on OpenVMS systems.
Chapter 6 describes the Point-to-Point Protocol utility (PPPD)
commands used to establish and manage PPP connections.
Appendix A lists vendors and the software products they supply for
TCP/IP networking services to OpenVMS systems. These products run as
layered software on the OpenVMS operating system.
Refer to the following documents for more information about TCP/IP
software features supported by OpenVMS.
OpenVMS DCL Dictionary
OpenVMS Version 7.1 Release Notes
See the appropriate vendor documentation for information about each of
the layered TCP/IP software products that run on OpenVMS systems. These
TCP/IP products are listed in Appendix A.
For additional information on the Open Systems Software Group (OSSG)
products and services, access the Digital OpenVMS World Wide Web site.
Use the following URL:
http://www.openvms.digital.com
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Conventions
The name of the OpenVMS AXP operating system has been changed to the
OpenVMS Alpha operating system. Any references to OpenVMS AXP or AXP
are synonymous with OpenVMS Alpha or Alpha.
The following conventions are also used in this manual:
( )
In command format descriptions, parentheses indicate that, if you
choose more than one option, you must enclose the choices in
parentheses.
[ ]
In command format descriptions, brackets indicate optional elements.
You can choose one, none, or all of the options. (Brackets are not
optional, however, in the syntax of a directory name in an OpenVMS file
specification or in the syntax of a substring specification in an
assignment statement.)
{ }
In command format descriptions, braces indicate a required choice of
options; you must choose one of the options listed.
text style
This text style represents the introduction of a new term or the name
of an argument, an attribute, or a reason.
This style is also used to show user input in Bookreader versions
of the manual.
italic text
Italic text indicates important information, complete titles of
manuals, or variables. Variables include information that varies in
system output (Internal error
number), in command lines (/PRODUCER=
name), and in command parameters in text (where
device-name contains up to five alphanumeric characters).
UPPERCASE TEXT
Uppercase text indicates a command, the name of a routine, the name of
a file, or the abbreviation for a system privilege.
Monospace type
Monospace type indicates code examples and interactive screen displays.
In the C programming language, monospace type in text identifies the
following elements: keywords, the names of independently compiled
external functions and files, syntax summaries, and references to
variables or identifiers introduced in an example.
-
A hyphen at the end of a command format description, command line, or
code line indicates that the command or statement continues on the
following line.
numbers
All numbers in text are assumed to be decimal unless otherwise noted.
Nondecimal radixes---binary, octal, or hexadecimal---are explicitly
indicated.
An increasingly important aspect of using computers is the capability
to communicate over open networks.
Computer systems of similar or different design should be able to
communicate with each other. In addition, various physical networks
must be interconnected to form large networks called
internets.
This chapter describes how Transmission Control Protocol/Internet
Protocol (TCP/IP) networking meets these needs and how OpenVMS systems
support TCP/IP networking.
The chapter also describes how TCP/IP internetworking capabilities have
made possible the global Internet, an openly accessible, worldwide
research and commercial network.
This section introduces the primary concepts and features that
characterize TCP/IP networking and summarizes networking capabilities
available on OpenVMS systems.
A network consists of two or more computer systems linked by
communications software and hardware for the purpose of exchanging
information and sharing resources. Data originated on one system can be
routed through the network until it reaches its destination on another
system. The design of communications software that supports the flow of
information is based on networking protocols: services
and rules for exchanging information between systems.
One of the most widely used networking software packages is TCP/IP. It
is a common set, or "suite," of protocols that work together
to provide the services necessary to interconnect computer systems and
to interconnect networks. TCP/IP was designed to permit connection of
computer systems of dissimilar design.
TCP/IP application programs allow users to interact with remote
processors. TCP/IP can also be used to communicate across many
interconnected networks.
The main characteristics of TCP/IP are openness, interoperability, and
distributed client/server design.
The TCP/IP suite of protocols implements open networking standards that
support open system interconnection. An open system is one for which
the specifications are available to the public. Open specifications do
not rely on a particular technology or product. They allow users to
determine what open systems and other capabilities the user needs.
TCP/IP technology, which accommodates a variety of underlying network
technologies, permits connection of multiple kinds of computers in an
open network environment. See Section 2.1 for a comparison of TCP/IP
architecture with the Open Systems Interconnection (OSI) model.
In a TCP/IP networking environment multiple systems from various
vendors can work together, share data, and integrate applications. A
TCP/IP internet is useful for running application programs that carry
out tasks such as accessing remote resources. These applications can
interoperate with different applications running on other systems that
support TCP/IP standards. A user does not need to know about TCP/IP
software or data paths in order to run the applications. See
Chapter 3 for information about commonly used TCP/IP applications.
TCP/IP software supports the use of client/server configurations in a
distributed networking environment. A distributed system stores data
and information on many computers, instead of on just one computer.
In the client/server model, two software programs running on separate
computers work together: one program, called the
client, makes use of resources supplied by the other
program, called the server. A server can receive a
request from a client anywhere in a TCP/IP network, accept the request,
and return the results or data to the client. Server programs are
application-level programs that can execute on one or more machines of
any size, including PCs, in a TCP/IP network.
One example of a client/server model is a bank clerk who uses client
software running on a PC to enter deposit information about a
customer's account. The server software, running on the computer at the
bank's main branch, processes the request about the customer account
and returns the customer's balance to the client software. Chapter 3
describes commonly used TCP/IP applications that implement the
client/server model.
No single vendor or organization owns TCP/IP technologies. The Internet
Architecture Board (IAB) currently oversees the TCP/IP standards. This
group assigns network addresses and specifies the protocols that can be
used on the Internet.
The Internet is based on numerous protocols and conventions. Each
protocol is explained in a technical publication called a
Request for Comment or RFC. RFCs are the working
documents that the Internet community uses to develop and record
technical information. RFCs document work on the Internet, proposals
for new or revised protocols, and the TCP/IP protocol standards. The
RFCs are numbered sequentially in the order in which they are written.
Each new or revised RFC is given a new number; an index is available to
help identify the latest version of a document. RFCs are publicly
available and are stored electronically at many Internet computer sites.
As an example, TCP/IP protocols and additional services are implemented
in the UNIX operating system available in the University of
California's Berkeley Software Distribution (BSD). The
BSD UNIX software supports basic TCP/IP protocols and also supplies a
set of utilities for network services in addition to the standard
TCP/IP application programs. The Berkeley R commands and services are a
set of client and server facilities that allow you to access remote
resources in a TCP/IP network. Examples are the rlogin
and rcp commands described in Chapter 3.
Each end system connected to a TCP/IP network is called a
host. Each host has a unique name and address. The
local host is the system you are using, and the remote host is the
system with which you are communicating.
Hosts are connected by lines that carry information
between the hosts. The line is the physical path over which data can
pass from one host to another. (Examples of lines are telephone lines,
fiber-optic cables, and satellites.)
A TCP/IP network is called a packet-switching network. Information is
transmitted in small packets of data rather than as a continuous stream
from host to host. For example, a file to be transmitted from one host
to another is divided into many small packets that are sent across the
network one at a time. Each packet contains information about the
address of the destination host. At the destination, the packets are
reassembled.
The packets that comprise the network traffic are combined
(multiplexed) onto high-capacity machine interconnections for
transmission across the network or internet. Because packets from
different sources are mixed together, many users can use the same line
simultaneously. Individual packets can take different paths to the
destination.
The basic unit of data transmitted by TCP/IP is called a
datagram.
The process of directing a data message from a source host to a
destination host is called routing. For hosts not
directly connected to each other, data can be forwarded from the source
to the destination through intervening hosts.
TCP/IP protocols are able to accommodate almost all underlying network
hardware technologies. TCP/IP hosts can be connected to a local area
network (LAN) or wide area network (WAN). A LAN is a network of systems
in a specific geographic area, while a WAN allows long-distance
communication. LAN interconnects include Ethernet cables, FDDI
fiber-optic interconnects, and token ring networks. Hosts on a WAN
connect through leased lines such as the U.S. telephone system or X.25
packet-switching data networks. Both LANs and WANs can be integrated in
a single network.
Two or more networks can be interconnected using gateways to form an
internet, as illustrated in Figure 1-1. A gateway is
a computer that is connected to two networks and routes packets from
one to the other.
TCP/IP gateways route traffic from one physical network to another
network, not to a destination host.
Figure 1-1 Two Networks Connected Through a TCP/IP
Gateway
TCP/IP application programs permit users to access remote resources
over the network, as described in Chapter 3. A user at a TCP/IP host
can connect to a remote host and establish an interactive session.
Users can also transfer large quantities of data from remote hosts
(such as file servers). Another significant service is the TCP/IP mail
system, which allows users to send and receive electronic mail.
Computer systems often contain sensitive data and critical processes
that require protection from intruders. A firewall can
be used to isolate a few critical systems or an entire internal network
from the external world. A firewall system works by replacing an IP
router with a host that does not forward packets, effectively severing
the connection between networks.
The firewall host employs very strict security practices that resist
any break-in attempts from intruders. The firewall system also provides:
Limited name service for the outside world. It does not provide
name or address information about any internal host.
E-mail forwarding by means of an alias to obscure the user's actual
login name.
File transfer and remote terminal services. Users must log in to a
carefully designed and restricted user account shared by all internal
users.
OpenVMS systems support optional layered networking software products
that permit users to communicate with other Digital systems and with
non Digital systems in open, worldwide networks.
Examples of layered networking software that can run concurrently on an
OpenVMS system include TCP/IP networking products, DECnet-Plus
software, and PATHWORKS software (supporting a broad range of network
transports such as TCP/IP, DECnet, NetWare, and AppleTalk).
OpenVMS systems running TCP/IP layered products support TCP/IP
connections to UNIX and other systems in open networking environments.
The TCP/IP layered products enable OpenVMS users to perform the
following operations:
Invoke the TCP/IP layered products, using UNIX style commands.
Invoke the TCP/IP layered products, using OpenVMS style commands.
Connect to the global Internet
Chapter 5 specifies DCL commands that support TCP/IP parameters and
qualifiers. Appendix A lists TCP/IP layered products that run on
OpenVMS systems. Other layered networking products can run concurrently
with TCP/IP on OpenVMS systems to communicate with OpenVMS, other
Digital systems, and systems supplied by other vendors.
In addition, TCP/IP, DECnet, NetWare, and AppleTalk network transports
permit OpenVMS servers to communicate with personal computer and
Macintosh clients in PATHWORKS environments.
Figure 1-2 shows an example of an open, multiprotocol network that
includes OpenVMS systems, Digital UNIX systems, and TCP/IP networking
software provided by other vendors. Wide area multiprotocol routers
connect the separate LANs into a single network. A corporate gateway,
running TCP/IP networking software, interconnects this network with the
global Internet.
TCP/IP protocols provide for the interconnection of networks and the
interconnection of computing systems in a network. This section
describes how TCP/IP protocols evolved to support interconnection of
networks, including the global Internet.
The technology called internetworking makes possible
the interconnection of multiple diverse networks into a coordinated
whole.
Internetworking adds physical connections and a new set of conventions
to permit networks with different underlying hardware technologies to
form an internet.
An internet is a collection of packet-switching networks interconnected
by either gateways or routers; an internet supports protocols that
permit the diverse networks to function as a large, virtual network.
The largest internet, the global network formed by research,
commercial, and governmental organizations, is referred to as the
Internet.
TCP/IP was developed as a result of research funded by the Defense
Advanced Research Projects Agency (DARPA), an agency of the U.S.
Department of Defense. The need to connect many computers with
different hardware, operating systems, and networking technologies led
to the development of the ARPANET, on which TCP/IP was first
implemented.
DARPA also made the TCP/IP implementation available to university
researchers for use with UNIX operating systems.
The growing diversity of new networking technologies caused DARPA to
study network connectivity, or internetworking. By 1983, the Department
of Defense mandated that all computers connected to long-haul networks
use TCP/IP. The success of the TCP/IP technology and internetworking
has resulted in the enormous growth of the global Internet (see
Section 1.2.3).
TCP/IP is widely used within organizations or industries to create
internets that may or may not be connected to the global Internet.
TCP/IP capabilities include the following:
Connect different types of computers (for example, connect an
OpenVMS system to a UNIX system)
Connect hosts at widely separated locations
Connect two or more networks of different hardware architecture
Connect a host or internet to the global Internet
Share resources such as files across networks or internets
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