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<META NAME="Author" Content="Steph Mineart">
<TITLE>Managing Multivendor Networks -- Ch 10 -- TCP/IP</TITLE>
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<FONT COLOR="#000077">Managing Multivendor Networks</FONT></H1>
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<H1><FONT COLOR="#000077">- 10 -<BR>
TCP/IP</FONT></H1>
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<UL>
<LI><A HREF="#Heading1">An Overview of TCP/IP</A>
<UL>
<LI><A HREF="#Heading2">A Brief History of TCP/IP</A>
<LI><A HREF="#Heading3">Core TCP/IP Protocols and Services</A>
<LI><A HREF="#Heading4">The TCP/IP Client/Server Model</A>
</UL>
<LI><A HREF="#Heading5">TCP/IP Host Name Resolution</A>
<UL>
<LI><A HREF="#Heading6">Informal and Formal Names</A>
<LI><A HREF="#Heading7">Making the Address Translation</A>
</UL>
<LI><A HREF="#Heading8">Name Servers</A>
<LI><A HREF="#Heading9">IP Address Construction</A>
<UL>
<LI><A HREF="#Heading10">Assigning IP Addresses</A>
<LI><A HREF="#Heading11">IP and MAC Addresses</A>
</UL>
<LI><A HREF="#Heading12">Combining Name and Address Resolution</A>
<LI><A HREF="#Heading13">IP Routing</A>
<LI><A HREF="#Heading14">Additional TCP/IP Protocols and Services</A>
<LI><A HREF="#Heading15">TCP/IP Drawbacks</A>
<LI><A HREF="#Heading16">Telnet and IBM Systems</A>
<UL>
<LI><A HREF="#Heading17">TN3270</A>
<LI><A HREF="#Heading18">TN5250</A>
</UL>
</UL>
<P>
<HR SIZE="4">
</P>
<H2><A NAME="Heading1"></A><FONT COLOR="#000077">An Overview of TCP/IP</FONT></H2>
<P>he TCP/IP network architecture distinctly influences how multiple vendor networks
are constructed and operated. The importance of TCP/IP in today's market is particularly
amazing when you consider that TCP/IP is a <I>public domain</I> architecture. Unlike
most private, commercially developed network architectures (for example, IBM's Systems
Network Architecture (SNA) or Digital's DECnet), TCP/IP was developed under the auspices
of the U.S. government. This development environment made TCP/IP an <I>open</I> network
because the TCP/IP architecture was not aligned with any particular vendor or machine
architecture.
<H3><A NAME="Heading2"></A><FONT COLOR="#000077">A Brief History of TCP/IP</FONT></H3>
<P>Just how did TCP/IP rise to such a level of importance? To fully understand this
you must go back to 1957--the year the Soviet Union launched Sputnik, the world's
first artificial satellite. When Sputnik went into orbit, President Eisenhower decided
that the United States needed to focus its efforts on meeting and exceeding Soviet
technology, so he created the <I>Advanced Research Projects Agency (ARPA).</I> The
purpose of ARPA was to conduct long-term research and development projects on behalf
of the U.S. government.</P>
<P>As the number of research projects handled by ARPA grew, so did the number of
researchers and sub-contractors, and the need to share resources. When computers
and computing devices became important research tools in the late 1960s, ARPA decided
to create a network that would enable ARPA researchers and sub-contractors to share
the growing number of computer systems. This network came to be known as <I>ARPANET.</I></P>
<P>Originally, ARPANET used packet-switching technology that was the precursor to
the X.25 standard for packet-switching networks. Simple tools were created and deployed
to allow terminal access, file transfer, and simple mail--these tools exist today
under TCP/IP as Telnet, File Transfer Protocol (FTP), and the Simple Mail Transfer
Protocol (SMTP).</P>
<P>ARPANET use continued to grow steadily through the 1960s and into the 1970s. In
the 70s, however, the fledgling networking industry was going through significant
technology and design changes. On the technology front, the Ethernet LAN hit the
market, offering new levels of performance for local connections. In the same timeframe,
the X.25 standard was approved by the CCITT, creating a universal standard for packet-switching
networks.</P>
<P>On the design front, Xerox released its Xerox Networking Services (XNS) architecture.
Although XNS was not a commercial success, it was a major influence on the design
and im-plementation of Novell NetWare and IBM/Microsoft's LAN Manager. However, Xerox
was not alone in developing and offering formal <I>network</I> <I>architectures</I>--IBM
released its System Network Architecture, and Digital Equipment Corporation introduced
its Digital Network Architecture (DNA), better known as DECnet.</P>
<P>Given this backdrop of new network links and architectures, ARPA decided to adopt
TCP/IP as the <I>standard</I> network architecture for the ARPANET. ARPA saw TCP/IP
as a tool that would enable them to quickly embrace new technology (like Ethernet
and X.25) as it became available. As a result of ARPA's interest and investment,
most of the major TCP/IP protocols were developed and deployed by the end of the
1970s.</P>
<P>The use of TCP/IP in ARPANET proved so successful that ARPA issued a directive
for all ARPANET hosts to use TCP/IP by the mid-1980s. This directive is a milestone
in the history of TCP/IP, because it insured that any computer manufacturer who wanted
to sell equipment to ARPA had to support TCP/IP, regardless of what their "native"
network architecture happened to be. So, thanks to the U.S. government, some level
of TCP/IP has been implemented in virtually every mainstream computer system.</P>
<P>As the use of ARPANET continued to grow and prosper, the network underwent dramatic
changes in the 1980s. President Reagan renamed ARPA to Defense Advanced Research
Projects Agency (DARPA) and thus ARPANET became DARPANET. Military agencies became
uncomfortable with the amount of non-military activity occurring over DARPANET and
so they split off and formed their own network, named MILNET.</P>
<P>The beginning of the end of DARPANET occurred when the National Science Foundation
(NSF) formed a separate network for science and academic research in 1985. The network,
NSFnet, was modeled after DARPANET, and in the spirit of sharing, the two networks
were interconnected. Over the course of the late 1980s, NSFnet absorbed DARPANET
and became what we now know as the Internet (but that's another story).</P>
<P>More importantly, although ARPANET never made it into the 1990s, the network architecture
it gave birth to--TCP/IP--lived on and prospered. For years, TCP/IP was the protocol
suite of choice for UNIX networks. Then, in the 1990s, almost all of the major computer
and network manufacturers followed suit and incorporated support for TCP/IP into
their products.</P>
<P>For example, Microsoft now looks at TCP/IP as its protocol of choice for NT networks,
and IBM has migrated a number of connectivity services from SNA to TCP/IP. In short,
TCP/IP has established itself as the premier protocol suite for many corporate networks.
<H3><A NAME="Heading3"></A><FONT COLOR="#000077">Core TCP/IP Protocols and Services</FONT></H3>
<P>The TCP/IP network architecture is named after its two core protocols--the Transmission
Control Protocol (TCP) and the Internet Protocol (IP). In truth, these two protocols
are only the tip of the iceberg--when you start digging into a TCP/IP network, you
typically encounter dozens of lower-level service and utility protocols. In this
chapter, you will review a number of these protocols, starting with the following
core TCP/IP protocols:
<UL>
<LI><I>The Internet Protocol (IP).</I> This protocol is responsible for the delivery
of messages between systems operating within the same network or operating in different
(but interconnected) networks. As part of this function, the Internet Protocol handles
all network-level addresses--for example, the Internet Protocol is ultimately responsible
for moving a message from a system at address "192.0.0.101" to a system
at address "192.0.0.102". (And that's also why these addresses are referred
to as <I>Internet addresses</I> or <I>IP addresses.</I>) The Internet Protocol is
a network-level protocol that acts as a carrier for transport-level protocols. The
two main protocols that operate at the transport level are TCP/IP and UDP.<BR>
<BR>
<LI><I>The Transmission Control Protocol (TCP/IP).</I> This is a connection-oriented
protocol that guarantees end-to-end delivery. TCP is used as the primary transport
for the majority of the TCP/IP utilities.<BR>
<BR>
<LI><I>The User Datagram Protocol (UDP).</I> This is a connectionless protocol that
does not guarantee end-to-end delivery. Because it is connectionless, UDP is faster
than TCP. UDP is typically used for real-time (client/server) program-to-program
applications or networking services that require the fastest possible response time.
</UL>
<P>TCP and UDP, in turn, carry application-oriented services (sometimes referred
to as <I>application protocols</I>). Although there are literally hundreds of services
that can run under the umbrella of TCP or UDP, the four major services are:
<UL>
<LI><I>Telnet.</I> This service provides a means for a TCP/IP workstation or a terminal
attached to a TCP/IP host to access a second host system. Telnet will be discussed
in more detail later in this chapter.<BR>
<BR>
<LI><I>The File Transfer Protocol (FTP).</I> This service enables the movement of
text and binary files between systems. FTP is a <I>bulk</I> file transfer service
that is unaware of field-level contents, although most FTP implementations have provisions
for ASCII/EBCDIC conversion. FTP can be used on an interactive or programmatic basis.<BR>
<BR>
<LI><I>The Simple Mail Transfer Protocol (SMTP).</I> This service handles the routing
of mail in a TCP/IP network. Note that SMTP is a delivery service that does not communicate
directly with end users. The end-user side of mail is handled by a front-end program
that deals with the user-oriented mail issues (that is, composing, reading, forward,
filing, and so on).<BR>
<BR>
<LI><I>The Simple Network Management Protocol (SNMP).</I> SNMP provides the framework
for systems to report problems, configuration information, and performance data to
a central network management location. Like SMTP, SNMP is not an end-user service--SNMP
reports its information to a central programs that analyzes the data and interacts
with an operator.
</UL>
<P>Figure 10.1 illustrates how these core protocols and services relate to one another.
And remember, these protocols and services are really just a sample of the entire
set of TCP/IP protocols and services. Later in this chapter we will look at additional
protocols and services commonly used in many TCP/IP networks.</P>
<P><A HREF="javascript:if(confirm('http://docs.rinet.ru:8080/MuNet/ch10/10fig01.gif \n\nThis file was not retrieved by Teleport Pro, because it was redirected to an invalid location. You should report this problem to the site\'s webmaster. \n\nDo you want to open it from the server?'))window.location='http://docs.rinet.ru:8080/MuNet/ch10/10fig01.gif'" tppabs="http://docs.rinet.ru:8080/MuNet/ch10/10fig01.gif"><B>FIG. 10.1</B></A> <I>Relationship of Core Protocols and
Services in a TCP/IP Architecture</I>
<H3><A NAME="Heading4"></A><FONT COLOR="#000077">The TCP/IP Client/Server Model</FONT></H3>
<P>Services such as Telnet, FTP, and SMTP follow the client/server model. This means
that a user initiating a service request uses client software and the request is
received by server software operating in the background of the target system. The
client/server model is certainly not new to the TCP/IP environment--in fact, the
entire architecture for TCP/IP is client/server oriented.</P>
<P>Under the TCP/IP client/server model, services are assigned <I>sockets</I>. Sockets
are logical ports associated with the TCP and UDP transport protocols. Programs can
attach to sockets in order to communicate with other partner programs. All of the
major TCP/IP protocols and applications services have defined socket numbers. For
example, Telnet uses TCP socket 23, FTP relies on TCP sockets 20 and 21, and SMTP
is assigned TCP socket 25.</P>
<P>When a client wants to establish a connection to its server counterpart, it initiates
either a TCP or UDP connection to the corresponding socket number on the target system.
For example, when you run the Telnet client and initiate a connection to a host,
the Telnet client requests a TCP connection to socket 23 on the target system. Figure
10.2 shows this basic connection architecture.</P>
<P><A HREF="javascript:if(confirm('http://docs.rinet.ru:8080/MuNet/ch10/10fig02.gif \n\nThis file was not retrieved by Teleport Pro, because it was redirected to an invalid location. You should report this problem to the site\'s webmaster. \n\nDo you want to open it from the server?'))window.location='http://docs.rinet.ru:8080/MuNet/ch10/10fig02.gif'" tppabs="http://docs.rinet.ru:8080/MuNet/ch10/10fig02.gif"><B>FIG. 10.2</B></A> <I>Basic Connection Architecture in
a TCP/IP Client/Server Model</I></P>
<P>On the other side of the equation, when the server system receives a socket connection,
it normally starts a new copy of the server program to handle the new client connection.
The client and server then establish a new socket assignment they can use for the
duration of the connection. This approach enables multiple client/server conversations
to use the same socket number to initiate connections.</P>
<P>After the client and server programs have established a link to one another, they
can start interacting. In many cases, the initial interaction often involves <I>negotiation</I>
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