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<td bgcolor="#336666"><b><font face="Arial" size="2" color="#FFFFFF">6.1</b></font></td>
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<td bgcolor="#336666" width="100%"><b><font face="Arial" size="2" color="#FFFFFF">
Workstations and Servers</font></b></td>
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<td bgcolor="#669999" height="25"><b>
<font face="Arial" size="2" color="#FFFFFF">6.1.8</font></b></td>
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<font face="Arial" size="2" color="#FFFFFF">Concept of service on servers</font></strong></td>
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<font face="Arial" size="2">Networking operating systems (NOSs) are
designed to provide network processes to clients. Network
services include the World Wide Web (WWW), file sharing, mail
exchange, directory services, remote management, and print services.
Remote management is a powerful service that allows administrators to
configure networked systems that are miles apart. It is important to
understand that these network processes are referred to as services in
Windows 2000 and daemons in UNIX and Linux. Network
processes all provide the same functions, but the way
processes are loaded and interact with the NOS are different in each
operating system.
<img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12">
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12">
<img border="0" src="../../images/3.gif" align="absmiddle" width="12" height="12"></font><p>
<font face="Arial" size="2">Depending on the NOS, some of these key
network processes may be enabled during a default installation. Most
popular network processes rely on the TCP/IP suite of protocols.
Because TCP/IP is an open, well-known set of protocols, TCP/IP-based
services are vulnerable to unauthorized scans and malicious
attacks. Denial of service (DoS) attacks, computer viruses, and
fast-spreading Internet worms have forced NOS designers to reconsider
which network services are started automatically.</font></p>
<p><font face="Arial" size="2">Recent versions of popular NOSs, such
as Windows 2000 and Red Hat Linux 7, restrict the number of network
services that are on by default. When deploying a NOS, key network
services will need to be enabled manually.</font></p>
<p><font face="Arial" size="2">When a user decides to print in a
networked printing environment, the job is sent to the appropriate
queue for the selected printer. Print queues stack the incoming print
jobs and services them using a first-in, first-out (FIFO) order. When a job is added to the queue, it is placed at the end of the
waiting list and printed last. The printing wait time can sometimes be long,
depending on the size of the print jobs at the head of the queue. A network print service will provide system administrators with the
necessary tools to manage the large number of print jobs being routed
throughout the network. This includes the ability to prioritize,
pause, and even delete print jobs that are waiting to be printed.</font></p>
<p><font face="Arial" size="2"><b>File sharing </b><br>
The ability to share files over a network is an important network
service. There are many file sharing protocols and applications in use
today. Within a corporate or home network, files are typically shared
using Windows File Sharing or the Network File Sharing (NFS) protocol.
In such environments, an end user may not even know if a given file is
on a local hard disk or on a remote server. Windows File Sharing and
NFS allow users to easily move, create, and delete files in remote
directories.</font></p>
<p><font face="Arial" size="2"><b>File Transfer Protocol (FTP)</b><br>
Many organizations make files available to remote employees, to
customers, and to the general public using FTP. FTP services are
made available to the public in conjunction with web services. For
example, a user may browse a website, read about a software update on
a web page, and then download the update using FTP. Smaller companies
may use a single server to provide FTP and HTTP services, while larger
companies may choose to use dedicated FTP servers. </font></p>
<p><font face="Arial" size="2">Although FTP clients must logon, many
FTP servers are configured to allow anonymous access. When users
access a server anonymously, they do not need to have a user account
on the system. The FTP protocol also allows users to upload, rename,
and delete files, so administrators must be careful to configure an
FTP server to control levels of access.</font></p>
<p><font face="Arial" size="2">FTP is a session-oriented protocol.
Clients must open an application layer session with the server,
authenticate, and then perform an action, such as download or upload.
If the client session is inactive for a certain length of time, the
server disconnects the client. This inactive length of time is called
an idle timeout. The length of an FTP idle timeout varies depending on
the software.</font></p>
<p><font face="Arial" size="2"><b>Web services</b><br>
The World Wide Web is now the most visible network service. In less
than a decade, the World Wide Web has become a global network of
information, commerce, education, and entertainment. Millions of
companies, organizations, and individuals maintain websites on the
Internet. Websites are collections of web pages stored on a server or
group of servers.</font></p>
<p><font face="Arial" size="2">The World Wide Web is based on a
client/server model. Clients attempt to establish TCP sessions with
web servers. Once a session is established, a client can request data
from the server. HTTP typically governs client requests and server
transfers. Web client software includes GUI web browsers, such as
Netscape Navigator and Internet Explorer.</font></p>
<p><font face="Arial" size="2">Web pages are hosted on computers
running web service software. The two most common web server software
packages are Microsoft Internet Information Services (IIS) and Apache
Web Server. Microsoft IIS runs on a Windows platform and Apache Web
Server runs on UNIX and Linux platforms. A Web
service software package is available for virtually all operating systems currently in
production.</font></p>
<p><font face="Arial" size="2"><b>Domain Name System (DNS) </b><br>
The Domain Name System (DNS) protocol translates an Internet name,
such as www.cisco.com, into an IP address. Many applications rely on
the directory services provided by DNS to do this work. Web browsers,
e-mail programs, and file transfer programs all use the names of
remote systems. The DNS protocol allows these clients to make requests
to DNS servers in the network for the translation of names to IP
addresses. Applications can then use the addresses to send their
messages. Without this directory lookup service, the Internet would be
almost impossible to use.</font></p>
<p><font face="Arial" size="2"><b>Dynamic Host Configuration Protocol
(DHCP)</b><br>
The purpose of Dynamic Host Configuration Protocol (DHCP) is to enable
individual computers on an IP network to learn their TCP/IP
configurations from the DHCP server or servers. DHCP servers
have no information about the individual computers until
information is requested. The overall purpose of this is to reduce the
work necessary to administer a large IP network. The most significant
piece of information distributed in this manner is the IP address that
identifies the host on the network. DHCP also allows for recovery and
the ability to automatically renew network IP addresses through a
leasing mechanism. This mechanism allocates an IP address for a
specific time period, releases it, and then assigns a new IP address. DHCP allows all this to be done by a DHCP server which saves the
system administrator considerable amount of time.</font></p>
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