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What is Telnet Server?

Telnet Technical Reference
All versions of Microsoft Windows Server 2003 operating systems include Telnet Client and Telnet Server components. Using Telnet Client and Server, you can create a remote command console session on a host. You can run command line programs, shell commands, and scripts in a remote command console session just as though you were locally logged on to the host and using a local command prompt window.


What Is Telnet?
Windows Server 2003 and Windows XP Professional include Telnet Client and Telnet Server, which allow users to make remote connections based on the Telnet protocol. Using Telnet Client and Server, you can create a remote command console session on a host. Using a local command prompt window, you can run command line programs, shell commands, and scripts in a remote command console session just as though you were locally logged on to the host. Thus, having Telnet client and server software solves two networking problems. It allows for interoperability between disparate operating systems, and it facilitates administration of remote systems, saving administrative time and network resources.

Interoperability
Telnet Client and Server are well suited for troubleshooting and configuring remote computers, especially in mixed environments that require interoperability between different operating systems. For example, you can use Windows Server 2003 Telnet Client to connect to a Telnet server that is running on another operating system such as UNIX. Likewise, you can use a Telnet client that is running on UNIX to connect to a computer running Windows Server 2003 Telnet Server. Telnet Client and Server are also ideal in situations where memory and processor resources are minimal on a client or host or where network bandwidth is limited. This is because computers running Telnet clients and servers use less memory and processor time than other remote management tools, and Telnet clients and servers transmit only plaintext (unencrypted characters) across the network.

Remote Administration
Remote administration is a method of managing one or more remote computers from a single location. In a large organization, you can use remote administration to centrally manage hundreds or even thousands of computers located in other buildings or even in other cities. In a small organization, you can use remote administration to manage a single server located in an adjacent office.
By its nature, remote administration lowers the Total Cost of Ownership (TCO) by making system management easier and more efficient. Using remote administration, server operators and technicians can manage and troubleshoot servers without having to locally log on to the server, thereby lowering the cost of on-site support. Remote administration also assists help desk technicians in solving problems more quickly by letting them take control of a user’s computer.

Telnet and Other Technologies
Telnet is closely related to two other technologies that provide an alternative for remote command console sessions, depending on your needs for distributed computing, security, configuration requirements, and so on.

Windows Server 2003 Terminal Services
Telnet and Terminal Services are similar in that they are both used for remote sessions. However, Terminal Services extends the model of distributed computing by allowing client computers to operate in a server-based computing environment. Whereas Telnet only allows terminal emulation between a Telnet server and client, Terminal Services running on Windows Server 2003-based computers allows clients to run applications, while data processing, and data storage occur on the server. Applications and user sessions are transmitted over the network and displayed via terminal emulation software. Similarly, print streams, keyboard input, and mouse clicks are also transmitted over the network between the server and the terminal emulation software. Each user logs on and sees only their individual session, which is managed transparently by the server operating system and is independent of any other client session. You might want to consider using Windows Server 2003 Terminal Services if you require more extensive distributed computing.

Windows Services for UNIX 3.5
Windows Services for UNIX 3.5 includes a Telnet character-mode client that provides functionality not included in Windows Server 2003. The Windows Services for UNIX character-mode client supports both stream mode and console mode. It also provides for logging and additional configuration settings.

Windows Services for UNIX 3.5 includes two Telnet servers:

  • The default, Windows-based Telnet server, which is functionally similar to the one included with all versions of Microsoft Windows since Windows 2000

  • The Interix telnetd

Only one of these Telnet servers can be enabled at a time. By default, neither Telnet server is enabled for security reasons.

The Windows Services for UNIX 3.5 Telnet server accepts logons from a variety of clients, including the Telnet clients shipped with Windows 2000, Windows NT, Windows 95, and Windows 98, as well as a variety of character-mode terminal clients from virtually any operating system. Additionally, it can be configured to meet specific site requirements to improve security, simplify logons, support stream or console mode, and so forth.

The Windows Services for UNIX 3.5 Telnet server should be familiar to users of Windows 2000, Windows XP, and Windows Server 2003. It is essentially the same as the server included in Windows XP Professional and Windows Server 2003, and it is very similar to the one included in Windows 2000 editions. It uses the Windows command shell (Cmd.exe) as the default shell. You can start and stop this server from either the Services MMC (Services.msc) or from the Windows Services for UNIX Administration MMC (Sfumgmt.msc). If you are using Windows and UNIX in a mixed networking environment, you might want to consider installing Windows Services for UNIX 3.5 to extend the capabilities of Telnet.


How Telnet Works
All Windows versions include Telnet Client and Telnet Server components. Using Telnet Client and Server, you can create a remote command console session on a host. You can run command line programs, shell commands, and scripts in a remote command console session just as though you were locally logged on to the host and using a local command prompt window.

Windows Server 2003 Telnet Client and Server are well suited for troubleshooting and configuring remote computers, especially in mixed environments that require interoperability between different operating systems. For example, you can use Telnet Client to connect to a Telnet server that is running on another operating system such as UNIX. Likewise, you can use a Telnet client that is running on UNIX to connect to a computer running Telnet Server. Windows Server 2003 Telnet Client and Server are also ideal in situations where memory and processor resources are minimal on a client or host or where network bandwidth is limited. This is because computers running Telnet clients and servers use less memory and processor time than other remote management tools, and Telnet clients and servers transmit only plaintext (unencrypted characters) across the network.

Understanding Telnet

Before using the Windows Server 2003 Telnet tools, you should consider the following:

  • Windows Server 2003 Telnet Client and Server are based on the Telnet protocol, which specifies a method for transmitting and receiving unencrypted ASCII characters (plaintext) across a network. Understanding how the protocol works, and how Telnet clients and servers use the Telnet protocol, helps you manage Telnet connections.

  • The Windows Server 2003 Telnet tools have several inherent limitations that affect the types of remote management tasks you can perform and the level of security that is in effect when you perform those tasks. Understanding these limitations helps you determine when and when not to use the Telnet tools.

  • You can configure Telnet Server settings by using the Windows Server 2003 Telnet administration tool (Tlntadmn.exe) and the registry editor (Regedit.exe). Although the default Telnet Server settings are sufficient for most Telnet client connections, you might need to change the default settings to better suit your organization. Examples of Telnet Server settings include: authentication type, default port assignment for Telnet connections, maximum number of client connections, and maximum number of failed logon attempts.

  • By default, members of the local administrators group can log on to a Telnet server. However, you might not want all Telnet users to have full administrative control of the host they log on to. In this case, you can use a Telnet clients group to grant users Telnet logon rights without granting them any administrative rights on the host. To configure these user rights from the graphical user interface, you must use the Active Directory Users and Groups snap-in or the Local Users and Groups snap-in. You can also use the Net User and Net Group commands to configure user rights from the command line.

  • You can configure several optional settings when you use Telnet Client to establish a Telnet session on a host. Depending on the type of Telnet server you are logging on to, and how the Telnet server is configured, you might need to enable or change some of these optional settings. Examples of Windows Server 2003 Telnet Client settings include: client-side logging, terminal type, port assignment, and alternate user name for logon.

  • You can manage active Telnet sessions on a host by using the Windows Server 2003 Telnet administration tool. Some of the administrative tasks you can perform include: terminating Telnet sessions, sending console messages to users with active Telnet sessions, and listing Telnet session information (for example, user name, logon time, idle time, and client IP address).

Note

  • The information in this document refers to the Telnet Client and Telnet Server components that are installed by default with Windows Server 2003 and Windows XP Professional operating systems.

Telnet Architecture

Most network operating systems provide a Telnet client and a Telnet server. Telnet clients and servers are small executable programs that allow a local computer (a client) to access services and programs on a remote computer (a host). Telnet clients and servers, including Windows Server 2003 Telnet Client and Telnet Server, are based on the Telnet protocol, which is a subset of the TCP/IP suite and is described in RFC 854. The Telnet protocol specifies two general mechanisms: how Telnet clients and servers establish a connection across a network and how they transmit and receive information across a network.

You usually run a Telnet client program on a local computer: for example, a workstation that you are logged on to. You usually run a Telnet server program on a remote computer: for example, a host you want to administer. Telnet client programs initiate connections with Telnet servers. Telnet servers run in the background on a host, listening for Telnet clients to request a connection.

Common Telnet Features

Because Telnet clients and servers are based on the same standard protocol, all Telnet clients and servers have several features in common. These common features are what make Telnet clients and servers well suited for performing remote administration tasks in environments that require interoperability among disparate operating systems. In short, the Telnet protocol makes it possible for you to connect a computer running Windows Server 2003 Telnet Client to a UNIX Telnet server. The key features that make this interoperability possible include the following:

Common communication protocols

All Telnet clients and servers use TCP/IP as the underlying communication protocol. This makes Telnet clients and servers particularly useful for remotely administering computers across the Internet or within wide area networks (WANs) that are connected to the Internet. If your network does not support TCP/IP, you will not be able to use a Telnet client or server.

Common communication ports

TCP port 23 is reserved for Telnet client and server communication. By default, most Telnet clients initiate communication on port 23, and most Telnet servers listen on port 23 for connection requests. You can change the default port assignments with some Telnet client and server software, such as Windows Server 2003 Telnet Client and Server, but port 23 is the universally accepted port for Telnet communication.

Common character set for communication

All Telnet clients and servers are capable of transmitting and receiving a predefined character set consisting of standard ASCII character codes and ASCII control codes. All Telnet clients and servers transmit the ASCII codes across a network in unencrypted form (plaintext).

Common implementation of the Network Virtual Terminal

All Telnet clients and servers implement a network virtual terminal (NVT). The NVT is responsible for translating operating system-specific instructions (keyboard codes or display codes) into a consistent set of codes that all Telnet clients and servers can transmit and receive. The NVT is what makes Telnet clients and servers capable of communicating with each other regardless of which operating system they are using.

Creating a Telnet Connection

To create a Telnet connection between a Telnet client and a Telnet server, you must do the following:

  • Start the Telnet Server program on the host. On Windows Server 2003, Telnet Server (Tlntsvr.exe) runs as a service. You can start the service manually every time you want to connect to a host, or you can configure the service so that it starts every time your computer starts. Telnet clients cannot connect to a host unless a Telnet server program (or service) is running and listening for connection requests.

  • Run the Telnet Client program on the local computer. When you run Windows Server 2003 Telnet Client (Telnet.exe), you must specify the host to which you want to connect. You can also configure several optional connection settings and features.

When you run a Telnet client, it makes a connection request to the host. If a Telnet server responds to the request, the Telnet client and server negotiate the details of the connection, such as flow control settings, window size, and terminal type. After the connection details are successfully negotiated, and logon credentials are validated, the Telnet server program creates a Telnet command console session.

On Windows Server 2003, each Telnet command console session consists of two processes: Tlntsess.exe and Cmd.exe. Tlntsess.exe is responsible for managing the Telnet session. Cmd.exe is the command interpreter, or shell program, that runs commands, programs, or scripts on the host.

Note

  • Cmd.exe is the default command interpreter for a Windows Server 2003 Telnet command console session. However, you can configure the Windows Server 2003 Telnet Server program to use as a default any command interpreter or shell program that is installed on the host.

Running Programs Remotely Using a Telnet Connection

After you establish a Telnet connection with Telnet Server, the following message appears in the command prompt window on the client:

*= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Welcome to Microsoft Telnet Server.
*= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

This message indicates that your credentials are valid and that you have an active Telnet session with Telnet Server. Assuming you have the appropriate administrative user rights, you can use this session to remotely run command-line programs, shell commands, and scripts on a host. Telnet client and server processes rely on the Telnet network virtual terminal (NVT) to translate operating system-specific keyboard and display codes to Telnet character codes that all Telnet clients and servers can understand.

Telnet Limitations

Telnet connections have several limitations. You can address many of these limitations by changing Windows Server 2003 security and Group Policy settings, but the following limitation cannot be eliminated or modified.

You cannot run GUI tools over a Telnet connection

Telnet is a character-based communication protocol. It is not designed to transmit cursor movements or graphical user interface information. Because of this, you can only run command line programs, shell commands, scripts, and batch files over a Telnet connection. Some editing programs, such as vi and Edit, can be run over a Telnet connection; however, these interactive programs are not true GUI programs because cursor movement is controlled by the keyboard, not the mouse.

Telnet Tools and Settings

Telnet Server tools and settings determine how Telnet Server handles auditing, authentication, idle session time-out, and other remote command console session options. Usually, you do not need to configure Telnet Server options to connect a Telnet client to Windows Server 2003-based Telnet Server: the default Telnet Server options are compatible with most Telnet clients. However, you must configure Telnet Server options if you want to do any of the following:

  • Audit logon and logoff information.

  • Disable NTLM or password authentication, or change the default domain for authenticating unqualified user names (by default, the domain in which the machine account resides is used to authenticate unqualified user names).

  • Prohibit authentication of user accounts in trusted domains, which restricts Telnet access to users whose user accounts are stored only in the local Security Accounts Manager (SAM) database (by default, Telnet Server authenticates user accounts in trusted domains and the local SAM database).

  • Change the default shell, or command interpreter, that is used for Telnet sessions (Cmd.exe is the default shell).

  • Specify an IP address on which you want the Telnet Server program to listen for connection requests.

  • Change the mode of operation from console mode to stream mode.

  • Ensure that all programs started in a Telnet session terminate when you disconnect a Telnet session.

  • Change the TCP port on which Telnet Server listens for a connection (by default, Telnet servers listen on TCP port 23).

  • Change the maximum number of Telnet sessions that Telnet Server will accept (the default is 2).

  • Change the maximum number of logon attempts before a user is disconnected (the default is 3).

  • Disable idle session time-out, or change the idle session time-out value (the default is 1 hour).

  • Disable Alt key mapping (by default, pressing Ctrl-A simulates the Alt key).

Telnet Tools

The following tools are associated with Telnet Server.

Telnet.exe: Telnet Command Prompt

Category

The Telnet command prompt tool is included with the Windows Server 2003 and Windows XP operating systems.

Version compatibility

Use this command on computers running Windows Server 2003 or Windows XP.

Once all of the settings and options are configured, you can use Telnet.exe to initiate and conduct a Telnet session. You can create a Telnet connection, configure Telnet.exe options, and use all Telnet.exe features by using the Telnet command prompt. The Telnet command prompt is useful if you are performing quick maintenance tasks on several different hosts or you need to use advanced Telnet options and features.

You can access the Telnet command prompt by running the Telnet command without any command-line parameters. You can also access the Telnet command prompt by typing the Telnet escape character during an active Telnet session. The default escape character is Ctrl+].

After you start the Telnet command prompt, the following message appears:

Welcome to Microsoft Telnet Client
Escape Character is 'Ctrl+]'
Microsoft Telnet >

You can close the Telnet command prompt by using the Quit command.

Telnet.exe with command-line parameters

You can create a Telnet connection and configure some Telnet.exe options by using the Telnet command in conjunction with various command-line parameters. Using the Telnet command with command-line parameters is helpful if you are creating Telnet connections within a script or batch file or you do not need to use advanced Telnet client options and features. When you use Telnet with command-line parameters, you can use a single command to create a connection with a host. The command-line syntax for Telnet.exe is:

                telnet [-a][-eescape_char][-flog_file][-luser_name][-tterm]host [port]

The command-line parameters are described in the following table.

Telnet.exe Command-Line Parameters

Parameter Description

-a

Instructs Telnet.exe to log on to the host using the credentials of the user who is currently logged on to the client.

-e escape_char

Specifies an escape character, which displays the Telnet command prompt. The default escape character is Ctrl+].

-f log_file

Creates a client-side log file and turns on client-side logging for the current session. The log_file parameter must consist of a path and file name.

-l user_name

Instructs Telnet.exe to log on to the host using the user account that is specified in user_name. The user account specified in user_name must have Telnet logon rights on the host.

-t term

Specifies the terminal type. The default terminal type is ANSI. Other valid terminal types include VT52, VT100, and VTNT.

host

Specifies the host with which you want to create a Telnet connection. The host parameter can be a NetBIOS name, a fully qualified domain name, or an IP address.

port

Specifies the TCP port on which you want to create a Telnet connection. The default Telnet port is 23.

For example, the following command uses the credentials of the user who is currently logged on to the client to create a Telnet connection on port 23 with a host named server01:

                Telnet Server01

Likewise, the following example creates the same Telnet connection and enables client-side logging to a log file named c:\telnet_logfile:

                telnet -f c:\telnet_logfile server01

The connection with the host remains active until you exit the Telnet session (by using the Exit command), or you use the Telnet Server administration tool to terminate the Telnet session on the host.

Tlntadmn.exe: Telnet Administration

Category

The Telnet administration command-line tool is included with the Windows Server 2003 and Windows XP operating systems.

Version compatibility

Run this command on computers running Windows Server 2003 or Windows XP.

Tlntadmn.exe is a command-line tool, and is installed by default when you install Windows Server 2003. Unlike the Telnet Server administration tool in Windows 2000, Tlntadmn.exe is a noninteractive tool that must be run with various command-line parameters. Because Tlntadmn.exe is noninteractive, and uses command-line parameters to configure Telnet Server options, you can use Tlntadmn.exe in scripts or batch files to automate Telnet Server configuration tasks. You must be a member of the Administrators local group to use the Telnet Server administration tool.

For more information about Tlntadmn.exe, see “Telnet commands” in the Command Line References in the Tools and Settings Collection.

Telnet Registry Entries

The following registry entries are associated with Telnet.

You can configure most Windows Server 2003 Telnet Server options by using the Telnet Server administration tool (Tlntadmn.exe). However, you can only configure some options by using the registry editor (Regedit.exe). You should use the registry editor to configure only the Telnet Server options that cannot be configured with the Telnet Server administration tool.

You must be a member of one of the following groups to use Regedit.exe: Administrators, Server Operators, and Power Users. You can use Regedit.exe to change registry settings on a local or a remote computer. However, only members of the Administrators group can use Regedit.exe to configure registry settings on a remote computer.

The information here is provided as a reference for use in troubleshooting or verifying that the required settings are applied. It is recommended that you do not directly edit the registry unless there is no other alternative. Modifications to the registry are not validated by the registry editor or by Windows before they are applied, and as a result, incorrect values can be stored. This can result in unrecoverable errors in the system. When possible, use Group Policy or other Windows tools, such as Microsoft Management Console (MMC), to accomplish tasks rather than editing the registry directly. If you must edit the registry, use extreme caution.

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\

The following registry entries are located under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\TelnetServer\1.0\.

AllowTrustedDomain

Registry path

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\TelnetServer\1.0.\

Version

The AllowTrustedDomain entry is included in Windows Server 2003 and Windows XP.

You can prevent the Telnet Server program from authenticating users on trusted domains by configuring this registry entry.

By default, the Telnet Server program authenticates user accounts in trusted domains and in the local SAM database. Preventing the Telnet Server program from authenticating user accounts in trusted domains restricts Telnet access to only those users whose user accounts are in the local SAM database. By default, the AllowTrustedDomain registry entry has a value of 1. To prevent Telnet Server from authenticating user accounts in trusted domains, you must set this registry entry to 0.

DefaultShell

Registry path

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\TelnetServer\1.0.\

Version

The DefaultShell entry is included in Windows Server 2003 and Windows XP.

You can change the default shell, or command interpreter, that the Telnet Server program uses for a Telnet session by configuring this registry entry.

By default, Telnet Server runs all commands in the Windows Server 2003-based command interpreter (Cmd.exe). You can change this to any command interpreter that is installed on the host. You must provide a path and file name for the command interpreter.

ListenToSpecificIpAddr

Registry path

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\TelnetServer\1.0.\

Version

The ListenToSpecificIpAddr entry is included in Windows Server 2003 and Windows XP.

You can configure the Telnet Server program so it listens for connection requests that are sent to a specific IP address. This is useful if a host has several network adapters, and you want to limit Telnet connections to only one of the network adapters. It is also useful if you have a firewall, and you want to filter Telnet traffic through the firewall to only a few IP addresses.

By default, this registry entry has the value INADDR_ANY, which instructs Telnet Server to listen for Telnet connection requests that are sent to all IP addresses assigned to the host. You can change the value of this registry entry to any IP address that is assigned to the host.

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What is Web Server?


A web server is a computer program that delivers (serves) content, such as web pages, using the Hypertext Transfer Protocol (HTTP), over the World Wide Web.

The primary function of a web server is to deliver web pages to clients. This means delivery of HTML documents and any additional content that may be included by a document, such as images, style sheets and JavaScripts.

A client, commonly a web browser or web crawler, initiates communication by making a request for a specific resource using HTTP and the server responds with the content of that resource, or an error message if unable to do so. The resource is typically a real file on the server's secondary memory, but this is not necessarily the case and depends on how the web server is implemented.

While the primary function is to serve content, a full implementation of HTTP also includes a way of receiving content from clients. This feature is used for submitting web forms, including uploading of files.

Many generic web servers also support server-side scripting, e.g., Apache HTTP Server and PHP. This means that the behaviour of the web server can be scripted in separate files, while the actual server software remains unchanged. Usually, this functionality is used to create HTML documents on-the-fly as opposed to return fixed documents. This is referred to as dynamic and static content respectively. The former is primarily used for retrieving and/or modifying information in databases. The latter is, however, typically much faster and easily cached.

Web servers are not always used for serving the world wide web, rather they can also be found embedded in devices such as printers, routers, webcams and serving only a local network. The web server may then be used as a part of a system for monitoring and/or administrating the device in question. This usually means that no additional software has to be installed on the client computer, since only a web browser is required (which by now is included with most operating systems).

A computer that delivers (serves up) Web pages. Every Web server has an IP address and possibly a domain name. For example, if you enter the URL http://networkingpupil.blogspot.com/index.html in your browser, this sends a request to the server whose domain name is networkingpupil.blogspot.com. The server then fetches the page named index.html and sends it to your browser.

Any computer can be turned into a Web server by installing server software and connecting the machine to the Internet. There are many Web server software applications, including public domain software from NCSA and Apache, and commercial packages from Microsoft, Netscape and others.

How Web Servers Work
Have you ever wondered just exactly how this Web page you are reading found its way into your browser and onto your computer screen? The process largely depends on Web servers. Read on as Networkingpupil.blogspot briefly explains the mechanisms that bring Web pages to your home, your office or your mobile computers.

Typically, users visit a Web site by either clicking on a hyperlink that brings them to that site or keying the site's URL directly into the address bar of a browser. But how does the same site appear on anyone's computer anywhere in the world and often on many computers at the same time?

Let's use Networkingpupil as an example. You decide to visit Networkingpupil.blogspot by typing its URL -- http://networkingpupil.blogspot.com -- into your Web browser. Through an Internet connection, your browser initiates a connection to the Web server that is storing the Networkingpupil.blogspot files by first converting the domain name into an IP address (through a domain name service DNS) and then locating the server that is storing the information for that IP address.

The Web server stores all of the files necessary to display Networkingpupil's pages on your computer -- typically all the individual pages that comprise the entirety of a Web site, any images/graphic files and any scripts that make dynamic elements of the site function.

Once contact has been made, the browser requests the data from the Web server, and using HTTP, the server delivers the data back to your browser. The browser in turn converts, or formats, the computer languages that the files are made up of into what you see displayed in your browser. In the same way the server can send the files to many client computers at the same time, allowing multiple clients to view the same page simultaneously.

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What is NAT Server?



NAT: Network Address Translation. an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic in other words Network Address Translation: Mechanism for reducing the need for globally unique IP addresses. NAT allows an organization with addresses that are not globally unique to connect to the Internet by translating those addresses into globally routable address spaces. Also known as Network Address Translator.

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What is Proxy Server?

A proxy server is a server (a computer system or an application program) that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server. The proxy server evaluates the request according to its filtering rules. For example, it may filter traffic by IP address or protocol. If the request is validated by the filter, the proxy provides the resource by connecting to the relevant server and requesting the service on behalf of the client. A proxy server may optionally alter the client's request or the server's response, and sometimes it may serve the request without contacting the specified server. In this case, it 'caches' responses from the remote server, and returns subsequent requests for the same content directly.

A proxy server has a large variety of potential purposes, including:

  • To keep machines behind it anonymous (mainly for security).
  • To speed up access to resources (using caching). Web proxies are commonly used to cache web pages from a web server.
  • To apply access policy to network services or content, e.g. to block undesired sites.
  • To log / audit usage, i.e. to provide company employee Internet usage reporting.
  • To bypass security/ parental controls.
  • To scan transmitted content for malware before delivery.
  • To scan outbound content, e.g., for data leak protection.
  • To circumvent regional restrictions.

A proxy server that passes requests and replies unmodified is usually called a gateway or sometimes tunneling proxy.

A proxy server can be placed in the user's local computer or at various points between the user and the destination servers on the Internet.

A reverse proxy is (usually) an Internet-facing proxy used as a front-end to control and protect access to a server on a private network, commonly also performing tasks such as load-balancing, authentication, decryption or caching.

In some cases, the proxy may alter the client's request or the server's response for various purposes.

Web proxies

A common proxy application is a caching Web proxy. This provides a nearby cache of Web pages and files available on remote Web servers, allowing local network clients to access them more quickly or reliably.

When it receives a request for a Web resource (specified by a URL), a caching proxy looks for the resulting URL in its local cache. If found, it returns the document immediately. Otherwise it fetches it from the remote server, returns it to the requester and saves a copy in the cache. The cache usually uses an expiry algorithm to remove documents from the cache, according to their age, size, and access history. Two simple cache algorithms are Least Recently Used (LRU) and Least Frequently Used (LFU). LRU removes the least-recently used documents, and LFU removes the least-frequently used documents.

Web proxies can also filter the content of Web pages served. Some censorware applications - which attempt to block offensive Web content - are implemented as Web proxies. Other web proxies reformat web pages for a specific purpose or audience; for example, Skweezer reformats web pages for cell phones and PDAs. Network operators can also deploy proxies to intercept computer viruses and other hostile content served from remote Web pages.

A special case of web proxies are "CGI proxies." These are web sites which allow a user to access a site through them. They generally use PHP or CGI to implement the proxying functionality. CGI proxies are frequently used to gain access to web sites blocked by corporate or school proxies. Since they also hide the user's own IP address from the web sites they access through the proxy, they are sometimes also used to gain a degree of anonymity.

You may see references to four different types of proxy servers:

  • Transparent Proxy

    This type of proxy server identifies itself as a proxy server and also makes the original IP address available through the http headers. These are generally used for their ability to cache websites and do not effectively provide any anonymity to those who use them. However, the use of a transparent proxy will get you around simple IP bans. They are transparent in the terms that your IP address is exposed, not transparent in the terms that you do not know that you are using it (your system is not specifically configured to use it.)

  • Anonymous Proxy

    This type of proxy server identifies itself as a proxy server, but does not make the original IP address available. This type of proxy server is detectable, but provides reasonable anonymity for most users.

  • Distorting Proxy

    This type of proxy server identifies itself as a proxy server, but make an incorrect original IP address available through the http headers.

  • High Anonymity Proxy

    This type of proxy server does not identify itself as a proxy server and does not make available the original IP address

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What is DC?


Primary Domain Controller (PDC) and Backup Domain Controller (BDC) are roles that can be assigned to a server in a network of computers that use the Windows Server (NT/2000/2003/2008) operating system. Windows Server uses the idea of a domain to manage access to a set of network resources (applications, printers, and so forth) for a group of users. The user need only to log in to the domain to gain access to the resources, which may be located on a number of different servers in the network. One server, known as the primary domain controller, manages the master user database for the domain. One or more other servers are designated as backup domain controllers. The primary domain controller periodically sends copies of the database to the backup domain controllers. A backup domain controller can step in as primary domain controller if the PDC server fails and can also help balance the workload if the network is busy enough.

In Windows Servers, a domain combines some of the advantages of a workgroup (a group of users who exchange access to each others' resources on different computers) and a Active Directorytrust relationship. In this arrangement, the user need only log in to the first domain to also have access to the second domain's resources as well. (AD: a group of users who are managed centrally by an administrator). The domain concept not only allows a user to have access to resources that may be on different servers, but it also allows one domain to be given access to another domain in a

In a Windows Server network, not all servers need to be a PDC or BDC. A server can be designated as a member server whose resources become part of a Domain without having a role in the logon process.

Setting up and maintaining PDCs and BDCs and domain information is a major activity for the administrator of a Windows Server network. In Windows 2000, the domain controller concept is retained but the PDC and BDC server roles are generally replaced by the Active Directory.

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What is DNS?

In computing, a name server (also spelled nameserver) consists of a program or computer server that implements a name-service protocol. It maps a human-recognizable identifier to a system-internal, often numeric, identification or addressing component.

The Domain Name System (DNS) is a standard technology for managing the names of Web sites and other Internet domains. DNS technology allows you to type names into your Web browser like networkingpupil.blogspot.com and your computer to automatically find that address on the Internet. A key element of the DNS is a worldwide collection of DNS servers. What, then, is a DNS server?
Answer: A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-purpose networking software, features a public IP address, and contains a database of network names and addresses for other Internet hosts.

DNS Root Servers

DNS servers communicate with each other using private network protocols. All DNS servers are organized in a hierarchy. At the top level of the hierarchy, so-called root servers store the complete database of Internet domain names and their corresponding IP addresses. The Internet employs 13 root servers that have become somewhat famous for their special role. Maintained by various independent agencies, the servers are aptly named A, B, C and so on up to M. Ten of these servers reside in the United States, one in Japan, one in London, UK and one in Stockholm, Sweden.

DNS Server Hierarchy

The DNS is a distributed system, meaning that only the 13 root servers contain the complete database of domain names and IP addresses. All other DNS servers are installed at lower levels of the hierarchy and maintain only certain pieces of the overall database.

Most lower level DNS servers are owned by businesses or Internet Service Providers (ISPs). For example, Google maintains various DNS servers around the world that manage the google.com, google.co.uk, and other domains. Your ISP also maintains DNS servers as part of your Internet connection setup.

DNS networking is based on the client / server architecture. Your Web browser functions as a DNS client (also called DNS resolver) and issues requests to your Internet provider's DNS servers when navigating between Web sites.

When a DNS server receives a request not in its database (such as a geographically far away or rarely visited Web site), it temporarily transforms from a server to a DNS client. The server automatically passes that request to another DNS server or up to the next higher level in the DNS hierarchy as needed. Eventually the request arrives at a server that has the matching name and IP address in its database (all the way to the root level if necessary), and the response flows back through the chain of DNS servers to your client.

DNS Servers and Home Networking

Computers on your home network locate a DNS server through the Internet connection setup properties. Providers give their customers the public IP address(es) of primary and backup DNS servers. You can find the current IP addresses of your DNS server configuration via several methods:

  • on the configuration screens of a home network router
  • on the TCP/IP connection properties screens in Windows Control Panel (if configured via that method)
  • from ipconfig or similar command line utility

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What is DHCP?

Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.

Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users.

What is DHCP Server?

Dynamic Host Configuration Protocol (DHCP) is a network protocol that enables a server to automatically assign an IP address to a computer from a defined range of numbers (i.e., a scope) configured for a given network.

DHCP assigns an IP address when a system is started, for example:

  1. A user turns on a computer with a DHCP client.

  2. The client computer sends a broadcast request (called a DISCOVER or DHCPDISCOVER), looking for a DHCP server to answer.

  3. The router directs the DISCOVER packet to the correct DHCP server.

  4. The server receives the DISCOVER packet. Based on availability and usage policies set on the server, the server determines an appropriate address (if any) to give to the client. The server then temporarily reserves that address for the client and sends back to the client an OFFER (or DHCPOFFER) packet, with that address information. The server also configures the client's DNS servers, WINS servers, NTP servers, and sometimes other services as well.

  5. The client sends a REQUEST (or DHCPREQUEST) packet, letting the server know that it intends to use the address.

  6. The server sends an ACK (or DHCPACK [Acknowledge]) packet, confirming that the client has a been given a lease on the address for a server-specified period of time.

When a computer uses a static IP address, it means that the computer is manually configured to use a specific IP address. One problem with static assignment, which can result from user error or inattention to detail, occurs when two computers are configured with the same IP address. This creates a conflict that results in loss of service. Using DHCP to dynamically assign IP addresses minimizes these conflicts.


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The MAC Address

In computer networking, the Media Access Control (MAC) address is every bit as important as an IP address. Learn in this article how MAC addresses work and how to find the MAC addresses being used by a computer.
















What Is a MAC Address?
The MAC address is a unique value associated with a network adapter. MAC addresses are also known as hardware addresses or physical addresses. They uniquely identify an adapter on a LAN.

MAC addresses are 12-digit hexadecimal numbers (48 bits in length). By convention, MAC addresses are usually written in one of the following two formats:

MM:MM:MM:SS:SS:SS

MM-MM-MM-SS-SS-SS
The first half of a MAC address contains the ID number of the adapter manufacturer. These IDs are regulated by an Internet standards body. The second half of a MAC address represents the serial number assigned to the adapter by the manufacturer. In the example,
00:A0:C9:14:C8:29
The prefix
00A0C9
indicates the manufacturer is Intel Corporation.
Why MAC Addresses?
Recall that TCP/IP and other mainstream networking architectures generally adopt the OSI model. In this model, network functionality is subdivided into layers. MAC addresses function at the data link layer (layer 2 in the OSI model). They allow computers to uniquely identify themselves on a network at this relatively low level.
MAC vs. IP Addressing
Whereas MAC addressing works at the data link layer, IP addressing functions at the network layer (layer 3). It's a slight oversimplification, but one can think of IP addressing as supporting the software implementation and MAC addresses as supporting the hardware implementation of the network stack. The MAC address generally remains fixed and follows the network device, but the IP address changes as the network device moves from one network to another.

IP networks maintain a mapping between the IP address of a device and its MAC address. This mapping is known as the ARP cache or ARP table. ARP (Address Resolution Protocol), supports the logic for obtaining this mapping and keeping the cache up to date.

DHCP also usually relies on MAC addresses to manage the unique assignment of IP addresses to devices.

The method used to find a MAC address depends on the type of network device involved. All popular network operating systems contain utility programs that allow you to find (and sometimes change) MAC address settings.

Find a MAC Address in Windows

In Windows 95, Windows 98 and Windows ME, the winipcfg utility displays the computer's MAC address. Use the ipconfig utility (with the /all option) in Windows NT and any newer versions of Windows.

Both 'winipcfg' and 'ipconfig' may display multiple MAC addresses for one computer. One MAC address exists for each installed network card. Additionally, Windows maintains one or more MAC addresses that are not associated with hardware cards.

For example, Windows dial-up networking uses virtual MAC addresses to manage the phone connection as if it were a network card. Some Windows VPN clients likewise have their own MAC address. The MAC addresses of these "virtual" network adapters are the same length and format as true hardware addresses.

Find a MAC Address in Unix or Linux

The specific command used in Unix to find a MAC address varies depending on the version of the operating system. In Linux and in some forms of Unix, the command "ifconfig -a" returns MAC addresses.

You can also find MAC addresses in Unix and Linux in the boot message sequence. These operating systems display the computer's MAC address on-screen as the system reboots. Additionally, boot-up messages are retained in a log file (usually "/var/log/messages" or "/var/adm/messages").

Find a MAC Address on the Macintosh

You can find MAC addresses on the Macintosh in the TCP/IP Control Panel. If the system is running Open Transport, the MAC address appears under the "Info" or "User Mode/Advanced" screens. If the system is running MacTCP, the MAC address appears under the "Ethernet" icon.

Summary - How to Find a MAC Address

The list below summarizes options to find a computer's MAC address:
  • Windows 95 and newer: winipcfg
  • Windows NT and newer: ipconfig /all
  • Linux and some Unix: ifconfig -a
  • Macintosh with Open Transport: TCP/IP Control Panel - Info or User Mode/Advanced
  • Macintosh with MacTCP: TCP/IP Control Panel - Ethernet icon
MAC addresses were designed to be fixed numbers that cannot be changed. However, there are several valid reasons to want to change your MAC address

Changing a MAC Address To Work With Your ISP

Most Internet subscriptions allow the customer only a single IP address. The Internet Service Provider (ISP) may assign one static (fixed) IP address to each customer. However, this approach is an inefficient use of IP addresses that are currently in short supply. The ISP more commonly issues each customer dynamic IP address that may change each time the customer connects to the Internet.

ISPs ensure each customer receives only one dynamic address using several methods. Dial-up and many DSL services typically require the customer to log in with a username and password. Cable modem services, on the other hand, do this by registering and tracking the MAC address of the device that connects to the ISP.

The device whose MAC address is monitored by an ISP can be either the cable modem, a broadband router, or the PC that hosts the Internet connection. The customer is free to build a network behind this equipment, but the ISP expects the MAC address to match the registered value at all times.

Whenever a customer replaces that device, however, or changes the network adapter inside it, the MAC address of this new equipment will no longer match the one registered at the ISP. The ISP will often disable the customer's Internet connection for security (and billing) reasons.

Change a MAC Address through Cloning

Some people contact their ISP to request they update the MAC address associated with their subscription. This process works but takes time, and Internet service will be unavailable while waiting for the provider to take action.

A better way to quickly workaround this problem is to change the MAC address on the new device so that it matches the address of the original device. While an actual physical MAC address cannot be changed in hardware, the address can be emulated in software. This process is called cloning.

Many broadband routers today support MAC address cloning as an advanced configuration option. The emulated MAC address appears to the service provider identical to the original hardware address. The specific procedure of cloning varies depending on the type of router; consult product documentation for details.

MAC Addresses and Cable Modems

In addition to MAC addresses tracked by the ISP, some broadband modems also track the MAC address of the host computer's network adapter within the home network. If you swap the computer connected to the broadband modem, or change its network adapter, your cable Internet connection may not function afterward.

In this case, MAC address cloning is not required. Resetting (including recycling power) on both the cable modem and the host computer will automatically change the MAC address stored inside the modem.

Changing MAC Addresses through the Operating System

Starting with Windows 2000, users can sometimes change their MAC address through the Windows My Network Places interface. This procedure does not work for all network cards as it depends on a certain level of software support built into the adapter driver.

In Linux and versions of Unix, the "ifconfig" also supports changing MAC addresses if the necessary network card and driver support exists.

Summary - Change a MAC Address

The MAC address is an important element of computer networking. MAC addresses uniquely identify a computer on the LAN. MAC is an essential component required for network protocols like TCP/IP to function.

Computer operating systems and broadband routers support viewing and sometimes changing MAC addresses. Some ISPs track their customers by MAC address. Changing a MAC address can be necessary in some cases to keep an Internet connection working. Some broadband modems also monitor the MAC address of their host computer.

Although MAC addresses do not reveal any geographic location information like IP addresses do, changing MAC addresses may improve your Internet privacy in some situations.

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How do I Fix a Slow Computer?

Below you will find the resources you need to restore PC speed.

"My computer is slow!"

SLOW COMPUTER SYNDROME

What causes slow computer syndrome? Essentially, it has to do with limited resources. Over time, we add programs, utilities, device drivers, files, pictures, music, MOVIES!; and these begin to use up the finite resources of the computer. Before long, there are too many processes, too little RAM, and too little Disk Space.

BEGIN SPEEDING UP PC HERE!

This guide has been ordered for efficiency in MOST circumstances. You are certainly free to apply any or all as you like.

1. Backup Before anything else, make sure you save ALL your files: Documents, pictures, term papers, music, financial data, email, bookmarks, etc. You should always have and maintain backups.

Fix: Backup Software

2. Priority Updates. Make sure Windows and your device drivers are up-to-date: Our first line of defense against threats. We recommend using automatic updates.

Fix: Windows Update

3. Spies are watching. Spyware is a small program which records information about your internet activity and relays it back to thieves. Spyware will impede computer considerably.

If your PC is slower than normal at performing routine tasks, you may have spyware - MICROSOFT

Fix: AntiSpyware

4. Virus infection. These are small programs, using resources on YOUR computer, which you never asked for! Keep antivirus software up to date.

Fix: Antivirus software

5. Registry repair. Your registry is like a directory of all the programs and other files you have on your system. This too can become disorganized and cause your computer to run slowly. Speed up PC with registry cleaner.

Fix: Registry Cleaner

6. System breach. If you don't already have a firewall or don't think you need one you may want to review this step. Your computer could be sending and receiving unauthorized data. Do not be a spammer's zombie!

Fix: Firewall Protection

7. Unused Programs. Programs you do not use or do not need, require space on your hard drives, and in memory - making computer run slow, and possibly delay startup and shutdown.

Fix: Remove Programs

8. Wasted space. Remove temporary and unnecessary files from your hard drive. Freeing up operating space can speed up your PC.

Fix: Run Disk Cleanup

9. File fragmentation. Over time, the files on your hard drive get broken into pieces, making them harder to retrieve and update. Result: Files take longer to retrieve and save.

Fix: Run Disk Defragmenter

10. Disk Errors. Your PC spends much time reading and writing data to the hard drives. Low performance can be caused by badly arranged or erroneous files on your hard disk.

Fix: Run Check Disk

11. System Recovery. If your computer seems beyond all help, but is only a few years old, you have another option ... restore computer to factory condition.

Fix: System restore

12. Free utilities A collection of free utilities for the adventurous beginner and the technically savvy. Free antispyware, free antivirus software, free registry cleaner, and more, to speed up PC!

Fix: Free Utilities

13. Low Memory. Having enough memory can make the difference in speed. Eg., Windows XP runs very well with 2GB or more, and well enough for most people with 1G, but a PC runs slower with less. Adding memory can be the least expensive and yet one of the most significant ways to speed up computer.

Fix: Upgrade your memory

14. Old hardware. Technology changes fast. And with each new change comes more advanced software to take advantage of the speed. It may be, its time for you to consider trading in your slow system for a faster one.

Fix: Buy faster computer

15. Windows indexing service. The indexing service helps Windows OS find files faster. But if you are like most, it uses more resources than it is worth.

"Windows ... may run slowly" (due to indexing service) -MicroSoft

Fix: Turn off indexing

16. Eye candy. Some of the graphical options set by default are unnecessary. Speed up computer by turning off some of the glitter. Also extends battery charge on laptops.

Fix: Turn off video options

17. Dust in the machine. After hundreds of hours of sifting through household air, the computer literally accumulates dust in the fans and heat-sink.

Fix: Blow away the dust!

18. Hardware conflicts. Verify that the Device Manager has no conflicts. If any exist resolve these issues as they could be the cause of your problem.

Fix: Change the unsuitable hardware or change its connection (PCI Slut, USB port, serial Port and ...)

19. More advanced problem. If you're still asking, 'Why is my computer so slow?' after applying the above solutions, you may need to seek more advanced help.

Fix: Get more help


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Server Operating Systems

So you're looking at moving to a client-server model. You want to take the documents that are randomly scattered on the hard disks of the office PCs and manage them in a single directory, accessible at any time from any PC in the office. Maybe you want to get your own Internet domain name and have a Web site that you host locally, or build an Intranet for staff information and communication. Perhaps you just want to take your single DSL link and provide secure Net access for everybody in the office.

If you're running a small business and have more than two or three PCs in the office, it's time to start looking at setting up a server. One of your first considerations will be which server operating system (OS) to use.


What is a server operating system?

Server OSes are designed from the ground up to provide platforms for multi-user, frequently business-critical, networked applications. As such, the focus of such operating systems tends to be security, stability and collaboration, rather than user interface.

Server OSes provide a platform for multi-user applications, and most come bundled with a batch of common server applications, such as Web servers, e-mail agents and terminal services.


Contents
- What is a server operating system?
- Common applications for server OSes
- Do I need a different server for each application?
- Things to look for in a server OS
- Different server OSes
- Which OS should I choose?
- I'm confused by server licensing
- Mirroring, fail-over and redundant servers
- What about directory services?
- What are appliance servers?
- Running a server OS: What do I do?
- Operating Systems table


Common applications for server OSes

File and printer sharing: File sharing involves setting up a common storage point for a company's documents - a network drive, as it were. Print sharing allows multiple computers to use a single printer. Windows 95, 98 and ME do have file and print sharing, but are not recommended for use as server OSes.
Application services (including databases): a server OS's ability to run the applications you need is obviously crucial. Servers function as crucial database stores and shared environments for collaborative applications (such as networked MYOB or Quicken).
Web site services: A hypertext transfer protocol (HTTP) server is included with many server OSes, either via an integrated application, or other HTTP applications such as the Apache open source server. Some OSes also come with more advanced features, such as database integration (so you can dynamically build Web pages based on information in a database), personalisation and scripting. The world's most popular HTTP server application, Apache, comes with just about every version of Unix and also runs on Windows. Microsoft provides Internet Information Server (IIS) for Windows platforms.
E-mail, groupware and messaging: A central e-mail server allows you to forward and receive e-mails to and from your business, as well as control individual e-mail accounts based on a domain. Groupware applications, such as Lotus Notes, Microsoft Exchange or Novell GroupWise, provide email as well as much more sophisticated collaboration. These applications can include shared calendars, document version management, group forums, database/messaging integration, instant messaging and whiteboard sharing. Open source mail systems such as SendMail and Exim are also popular.
Terminal services: Allow a client to run a productivity application on a server, while seeing the visual results of the application on their screen. For instance, a client ('terminal') could be running Microsoft Word on the server from their desktop. The server does all the processing work, and just transmits the graphical changes to the terminal, while taking the user's input (mouse movements and key strokes) and sending them to the server. This model allows a company to use clients that don't have a lot of processing power (and enforces the storage of documents on the server, rather than on local hard drives). A server with a lot of memory and a fast processor is needed if it's going to be running productivity applications for the whole office. Nearly every current server OS can do this via Windows Terminal Server, Citrix MetaFrame or the X Window System (which is used by Novell and just about every Unix variant).
Caching: Speeding up network access (usually Internet access) by storing previously downloaded files in a cache - kind of like the way an Internet browser keeps a cache of the Web pages you have visited so it doesn't have to download the files all over again. Examples of caching server applications include Novell BorderManager, Microsoft Internet Security and Acceleration Server, Inktomi Traffic Server and Squid.


Do I need a different server for each application?

Sometimes - a typical server OS can handle two of more of these Services for a small number of clients. When a large number of clients are added, or the applications called for use a lot of processing power, you may need to add more servers and diversify their functions. Load monitoring (that is, reporting on the amount of work the server and network is doing) in server OSes can give a good indication of when a new server - or an upgraded server - might be necessary.



Things to look for in a server OS

Here's a quick list:
Administration - what tools are available and how easy are they to use.
Security - perhaps the most important feature, and the hardest to judge and get right. In general, the more tasks a server performs, the more potential holes hackers have to get in. For a comprehensive look at Server OS security issues.

Stability - downtime is an organisational killer.

Features - does it have the specific services you want built in (does it have an HTTP server for your planned Intranet, for instance, or an FTP server for remote file access)?

Performance - is the server OS, and the hardware platform it runs on, fast enough for your needs? Simple applications like file and print sharing do not require a fast PC - a Pentium-based server with a large hard disk does the trick - while Terminal services or high-volume database servers frequently require very powerful server hardware.

Hardware requirements - whether the server OS can run on Intel or AMD hardware, or whether it requires a proprietary platform, for example Sun's Solaris operating system runs only on Sun hardware, (note, the latter is not necessarily a bad thing; a proprietary platform can provide a holistic approach from the vendor).

Scalability - how many clients can reasonably access this system, and how far can the OS scale in the future (to new hardware or more processors, for instance) if needed.

TCO - how much the ancillary costs of the operating system are - in terms of productivity, administration and downtime.

Third-party applications - what products are available for the platforms that aren't covered by the basic set included in the OS.


Different server OSes

The table shows a short list of some of the server OSes available today. Most of these are based on a Unix core.


Which OS should I choose?

Each has its strengths and weaknesses, and its use may depend on your level of technical competence.

Windows 2000 Professional, Server and Advanced Server can be readily used as small business servers. The strength of Windows lies in the familiarity of the interface; wide support – there is a mass of third party development for the platform, a reasonable price tag and a plentiful supply of available expertise.

The weaknesses of these OSes is the need for user-based licensing. Additionally, significant maintenance for security resources is required (there is a history of viruses infecting IIS in particular).

Linux and FreeBSD actually cover a large range of products. The purchase price ranges from freely downloadable to packaged and supported corporate products costing hundreds of dollars. Linux, in particular, comes in a huge variety of distributions; some act and look much like Windows; others can be used to build an appliance server (see below) that are totally administered through a Web or other interfaces. The core, or Kernel, of the operating systems are the same, however (although there may be variations in the version of the kernel used in a given distribution).

Mac OS X shares origins with FreeBSD, and has many of the same features and stability. The interface is very Macintosh, and you need to buy Apple hardware to use it. There aren't many third party applications for it as yet. It comes with an unlimited user licence.

In contrast to Mac OS X, Novell NetWare 6 is a very mature server OS. It was long sidelined as purely a 'file and print server', and missed out on picking up on a lot of the application server business. It still makes a very capable workgroup or enterprise server. Its file and Web services are first-rate, and it has a wide range of management interfaces, including a Web interface. Unfortunately, there are few third-party applications for it, installation is quite technical and it's not cheap.


I'm confused by server licensing

Server OS vendors approach licensing in a variety of ways. In the case of products like Linux, FreeBSD or Mac OS X, there are no real licensing issues. After the initial purchase of the software, you're free to have as many clients attached to the server and as many processors in it as the software can handle. In the case of Linux, FreeBSD and NetBSD, the open source licenses also allow you to install the products on multiple servers.

Windows and NetWare have user licences. That is, only as many desktops as you have client access licenses (CALs) can connect to the server. If you want to add more PCs to your network, you need to purchase more licences. This cost is on top of the original purchase price of the operating system. When initially purchased, the OS will come with a given number of licences.

Alternately, Microsoft offers a per-CPU server licensing model, as do a few other vendors, such as Sun Microsystems. They charge by the number of CPUs the OS is running on. Sun Solaris 9, for instance, can be put on a single CPU server (or workstation) for free, but a multiprocessor machine will cost a given amount, based on the number of CPUs. In these license agreements, an unlimited number of clients can access the server. If you choose to go with a Microsoft solution, perform a quick comparison between the two options, taking into account current a future desktop numbers.



Mirroring, fail-over and redundant servers

Enterprises commonly have backup servers in case of a failure of some sort. Such server clusters are also used to increase computing capacity by distributing the processing load between the servers.

There are various configurations, but generally speaking a clustering server operating system (which is available only in a few server OSes) keeps track of which servers are currently alive, and shares the load between them (occasionally using a load-balancing server for this task). When one server disappears, through hardware, software or network failure, the load is redistributed to the remaining systems, keeping the server running.

It's probably overkill to have a cluster for most small businesses. Aside from the cost of multiple servers, clustering requires expert knowledge to set up and maintain - the kind of expert knowledge that charges a very high hourly rate. A cost-benefit analysis would be helpful in these circumstances: compare the cost of having redundant servers to the cost of having the server inoperative for a day or more.


What about directory services?

This is another feature that might not directly affect small business, but is worth explaining. Directory Services, of which the two best-known varieties are Novell eDirectory and Microsoft Active Directory, keep track of an organisation's resources and user access permissions.

To best illustrate what directory services do, an example is probably in order. Using directory services, the server administrator could define user John Doe as a sales representative. The directory determines that John Doe, as a sales rep, has access to applications A, B and C, can access the shared network directory X, and can print to printer Y. It also keeps his contacts and other personal details on file. When John logs onto the server, he finds these things (and only these things) accessible. If John got promoted, the server administrator simply changes his classification.

Directories are a convenient way for large enterprises to organize permissions and keep track of inventories and access controls for individuals. The best tools allow drag-and-drop style access to people, locations and resources.

Using and configuring them requires a bit of training, however, and they may not be necessary for small offices, where user mobility is not a great issue. In many cases setting user permissions in the desktop login may prove more fruitful - assuming you're using a desktop OS (such as Windows 2000 or XP) that has significant user permission controls.


What are appliance servers (and can they work for me)?

Appliance servers, a.k.a. turnkey servers, can be a very simple way of providing for a small business's needs at low cost. The appliance server concept covers a range of ideas, but the fundamental idea is that you just plug them into the network, and voila! - you have a server. You administer the server by logging onto it with a Web browser, and clients can access it just as they would any other server.

Simplicity is the key to the appliance server. They come preconfigured for basic common services: usually file and print, DNS, gateway, e-mail, Web and caching. They're a good idea for a company with low technical expertise and little stomach for paying for it. They can't expand beyond their original functions (being, in effect 'closed boxes').

Sun's Cobalt servers are a good example of all-purpose appliance servers. Single purpose servers, such as appliance Web servers are far more common. Dell, IBM, Compaq, Mitac and other major vendors have ranges of appliance-like servers which perform single functions, such as the PowerEdge Web Servers and Tasksmart caching. Similarly, network attached storage devices like Quantum's Snap Servers could be considered appliance file servers.


Running a server OS: What do I do?

Contractors are available for all major server OSes, including free platforms such as Linux and FreeBSD. They can give you advice on a suitable server for your needs.

A support contract is important in this circumstance. Look for uptime guarantees, support response times and availability. Make sure they document the installation properly (in case they suddenly disappear). Get several opinions from suppliers using different platforms and make sure that the product is suitably customised for your business. The server will need maintenance and patching, and proper security takes time to configure, no matter which platform is used.

Managing a support contract well can save you time and lot of headaches. It will also allow you to switch support providers at any time. Manage it badly, and you'll quickly find that your total cost of ownership starts to skyrocket.


Server Operating Systems
Operating System Company Hardware Platform No. of processors Appropriate for:
Windows 2000 Server/Advanced Server/Datacentre Microsoft Intel/AMD 4 (Server)
8 (Advanced)
32 (Datacentre)		 Small, medium and large servers
Windows Server 2003 R2 Standard/Enterprise/Datacentre/Web Server/Small Business Microsoft Intel/AMD & IA-64, Opteron for 64-bit versions of Windows Server 2003 4 (Standard)
Up to 8 (Enterprise)
Minimum 8, Maximum 64 (Datacentre)		 Small, medium and large servers
Linux (Red Hat, Mandrake, Debian, SuSE, etc.) Open Source Many (esp. Intel/AMD) 32 (Linux is readily used on more than 4 CPUs) Small to large servers
FreeBSD 7.0 Open Source x86, Alpha, IA-64, PC-98 and UltraSPARC 4 Small to large servers
Mac OSX Server v10.4 Apple PowerPC with a G3, G4, or G5 processor (Apple) 2 (4 available later) Small to medium servers
NetWare 6.5 Novell Intel/AMD 32 Medium to large servers
Solaris 10 Sun Microsystems Sparc, Intel x64 or x86 128 Medium to enterprise servers
HP-UX 11i v1.6 & HP-UX 11i v2 Hewlett-Packard PA-RISC, Intel Itanium 64 Enterprise servers
IRIX 6.5 SGI MIPS 64 Enterprise servers
AIX 5L 5.2 IBM PowerPC (RS/6000) 32 Enterprise servers

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