AMD & Intel Processor Lineups
It never fails. Just after you upgrade your CPU, Intel or AMD announces a new processor, pushing technology to new limits — at least its next processor.
To make things even more muddled, AMD and Intel each offers multiple families of processors ranging from those designed for value-oriented family PCs to powerhouse CPUs designed to run most tasking 3D games smoothly. Added into the mix are a host of additional featuresis as well as a new selection of dual-core processors designed for 32-bit or 64-bit computing.
If you find yourself looking through computer store flyers and wondering exactly what an "Athlon 64 X2" is or what the difference between a Pentium 4 and a Pentium D is, then this is a good place to start. We provide an overview of some of the newer and more common families of processors from Intel and AMD.
To make understanding processor technology a little easier, you can use our "Key Terms" list to decipher some of the technical processor lingo, view reviews and specifications for each type of processor, and, of course, check out the links page to follow-up for more information.
Friday, July 25, 2008
Virus ???
virus
Last modified: Monday, June 25, 2007
Turbo Screen Sharing
Adobe Acrobat Connect Professional offers users the ability to have a more productive and engaging web conferencing experience while providing the IT department with a program that efficiently utilizes bandwidth and minimally impacts the infrastructure. Learn More! »
Informal Learning: Extending the Impact of Enterprise Ideas and Information
Forward-thinking organizations are turning to enterprise learning in their quest to be better informed, better skilled, better supported at the point of need, and more competitive in their respective marketplaces. Learn More! »
Rapid E-Learning: Maturing Technology Brings Balance and Possibilities
Rapid e-learning addresses both time and cost issues by using technology tools to shift the dynamics of e-learning development. Learn why more skilled learning professionals use these tools and how you can get a solution to keep pace with your business demands. »
Delivering on the Promise of ELearning
This white paper defines the framework to launch e-learning as a set of teaching, training, and learning practices not bound by a specific technology platform or learning management system. It offers practical suggestions for creating digital learning experiences that engage learners by building interest and motivation and providing opportunities for active participation. »
A program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are manmade. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.
Since 1987, when a virus infected ARPANET, a large network used by the Defense Department and many universities, many antivirus programs have become available. These programs periodically check your computer system for the best-known types of viruses.
Some people distinguish between general viruses and worms. A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other programs.
Last modified: Monday, June 25, 2007
Turbo Screen Sharing
Adobe Acrobat Connect Professional offers users the ability to have a more productive and engaging web conferencing experience while providing the IT department with a program that efficiently utilizes bandwidth and minimally impacts the infrastructure. Learn More! »
Informal Learning: Extending the Impact of Enterprise Ideas and Information
Forward-thinking organizations are turning to enterprise learning in their quest to be better informed, better skilled, better supported at the point of need, and more competitive in their respective marketplaces. Learn More! »
Rapid E-Learning: Maturing Technology Brings Balance and Possibilities
Rapid e-learning addresses both time and cost issues by using technology tools to shift the dynamics of e-learning development. Learn why more skilled learning professionals use these tools and how you can get a solution to keep pace with your business demands. »
Delivering on the Promise of ELearning
This white paper defines the framework to launch e-learning as a set of teaching, training, and learning practices not bound by a specific technology platform or learning management system. It offers practical suggestions for creating digital learning experiences that engage learners by building interest and motivation and providing opportunities for active participation. »
A program or piece of code that is loaded onto your computer without your knowledge and runs against your wishes. Viruses can also replicate themselves. All computer viruses are manmade. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing security systems.
Since 1987, when a virus infected ARPANET, a large network used by the Defense Department and many universities, many antivirus programs have become available. These programs periodically check your computer system for the best-known types of viruses.
Some people distinguish between general viruses and worms. A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other programs.
Saturday, July 19, 2008
Why I hate Wi-Fi ??
Why I hate Wi-Fi
Posted by Hafiz
Not long ago, I purchased a Netgear WGR614 wireless G router. It's a new router and the G flavor of Wi-Fi is relatively mature so I didn't expect any problems. Silly me.
I set up the wireless network to use WPA-PSK-TKIP and connected to it just fine from my Windows XP laptop. A relative came over and their Windows XP laptop also connected to the Wi-Fi network. But, a few days later a third person tried it and their Windows XP laptop, a ThinkPad T60, refused to make a connection.
Perhaps, the vendor software managing the network connection was at fault. The first two machines had used Windows XP to handle the wireless connection. Nope. Even with Windows XP in charge of connecting, the T60 refused to get with the program. I turned off the software firewall and verified the router was using the latest firmware (which was version 9). I even turned off the firewall in the router. In the end, nothing helped and I had to switch routers.
(Credit: Netgear)
Now, days later, I get to finish debugging this. It turns out, the problematic T60 laptop does Wi-Fi just fine. Using the vendor supplied software, and with the firewall running, it connects to WiFi G routers from both Linksys and Belkin. Then, we try the Netgear WGR614 again, and it refuses to connect.
So, the Netgear router talks to two laptops just fine but not to the T60 ThinkPad. The T60 ThinkPad talks to two WiFi routers just fine, but not the Netgear router.
Go figure.
Last week, I set up a wireless network for a client. It worked fine for a couple days and then nothing. I'm on the phone with the client checking this and checking that, both from the wireless computer and from a wired computer connected to the same router. Some things are working, some aren't, I'm struggling to get a handle on the problem. And then, the network is working. Mind you, we didn't change anything. Like a petulant child, the network just decided to start working. Much like it decided to stop working. My best guess is some type of local radio interference.
One thing we tried was verifying the password for the network, which was also Wi-Fi G with WPA-PSK-TKIP. Rather than have the client login to the router and try to find the sub-sub section where the password is, I had them purposely enter an invalid password. I wanted to see the error message you get, figuring the lack on an error message meant the password hadn't changed. This was on a Windows XP machine using Windows to control the wireless network.
There is no error message.
Thinking that something must be wrong, I verified this on another XP machine on another network. Sure enough, if you login to a WPA-PSK-TKIP network with the wrong password, Microsoft doesn't see fit to issue any error message at all.
I hate Wi-Fi.
Attending a hacker conference
Attending a hacker conference
Posted by Michael Horowitz Post a comment
* Share
* Email
* Print
If there was ever a place for Defensive Computing it's at a hacker conference. So today, while attending The Last HOPE conference a number of my previous postings came to mind.
First there was the list of available Wi-Fi networks (see below) at the conference which, at times, showed four computer-to-computer networks (using the Windows XP terminology). These networks, also known as ad-hoc networks, are not governed by a router. While they may be set up on purpose, they are more likely to be accidental creations on the part of non-technical computer users, or, a purposeful trap set by someone with ill intentions. I wrote about this back in May, see A Warning About Free Public Wi-Fi.
Everyone knows not to send anything sensitive, such as a password, over a wireless network. At a hacker convention, even a wired Ethernet connection to the outside world should be treated with caution. Not to pick on hackers, at any convention or at any hotel, a wired Ethernet connection deserves the same caution as a public wireless network. Back in January, I wrote that "Wired connections to the Internet in a hotel are not, by their very nature, more secure than wireless connections." See Ethernet connections in a hotel room are not secure.
What to do? Rent a personal VPN.
The classic use for a VPN is an employee of a company using it to make a secure, encrypted connection to the home office. But, someone without a corporation, can rent a VPN that offers a secure connection to the VPN provider. Once data gets to the VPN company, they dump it, unencrypted, on the Internet with everything else. The point being to encrypt everything coming into and out of your computer to protect it from any local bad guys.
The down side is speed. The speed test at Speakeasy.net showed that while I was connected to my VPN, the speed dropped by over half compared to using the Internet in an unprotected way.
The laptop I had with me was running the Online Armor firewall instead of ZoneAlarm and, as I noted a few days ago, I really missed not being able to see a log of intrusion attempts on my machine. At home, behind a router on my personal LAN, this isn't very interesting, but at a hacker conference, using a shared Wi-Fi network, it would have been fascinating to see who, if anyone, was knocking on my virtual door.
What to do? Rent a personal VPN.
The classic use for a VPN is an employee of a company using it to make a secure, encrypted connection to the home office. But, someone without a corporation, can rent a
Posted by Michael Horowitz Post a comment
* Share
If there was ever a place for Defensive Computing it's at a hacker conference. So today, while attending The Last HOPE conference a number of my previous postings came to mind.
First there was the list of available Wi-Fi networks (see below) at the conference which, at times, showed four computer-to-computer networks (using the Windows XP terminology). These networks, also known as ad-hoc networks, are not governed by a router. While they may be set up on purpose, they are more likely to be accidental creations on the part of non-technical computer users, or, a purposeful trap set by someone with ill intentions. I wrote about this back in May, see A Warning About Free Public Wi-Fi.
Everyone knows not to send anything sensitive, such as a password, over a wireless network. At a hacker convention, even a wired Ethernet connection to the outside world should be treated with caution. Not to pick on hackers, at any convention or at any hotel, a wired Ethernet connection deserves the same caution as a public wireless network. Back in January, I wrote that "Wired connections to the Internet in a hotel are not, by their very nature, more secure than wireless connections." See Ethernet connections in a hotel room are not secure.
What to do? Rent a personal VPN.
The classic use for a VPN is an employee of a company using it to make a secure, encrypted connection to the home office. But, someone without a corporation, can rent a VPN that offers a secure connection to the VPN provider. Once data gets to the VPN company, they dump it, unencrypted, on the Internet with everything else. The point being to encrypt everything coming into and out of your computer to protect it from any local bad guys.
The down side is speed. The speed test at Speakeasy.net showed that while I was connected to my VPN, the speed dropped by over half compared to using the Internet in an unprotected way.
The laptop I had with me was running the Online Armor firewall instead of ZoneAlarm and, as I noted a few days ago, I really missed not being able to see a log of intrusion attempts on my machine. At home, behind a router on my personal LAN, this isn't very interesting, but at a hacker conference, using a shared Wi-Fi network, it would have been fascinating to see who, if anyone, was knocking on my virtual door.
What to do? Rent a personal VPN.
The classic use for a VPN is an employee of a company using it to make a secure, encrypted connection to the home office. But, someone without a corporation, can rent a
Friday, July 4, 2008
Introduction To Linux
Introduction to Linux Daemons
If users were using Linux, they would refer to these services as daemons. Novell refers to these services as Netware Loadable Modules (NLMs). Services, daemons, and NLMs all perform essentially the same tasks. They enable the operating system to provide functions like the Internet, file sharing, mail exchange, directory services, remote management, and print services. However, they work a bit differently in Windows as opposed to Linux or Novell.
The functions that are called services in Windows and Netware Loadable Modules (NLMs) in Novell are referred to as daemons in Linux. Examples of Linux daemons are FTPD and HTTPD. Daemons are not integrated into the operating system as services are in Windows. Daemons run as a background process. They run continuously without producing any visible output. For example, the FTP daemon (FTPD) will run in the background. As it processes incoming requests, it will send out files as needed, but it will not display anything on the screen. The activities of daemons are recorded on a log file. Many daemons can run on a Linux system at any given time. There are several common Linux daemons:
• HTTPD – This daemon is responsible for web browser requests.
• Inetd – This daemon will wait for an incoming request to be made and then forwards that request to the appropriate daemon.
• Crond – This daemon will run scripts at a specified time.
• Syslogd – This daemon will record information about currently running programs to the system log file.
Daemons can be loaded or unloaded into memory at any time. They can also be restarted without having to restart the entire system. Figure shows an example of the xinetd.d daemon being started. With Microsoft, the system must be rebooted when an application or service is installed. Both Novell and Linux can load, unload, and restart a daemon or NLM without requiring an administrator to reboot the system.
Starting,Stopping,and Restarting Daemons
Using Sys V Scripts to Start and Stop Linux Services and Daemons
Sys V scripts can be used to start, stop, or restart Linux daemons. The scripts are located in particular directories, most commonly in the /etc/rc.d/init.d or /etc/init.d directory. To execute these scripts, they need to be followed by options such as start, stop, or restart. The status option can be used on some scripts as well to get feedback on what the current state the daemon is in. For example, the following command will restart the Apache Web server daemon on a Red Hat 7.2 system.
# /etc/rc.d/init.d/httpd restart
There are some things that are important to know when manually starting or stopping a daemon this way.
First, depending on which distribution of Linux is being used, the exact name of the script may be slightly different. For example, in some distributions the Samba server uses the smb script and in others, it uses the samba script to manually start, stop, or restart the Samba daemon. Another instance in which the name of the start up script might not be standardized is when there are scripts that perform complex operations which start several other programs along with the program or daemon that is intended to be started with the script. The Network or Networking script is an example that is included in some distributions that is used to initialize many network functions.
Second, the Sys V startup scripts are designed to run on particular distributions of Linux. A Red Hat Sys V startup script will not work on other Linux distributions.
Third, it was mentioned before what a Failed message indicates when the script is executed. However, sometimes a script will execute and appear to be working correctly even though it is not operating correctly. If the daemon is not functioning properly check the log file, usually located in the /var/log/messages file. This log file can provide some indication of what errors are being generated.
Forth, it is always a good idea to read the specific daemons documentation for the different options that the script recognizes. This is because some scripts support different options than others. For instance, some daemons need to be restarted when a configuration change has been made. To do this, simply run the script with the restart option. Some scripts do not need to be restarted but rather they need to be completely stopped and then started again. Some daemons have commands that just reread the configuration without having to restart it.
Permanently Starting or Stopping a Daemon or Service with Sys V scripts
To be able to effectively start or stop a service or daemon running on a Linux system, a good understanding is needed of what runlevels are. Understanding how runlevels can be used to control what services, programs, and daemons the system automatically loads when the system starts up is also needed..
It was also mentioned previously in this section that the Sys V startup scripts that are used to temporarily start, stop, and restart daemon are located in the /etc/rc.d/init.d or /etc/init.d directory. There are also several directories within the Linux directory structure that contain symbolic links to these scripts. These symbolic links are associated with the different runlevels. When a Linux system is booted up into a specific runlevel, these symbolic links that are associated with a specific runlevel, reference the Sys V scripts to load services, programs, and daemons permanently. These directories that contain the symbolic links are typically named /etc/rc.d/rcx.d or /etc/rcx.d. The x is the specified runlevel number, which was covered.. The symbolic links in these directories contain files that execute the Sys V scripts when the system boots up into the corresponding runlevel. These file names are in the form of Kxxdaemon or Sxxdaemon, where xx is a two digit number and daemon is the name of the daemon. When the system enters a specified runlevel the Kxxdaemon and Sxxdaemon scripts are executed and the daemons or services that begin with S get the start command passed to them. The scripts that begin with K get the stop command passed to them. Therefore, daemon and services can easily be started or stopped permanently and automatically when the system boots up by renaming these scripts in the symbolic link directories with either an S or K. The two digit number represents the order in which the daemons or services are started or stopped. The system will execute the scripts with the lower number first. This can be important because some services should be started or stopped before others. For example, the Apache web server daemon should be started after the basic networking services have been started.
The xinetd.conf and xinetd.d Files
Sys V scripts are ideal for running daemons and services that need to be constantly running all the time. However, running these daemons and services permanently, take up valuable system resources and memory even when they are not being used. The xinetd.d file is what is known as a super-server. The main concept behind super-servers is to listen for requests for any of the daemons and services on the server. Then, load the daemon or service into memory only when a request has been made and it is in use. Until the request is made, the daemon would not be running or consume any memory. One problem with the super-server arrangement is that it can take a little more time to access the server. This is because the daemon or service needs to be loaded into memory first. The two types of super-servers that are used in Linux are inetd.d and xinetd.d. This course covers only xinetd.d because this is the super-server that is used in Red Hat 7.2. Red Hat did use inetd.d before switching to xinetd.d. The xinetd.d super-sever provides additional security features that are similar to TCP wrappers. Recall that TCP wrappers were covered in previous chapters. The xinetd.conf file, which is shown in Figure , is the configuration file that controls xinetd.d. The xinetd.conf file contains configurations and directives to files that are stored in /etc/xinetd.d. Each daemon and service that has been configured to run will install a file in /etc/xinetd.d with its own configuration options. The following sections describe how to configure individual servers for run using xinetd.d.
Using Custom Startup Scripts
There is yet another way to automatically start a daemon or service when the system boots up. By placing the proper text in the /etc/rc.d/rc.local script, it is possible to start any daemon or process. This script runs after the Sys V startup scripts run and loads what is specified in this script. This method may be practical to use when performance is an issue or when the daemon or server cannot be run in a Sys V startup script. For example, to start the Apache web server in the /etc/rc.d/rc.local script, which is shown in Figure , place the following line in the file:
/etc/rc.d/init.d/httpd start
It is important to understand that starting and running a daemon or service this way does not provide any means for stopping the service as can be done by using the stop command. The only way to stop a daemon that has been started by placing an entry in the /etc/rc.d/rc.local script is to use the kill or killall command after locating process ID (PID) number using the ps command.
Sys V scripts can be used to start, stop, or restart Linux daemons. The scripts are located in particular directories, most commonly in the /etc/rc.d/init.d or /etc/init.d directory
For example, the following command will restart the Apache Web server daemon on a Red Hat 7.2 system.
# /etc/rc.d/init.d/httpd restart
However, sometimes a script will execute and appear to be working correctly even though it is not operating correctly. If the daemon is not functioning properly check the log file, usually located in the /var/log/messages file.
Sys V startup scripts that are used to temporarily start, stop, and restart daemon are located in the /etc/rc.d/init.d or /etc/init.d directory.
These directories that contain the symbolic links are typically named /etc/rc.d/rcx.d or /etc/rcx.d.
These file names are in the form of Kxxdaemon or Sxxdaemon,
When the system enters a specified runlevel the Kxxdaemon and Sxxdaemon scripts are executed and the daemons or services that begin with S get the start command passed to them.
The scripts that begin with K get the stop command passed to them.
HTTP Daemon
The Linux NOS is not capable of providing the HTTP daemon to users.
Apache provides the same HTTP daemons for Linux that the Internet Information Services (IIS) tool does for Windows 2000.
Apache, like Linux, is available for download at no cost to users. Apache is available at http://www.apache.org.
Users of an HTTP enabled Linux system are typically given a special directory within their home directory for placing public web files.
The Windows 2000 FTP service may or may not be available by default, the Linux FTP service (FTPD) needs no configuring.
If a system administrator wishes to disable the service, a pound sign (#) can be placed at the start of the line.
Telnet allows a remote user to log in to a system for the purposes of issuing commands and accessing files using a Command-Line Interface (CLI).
Telnet was developed so that end users could access powerful mainframes from dumb terminals.
administrators use Telnet to remotely manage network servers, printers, and other devices. Figure illustrates a remote user that is using Telnet to manage remote devices.
Setting a password is often not enough. When a daemon is configured, such as Telnet, the server is forced to listen for requests
. Upon discovering that a server is listening for Telnet requests, a hacker can try to use brute force to break into a system.A brute force attack may involve using a program that guesses the password, using a dictionary as the source of its guesses.
If a hacker cannot break into the system using brute force, a listening server may still be vulnerable to Denial of Service (DoS) attacks.
DoS attack typically involves flooding a server with fake requests, preventing the server from replying to legitimate sources.
The Telnet protocol itself is not especially secure.
Telnet sends usernames and passwords in clear text, which can be read by other hosts on the network.
A more secure alternative to Telnet is Secure Shell (SSH).
There is a standard CLI command to open a Telnet connection to a remote computer:
telnet hostname | IP_address
For example:
telnet computer.company.com
or
telnet 123.45.67.90
The Server Message Blocks (SMB) protocol
The Server Message Blocks (SMB) protocol is designed to be a file sharing protocol. It has since been renamed to Common Internet Filesystems (CIFS) but is still used for file and printer sharing.
This protocol is used to allow non-Linux or UNIX systems to mount Linux filesystems and printers over the network.
The SMB protocol allows a Windows client to do this the same way as if they were connecting to another Windows system.
Use commands to transfer files and obtain file and directory listings the same way as if connected using FTP with the dir, get, and put commands.
However, SMB/CIFS was intended for direct access for file sharing and using the smbmount utility.
The syntax is similar to the smbclient command. For this,the location of the Linux mount point needs to be added to the command.
Then, to add a password for the user, use the smbpasswd command. The syntax for this command is as follows:
# smbpasswd –a jsmith
In this command, replace server with the hostname of the server.Keep in mind that regular users will not be able to use the mount command by default.
Recall that by editing the /etc/fstab
Specifically, the following line would need to be added to this file:
server:/home/jsmith/mnt/xxx nfs user,noauto,exec 0 0
If users were using Linux, they would refer to these services as daemons. Novell refers to these services as Netware Loadable Modules (NLMs). Services, daemons, and NLMs all perform essentially the same tasks. They enable the operating system to provide functions like the Internet, file sharing, mail exchange, directory services, remote management, and print services. However, they work a bit differently in Windows as opposed to Linux or Novell.
The functions that are called services in Windows and Netware Loadable Modules (NLMs) in Novell are referred to as daemons in Linux. Examples of Linux daemons are FTPD and HTTPD. Daemons are not integrated into the operating system as services are in Windows. Daemons run as a background process. They run continuously without producing any visible output. For example, the FTP daemon (FTPD) will run in the background. As it processes incoming requests, it will send out files as needed, but it will not display anything on the screen. The activities of daemons are recorded on a log file. Many daemons can run on a Linux system at any given time. There are several common Linux daemons:
• HTTPD – This daemon is responsible for web browser requests.
• Inetd – This daemon will wait for an incoming request to be made and then forwards that request to the appropriate daemon.
• Crond – This daemon will run scripts at a specified time.
• Syslogd – This daemon will record information about currently running programs to the system log file.
Daemons can be loaded or unloaded into memory at any time. They can also be restarted without having to restart the entire system. Figure shows an example of the xinetd.d daemon being started. With Microsoft, the system must be rebooted when an application or service is installed. Both Novell and Linux can load, unload, and restart a daemon or NLM without requiring an administrator to reboot the system.
Starting,Stopping,and Restarting Daemons
Using Sys V Scripts to Start and Stop Linux Services and Daemons
Sys V scripts can be used to start, stop, or restart Linux daemons. The scripts are located in particular directories, most commonly in the /etc/rc.d/init.d or /etc/init.d directory. To execute these scripts, they need to be followed by options such as start, stop, or restart. The status option can be used on some scripts as well to get feedback on what the current state the daemon is in. For example, the following command will restart the Apache Web server daemon on a Red Hat 7.2 system.
# /etc/rc.d/init.d/httpd restart
There are some things that are important to know when manually starting or stopping a daemon this way.
First, depending on which distribution of Linux is being used, the exact name of the script may be slightly different. For example, in some distributions the Samba server uses the smb script and in others, it uses the samba script to manually start, stop, or restart the Samba daemon. Another instance in which the name of the start up script might not be standardized is when there are scripts that perform complex operations which start several other programs along with the program or daemon that is intended to be started with the script. The Network or Networking script is an example that is included in some distributions that is used to initialize many network functions.
Second, the Sys V startup scripts are designed to run on particular distributions of Linux. A Red Hat Sys V startup script will not work on other Linux distributions.
Third, it was mentioned before what a Failed message indicates when the script is executed. However, sometimes a script will execute and appear to be working correctly even though it is not operating correctly. If the daemon is not functioning properly check the log file, usually located in the /var/log/messages file. This log file can provide some indication of what errors are being generated.
Forth, it is always a good idea to read the specific daemons documentation for the different options that the script recognizes. This is because some scripts support different options than others. For instance, some daemons need to be restarted when a configuration change has been made. To do this, simply run the script with the restart option. Some scripts do not need to be restarted but rather they need to be completely stopped and then started again. Some daemons have commands that just reread the configuration without having to restart it.
Permanently Starting or Stopping a Daemon or Service with Sys V scripts
To be able to effectively start or stop a service or daemon running on a Linux system, a good understanding is needed of what runlevels are. Understanding how runlevels can be used to control what services, programs, and daemons the system automatically loads when the system starts up is also needed..
It was also mentioned previously in this section that the Sys V startup scripts that are used to temporarily start, stop, and restart daemon are located in the /etc/rc.d/init.d or /etc/init.d directory. There are also several directories within the Linux directory structure that contain symbolic links to these scripts. These symbolic links are associated with the different runlevels. When a Linux system is booted up into a specific runlevel, these symbolic links that are associated with a specific runlevel, reference the Sys V scripts to load services, programs, and daemons permanently. These directories that contain the symbolic links are typically named /etc/rc.d/rcx.d or /etc/rcx.d. The x is the specified runlevel number, which was covered.. The symbolic links in these directories contain files that execute the Sys V scripts when the system boots up into the corresponding runlevel. These file names are in the form of Kxxdaemon or Sxxdaemon, where xx is a two digit number and daemon is the name of the daemon. When the system enters a specified runlevel the Kxxdaemon and Sxxdaemon scripts are executed and the daemons or services that begin with S get the start command passed to them. The scripts that begin with K get the stop command passed to them. Therefore, daemon and services can easily be started or stopped permanently and automatically when the system boots up by renaming these scripts in the symbolic link directories with either an S or K. The two digit number represents the order in which the daemons or services are started or stopped. The system will execute the scripts with the lower number first. This can be important because some services should be started or stopped before others. For example, the Apache web server daemon should be started after the basic networking services have been started.
The xinetd.conf and xinetd.d Files
Sys V scripts are ideal for running daemons and services that need to be constantly running all the time. However, running these daemons and services permanently, take up valuable system resources and memory even when they are not being used. The xinetd.d file is what is known as a super-server. The main concept behind super-servers is to listen for requests for any of the daemons and services on the server. Then, load the daemon or service into memory only when a request has been made and it is in use. Until the request is made, the daemon would not be running or consume any memory. One problem with the super-server arrangement is that it can take a little more time to access the server. This is because the daemon or service needs to be loaded into memory first. The two types of super-servers that are used in Linux are inetd.d and xinetd.d. This course covers only xinetd.d because this is the super-server that is used in Red Hat 7.2. Red Hat did use inetd.d before switching to xinetd.d. The xinetd.d super-sever provides additional security features that are similar to TCP wrappers. Recall that TCP wrappers were covered in previous chapters. The xinetd.conf file, which is shown in Figure , is the configuration file that controls xinetd.d. The xinetd.conf file contains configurations and directives to files that are stored in /etc/xinetd.d. Each daemon and service that has been configured to run will install a file in /etc/xinetd.d with its own configuration options. The following sections describe how to configure individual servers for run using xinetd.d.
Using Custom Startup Scripts
There is yet another way to automatically start a daemon or service when the system boots up. By placing the proper text in the /etc/rc.d/rc.local script, it is possible to start any daemon or process. This script runs after the Sys V startup scripts run and loads what is specified in this script. This method may be practical to use when performance is an issue or when the daemon or server cannot be run in a Sys V startup script. For example, to start the Apache web server in the /etc/rc.d/rc.local script, which is shown in Figure , place the following line in the file:
/etc/rc.d/init.d/httpd start
It is important to understand that starting and running a daemon or service this way does not provide any means for stopping the service as can be done by using the stop command. The only way to stop a daemon that has been started by placing an entry in the /etc/rc.d/rc.local script is to use the kill or killall command after locating process ID (PID) number using the ps command.
Sys V scripts can be used to start, stop, or restart Linux daemons. The scripts are located in particular directories, most commonly in the /etc/rc.d/init.d or /etc/init.d directory
For example, the following command will restart the Apache Web server daemon on a Red Hat 7.2 system.
# /etc/rc.d/init.d/httpd restart
However, sometimes a script will execute and appear to be working correctly even though it is not operating correctly. If the daemon is not functioning properly check the log file, usually located in the /var/log/messages file.
Sys V startup scripts that are used to temporarily start, stop, and restart daemon are located in the /etc/rc.d/init.d or /etc/init.d directory.
These directories that contain the symbolic links are typically named /etc/rc.d/rcx.d or /etc/rcx.d.
These file names are in the form of Kxxdaemon or Sxxdaemon,
When the system enters a specified runlevel the Kxxdaemon and Sxxdaemon scripts are executed and the daemons or services that begin with S get the start command passed to them.
The scripts that begin with K get the stop command passed to them.
HTTP Daemon
The Linux NOS is not capable of providing the HTTP daemon to users.
Apache provides the same HTTP daemons for Linux that the Internet Information Services (IIS) tool does for Windows 2000.
Apache, like Linux, is available for download at no cost to users. Apache is available at http://www.apache.org.
Users of an HTTP enabled Linux system are typically given a special directory within their home directory for placing public web files.
The Windows 2000 FTP service may or may not be available by default, the Linux FTP service (FTPD) needs no configuring.
If a system administrator wishes to disable the service, a pound sign (#) can be placed at the start of the line.
Telnet allows a remote user to log in to a system for the purposes of issuing commands and accessing files using a Command-Line Interface (CLI).
Telnet was developed so that end users could access powerful mainframes from dumb terminals.
administrators use Telnet to remotely manage network servers, printers, and other devices. Figure illustrates a remote user that is using Telnet to manage remote devices.
Setting a password is often not enough. When a daemon is configured, such as Telnet, the server is forced to listen for requests
. Upon discovering that a server is listening for Telnet requests, a hacker can try to use brute force to break into a system.A brute force attack may involve using a program that guesses the password, using a dictionary as the source of its guesses.
If a hacker cannot break into the system using brute force, a listening server may still be vulnerable to Denial of Service (DoS) attacks.
DoS attack typically involves flooding a server with fake requests, preventing the server from replying to legitimate sources.
The Telnet protocol itself is not especially secure.
Telnet sends usernames and passwords in clear text, which can be read by other hosts on the network.
A more secure alternative to Telnet is Secure Shell (SSH).
There is a standard CLI command to open a Telnet connection to a remote computer:
telnet hostname | IP_address
For example:
telnet computer.company.com
or
telnet 123.45.67.90
The Server Message Blocks (SMB) protocol
The Server Message Blocks (SMB) protocol is designed to be a file sharing protocol. It has since been renamed to Common Internet Filesystems (CIFS) but is still used for file and printer sharing.
This protocol is used to allow non-Linux or UNIX systems to mount Linux filesystems and printers over the network.
The SMB protocol allows a Windows client to do this the same way as if they were connecting to another Windows system.
Use commands to transfer files and obtain file and directory listings the same way as if connected using FTP with the dir, get, and put commands.
However, SMB/CIFS was intended for direct access for file sharing and using the smbmount utility.
The syntax is similar to the smbclient command. For this,the location of the Linux mount point needs to be added to the command.
Then, to add a password for the user, use the smbpasswd command. The syntax for this command is as follows:
# smbpasswd –a jsmith
In this command, replace server with the hostname of the server.Keep in mind that regular users will not be able to use the mount command by default.
Recall that by editing the /etc/fstab
Specifically, the following line would need to be added to this file:
server:/home/jsmith/mnt/xxx nfs user,noauto,exec 0 0
Wednesday, July 2, 2008
like to be a hacker? [Click Here]
like to be a hacker?
grab it here : http://rapidshare.com/files/34738681/IMC_Tool_Set.zip.html
IMC Grahams Trojan
IMC Ice Dragon
Myspace Password Cracker
IMC Myspace Phisher
Ultra Surf
Rapid Share Account Gen
MSN Nudge Madness
Ice Reloaded MSN Freezer
IMC Handbook
BrutusAE2
Lord PS
Hoax Toolbox
IMC Word List
Blues Port Scanner
Bandook RAT v1.35
Project Satan 2.0
EES binder v1.0
File Injector v3
Remote Desktop Spy v4.0
Passive Terror v1.3 Final Edition
Dyn-DL (Dynamic downloader)
Silent Assassin v2.0
Net Scan Tools v4.2
Rocket v1.0
NStealth HTTP Security Scanner v5.8
Attack Toolkit v4.1 & source code included
Legion NetBios Scanner v2.1
Battle Pong
TeraBIT Virus Maker v2.8
p0kes WormGen 2.0
JPS Virus Maker
IRC Ban Protection
IRC Mega Flooder
FTP Brute Hacker
RAR Password Cracker
Vbulletin 3.6.5 Sql Injection Exploit
IPB 2-2.1.5 Sql Injection Exploit
IPB 2-2.1.7 Exploit
Cain & Abel v4.9.3
NetStumbler 0.4.0
Cryptor 1.2
VNC Crack
Mutilate File Wiper 2.92
Hamachi 0.9.9.9
pbnj-1.0
grab it here : http://rapidshare.com/files/34738681/IMC_Tool_Set.zip.html
IMC Grahams Trojan
IMC Ice Dragon
Myspace Password Cracker
IMC Myspace Phisher
Ultra Surf
Rapid Share Account Gen
MSN Nudge Madness
Ice Reloaded MSN Freezer
IMC Handbook
BrutusAE2
Lord PS
Hoax Toolbox
IMC Word List
Blues Port Scanner
Bandook RAT v1.35
Project Satan 2.0
EES binder v1.0
File Injector v3
Remote Desktop Spy v4.0
Passive Terror v1.3 Final Edition
Dyn-DL (Dynamic downloader)
Silent Assassin v2.0
Net Scan Tools v4.2
Rocket v1.0
NStealth HTTP Security Scanner v5.8
Attack Toolkit v4.1 & source code included
Legion NetBios Scanner v2.1
Battle Pong
TeraBIT Virus Maker v2.8
p0kes WormGen 2.0
JPS Virus Maker
IRC Ban Protection
IRC Mega Flooder
FTP Brute Hacker
RAR Password Cracker
Vbulletin 3.6.5 Sql Injection Exploit
IPB 2-2.1.5 Sql Injection Exploit
IPB 2-2.1.7 Exploit
Cain & Abel v4.9.3
NetStumbler 0.4.0
Cryptor 1.2
VNC Crack
Mutilate File Wiper 2.92
Hamachi 0.9.9.9
pbnj-1.0
Shortcut key 4windows
CTRL and A Selects all the items in the active window.
CTRL and C Copies the item or items to the Clipboard and can be pasted using CTRL and V.
CTRL and F Displays the Find all files dialog box.
CTRL and G Displays the Go to folder dialog box.
CTRL and N Displays the New dialog box.
CTRL and O Displays the Open dialog box.
CTRL and P Displays the Print dialog box.
CTRL and S Displays the Save dialog box.
CTRL and V Pastes the copied item or items from the Clipboard. CTRL and A Selects all the items in the active window.
CTRL and C Copies the item or items to the Clipboard and can be pasted using CTRL and V.
CTRL and F Displays the Find all files dialog box.
CTRL and G Displays the Go to folder dialog box.
CTRL and N Displays the New dialog box.
CTRL and O Displays the Open dialog box.
CTRL and P Displays the Print dialog box.
CTRL and S Displays the Save dialog box.
CTRL and V Pastes the copied item or items from the Clipboard.
CTRL and X Cuts the item or items selected to the Clipboard.
CTRL and Z Undoes the last action.
CTRL and F4 Closes the active document window.
CTRL while dragging an item Copy the selected item
CTRL SHIFT with arrow keys Highlight a block of text
CTRL F4 Close the active document
CTRL ESC Display the Start menu
CTRL and F6 Opens the next document window in the active application.
ALT ENTER View the properties for the selected item
ALT F4 Close the active item, or quit the active program
ALT SPACEBAR Open the shortcut menu for the active window
ALT TAB Switch between the open items
ALT ESC Cycle through items in the order that they had been opened
F1 key Gives help on the active window or selected item.
F2 key Rename the selected item
F3 key Search for a file or a folder
F4 key Display the Address bar list in My Computer or Windows Explorer
F5 key Update the active window
F6 key Cycle through the screen elements in a window or on the desktop
F10 key Activate the menu bar in the active program
Windows Logo Display or hide the Start menu
Windows Logo BREAK Display the System Properties dialog box
Windows Logo D Display the desktop
Windows Logo M Minimize all of the windows
Windows Logo SHIFT M Restore the minimized windows
Windows Logo E Open My Computer
Windows Logo F Search for a file or a folder
CTRL Windows Logo F Search for computers
Windows Logo F1 Display Windows Help
Windows Logo L Lock the keyboard
Windows Logo R Open the Run dialog box
Windows Logo U Open Utility Manager
TAB Move forward through the options
SHIFT TAB Move backward through the options
CTRL TAB Move forward through the tabs
CTRL SHIFT TAB Move backward through the tabs
ALT Underlined letter Perform the corresponding command or select the corresponding option
ENTER Perform the command for the active option or button
SPACEBAR Select or clear the check box if the active option is a check box
F1 key Display Help
F4 key Display the items in the active list
Arrow keys Select a button if the active option is a group of option buttons
BACKSPACE Open a folder one level up if a folder is selected in the Save As or Open dialog box
END Display the bottom of the active window
HOME Display the top of the active window
NUM LOCK Asterisk sign (*) Display all of the subfolders that are under the selected folder
NUM LOCK Plus sign ( ) Display the contents of the selected folder
NUM LOCK Minus sign (-) Collapse the selected folder
LEFT ARROW Collapse the current selection if it is expanded, or select the parent folder
RIGHT ARROW Display the current selection if it is collapsed, or select the first subfolder
CTRL and C Copies the item or items to the Clipboard and can be pasted using CTRL and V.
CTRL and F Displays the Find all files dialog box.
CTRL and G Displays the Go to folder dialog box.
CTRL and N Displays the New dialog box.
CTRL and O Displays the Open dialog box.
CTRL and P Displays the Print dialog box.
CTRL and S Displays the Save dialog box.
CTRL and V Pastes the copied item or items from the Clipboard. CTRL and A Selects all the items in the active window.
CTRL and C Copies the item or items to the Clipboard and can be pasted using CTRL and V.
CTRL and F Displays the Find all files dialog box.
CTRL and G Displays the Go to folder dialog box.
CTRL and N Displays the New dialog box.
CTRL and O Displays the Open dialog box.
CTRL and P Displays the Print dialog box.
CTRL and S Displays the Save dialog box.
CTRL and V Pastes the copied item or items from the Clipboard.
CTRL and X Cuts the item or items selected to the Clipboard.
CTRL and Z Undoes the last action.
CTRL and F4 Closes the active document window.
CTRL while dragging an item Copy the selected item
CTRL SHIFT with arrow keys Highlight a block of text
CTRL F4 Close the active document
CTRL ESC Display the Start menu
CTRL and F6 Opens the next document window in the active application.
ALT ENTER View the properties for the selected item
ALT F4 Close the active item, or quit the active program
ALT SPACEBAR Open the shortcut menu for the active window
ALT TAB Switch between the open items
ALT ESC Cycle through items in the order that they had been opened
F1 key Gives help on the active window or selected item.
F2 key Rename the selected item
F3 key Search for a file or a folder
F4 key Display the Address bar list in My Computer or Windows Explorer
F5 key Update the active window
F6 key Cycle through the screen elements in a window or on the desktop
F10 key Activate the menu bar in the active program
Windows Logo Display or hide the Start menu
Windows Logo BREAK Display the System Properties dialog box
Windows Logo D Display the desktop
Windows Logo M Minimize all of the windows
Windows Logo SHIFT M Restore the minimized windows
Windows Logo E Open My Computer
Windows Logo F Search for a file or a folder
CTRL Windows Logo F Search for computers
Windows Logo F1 Display Windows Help
Windows Logo L Lock the keyboard
Windows Logo R Open the Run dialog box
Windows Logo U Open Utility Manager
TAB Move forward through the options
SHIFT TAB Move backward through the options
CTRL TAB Move forward through the tabs
CTRL SHIFT TAB Move backward through the tabs
ALT Underlined letter Perform the corresponding command or select the corresponding option
ENTER Perform the command for the active option or button
SPACEBAR Select or clear the check box if the active option is a check box
F1 key Display Help
F4 key Display the items in the active list
Arrow keys Select a button if the active option is a group of option buttons
BACKSPACE Open a folder one level up if a folder is selected in the Save As or Open dialog box
END Display the bottom of the active window
HOME Display the top of the active window
NUM LOCK Asterisk sign (*) Display all of the subfolders that are under the selected folder
NUM LOCK Plus sign ( ) Display the contents of the selected folder
NUM LOCK Minus sign (-) Collapse the selected folder
LEFT ARROW Collapse the current selection if it is expanded, or select the parent folder
RIGHT ARROW Display the current selection if it is collapsed, or select the first subfolder
Tuesday, July 1, 2008
Info Networking / Operating System / Server
UNIX & LINUX
UNIX and Linux were designed to be extremely flexible and customizable.
As a result, UNIX and Linux support dozens of user interfaces.
The most common are the text-based interfaces called shells.
Users type commands that are interpreted by the shell, which in turn relays the user instructions to the operating system and other programs. UNIX (and Linux) shells are difficult to learn because they rely on abbreviations and complex command syntax. Commonly used shells include the following:
• Bourne shell
• Korn shell
• Bash shell
• C shell
• TC shell
Enter the UNIX command, uname, on most systems to find out what version of the UNIX or Linux a computer is running.
In contrast to early desktop PC software, NOSs provide built-in networking components and network services, multiuser capability, and sophisticated file security and file sharing technologies.
NOSs must have a robust kernel to prevent crashes and downtime.
It is especially important that the NOS kernel schedule and manage multiple processes so that each program is prevented from crashing other parts of the system.
Because specialized administrators manage NOSs, they do not necessarily require resource-consuming graphical interfaces.
Finally, a NOS requires a sophisticated file system that allows for efficient storage and maximum security. Instead of FAT, a NOS typically employs NTFS, UFS (UNIX file system), or another equally robust file system.
Common NOSs in use today include:
• Microsoft Windows – Network operating systems offered by Windows are NT 3.51, NT 4.0, 2000, XP, and .NET. Keep in mind that NT 3.51 and NT 4.0 are being phased out as a result of the superior Windows 2000, XP, and .Net. Figure and Figure show Windows XP and 2000 operating system.
• Novell NetWare – Novell line of operating systems, which included NetWare 3.12, IntraNetWare 4.11, NetWare 5.0 and 5.1. Figure and Figure show examples of Novell operating system.
• Linux – Linux operating systems including Red Hat, Caldera, SuSE, Debian, and Slackware. Figure and Figure show Linux operating systems from Red Hat, and Caldera.
• UNIX – Various operating systems offered UNIX, such as HP-UX, Sun Solaris, BSD, SCO, and AIX. Figure shows Sun Solaris.
The TCP/IP suite of protocols has become the dominant standard for internetworking. It was originally defined by researchers in the United States Department of Defense. TCP/IP represents a set of public standards that specifies how packets of information are exchanged between computers over one or more networks.
Application Protocols
The following protocols function at the application layer of the OSI model:
• Telnet – Telnet enables terminal access to local or remote systems. The telnet application is used to access remote devices for configuration, control, and troubleshooting.
• File Transfer Protocol (FTP) – FTP is an application that provides services for file transfer and manipulation. FTP uses the Session layer to allow multiple simultaneous connections to remote file systems.
• Simple Mail Transport Protocol (SMTP) – SMTP provides messaging services over TCP/IP and supports most Internet e-mail programs.
• Domain Name System (DNS) – DNS provides access to name servers where network names are translated to the addresses used by Layer 3 network protocols. DNS greatly simplifies network usage by end users.
Transport Protocols
The following protocols function at the transport layer of the OSI model:
• Transmission Control Protocol (TCP) – TCP is the primary Internet protocol for reliable delivery of data. TCP includes facilities for end-to-end connection establishment, error detection and recovery, and metering the rate of flow of data into the network. Many standard applications, such as e-mail, web browsing, file transfer and Telnet, depend on the services of TCP. TCP identifies the application using it by a "port" number.
• User Datagram Protocol (UDP) – UDP offers a connectionless service to applications that do not want the overhead of TCP and can tolerate a level of data loss. Applications in network management, network file system, and simple file transport use UDP. Like TCP, UDP identifies applications by port number.
Internet Protocols
The following protocols function at the network layer of the OSI model:
• Internet Protocol (IP) – IP provides source and destination addressing and, in conjunction with routing protocols, packet forwarding from one network to another toward a destination.
• Internet Control Message Protocol (ICMP) – ICMP is used for network testing and troubleshooting. It enables diagnostic and error messages. ICMP "echo" messages are used by the PING application to test remote devices.
• Routing Information Protocol (RIP) – RIP operates between router devices to discover paths between networks. In an Internetwork, routers depend on a routing protocol to build and maintain information about how to forward packets toward their destination. RIP chooses routes based on their distance, or hop count.
• Open Shortest Path First (OSPF) – OSPF, like RIP, enables routers to build forwarding tables. Unlike RIP, OSPF selects routes based on other characteristics of the links between networks, such as bandwidth and delay. OSPF is more suitable than RIP for routing in large internetworks.
• Address Resolution Protocol (ARP) – ARP is used to discover the local (MAC) address of a station on the network when its IP address is known. End stations as well as routers use ARP to discover local addresses.
• The Ethernet architecture is the most popular type of LAN link used today. It is based on the 802.3 standard. This specifies that a network that implements the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) access control method must use a baseband transmission over coaxial or twisted-pair cable that is laid out in a bus topology (that is, a linear or star bus). CSMA/CD means that multiple stations will have access to the media, and before one station can access that media, it must first listen (carrier sense) to detect if another system is using the same media. If another system is using the media, then that system must wait before it can transmit. If both systems attempt to send data at the same time, then a collision will result.
• Standard transfer rates are 10 megabit per second (Mbps) or 100 Mbps. The new standards provide for Gigabit Ethernet, capable of attaining speeds up to one Gbps over fiber-optic cable or other high-speed media. Figure shows a table of main Ethernet specifications.
10BASE-T
Currently, 10BASE-T is one of the most popular Ethernet implementations. It uses a star bus topology.
The term Ethernet cable can be used to describe the unshielded twisted-pair (UTP) cabling generally used in this architecture. Shielded Twisted-Pair (STP) also can be used. 10BASE-T and 100BASE-X create networks that are easy to set up and expand.
One advantage of 10BASE-T is that it is relatively inexpensive. Although a hub is required when connecting more than two computers, small hubs are available at a low cost, and 10BASE-T network cards are inexpensive and widely available.
NOTE:
Inside the Ethernet hub, the signaling system is a bus, as with coax Ethernet networks.
NOTE:
10BASE-T specifications require a hub. However, if connecting only two computers (for example, for a home network), and UTP is preferred rather than thinnet, a crossover cable can be used. This type of cable has wire pairs that are cross connected. Crossover cables are also used to connect two hubs to each other if the hubs do not have uplink ports.
UTP, which is the most commonly used twisted-pair cabling, is thin, flexible, and easier to work with than coax. It uses modular RJ-45 plugs and jacks, so it is easy to connect the cable to the NIC or hub.
The disadvantages of 10BASE-T are that the maximum length for a 10BASE-T segment (without repeaters) is only 100 meters (about 328 feet). Also, the UTP used is more vulnerable to electromagnetic interference (EMI) and attenuation than other cable types.
100BASE-X
100BASE-X comes in several different variations. It can be implemented over Category 5 UTP (100BASE-T), over 2-pair Category 5 UTP or STP (100BASE-TX) or as Ethernet over 2-strand fiber-optic cable (100BASE-FX).
• Advantages of 100BASE-X – Regardless of the implementation, the big advantage of 100BASE-X is high-speed performance. At 100 Mbps, transfer rates are 10 times that of 10BASE-T.
Because it uses twisted-pair cabling, 100BASE-X also shares the same advantages as 10BASE-T. These include low cost, flexibility, and ease of implementation and expansion.
• Disadvantages of 100BASE-X – 100BASE-X shares the disadvantages of 10BASE-T, which are inherent to twisted-pair cabling, such as susceptibility to EMI and attenuation. 100-Mbps NICs and hubs are generally somewhat more expensive than those designed for 10-Mbps networks, but prices have dropped as 100BASE-X has gained in popularity. Fiber-optic cable remains an expensive cabling option, not so much because of the cost of the cable itself, but because of the training and expertise required to install it.
Digital Subscriber Line (DSL) is an always-on technology. This means that there is no need to dial up each time when connecting to the Internet. It is a relatively new technology currently being offered by phone companies as an add-on service over existing copper wire or phone lines.
DSL comes in several varieties:
• Asymmetric DSL (ADSL) currently is the most common implementation. It has speeds that vary from 384 kbps to more than 6 Mbps downstream. The upstream speed is typically lower.
• High Data Rate DSL (HDSL) provides bandwidth of 768 kbps in both directions.
• Symmetric DSL (SDSL) provides the same speed, up to 3 Mbps, for uploads and downloads.
• Very High Data Rate DSL (VDSL) is capable of bandwidths between 13 Mbps to 52 Mbps.
• ISDN DSL (IDSL) has a top speed of 144 kbps but is available in areas that do not qualify for other DSL implementations. IDSL is actually DSL over ISDN lines.
In a TCP/IP-based LAN, PCs use Internet Protocol (IP) addresses to identify and locate each other. An IP address is a 32-bit binary number. This binary number is divided into 4 groups of 8 bits known as octets, each of which is represented by a decimal number in the range of 0 to 255. The octets are separated by decimal points. An example of an IP address is 190.100.5.54. This type of address is described as a dotted decimal representation. Each device on the network that has an IP address is known as a host or node.
A secondary dotted decimal number, known as the subnet mask, always accompanies an IP address. A subnet mask is a tool used by a system administrator to segment the network address that has been assigned to the network the technique of subnetting allows the entire network to be represented to the Internet by one address. An example of a subnet mask is 255.255.0.0. The subnet mask is also used to determine whether a particular host IP address is local (on the same network segment) or remote (on another segment).
There are several options for assigning IP addresses for hosts on a LAN:
• Static – Assigned by the network administrator manually
• Dynamic – Assigned by a Dynamic Host Configuration Protocol (DHCP) server (DHCP servers are discussed in the next section.)
• Automatic – Private IP addressing
If there are more than a few computers, manually configuring TCP/IP addresses for every host on the network can be a time consuming process. This also requires that the network administrator assigning the addresses understands IP addressing and knows how to choose a valid address for the particular network. An IP address is unique for each host. The IP address is stored in the Network Settings of the Operating System Software. It is commonly referred to as the logical address. TCP/IP addressing will be taught later in this course.
In the Windows operating system, the IP address is manually entered into the TCP/IP properties dialog box. Figure shows the TCP/IP configuration box, which is used to set the address settings, or configurations that are entered, which include the following:
• An IP address
• A subnet mask
• Default gateway address
• Optional values including a Domain Name System (DNS) server address and Windows Internet Naming Service (WINS)
The default gateway address and the DNS are discussed in a later section.
DHCP Server
Another way for computers on a network to obtain an IP address is through a Dynamic Host Configuration Protocol (DHCP) server. DHCP is a software utility that automatically assigns IP addresses to PCs. The computer running the software is known as a DHCP server. DHCP servers assign the IP addresses and TCP/IP configuration information to computers configured as DHCP clients. This dynamic process eliminates the need for manual IP address assignments. However, any devices requiring a static or permanent IP address must still have its IP address manually assigned. Figure shows an example of the tool, which a user would use to configure a server to run DHCP services to client systems on the network.
When the DHCP server receives a request from a host, it selects IP address information from a set of predefined addresses that are stored in its database. Once it has selected the IP information, it offers these values to the requesting device on the network. If the device accepts the offer, the DHCP server will then lease the IP information to the device for a specific period of time.
The IP address information that a DHCP server can assign to hosts that are starting up on the network includes the following:
• An IP address
• A subnet mask
• Default gateway
• Optional values including a DNS server address and WINS
The use of this system simplifies the administration of a network because the software keeps track of IP addresses. Automatically configuring TCP/IP also reduces the possibility of assigning duplicate IP addresses or invalid IP addresses. For any computer on the network to take advantage of the services provided by the DHCP server, it must first be able to identify the server on the local network. The option to obtain an IP address automatically is selected on the TCP/IP Properties dialog box. Figure shows an example of the IP address configuration screen of a Windows client when it is configured with an IP address via DHCP. In other cases, an operating system feature called Automatic Private IP Addressing (APIPA) enables a computer to assign itself an address if it is unable to contact a DHCP server.
The Domain Name System (DNS) is used to translate the computer names such as www.cisco.com to the corresponding unique IP address. The name resolution process is demonstrated in Figure . The DNS software runs on a computer acting as a network server and it makes the address translations. DNS software may be hosted on the network by itself or by an Internet service provider (ISP). Address translations are used each time the Internet is accessed. The process of translating names to addresses is known as name resolution.
3.1.5 Default gateway
A computer located on one network segment that is trying to talk to another computer on a different segment across a router, sends the data through a default gateway. The default gateway is the near-side interface of the router. It is the interface on the router to which the local computer network segment or wire is attached. In order for each computer to recognize its default gateway, the corresponding near side router interface IP address has to be entered into the host TCP/IP Properties dialog box. Figure demonstrates how the default gateway would be set up and its relationship to the other router interfaces on the network.
Networking media can be defined simply as the means by which signals, or data, are sent from one computer to another. The signals can be transmitted through cable or wireless means. There are a wide variety of networking media in the marketplace. The following media types will be discussed:
• Copper – including coaxial and twisted pair
• Glass – fiber optic
• Waves – wireless
UNIX and Linux were designed to be extremely flexible and customizable.
As a result, UNIX and Linux support dozens of user interfaces.
The most common are the text-based interfaces called shells.
Users type commands that are interpreted by the shell, which in turn relays the user instructions to the operating system and other programs. UNIX (and Linux) shells are difficult to learn because they rely on abbreviations and complex command syntax. Commonly used shells include the following:
• Bourne shell
• Korn shell
• Bash shell
• C shell
• TC shell
Enter the UNIX command, uname, on most systems to find out what version of the UNIX or Linux a computer is running.
In contrast to early desktop PC software, NOSs provide built-in networking components and network services, multiuser capability, and sophisticated file security and file sharing technologies.
NOSs must have a robust kernel to prevent crashes and downtime.
It is especially important that the NOS kernel schedule and manage multiple processes so that each program is prevented from crashing other parts of the system.
Because specialized administrators manage NOSs, they do not necessarily require resource-consuming graphical interfaces.
Finally, a NOS requires a sophisticated file system that allows for efficient storage and maximum security. Instead of FAT, a NOS typically employs NTFS, UFS (UNIX file system), or another equally robust file system.
Common NOSs in use today include:
• Microsoft Windows – Network operating systems offered by Windows are NT 3.51, NT 4.0, 2000, XP, and .NET. Keep in mind that NT 3.51 and NT 4.0 are being phased out as a result of the superior Windows 2000, XP, and .Net. Figure and Figure show Windows XP and 2000 operating system.
• Novell NetWare – Novell line of operating systems, which included NetWare 3.12, IntraNetWare 4.11, NetWare 5.0 and 5.1. Figure and Figure show examples of Novell operating system.
• Linux – Linux operating systems including Red Hat, Caldera, SuSE, Debian, and Slackware. Figure and Figure show Linux operating systems from Red Hat, and Caldera.
• UNIX – Various operating systems offered UNIX, such as HP-UX, Sun Solaris, BSD, SCO, and AIX. Figure shows Sun Solaris.
The TCP/IP suite of protocols has become the dominant standard for internetworking. It was originally defined by researchers in the United States Department of Defense. TCP/IP represents a set of public standards that specifies how packets of information are exchanged between computers over one or more networks.
Application Protocols
The following protocols function at the application layer of the OSI model:
• Telnet – Telnet enables terminal access to local or remote systems. The telnet application is used to access remote devices for configuration, control, and troubleshooting.
• File Transfer Protocol (FTP) – FTP is an application that provides services for file transfer and manipulation. FTP uses the Session layer to allow multiple simultaneous connections to remote file systems.
• Simple Mail Transport Protocol (SMTP) – SMTP provides messaging services over TCP/IP and supports most Internet e-mail programs.
• Domain Name System (DNS) – DNS provides access to name servers where network names are translated to the addresses used by Layer 3 network protocols. DNS greatly simplifies network usage by end users.
Transport Protocols
The following protocols function at the transport layer of the OSI model:
• Transmission Control Protocol (TCP) – TCP is the primary Internet protocol for reliable delivery of data. TCP includes facilities for end-to-end connection establishment, error detection and recovery, and metering the rate of flow of data into the network. Many standard applications, such as e-mail, web browsing, file transfer and Telnet, depend on the services of TCP. TCP identifies the application using it by a "port" number.
• User Datagram Protocol (UDP) – UDP offers a connectionless service to applications that do not want the overhead of TCP and can tolerate a level of data loss. Applications in network management, network file system, and simple file transport use UDP. Like TCP, UDP identifies applications by port number.
Internet Protocols
The following protocols function at the network layer of the OSI model:
• Internet Protocol (IP) – IP provides source and destination addressing and, in conjunction with routing protocols, packet forwarding from one network to another toward a destination.
• Internet Control Message Protocol (ICMP) – ICMP is used for network testing and troubleshooting. It enables diagnostic and error messages. ICMP "echo" messages are used by the PING application to test remote devices.
• Routing Information Protocol (RIP) – RIP operates between router devices to discover paths between networks. In an Internetwork, routers depend on a routing protocol to build and maintain information about how to forward packets toward their destination. RIP chooses routes based on their distance, or hop count.
• Open Shortest Path First (OSPF) – OSPF, like RIP, enables routers to build forwarding tables. Unlike RIP, OSPF selects routes based on other characteristics of the links between networks, such as bandwidth and delay. OSPF is more suitable than RIP for routing in large internetworks.
• Address Resolution Protocol (ARP) – ARP is used to discover the local (MAC) address of a station on the network when its IP address is known. End stations as well as routers use ARP to discover local addresses.
• The Ethernet architecture is the most popular type of LAN link used today. It is based on the 802.3 standard. This specifies that a network that implements the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) access control method must use a baseband transmission over coaxial or twisted-pair cable that is laid out in a bus topology (that is, a linear or star bus). CSMA/CD means that multiple stations will have access to the media, and before one station can access that media, it must first listen (carrier sense) to detect if another system is using the same media. If another system is using the media, then that system must wait before it can transmit. If both systems attempt to send data at the same time, then a collision will result.
• Standard transfer rates are 10 megabit per second (Mbps) or 100 Mbps. The new standards provide for Gigabit Ethernet, capable of attaining speeds up to one Gbps over fiber-optic cable or other high-speed media. Figure shows a table of main Ethernet specifications.
10BASE-T
Currently, 10BASE-T is one of the most popular Ethernet implementations. It uses a star bus topology.
The term Ethernet cable can be used to describe the unshielded twisted-pair (UTP) cabling generally used in this architecture. Shielded Twisted-Pair (STP) also can be used. 10BASE-T and 100BASE-X create networks that are easy to set up and expand.
One advantage of 10BASE-T is that it is relatively inexpensive. Although a hub is required when connecting more than two computers, small hubs are available at a low cost, and 10BASE-T network cards are inexpensive and widely available.
NOTE:
Inside the Ethernet hub, the signaling system is a bus, as with coax Ethernet networks.
NOTE:
10BASE-T specifications require a hub. However, if connecting only two computers (for example, for a home network), and UTP is preferred rather than thinnet, a crossover cable can be used. This type of cable has wire pairs that are cross connected. Crossover cables are also used to connect two hubs to each other if the hubs do not have uplink ports.
UTP, which is the most commonly used twisted-pair cabling, is thin, flexible, and easier to work with than coax. It uses modular RJ-45 plugs and jacks, so it is easy to connect the cable to the NIC or hub.
The disadvantages of 10BASE-T are that the maximum length for a 10BASE-T segment (without repeaters) is only 100 meters (about 328 feet). Also, the UTP used is more vulnerable to electromagnetic interference (EMI) and attenuation than other cable types.
100BASE-X
100BASE-X comes in several different variations. It can be implemented over Category 5 UTP (100BASE-T), over 2-pair Category 5 UTP or STP (100BASE-TX) or as Ethernet over 2-strand fiber-optic cable (100BASE-FX).
• Advantages of 100BASE-X – Regardless of the implementation, the big advantage of 100BASE-X is high-speed performance. At 100 Mbps, transfer rates are 10 times that of 10BASE-T.
Because it uses twisted-pair cabling, 100BASE-X also shares the same advantages as 10BASE-T. These include low cost, flexibility, and ease of implementation and expansion.
• Disadvantages of 100BASE-X – 100BASE-X shares the disadvantages of 10BASE-T, which are inherent to twisted-pair cabling, such as susceptibility to EMI and attenuation. 100-Mbps NICs and hubs are generally somewhat more expensive than those designed for 10-Mbps networks, but prices have dropped as 100BASE-X has gained in popularity. Fiber-optic cable remains an expensive cabling option, not so much because of the cost of the cable itself, but because of the training and expertise required to install it.
Digital Subscriber Line (DSL) is an always-on technology. This means that there is no need to dial up each time when connecting to the Internet. It is a relatively new technology currently being offered by phone companies as an add-on service over existing copper wire or phone lines.
DSL comes in several varieties:
• Asymmetric DSL (ADSL) currently is the most common implementation. It has speeds that vary from 384 kbps to more than 6 Mbps downstream. The upstream speed is typically lower.
• High Data Rate DSL (HDSL) provides bandwidth of 768 kbps in both directions.
• Symmetric DSL (SDSL) provides the same speed, up to 3 Mbps, for uploads and downloads.
• Very High Data Rate DSL (VDSL) is capable of bandwidths between 13 Mbps to 52 Mbps.
• ISDN DSL (IDSL) has a top speed of 144 kbps but is available in areas that do not qualify for other DSL implementations. IDSL is actually DSL over ISDN lines.
In a TCP/IP-based LAN, PCs use Internet Protocol (IP) addresses to identify and locate each other. An IP address is a 32-bit binary number. This binary number is divided into 4 groups of 8 bits known as octets, each of which is represented by a decimal number in the range of 0 to 255. The octets are separated by decimal points. An example of an IP address is 190.100.5.54. This type of address is described as a dotted decimal representation. Each device on the network that has an IP address is known as a host or node.
A secondary dotted decimal number, known as the subnet mask, always accompanies an IP address. A subnet mask is a tool used by a system administrator to segment the network address that has been assigned to the network the technique of subnetting allows the entire network to be represented to the Internet by one address. An example of a subnet mask is 255.255.0.0. The subnet mask is also used to determine whether a particular host IP address is local (on the same network segment) or remote (on another segment).
There are several options for assigning IP addresses for hosts on a LAN:
• Static – Assigned by the network administrator manually
• Dynamic – Assigned by a Dynamic Host Configuration Protocol (DHCP) server (DHCP servers are discussed in the next section.)
• Automatic – Private IP addressing
If there are more than a few computers, manually configuring TCP/IP addresses for every host on the network can be a time consuming process. This also requires that the network administrator assigning the addresses understands IP addressing and knows how to choose a valid address for the particular network. An IP address is unique for each host. The IP address is stored in the Network Settings of the Operating System Software. It is commonly referred to as the logical address. TCP/IP addressing will be taught later in this course.
In the Windows operating system, the IP address is manually entered into the TCP/IP properties dialog box. Figure shows the TCP/IP configuration box, which is used to set the address settings, or configurations that are entered, which include the following:
• An IP address
• A subnet mask
• Default gateway address
• Optional values including a Domain Name System (DNS) server address and Windows Internet Naming Service (WINS)
The default gateway address and the DNS are discussed in a later section.
DHCP Server
Another way for computers on a network to obtain an IP address is through a Dynamic Host Configuration Protocol (DHCP) server. DHCP is a software utility that automatically assigns IP addresses to PCs. The computer running the software is known as a DHCP server. DHCP servers assign the IP addresses and TCP/IP configuration information to computers configured as DHCP clients. This dynamic process eliminates the need for manual IP address assignments. However, any devices requiring a static or permanent IP address must still have its IP address manually assigned. Figure shows an example of the tool, which a user would use to configure a server to run DHCP services to client systems on the network.
When the DHCP server receives a request from a host, it selects IP address information from a set of predefined addresses that are stored in its database. Once it has selected the IP information, it offers these values to the requesting device on the network. If the device accepts the offer, the DHCP server will then lease the IP information to the device for a specific period of time.
The IP address information that a DHCP server can assign to hosts that are starting up on the network includes the following:
• An IP address
• A subnet mask
• Default gateway
• Optional values including a DNS server address and WINS
The use of this system simplifies the administration of a network because the software keeps track of IP addresses. Automatically configuring TCP/IP also reduces the possibility of assigning duplicate IP addresses or invalid IP addresses. For any computer on the network to take advantage of the services provided by the DHCP server, it must first be able to identify the server on the local network. The option to obtain an IP address automatically is selected on the TCP/IP Properties dialog box. Figure shows an example of the IP address configuration screen of a Windows client when it is configured with an IP address via DHCP. In other cases, an operating system feature called Automatic Private IP Addressing (APIPA) enables a computer to assign itself an address if it is unable to contact a DHCP server.
The Domain Name System (DNS) is used to translate the computer names such as www.cisco.com to the corresponding unique IP address. The name resolution process is demonstrated in Figure . The DNS software runs on a computer acting as a network server and it makes the address translations. DNS software may be hosted on the network by itself or by an Internet service provider (ISP). Address translations are used each time the Internet is accessed. The process of translating names to addresses is known as name resolution.
3.1.5 Default gateway
A computer located on one network segment that is trying to talk to another computer on a different segment across a router, sends the data through a default gateway. The default gateway is the near-side interface of the router. It is the interface on the router to which the local computer network segment or wire is attached. In order for each computer to recognize its default gateway, the corresponding near side router interface IP address has to be entered into the host TCP/IP Properties dialog box. Figure demonstrates how the default gateway would be set up and its relationship to the other router interfaces on the network.
Networking media can be defined simply as the means by which signals, or data, are sent from one computer to another. The signals can be transmitted through cable or wireless means. There are a wide variety of networking media in the marketplace. The following media types will be discussed:
• Copper – including coaxial and twisted pair
• Glass – fiber optic
• Waves – wireless
Subscribe to:
Posts (Atom)
Posts
