Very Easy Home Network
By: Manbeer Singh
Ahhh yes, life’s pretty sweet with that high speed DSL line. But there is a glitch. The normal ISP dial up account can be used from any computer in the world. A DSL line connects to only one computer.
The obvious solution would be to install a network to carry the line to every computer in the house. I've steered clear of a having network in my home office. I once spent several days trying to hook up 2 computers using Windows 95, and finally gave up after only intermittently being able to make the computers communicate. I swore that my days on the floor with my computers were over and I ran my own "network" by transferring Zip disks from one computer to another.
A new technology is on the horizon, the Home PNA (Phone Networking Alliance) network. I remembered reading about this network that would connect through existing home phone lines. It was in its infancy - so I checked around.
HPNA has made some amazing strides. Now in version 2.0, it will run your home network at ethernet speed, 10Mbps (ten megabytes per second - the same speed as a real corporate network) and extend your high-speed internet connection to anywhere in your home or office. After checking out all the reviews, the same name kept coming up: Netgear.
Netgear offers a home PNA card that not only is plug and play, but also allows you to talk on the phone while using the network. Netgear's "do-not-disturb" feature causes it not to completely take over the phone line, nor will talking on the phone degrade the speed of the network connection.
The card was simple enough to install, just open the computer case and snap it into an available slot. Of course, this is usually the time that things go sour - when you start up the computer. Amazingly, "plug-and-play" was never easier. At first glance the instructions supplied on a single page fold-out sheet look like they’d never do the trick, but they do. Netgear includes a CD with all the software that you need. No need to search for the required drivers, their set-up program takes you step by step. Within a few minutes, you’ll be able to print a page on a remote computer’s printer or share files.
My teenage daughter installed the network on her own computer, and we can now share printers, files, a CD-burner and internet connections without using our "sneakernet" of the past.
My favorite part of the setup is the new Home Network USB adapter. I clipped the small unit to the back of my laptop, and literally within seconds, connected to my other computers!
If this sounds too easy, it probably is. I’m no techie and it worked for me on first try. One caveat though, when it comes to sharing a high speed internet connection over a Home Network line, there are a few more steps. You need to set up a TCP/IP connection. My advice? Don’t even attempt to do it unless you know what you’re doing. Call Netgear’s 24/7 tech support at 888-NETGEAR. They’ll patiently walk you through it, step by step.
I feel like I've really accomplished something, it's not "black-magic" any more. I have a flawless network that I never realized could be as useful as it is. I have a warp speed internet connection that goes beyond my wildest dreams. I passed the boundaries from novice to geek with the help of modern technology. Now my mornings are complete. I can stay that extra ½ hour in bed, watching Matt Lauer and Katie Couric on the Today show. No need to zoom into the office to check my auctions and email. I can just plug the laptop into the phone jack and fly like the wind.
Article Directory Source: http://www.1articleworld.com
Wednesday, July 2, 2008
Why Use Ethernet Routers
By: Benjamin Brook
Ethernet routers are a key component of your home computer system if you have many devices that need to be connected to your computer. For example, printers, modems, other computers and game consoles. Having Ethernet routers at home is a good way to connect all these devices seamlessly into one machine and the Internet.
Usually you can connect up to four devices with Ethernet routers. Depending on how many devices you need connected to your computer and the Internet you can find a router, which allows more devices. Any device that you wish to connect Ethernet routers must have an Ethernet network adaptor.
Adding On
If you have looked at Ethernet routers that have less Ethernet connections than you need but think that such models fit into your budget you can simply adjust them. Using a network switch will allow you to expand the number of devices that you can connect.
Having a wireless access port is a handy thing to have; it will take up on of the access ports but at the same time will allow many wireless devices to work. The drawback is that other Wifi computers using the network at the same time will slow down the system significantly.
Advantages
Ethernet routers have an advantage over simple Ethernet cables in that you can connect more devices to your home network system. Ethernet cables restrict you to only two devices or two computers. If you find yourself with an increasing amount of devices that need to be connected to one central computer then Ethernet routers are the way to go.
You may also be tempted to use an ad hoc Wifi system instead of an Ethernet router. While this does allow you greater flexibility in terms of distance from the central system and the number of devices, it does have drawbacks. It is a less secure system and is usually used on a temporary basis. Ethernet routers are more secure.
For an ad hoc system to work properly all devices must have a Wifi network adaptor. You may also have to configure the adaptors to ad hoc mode as usually they are configured for the typical infrastructure mode. This might take up some extra time to set up and is a lot more complex than simple Ethernet routers.
If you have multiple computers that need to be connected it may be worth it to use an Ethernet switch or hub. The only disadvantage being that one computer must be connected to the Internet. The other computers will access the Internet through this central computer.
Article Directory Source: http://www.1articleworld.com
Ethernet routers are a key component of your home computer system if you have many devices that need to be connected to your computer. For example, printers, modems, other computers and game consoles. Having Ethernet routers at home is a good way to connect all these devices seamlessly into one machine and the Internet.
Usually you can connect up to four devices with Ethernet routers. Depending on how many devices you need connected to your computer and the Internet you can find a router, which allows more devices. Any device that you wish to connect Ethernet routers must have an Ethernet network adaptor.
Adding On
If you have looked at Ethernet routers that have less Ethernet connections than you need but think that such models fit into your budget you can simply adjust them. Using a network switch will allow you to expand the number of devices that you can connect.
Having a wireless access port is a handy thing to have; it will take up on of the access ports but at the same time will allow many wireless devices to work. The drawback is that other Wifi computers using the network at the same time will slow down the system significantly.
Advantages
Ethernet routers have an advantage over simple Ethernet cables in that you can connect more devices to your home network system. Ethernet cables restrict you to only two devices or two computers. If you find yourself with an increasing amount of devices that need to be connected to one central computer then Ethernet routers are the way to go.
You may also be tempted to use an ad hoc Wifi system instead of an Ethernet router. While this does allow you greater flexibility in terms of distance from the central system and the number of devices, it does have drawbacks. It is a less secure system and is usually used on a temporary basis. Ethernet routers are more secure.
For an ad hoc system to work properly all devices must have a Wifi network adaptor. You may also have to configure the adaptors to ad hoc mode as usually they are configured for the typical infrastructure mode. This might take up some extra time to set up and is a lot more complex than simple Ethernet routers.
If you have multiple computers that need to be connected it may be worth it to use an Ethernet switch or hub. The only disadvantage being that one computer must be connected to the Internet. The other computers will access the Internet through this central computer.
Article Directory Source: http://www.1articleworld.com
Cisco CBAC – The Poor Mans Firewall
By: Nicholas Evra
CBAC Overview
The Cisco IOS Firewall Feature Set is a module that can be added to the existing IOS to provide firewall functionality without the need for hardware upgrades. There are two components to the Cisco IOS Firewall Feature Set in Intrusion Detection (which is an optional bolt-on) and Context-Based Access Control (CBAC). CBAC maintains a state table for all of the outbound connections on a Cisco router by inspecting tcp and udp connections at layer seven of the OSI model and populating the table accordingly. When return traffic is received on the external interface it is compared against the state table to see if the connection was originally established from within the internal network, and then either permitted or denied. Although basic this is a very effective mechanism to prevent unauthorized access to the internal network from external sources such as the internet.
CBAC Application-specific support
Cisco have also built in some additional functionality into CBAC in terms of application-specific inspection that enables the router to recognize and identify application specific data flows such as HTTP, SMTP, TFTP, and FTP. Understanding these applications and their data flows empowers the router to identify malformed packets or suspect application data flows and permit or deny accordingly. CBAC also provides the flexibility of downloading Java code from trusted sites, but it denying untrusted sites.
CBAC and Denial of Service (DOS) Attacks
Denial-Of-Service (DOS) attack protection is also in-built with real-time logging of alerts as well as pro-active responses to mitigate the threat. To do this CBAC can be configured to manage half-open TCP connections which are used in TCP SYN flood attacks to overload a targets resources resulting in a denial of service to legitimate users. To do this CBAC uses timeouts and thresholds, which are configurable, to determine how long state information for each connection should be kept for sessions and when to drop them. Note that UDP and ICMP require that an idle-timer limit is used to determine when a connection should be terminated. A very useful command to identify a DOS attack is ‘ip inspect audit-trail’ which logs all DOS connections including source and destination IP address and TCP or UDP ports allowing you to pin-point the exact source and destination of the attack.
Configuring CBAC
There are five steps to configuring CBAC on a Cisco router in order for it to function correctly. These are as follows:
1. Choose an interface to which inspection will be applied. This can be an internal or external interface as CBAC is only concerned with the direction of the first packet initiating the connection which is identified when applying CBAC to an interface.
2. Configure an IP access list in the correct direction on the selected interface to allow traffic through for CBAC to inspect.
3. Configure global timeouts and thresholds for established connections or sessions.
4. Define an inspection rule specifying exactly which protocols will be inspected by CBAC.
5. Apply the inspection rule to the interface in the correct direction.
Article Directory Source: http://www.1articleworld.com
CBAC Overview
The Cisco IOS Firewall Feature Set is a module that can be added to the existing IOS to provide firewall functionality without the need for hardware upgrades. There are two components to the Cisco IOS Firewall Feature Set in Intrusion Detection (which is an optional bolt-on) and Context-Based Access Control (CBAC). CBAC maintains a state table for all of the outbound connections on a Cisco router by inspecting tcp and udp connections at layer seven of the OSI model and populating the table accordingly. When return traffic is received on the external interface it is compared against the state table to see if the connection was originally established from within the internal network, and then either permitted or denied. Although basic this is a very effective mechanism to prevent unauthorized access to the internal network from external sources such as the internet.
CBAC Application-specific support
Cisco have also built in some additional functionality into CBAC in terms of application-specific inspection that enables the router to recognize and identify application specific data flows such as HTTP, SMTP, TFTP, and FTP. Understanding these applications and their data flows empowers the router to identify malformed packets or suspect application data flows and permit or deny accordingly. CBAC also provides the flexibility of downloading Java code from trusted sites, but it denying untrusted sites.
CBAC and Denial of Service (DOS) Attacks
Denial-Of-Service (DOS) attack protection is also in-built with real-time logging of alerts as well as pro-active responses to mitigate the threat. To do this CBAC can be configured to manage half-open TCP connections which are used in TCP SYN flood attacks to overload a targets resources resulting in a denial of service to legitimate users. To do this CBAC uses timeouts and thresholds, which are configurable, to determine how long state information for each connection should be kept for sessions and when to drop them. Note that UDP and ICMP require that an idle-timer limit is used to determine when a connection should be terminated. A very useful command to identify a DOS attack is ‘ip inspect audit-trail’ which logs all DOS connections including source and destination IP address and TCP or UDP ports allowing you to pin-point the exact source and destination of the attack.
Configuring CBAC
There are five steps to configuring CBAC on a Cisco router in order for it to function correctly. These are as follows:
1. Choose an interface to which inspection will be applied. This can be an internal or external interface as CBAC is only concerned with the direction of the first packet initiating the connection which is identified when applying CBAC to an interface.
2. Configure an IP access list in the correct direction on the selected interface to allow traffic through for CBAC to inspect.
3. Configure global timeouts and thresholds for established connections or sessions.
4. Define an inspection rule specifying exactly which protocols will be inspected by CBAC.
5. Apply the inspection rule to the interface in the correct direction.
Article Directory Source: http://www.1articleworld.com
Home Computer Networking
By: travis klein
Numbers of people these days have two computers in their homes; one is usually kept in the children's room and another in their personal room. So its important for you to know about home networking and its benefits that you can have from both systems in your home. But for this you should know certain things like how to set up home networking, what all you will need for it etc.
In order to make home network set-up easy and useful, you need to install a network friendly OS (operating system) like Windows ME or XP. But this again is not very important; it all depends upon your requirement. Further you will need many more items to make home networking successful. They are:
Two Network cards - If your computer is quite new, ask the shopkeeper for two PCI network cards of 10/100mbps specification.
RJ-45 crossover cable - This is the cable needed to join the machines together so ensure that the length is long enough.
Basic knowledge of using a Windows PC. We will discuss advantages of Home Networking now. Here are some of the benefits that you will get through home networking:
You can play various games across the network say with your kid in another room. Also, you will be able to share the pieces of hardware. For instance, if you have single printer but two computers, you could use the same printer for both computers.
If you have lots of files in any one computer and want both the systems to have access over it, it will be possible using a home network.
Steps for Home Networking
1. The first step is to take the cover/lid out of both the computers and then fit the Network cards into a free PCI slot. Screw them down into the case and close the lid.
2. After restarting the computer, Windows should reappear mentioning about the finding of a new hardware and will ask for a driver disk. Then you need to insert the CD into the drive and wait for the drivers to get installed. Do the same with second computer and thus computers are enabled to communicate after this step.
3. Now, click on Start, then Settings, Control Panel and Network Connections and finally click at Set up a home network. Then you will be asked several questions and the system will ask you to insert a floppy disk into the computer, repeat the same with second computer.
Your home network base is installed so start doing what you want. If you face major problems take help of professionals and for minor difficulties just click on Help option for assistance.
Article Directory Source: http://www.1articleworld.com
Numbers of people these days have two computers in their homes; one is usually kept in the children's room and another in their personal room. So its important for you to know about home networking and its benefits that you can have from both systems in your home. But for this you should know certain things like how to set up home networking, what all you will need for it etc.
In order to make home network set-up easy and useful, you need to install a network friendly OS (operating system) like Windows ME or XP. But this again is not very important; it all depends upon your requirement. Further you will need many more items to make home networking successful. They are:
Two Network cards - If your computer is quite new, ask the shopkeeper for two PCI network cards of 10/100mbps specification.
RJ-45 crossover cable - This is the cable needed to join the machines together so ensure that the length is long enough.
Basic knowledge of using a Windows PC. We will discuss advantages of Home Networking now. Here are some of the benefits that you will get through home networking:
You can play various games across the network say with your kid in another room. Also, you will be able to share the pieces of hardware. For instance, if you have single printer but two computers, you could use the same printer for both computers.
If you have lots of files in any one computer and want both the systems to have access over it, it will be possible using a home network.
Steps for Home Networking
1. The first step is to take the cover/lid out of both the computers and then fit the Network cards into a free PCI slot. Screw them down into the case and close the lid.
2. After restarting the computer, Windows should reappear mentioning about the finding of a new hardware and will ask for a driver disk. Then you need to insert the CD into the drive and wait for the drivers to get installed. Do the same with second computer and thus computers are enabled to communicate after this step.
3. Now, click on Start, then Settings, Control Panel and Network Connections and finally click at Set up a home network. Then you will be asked several questions and the system will ask you to insert a floppy disk into the computer, repeat the same with second computer.
Your home network base is installed so start doing what you want. If you face major problems take help of professionals and for minor difficulties just click on Help option for assistance.
Article Directory Source: http://www.1articleworld.com
Networking (Computers)
By: Christoff Genviere
There are many kinds of networks, however this paper will be about networking computers. As we move further and further into the paperless society, the need for people to be connected and able to exchange data just as fast as they could by handing a paper to someone increases. This can be accomplished by having a group of computers connected by a network, so that as soon as data is entered into one computer, it can be immediately accessed by someone else on a connected computer, no matter how far away it may be (though usually it is in the same building). There is much work involved in this and it in includes a lot of math, from equations to basic problems. This report will be based around the mathematical aspects of setting up a network.
The first mathematical question in setting up a network is very basic. How many computers will be connected to this network and how many guest computers might come on at one time is the question. An example of a guest computer is if someone brought a laptop and connected it for a short while to download or access data. To find the answer to the question, simply count the desktop computers that will be connected and how many guest computers you expect to be connected at one time.
The second mathematical problem that occurs is best solved using an algebraic equation. Let x=the amount of desktop computers that will always be connected, y=the amount of guest computers that you expect to be connected at one time. So, the equation is: x+y+1. The one added on the end of the equation is another guest file just to make sure you don't fall short. So, this tells you how many files you need to create. The guest files will all be generically named so that all guests have the same access privileges, and all the permanent computers will have their own named file so they can have more personalized access privileges. These files are put on one main computer, the server. This controls all access privileges and any data put into a computer branching off from it in it's network can be accessed from this all-powerful server computer. The previously stated problems are a large part of networking, although I couldn't possibly tell about all the math involved without going on for another 3 or 4 pages. Those problems help with networking as far as setting up the network on the computer goes, but there is a whole nother side. The physical side.
The physical side of computer networking involves problems such as how many feet of cable are you going to need to connect the computers. Some large office buildings can have 1 mile of cable between their networked computers! If someone has 2 computers in their house, it may only involve 3 feet. The mathematical procedure is quite simple although it might take a while to complete. Just take out the old meter stick and start measuring. Don't measure direct lines between the computers unless you want the cable stretching in a straight line between them. Chances are you will want it to run along a wall or around another object. Once the measuring is done, just add up the cable length and you have the answer to the problem.
If you don't have a very tight budget, you can afford faster networks than cable networks. These are more sophisticated but I was lucky enough to get to try it this summer. It is called infrared data transfer (IDT). Instead of cables, you have an infrared connector hooked to your computer. Just aim the little infrared panel at the infrared panel on the other computer and it will trade information with infrared light. These panels are usually about 1 square inch in size.
This is much quicker and doesn't involve annoying cables. You still need to gauge distance because there is a distance limit on how far apart they can be and still work. When you install them, your computer will ask you questions such as how many lumens (measurement of brightness of light) you would like your panel to emit.
It is invisible to the naked eye but the amount of lumens it outputs is critical. If you have a fast computer, you might want more lumens so that your computer doesn't crash because of lagging. If you have a slower computer you will want less lumens because other wise you will be sending data too fast for your computer and there will end up being a lot of gibberish that will mess up the receiving computer.
The mathematical things that networking involves are almost endless depending on the situation. I couldn't adequately explain them if I had the time, because anybody who didn't understand quite a bit about computers wouldn't know what I was talking about, forcing me to explain many things that are off the subject of mathematics in networking. I hope I have given you an idea of what it involves, but if you want to know about all of the mathematics, you will just have to network some computers yourself.
Article Directory Source: http://www.1articleworld.com
There are many kinds of networks, however this paper will be about networking computers. As we move further and further into the paperless society, the need for people to be connected and able to exchange data just as fast as they could by handing a paper to someone increases. This can be accomplished by having a group of computers connected by a network, so that as soon as data is entered into one computer, it can be immediately accessed by someone else on a connected computer, no matter how far away it may be (though usually it is in the same building). There is much work involved in this and it in includes a lot of math, from equations to basic problems. This report will be based around the mathematical aspects of setting up a network.
The first mathematical question in setting up a network is very basic. How many computers will be connected to this network and how many guest computers might come on at one time is the question. An example of a guest computer is if someone brought a laptop and connected it for a short while to download or access data. To find the answer to the question, simply count the desktop computers that will be connected and how many guest computers you expect to be connected at one time.
The second mathematical problem that occurs is best solved using an algebraic equation. Let x=the amount of desktop computers that will always be connected, y=the amount of guest computers that you expect to be connected at one time. So, the equation is: x+y+1. The one added on the end of the equation is another guest file just to make sure you don't fall short. So, this tells you how many files you need to create. The guest files will all be generically named so that all guests have the same access privileges, and all the permanent computers will have their own named file so they can have more personalized access privileges. These files are put on one main computer, the server. This controls all access privileges and any data put into a computer branching off from it in it's network can be accessed from this all-powerful server computer. The previously stated problems are a large part of networking, although I couldn't possibly tell about all the math involved without going on for another 3 or 4 pages. Those problems help with networking as far as setting up the network on the computer goes, but there is a whole nother side. The physical side.
The physical side of computer networking involves problems such as how many feet of cable are you going to need to connect the computers. Some large office buildings can have 1 mile of cable between their networked computers! If someone has 2 computers in their house, it may only involve 3 feet. The mathematical procedure is quite simple although it might take a while to complete. Just take out the old meter stick and start measuring. Don't measure direct lines between the computers unless you want the cable stretching in a straight line between them. Chances are you will want it to run along a wall or around another object. Once the measuring is done, just add up the cable length and you have the answer to the problem.
If you don't have a very tight budget, you can afford faster networks than cable networks. These are more sophisticated but I was lucky enough to get to try it this summer. It is called infrared data transfer (IDT). Instead of cables, you have an infrared connector hooked to your computer. Just aim the little infrared panel at the infrared panel on the other computer and it will trade information with infrared light. These panels are usually about 1 square inch in size.
This is much quicker and doesn't involve annoying cables. You still need to gauge distance because there is a distance limit on how far apart they can be and still work. When you install them, your computer will ask you questions such as how many lumens (measurement of brightness of light) you would like your panel to emit.
It is invisible to the naked eye but the amount of lumens it outputs is critical. If you have a fast computer, you might want more lumens so that your computer doesn't crash because of lagging. If you have a slower computer you will want less lumens because other wise you will be sending data too fast for your computer and there will end up being a lot of gibberish that will mess up the receiving computer.
The mathematical things that networking involves are almost endless depending on the situation. I couldn't adequately explain them if I had the time, because anybody who didn't understand quite a bit about computers wouldn't know what I was talking about, forcing me to explain many things that are off the subject of mathematics in networking. I hope I have given you an idea of what it involves, but if you want to know about all of the mathematics, you will just have to network some computers yourself.
Article Directory Source: http://www.1articleworld.com
Why Use Ethernet Routers
By: Benjamin Brook
Ethernet routers are a key component of your home computer system if you have many devices that need to be connected to your computer. For example, printers, modems, other computers and game consoles. Having Ethernet routers at home is a good way to connect all these devices seamlessly into one machine and the Internet.
Usually you can connect up to four devices with Ethernet routers. Depending on how many devices you need connected to your computer and the Internet you can find a router, which allows more devices. Any device that you wish to connect Ethernet routers must have an Ethernet network adaptor.
Adding On
If you have looked at Ethernet routers that have less Ethernet connections than you need but think that such models fit into your budget you can simply adjust them. Using a network switch will allow you to expand the number of devices that you can connect.
Having a wireless access port is a handy thing to have; it will take up on of the access ports but at the same time will allow many wireless devices to work. The drawback is that other Wifi computers using the network at the same time will slow down the system significantly.
Advantages
Ethernet routers have an advantage over simple Ethernet cables in that you can connect more devices to your home network system. Ethernet cables restrict you to only two devices or two computers. If you find yourself with an increasing amount of devices that need to be connected to one central computer then Ethernet routers are the way to go.
You may also be tempted to use an ad hoc Wifi system instead of an Ethernet router. While this does allow you greater flexibility in terms of distance from the central system and the number of devices, it does have drawbacks. It is a less secure system and is usually used on a temporary basis. Ethernet routers are more secure.
For an ad hoc system to work properly all devices must have a Wifi network adaptor. You may also have to configure the adaptors to ad hoc mode as usually they are configured for the typical infrastructure mode. This might take up some extra time to set up and is a lot more complex than simple Ethernet routers.
If you have multiple computers that need to be connected it may be worth it to use an Ethernet switch or hub. The only disadvantage being that one computer must be connected to the Internet. The other computers will access the Internet through this central computer.
Article Directory Source: http://www.1articleworld.com
For more information about routers please visit my website cordless phones and wireless routers problems
Ethernet routers are a key component of your home computer system if you have many devices that need to be connected to your computer. For example, printers, modems, other computers and game consoles. Having Ethernet routers at home is a good way to connect all these devices seamlessly into one machine and the Internet.
Usually you can connect up to four devices with Ethernet routers. Depending on how many devices you need connected to your computer and the Internet you can find a router, which allows more devices. Any device that you wish to connect Ethernet routers must have an Ethernet network adaptor.
Adding On
If you have looked at Ethernet routers that have less Ethernet connections than you need but think that such models fit into your budget you can simply adjust them. Using a network switch will allow you to expand the number of devices that you can connect.
Having a wireless access port is a handy thing to have; it will take up on of the access ports but at the same time will allow many wireless devices to work. The drawback is that other Wifi computers using the network at the same time will slow down the system significantly.
Advantages
Ethernet routers have an advantage over simple Ethernet cables in that you can connect more devices to your home network system. Ethernet cables restrict you to only two devices or two computers. If you find yourself with an increasing amount of devices that need to be connected to one central computer then Ethernet routers are the way to go.
You may also be tempted to use an ad hoc Wifi system instead of an Ethernet router. While this does allow you greater flexibility in terms of distance from the central system and the number of devices, it does have drawbacks. It is a less secure system and is usually used on a temporary basis. Ethernet routers are more secure.
For an ad hoc system to work properly all devices must have a Wifi network adaptor. You may also have to configure the adaptors to ad hoc mode as usually they are configured for the typical infrastructure mode. This might take up some extra time to set up and is a lot more complex than simple Ethernet routers.
If you have multiple computers that need to be connected it may be worth it to use an Ethernet switch or hub. The only disadvantage being that one computer must be connected to the Internet. The other computers will access the Internet through this central computer.
Article Directory Source: http://www.1articleworld.com
For more information about routers please visit my website cordless phones and wireless routers problems
Sunday, June 15, 2008
IP Addresses, Subnetting and Sub-subnetting
This page will give you a basic understanding of the structure of IP addresses and subnets as well as specific information about sub-subnetting at Cornell. We recommend that you read through the entire page; however, if you're familiar with these issues, use the table of contents to click ahead to the section you're most interested in.
Contents of this page:
What are IP addresses and how are they used?
IP Addressing Space
How does Sub-subnetting work?
Understanding Static vs. Dynamic Addressing
Changing the UNIX Operating System to Work with Sub-subnetting
Host registration
What Are IP Addresses and How Are They Used?
IP (Internet Protocol) addresses are used to identify hosts on the campus Internet, a Cornell network that ties into the Internet, a global network. If the computer is attached to Cornell's network, it needs an IP address to be recognized as part of the campus Internet.
IP addresses are constructed according to a set of specific rules so that hosts on any part of the Internet can communicate with each other. This document describes IP addresses only as they apply to Cornell's campus network. (If you want to know more about Internet addressing, refer to Internetworking with TCP/IP: Principles, Protocols, and Architecture by Douglas Comer, Prentice Hall).
An IP address consists of a 32-bit binary number, which is typically presented as four decimal numbers (one for each 8-bit byte) separated by decimal points. For example, 128.253.21.58.
Internet addresses at Cornell have three parts:
network address
subnet address
host address
When you configure a host for sub-subnetting, you are primarily concerned about the host address, but some understanding of the network address and subnet address is useful.
Network Address
Cornell has four addresses for its backbone networks. They are 128.253.0.0, 128.84.0.0, 132.236.0.0, and 140.251.0.0. The latter is used only by the Cornell University College. These addresses are assigned to Cornell. Cornell cannot change the first two parts of each address, but is free to use the last two parts in any way it chooses in order to identify Local Area Networks (subnets) and hosts that are connected to the campus Internet.
Subnet Address
The subnet address is the address given to your Local Area Network (LAN). Cornell's system provides for 254 LANs connected to each of the main networks. So, for example, if your LAN is identified on the network as 128.253.0.0, a possible subnet addresses (or LAN address) might be 128.253.21.0. The third number, 21, identifies the subnet.
Host Address
The host address is the address given to the workstation, other computer, or device that is connected to the LAN. Cornell's system provides for 256 host addresses on each LAN. So, for example, if your host is identified on the LAN as 128.253.21.0 a possible host address is 128.253.21.58. The last number, 58, identifies the host.
Not all 256 numbers are available as host addresses on any given LAN. Zero (0) and 255 are reserved for broadcast purposes. (Hosts are set up to "grab" any message marked with their own address or a broadcast address; for example, if your host address is 128.253.21.58 and it "sees" a message addressed to 128.253.21.255, it will grab the message. In this way, hosts can send messages to large groups without having to know each address on their LAN.)
One (1) is reserved for the gateway/router that sits between the LAN and next network level. The numbers 2-5 are reserved by CIT for diagnostic and management use.
IP Addressing Space
This addressing scheme has worked well for Cornell, but it has some limitations:
Contents of this page:
What are IP addresses and how are they used?
IP Addressing Space
How does Sub-subnetting work?
Understanding Static vs. Dynamic Addressing
Changing the UNIX Operating System to Work with Sub-subnetting
Host registration
What Are IP Addresses and How Are They Used?
IP (Internet Protocol) addresses are used to identify hosts on the campus Internet, a Cornell network that ties into the Internet, a global network. If the computer is attached to Cornell's network, it needs an IP address to be recognized as part of the campus Internet.
IP addresses are constructed according to a set of specific rules so that hosts on any part of the Internet can communicate with each other. This document describes IP addresses only as they apply to Cornell's campus network. (If you want to know more about Internet addressing, refer to Internetworking with TCP/IP: Principles, Protocols, and Architecture by Douglas Comer, Prentice Hall).
An IP address consists of a 32-bit binary number, which is typically presented as four decimal numbers (one for each 8-bit byte) separated by decimal points. For example, 128.253.21.58.
Internet addresses at Cornell have three parts:
network address
subnet address
host address
When you configure a host for sub-subnetting, you are primarily concerned about the host address, but some understanding of the network address and subnet address is useful.
Network Address
Cornell has four addresses for its backbone networks. They are 128.253.0.0, 128.84.0.0, 132.236.0.0, and 140.251.0.0. The latter is used only by the Cornell University College. These addresses are assigned to Cornell. Cornell cannot change the first two parts of each address, but is free to use the last two parts in any way it chooses in order to identify Local Area Networks (subnets) and hosts that are connected to the campus Internet.
Subnet Address
The subnet address is the address given to your Local Area Network (LAN). Cornell's system provides for 254 LANs connected to each of the main networks. So, for example, if your LAN is identified on the network as 128.253.0.0, a possible subnet addresses (or LAN address) might be 128.253.21.0. The third number, 21, identifies the subnet.
Host Address
The host address is the address given to the workstation, other computer, or device that is connected to the LAN. Cornell's system provides for 256 host addresses on each LAN. So, for example, if your host is identified on the LAN as 128.253.21.0 a possible host address is 128.253.21.58. The last number, 58, identifies the host.
Not all 256 numbers are available as host addresses on any given LAN. Zero (0) and 255 are reserved for broadcast purposes. (Hosts are set up to "grab" any message marked with their own address or a broadcast address; for example, if your host address is 128.253.21.58 and it "sees" a message addressed to 128.253.21.255, it will grab the message. In this way, hosts can send messages to large groups without having to know each address on their LAN.)
One (1) is reserved for the gateway/router that sits between the LAN and next network level. The numbers 2-5 are reserved by CIT for diagnostic and management use.
IP Addressing Space
This addressing scheme has worked well for Cornell, but it has some limitations:
- Each of Cornell's fiber backbones can have no more than 256 LANs attached to them.
- Each LAN can have no more than 256 (249 if reserved addresses are taken into account) hosts. Most LANs are constructed with far fewer than the maximum number of hosts addresses available.
- Ethernet LANs performance is reduced with a large number (100 or more) of connections. Performance is most affected by how people are using the LAN: a small number of heavy users can bog down the performance of any LAN. Therefore, the limitations on the number of host addresses hasn't been and isn't expected to be a problem for most LANs at Cornell.
To make room for additional subnet addresses, or LANs, CIT has used a system called sub-subnetting. With this system, up to four LANs can use one full subnet address, thus effectively quadrupling the number of subnet addresses available.
How Does Sub-Subnetting Work?
Subnetting
The subnet mask address is 255.255.255.0, and it currently is the same for all LANs. If you convert the subnet mask address to its binary form, it looks like this:
Subnet mask: 11111111 11111111 11111111 00000000
If you convert our example host address (128.253.21.58) to its binary form, it looks like this:
Host address: 10000000 11111101 00010101 00111010
Together they look like this:
Subnet mask: 11111111 11111111 11111111 00000000
Host address: 10000000 11111101 00010101 00111010
The subnet mask when shown this way, as an overlay on the host address, essentially tells the computer which part of the IP address is a network address and which part is a host address. Everything in the host address that corresponds to a 1 in the subnet mask is a network address and everything in the host address that corresponds to a 0 in the subnet mask is a host address.
Sub-subnetting
Many LANs at Cornell are sub-subnetted.
Sub-subnetting is based on the same concept as subnetting. With sub-subnetting, the mask will be 255.255.255.192. In binary form, this address looks like this:
Sub-subnet mask: 11111111 11111111 11111111 11000000
When you compare the sub-subnet mask to the example IP host address (128.253.21.58), they look like this:
Sub-subnet mask: 11111111 11111111 11111111 11000000
Host address: 10000000 11111101 00010101 00111010
Like the old subnet mask, the sub-subnet mask tells the computer which part of the IP address is the network address and which part is a host address. As explained above, everything in the host address that corresponds to a "1" in the sub-subnet mask is a network address and everything in the host address that corresponds to a 0 in the sub-subnet mask is a host address.
As you can see, there are now ones (1's) in the last byte of the sub-subnet mask. (This is the part, in the subnet mask, that was all zeros (0's) and that identified the host portion of an address.) The ones (1's) that appear in this byte of the sub-subnet mask identify the first two bits of the last byte of an IP address as part of the network portion of the address. The remaining zeros (0's) identify the host portion of the address. By increasing the number of bits assigned to network addressing, the number of possible network addresses increases and the number of possible host addresses for each LAN decreases.
Why is this important?
Gateways need to forward packets to other gateways to get them to the destination LAN. Each network interface card on the gateway is assigned an IP address and a sub-subnet mask. This enables the gateways to route packets from one LAN to another LAN. Once the packet arrives at a gateway that is attached to the destination LAN, the gateway then uses the two bits of the sub-subnet portion of the IP address (the first two bits of the last byte of the IP address) to decide to which sub-subnetted LAN to send the packet.
In order for this to work, each of the LANs connected to a given gateway must have a different set of host addresses. As you know, the host address you assign, for example 58, is translated into a binary address (00111010). Remember, even though you think of this as a host address, the sub-subnet mask forces the gateway to think of the first two bits as part of the network address. If two LANs attached to the same gateway each have hosts with an address of 58, the first two bits in the binary translation will be the same, and even though the hosts are physically on two separate LANs, the gateway won't know to which LAN to send a packet.
To make sure each LAN has a unique set of host addresses, network administrators can no longer assign host numbers from the entire range. Now, each administrator will be assigned a subset of the host addresses available. Within each subset, broadcast, gateway, and diagnostic addresses must be reserved. So, for example, Administrator X can have server addresses at 6 through 9 and workstation addresses at 10 through 63; Administrator Y can have server addresses at 70 through 73 and workstation addresses 74 through 126, etc. If your current host addresses fall outside the range assigned to your LAN, you need to reassign host addresses on your network.
Understanding Static vs. Dynamic Addressing
If you use static addressing on your network, this means you assign each host a permanent IP address. If you use dynamic addressing, the hosts use any available address within a range you specify. The information below explains some of the advantages and disadvantages of static and dynamic addressing.
Before you begin reconfiguring your applications, you should decide which scheme you plan to use: static, dynamic, or a combination. CIT recommends that you use static addressing; it helps you, as the network administrator, keep track of machines and figure out which one is causing problems. Some network applications require static addressing.
If you want to consider dynamic addressing because it is easier to set up, CIT advises that you limit the range for dynamically assigned addresses to start at 21, thus leaving 6-20 reserved for hosts that need fixed addresses because they will offer IP services. If you think you will have more than 15 IP server hosts, you should raise the start point for dynamically assigned addresses.
Changing the UNIX Operating System to Work with Sub-subnetting
Because UNIX has TCP/IP protocols built into the operating system, you can alter the configuration of the operating system itself instead of the applications that run on it. Follow these instructions:
- Go to the interface configuration command, called ifconfig, in your startup script. Most UNIX startup scripts are called /etc/rc/local. You will see a line that looks like this:ifconfig le0 $hostname netmask 255.255.255.0 broadcast 128.253.180.255 -trailers up
Change the value of the netmask to 255.255.255.192. - Note: ifconfig also accepts netmask values in hexadecimal notation. Therefore you may see 0xffffff00 as the value of the netmask. If this is the case, change the value to 0xffffffc0.
- Change the host portion of the broadcast address to one of the following values, depending on the sub-subnet your host is in:
- If the host's IP address is between 1 and 64, use 63.
- If the host's IP address is between 65 and 128, use 127.
- If the host's IP address is between 129 and 192, use 191.
- If the host's IP address is between 193 and 256, use 255.
If your IP address is between 1 and 64, on subnet 180, your ifconfig command would look like this: ifconfig le0 $hostname netmask 255.255.255.192 broadcast 128.253.180.63 -trailers up
4. If you use static routing, you need to change your default gateway. For example:
route add default 128.253.180.1 1
Host Registration
Network administrators are strongly encouraged to register all devices on their networks (desktop workstations, servers, printers, etc.) with the Network Operations Center (NOC). Visit the Network and Host Registration web site for more information.
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