Router is a computer device that receives or forwards data packets to and from the Internet towards a destination in the process called routing. Router is the essential component of the computer networking that enables any sent data to arrive at the right destination.
As an illustration, imagine that the Internet is the world and one computer is one household. Other computers connected through the Internet are households around the world. Say one household will send a letter to another household in any part of the world. The letter has an address right? And that address would determine the destination of the letter. But without one reading the address, the letter would not arrive to the right receiver. The letter also would not be able to reach the intended receiver if there is not medium. This medium would be the courier. And the courier of the computer data is the router.
A router (broadband router) is also a device that enables two or more computer to receive data packets from the Internet under one IP address at the same time.
Remember that to be able to connect to the Internet, a computer must have an IP address unique from the rest of the computers. Therefore, every computer connected to the Internet has it own IP address. It is like having a fingerprint or ID as an access pass to be able to enter the web. With the presence of the router, this “fingerprint” or “ID” could be shared by two or more computer at the same time.
In simplest form, a router makes two or more computer use the Internet at the same with one access pass.
One more thing: a computer with cable modem could also be considered as a router. In this, the computer would do the process of routing like normal routers do. Other computers are then connected to the computer with Internet connection that would give it with the Internet connection. The computer with cable modem has the direct contact with the Internet and the ones connected to it are sharing the connection.
Why would anyone need a router?
For households with two or more computers who would want to have Internet connection to every computers they have, taking subscription for each would be too much. The solution is to buy a router that would enable every computer in the house to have an Internet connection. In the definition above, the broadband router would act as a hub to the existing Internet connection.
If the router is comparable to a hub, would it affect the Internet speed?
It should be taken into consideration that once a single Internet connection is divided, the connection speed is affected. But there are some broadband routers that would bring minimal slowdown to the Internet speed and the effect might not even be big.
Internet speed would also depend on the type of application used in a router. While some would inflict little effect on the speed like online games, others would terribly slowdown your connection and even hinder you to use the Internet at all.
Usually, offices use a more sophisticated router to redirect Internet connections to the large number of computers. These routers would give better data packeting compared to a typical router used at home that results to faster Internet speed
A Router is a layer 3 network device that moves data between different network segments and can look into a packet header to determine the best path for the packet to travel. Routers can connect network segments that use different protocols. They also allow all users in a network to share a single connection to the Internet or a WAN. It is used to improve network performance by:-
• segmenting the network and creating separate collision & broadcast domains.
• reducing competition for bandwidth.
• Broadcasts are not forwarded to other network segments.
• Increases security by using Access Lists
Router Components (internal)
ROM
ROM is used to store the router's bootstrap startup program, operating system software, and power-on diagnostic tests programs. In order to perform ROM upgrades you remove and replace pluggable chips on the motherboard.
Flash Memory
It holds operating system image(s). Flash memory is erasable, reprogrammable ROM. You can perform Cisco® IOS software upgrades without having to remove and replace chips. Flash content is retained when you switch off or restart the router.
RAM
RAM is used to store operational information such as routing tables, router's running configuration file. RAM also provides caching and packet buffering capabilities. Its contents are lost when you switch off or restart the router.
NVRAM
NVRAM (nonvolatile RAM), is used to store the router's startup configuration file. It does not lose data when power is switched off. So the contents of the startup configuration file are maintained even when you switch off or restart the router.
Network Interfaces
The router's network interfaces are located on the motherboard or on separate interface modules. You configure Ethernet or Token Ring interfaces to allow connection to a LAN. The synchronous serial interfaces are configured to allow connection to WANs. You can also configure ISDN BRI interfaces to allow connection to an ISDN WAN..
Router Components (External)
A router can be configured over any of its network interfaces. You can supply configuration information to a router using:-
TFTP servers : Trivial File Transfer Protocol; A simplified version of FTP that allows files to be transferred from one computer to another over a network.
virtual terminals
network management stations
Router's Startup Procedure
Each time you switch on the router, it goes through power-on self-test diagnostics to verify basic operation of the CPU, memory and network interfaces.
The system bootstrap software in ROM (boot image) executes and searches for valid router operating system software (Cisco® IOS image). IOS is acronym for Internetwork Operating System.
There are three places to find the Cisco® IOS image to load:
• Flash memory
• A TFTP server on the network
• ROM
The source of the Cisco® IOS image is determined from the boot field setting of the router's configuration register.
Configuration Registration: A 16-bit register used to control how the router boots up, where the IOS image, how to deal with the NVRAM configuration, setting the console baud rate and enabling or disabling the break function.
The default setting for the configuration register indicates that the router should attempt to load a Cisco® IOS image from flash memory.
If the router finds a valid IOS image, it searches for a valid configuration file. If your router does not find a valid system image, or if its configuration file is corrupted at startup, and the configuration register (bit 13) is set to enter ROM monitor mode, the system will bypass the NVRAM setting and enters ROM monitor mode. This also allow access to the router in the event a password is lost.
The configuration file, saved in NVRAM, is loaded into main memory and executed one line at a time. These configuration commands start routing processes, supply addresses for interfaces, and set media characteristics.
If no configuration file exists in NVRAM, the operating system executes a question-driven initial configuration routine called the system configuration dialog.
This special mode is also called the Setup mode.
The Cisco® IOS software provides you with access to several different command modes. Each command mode provides a different group of related commands.
The Cisco® Command Line Interface (CLI) is called EXEC. EXEC has two modes:-
• User mode
• Privileged mode
EXEC user commands allow you to
• connect to remote devices
• make temporary changes to terminal settings
• perform basic tests
• list system information
If you want to access privileged mode you have to enter a password. The commands available in Privileged mode also include all those available in User mode. You can use Privileged EXEC commands to:-
• set operating parameters
• perform a detailed examination of the router's status
• test and debug router operation
• access global and other included configuration modes
From Privileged mode you can enter global configuration mode. This gives you access to configuration commands that affect the system as a whole, and to other configuration modes.
You can specify the source of the configuration commands as being from :-
• a terminal
• memory
• the network
You can access many other specific configuration modes from Global Configuration mode that allow complex configurations to be performed.
Setup Mode: If the router does not have a configuration file it will automatically enter Setup mode when you switch it on. Setup mode presents you with a prompted dialog, called the system configuration dialog, in which you establish an initial configuration.
Rom Monitor Mode: If the router does not find a valid operating system image, or if you interrupt the boot sequence, the system may enter ROM monitor mode. From ROM monitor mode you can boot the device or perform diagnostic tests.
As an illustration, imagine that the Internet is the world and one computer is one household. Other computers connected through the Internet are households around the world. Say one household will send a letter to another household in any part of the world. The letter has an address right? And that address would determine the destination of the letter. But without one reading the address, the letter would not arrive to the right receiver. The letter also would not be able to reach the intended receiver if there is not medium. This medium would be the courier. And the courier of the computer data is the router.
A router (broadband router) is also a device that enables two or more computer to receive data packets from the Internet under one IP address at the same time.
Remember that to be able to connect to the Internet, a computer must have an IP address unique from the rest of the computers. Therefore, every computer connected to the Internet has it own IP address. It is like having a fingerprint or ID as an access pass to be able to enter the web. With the presence of the router, this “fingerprint” or “ID” could be shared by two or more computer at the same time.
In simplest form, a router makes two or more computer use the Internet at the same with one access pass.
One more thing: a computer with cable modem could also be considered as a router. In this, the computer would do the process of routing like normal routers do. Other computers are then connected to the computer with Internet connection that would give it with the Internet connection. The computer with cable modem has the direct contact with the Internet and the ones connected to it are sharing the connection.
Why would anyone need a router?
For households with two or more computers who would want to have Internet connection to every computers they have, taking subscription for each would be too much. The solution is to buy a router that would enable every computer in the house to have an Internet connection. In the definition above, the broadband router would act as a hub to the existing Internet connection.
If the router is comparable to a hub, would it affect the Internet speed?
It should be taken into consideration that once a single Internet connection is divided, the connection speed is affected. But there are some broadband routers that would bring minimal slowdown to the Internet speed and the effect might not even be big.
Internet speed would also depend on the type of application used in a router. While some would inflict little effect on the speed like online games, others would terribly slowdown your connection and even hinder you to use the Internet at all.
Usually, offices use a more sophisticated router to redirect Internet connections to the large number of computers. These routers would give better data packeting compared to a typical router used at home that results to faster Internet speed
A Router is a layer 3 network device that moves data between different network segments and can look into a packet header to determine the best path for the packet to travel. Routers can connect network segments that use different protocols. They also allow all users in a network to share a single connection to the Internet or a WAN. It is used to improve network performance by:-
• segmenting the network and creating separate collision & broadcast domains.
• reducing competition for bandwidth.
• Broadcasts are not forwarded to other network segments.
• Increases security by using Access Lists
Router Components (internal)
ROM
ROM is used to store the router's bootstrap startup program, operating system software, and power-on diagnostic tests programs. In order to perform ROM upgrades you remove and replace pluggable chips on the motherboard.
Flash Memory
It holds operating system image(s). Flash memory is erasable, reprogrammable ROM. You can perform Cisco® IOS software upgrades without having to remove and replace chips. Flash content is retained when you switch off or restart the router.
RAM
RAM is used to store operational information such as routing tables, router's running configuration file. RAM also provides caching and packet buffering capabilities. Its contents are lost when you switch off or restart the router.
NVRAM
NVRAM (nonvolatile RAM), is used to store the router's startup configuration file. It does not lose data when power is switched off. So the contents of the startup configuration file are maintained even when you switch off or restart the router.
Network Interfaces
The router's network interfaces are located on the motherboard or on separate interface modules. You configure Ethernet or Token Ring interfaces to allow connection to a LAN. The synchronous serial interfaces are configured to allow connection to WANs. You can also configure ISDN BRI interfaces to allow connection to an ISDN WAN..
Router Components (External)
A router can be configured over any of its network interfaces. You can supply configuration information to a router using:-
TFTP servers : Trivial File Transfer Protocol; A simplified version of FTP that allows files to be transferred from one computer to another over a network.
virtual terminals
network management stations
Router's Startup Procedure
Each time you switch on the router, it goes through power-on self-test diagnostics to verify basic operation of the CPU, memory and network interfaces.
The system bootstrap software in ROM (boot image) executes and searches for valid router operating system software (Cisco® IOS image). IOS is acronym for Internetwork Operating System.
There are three places to find the Cisco® IOS image to load:
• Flash memory
• A TFTP server on the network
• ROM
The source of the Cisco® IOS image is determined from the boot field setting of the router's configuration register.
Configuration Registration: A 16-bit register used to control how the router boots up, where the IOS image, how to deal with the NVRAM configuration, setting the console baud rate and enabling or disabling the break function.
The default setting for the configuration register indicates that the router should attempt to load a Cisco® IOS image from flash memory.
If the router finds a valid IOS image, it searches for a valid configuration file. If your router does not find a valid system image, or if its configuration file is corrupted at startup, and the configuration register (bit 13) is set to enter ROM monitor mode, the system will bypass the NVRAM setting and enters ROM monitor mode. This also allow access to the router in the event a password is lost.
The configuration file, saved in NVRAM, is loaded into main memory and executed one line at a time. These configuration commands start routing processes, supply addresses for interfaces, and set media characteristics.
If no configuration file exists in NVRAM, the operating system executes a question-driven initial configuration routine called the system configuration dialog.
This special mode is also called the Setup mode.
The Cisco® IOS software provides you with access to several different command modes. Each command mode provides a different group of related commands.
The Cisco® Command Line Interface (CLI) is called EXEC. EXEC has two modes:-
• User mode
• Privileged mode
EXEC user commands allow you to
• connect to remote devices
• make temporary changes to terminal settings
• perform basic tests
• list system information
If you want to access privileged mode you have to enter a password. The commands available in Privileged mode also include all those available in User mode. You can use Privileged EXEC commands to:-
• set operating parameters
• perform a detailed examination of the router's status
• test and debug router operation
• access global and other included configuration modes
From Privileged mode you can enter global configuration mode. This gives you access to configuration commands that affect the system as a whole, and to other configuration modes.
You can specify the source of the configuration commands as being from :-
• a terminal
• memory
• the network
You can access many other specific configuration modes from Global Configuration mode that allow complex configurations to be performed.
Setup Mode: If the router does not have a configuration file it will automatically enter Setup mode when you switch it on. Setup mode presents you with a prompted dialog, called the system configuration dialog, in which you establish an initial configuration.
Rom Monitor Mode: If the router does not find a valid operating system image, or if you interrupt the boot sequence, the system may enter ROM monitor mode. From ROM monitor mode you can boot the device or perform diagnostic tests.