what's the router?

A device that forwards data packets along networks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP’s network. Routers are located at gateways, the places where two or more networks connect .

Very little filtering of data is done through routers.



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Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as ICMP
to communicate with each other and configure the best route between any two hosts.



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This page will provide a brief review of routers.

A router is a special type of computer. It has the same basic components as a standard desktop PC. It has a CPU, memory, a system bus, and various input/output interfaces. However, routers are designed to perform some very specific functions that are not typically performed by desktop computers. For example, routers connect and allow communication between two networks and determine the best path for data to travel through the connected networks.




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Just as computers need operating systems to run software applications, routers need the Internetwork Operating System (IOS) software to run configuration files. These configuration files contain the instructions and parameters that control the flow of traffic in and out of the routers. Routers use routing protocols to determine the best path for packets. The configuration file specifies all the information for the correct setup and use of the selected, or enabled, routing and routed protocols on a router.



RAM has the following characteristics and functions:

Stores routing tables
Holds ARP cache
Holds fast-switching cache
Performs packet buffering as shared RAM
Maintains packet-hold queues
Provides temporary memory for the configuration file of a router while the router is powered on
Loses content when a router is powered down or restarted
NVRAM has the following characteristics and functions:

Provides storage for the startup configuration file
Retains content when a router is powered down or restarted

Flash memory has the following characteristics and functions:

Holds the IOS image
Allows software to be updated without removing and replacing chips on the processor
Retains content when a router is powered down or restarted
Can store multiple versions of IOS software
Is a type of electrically erasable programmable read-only memory (EEPROM)

ROM has the following characteristics and functions:

Maintains instructions for power-on self test (POST) diagnostics
Stores bootstrap program and basic operating system software
Requires replacing pluggable chips on the motherboard for software upgrades

Interfaces have the following characteristics and functions:

Connect routers to a network for packet entry and exit
Can be on the motherboard or on a separate module
The next page will describe the role of routers in WANs and LANs.


Routers can be used to segment LANs, but they are mainly used as WAN devices. This page will explain how routers are used in a network.




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Routers have both LAN and WAN interfaces.





WAN technologies are frequently used to connect routers. Routers use WAN connections to communicate with each other. Routers are the backbone devices of large intranets and of the Internet. They operate at Layer 3 of the OSI model, making decisions based on network addresses. The two main functions of a router are to select the best path for packets and to route packets to the proper interface. To accomplish this, routers build routing tables and exchange network information with other routers.

An administrator can configure static routes to maintain routing tables. However, most routing tables are maintained dynamically through the use of a routing protocol that exchanges network topology information with other routers.


network topology







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this routers from Lebanon - BCU - Cisco Laboratory .

cisco lab at (BCU):

Why Would I Need a Router?
For most home users, they may want to set-up a LAN (local Area Network) or WLAN (wireless LAN) and connect all computers to the Internet without having to pay a full broadband subscription service to their ISP for each computer on the network. In many instances, an ISP will allow you to use a router and connect multiple computers to a single Internet connection and pay a nominal fee for each additional computer sharing the connection. This is when home users will want to look at smaller routers, often called broadband routers that enable two or more computers to share an Internet connection. Within a business or organization, you may need to connect multiple computers to the Internet, but also want to connect multiple private networks — and these are the types of functions a router is designed for.



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Thanks Hamid for the useful information.
Concerning the last paragraph why we use router: For ordinary user who wants to share internet connection with many computers without paying extra money, another useful and cheap device could be appropriate. It is the HUB. From 8-15 computers can be connected to the internet.
Routers mainly used for connecting WANs & LANs.

Thank you,

Gamal Karrar
ICT Specialist
UNDP
Sudan

Thaks Hamid and peace builder

Just a note that HUBs do not work by themselves and they must be used with routers.
In a typical LAN network, the output of the modem must go to the router, and then
one of the routers outputs can be connected to the HUB.
if you have less than 9 computers in your network then it is not a good idea to use a HUB
because you are going to buy an 8-port router anyway.

in cisco technology use switchs & bridges instate of hubs ..
The bridge adds the source address of the frame to its bridge table..
this mean .. smart than hub .

Thank you very much Hamid

It is realy a very good and a very interesting topic

May ALLAH bless you