What are the usage and functioning of Router ?

A router is a device that forwards data packets between computer networks.

This creates an overlay internetwork, as a router is connected to two or more data lines from different networks.

Example of common usage of Router

• Home and small office routers, simply pass data, such as web pages, email, IM, and videos between the home computers and the Internet.
• Owner's cable or DSL router, which connects to the Internet through an ISP.
• Enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone.

Router functioning

When a data packet comes in one of the lines, the router reads the address information in the packet to determine its ultimate destination.

Then, using information in its routing table or routing policy, it directs the packet to the next network.

Routers perform the "traffic directing" functions on the Internet. 

A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it reaches its destination node.

2 stage operation

1. Control plane

A router records a routing table listing what route should be used to forward a data packet, and through which physical interface connection.

It does this using internal pre-configured directives, called static routes, or by learning routes using a dynamic routing protocol.

Static and dynamic routes are stored in the Routing Information Base (RIB).

The control-plane logic then strips the RIB from non essential directives and builds a Forwarding Information Base (FIB) to be used by the forwarding-plane.

A typical home or small office router showing the ADSL telephone line and Ethernet network cable connections

2. Forwarding plane

The router forwards data packets between incoming and outgoing interface connections.

It routes it to the correct network type using information that the packet header contains. It uses data recorded in the routing table control plane.

When multiple routers are used in interconnected networks, the routers exchange information about destination addresses using a dynamic routing protocol. Each router builds up a table listing the preferred routes between any two systems on the interconnected networks. A router has interfaces for different physical types of network connections, (such as copper cables, fiber optic, or wireless transmission).

It also contains firmware for different networking Communications protocol standards.

Each network interface uses this specialized computer software to enable data packets to be forwarded from one protocol transmission system to another.

Routers may also be used to connect two or more logical groups of computer devices known as subnets, each with a different sub-network address. The subnets addresses recorded in the router do not necessarily map directly to the physical interface connections.

Internet and internal use of Router

Edge router

Also called a Provider Edge router, is placed at the edge of an ISP network.

The router uses External BGP to EBGP protocol routers in other ISPs, or a large enterprise Autonomous System.

Subscriber edge router

Also called a Customer Edge router, is located at the edge of the subscriber's network, it also uses EBGP protocol to its provider's Autonomous System.

It is typically used in an (enterprise) organization.

Inter-provider border router

Interconnecting ISPs, is a BGP-protocol router that maintains BGP sessions with other BGP protocol routers in ISP Autonomous Systems.

Core router

A core router resides within an Autonomous System as a back bone to carry traffic between edge routers.

Within an ISP

In the ISPs Autonomous System, a router uses internal BGP protocol to communicate with other ISP edge routers, other intranet core routers, or the ISPs intranet provider border routers.

Internet backbone

The Internet no longer has a clearly identifiable backbone, unlike its predecessor networks.

The major ISPs system routers make up what could be considered to be the current Internet backbone core.

ISPs operate all four types of the BGP-protocol routers described here.

An ISP "core" router is used to interconnect its edge and border routers.

Core routers may also have specialized functions in virtual private networks based on a combination of BGP and Multi-Protocol Label Switching protocols.

Port forwarding

Routers are also used for port forwarding between private internet connected servers.

Voice/Data/Fax/Video Processing Routers

Commonly referred to as access servers or gateways, these devices are used to route and process voice, data, video, and fax traffic on the internet. Since 2005, most long-distance phone calls have been processed as IP traffic (VOIP) through a voice gateway.

Voice traffic that the traditional cable networks once carried.

Use of access server type routers expanded with the advent of the internet, first with dial-up access, and another resurgence with voice phone service.