Basics about networking (CCNA) part-5

What is router and why it is required?

Router is basically a computing device and it forwards data packets between computer networks, creating an overlay inter network  A router is connected to two or more data lines from different networks. 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 on its journey with the help of process called Routing. Router do routing to process data, Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for much kind of networks, including the telephone network (Circuit Switching), Electronic data networks (internet) and transportation networks.

Traffic directing function performed by routers on the internet, data packet is forwarded from one router to another through the networks that constitute the inter network until it reaches its destination node. Routers works on Layer 3 (OSI Model) which is also called as Network layer, when a router receives a packet, it looks at the layer 3 source and destination addresses to determine the path the packet should take to reach destination. A standard switch relies on the MAC Addresses to determine the source and destination of a packet, which is layer 2 networking (OSI Model) also called as Data Link Layer. There is a device called L3 Switch is also having the same functionality of router but the fundamental difference between a router and a layer 3 switch is that Layer 3 switches have optimized hardware to pass data as fast as layer 2 switches, yet they make decision on how to transmit traffic at layer 3, just like a router. L3 switches actually works at Network Layer; L3 switches are faster as compared to routers in LAN environment because it is built on switching hardware.

However, a Layer 3 switch has the ability to reprogram the hardware dynamically with the current layer 3 routing information. This is what allows for faster packet processing, In fact, many of Cisco's Layer 3 switches are actually routers that operate faster because they are built on "switching" hardware with customized chips inside the box. The pattern matching and caching on layer 3 switches is similar to the pattern matching and caching on a router. Both use a routing protocol and routing table to determine the best path.

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.