What is Router ? and its Work - Definition from akhileshnetworking

 WHAT IS ROUTER ?
             
     Router is a network layer Layer 3 device of the OSI reference model device that means it can connect multiple computer networks via wired or wireless connections. Network router can receive, analyze, perform the traffic directing functions and forwards data packet from one network to its destination node. A router is a device that forwards packets between networks by processing the routing information included in the packet.     

Routers use logical and physical addressing to connect two or more logically separate networks. They accomplish this connection by organizing the large network into logical network segments or sub-networks. Each of these sub networks is given a logical address. This allows the networks to be separate but still access each other and exchange data when necessary. Data is grouped into packets, or blocks of data. Each packet, in addition to having a physical device address, has a logical network address. 

Network Router containing  a software that help in determining the best path out of the available paths, for a particular transmission. They consist of a combination of hardware and software. The hardware includes the physical interfaces to the various networks in the internetwork. The two main pieces of software in a router are the operating system and the routing protocol.

Routers are frequently used to interconnect identical networks as well as to interconnect networks with different types of hardware. Compared to one giant LAN, a series of smaller LANs connected through routers has some highly desirable benefits.

 

How Do Routers Work?                                                                  

1. The router powers on and loads it's OS from flash
2. The router loads the configuration file last saved to NVRAM and sets up the network interfaces and routing protocols it will run.
3. The router adds the network address and subnet for each interface to it's routing table along with the name of the interface itself.
4. The router has a simple static default route to send all non-local data out the network port connected to the cable company.
5. When the router receives a web page request from your computer, it checks the destination IP address against its routing table.
6. The bits forming the destination IP address in the IP packet are used as a hash key to point to the correct route, which in turn points to the correct network interface that the packet should be forwarded out of.
7. The router transmits the packet out the correct interface, to the next router, which repeats the process until the packet reaches the destination.
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Components of Router  

Since routers are just specialized computers, the have the same "parts" as other computers:

• *Central Processing Unit (CPU)
• *Flash Memory
• *Non-Volitile RAM
• *RAM
• *Network Interfaces
• *Console

Central Processing Unit:  Runs special software called an "operating system" such as JunOS on Juniper routers, or Cisco IOS (Nexus OS) for Cisco routers. The operating system manages the router's components and provies all the logical networking functions of the router.

Flash Memory is where the operating system is stored, and in this respect, is like the hard disk drive in your computer. If you use a Solid State Disk Drive (SSD), then your computer uses Flash RAM, just like the router does. 

Non-Volitile RAM:  This is additional memory for storing the backup or startup version of the operating system being used. The router will boot from this memory and load all it's programs from here.

RAM: When the router starts up, the operating system is loaded into RAM. Once the router finishes starting up, it begins to calculate its own routes and, if configured to do so, learns network routes from other routers via RIP (v1 and v2), OSPF, EIGRP, IS-IS or BGP. RAM is also used for caching ARP tables, routing tables, routing metrics and other data that can speed up the process of forwarding of packets.

Network Interfaces:  Routers always have lots of network interfaces. The operating system contains 'drivers' that allow the operating sytem to access the network hardware in the interface modules. Routers will learn which networks are configured on which ports as they start up. After that, they will 'learn' routes from other routers they are connected to, and learn which interface to transmit packets on to reach a remote network destination.

Console:  Last, but not least, is the console. In "Ye Olden Days" managing and configuring a router was performed at the console of individual devices, as was most troubleshooting and diagnostics. Network certification exams will contain a large selection of questions on the configuration and troubleshooting commands you can issue from the console. However, manufacturers are rapidly doing away with a console on each device and building management systems for managing large numbers of network devices from a centralized location.