A router checks the source and destination IP addresses of each packet, looks up the destination of the packet in the router’s IP routing table, and routes the packet to another router or a switch. The process keeps happening until the destination IP address is reached and responds back. When there is more than one way to go to the destination IP address, routers can smartly choose the most economical one. When the destination of the packet is not listed in the routing table, the packet will be sent to the default router (if it has one). If there’s no destination existing for the packet, it will be dropped.
How routers route packets from the source IP to the destination IP
Figure 3: How routers route packets from the source to the destination.
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Generally, your router is provided by your Internet Service Providers (ISP). Your Internet provider assigns you one router IP address, which is a public IP address. When you browse the Internet, you’re identified to the outside world by the public IP address and your private IP address is protected. However, the private IP addresses of your desktop, laptop, iPad, TV media box, network copier are completely different. Otherwise, the router cannot recognize which device is requesting what.
What Does a Router Do?
Routers interpret different networks. Apart from the most commonly used Ethernet, there are many other different networks, such as ATM and Token Ring. The networks encapsulate data in different methods so they cannot communicate directly. Routers can “translate” these packets from different networks so they can understand each other.
Routers prevent broadcast storm. Without a router, a broadcast will go to every port of every device and be processed by every device. When the amount of broadcasts is too large, chaos can occur in the whole network. A router subdivides the network into two or more smaller networks that are connected by it, and it won’t allow the broadcast to flow between subnets.