Question

Two key network layer functions are forwarding and routing.

What are forwarding and routing? How does a router work ?

Answer 1

Forwarding refers to the router-local action of transferring the packet from an input link interface to the appropriate output link interface.

Routing refers to the network-wide process that determines end-to-end paths that packets take from source to destination.

HOW DOES ROUTER WORK

Router work in following manner.

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.