IP routing is a set of protocols that provide basic infrastructure for delivery of Packets to the Destination device. Routing protocols learn about the networks dynamically and exchange all routing information with other Devices on the internal or external Network. Routing protocols determine the best path for routing and routed protocols are the one to send data, e.g IP ( Internet Protocol).
There are many types of routing protocols used in the field of Networking and they differ in the way they determine best and optimal path to another network. Routing protocols that respond quickly to changes in the network architecture are said to converge rapidly. There is probably intermittent packet losses and poor network connectivity between networks if the convergence of a routing protocol takes long. Slow convergence will also result in network routing loops,.What determines the convergence is the routing protocol used.
How does a router handle packets?
When a router receives a packet for a directly connected network, it checks its routing table for the exit interface to that network then automatically forwards the packet to that network. But if the packet is destined for a remote network, the routing table is also checked. If there is a default route, the packet is forwarded to the next-hop (i.e next router) default gateway router. The packet destined for a network, not in the routing table and no default route defined, the packet is dropped.
How does a packet reach the Destination?
The router accepts incoming packet through one interface and Encapsulates it in the appropriate Data Link frame before sending it out the outgoing interface.
The router receiving the Packet decapsulates the Layer three packet by removing the Layer 2 frame header and trailer, determines the destination IP address and forwards the frame to the switch connecting the destination host or to the Device if directly connected to one of the router’s interfaces.
NOTE: Source and Destination IP Address will never change as a packet goes to its destination, Only The MAC address will change to permit transportation of the packet between intermediary devices.