Routing is a layer three phenomina that means to forward a 
packet to the destination address based on the ip address 
fiend of the packet.As we know the the devices used at 
layer three are aware of the routing table(Routers or layre 
three switches) when these devices receives a packet they 
look into there routing table which they dynamically learns 
from the protocols or mannually by the administrator(static 
routing). routing table maps the ip address to a particular 
interface for forwarding . the packet is forwarded out to 
that network .......same phenomina takes place untill the 
packet reachec its destination