What Do You Mean By Hierarchical Routing?

To solve the problems of gigantic routing tables, we create a sense of a hierarchy in the internet architecture and so that we have created hierarchical routing. As we know that internet today has a sense of hierarchy. So, if the routing table has a sense of hierarchy like the internet architecture, the routing table can decrease in size. But how can this size be reduced? The rest of the internet does not have to be aware of this whole division.

All customers of the local ISP are defined as A.B.C.D/n to rest of the internet. Every packet destined for one of the addresses in this large block is routed to local ISP. There is only one entry in every router in the world for all these customers. They all belong to the same group in actual. Inside the local ISP, router must recognize the subblocks and route the packet to the destined customer. If one of the customers is a large organization, it can also create another level of hierarchy by sub-netting and dividing its subblock into the smaller subblocks or sub-subblocks. In type of classless routing, the levels of hierarchy are unlimited as long as we follow the rules of the classless addressing.