Subnetting

Subnetting means dividing a larger network into several smaller networks. You can find some matching with branching of a tree. Nutrition's from ground travels trough the branches, first come to the main thick vertical branch then thin brunches and at the last fruit or leafs. Networks must follow such branching or hierarchy where internet is like the ground (largest data container and service provider) then large networks (regional/national service organization) are like the thick vertical branch then sub-networks or route to group of hosts are like thin branches and hosts/nodes are like fruits/leafs.

Subnetting or branching or sub-grouping an IP Network is done for a variety of reasons, such as preservation of address space, use of different physical media (such as Ethernet, FDDI, WAN, etc.), organization/business and security. The most important issue is to control network traffic. All nodes on a segment observe all the packets transmitted by all the other nodes on that segment, in an Ethernet network. Due to collisions, performance can be adversely affected under heavy traffic loads and the resulting retransmissions.  Routers are used to connect networks/sub-networks to minimize the amount of traffic each segment must receive.