Cisco Routers use the Internetwork Operating System(IOS) to control and manage the hardware it is running on.IOS provides the interface between the user and the hardware, enabling the user to execute the command to configure and manage the device using Command Line Interface (CLI.)

Cisco® IOS Features:

1. Command Line Interface (CLI)

a. User EXEC Mode

b. Privileged EXEC Mode

c. Global Configuration Mode

d. Sub-Configuration Mode

2. Router Interface Configuration

3. RIP Configuration Using Cisco® IOS™

1. Command Line Interface (CLI)

Summary:
Subnetting an IP Network is done primarily for better utilization of available IP address space, and routing purpose. Other reasons include better organization, use of different physical media (such as Ethernet, WAN, etc.), and securing network resources.

Body:
A subnet mask enables you to identify the network and node parts of the address. The network bits are represented by the 1s in the mask, and the node bits are represented by the 0s. A logical AND operation between the IP address and the subnet mask provides the Network Address.