The introduction of cisco IOS

Router or switch will not work without operating system. Without operating system, hardware will be useless. Cisco IOS has the ability to:
- Basic routing and switching functions- Access to the secured network keamannya- Operates at the network scale
CLI can be accessed in several ways. In general, the CLI is accessed through a console terminal. Console using low-speed serial connection that plugs directly from the router to the PC. CLI can also be accessed via a remote connection via dialup modem to the router AUX port. The third way is via telnet to the router. To access via telnet, at least one router interface is configured network address (IP address), and virtual terminal must be configured for the login and password.
CLI on a cisco has a hierarchical structure. This structure is useful for other types of commands to the router. Example, to configure a router interface, the user must enter the configuration mode. All configuration is inserted into the interface was only valid for a configurable inetrface only. IOS provide interpreter service known as the command executive (EXEC). After each command entered, the EXEC will validate and execute commands.
Cisco IOS is divided into two levels of access, the user EXEC mode and privileged EXEC mode. Privileged EXEC mode is also known as enable mode. Below are the features of the user EXEC mode and privileged EXEC mode:
- User EXEC mode commands are only limited. Usually includes only the commands that are monitoring or view.User EXEC does not allow users to make configuration changes on the router. User EXEC mode is characterized by prompt>- Privileged EXEC mode contains a command = command for access to the router. This mode can be used to configure the password. And usually this mode is often used by administrators to commands that are configuration and management. Global configuration mode and other configuration modes can only be done through this mode. Privileged EXEC mode prompt is marked with # 

For access to privileged EXEC mode level, a user who is a user-level EXEC must type enable at the command prompt>, if the password is entered correctly then the prompt will change to #. This suggests that the current user is in privileged EXEC level. At the time the command inserted?, It will show what commands are allowed to do at the time. 
At startup, Cisco is normally called the RAM and run one of the three modes. System administrators can use the configuration register to set the default startup settings.ROM monitor is used to bootstrap the process and provide a low-level functions and for purposes of diagnosis. This mode is used to restore a system failure (system failures) and returns the password. This mode is not accessible via the network interface, and can only be accessed via a physical connection via the console port. 
At the router the way in ROM mode, only a few features of IOS can walk. Boot ROM allows storage operations to the flash memory and used to replace the Cisco IOS image stored in flash. Cisco IOS can be modified in the boot ROM with the command copy tftp flash. This command to copy the IOS image in the TFTP server to the router's flash memory. 
Normally the router using the full Cisco IOS image stored in flash. Some devices, IOS run directly from flash. However, most Cisco routers require a copy of the IOS to the RAM and run from RAM. Some of the IOS image stored in flash in a compressed state and must be extracted when copied into RAM.To find the IOS image and version being used road show version command. Show flash command is used to verify the memory required to load a new Cisco IOS image.

Posted in: CCNA