Chap2:Introduction to Routers
From Mycomputer Notes
A router also needs an Operating System (O/S)to properly function, as any other computer. On a router the Operating System (OS) is called IOS developped by CISCO
Internetwork Operating System (IOS)
The CISCO IOS provides the following network procedures:
- Basic Routing & switching functions
- Reliable & secured access to network resources
- Network Scalability
Command Line Environment (CLI)
Commands are entered like in DOS or Unix/Linux. This commands offered the following avantages:
- Commande completion
- Syntax verification
- Help Levels
- Keyboard shortcuts
The Cisco CLI uses a hierarchical structure. This structure requires entry into different modes to accomplish particular tasks. For example, to configure a router interface, the user must enter interface configuration mode. All configurations that are entered in interface configuration mode apply only to that interface. Each configuration mode is indicated with a distinctive prompt and allows only commands that are appropriate for that mode.
As a security feature the Cisco IOS software separates the EXEC sessions into two access levels. These levels are user:
- EXEC mode and
- Privileged EXEC mode
The privileged EXEC mode is also known as enable mode. The following are the features of the user EXEC mode and privileged EXEC mode:
- user EXEC mode
- allows only a limited number of basic monitoring commands. This is often referred to as a view only mode. The user EXEC level does not allow any commands that might change the configuration of the router. The user EXEC mode can be identified by the > prompt
- privileged EXEC mode
- provides access to all router commands. This mode can be configured to require a password. For added protection, it can also be configured to require a user ID. This allows only authorized users to access the router. Configuration and management commands require that the network administrator be at the privileged EXEC level. Global configuration mode and all other more specific configuration modes can only be reached from the privileged EXEC mode. The privileged EXEC mode can be identified by the # prompt.
