Cisco IOS Basics for the ICND1 and ICND2 Certification Exams
The ICND1 and ICND2 certification exams will test you on the basics of the Cisco IOS (network infrastructure software) and how to configure the IOS. The following are some key points that summarize the IOS basics to remember for the CCENT certification exam:
Types of Memory: There are different types of memory on a Cisco device:
ROM: The Read Only Memory (ROM) on a Cisco device is like the ROM on a computer in the sense that it stores the POST and the boot loader program. The boot loader program is responsible for locating the IOS.
Flash: The flash memory is memory that is used to store the Cisco IOS.
RAM: RAM is used to store things like the routing table on a router, or the MAC address table on a switch. It is also used to store the running-config. RAM is also known as volatile RAM, or VRAM.
NVRAM: Non-volatile RAM (NVRAM) is used to store the startup-config which is copied to the running-config on bootup after the IOS is loaded.
The Boot Process: For the CCENT certification exam you need to know the high level steps that occur when a Cisco device startups up. The following is a quick review of the boot process of a Cisco router:
1. POST: The first thing that occurs when a Cisco device boots up is the POST routine which is responsible for performing a self diagnostic to verify everything is correctly functioning on the router or switch.
2. Locate IOS: After the POST the bootloader program, which is stored in ROM locates the IOS in flash memory and loads it into RAM.
3. Startup-config Applied: After the IOS is loaded into memory the bootloader program then locates the startup-config and applies it to the device.
Configuration Modes: When making changes to the Cisco device there are a number of different configuration modes and each change is made in a specific configuration mode. The following summarizes the major configuration modes:
User Exec: When you connect to a Cisco device the default configuration mode is user exec mode. With user exec mode you can view the settings on the device but not make any changes. You know you are in user exec mode because the IOS prompt displays a ">".
Priv Exec: In order to make changes to the device you must navigate to priv exec mode where you may be required to input a password. Priv exec mode displays with a "#" in the prompt.
Global Config: Global configuration mode is where you go to make global changes to the router such as the hostname. To navigate to global configuration mode from priv exec mode, type config term where you will be placed at the (config)# prompt.
Sub Prompts: There are a number of different sub prompts from global configuration mode you can navigate to such as the interface prompts to modify settings on a specific interface, or the line prompts to modify the different ports on the device.