Cisco Router Booting process let us help in troubleshooting like IOS corrupt, Password recovery etc.
Router and Switches have 4 main memory:
- ROM: used to start and store component (POST, Bootstrap, Mini IOS, ROMMON mode).
- Post: Check basic functionality of Router.
- Bootstrap: Bootstrap is the second diagnostic tool when the router gets start. Bootstrap responsible for locating and Load the IOS.
- ROMMON: ROMMON stands for ROM Monitoring, This mode is responsible to change the password and corrupted IOS. Manually, you can enter in this mode using Ctrl+C (Control key+ C) in starting of router boot
- RAM: This is used to hold packet filtering, routing table, running-config. RAM contents are lost when the router goes down or reload because it’s volatile memory.
- Flash: This is responsible for store the IOS image and the file can be taken as a backup. This is an erasable and programmable memory. Flas memory contents aren’t lost on reload or shut down.
- NVRAM: This is non-volatile memory same flas. This is used to hold router or switch configuration permanently (Startup-Config)
- The router is powered on.
- Bootstrap programs is load from ROM
- Bootstrap program runs a diagnosis called POST(Power-on-Self-Test).
- If POST completes successfully, a Bootstrap load IOS into RAM from FLASH.
- If POST not completed, a stripped down version of IOS load from ROM.
After Load the IOS Into FLASH:>
- IOS attempts to load the Startup config from NVRAM.
- IF Not found Startup configuration, IOS try to load from TFTP, if not found from TFTP, the router enters initial configuration mode.
- IF Yes, Its load into RAM
- Startup-Configurations become a Running Configuration in RAM.