Cisco router startup sequence

Understanding the Starting sequence of a vro is essential for troubleshooting vro faults. The key to understanding the internal composition of a vro is configuring the register value. Vro startup involves the following steps: 1. Power-on self-check (POST) 2. Load and run boot guide code 3. Search for IOS4, load IOS5, search for configuration files 6. load configuration files 7. Normal Operation
Www.2cto.com to understand the router startup sequence, you must understand the configuration register value. The configuration register value is composed of sixteen bits. 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 the minimum four bits are the boot option bits. That is to say, based on the four bits, select the router from where to start. Example: 3 2 1 0 0 0 0 enter ROM Monitor ROMMON> you can set the last four digits of the register to 0, or press ctrl + break when the vro is started to add an interrupt 0 0 1 to enter IOS (provide a complete subset of IOS) Router (boot)> 0 0 1 0-1111 check the boot system in NVRAM and provide the detailed procedure for starting the vro: www.2cto.com
1. Check whether the register value is equal to 0. If it is equal to 0, go to ROM Monitor mode. If it is not equal to 0-> 23, check whether the configuration file in NVRAM has configured the boot system command, if the configuration file contains this command, start it according to its configuration. If there is no command-> 42, check whether the register value is equal to 1. If it is equal to 1, enter Mini IOS, if it is not equal to 1-> 34, check whether there is a valid IOS in flash, if there is, use a valid IOS boot, if not-> 55, try to find IOS from the network, if IOS is found on the network, start it with this IOS. If no-> 6
6. Check the 13th-bit value of the Register. If the value is equal to 1, the system checks whether IOS has experienced 5 failures on the network. If it reaches 5 times, it will not continue searching on the network, go to Mini IOS. If the 13th-bit value is 0, you will not judge the number of failures. keep searching until you find it. After loading IOS 7 and loading IOS, if the value of the 6th-bit register is 1 or 1, the system directly enters Setup Dialog, which is not equal to 1-> 88. Check whether valid configurations exist in NVRAM, if yes, use this configuration. If not, enter Setup Dialog.