When a rocket boots up it's so just for Siska iris image in a specific sequence.
It will search for the Cisco IOS based on what's configured in the configuration register whether there's
a Iowas in Flash.
If a TFT server is available or it will use run monitor.
So when the router boots up the first thing it checks is the configuration register boot field.
If the boot field is set to zero in hexadecimal it will load run monitor remember the configuration
registers 16 binary bytes.
By default it would be 0 x 2 1 0 to the last hexadecimal value specifies the boot field.
So if that's set to 0 it will go into run monitor mode if it's set to a greater.
In other words two three four five six seven eight and so forth up to f it will check for Buddh commands
and load the Cisco Iowa image as specified in the boot command if no boot command is being configured
it will boot an image in Flash.
And typically it will boot the first Iowas image found in Flash.
Unless you specify a boot command telling it to boot off a different operating system if no files are
available in flash it will look for an Iowa image on a TV B server so it'll try and load a Cisco iris
image from A to B server but if none is available then it will load Romont after the Strada.
It has multiple files in flash so it has this operating system and this operating system in Flash.
Notice the difference in the name.
The one that was loaded is the one with underscore two in the name that was loaded from flash.
The reason why that operating system was loaded is the configuration register set to the default.
So the boot field is set to two but in the running configuration there is a boot command telling the
router to boot from that second operating system.
So the two files in flash this one and this one put the router was configured to boot off the second
image has the full show run command.
Notice she has the command in the running config telling the Rodda which image to boot from.
So show version shows that image was loaded by the router on this router.
However there are no boot commands.
So show run pipe.
Include boot doesn't show any boot commands specifying that the Rodda should boot from some other operating
system.
Short version shows which operating system was loaded and we can see that the configuration registers
using the default value.
So the router loaded the first operating system that it found in Flash.
In other words the operating system.
So you can specify with boot commands which operating system should be loaded by the router but by default
it will simply use the first operating system found in Flash.
Unless you override that with the boot system command.
You could as an example specify that it boot from a TFT server or server as an example.
So how do Cisco routers load highway configuration files when the operating system is loaded and started
the rot it needs to be configured with IP addresses and other valleys to make it of any use.
So it will typically look for the startup config in NV RAM.
If there's no startup config and nv ram it will either begin or to install or enter the setup utility.
So when the router boots up it looks for a startup config and nv ram.
If it exists it will load that startup config.
If there's no startup config it looks for an active link to another router and then tries to load a
configuration from a TFT server using a protocol called slop.
If that doesn't work it will prompt for the initial configuration dialog.