Top Document: comp.dcom.sys.cisco Frequently Asked Questions (FAQ)
What really happens when a cisco router boots, from boot start to live
interfaces?
First it boots the ROM os version. It reads the config. Now, it
realizes that you want to netboot. It loads the netbooted copy in on
top of itself. It then re-initializes the box and re-reads the
config. Manly, yes, but we like it too....
[[ Ummm... in particular it loads the netbooted copy in as WELL as
itself, decompresses it, if necessary, and THEN loads on top of
itself. Note that this is important because it tells you what the
memory requirements are for netbooting: RAM for ROM image (if it's a
run from RAM image), plus dynamic data structures, plus RAM for
netbooted image. ]]
The four ways to boot and what happens (sort of):
I (from bootstrap mode)
The ROM monitor is running. The I command causes the ROM monitor to
walk all of the hardware in the bus and reset it with a brute force
hammer. If the bits in the config register say to auto-boot, then
goto B
B (from bootstrap mode)
Load the OS from ROM. If a name is given, tell that image to start
silently and then load a new image. If the boot system command is
given, then start silently and load a new image.
powercycle
Does some delay stuff to let the power settle. Goto I.
reload (from the EXEC)
Goto I.
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