Probably a dumb question, but...

[GeneralDzur]

When I type Show Version I have two numbers for Software Image: The IOS Image, and then the System Bootstrap image. What is the difference between the two? Sorry if this is a stupid question, but it's kind of confusing me.

- stephan

P.S. i pulled some lines from the "show version" below to make it shorter.

Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-IS-M), Version 12.0(7)T, RELEASE SOFTWARE (fc2)
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Tue 07-Dec-99 02:21 by phanguye
Image text-base: 0x80008088, data-base: 0x80C524F8

ROM: System Bootstrap, Version 12.1(3r)T2, RELEASE SOFTWARE (fc1)

917_gw_rtr uptime is 5 days, 23 hours, 26 minutes
System image file is "flash:c2600-is-mz.120-7.T"

 

[ADB100]

On most Cisco routers there are 2 images available for the router to boot from - usually one in FLASH and one in Read-Only ROM. Generally a router will boot from the IOS image in FLASH. If this is corrupt then the image in ROM can be booted although this usually has only limited features - enough to get an interface active and assign an IP address to it so a new image can be installed.
Most (maybe all?) Cisco routers have a ROMMON that allows VERY limited things to be done, on a lot of routers you cannot even enable an interface in ROMMON so the IOS in ROM is the next step up in router image recovery.

Hope that sort of explains it? It's sort of a failsafe IOS in case you loose the IOS in FLASH.

Andy

 

[GeneralDzur]

Thanks Andy thats really helpful. So does the ROM IOS and ROMMON are two different things? In what situation would the router boot to the ROM IOS?

- Stephan

 

[wabob]

The only way the router will boot from ROM is if you change the Configuration Register. The default setting on Cisco routers is 0x2102, which causes the router to load the IOS from flash and to look for (and load) the startup-config file from NVRAM.

If you change the config-register to 2100, the router will boot to ROM monitor mode.

If you change the config-register to 2101, the router will boot from an IOS image stored in ROM.

Changing the Configuration Register is also necessary if you are doing password recovery.

 

[GeneralDzur]

Thanks again - you guys are lifesavers.

- stephan