![]() Main memory is configured to 64 bit mode with ECC enabled When the router boots, hit the CTRL+BREAK combination to get into ROMMON: System Bootstrap, Version 12.4(13r)T, RELEASE SOFTWARE (fc1)Ĭopyright (c) 2006 by cisco Systems, Inc.Ĭ2811 platform with 786432 Kbytes of main memory What if your flash memory is defective but you still want to run IOS somehow? It is possible with ROMMON to download the image and then extract and run it in RAM, without touching your flash memory. Booting IOS image from network through ROMMON ![]() Your router will now run the IOS image from the TFTP server. Program load complete, entry point: 0x8000f000, size: 0x40c8438 Once the transfer is completed, it extracts and loads the image: %SYS-6-BOOT_MESSAGES: Messages above this line are from the boot loader. It downloads the IOS image that we specified from the TFTP server. Once it is loaded, instead of showing you the command prompt you will see this: Loading from 192.168.1.2 (via FastEthernet0/0): The router does its POST, initializes ROMMON and then loads the IOS image on the flash memory as usual. Program load complete, entry point: 0x8000f000, size: 0x40c7678 Program load complete, entry point: 0x8000f000, size: 0xcb80 Once you do, you will see this: Readonly ROMMON initialized Now we can save our configuration and reload the router. Let’s enable an interface with an IP address that is in the same subnet as our TFTP server: Router(config)# interface FastEthernet 0/0 We also have to make sure the router is able to reach our TFTP server. This tells the router to look for an IOS image on the network, not on the local flash drive. We have to change it to tell the router to look for the IOS image on the network: Router(config)# config-register 0x210F The default configuration register will only look for the IOS image on the flash memory. The command above however is only half of the story. This tells the router to look for the specified filename on the TFTP server with IP address 192.168.1.2. Let’s see if we can boot from a TFTP server: Router(config)# boot system tftp 192.168.1.2 The boot system command has some options: Router(config)# boot system ? Perhaps your flash memory is too small to fit the latest IOS image or maybe you want to make sure all routers run the same IOS image without manually copying the images to the flash memory of each router. What if I want to boot an IOS image from the network? This could be useful. System image file is "flash:" Booting IOS image from network I can configure the router to boot the other IOS image on my flash memory with the boot system command: Router(config)# boot system flash Īfter reloading the router, I can verify that it has booted the newer image: Router# show version | include image Let’s see how I can select a different image. ![]() System image file is "flash:" Booting IOS image from flash We can see which image was booted: Router# show version | include image Cisco IOS uses a number for each filename and will prefer the lowest file number. The default value is 0001 which means that it will use the first IOS image that it finds on the flash memory. The first 4 bits define where the router will look for the IOS image. You can find the meaning of the bits in this Cisco document. The default value of the configuration register is 0x2101: Router# show version | include register The configuration-register boot option.Which IOS image the router wants to use depends on two options: Let’s see how we can configure the router to boot another IOS image. You can also configure the router so that it looks for the startup-config somewhere else. It’s possible to configure the router so that it will look for an IOS image in another location, like a TFTP server on your network. ![]() There is nothing we can change in step 1 and 2 but we are able to make some changes to step 3 and 4. You can also use it for password recovery. One of the things it is used for is to copy an IOS image to the flash memory in case you accidentally deleted it. ROMMON is a very simple OS with a few features. ![]()
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