Operational Best Practices for the Cisco Catalyst 6500 Series
2.6 Backup Cisco IOS Software and Configuration
Normal operation of the switch requires an image to boot the system. Bootable images are typically stored on the supervisor bootflash located on the supervisor module. The switch can load an OS image from local flash memory (for example, compact flash), or from a device reachable through the network such as a TFTP/FTP server. It is a good practice to have a backup copy of the current OS image located either on the supervisor flash or on a separate compact flash. Both Cisco Catalyst 6500 Series Supervisor Engine 720 and Cisco Catalyst 6500 Supervisor Engine 32 support a compact flash slot on the front panel. Should the image on bootflash be deleted accidentally or become inaccessible, locating a backup image on the flash card will save time in getting the switch back up and running.
There is a 16-bit configuration register that is used to instruct the switch at bootup time where to locate the boot p image. The default configuration register value on the Catalyst 6500 is 0x2102 (the register is stored as a hexadecimal number). The default value instructs the switch to boot using an image specified by the boot system command that is found in the configuration file. The Catalyst 6500 supports multiple boot commands in the configuration file. The switch will work in a top-down fashion, starting with the first image in the list. If that image is not accessible, it will try booting the image on the second and subsequent lines.
The following gives an example of such boot commands:
6K-LV2-CL3(config)# boot system flash sup-bootflash:s72033-jk9sv-mz.122-18.SXD.bin
6K-LV2-CL3(config)# boot system flash disk0:s72033-jk9sv-mz.122-18.SXD.bin
The commands above only differ in the location of the OS image. The first line points to "sup-bootflash," which refers to the onboard flash resident on the supervisor module. The Catalyst 6500 has two flash memories, one being the route processor flash and the other being the switch processor flash. The switch processor flash ("sup-bootflash") must be used to boot a Cisco IOS Software image in the so-called "native" configuration. The route processor flash instead is referred to simply as "bootflash."
The second line in the above example points to the same image, which is located on compact flash. The compact flash drive is referred to as disk0. The Supervisor Engine 720 has a second compact flash slot, and this is referred to as disk1. In both cases, sup-bootflash and disk0 use a ":" as an ending delimiter in the boot command. This must be present for the system to successfully locate the device.
Another tip to consider when typing in the boot command is to copy and paste the image name after it is loaded into the boot system flash command. Failure to type the exact name of the image as it is known on the storage device will result in the system failing to find the image and potentially have it fall back to ROMMON mode. After an image is loaded onto the switch, one should issue a show sup-bootflash command to see and verify the image name. Then one could simply highlight the image name, copy it, and then paste it into the boot system flash command. An example of the show command is shown below:
6K-LV2-CL3# show sup-bootflash:
-#- ED ----type---- --crc--- -seek-- nlen -length- ---------date/time--------- name
1 .. image C10CAA82 2E7D270 30 76599844 May 02 2006 19:56:17 +00:00 s72033-advipservicesk9_wan-mz.122-18.SXF.bin
In addition to having a copy of the OS image on compact flash, it can prove useful to have a copy of the configuration located there as well. If no configuration management tool is used, then copying the configuration to the bootflash or compact flash drive prior to making a configuration change could help you out of an awkward situation, should a mistake be made.
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