Cisco IOS Cookbook, 2nd Edition

Warm Reload

Problem

You want to reload the router with minimal service interruption.

Solution

To enable warm reload, use the warm-reboot command:

Router1#configure  terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#warm-reboot
Router1(config)#end
Router1#

Tip

After enabling this feature, you must perform a cold reboot before it will take effect.

Discussion

Beginning with IOS Version 12.3(2)T, Cisco introduced the ability to perform a warm reload of the router. The primary benefit of this feature is increased system availability, since the router is able to load the IOS version directly from memory without the need to copy the image from flash to RAM or wait for decompression of the IOS image. In addition, the router is able to reload without ROM monitor mode (ROMMON) intervention. This allows the router to complete its reload significantly quicker than a normal cold reload. For example, a cold reboot took more than four minutes longer than a warm reboot on our test router.

Although this feature requires addition memory to be consumed, its impact is minimized by the compressing of initialized variables store in RAM. To prevent corruption of the initial variables, they are marked “read-only.”

This feature not only allows you to perform manual warm reloads, but also allows the router to recover from software forced crashes. Since software forced crashes are unplanned outages, the ability to recover quickly is quite useful. By default, the router will allow ...