Network administrators are often hesitant to patch the operating systems on CISCO router and switch...

Many administrators are hesitant to upgrade the IOS on routers based on past experience with the code introducing instability into the network. It is often difficult to completely test an IOS software upgrade in a production environment because the monolithic kernel requires that the IOS be replaced before the device can be tested. Because of these reasons, IOS upgrades to resolve security flaws are often left undone in many organizations.