Definition - What does Out-of-Band Management mean?
Out-of-band management is a device and system management technique primarily used in computer networking, but is also applied to other fields of IT where similar methods are used. This management method involves an alternate and dedicated connection to the system separate from the actual network that the system runs on. This allows an administrator to ensure the establishment of trust boundaries since there would only be a single entry point for the management interface.
Techopedia explains Out-of-Band Management
Device management through out-of-band management is still done via a network connection, but this is entirely separate physically from the "in-band" network connection that the system is serving. Think of this as the door marked as "employees only" found in restaurants and shopping centers. No unauthorized user would be able to access the out-of-band network channel because there is simply no connection to it from the regular network channel that everyone uses, making this a very secure channel.
The out-of-band channel management interface is usually available even though the network may be down or even if the device is turned off, in sleep mode, hibernating or otherwise simply inaccessible through the operating system, making this a very powerful management control tool. This can be used to remotely manage powered-down devices outside working hours or during holidays, or it can be used to reboot devices whose operating system has hung or crashed. This is usually done through special operating system extensions and dedicated hardware specifically designed for out-of-band management.
An example configuration for out-of-band management is the use of Microsoft's System Center together with Intel's Active Management Technology and using Microsoft public key infrastructure.