In systems management, out-of-band management involves the use of management interfaces (or serial ports) for managing servers and networking equipment.
Out-of-band management allows the network operator to establish trust boundaries in accessing the management function to apply it to network resources. It also can be used to ensure management connectivity (including the ability to determine the status of any network component) independent of the status of other in-band network components.
In computing, one form of out-of-band management is sometimes called lights-out management (LOM) and involves the use of a dedicated management channel for device maintenance. It allows a system administrator to monitor and manage servers and other network-attached equipment by remote control regardless of whether the machine is powered on, or whether an operating system is installed or functional.
By contrast, in-band management through VNC, SSH or even serial ports is based on in-band connectivity and software that must be installed on the remote system being managed and only works after the operating system has been booted.
This solution may be cheaper, but it does not allow access to firmware (BIOS or UEFI) settings, does not make it possible to reinstall the operating system remotely, and it cannot be used to fix problems that prevent the system from booting. In networking, it does not allow management of remote network components independently of the current status of other network components.
Both in-band and out-of-band (OOB) management are usually done through a network connection, but an out-of-band management card can use a physically separated network connector if preferred. A remote management card usually has at least a partially independent power supply and can switch the main machine on and off through the network.