In computing, out-of-band management (sometimes called lights-out management or LOM) involves the use of a dedicated management channel for device maintenance. It allows a system administrator to monitor and manage servers and other network equipment by remote control regardless of whether the machine is powered on.
By contrast, in-band management like VNC or SSH is based on 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 BIOS settings, or the reinstallation of the operating system and cannot be used to fix problems that prevent the system from booting. (New version of RealVNC demonstrated at the Intel Developers Conference[1] has shown out-of-band management)
Both in-band and out-of-band management is usually done through the network connection, but an out-of-band management card can use a physically separated network connector if preferred. A remote management card usually has an at least partially independent power supply, and can power the main machine on and off through the network.
A complete remote management system allows[2] remote reboot, shutdown, powering on, hardware sensor monitoring (fan speed, power voltages, chassis intrusion, etc), broadcasts video output to remote terminal and receives input from the remote keyboard and mouse. It also can access local media like DVD drive from the remote machine. If necessary, this allows one to perform remote installation of the operating system. Remote management can be used to adjust BIOS settings that may not be accessible after the operating system has already booted. Settings of hardware RAID or RAM clocking can be also be adjusted as the management card needs no hard drives or main memory to operate.
As management via a serial port has traditionally been important on servers, a complete remote management system also allows one to talk with the server through this port (SOL console).
As sending monitor output through the network is bandwidth intensive, cards like MegaRAC use built-in video compression.[3] Devices like Dell DRAC also have a slot for a memory card where an administrator may keep server-related information independently from the main hard drive.
The remote system can be accessed either through SSH Command line interface, a specialized client software or through various web browser based solutions.[4] Client software is usually optimized to manage multiple systems easily.
There are also various down-scaled versions, up to devices that only allow remote reboot by power cycling the server. This helps if the operating system hangs but only needs reboot to recover.
Remote management can be enabled on many computers (not necessarily servers) by adding the remote management card (while some cards only support limited list of motherboards). Newer server motherboards often have the built-in remote management and need no separate management card.