In computer networks, out-of-band management involves the use of a dedicated channel for
managing network devices. This 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 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
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 if an operating
system is installed or functional. By contrast, in-band management like VNC or
SSH 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 in computing it does not allow access to firmware 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 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 partially independent power supply,
and can power the main machine on and off through the network.
This article focuses mainly on out-of-band management of servers, but also many network
devices offer out-of-band management. Modular/blade systems with dedicated management modules
often offer a dedicated OOB Ethernet port or Lights out management port.
Capabilities A complete remote management system allows
remote reboot, shutdown, powering on; hardware sensor monitoring; broadcasting of video output
to remote terminals and receiving of input from remote keyboard and mouse. It also can
access local media like a DVD drive, or disk images, 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 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.
As sending monitor output through the network is bandwidth intensive, cards like MegaRAC
use built-in video compression. 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
an SSH command line interface, specialized client software, or through various web browser-based
solutions. Client software is usually optimized to manage multiple systems easily.
There are also various scaled-down versions, up to devices that only allow remote reboot
by power cycling the server. This helps if the operating system hangs but only needs
a reboot to recover. Implementation
Remote management can be enabled on many computers by adding a remote management card. Newer
server motherboards often have built-in remote management and need no separate management
card. Internally, Ethernet-based out-of-band management
can either utilize a dedicated separate Ethernet connection, or some kind of multiplexing can
be performed on the system's regular Ethernet connection. That way, a common Ethernet connection
becomes shared between the computer's operating system and the integrated baseboard management
controller, usually by configuring the network interface controller to perform RMCP ports
filtering, use a separate MAC address, or to utilize VLAN tagging. In a shared connection
scenario, out-of-band nature of the management traffic is ensured by the NIC extracting it
from the incoming traffic flow, and routing it to the BMC.
Remote CLI access Another, older, version of out-of-band management
is a layout involving availability of a separate network which allows network administrators
to get command-line interface access over console ports of network equipment, even when
those devices are not forwarding any payload traffic.
If a location has several network devices, a terminal server can provide access to different
console ports for direct CLI access. In case there is only one or just a few network devices,
some of them provide AUX ports making it possible to connect a dial-in modem for direct CLI
access. The mentioned terminal server can often be accessed via a separate network that
does not use managed switches and routers for a connection to the central site, and/or
it has a modem connected via dial-in access through POTS or ISDN.
See also Intelligent Platform Management Interface
Management Component Transport Protocol Desktop and mobile Architecture for System
Hardware Intel Active Management Technology
HP's Guardian Service Processor HP Integrated Lights-Out
Dell DRAC IBM Remote Supervisor Adapter or Integrated
Management Module Management interface M1000e
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^ Oracle Sun Server ILOM ^ "Intel Ethernet Controller I210 Datasheet".
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