in-band network management and out-of-band management

from：http://www.outpostsentinel.com/inband.shtml

In-Band Network Access
There are primarily two ways to manage a network: in-band network management and out-of-band management (OBM). In-band is managing locally through the network itself, using a telnet connection to a router or by using SNMP-based tools (such as HP’s Open View). In-band is the most common way to manage a network. However, for large or business-critical networks, in-band network management alone is not enough. If the network is down, you cannot use the network to reach the affected devices and resolve the problem. You need an alternate or secondary access path to get around the problem or to access the source of the problem―that is essentially what Out-of-Band Management (OBM) provides. 

Out-of-Band Management 
If there is a problem with a device such a server or a router, and traffic cannot flow through the network, you need an alternate path to reach the network nodes even when the network is down. Management using independent dedicated channels is called OBM.

OBM provides accessibility when an alternate path is needed to access the network nodes. In addition, OBM can provide coverage to many pieces of manageable equipment or intelligent devices that may not have a direct network connection to the data network, such as uninterruptible power supplies, PBX phone systems and intelligent thermal controls. For some of these intelligent devices that are not networked OBM may provide the only support and management tool.

 For mission-critical networks, in-band management tools are not enough. You need a secure remote emergency network access path to manage and troubleshoot when the device is not on the network, the device is not network manageable or the data network is down. That is the benefit of OBM console management.
 OutPost Sentinel’s Emergency Network Specialist (ENS 8) and Cyber Command Center offer a suite of both in-band and OBM tools.