8.2 The Infrastructure for Network Management
We've seen in the previous section that network management requires
the ability to "monitor, test, poll, configure, ... and control" the hardware
and software and components in a network. Because the network devices
are distributed, this will minimally require that the network administrator
be able to gather data (e.g., for monitoring purposes) from a remote entity
and be able to affect changes (e.g., control) at that remote entity.
A human analogy will prove useful here for understanding the infrastructure
needed for network management.
Imagine that you're the head of a large organization that has branch
offices around the world. It's your job to make sure that the pieces of
your organization are operating smoothly. How would you do so?
At a minimum, you'll periodically gather data from your branch offices
in the form of reports and various quantitative measures of activity, productivity,
and budget. You'll occasionally (but not always) be explicitly notified
when there's a problem in one of the branch offices; the branch manager
who wants to climb the corporate ladder (perhaps to get your job) may send
you unsolicited reports indicating how smoothly things are running at his/her
branch. You'll sift through the reports you receive, hoping to find
smooth operations everywhere, but no doubt finding problems in need of
your attention. You might initiate a one-on-one dialogue with one
of your problem branch offices, gather more data in order to understand
the problem, and then pass down an executive order ("Make this change!")
to the branch office manager. Implicit in this very common human
scenario is an infrastructure for controlling the organization - the boss
(you), the remotes sites being controlled (the branch offices), your remote
agents (the branch office managers), communication protocols (for transmitting
standard reports and data, and for one-on-one dialogues), and data (the
report contents and the quantitative measures of activity, productivity,
and budget). Each of these components in human organizational management
has an exact counterpart in network management.
The architecture of a network management system is conceptually
identical to this simple human organizational analogy. The network
management field has its own specific terminology for the various
components of a network management architecture, and so we adopt
that terminology here. As shown in Figure 8.2-1, there are three principle
components of a network management architecture: a managing entity (e.g.,
the boss in our above analogy - you), the managed devices (the branch office),
and a network management protocol.
Figure 8.2-1: principal components of a network management architecture
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The managing entity is an application, typically with a human-in-the-loop,
running in a centralized network management station in the network operations
center (NOC). The managing entity is the central locus of activity
for network management - it controls the collection, processing,
analysis, and/or display of network management information. It is
here that actions are initiated to control network behavior and here that
the human network administrator interacts with the network devices.
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A managed device is a piece of network equipment (including its
software) that resides on a managed network. This is the branch office
in our human analogy. A managed device might be a host, router, bridge,
hub, printer, or modem device. Within a managed device, there may be several
so-called managed objects. These managed objects are the actual
pieces of hardware within the managed device (e.g., a network interface
card), and the sets of configuration parameters for the pieces of
hardware and software (e.g., an intradomain routing protocol such as RIP).
In our human analogy, the managed objects might be the departments within
the branch office. These managed objects have pieces information
associated with them that are collected into a management information
base (MIB); we'll see that the values of these pieces of information
are available to (and in many cases setable by) the managing entity.
In our human analogy, the MIB corresponds to quantitative data (measures
of activity, productivity, and budget, with the latter being setable by
the managing entity!) exchanged between the branch office and the main
office. We'll study MIBs in detail in section 8.3. Finally, also
resident in each managed device is a network management agent,
a process running in the managed device that communicates with the
managing entity, taking local actions on the managed device under the command
and control of the managing entity. The network management agent is the
branch manager in our human analogy.
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The third piece of a network management architecture is the network
management protocol. The protocol runs between the managing
entity and the managed devices, allowing the managing entity to query the
status of managed devices and indirectly effect actions in these devices
via its agents. Agents can use the the network management protocol
to inform the managing entity of exceptional events (e.g., component failures
or violation of performance thresholds).
Although the infrastructure for network management is conceptually simple,
one can often get bogged down with the network-management-speak vocabulary
of "managing entity," "managed device," "managing agent," and "management
information base." Hopefully, keeping the human organizational analogy
and its obvious parallels with network management in mind will be
of help as we continue through this chapter.
Our discussion of network management architecture above has been generic,
and broadly applied to a number of the network management standards and
efforts that have been proposed over the years. Network management
standards began maturing in the late 1980's, with OSI CMISE/CMIP (the
Common Management Service Element/Common Management Information Protocol)
[Piscatello 1993, Stallings
1993, Glitho 1998] and the Internet SNMP
(Simple Network Management Protocol) [Stallings
1993, RFC 2570, Stallings
1999, Rose 1996] emerging as the two most
important standards. Both are designed to be independent of vendor-specific
products or networks. Because SNMP was quickly designed and deployed at
a time when the need for network management was becoming painfully clear,
SNMP found widespread use and acceptance. Today, SNMP has emerged as the
most widely used and deployed network management framework. We cover
SNMP in detail in the following section
References
[Glitho 1998] R. Glitho, "Contrasting
OSI Systems Management to SNMP and TMN," Journal of Network and Systems
Management, Vol. 6, No. 2, (June 1998), pp. 113-131.
[Piscatello 1993] D. Piscatello
and A. Lyman Chapin, "Open Systems Networking", Addison Wesley, 1993.
[RFC 2570] J. Case, R. Mundy,
D. Partain, B. Stewart, "Introduction to Version 3 of the Internet-standard
Network Management Framework" RFC 2570, May 1999.
[Rose 1996] M. Rose, "Simple Book,
The: An Introduction to Internet Management, Revised Second Edition," Prentice
Hall, 1996.
[Stallings 1993] W Stallings,
"SNMP. SNMP v2. and CMIP The Practical Guide to Network Management Standards,"
Addison Wesley 1993.
[Stallings 1999] W. Stallings,
"Snmp, Snmpv2, Snmpv3, and Rmon 1 and 2," Addison Wesley, 1999.
Copyright 1999. James F. Kurose and Keith W. Ross. All Rights
Reserved.