High-level Entity Management System (HEMS)
RFC - Historic
(October 1987; No errata)
||RFC Editor Note
RFC 1021 (Historic)
||Send notices to
Network Working Group C. Partridge
Request For Comment: 1021 BBN/NNSC
THE HIGH-LEVEL ENTITY MANAGEMENT SYSTEM (HEMS)
STATUS OF THIS MEMO
An overview of the RFCs which comprise the High-Level Entity
Management System is provided. This system is experimental, and is
currently being tested in portions of the Internet. It is hoped that
this work will help lead to a standard for IP internetwork
management. Distribution of this memo is unlimited.
Until recently, a majority of critical components in IP networks,
such as gateways, have come from a very small set of vendors. While
each vendor had their own set of management protocols and mechanisms,
the collection was small, and a knowledgeable system administrator
could be expected to learn them all.
Now, however, the number of vendors has grown quite large, and the
lack of an accepted standard for management of network components is
causing severe management problems. Compounding this problem is the
explosive growth of the connected IP networks known as the Internet.
The combination of increased size and heterogeneity is making
internetwork management extremely difficult. This memo discusses an
effort to devise a standard protocol for all devices, which should
help alleviate the management problem.
The RFCs that currently define the High-Level Entity Management
System are this memo along with RFC-1022, 1024, and 1023. This list
is expected to change and grow over time, and readers are strongly
encouraged to check the RFC Index to find the most current versions.
MONITORING AND CONTROL
Historically, the IP community has divided network management into
two distinct types of activities: monitoring and control. Monitoring
is the activity of extracting or collecting data from the network or
a part of the network to observe its behavior. Control is the
activity of taking actions to effect changes in the behavior of the
network or a part of the network in real-time, typically in an
attempt to improve the network's performance.
Partridge & Trewitt [Page 1]
RFC 1021 HEMS Overview October 1987
Note that the ability to control presupposes the ability to monitor.
Changing the behavior of the network without being able to observe
the effects of the changes is not useful. On the other hand,
monitoring without control makes some sense. Simply understanding
what is causing a network to misbehave can be useful.
Control is also a more difficult functionality to define. Control
operations other than the most generic, are usually device-specific.
The problem is not just a matter of providing a mechanism for
control, but also defining a set of control operations which are
generally applicable across a diverse set of devices. Permitting
remote applications to exercise control over an entity also implies
the need for a suite of safeguards to ensure that unauthorized
applications cannot harm the network.
Because monitoring is the key first step, in this initial design of
the system, the authors have concentrated more heavily on the
problems of effective monitoring. Although the basic control
mechanisms are defined, many components need for control, such as
strong access control mechanisms, have not been fully defined.
OVERVIEW OF THE HEMS
The HEMS is made up of three parts: a query processor which can
reside on any addressable entity, an event generator which also
resides on entities, and applications which know how to send requests
to the query processor and interpret the replies. The query
processor and applications communicate using a message protocol which
runs over a standard transport protocol.
The Query Processor
The query processor is the key to the management system. It
interprets all monitoring and control requests. For optimal network
management, we would like to see query processors on most network
To encourage the implementations of query processors, one of the
primary goals in designing the query processor was to make it as
small and simple as possible, consistent with management
Defining the management requirements was no small task, since the
networking community has not yet reached a consensus about what kinds
of monitoring information should be available from network entities,
nor what control functions are required to properly manage those
entities. The standards for HEMS were developed through discussions
with several interest groups, and represent the authors' best effort
Show full document text