High-level Entity Management System (HEMS)
RFC 1021

Document Type RFC - Historic (October 1987; No errata)
Last updated 2013-03-02
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Network Working Group                                      C. Partridge
Request For Comment: 1021                                      BBN/NNSC
                                                             G. Trewitt
                                                           October 1987



   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.


   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.


   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
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