rfc1109.txt

<VC++网络游戏建摸与实现>源代码

Network Working Group                                            V. Cerf
Request for Comments:  1109                                          NRI
                                                             August 1989


      Report of the Second Ad Hoc Network Management Review Group



Status of this Memo

   This RFC reports an official Internet Activities Board (IAB) policy
   position on the treatment of Network Management in the Internet. This
   RFC presents the results and recommendations of the second Ad Hoc
   Network Management Review on June 12, 1989.  The results of the first
   such meeting were reported in RFC 1052 [1].  This report was approved
   and its recommendations adopted by the IAB as assembled on July 11-
   13, 1989.  Distribution of this memo is unlimited.

INTRODUCTION

   On February 29, 1988, an Ad Hoc Network Management Review Group was
   convened to consider the state of network management technology for
   the Internet and to make recommendations to the Internet Activities
   Board as to network management policy.  The outcome of that meeting
   was summarized in RFC 1052 and essentially established a framework in
   which two network management protocols now known respectively as
   Simple Network Management Protocol (SNMP) and Common Management
   Information Protocol on TCP (CMOT) were selected for further work.
   Subsequently, both SNMP [6] and CMOT [5] were advanced to Draft-
   Standard/Recommended status for use in the Internet [SNMP: RFC 1098,
   CMOT: RFC 1095].

   Simultaneously, it was agreed to establish a working group to
   coordinate the definition and specification of managed objects to be
   used in common with either protocol.  In addition, it was agreed to
   use the then current ISO Structure of Management Information (SMI)
   specification as a reference standard to guide the naming and
   abstraction conventions that would be followed in constructing the
   common Internet Management Information Base (MIB).  The Internet
   versions of SMI and MIB were specified in RFC 1065 [2] and RFC 1066
   [3] respectively.

   In the intervening fifteen months, considerable progress has been
   made in the specification of a common Management Information Base and
   in the implementation, deployment and use of network management tools
   in the Internet.




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RFC 1109                  Internet Management                August 1989


   The current public subtree of the Internet MIB contains roughly 100
   variables (i.e., managed objects) agreed by the SNMP and CMOT working
   groups as mandatory for Internet network management.  The June 12,
   1989 meeting which this document reports was convened to review the
   progress to date, to determine whether actions were needed to foster
   further evolution of network management tools and to recommend
   specific actions in this area to the IAB.

SNMP STATUS

   Immediately after the meeting reported in RFC 1052, a group was
   convened to make extensions and changes to the predecessor to SNMP:
   Simple Gateway Monitoring Protocol.  A "connectathon" was held at
   NYSERNet, an RFC published, and demonstrations of network management
   tools using SNMP were offered in the Fall at Interop 88 [a conference
   and show presented by Advanced Computing Environments (ACE)].  The
   protocol is in use in a number of networks within the Internet as
   well as in private packet networks internationally.  A number of
   vendor implementations are in the field (e.g., cisco Systems,
   Proteon, The Wollongong Group), vendor independent reference
   implementations (e.g., NYSERNet, Case and Key in Tennessee) along
   with some freely available versions (e.g., MIT, CMU).

   It is important to note that while the common Internet Management
   Information Base has roughly 100 variables, a typical SNMP monitoring
   system may support anywhere from 100 to 200 ADDITIONAL objects which
   have been defined in private or experimental MIB space.  Many of
   these are device or protocol dependent variables.

   Scaling to include larger numbers of monitored objects and subsystems
   remains a challenge.  It was observed that fault monitoring was
   easier to scale than performance and configuration monitoring, since
   the former may operate on an exception basis while the latter is more
   likely to require periodic reporting.

CMOT STATUS

   RFC 1095 (CMOT) was recently published and built upon experience
   gained earlier with prototype implementations demonstrated at Interop
   88 in the Fall of that year.  The present specification for CMOT is
   based on the ISO Draft International Standard version of Common
   Management Information Protocol (CMIP).  The CMIP is being moved to
   International Standard status, though the precise timing is not
   perfectly clear.  It will happen late in 1989 or perhaps in the first
   quarter of 1990.  Some changes will be made to correct known errors
   and the CMIP document itself will probably be restructured.

   During this discussion, it was pointed out that there is much to



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RFC 1109                  Internet Management                August 1989


   network management which is not addressed by either the CMOT or the
   SNMP specifications: for example, down loading of software,
   configuration management and user access control.  Authentication of
   the source of network management commands and responses is another
   area important to providers and users of network management tools.

   The National Institute for Standards and Technology (NIST) is
   sponsoring the development of implementors' agreements on the
   functional behavior of network management tools including, inter
   alia, logging, event reporting, error reporting, structured object
   management, and alarm reporting.

   Although at the time of the meeting, there were no publicly available
   implementations of CMOT reported, developments were reportedly
   planned by a number of vendors both in the form of agents and network
   management tools.  The University of Wisconsin plans to demonstrate
   CMOT using the ISODE software at Interop 89 [(tm) ACE] in September
   1989.

MIB AND SMI STATUS

   In the Fall of 1988, two RFCs were published (1065 and 1066) to
   specify the Structure of Management Information (SMI) and the initial
   Internet Management Information Base (MIB) respectively.  There were
   some challenges in crafting this set of commonly agreed variables; in
   the end, roughly 100 were agreed and defined as mandatory for
   Internet management.

   It was recognized in this process that the definition of the layer
   BELOW IP was a difficult task.  IP is sufficiently simple and general
   that it has been moved in encapsulated form over many media including
   the MAC level of various local nets, X.25 packet level, serial line
   protocols, multiplexors, tunnels and, it is rumored, tin cans and
   string.

   At the Transport level, specifically for TCP, it was observed that
   information about the transient status of connections was potentially
   inaccessible to the network management tools since the loss of a TCP
   connection typically meant loss of its Transmission Control Block
   (status block) just when you wanted to look back into the history of
   its state.  Countervailing this observation was evidence that looking
   at TCBs with network management tools yielded far more insight into
   the transient behavior of TCP than looking at aggregated network
   statistics.

   It was clear from the discussion that there is strong interest in
   extending the variables accessible via network management tools.
   Adding new devices, new higher level protocols and the ability to



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RFC 1109                  Internet Management                August 1989


   manipulate configuration information were high on the list of
   desirable extensions, although several participants felt that this
   desire needed some moderation.

   A vital, but unsettled research area has to do with relationships
   among groups of monitored variables.  A particular implementation may
   have IP operating atop X.25.  The problem is to be able to make
   queries about the condition of monitored variables so that those for
   the IP level can be correlated with those for a lower layer, for
   instance.  This notion of relationship is especially important as
   network devices (including hosts) begin to sport multiple network
   connections and multiple protocol suites operating in parallel.  Just
   how the dynamics of such relationships are to be specified, defined
   and instantiated is the research question.  What sort of SMI is
   appropriate? What generic structure is needed for the management
   objects?

   Another difficult topic has to do with version numbers for SMI.  The
   issue is "which version of MIB is instantiated in this monitored
   system?"  As consideration of extensions to the currently agreed SMI
   were contemplated during the last fifteen months, it became apparent
   that the question of versions was central.

   Not far behind was the question of functionality of the underlying
   support protocols (SNMP and CMOT).  The RFC 1052 recommendation was
   to tightly link the MIB/SMI, keeping only one such definition for
   both protocols.  In theory, this plan would make it easier to move
   from one protocol base to another.  In practice, it appears to have
   stifled exploration of new variable and function definitions in
   operating network environments.  This point needs to be underscored:
   it is essential for the Internet community to have the freedom to
   explore the utility of the OSI offerings while, at the same time,
   having the freedom to respond to operational needs through the
   definition and use of new MIB variables and SMI features.

   Yet another area still needing development has to do with the
   archiving of operational data collected by means of a network
   management tool.  The ISO Common Management Information Service
   (CMIS) specifications do not treat this matter.

   Finally, it was pointed out that registration of managed objects and
   their definitions was still an open area although the NIST has
   apparently made progress through its Network Management Special
   Interest Group (NMSIG) in planning for cataloging of defined
   management information objects.






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