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RFC 2021

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Remote Network Monitoring Management Information Base Version 2 using SMIv2

Part 1 of 5, p. 1 to 12
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Network Working Group                                     S. Waldbusser
Request for Comments: 2021                                          INS
Category: Standards Track                                  January 1997

         Remote Network Monitoring Management Information Base
                               Version 2
                              using SMIv2

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   This memo defines a portion of the Management Information Base (MIB)
   for use with network management protocols in TCP/IP-based internets.
   In particular, it defines objects for managing remote network
   monitoring devices.

Table of Contents

 1 The Network Management Framework .....................    2
 2 Overview .............................................    2
 2.1 Remote Network Management Goals ....................    3
 2.2 Structure of MIB ...................................    5
 3 Control of Remote Network Monitoring Devices .........    6
 3.1 Resource Sharing Among  Multiple  Management  Sta-
      tions .............................................    7
 3.2 Row Addition Among Multiple Management Stations ....    9
 4 Conventions ..........................................   10
 5 RMON 2 Conventions ...................................   10
 5.1 Usage of the term Application Level ................   10
 5.2 Protocol Directory and Limited Extensibility .......   11
 5.3 Errors in packets ..................................   11
 6 Definitions ..........................................   12
 7 Security Considerations ..............................  122
 8 Appendix - TimeFilter Implementation Notes ..........   123
 9 Acknowledgments .....................................   129
 10 References ..........................................  129
 11 Author's Address.....................................  130

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1.  The Network Management Framework

   The Internet-standard Network Management Framework consists of three
   components.  They are:

   RFC 1902 [1] which defines the SMI, the mechanisms used for
   describing and naming objects for the purpose of management.

   RFC 1213, STD 17, [3] which defines MIB-II, the core set of
   managed objects for the Internet suite of protocols.

   RFC 1905 [4] which defines the SNMP, the protocol used for
   network access to managed objects.

   The Framework permits new objects to be defined for the purpose of
   experimentation and evaluation.

   Managed objects are accessed via a virtual information store, termed
   the Management Information Base or MIB.  Within a given MIB module,
   objects are defined using the SMI's OBJECT-TYPE macro.  At a minimum,
   each object has a name, a syntax, an access-level, and an

   The name is an object identifier, an administratively assigned name,
   which specifies an object type.  The object type together with an
   object instance serves to uniquely identify a specific instantiation
   of the object.  For human convenience, we often use a textual string,
   termed the object descriptor, to also refer to the object type.

   The syntax of an object type defines the abstract data structure
   corresponding to that object type.  The ASN.1 [6] language is used
   for this purpose.  However, RFC 1902 purposely restricts the ASN.1
   constructs which may be used.  These restrictions are explicitly made
   for simplicity.

   The access-level of an object type defines whether it makes "protocol
   sense" to read and/or write the value of an instance of the object
   type.  (This access-level is independent of any administrative
   authorization policy.)

   The implementation-status of an object type indicates whether the
   object is mandatory, optional, obsolete, or deprecated.

2.  Overview

   This document continues the architecture created in the RMON MIB [RFC
   1757] by providing a major feature upgrade, primarily by providing
   RMON analysis up to the application layer.

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   Remote network monitoring devices, often called monitors or probes,
   are instruments that exist for the purpose of managing a network.
   Often these remote probes are stand-alone devices and devote
   significant internal resources for the sole purpose of managing a
   network.  An organization may employ many of these devices, one per
   network segment, to manage its internet.  In addition, these devices
   may be used for a network management service provider to access a
   client network, often geographically remote.

   The objects defined in this document are intended as an interface
   between an RMON agent and an RMON management application and are not
   intended for direct manipulation by humans.  While some users may
   tolerate the direct display of some of these objects, few will
   tolerate the complexity of manually manipulating objects to
   accomplish row creation.  These functions should be handled by the
   management application.

2.1.  Remote Network Management Goals

    o Offline Operation
        There are sometimes conditions when a management
        station will not be in constant contact with its
        remote monitoring devices.  This is sometimes by
        design in an attempt to lower communications costs
        (especially when communicating over a WAN or
        dialup link), or by accident as network failures
        affect the communications between the management
        station and the probe.

        For this reason, this MIB allows a probe to be
        configured to perform diagnostics and to collect
        statistics continuously, even when communication with
        the management station may not be possible or
        efficient.  The probe may then attempt to notify
        the management station when an exceptional condition
        occurs.  Thus, even in circumstances where
        communication between management station and probe is
        not continuous, fault, performance, and configuration
        information may be continuously accumulated and
        communicated to the management station conveniently
        and efficiently.

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    o Proactive Monitoring
        Given the resources available on the monitor, it
        is potentially helpful for it continuously to run
        diagnostics and to log network performance.  The
        monitor is always available at the onset of any
        failure.  It can notify the management station of the
        failure and can store historical statistical
        information about the failure.  This historical
        information can be played back by the management
        station in an attempt to perform further diagnosis
        into the cause of the problem.

    o Problem Detection and Reporting
        The monitor can be configured to recognize
        conditions, most notably error conditions, and
        continuously to check for them.  When one of these
        conditions occurs, the event may be logged, and
        management stations may be notified in a number of

    o Value Added Data
        Because a remote monitoring device represents a
        network resource dedicated exclusively to network
        management functions, and because it is located
        directly on the monitored portion of the network, the
        remote network monitoring device has the opportunity
        to add significant value to the data it collects.
        For instance, by highlighting those hosts on the
        network that generate the most traffic or errors, the
        probe can give the management station precisely the
        information it needs to solve a class of problems.

    o Multiple Managers
        An organization may have multiple management stations
        for different units of the organization, for different
        functions (e.g. engineering and operations), and in an
        attempt to provide disaster recovery.  Because
        environments with multiple management stations are
        common, the remote network monitoring device has to
        deal with more than own management station,
        potentially using its resources concurrently.

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2.2.  Structure of MIB

   The objects are arranged into the following groups:

        - protocol directory

        - protocol distribution

        - address mapping

        - network layer host

        - network layer matrix

        - application layer host

        - application layer matrix

        - user history

        - probe configuration

   These groups are the basic units of conformance.  If a remote
   monitoring device implements a group, then it must implement all
   objects in that group.  For example, a managed agent that implements
   the network layer matrix group must implement the nlMatrixSDTable and
   the nlMatrixDSTable.

   Implementations of this MIB must also implement the system and
   interfaces group of MIB-II [3].  MIB-II may also mandate the
   implementation of additional groups.

   These groups are defined to provide a means of assigning object
   identifiers, and to provide a method for managed agents to know which
   objects they must implement.

   This document also contains enhancements to tables defined in the
   RMON MIB [RFC 1757].  These enhancements include:

    1) Adding the DroppedFrames and LastCreateTime
       conventions to each table defined in the RMON MIB.

    2) Augmenting the RMON filter table with a mechanism
       that allows filtering based on an offset from the
       beginning of a particular protocol, even if the
       protocol headers are variable length.

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    3) Augmenting the RMON filter and capture status bits
       with additional bits for WAN media and generic media.
       These bits are defined here as:

        Bit     Definition
        6       For WAN media, this bit is set for packets
                coming from one direction and cleared for
                packets coming from the other direction.
                It is an implementation specific matter
                as to which bit is assigned to which
                direction, but it must be consistent for
                all packets received by the agent, and if
                the agent knows which end of the link is
                "local" and which end is "network", the bit
                should be set for packets from the "local"
                side and should be cleared for packets from
                the "network" side.

        7       For any media, this bit is set for any packet
                with a physical layer error. This bit may be
                set in addition to other media-specific bits
                that denote the same condition.

        8       For any media, this bit is set for any packet
                that is too short for the media. This bit may
                be set in addition to other media-specific
                bits that denote the same condition.
        9       For any media, this bit is set for any packet
                that is too long for the media. This bit may
                be set in addition to other media-specific bits
                that denote the same condition.

   These enhancements are implemented by RMON-2 probes that also
   implement RMON and do not add any requirements to probes that are
   compliant to just RMON.

3.  Control of Remote Network Monitoring Devices

   Due to the complex nature of the available functions in these
   devices, the functions often need user configuration.  In many cases,
   the function requires parameters to be set up for a data collection
   operation.  The operation can proceed only after these parameters are
   fully set up.

   Many functional groups in this MIB have one or more tables in which
   to set up control parameters, and one or more data tables in which to
   place the results of the operation.  The control tables are typically
   read/write in nature, while the data tables are typically read/only.

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   Because the parameters in the control table often describe resulting
   data in the data table, many of the parameters can be modified only
   when the control entry is not active.  Thus, the method for modifying
   these parameters is to de-activate the entry, perform the SNMP Set
   operations to modify the entry, and then re-activate the entry.
   Deleting the control entry causes the deletion of any associated data
   entries, which also gives a convenient method for reclaiming the
   resources used by the associated data.

   Some objects in this MIB provide a mechanism to execute an action on
   the remote monitoring device.  These objects may execute an action as
   a result of a change in the state of the object.  For those objects
   in this MIB, a request to set an object to the same value as it
   currently holds would thus cause no action to occur.

   To facilitate control by multiple managers, resources have to be
   shared among the managers.  These resources are typically the memory
   and computation resources that a function requires.

3.1.  Resource Sharing Among Multiple Management Stations

   When multiple management stations wish to use functions that compete
   for a finite amount of resources on a device, a method to facilitate
   this sharing of resources is required.  Potential conflicts include:

    o Two management stations wish to simultaneously use
      resources that together would exceed the capability of
      the device.
    o A management station uses a significant amount of
      resources for a long period of time.
    o A management station uses resources and then crashes,
      forgetting to free the resources so others may
      use them.

   The OwnerString mechanism is provided for each management station
   initiated function in this MIB to avoid these conflicts and to help
   resolve them when they occur.  Each function has a label identifying
   the initiator (owner) of the function.  This label is set by the
   initiator to provide for the following possibilities:

    o A management station may recognize resources it owns
      and no longer needs.
    o A network operator can find the management station that
      owns the resource and negotiate for it to be freed.
    o A network operator may decide to unilaterally free
      resources another network operator has reserved.

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    o Upon initialization, a management station may recognize
      resources it had reserved in the past.  With this
      information it may free the resources if it no longer
      needs them.

   Management stations and probes should support any format of the owner
   string dictated by the local policy of the organization.  It is
   suggested that this name contain one or more of the following: IP
   address, management station name, network manager's name, location,
   or phone number.  This information will help users to share the
   resources more effectively.

   There is often default functionality that the device or the
   administrator of the probe (often the network administrator) wishes
   to set up.  The resources associated with this functionality are then
   owned by the device itself or by the network administrator, and are
   intended to be long-lived.  In this case, the device or the
   administrator will set the relevant owner object to a string starting
   with 'monitor'.  Indiscriminate modification of the monitor-owned
   configuration by network management stations is discouraged.  In
   fact, a network management station should only modify these objects
   under the direction of the administrator of the probe.

   Resources on a probe are scarce and are typically allocated when
   control rows are created by an application.  Since many applications
   may be using a probe simultaneously, indiscriminate allocation of
   resources to particular applications is very likely to cause resource
   shortages in the probe.

   When a network management station wishes to utilize a function in a
   monitor, it is encouraged to first scan the control table of that
   function to find an instance with similar parameters to share.  This
   is especially true for those instances owned by the monitor, which
   can be assumed to change infrequently.  If a management station
   decides to share an instance owned by another management station, it
   should understand that the management station that owns the instance
   may indiscriminately modify or delete it.

   It should be noted that a management application should have the most
   trust in a monitor-owned row because it should be changed very
   infrequently.  A row owned by the management application is less
   long-lived because a network administrator is more likely to re-
   assign resources from a row that is in use by one user than from a
   monitor-owned row that is potentially in use by many users.  A row
   owned by another application would be even less long-lived because
   the other application may delete or modify that row completely at its

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3.2.  Row Addition Among Multiple Management Stations

   The addition of new rows is achieved using the RowStatus method
   described in RFC 1903 [2].  In this MIB, rows are often added to a
   table in order to configure a function.  This configuration usually
   involves parameters that control the operation of the function.  The
   agent must check these parameters to make sure they are appropriate
   given restrictions defined in this MIB as well as any implementation
   specific restrictions such as lack of resources.  The agent
   implementor may be confused as to when to check these parameters and
   when to signal to the management station that the parameters are
   invalid.  There are two opportunities:

    o When the management station sets each parameter object.

    o When the management station sets the row status object
      to active.

   If the latter is chosen, it would be unclear to the management
   station which of the several parameters was invalid and caused the
   badValue error to be emitted.  Thus, wherever possible, the
   implementor should choose the former as it will provide more
   information to the management station.

   A problem can arise when multiple management stations attempt to set
   configuration information simultaneously using SNMP.  When this
   involves the addition of a new conceptual row in the same control
   table, the managers may collide, attempting to create the same entry.
   To guard against these collisions, each such control entry contains a
   status object with special semantics that help to arbitrate among the
   managers.  If an attempt is made with the row addition mechanism to
   create such a status object and that object already exists, an error
   is returned.  When more than one manager simultaneously attempts to
   create the same conceptual row, only the first will succeed.  The
   others will receive an error.

   In the RMON MIB [RFC 1757], the EntryStatus textual convention was
   introduced to provide this mutual exclusion function.  Since then,
   this function was added to the SNMP framework as the RowStatus
   textual convention.  The RowStatus textual convention is used for the
   definition of all new tables.

   When a manager wishes to create a new control entry, it needs to
   choose an index for that row.  It may choose this index in a variety
   of ways, hopefully minimizing the chances that the index is in use by
   another manager.  If the index is in use, the mechanism mentioned
   previously will guard against collisions.  Examples of schemes to
   choose index values include random selection or scanning the control

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   table looking for the first unused index.  Because index values may
   be any valid value in the range and they are chosen by the manager,
   the agent must allow a row to be created with any unused index value
   if it has the resources to create a new row.

   Some tables in this MIB reference other tables within this MIB.  When
   creating or deleting entries in these tables, it is generally
   allowable for dangling references to exist.  There is no defined
   order for creating or deleting entries in these tables.

4.  Conventions

   The following conventions are used throughout the RMON MIB and its
   companion documents.

   Good Packets

   Good packets are error-free packets that have a valid frame length.
   For example, on Ethernet, good packets are error-free packets that
   are between 64 octets long and 1518 octets long.  They follow the
   form defined in IEEE 802.3 section 3.2.all.

   Bad Packets

   Bad packets are packets that have proper framing and are therefore
   recognized as packets, but contain errors within the packet or have
   an invalid length.  For example, on Ethernet, bad packets have a
   valid preamble and SFD, but have a bad CRC, or are either shorter
   than 64 octets or longer than 1518 octets.

5.  RMON 2 Conventions

   The following practices and conventions are introduced in the RMON 2

5.1.  Usage of the term Application Level

   There are many cases in this MIB where the term Application Level is
   used to describe a class of protocols or a capability.  This does not
   typically mean a protocol that is an OSI Layer 7 protocol.  Rather,
   it is used to identify a class of protocols that is not limited to
   MAC-layer and network-layer protocols, but can also include
   transport, session, presentation, and application-layer protocols.

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5.2.  Protocol Directory and Limited Extensibility

   Every RMON 2 implementation will have the capability to parse certain
   types of packets and identify their protocol type at multiple levels,
   The protocol directory presents an inventory of those protocol types
   the probe is capable of monitoring, and allows the addition,
   deletion, and configuration of protocol types in this list.

   One concept deserves special attention: the "limited extensibility"
   of the protocol directory table.  The RMON 2 model is that protocols
   are detected by static software that has been written at
   implementation time.  Therefore, as a matter of configuration, an
   implementation does not have the ability to suddenly learn how to
   parse new packet types.  However, an implementation may be written
   such that the software knows where the demultiplexing field is for a
   particular protocol, and can be written in such a way that the
   decoding of the next layer up is table-driven.  This works when the
   code has been written to accomodate it and can be extended no more
   than one level higher.  This extensibility is called "limited
   extensibility" to highlight these limitations.  However, this can be
   a very useful tool.

   For example, suppose that an implementation has C code that
   understands how to decode IP packets on any of several ethernet
   encapsulations, and also knows how to interpret the IP protocol field
   to recognize UDP packets and how to decode the UDP port number
   fields.  That implementation may be table- driven so that among the
   many different UDP port numbers possible, it is configured to
   recognize 161 as SNMP, port 53 as DNS, and port 69 as TFTP.  The
   limited extensibility of the protocol directory table would allow an
   SNMP operation to create an entry that would create an additional
   table mapping for UDP that would recognize UDP port 123 as NTP and
   begin counting such packets.

   This limited extensibility is an option that an implementation can
   choose to allow or disallow for any protocol that has child

5.3.  Errors in packets

   Packets with link-level errors are not counted anywhere in this MIB
   because most variables in this MIB requires the decoding of the
   contents of the packet, which is meaningless if there is a link-level

   Packets in which protocol errors are detected are counted for all
   protocols below the layer in which the error was encountered.  The
   implication of this is that packets in which errors are detected at

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   the network-layer are not counted anywhere in this MIB, while packets
   with errors detected at the transport layer may have network-layer
   statistics counted.

(page 12 continued on part 2)

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