rfc2021.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   read/write in nature, while the data tables are typically read/only.



Waldbusser                  Standards Track                     [Page 6]

RFC 2021             Remote Network Monitoring MIB          January 1997


   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.





Waldbusser                  Standards Track                     [Page 7]

RFC 2021             Remote Network Monitoring MIB          January 1997


    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
   discretion.




Waldbusser                  Standards Track                     [Page 8]

RFC 2021             Remote Network Monitoring MIB          January 1997


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



Waldbusser                  Standards Track                     [Page 9]

RFC 2021             Remote Network Monitoring MIB          January 1997


   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
   MIB.

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.








Waldbusser                  Standards Track                    [Page 10]

RFC 2021             Remote Network Monitoring MIB          January 1997


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
   protocols.

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
   error.

   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



Waldbusser                  Standards Track                    [Page 11]

RFC 2021             Remote Network Monitoring MIB          January 1997


   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.

6.  Definitions

RMON2-MIB DEFINITIONS ::= BEGIN
IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE, Counter32, Integer32,
        Gauge32, IpAddress, TimeTicks            FROM SNMPv2-SMI
    TEXTUAL-CONVENTION, RowStatus, DisplayString, TimeStamp
                                                 FROM SNMPv2-TC
    MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
    mib-2, ifIndex                  FROM RFC1213-MIB
    OwnerString, statistics, history, hosts,
    matrix, filter, etherStatsEntry, historyControlEntry,
    hostControlEntry, matrixControlEntry, filterEntry,
    channelEntry                    FROM RMON-MIB
    tokenRing, tokenRingMLStatsEntry, tokenRingPStatsEntry,
    ringStationControlEntry, sourceRoutingStatsEntry
                                    FROM TOKEN-RING-RMON-MIB;
--  Remote Network Monitoring MIB

rmon MODULE-IDENTITY
    LAST-UPDATED "9605270000Z"
    ORGANIZATION "IETF RMON MIB Working Group"
    CONTACT-INFO
        "Steve Waldbusser   (WG Editor)
         Postal: International Network Services
         650 Castro Street, Suite 260
         Mountain View, CA 94041
         Phone:  [phone]
         Email:  [e-mail]


         Andy Bierman   (WG Chair)
         Phone:  [phone]
         Email:  [e-mail]"
    DESCRIPTION
        "The MIB module for managing remote monitoring
         device implementations. This MIB module
         augments the original RMON MIB as specified in
         RFC 1757."
    ::= { mib-2 16 }