Network Working Group S. Waldbusser Request for Comments: 1271 Carnegie Mellon University November 1991 Remote Network Monitoring Management Information Base Status of this Memo This memo is an extension to the SNMP MIB. This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. Distribution of this memo is unlimited. Table of Contents 1. Abstract .............................................. 2 2. The Network Management Framework....................... 2 3. Objects ............................................... 2 3.1 Format of Definitions ................................ 3 4. Overview .............................................. 3 4.1 Remote Network Management Goals ...................... 3 4.2 Textual Conventions .................................. 5 4.3 Structure of MIB ..................................... 5 4.3.1 The Statistics Group ............................... 6 4.3.2 The History Group .................................. 6 4.3.3 The Alarm Group .................................... 6 4.3.4 The Host Group ..................................... 6 4.3.5 The HostTopN Group ................................. 6 4.3.6 The Matrix Group ................................... 7 4.3.7 The Filter Group ................................... 7 4.3.8 The Packet Capture Group ........................... 7 4.3.9 The Event Group .................................... 7 5. Control of Remote Network Monitoring Devices .......... 7 5.1 Resource Sharing Among Multiple Management Stations .. 8 5.2 Row Addition Among Multiple Management Stations ...... 9 6. Definitions ........................................... 10 7. Acknowledgments ....................................... 80 8. References ............................................ 80 Security Considerations................................... 81 Author's Address.......................................... 81
1. Abstract 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. 2. The Network Management Framework The Internet-standard Network Management Framework consists of three components. They are: RFC 1155 which defines the SMI, the mechanisms used for describing and naming objects for the purpose of management. RFC 1212 defines a more concise description mechanism, which is wholly consistent with the SMI. RFC 1156 which defines MIB-I, the core set of managed objects for the Internet suite of protocols. RFC 1213, defines MIB-II, an evolution of MIB-I based on implementation experience and new operational requirements. RFC 1157 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. 3. Objects Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. Objects in the MIB are defined using the subset of Abstract Syntax Notation One (ASN.1)  defined in the SMI. In particular, each object has a name, a syntax, and an encoding. 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 language is used for this purpose. However, the SMI  purposely restricts the ASN.1 constructs which may be used. These restrictions are explicitly made for simplicity. The encoding of an object type is simply how that object type
is represented using the object type's syntax. Implicitly tied to the notion of an object type's syntax and encoding is how the object type is represented when being transmitted on the network. The SMI specifies the use of the basic encoding rules of ASN.1 , subject to the additional requirements imposed by the SNMP. 3.1. Format of Definitions Section 6 contains the specification of all object types contained in this MIB module. The object types are defined using the conventions defined in the SMI, as amended by the extensions specified in [9,10]. 4. Overview Remote network monitoring devices 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. While many of the objects in this document are suitable for the management of any type of network, there are some which are specific to managing Ethernet networks. The design of this MIB allows similar objects to be defined for other network types. It is intended that future versions of this document will define extensions for other network types such as Token Ring and FDDI. 4.1. 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. o Preemptive 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 ways. 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. 4.2. Textual Conventions Two new data types are introduced as a textual convention in this MIB document. These textual conventions enhance the readability of the specification and can ease comparison with other specifications if appropriate. It should be noted that the introduction of the these textual conventions has no effect on either the syntax nor the semantics of any managed objects. The use of these is merely an artifact of the explanatory method used. Objects defined in terms of one of these methods are always encoded by means of the rules that define the primitive type. Hence, no changes to the SMI or the SNMP are necessary to accommodate these textual conventions which are adopted merely for the convenience of readers and writers in pursuit of the elusive goal of clear, concise, and unambiguous MIB documents. The new data types are: OwnerString and EntryStatus. 4.3. Structure of MIB The objects are arranged into the following groups: - statistics - history - alarm - host - hostTopN - matrix - filter - packet capture - event These groups are the basic unit 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 host group must implement the hostControlTable, the hostTable and the hostTimeTable.
All groups in this MIB are optional. Implementations of this MIB must also implement the system and interfaces group of MIB-II . 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. 4.3.1. The Statistics Group The statistics group contains statistics measured by the probe for each monitored interface on this device. This group currently consists of the etherStatsTable but in the future will contain tables for other media types including Token Ring and FDDI. 4.3.2. The History Group The history group records periodic statistical samples from a network and stores them for later retrieval. This group currently consists of the historyControlTable and the etherHistoryTable. In future versions of the MIB, this group may contain tables for other media types including Token Ring and FDDI. 4.3.3. The Alarm Group The alarm group periodically takes statistical samples from variables in the probe and compares them to previously configured thresholds. If the monitored variable crosses a threshold, an event is generated. A hysteresis mechanism is implemented to limit the generation of alarms. This group consists of the alarmTable and requires the implementation of the event group. 4.3.4. The Host Group The host group contains statistics associated with each host discovered on the network. This group discovers hosts on the network by keeping a list of source and destination MAC Addresses seen in good packets promiscuously received from the network. This group consists of the hostControlTable, the hostTable, and the hostTimeTable. 4.3.5. The HostTopN Group The hostTopN group is used to prepare reports that describe the hosts that top a list ordered by one of their statistics. The available statistics are samples of one of their base statistics over an interval specified by the management station. Thus, these statistics are rate based. The management station also selects how many such
hosts are reported. This group consists of the hostTopNControlTable and the hostTopNTable, and requires the implementation of the host group. 4.3.6. The Matrix Group The matrix group stores statistics for conversations between sets of two addresses. As the device detects a new conversation, it creates a new entry in its tables. This group consists of the matrixControlTable, the matrixSDTable and the matrixDSTable. 4.3.7. The Filter Group The filter group allows packets to be matched by a filter equation. These matched packets form a data stream that may be captured or may generate events. This group consists of the filterTable and the channelTable. 4.3.8. The Packet Capture Group The Packet Capture group allows packets to be captured after they flow through a channel. This group consists of the bufferControlTable and the captureBufferTable, and requires the implementation of the filter group. 4.3.9. The Event Group The event group controls the generation and notification of events from this device. This group consists of the eventTable and the logTable. 5. 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. 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 invalid. Thus, the method for modifying these parameters is to invalidate the control entry, causing its deletion and the deletion of any associated data entries, and then
create a new control entry with the proper parameters. Deleting the control entry 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. 5.1. 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. A 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. 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 wishes to set up. The resources associated with this functionality are then owned by the device itself. In this case, the device 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, often the network administrator. 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. 5.2. Row Addition Among Multiple Management Stations The addition of new rows is achieved using the method described in . 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 entry status object to valid. 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.