Network Working Group D. Levi Request for Comments: 2273 SNMP Research, Inc. Obsoletes: 2263 P. Meyer Category: Standards Track Secure Computing Corporation B. Stewart Cisco Systems January 1998 SNMPv3 Applications 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. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved. IANA Note Due to a clerical error in the assignment of the snmpModules in this memo, this RFC provides the corrected number assignments for this protocol. This memo obsoletes RFC 2263. Abstract This memo describes five types of SNMP applications which make use of an SNMP engine as described in [RFC2271]. The types of application described are Command Generators, Command Responders, Notification Originators, Notification Receivers, and Proxy Forwarders. This memo also defines MIB modules for specifying targets of management operations, for notification filtering, and for proxy forwarding. Table of Contents 1 Overview ..................................................... 2 1.1 Command Generator Applications ............................. 3 1.2 Command Responder Applications ............................. 3 1.3 Notification Originator Applications ....................... 3 1.4 Notification Receiver Applications ......................... 3 1.5 Proxy Forwarder Applications ............................... 3 2 Management Targets ........................................... 5 Levi, et. al. Standards Track [Page 1] RFC 2273 SNMPv3 Applications January 1998 3 Elements Of Procedure ........................................ 6 3.1 Command Generator Applications ............................. 6 3.2 Command Responder Applications ............................. 8 3.3 Notification Originator Applications ....................... 13 3.4 Notification Receiver Applications ......................... 16 3.5 Proxy Forwarder Applications ............................... 18 3.5.1 Request Forwarding ....................................... 19 3.5.1.1 Processing an Incoming Request ......................... 19 3.5.1.2 Processing an Incoming Response ........................ 22 3.5.1.3 Processing an Incoming Report Indication ............... 23 3.5.2 Notification Forwarding .................................. 24 4 The Structure of the MIB Modules ............................. 27 4.1 The Management Target MIB Module ........................... 27 4.1.1 Tag Lists ................................................ 28 4.1.2 Definitions .............................................. 28 4.2 The Notification MIB Module ................................ 41 4.2.1 Definitions .............................................. 42 4.3 The Proxy MIB Module ....................................... 53 4.3.1 Definitions .............................................. 53 5 Identification of Management Targets in Notification Originators ............................................... 59 6 Notification Filtering ....................................... 60 7 Management Target Translation in Proxy Forwarder Applications .............................................. 61 7.1 Management Target Translation for Request Forwarding ....... 61 7.2 Management Target Translation for Notification Forwarding ........................................................... 62 8 Intellectual Property ........................................ 63 9 Acknowledgments .............................................. 64 10 Security Considerations ..................................... 65 11 References .................................................. 65 12 Editors' Address ............................................ 67 A. Trap Configuration Example .................................. 68 B. Full Copyright Statement .................................... 70 1. Overview This document describes five types of SNMP applications: - Applications which initiate SNMP Get, GetNext, GetBulk, and/or Set requests, called 'command generators.' - Applications which respond to SNMP Get, GetNext, GetBulk, and/or Set requests, called 'command responders.' - Applications which generate notifications, called 'notification originators.' Levi, et. al. Standards Track [Page 2] RFC 2273 SNMPv3 Applications January 1998 - Applications which receive notifications, called 'notification receivers.' - Applications which forward SNMP Get, GetNext, GetBulk, and/or Set requests or notifications, called 'proxy forwarder.' Note that there are no restrictions on which types of applications may be associated with a particular SNMP engine. For example, a single SNMP engine may, in fact, be associated with both command generator and command responder applications. 1.1. Command Generator Applications A command generator application initiates SNMP Get, GetNext, GetBulk, and/or Set requests, as well as processing the response to a request which it generated. 1.2. Command Responder Applications A command responder application receives SNMP Get, GetNext, GetBulk, and/or Set requests destined for the local system as indicated by the fact that the contextEngineID in the received request is equal to that of the local engine through which the request was received. The command responder application will perform the appropriate protocol operation, using access control, and will generate a response message to be sent to the request's originator. 1.3. Notification Originator Applications A notification originator application conceptually monitors a system for particular events or conditions, and generates Trap and/or Inform messages based on these events or conditions. A notification originator must have a mechanism for determining where to send messages, and what SNMP version and security parameters to use when sending messages. A mechanism and MIB module for this purpose is provided in this document. 1.4. Notification Receiver Applications A notification receiver application listens for notification messages, and generates response messages when a message containing an Inform PDU is received. 1.5. Proxy Forwarder Applications A proxy forwarder application forwards SNMP messages. Note that implementation of a proxy forwarder application is optional. The sections describing proxy (4.5, 5.3, and 8) may be skipped for Levi, et. al. Standards Track [Page 3] RFC 2273 SNMPv3 Applications January 1998 implementations that do not include a proxy forwarder application. The term "proxy" has historically been used very loosely, with multiple different meanings. These different meanings include (among others): (1) the forwarding of SNMP requests to other SNMP entities without regard for what managed object types are being accessed; for example, in order to forward an SNMP request from one transport domain to another, or to translate SNMP requests of one version into SNMP requests of another version; (2) the translation of SNMP requests into operations of some non-SNMP management protocol; and (3) support for aggregated managed objects where the value of one managed object instance depends upon the values of multiple other (remote) items of management information. Each of these scenarios can be advantageous; for example, support for aggregation of management information can significantly reduce the bandwidth requirements of large-scale management activities. However, using a single term to cover multiple different scenarios causes confusion. To avoid such confusion, this document uses the term "proxy" with a much more tightly defined meaning. The term "proxy" is used in this document to refer to a proxy forwarder application which forwards either SNMP requests, notifications, and responses without regard for what managed objects are contained within requests or notifications. This definition is most closely related to the first definition above. Note, however, that in the SNMP architecture [RFC2271], a proxy forwarder is actually an application, and need not be associated with what is traditionally thought of as an SNMP agent. Specifically, the distinction between a traditional SNMP agent and a proxy forwarder application is simple: - a proxy forwarder application forwards requests and/or notifications to other SNMP engines according to the context, and irrespective of the specific managed object types being accessed, and forwards the response to such previously forwarded messages back to the SNMP engine from which the original message was received; - in contrast, the command responder application that is part of what is traditionally thought of as an SNMP agent, and which processes SNMP requests according to the (names of the) Levi, et. al. Standards Track [Page 4] RFC 2273 SNMPv3 Applications January 1998 individual managed object types and instances being accessed, is NOT a proxy forwarder application from the perspective of this document. Thus, when a proxy forwarder application forwards a request or notification for a particular contextEngineID / contextName pair, not only is the information on how to forward the request specifically associated with that context, but the proxy forwarder application has no need of a detailed definition of a MIB view (since the proxy forwarder application forwards the request irrespective of the managed object types). In contrast, a command responder application must have the detailed definition of the MIB view, and even if it needs to issue requests to other entities, via SNMP or otherwise, that need is dependent on the individual managed object instances being accessed (i.e., not only on the context). Note that it is a design goal of a proxy forwarder application to act as an intermediary between the endpoints of a transaction. In particular, when forwarding Inform requests, the associated response is forwarded when it is received from the target to which the Inform request was forwarded, rather than generating a response immediately when an Inform request is received. 2. Management Targets Some types of applications (notification generators and proxy forwarders in particular) require a mechanism for determining where and how to send generated messages. This document provides a mechanism and MIB module for this purpose. The set of information that describes where and how to send a message is called a 'Management Target', and consists of two kinds of information: - Destination information, consisting of a transport domain and a transport address. This is also termed a transport endpoint. - SNMP parameters, consisting of message processing model, security model, security level, and security name information. The SNMP-TARGET-MIB module described later in this document contains one table for each of these types of information. There can be a many-to-many relationship in the MIB between these two types of information. That is, there may be multiple transport endpoints associated with a particular set of SNMP parameters, or a particular transport endpoint may be associated with several sets of SNMP parameters. Levi, et. al. Standards Track [Page 5] RFC 2273 SNMPv3 Applications January 1998 3. Elements Of Procedure The following sections describe the procedures followed by each type of application when generating messages for transmission or when processing received messages. Applications communicate with the Dispatcher using the abstract service interfaces defined in [RFC2271]. 3.1. Command Generator Applications A command generator initiates an SNMP request by calling the Dispatcher using the following abstract service interface: statusInformation = -- sendPduHandle if success -- errorIndication if failure sendPdu( IN transportDomain -- transport domain to be used IN transportAddress -- destination network address IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE ) Where: - The transportDomain is that of the destination of the message. - The transportAddress is that of the destination of the message. - The messageProcessingModel indicates which Message Processing Model the application wishes to use. - The securityModel is the security model that the application wishes to use. - The securityName is the security model independent name for the principal on whose behalf the application wishes the message is to be generated. - The securityLevel is the security level that the application wishes to use. Levi, et. al. Standards Track [Page 6] RFC 2273 SNMPv3 Applications January 1998 - The contextEngineID is provided by the command generator if it wishes to explicitly specify the location of the management information it is requesting. - The contextName is provided by the command generator if it wishes to explicitly specify the local context name for the management information it is requesting. - The pduVersion indicates the version of the PDU to be sent. - The PDU is a value constructed by the command generator containing the management operation that the command generator wishes to perform. - The expectResponse argument indicates that a response is expected. The result of the sendPdu interface indicates whether the PDU was successfully sent. If it was successfully sent, the returned value will be a sendPduHandle. The command generator should store the sendPduHandle so that it can correlate a response to the original request. The Dispatcher is responsible for delivering the response to a particular request to the correct command generator application. The abstract service interface used is: processResponsePdu( -- process Response PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN statusInformation -- success or errorIndication IN sendPduHandle -- handle from sendPDU ) Where: - The messageProcessingModel is the value from the received response. - The securityModel is the value from the received response. - The securityName is the value from the received response. Levi, et. al. Standards Track [Page 7] RFC 2273 SNMPv3 Applications January 1998 - The securityLevel is the value from the received response. - The contextEngineID is the value from the received response. - The contextName is the value from the received response. - The pduVersion indicates the version of the PDU in the received response. - The PDU is the value from the received response. - The statusInformation indicates success or failure in receiving the response. - The sendPduHandle is the value returned by the sendPdu call which generated the original request to which this is a response. The procedure when a command generator receives a message is as follows: (1) If the received values of messageProcessingModel, securityModel, securityName, contextEngineID, contextName, and pduVersion are not all equal to the values used in the original request, the response is discarded. (2) The operation type, request-id, error-status, error-index, and variable-bindings are extracted from the PDU and saved. If the request-id is not equal to the value used in the original request, the response is discarded. (3) At this point, it is up to the application to take an appropriate action. The specific action is implementation dependent. If the statusInformation indicates that the request failed, an appropriate action might be to attempt to transmit the request again, or to notify the person operating the application that a failure occurred. 3.2. Command Responder Applications Before a command responder application can process messages, it must first associate itself with an SNMP engine. The abstract service interface used for this purpose is: Levi, et. al. Standards Track [Page 8] RFC 2273 SNMPv3 Applications January 1998 statusInformation = -- success or errorIndication registerContextEngineID( IN contextEngineID -- take responsibility for this one IN pduType -- the pduType(s) to be registered ) Where: - The statusInformation indicates success or failure of the registration attempt. - The contextEngineID is equal to the snmpEngineID of the SNMP engine with which the command responder is registering. - The pduType indicates a Get, GetNext, GetBulk, or Set pdu. Note that if another command responder application is already registered with an SNMP engine, any further attempts to register with the same contextEngineID and pduType will be denied. This implies that separate command responder applications could register separately for the various pdu types. However, in practice this is undesirable, and only a single command responder application should be registered with an SNMP engine at any given time. A command responder application can disassociate with an SNMP engine using the following abstract service interface: unregisterContextEngineID( IN contextEngineID -- give up responsibility for this one IN pduType -- the pduType(s) to be unregistered ) Where: - The contextEngineID is equal to the snmpEngineID of the SNMP engine with which the command responder is cancelling the registration. - The pduType indicates a Get, GetNext, GetBulk, or Set pdu. Once the command responder has registered with the SNMP engine, it waits to receive SNMP messages. The abstract service interface used for receiving messages is: processPdu( -- process Request/Notification PDU IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal Levi, et. al. Standards Track [Page 9] RFC 2273 SNMPv3 Applications January 1998 IN securityLevel -- Level of Security IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information ) -- needed when sending a response Where: - The messageProcessingModel indicates which Message Processing Model received and processed the message. - The securityModel is the value from the received message. - The securityName is the value from the received message. - The securityLevel is the value from the received message. - The contextEngineID is the value from the received message. - The contextName is the value from the received message. - The pduVersion indicates the version of the PDU in the received message. - The PDU is the value from the received message. - The maxSizeResponseScopedPDU is the maximum allowable size of a ScopedPDU containing a Response PDU (based on the maximum message size that the originator of the message can accept). - The stateReference is a value which references cached information about each received request message. This value must be returned to the Dispatcher in order to generate a response. The procedure when a message is received is as follows. (1) The operation type is determined from the ASN.1 tag value associated with the PDU parameter. The operation type should always be one of the types previously registered by the application. (2) The request-id is extracted from the PDU and saved. Levi, et. al. Standards Track [Page 10] RFC 2273 SNMPv3 Applications January 1998 (3) If the SNMPv2 operation type is GetBulk, the non-repeaters and max-repetitions values are extracted from the PDU and saved. (4) The variable-bindings are extracted from the PDU and saved. (5) The management operation represented by the SNMPv2 operation type is performed with respect to the relevant MIB view within the context named by the contextName, according to the procedures set forth in [RFC1905]. The relevant MIB view is determined by the securityLevel, securityModel, contextName, securityName, and SNMPv2 operation type. To determine whether a particular object instance is within the relevant MIB view, the following abstract service interface is called: statusInformation = -- success or errorIndication isAccessAllowed( IN securityModel -- Security Model in use IN securityName -- principal who wants to access IN securityLevel -- Level of Security IN viewType -- read, write, or notify view IN contextName -- context containing variableName IN variableName -- OID for the managed object ) Where: - The securityModel is the value from the received message. - The securityName is the value from the received message. - The securityLevel is the value from the received message. - The viewType indicates whether the PDU type is a read or write operation. - The contextName is the value from the received message. - The variableName is the object instance of the variable for which access rights are to be checked. Normally, the result of the management operation will be a new PDU value, and processing will continue in step (6) below. However, at any time during the processing of the management operation: - If the isAccessAllowed ASI returns a noSuchView, noAccessEntry, or noGroupName error, processing of the management operation is halted, a PDU value is contructed using the values from the originally received PDU, but Levi, et. al. Standards Track [Page 11] RFC 2273 SNMPv3 Applications January 1998 replacing the error_status with an authorizationError code, and error_index value of 0, and control is passed to step (6) below. - If the isAccessAllowed ASI returns an otherError, processing of the management operation is halted, a different PDU value is contructed using the values from the originally received PDU, but replacing the error_status with a genError code, and control is passed to step (6) below. - If the isAccessAllowed ASI returns a noSuchContext error, processing of the management operation is halted, no result PDU is generated, the snmpUnknownContexts counter is incremented, and control is passed to step (6) below. - If the context named by the contextName parameter is unavailable, processing of the management operation is halted, no result PDU is generated, the snmpUnavailableContexts counter is incremented, and control is passed to step (6) below. (6) The Dispatcher is called to generate a response or report message. The abstract service interface is: returnResponsePdu( IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model in use IN securityName -- on behalf of this principal IN securityLevel -- same as on incoming request IN contextEngineID -- data from/at this SNMP entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU IN PDU -- SNMP Protocol Data Unit IN maxSizeResponseScopedPDU -- maximum size of the Response PDU IN stateReference -- reference to state information -- as presented with the request IN statusInformation -- success or errorIndication ) -- error counter OID/value if error Where: - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. Levi, et. al. Standards Track [Page 12] RFC 2273 SNMPv3 Applications January 1998 - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion indicates the version of the PDU to be returned. If no result PDU was generated, the pduVersion is an undefined value. - The PDU is the result generated in step (5) above. If no result PDU was generated, the PDU is an undefined value. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation either contains an indication that no error occurred and that a response should be generated, or contains an indication that an error occurred along with the OID and counter value of the appropriate error counter object. Note that a command responder application should always call the returnResponsePdu abstract service interface, even in the event of an error such as a resource allocation error. In the event of such an error, the PDU value passed to returnResponsePdu should contain appropriate values for errorStatus and errorIndex. 3.3. Notification Originator Applications A notification originator application generates SNMP notification messages. A notification message may, for example, contain an SNMPv2-Trap PDU or an Inform PDU. However, a particular implementation is not required to be capable of generating both types of messages. Notification originator applications require a mechanism for identifying the management targets to which notifications should be sent. The particular mechanism used is implementation dependent. However, if an implementation makes the configuration of management targets SNMP manageable, it MUST use the SNMP-TARGET-MIB module described in this document. When a notification originator wishes to generate a notification, it must first determine in which context the information to be conveyed in the notification exists, i.e., it must determine the contextEngineID and contextName. It must then determine the set of Levi, et. al. Standards Track [Page 13] RFC 2273 SNMPv3 Applications January 1998 management targets to which the notification should be sent. The application must also determine, for each management target, whether the notification message should contain an SNMPv2-Trap PDU or Inform PDU, and if it is to contain an Inform PDU, the number of retries and retransmission algorithm. The mechanism by which a notification originator determines this information is implementation dependent. Once the application has determined this information, the following procedure is performed for each management target: (1) Any appropriate filtering mechanisms are applied to determine whether the notification should be sent to the management target. If such filtering mechanisms determine that the notification should not be sent, processing continues with the next management target. Otherwise, (2) The appropriate set of variable-bindings is retrieved from local MIB instrumentation within the relevant MIB view. The relevant MIB view is determined by the securityLevel, securityModel, contextName, and securityName of the management target. To determine whether a particular object instance is within the relevant MIB view, the isAccessAllowed abstract service interface is used, in the same manner as described in the preceding section. If the statusInformation returned by isAccessAllowed does not indicate accessAllowed, the notification is not sent to the management target. (3) A PDU is constructed using a locally unique request-id value, an operation type of SNMPv2-Trap or Inform, an error-status and error-index value of 0, and the variable-bindings supplied previously in step (2). (4) If the notification contains an SNMPv2-Trap PDU, the Dispatcher is called using the following abstract service interface: statusInformation = -- sendPduHandle if success -- errorIndication if failure sendPdu( IN transportDomain -- transport domain to be used IN transportAddress -- destination network address IN messageProcessingModel -- typically, SNMP version IN securityModel -- Security Model to use IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN contextEngineID -- data from/at this entity IN contextName -- data from/in this context IN pduVersion -- the version of the PDU Levi, et. al. Standards Track [Page 14] RFC 2273 SNMPv3 Applications January 1998 IN PDU -- SNMP Protocol Data Unit IN expectResponse -- TRUE or FALSE ) Where: - The transportDomain is that of the management target. - The transportAddress is that of the management target. - The messageProcessingModel is that of the management target. - The securityModel is that of the management target. - The securityName is that of the management target. - The securityLevel is that of the management target. - The contextEngineID is the value originally determined for the notification. - The contextName is the value originally determined for the notification. - The pduVersion is the version of the PDU to be sent. - The PDU is the value constructed in step (3) above. - The expectResponse argument indicates that no response is expected. Otherwise, (5) If the notification contains an Inform PDU, then: a) The Dispatcher is called using the sendPdu abstract service interface as described in step (4) above, except that the expectResponse argument indicates that a response is expected. b) The application caches information about the management target. c) If a response is received within an appropriate time interval from the transport endpoint of the management target, the notification is considered acknowledged and the cached information is deleted. Otherwise, Levi, et. al. Standards Track [Page 15] RFC 2273 SNMPv3 Applications January 1998 d) If a response is not received within an appropriate time period, or if a report indication is received, information about the management target is retrieved from the cache, and steps a) through d) are repeated. The number of times these steps are repeated is equal to the previously determined retry count. If this retry count is exceeded, the acknowledgement of the notification is considered to have failed, and processing of the notification for this management target is halted. Responses to Inform PDU notifications will be received via the processResponsePDU abstract service interface. 3.4. Notification Receiver Applications Notification receiver applications receive SNMP Notification messages from the Dispatcher. Before any messages can be received, the notification receiver must register with the Dispatcher using the registerContextEngineID abstract service interface. The parameters used are: - The contextEngineID is an undefined 'wildcard' value. Notifications are delivered to a registered notification receiver regardless of the contextEngineID contained in the notification message. - The pduType indicates the type of notifications that the application wishes to receive (for example, SNMPv2-Trap PDUs or Inform PDUs). Once the notification receiver has registered with the Dispatcher, messages are received using the processPdu abstract service interface. Parameters are: - The messageProcessingModel indicates which Message Processing Model received and processed the message. - The securityModel is the value from the received message. - The securityName is the value from the received message. - The securityLevel is the value from the received message. - The contextEngineID is the value from the received message. - The contextName is the value from the received message. Levi, et. al. Standards Track [Page 16] RFC 2273 SNMPv3 Applications January 1998 - The pduVersion indicates the version of the PDU in the received message. - The PDU is the value from the received message. - The maxSizeResponseScopedPDU is the maximum allowable size of a ScopedPDU containing a Response PDU (based on the maximum message size that the originator of the message can accept). - If the message contains an SNMPv2-Trap PDU, the stateReference is undefined and unused. Otherwise, the stateReference is a value which references cached information about the notification. This value must be returned to the Dispatcher in order to generate a response. When an SNMPv2-Trap PDU is delivered to a notification receiver application, it first extracts the SNMP operation type, request-id, error-status, error-index, and variable-bindings from the PDU. After this, processing depends on the particular implementation. When an Inform PDU is received, the notification receiver application follows the following procedure: (1) The SNMPv2 operation type, request-id, error-status, error-index, and variable-bindings are extracted from the PDU. (2) A Response PDU is constructed using the extracted request-id and variable-bindings, and with error-status and error-index both set to 0. (3) The Dispatcher is called to generate a response message using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion indicates the version of the PDU to be returned. Levi, et. al. Standards Track [Page 17] RFC 2273 SNMPv3 Applications January 1998 - The PDU is the result generated in step (2) above. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation indicates that no error occurred and that a response should be generated. 3.5. Proxy Forwarder Applications A proxy forwarder application deals with forwarding SNMP messages. There are four basic types of messages which a proxy forwarder application may need to forward. These are grouped according to the PDU type contained in a message, or according to whether a report indication is contained in the message. The four basic types of messages are: - Those containing PDU types which were generated by a command generator application (for example, Get, GetNext, GetBulk, and Set PDU types). These deal with requesting or modifying information located within a particular context. - Those containing PDU types which were generated by a notification originator application (for example, SNMPv2-Trap and Inform PDU types). These deal with notifications concerning information located within a particular context. - Those containing a Response PDU type. Forwarding of Response PDUs always occurs as a result of receiving a response to a previously forwarded message. - Those containing a report indication. Forwarding of report indications always occurs as a result of receiving a report indication for a previously forwarded message. For the first type, the proxy forwarder's role is to deliver a request for management information to an SNMP engine which is "closer" or "downstream in the path" to the SNMP engine which has access to that information, and to deliver the response containing the information back to the SNMP engine from which the request was received. The context information in a request is used to determine which SNMP engine has access to the requested information, and this is used to determine where and how to forward the request. Levi, et. al. Standards Track [Page 18] RFC 2273 SNMPv3 Applications January 1998 For the second type, the proxy forwarder's role is to determine which SNMP engines should receive notifications about management information from a particular location. The context information in a notification message determines the location to which the information contained in the notification applies. This is used to determine which SNMP engines should receive notification about this information. For the third type, the proxy forwarder's role is to determine which previously forwarded request or notification (if any) the response matches, and to forward the response back to the initiator of the request or notification. For the fourth type, the proxy forwarder's role is to determine which previously forwarded request or notification (if any) the report indication matches, and to forward the report indication back to the initiator of the request or notification. When forwarding messages, a proxy forwarder application must perform a translation of incoming management target information into outgoing management target information. How this translation is performed is implementation specific. In many cases, this will be driven by a preconfigured translation table. If a proxy forwarder application makes the contents of this table SNMP manageable, it MUST use the SNMP-PROXY-MIB module defined in this document. 3.5.1. Request Forwarding There are two phases for request forwarding. First, the incoming request needs to be passed through the proxy application. Then, the resulting response needs to be passed back. These phases are described in the following two sections. 3.5.1.1. Processing an Incoming Request A proxy forwarder application that wishes to forward request messages must first register with the Dispatcher using the registerContextEngineID abstract service interface. The proxy forwarder must register each contextEngineID for which it wishes to forward messages, as well as for each pduType. Note that as the configuration of a proxy forwarder is changed, the particular contextEngineID values for which it is forwarding may change. The proxy forwarder should call the registerContextEngineID and unregisterContextEngineID abstract service interfaces as needed to reflect its current configuration. Levi, et. al. Standards Track [Page 19] RFC 2273 SNMPv3 Applications January 1998 A proxy forwarder application should never attempt to register a value of contextEngineID which is equal to the snmpEngineID of the SNMP engine to which the proxy forwarder is associated. Once the proxy forwarder has registered for the appropriate contextEngineId values, it can start processing messages. The following procedure is used: (1) A message is received using the processPdu abstract service interface. The incoming management target information received from the processPdu interface is translated into outgoing management target information. Note that this translation may vary for different values of contextEngineID and/or contextName. The translation should result in a single management target. (2) If appropriate outgoing management target information cannot be found, the proxy forwarder increments the snmpProxyDrops counter [RFC1907], and then calls the Dispatcher using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel is the value from the processPdu call. - The securityModel is the value from the processPdu call. - The securityName is the value from the processPdu call. - The securityLevel is the value from the processPdu call. - The contextEngineID is the value from the processPdu call. - The contextName is the value from the processPdu call. - The pduVersion is the value from the processPdu call. - The PDU is an undefined value. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value from the processPdu call. - The statusInformation indicates that an error occurred and includes the OID and value of the snmpProxyDrops object. Processing of the message stops at this point. Otherwise, Levi, et. al. Standards Track [Page 20] RFC 2273 SNMPv3 Applications January 1998 (3) A new PDU is constructed. A unique value of request-id should be used in the new PDU (this value will enable a subsequent response message to be correlated with this request). The remainder of the new PDU is identical to the received PDU, unless the incoming SNMP version is SNMPv2 or SNMPv3 and the outgoing SNMP version is SNMPv1, in which case the proxy forwarder must apply the translation rules as documented in [RFC1908]. (4) The proxy forwarder calls the Dispatcher to generate the forwarded message, using the sendPdu abstract service interface. The parameters are: - The transportDomain is that of the outgoing management target. - The transportAddress is that of the outgoing management target. - The messageProcessingModel is that of the outgoing management target. - The securityModel is that of the outgoing management target. - The securityName is that of the outgoing management target. - The securityLevel is that of the outgoing management target. - The contextEngineID is the value originally received. - The contextName is the value originally received. - The pduVersion is the version of the PDU to be sent. - The PDU is the value constructed in step (3) above. - The expectResponse argument indicates that a response is expected. If the sendPdu call is unsuccessful, the proxy forwarder performs the steps described in (2) above. Otherwise: (5) The proxy forwarder caches the following information in order to match an incoming response to the forwarded request: - The sendPduHandle returned from the call to sendPdu, - The request-id from the received PDU. - the contextEngineID, Levi, et. al. Standards Track [Page 21] RFC 2273 SNMPv3 Applications January 1998 - the contextName, - the stateReference, - the incoming management target information, - the outgoing management information, - any other information needed to match an incoming response to the forwarded request. If this information cannot be cached (possibly due to a lack of resources), the proxy forwarder performs the steps described in (2) above. Otherwise: (6) Processing of the request stops until a response to the forwarded request is received, or until an appropriate time interval has expired. If this time interval expires before a response has been received, the cached information about this request is removed. 3.5.1.2. Processing an Incoming Response A proxy forwarder follows the following procedure when an incoming response is received: (1) The incoming response is received using the processResponsePdu interface. The proxy forwarder uses the received parameters to locate an entry in its cache of pending forwarded requests. This is done by matching the received parameters with the cached values of sendPduHandle, contextEngineID, contextName, outgoing management target information, and the request-id contained in the received PDU (the proxy forwarder must extract the request-id for this purpose). If an appropriate cache entry cannot be found, processing of the response is halted. Otherwise: (2) The cache information is extracted, and removed from the cache. (3) A new Response PDU is constructed, using the request-id value from the original forwarded request (as extracted from the cache). All other values are identical to those in the received Response PDU. (4) If the incoming SNMP version is SNMPv1 and the outgoing SNMP version is SNMPv2 or SNMPv3, the proxy forwarder must apply the translation rules documented in [RFC1908]. (5) The proxy forwarder calls the Dispatcher using the returnResponsePdu abstract service interface. Parameters are: Levi, et. al. Standards Track [Page 22] RFC 2273 SNMPv3 Applications January 1998 - The messageProcessingModel indicates the Message Processing Model by which the original incoming message was processed. - The securityModel is that of the original incoming management target extracted from the cache. - The securityName is that of the original incoming management target extracted from the cache. - The securityLevel is that of the original incoming management target extracted from the cache. - The contextEngineID is the value extracted from the cache. - The contextName is the value extracted from the cache. - The pduVersion indicates the version of the PDU to be returned. - The PDU is the (possibly translated) Response PDU. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value extracted from the cache. - The statusInformation indicates that no error occurred and that a Response PDU message should be generated. 3.5.1.3. Processing an Incoming Report Indication A proxy forwarder follows the following procedure when an incoming report indication is received: (1) The incoming report indication is received using the processResponsePdu interface. The proxy forwarder uses the received parameters to locate an entry in its cache of pending forwarded requests. This is done by matching the received parameters with the cached values of sendPduHandle. If an appropriate cache entry cannot be found, processing of the report indication is halted. Otherwise: (2) The cache information is extracted, and removed from the cache. (3) If the original incoming management target information indicates SNMPv1, processing of the report indication is halted. Levi, et. al. Standards Track [Page 23] RFC 2273 SNMPv3 Applications January 1998 (4) The proxy forwarder calls the Dispatcher using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel indicates the Message Processing Model by which the original incoming message was processed. - The securityModel is that of the original incoming management target extracted from the cache. - The securityName is that of the original incoming management target extracted from the cache. - The securityLevel is that of the original incoming management target extracted from the cache. - The contextEngineID is the value extracted from the cache. - The contextName is the value extracted from the cache. - The pduVersion indicates the version of the PDU to be returned. - The PDU is unused. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the value extracted from the cache. - The statusInformation contain the contextEngineID, contextName, counter OID, and counter value received in the report indication. 3.5.2. Notification Forwarding A proxy forwarder receives notifications in the same manner as a notification receiver application, using the processPdu abstract service interface. The following procedure is used when a notification is received: (1) The incoming management target information received from the processPdu interface is translated into outgoing management target information. Note that this translation may vary for different values of contextEngineId and/or contextName. The translation may result in multiple management targets. Levi, et. al. Standards Track [Page 24] RFC 2273 SNMPv3 Applications January 1998 (2) If appropriate outgoing management target information cannot be found and the notification was a Trap, processing of the notification is halted. If appropriate outgoing management target information cannot be found and the notification was an Inform, the proxy forwarder increments the snmpProxyDrops object, and calls the Dispatcher using the returnResponsePdu abstract service interface. The parameters are: - The messageProcessingModel is the received value. - The securityModel is the received value. - The securityName is the received value. - The securityLevel is the received value. - The contextEngineID is the received value. - The contextName is the received value. - The pduVersion is the received value. - The PDU is an undefined and unused value. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the received value. - The statusInformation indicates that an error occurred and that a Report message should be generated. Processing of the message stops at this point. Otherwise, (3) The proxy forwarder generates a notification using the procedures described in the preceding section on Notification Originators, with the following exceptions: - The contextEngineID and contextName values from the original received notification are used. - The outgoing management targets previously determined are used. - No filtering mechanisms are applied. Levi, et. al. Standards Track [Page 25] RFC 2273 SNMPv3 Applications January 1998 - The variable-bindings from the original received notification are used, rather than retrieving variable-bindings from local MIB instrumentation. In particular, no access-control is applied to these variable-bindings. - If for any of the outgoing management targets, the incoming SNMP version is SNMPv1 and the outgoing SNMP version is SNMPv2 or SNMPv3, the proxy forwarder must apply the translation rules as documented in [RFC1908]. - If for any of the outgoing management targets, the incoming SNMP version is SNMPv2 or SNMPv3, and the outgoing SNMP version is SNMPv1, this outgoing management target is not used when generating the forwarded notifications. (4) If the original received notification contains an SNMPv2-Trap PDU, processing of the notification is now completed. Otherwise, the original received notification must contain an Inform PDU, and processing continues. (5) If the forwarded notifications included any Inform PDUs, processing continues when the procedures described in the section for Notification Originators determine that either: - None of the generated notifications containing Inform PDUs have been successfully acknowledged within the longest of the time intervals, in which case processing of the original notification is halted, or, - At least one of the generated notifications containing Inform PDUs is successfully acknowledged, in which case a response to the original received notification containing an Inform PDU is generated as described in the following steps. (6) A Response PDU is constructed, using the values of request-id and variable-bindings from the original received Inform PDU, and error-status and error-index values of 0. (7) The Dispatcher is called using the returnResponsePdu abstract service interface. Parameters are: - The messageProcessingModel is the originally received value. - The securityModel is the originally received value. - The securityName is the originally received value. - The securityLevel is the originally received value. Levi, et. al. Standards Track [Page 26] RFC 2273 SNMPv3 Applications January 1998 - The contextEngineID is the originally received value. - The contextName is the originally received value. - The pduVersion indicates the version of the PDU constructed in step (6) above. - The PDU is the value constructed in step (6) above. - The maxSizeResponseScopedPDU is a local value indicating the maximum size of a ScopedPDU that the application can accept. - The stateReference is the originally received value. - The statusInformation indicates that no error occurred and that a Response PDU message should be generated. 4. The Structure of the MIB Modules There are three separate MIB modules described in this document, the management target MIB, the notification MIB, and the proxy MIB. The following sections describe the structure of these three MIB modules. The use of these MIBs by particular types of applications is described later in this document: - The use of the management target MIB and the notification MIB in notification originator applications is described in section 6. - The use of the notification MIB for filtering notifications in notification originator applications is described in section 7. - The use of the management target MIB and the proxy MIB in proxy forwarding applications is described in section 8. 4.1. The Management Target MIB Module The SNMP-TARGET-MIB module contains objects for defining management targets. It consists of two tables and conformance/compliance statements. The first table, the snmpTargetAddrTable, contains information about transport domains and addresses. It also contains an object, snmpTargetAddrTagList, which provides a mechanism for grouping entries. Levi, et. al. Standards Track [Page 27] RFC 2273 SNMPv3 Applications January 1998 The second table, the snmpTargetParamsTable, contains information about SNMP version and security information to be used when sending messages to particular transport domains and addresses. 4.1.1. Tag Lists The snmpTargetAddrTagList object is used for grouping entries in the snmpTargetAddrTable. The value of this object contains a list of tag values which are used to select target addresses to be used for a particular operation. A tag value, which may also be used in MIB objects other than snmpTargetAddrTagList, is an arbitrary string of octets, but may not contain a delimiter character. Delimiter characters are defined to be one of the following characters: - An ASCII space character (0x20). - An ASCII TAB character (0x09). - An ASCII carriage return (CR) character (0x0D). - An ASCII line feed (LF) character (0x0B). In addition, a tag value may not have a zero length. Generally, a particular MIB object may contain either - a single tag value, in which case the value of the MIB object may not contain a delimiter character, or: - a MIB object may contain a list of tag values, separated by single delimiter characters. For a list of tag values, these constraints imply certain restrictions on the value of a MIB object: - There cannot be a leading or trailing delimiter character. - There cannot be multiple adjacent delimiter charaters. 4.1.2. Definitions SNMP-TARGET-MIB DEFINITIONS ::= BEGIN IMPORTS TEXTUAL-CONVENTION, MODULE-IDENTITY, OBJECT-TYPE, Levi, et. al. Standards Track [Page 28] RFC 2273 SNMPv3 Applications January 1998 snmpModules, Integer32 FROM SNMPv2-SMI TDomain, TAddress, TimeInterval, RowStatus, StorageType, TestAndIncr FROM SNMPv2-TC SnmpSecurityModel, SnmpMessageProcessingModel, SnmpSecurityLevel, SnmpAdminString FROM SNMP-FRAMEWORK-MIB OBJECT-GROUP FROM SNMPv2-CONF; snmpTargetMIB MODULE-IDENTITY LAST-UPDATED "9711210000Z" ORGANIZATION "IETF SNMPv3 Working Group" CONTACT-INFO "WG-email: snmpv3@tis.com Subscribe: majordomo@tis.com In message body: subscribe snmpv3 Chair: Russ Mundy Trusted Information Systems Postal: 3060 Washington Rd Glenwood MD 21738 USA Email: mundy@tis.com Phone: +1-301-854-6889 Co-editor: David B. Levi SNMP Research, Inc. Postal: 3001 Kimberlin Heights Road Knoxville, TN 37920-9716 E-mail: levi@snmp.com Phone: +1 423 573 1434 Co-editor: Paul Meyer Secure Computing Corporation Postal: 2675 Long Lake Road Roseville, MN 55113 E-mail: paul_meyer@securecomputing.com Levi, et. al. Standards Track [Page 29] RFC 2273 SNMPv3 Applications January 1998 Phone: +1 612 628 1592 Co-editor: Bob Stewart Cisco Systems, Inc. Postal: 170 West Tasman Drive San Jose, CA 95134-1706 E-mail: bstewart@cisco.com Phone: +1 603 654 6923" DESCRIPTION "This MIB module defines MIB objects which provide mechanisms to remotely configure the parameters used by an SNMP entity for the generation of SNMP messages." REVISION "9707140000Z" DESCRIPTION "The initial revision." ::= { snmpModules 12 } snmpTargetObjects OBJECT IDENTIFIER ::= { snmpTargetMIB 1 } snmpTargetConformance OBJECT IDENTIFIER ::= { snmpTargetMIB 3 } SnmpTagValue ::= TEXTUAL-CONVENTION