HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 12:01:37 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Tue, 12 Sep 1995 22:00:00 GMT ETag: "3ddb6c-fb3e-305602e0" Accept-Ranges: bytes Content-Length: 64318 Connection: close Content-Type: text/plain Internet Draft Protocol Operations for SNMPv2 September 1995 Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2) Fri Sep 08 1995 draft-various-snmpv2-proto-syn-00.txt Tell U. Later snmpv2@tis.com Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). Expires January 1996 [Page 1] Internet Draft Protocol Operations for SNMPv2 September 1995 running list of open issues reference list reference citations acknowledgements authors author addresses spell check Expires January 1996 [Page 2] Internet Draft Protocol Operations for SNMPv2 September 1995 1. Introduction A management system contains: several (potentially many) manageable nodes, each with a processing entity, termed an agent, which has access to management instrumentation; at least one management station; and, a management protocol. The management protocol is used to convey management information between the agents and management stations; and, for manager-to-manager communications, between management stations. Operations of the protocol are carried out under an administrative framework which defines authentication, authorization, access control, and privacy policies. Management stations execute management applications which monitor and control managed elements. Managed elements are devices such as hosts, routers, terminal servers, etc., which are monitored and controlled via access to their management information. Management information is viewed as a collection of managed objects, residing in a virtual information store, termed the Management Information Base (MIB). Collections of related objects are defined in MIB modules. These modules are written using a subset of OSI's Abstract Syntax Notation One (ASN.1) [@ref asn.1], termed the Structure of Management Information (SMI) [@ref v2smi]. The management protocol, version 2 of the Simple Network Management Protocol, provides for the exchange of messages which convey management information between the agents and the management stations. The form of these messages is a message "wrapper" which encapsulates a Protocol Data Unit (PDU). The form and meaning of the "wrapper" is determined by an administrative framework which defines both authentication and authorization policies. It is the purpose of this document, Protocol Operations for SNMPv2, to define the operations of the protocol with respect to the sending and receiving of the PDUs. 1.1. A Note on Terminology For the purpose of exposition, the original Internet-standard Network Management Framework, as described in RFCs 1155, 1157, and 1212, is termed the SNMP version 1 framework (SNMPv1). The current framework is termed the SNMP version 2 framework (SNMPv2). Expires January 1996 [Page 3] Internet Draft Protocol Operations for SNMPv2 September 1995 2. Overview 2.1. Roles of Protocol Entities A SNMPv2 entity may operate in a manager role or an agent role. A SNMPv2 entity acts in an agent role when it performs SNMPv2 management operations in response to received SNMPv2 protocol messages (other than an inform notification) or when it sends trap notifications. A SNMPv2 entity acts in a manager role when it initiates SNMPv2 management operations by the generation of SNMPv2 protocol messages or when it performs SNMPv2 management operations in response to received trap or inform notifications. A SNMPv2 entity may support either or both roles, as dictated by its implementation and configuration. Further, a SNMPv2 entity can also act in the role of a proxy agent, in which it appears to be acting in an agent role, but satisfies management requests by acting in a manager role with a remote entity. The use of proxy agents and the transparency principle that defines their behavior is described in [@ref v2admin]. 2.2. Management Information The term, variable, refers to an instance of a non-aggregate object type defined according to the conventions set forth in the SMI [@ref v2smi] or the textual conventions based on the SMI [@ref tc]. The term, variable binding, normally refers to the pairing of the name of a variable and its associated value. However, if certain kinds of exceptional conditions occur during processing of a retrieval request, a variable binding will pair a name and an indication of that exception. A variable-binding list is a simple list of variable bindings. The name of a variable is an OBJECT IDENTIFIER which is the concatenation of the OBJECT IDENTIFIER of the corresponding object-type together with an OBJECT IDENTIFIER fragment identifying the instance. The OBJECT IDENTIFIER of the corresponding object-type is called the OBJECT IDENTIFIER prefix of the variable. Expires January 1996 [Page 4] Internet Draft Protocol Operations for SNMPv2 September 1995 2.3. Access to Management Information Three types of access to management information are provided by the protocol. One type is a request-response interaction, in which a SNMPv2 entity, acting in a manager role, sends a request to a SNMPv2 entity, acting in an agent role, and the latter SNMPv2 entity then responds to the request. This type is used to retrieve or modify management information associated with the managed device. A second type is also a request-response interaction, in which a SNMPv2 entity, acting in a manager role, sends a request to a SNMPv2 entity, also acting in a manager role, and the latter SNMPv2 entity then responds to the request. This type is used to notify a SNMPv2 entity, acting in a manager role, of management information associated with another SNMPv2 entity, also acting in a manager role. The third type of access is an unconfirmed interaction, in which a SNMPv2 entity, acting in an agent role, sends a unsolicited message, termed a trap, to a SNMPv2 entity, acting in a manager role, and no response is returned. This type is used to notify a SNMPv2 entity, acting in a manager role, of an exceptional situation, which has resulted in changes to management information associated with the managed device. 2.4. Retransmission of Requests For all types of requests in this protocol, the receiver is required under normal circumstances, to generate and transmit a response to the originator of the request. Whether or not a request should be retransmitted if no corresponding response is received in an appropriate time interval, is at the discretion of the application originating the request. This will normally depend on the urgency of the request. However, such an application needs to act responsibly in respect to the frequency and duration of re-transmissions. 2.5. Message Sizes The maximum size of a SNMPv2 message is limited by the minimum of: (1) the maximum message size which the destination SNMPv2 entity can accept; and, Expires January 1996 [Page 5] Internet Draft Protocol Operations for SNMPv2 September 1995 (2) the maximum message size which the source SNMPv2 entity can generate. The former may be known on a per-recipient basis; and in the absence of such knowledge, is indicated by transport domain used when sending the message. The latter is imposed by implementation-specific local constraints. Each transport mapping for the SNMPv2 indicates the minimum message size which a SNMPv2 implementation must be able to produce or consume. Although implementations are encouraged to support larger values whenever possible, a conformant implementation must never generate messages larger than allowed by the receiving SNMPv2 entity. One of the aims of the GetBulkRequest-PDU, specified in this protocol, is to minimize the number of protocol exchanges required to retrieve a large amount of management information. As such, this PDU type allows a SNMPv2 entity acting in a manager role to request that the response be as large as possible given the constraints on message sizes. These constraints include the limits on the size of messages which the SNMPv2 entity acting in an agent role can generate, and the SNMPv2 entity acting in a manager role can receive. However, it is possible that such maximum sized messages may be larger than the Path MTU of the path across the network traversed by the messages. In this situation, such messages are subject to fragmentation. Fragmentation is generally considered to be harmful [@ref fragmentation], since among other problems, it leads to a decrease in the reliability of the transfer of the messages. Thus, a SNMPv2 entity which sends a GetBulkRequest-PDU must take care to set its parameters accordingly, so as to reduce the risk of fragmentation. In particular, under conditions of network stress, only small values should be used for max-repetitions. 2.6. Transport Mappings It is important to note that the exchange of SNMPv2 messages requires only an unreliable datagram service, with every message being entirely and independently contained in a single transport datagram. Specific transport mappings and encoding rules are specified elsewhere [@ref tm]. However, the preferred mapping is the use of the User Datagram Protocol [@ref udp]. Expires January 1996 [Page 6] Internet Draft Protocol Operations for SNMPv2 September 1995 3. Definitions SNMPv2-PDU DEFINITIONS ::= BEGIN IMPORTS ObjectName, ObjectSyntax, Integer32 FROM SNMPv2-SMI; -- protocol data units -- These are carried in an SnmpV2Message defined in [@ref v2admin] or -- an SNMPV1Point5Message defined in [@ref v1.5admin] PDUs ::= CHOICE { get-request GetRequest-PDU, get-next-request GetNextRequest-PDU, get-bulk-request GetBulkRequest-PDU, response Response-PDU, set-request SetRequest-PDU, inform-request InformRequest-PDU, snmpV2-trap SNMPv2-Trap-PDU } Expires January 1996 [Page 7] Internet Draft Protocol Operations for SNMPv2 September 1995 -- PDUs GetRequest-PDU ::= [0] IMPLICIT PDU GetNextRequest-PDU ::= [1] IMPLICIT PDU Response-PDU ::= [2] IMPLICIT PDU SetRequest-PDU ::= [3] IMPLICIT PDU -- [4] is obsolete GetBulkRequest-PDU ::= [5] IMPLICIT BulkPDU InformRequest-PDU ::= [6] IMPLICIT PDU SNMPv2-Trap-PDU ::= [7] IMPLICIT PDU Report-PDU ::= [8] IMPLICIT PDU Expires January 1996 [Page 8] Internet Draft Protocol Operations for SNMPv2 September 1995 max-bindings INTEGER ::= 2147483647 PDU ::= SEQUENCE { request-id Integer32, error-status -- sometimes ignored INTEGER { noError(0), tooBig(1), noSuchName(2), -- for proxy compatibility badValue(3), -- for proxy compatibility readOnly(4), -- for proxy compatibility genErr(5), noAccess(6), wrongType(7), wrongLength(8), wrongEncoding(9), wrongValue(10), noCreation(11), inconsistentValue(12), resourceUnavailable(13), commitFailed(14), undoFailed(15), authorizationError(16), notWritable(17), inconsistentName(18) }, error-index -- sometimes ignored INTEGER (0..max-bindings), variable-bindings -- values are sometimes ignored VarBindList } Expires January 1996 [Page 9] Internet Draft Protocol Operations for SNMPv2 September 1995 BulkPDU ::= -- MUST be identical in SEQUENCE { -- structure to PDU request-id Integer32, non-repeaters INTEGER (0..max-bindings), max-repetitions INTEGER (0..max-bindings), variable-bindings -- values are ignored VarBindList } Expires January 1996 [Page 10] Internet Draft Protocol Operations for SNMPv2 September 1995 -- variable binding VarBind ::= SEQUENCE { name ObjectName, CHOICE { value ObjectSyntax, unSpecified -- in retrieval requests NULL, -- exceptions in responses noSuchObject[0] IMPLICIT NULL, noSuchInstance[1] IMPLICIT NULL, endOfMibView[2] IMPLICIT NULL } } -- variable-binding list VarBindList ::= SEQUENCE (SIZE (0..max-bindings)) OF VarBind END Expires January 1996 [Page 11] Internet Draft Protocol Operations for SNMPv2 September 1995 4. Protocol Specification 4.1. Common Constructs The value of the request-id field in a Response-PDU takes the value of the request-id field in the request PDU to which it is a response. By use of the request-id value, a SNMPv2 application can distinguish the (potentially multiple) outstanding requests, and thereby correlate incoming responses with outstanding requests. In cases where an unreliable datagram service is used, the request-id also provides a simple means of identifying messages duplicated by the network. Use of the same request-id on a retransmission of a request allows the response to either the original transmission or the retransmission to satisfy the request. However, in order to calculate the round trip time for transmission and processing of a request-response transaction, the SNMPv2 application needs to use a different request-id value on a retransmitted request. The latter strategy is recommended for use in the majority of situations. A non-zero value of the error-status field in a Response-PDU is used to indicate that an exception occurred to prevent the processing of the request. In these cases, a non-zero value of the Response-PDU's error- index field provides additional information by identifying which variable binding in the list caused the exception. A variable binding is identified by its index value. The first variable binding in a variable-binding list is index one, the second is index two, etc. SNMPv2 limits OBJECT IDENTIFIER values to a maximum of 128 sub- identifiers, where each sub-identifier has a maximum value of 2**32-1. 4.2. PDU Processing SNMPv2 entities acting in a manager role generate the following PDU types: GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU, SetRequest-PDU, InformRequest-PDU, Response-PDU, and Report-PDU; further, such implementations receive the following PDU types: Response-PDU, SNMPv2-Trap-PDU, InformRequest-PDU, and Report-PDU. SNMPv2 entities acting in an agent role generate the following PDU types: Response-PDU, SNMPv2-Trap-PDU, and Report-PDU; further, such implementations receive the following PDU types: GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU, and SetRequest-PDU. Expires January 1996 [Page 12] Internet Draft Protocol Operations for SNMPv2 September 1995 In the elements of procedure below, any field of a PDU which is not referenced by the relevant procedure is ignored by the receiving SNMPv2 entity. However, all components of a PDU, including those whose values are ignored by the receiving SNMPv2 entity, must have valid ASN.1 syntax and encoding. For example, some PDUs (e.g., the GetRequest-PDU) are concerned only with the name of a variable and not its value. In this case, the value portion of the variable binding is ignored by the receiving SNMPv2 entity. The unSpecified value is defined for use as the value portion of such bindings. For all generated PDUs, the message "wrapper" to encapsulate the PDU is generated according to the "Elements of Procedure" of the Administrative Framework as specified in [@ref v2admin], including the invocation of the specific procedures called for by the authentication and privacy mechanisms, if any, in effect for the message. While the definition of "max-bindings" does impose an upper-bound on the number of variable bindings, in practice, the size of a message is limited only by constraints on the maximum message size -- it is not limited by the number of variable bindings. On receiving a management communication, the message "wrapper" which encapsulates the PDU is processed according to the "Elements of Procedure" of the Administrative Framework as specified in [@ref v2admin], including the invocation of the specific procedures called for by the authentication and privacy mechanism, if any, in effect for the message. If those procedures indicate that the operation contained within the message is to be performed locally, then those procedures also indicate the MIB view which is visible to the operation, and, if applicable, the maximum message size associated with the originator of the message. 4.2.1. The GetRequest-PDU A GetRequest-PDU is generated and transmitted at the request of a SNMPv2 application. Upon receipt of a GetRequest-PDU, the receiving SNMPv2 entity processes each variable binding in the variable-binding list to produce a Response-PDU. All fields of the Response-PDU have the same values as the corresponding fields of the received request except as indicated below. Each variable binding is processed as follows: (1) If the variable binding's name exactly matches the name of a variable accessible by this request, then the variable binding's Expires January 1996 [Page 13] Internet Draft Protocol Operations for SNMPv2 September 1995 value field is set to the value of the named variable. (2) Otherwise, if the variable binding's name does not have an OBJECT IDENTIFIER prefix which exactly matches the OBJECT IDENTIFIER prefix of any (potential) variable accessible by this request, then its value field is set to `noSuchObject'. (3) Otherwise, the variable binding's value field is set to to `noSuchInstance'. If the processing of any variable binding fails for a reason other than listed above, then the Response-PDU is re-formatted with the same values in its request-id and variable-bindings fields as the received GetRequest-PDU, with the value of its error-status field set to `genErr', and the value of its error-index field is set to the index of the failed variable binding. Otherwise, the value of the Response-PDU's error-status field is set to `noError', and the value of its error-index field is zero. The generated Response-PDU is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the GetRequest-PDU. Otherwise, an alternate Response-PDU is generated. This alternate Response-PDU is formatted with the same value in its request-id field as the received GetRequest-PDU, with the value of its error-status field set to `tooBig', the value of its error-index field set to zero, and an empty variable-bindings field. This alternate Response-PDU is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the GetRequest-PDU. Otherwise, the snmpStatsSilentDrops [@ref v2mib4v2] counter is incremented and the resultant message is discarded. 4.2.2. The GetNextRequest-PDU A GetNextRequest-PDU is generated and transmitted at the request of a SNMPv2 application. Upon receipt of a GetNextRequest-PDU, the receiving SNMPv2 entity processes each variable binding in the variable-binding list to produce a Response-PDU. All fields of the Response-PDU have the same values as Expires January 1996 [Page 14] Internet Draft Protocol Operations for SNMPv2 September 1995 the corresponding fields of the received request except as indicated below. Each variable binding is processed as follows: (1) The variable is located which is in the lexicographically ordered list of the names of all variables which are accessible by this request and whose name is the first lexicographic successor of the variable binding's name in the incoming GetNextRequest-PDU. The corresponding variable binding's name and value fields in the Response-PDU are set to the name and value of the located variable. (2) If the requested variable binding's name does not lexicographically precede the name of any variable accessible by this request, i.e., there is no lexicographic successor, then the corresponding variable binding produced in the Response-PDU has its value field set to `endOfMibView', and its name field set to the variable binding's name in the request. If the processing of any variable binding fails for a reason other than listed above, then the Response-PDU is re-formatted with the same values in its request-id and variable-bindings fields as the received GetNextRequest-PDU, with the value of its error-status field set to `genErr', and the value of its error-index field is set to the index of the failed variable binding. Otherwise, the value of the Response-PDU's error-status field is set to `noError', and the value of its error-index field is zero. The generated Response-PDU is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the GetNextRequest-PDU. Otherwise, an alternate Response-PDU is generated. This alternate Response-PDU is formatted with the same values in its request-id field as the received GetNextRequest-PDU, with the value of its error-status field set to `tooBig', the value of its error-index field set to zero, and an empty variable-bindings field. This alternate Response-PDU is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the GetNextRequest-PDU. Otherwise, the snmpStatsSilentDrops [@ref v2mib4v2] counter is incremented and the resultant message is discarded. Expires January 1996 [Page 15] Internet Draft Protocol Operations for SNMPv2 September 1995 4.2.2.1. Example of Table Traversal An important use of the GetNextRequest-PDU is the traversal of conceptual tables of information within a MIB. The semantics of this type of request, together with the method of identifying individual instances of objects in the MIB, provides access to related objects in the MIB as if they enjoyed a tabular organization. In the protocol exchange sketched below, a SNMPv2 application retrieves the media-dependent physical address and the address-mapping type for each entry in the IP net-to-media Address Translation Table [@ref v2ipmib2] of a particular network element. It also retrieves the value of sysUpTime [@ref v2mib4v2], at which the mappings existed. Suppose that the agent's IP net-to-media table has three entries: Interface-Number Network-Address Physical-Address Type 1 10.0.0.51 00:00:10:01:23:45 static 1 9.2.3.4 00:00:10:54:32:10 dynamic 2 10.0.0.15 00:00:10:98:76:54 dynamic The SNMPv2 entity acting in a manager role begins by sending a GetNextRequest-PDU containing the indicated OBJECT IDENTIFIER values as the requested variable names: GetNextRequest ( sysUpTime, ipNetToMediaPhysAddress, ipNetToMediaType ) The SNMPv2 entity acting in an agent role responds with a Response-PDU: Response (( sysUpTime.0 = "123456" ), ( ipNetToMediaPhysAddress.1.9.2.3.4 = "000010543210" ), ( ipNetToMediaType.1.9.2.3.4 = "dynamic" )) The SNMPv2 entity acting in a manager role continues with: GetNextRequest ( sysUpTime, ipNetToMediaPhysAddress.1.9.2.3.4, ipNetToMediaType.1.9.2.3.4 ) Expires January 1996 [Page 16] Internet Draft Protocol Operations for SNMPv2 September 1995 The SNMPv2 entity acting in an agent role responds with: Response (( sysUpTime.0 = "123461" ), ( ipNetToMediaPhysAddress.1.10.0.0.51 = "000010012345" ), ( ipNetToMediaType.1.10.0.0.51 = "static" )) The SNMPv2 entity acting in a manager role continues with: GetNextRequest ( sysUpTime, ipNetToMediaPhysAddress.1.10.0.0.51, ipNetToMediaType.1.10.0.0.51 ) The SNMPv2 entity acting in an agent role responds with: Response (( sysUpTime.0 = "123466" ), ( ipNetToMediaPhysAddress.2.10.0.0.15 = "000010987654" ), ( ipNetToMediaType.2.10.0.0.15 = "dynamic" )) The SNMPv2 entity acting in a manager role continues with: GetNextRequest ( sysUpTime, ipNetToMediaPhysAddress.2.10.0.0.15, ipNetToMediaType.2.10.0.0.15 ) As there are no further entries in the table, the SNMPv2 entity acting in an agent role responds with the variables that are next in the lexicographical ordering of the accessible object names, for example: Response (( sysUpTime.0 = "123471" ), ( ipNetToMediaNetAddress.1.9.2.3.4 = "9.2.3.4" ), ( ipRoutingDiscards.0 = "2" )) This response signals the end of the table to the SNMPv2 entity acting in a manager role. It is worthwhile to note that the data an agent accesses may be stored internally in any arbitrary order. It is the agent's responsibility to provide external access in the prescribed lexicographic order. Expires January 1996 [Page 17] Internet Draft Protocol Operations for SNMPv2 September 1995 4.2.3. The GetBulkRequest-PDU A GetBulkRequest-PDU is generated and transmitted at the request of a SNMPv2 application. The purpose of the GetBulkRequest-PDU is to request the transfer of a potentially large amount of data, including, but not limited to, the efficient and rapid retrieval of large tables. Upon receipt of a GetBulkRequest-PDU, the receiving SNMPv2 entity processes each variable binding in the variable-binding list to produce a Response-PDU with its request-id field having the same value as in the request. Processing begins by examining the values in the non-repeaters and max-repetitions fields. If the value in the non-repeaters field is less than zero, then the value of the field is set to zero. Similarly, if the value in the max-repetitions field is less than zero, then the value of the field is set to zero. For the GetBulkRequest-PDU type, the successful processing of each variable binding in the request generates zero or more variable bindings in the Response-PDU. That is, the one-to-one mapping between the variable bindings of the GetRequest-PDU, GetNextRequest-PDU, and SetRequest-PDU types and the resultant Response-PDUs does not apply for the mapping between the variable bindings of a GetBulkRequest-PDU and the resultant Response-PDU. The values of the non-repeaters and max-repetitions fields in the request specify the processing requested. One variable binding in the Response-PDU is requested for the first N variable bindings in the request and M variable bindings are requested for each of the R remaining variable bindings in the request. Consequently, the total number of requested variable bindings communicated by the request is given by N + (M * R), where N is the minimum of: a) the value of the non-repeaters field in the request, and b) the number of variable bindings in the request; M is the value of the max-repetitions field in the request; and R is the maximum of: a) number of variable bindings in the request - N, and b) zero. The receiving SNMPv2 entity produces a Response-PDU with up to the total number of requested variable bindings communicated by the request. The request-id shall have the same value as the received GetBulkRequest-PDU. If N is greater than zero, the first through the (N)-th variable bindings of the Response-PDU are each produced as follows: (1) The variable is located which is in the lexicographically ordered list of the names of all variables which are accessible by this Expires January 1996 [Page 18] Internet Draft Protocol Operations for SNMPv2 September 1995 request and whose name is the first lexicographic successor of the variable binding's name in the incoming GetBulkRequest-PDU. The corresponding variable binding's name and value fields in the Response-PDU are set to the name and value of the located variable. (2) If the requested variable binding's name does not lexicographically precede the name of any variable accessible by this request, i.e., there is no lexicographic successor, then the corresponding variable binding produced in the Response-PDU has its value field set to `endOfMibView', and its name field set to the variable binding's name in the request. If M and R are non-zero, the (N + 1)-th and subsequent variable bindings of the Response-PDU are each produced in a similar manner. For each iteration i, such that i is greater than zero and less than or equal to M, and for each repeated variable, r, such that r is greater than zero and less than or equal to R, the (N + ( (i-1) * R ) + r)-th variable binding of the Response-PDU is produced as follows: (1) The variable which is in the lexicographically ordered list of the names of all variables which are accessible by this request and whose name is the (i)-th lexicographic successor of the (N + r)-th variable binding's name in the incoming GetBulkRequest-PDU is located and the variable binding's name and value fields are set to the name and value of the located variable. (2) If there is no (i)-th lexicographic successor, then the corresponding variable binding produced in the Response-PDU has its value field set to `endOfMibView', and its name field set to either the last lexicographic successor, or if there are no lexicographic successors, to the (N + r)-th variable binding's name in the request. While the maximum number of variable bindings in the Response-PDU is bounded by N + (M * R), the response may be generated with a lesser number of variable bindings (possibly zero) for either of three reasons. (1) If the size of the message encapsulating the Response-PDU containing the requested number of variable bindings would be greater than either a local constraint or the maximum message size of the originator, then the response is generated with a lesser number of variable bindings. This lesser number is the ordered set of variable bindings with some of the variable bindings at the end of the set removed, such that the size of the message encapsulating the Response-PDU is approximately equal to but no greater than Expires January 1996 [Page 19] Internet Draft Protocol Operations for SNMPv2 September 1995 either a local constraint or the maximum message size of the originator. Note that the number of variable bindings removed has no relationship to the values of N, M, or R. (2) The response may also be generated with a lesser number of variable bindings if for some value of iteration i, such that i is greater than zero and less than or equal to M, that all of the generated variable bindings have the value field set to the `endOfMibView'. In this case, the variable bindings may be truncated after the (N + (i * R))-th variable binding. (3) In the event that the processing of a request with many repetitions requires a significantly greater amount of processing time than a normal request, then an agent may terminate the request with less than the full number of repetitions, providing at least one repetition is completed. If the processing of any variable binding fails for a reason other than listed above, then the Response-PDU is re-formatted with the same values in its request-id and variable-bindings fields as the received GetBulkRequest-PDU, with the value of its error-status field set to `genErr', and the value of its error-index field is set to the index of the variable binding in the original request which corresponds to the failed variable binding. Otherwise, the value of the Response-PDU's error-status field is set to `noError', and the value of its error-index field to zero. The generated Response-PDU (possibly with an empty variable-bindings field) is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the GetBulkRequest-PDU. Otherwise, the snmpStatsSilentDrops [@ref v2mib4v2] counter is incremented and the resultant message is discarded. 4.2.3.1. Another Example of Table Traversal This example demonstrates how the GetBulkRequest-PDU can be used as an alternative to the GetNextRequest-PDU. The same traversal of the IP net-to-media table as shown in Section 4.2.2.1 is achieved with fewer exchanges. Expires January 1996 [Page 20] Internet Draft Protocol Operations for SNMPv2 September 1995 The SNMPv2 entity acting in a manager role begins by sending a GetBulkRequest-PDU with the modest max-repetitions value of 2, and containing the indicated OBJECT IDENTIFIER values as the requested variable names: GetBulkRequest [ non-repeaters = 1, max-repetitions = 2 ] ( sysUpTime, ipNetToMediaPhysAddress, ipNetToMediaType ) The SNMPv2 entity acting in an agent role responds with a Response-PDU: Response (( sysUpTime.0 = "123456" ), ( ipNetToMediaPhysAddress.1.9.2.3.4 = "000010543210" ), ( ipNetToMediaType.1.9.2.3.4 = "dynamic" ), ( ipNetToMediaPhysAddress.1.10.0.0.51 = "000010012345" ), ( ipNetToMediaType.1.10.0.0.51 = "static" )) The SNMPv2 entity acting in a manager role continues with: GetBulkRequest [ non-repeaters = 1, max-repetitions = 2 ] ( sysUpTime, ipNetToMediaPhysAddress.1.10.0.0.51, ipNetToMediaType.1.10.0.0.51 ) The SNMPv2 entity acting in an agent role responds with: Response (( sysUpTime.0 = "123466" ), ( ipNetToMediaPhysAddress.2.10.0.0.15 = "000010987654" ), ( ipNetToMediaType.2.10.0.0.15 = "dynamic" ), ( ipNetToMediaNetAddress.1.9.2.3.4 = "9.2.3.4" ), ( ipRoutingDiscards.0 = "2" )) This response signals the end of the table to the SNMPv2 entity acting in a manager role. Expires January 1996 [Page 21] Internet Draft Protocol Operations for SNMPv2 September 1995 4.2.4. The Response-PDU The Response-PDU is generated by a SNMPv2 entity only upon receipt of a GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU, SetRequest-PDU, or InformRequest-PDU, as described elsewhere in this document. If the error-status field of the Response-PDU is non-zero, the value fields of the variable bindings in the variable binding list are ignored. If both the error-status field and the error-index field of the Response-PDU are non-zero, then the value of the error-index field is the index of the variable binding (in the variable-binding list of the corresponding request) for which the request failed. The first variable binding in a request's variable-binding list is index one, the second is index two, etc. A compliant SNMPv2 entity acting in a manager role must be able to properly receive and handle a Response-PDU with an error-status field equal to `noSuchName', `badValue', or `readOnly', in addition to the error-status values generated by SNMPv2 entities. (See Section 3.1.2 of [@ref coex].) Upon receipt of a Response-PDU, the receiving SNMPv2 entity presents its contents to the SNMPv2 application which generated the request with the same request-id value. 4.2.5. The SetRequest-PDU A SetRequest-PDU is generated and transmitted at the request of a SNMPv2 application. Upon receipt of a SetRequest-PDU, the receiving SNMPv2 entity determines the size of a message encapsulating a Response-PDU having the same values in its request-id and variable-bindings fields as the received SetRequest-PDU, and the largest possible sizes of the error-status and error-index fields. If the determined message size is greater than either a local constraint or the maximum message size of the originator, then an alternate Response-PDU is generated, transmitted to the originator of the SetRequest-PDU, and processing of the SetRequest-PDU terminates immediately thereafter. This alternate Response-PDU is formatted with the same values in its request-id field as the received SetRequest-PDU, with the value of its error-status field set to `tooBig', the value of its error-index field set to zero, and an empty Expires January 1996 [Page 22] Internet Draft Protocol Operations for SNMPv2 September 1995 variable-bindings field. This alternate Response-PDU is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the SetRequest-PDU. Otherwise, the snmpStatsSilentDrops [@ref v2mib4v2] counter is incremented and the resultant message is discarded. Regardless, processing of the SetRequest-PDU terminates. Otherwise, the receiving SNMPv2 entity processes each variable binding in the variable-binding list to produce a Response-PDU. All fields of the Response-PDU have the same values as the corresponding fields of the received request except as indicated below. The variable bindings are conceptually processed as a two phase operation. In the first phase, each variable binding is validated; if all validations are successful, then each variable is altered in the second phase. Of course, implementors are at liberty to implement either the first, or second, or both, of these conceptual phases as multiple implementation phases. Indeed, such multiple implementation phases may be necessary in some cases to ensure consistency. The following validations are performed in the first phase on each variable binding until they are all successful, or until one fails: (1) If the variable binding's name specifies an existing or non- existent variable to which this request is/would be denied access because it is/would not be in the appropriate MIB view, then the value of the Response-PDU's error-status field is set to `noAccess', and the value of its error-index field is set to the index of the failed variable binding. (2) Otherwise, if there are no variables which share the same OBJECT IDENTIFIER prefix as the variable binding's name, and which are able to be created or modified no matter what new value is specified, then the value of the Response-PDU's error-status field is set to `notWritable', and the value of its error-index field is set to the index of the failed variable binding. (3) Otherwise, if the variable binding's value field specifies, according to the ASN.1 language, a type which is inconsistent with that required for all variables which share the same OBJECT IDENTIFIER prefix as the variable binding's name, then the value of the Response-PDU's error-status field is set to `wrongType', and the value of its error-index field is set to the index of the failed variable binding. Expires January 1996 [Page 23] Internet Draft Protocol Operations for SNMPv2 September 1995 (4) Otherwise, if the variable binding's value field specifies, according to the ASN.1 language, a length which is inconsistent with that required for all variables which share the same OBJECT IDENTIFIER prefix as the variable binding's name, then the value of the Response-PDU's error-status field is set to `wrongLength', and the value of its error-index field is set to the index of the failed variable binding. (5) Otherwise, if the variable binding's value field contains an ASN.1 encoding which is inconsistent with that field's ASN.1 tag, then the value of the Response-PDU's error-status field is set to `wrongEncoding', and the value of its error-index field is set to the index of the failed variable binding. (Note that not all implementation strategies will generate this error.) (6) Otherwise, if the variable binding's value field specifies a value which could under no circumstances be assigned to the variable, then the value of the Response-PDU's error-status field is set to `wrongValue', and the value of its error-index field is set to the index of the failed variable binding. (7) Otherwise, if the variable binding's name specifies a variable which does not exist and could not ever be created (even though some variables sharing the same OBJECT IDENTIFIER prefix might under some circumstances be able to be created), then the value of the Response-PDU's error-status field is set to `noCreation', and the value of its error-index field is set to the index of the failed variable binding. (8) Otherwise, if the variable binding's name specifies a variable which does not exist but can not be created under the present circumstances (even though it could be created under other circumstances), then the value of the Response-PDU's error-status field is set to `inconsistentName', and the value of its error- index field is set to the index of the failed variable binding. (9) Otherwise, if the variable binding's name specifies a variable which exists but can not be modified no matter what new value is specified, then the value of the Response-PDU's error-status field is set to `notWritable', and the value of its error-index field is set to the index of the failed variable binding. (10) Otherwise, if the variable binding's value field specifies a value that could under other circumstances be held by the variable, but is presently inconsistent or otherwise unable to be assigned to the Expires January 1996 [Page 24] Internet Draft Protocol Operations for SNMPv2 September 1995 variable, then the value of the Response-PDU's error-status field is set to `inconsistentValue', and the value of its error-index field is set to the index of the failed variable binding. (11) When, during the above steps, the assignment of the value specified by the variable binding's value field to the specified variable requires the allocation of a resource which is presently unavailable, then the value of the Response-PDU's error-status field is set to `resourceUnavailable', and the value of its error- index field is set to the index of the failed variable binding. (12) If the processing of the variable binding fails for a reason other than listed above, then the value of the Response-PDU's error- status field is set to `genErr', and the value of its error-index field is set to the index of the failed variable binding. (13) Otherwise, the validation of the variable binding succeeds. At the end of the first phase, if the validation of all variable bindings succeeded, then the value of the Response-PDU's error-status field is set to `noError' and the value of its error-index field is zero, and processing continues as follows. For each variable binding in the request, the named variable is created if necessary, and the specified value is assigned to it. Each of these variable assignments occurs as if simultaneously with respect to all other assignments specified in the same request. However, if the same variable is named more than once in a single request, with different associated values, then the actual assignment made to that variable is implementation-specific. If any of these assignments fail (even after all the previous validations), then all other assignments are undone, and the Response- PDU is modified to have the value of its error-status field set to `commitFailed', and the value of its error-index field set to the index of the failed variable binding. If and only if it is not possible to undo all the assignments, then the Response-PDU is modified to have the value of its error-status field set to `undoFailed', and the value of its error-index field is set to zero. Note that implementations are strongly encouraged to take all possible measures to avoid use of either `commitFailed' or `undoFailed' - these two error-status codes are not to be taken as license to take the easy way out in an implementation. Expires January 1996 [Page 25] Internet Draft Protocol Operations for SNMPv2 September 1995 Finally, the generated Response-PDU is encapsulated into a message, and transmitted to the originator of the SetRequest-PDU. 4.2.6. The SNMPv2-Trap-PDU A SNMPv2-Trap-PDU is generated and transmitted by a SNMPv2 entity acting in an agent role when an exceptional situation occurs. An SNMPv2 entity wishing to send an SNMPv2-Trap, provides: - A trap type (a snmpTrapOID.0 value) - A context local entity value - A variable binding list A variable binding list is constructed with the first two variable bindings in the variable binding list as sysUpTime.0 [@ref v2mib4v2] and snmpTrapOID.0 [@ref v2mib4v2] respectively, followed by any additional variables which the generating SNMPv2 entity provides to include within this SNMPv2-Trap-PDU. The notifyTable is scanned in conjunction with the v2ContextTable to select all notifyTable entries such that the context local entity provided by the application is equal to the context local entity associated with the context named in the notifyTable entry. For each such selected entry in which all variable bindings in the constructed variable binding list are included in the view named by that selected entry, - the values for notifySPI, notifyIdentityName, notifyContextName, and notifyTransportLabel are extracted from the selected entry; - a request id is generated, and a pdu is built with the generated value of request id, zero-valued error status and error index fields, and the constructed variable bindings list; - a ScopedPDU is constructed using the extracted value of notifyContextName, the local value of snmpID, and the just-built PDUs value; and - According to the SNMPv2 administrative model, [@ref v2admin], a requesting application must provide the required sPI, authSnmpID, Expires January 1996 [Page 26] Internet Draft Protocol Operations for SNMPv2 September 1995 identityName, ScopedPDU, and transport information in order to generate a message. Consequently, the generating entity then requests that an appropriate SnmpV2Message value be generated and sent, using - the extracted value of notifySPI as the sPI; - the local value of snmpID as the authSnmpID; - the selected entry's value of notifyIdentityName as the identityName; - the ScopedPDU value; and - the [possibly multiple] destinations named by the extracted value of notifyTransportLabel. In the interest of clarity, it is worth noting that the request-id of the generated traps is the same within a given selected notifyTable entry, but different between notifyTable entries. That is, this procedure generates potentially multiple trap messages due to potentially multiple notifyTable entries being selected and potentially multiple transportTable entries associated with one or more selections. The request-id should be the same for all traps emitted for a given event and a given notifyTable entry (where multiple messages are due to multiple transports entries), but should different for all traps emitted across various notifyTable entries. 4.2.7. The InformRequest-PDU An InformRequest-PDU is generated and transmitted at the request an application in a SNMPv2 entity acting in a manager role, that wishes to notify another application (in a SNMPv2 entity also acting in a manager role) of information known by the sending application. The destination(s) to which an InformRequest-PDU is sent is specified by the requesting application and/or in consultation with appropriate MIB objects such as the notificationTable [@ref adminmib]. The first two variable bindings in the variable binding list of an InformRequest-PDU are sysUpTime.0 [@ref v2mib4v2] and snmpTrapOID.0 [@ref v2mib4v2] respectively. If the OBJECTS clause is present in the invocation of the corresponding NOTIFICATION-TYPE macro, then each corresponding variable, as instantiated by this notification, is copied, in order, to the variable-bindings field. The application may also Expires January 1996 [Page 27] Internet Draft Protocol Operations for SNMPv2 September 1995 choose to add additional variable bindings to the InformRequest-PDU. Upon receipt of an InformRequest-PDU, the receiving SNMPv2 entity determines the size of a message encapsulating a Response-PDU with the same values in its request-id, error-status, error-index and variable- bindings fields as the received InformRequest-PDU. If the determined message size is greater than either a local constraint or the maximum message size of the originator, then an alternate Response-PDU is generated, transmitted to the originator of the InformRequest-PDU, and processing of the InformRequest-PDU terminates immediately thereafter. This alternate Response-PDU is formatted with the same values in its request-id field as the received InformRequest-PDU, with the value of its error-status field set to `tooBig', the value of its error-index field set to zero, and an empty variable-bindings field. This alternate Response-PDU is then encapsulated into a message. If the size of the resultant message is less than or equal to both a local constraint and the maximum message size of the originator, it is transmitted to the originator of the InformRequest-PDU. Otherwise, the snmpStatsSilentDrops [@ref v2mib4v2] counter is incremented and the resultant message is discarded. Regardless, processing of the InformRequest-PDU terminates. Otherwise, the receiving SNMPv2 entity: (1) presents its contents to the appropriate SNMPv2 application; (2) generates a Response-PDU with the same values in its request-id and variable-bindings fields as the received InformRequest-PDU, with the value of its error-status field is set to `noError' and the value of its error-index field is zero; and (3) transmits the generated Response-PDU to the originator of the InformRequest-PDU. 4.2.8. Report-PDU A Report-PDU is generated and transmitted at the request of the SNMPv2 protocol entity implementing the administrative model or an authentication and privacy service within that model. In this regard, messages containing Report-PDUs are somewhat akin to IP [@ref ip] messages containing ICMP [@ref icmp] information. The sending application is the SNMPv2 protocol entity itself or the authentication and privacy service. Expires January 1996 [Page 28] Internet Draft Protocol Operations for SNMPv2 September 1995 Messages containing a Report-PDU are almost always generated in response to a problem or error condition encountered when processing a received message. While processing a received communication, an SNMPv2 protocol entity may determine that the message is unacceptable. In this case, the appropriate counter from the snmpStatsGroup [@ref v2mib4v2] or from an appropriate MIB which accompanies the definition of an authentication and privacy service, e.g., [@ref newusec]. If, after incrementing the appropriate counter, the procedures require the generation of a report, then the PDU is constructed as follows: the request-id field is set to the value of the request-id of the received communication which caused the error if it can be determined, and 2147483647 otherwise; the error-status and error-index fields of the report PDU are always set to zero; and the variable-bindings field. As of this writing, all uses of the the report PDU require that the variable-bindings field contain that single variable: the identity of the statistics counter which was incremented when the error condition was detected. Future uses of the Report-PDU may include additional variable-bindings. Upon receipt of a Report-PDU, the receiving SNMPv2 protocol entity invokes the proper corrective behavior, (e.g., time synchronization, proxy error propagation, etc.), if any. Expires January 1996 [Page 29] Internet Draft Protocol Operations for SNMPv2 September 1995 5. Acknowledgements To be provided here. 6. References To be provided here. Expires January 1996 [Page 30] Internet Draft Protocol Operations for SNMPv2 September 1995 7. Security Considerations Security issues are not discussed in this memo. 8. Authors' Addresses Tell U. Later snmpv2@tis.com Expires January 1996 [Page 31] Internet Draft Protocol Operations for SNMPv2 September 1995 Table of Contents 1 Introduction .................................................... 3 1.1 A Note on Terminology ......................................... 3 2 Overview ........................................................ 4 2.1 Roles of Protocol Entities .................................... 4 2.2 Management Information ........................................ 4 2.3 Access to Management Information .............................. 5 2.4 Retransmission of Requests .................................... 5 2.5 Message Sizes ................................................. 5 2.6 Transport Mappings ............................................ 6 3 Definitions ..................................................... 7 4 Protocol Specification .......................................... 12 4.1 Common Constructs ............................................. 12 4.2 PDU Processing ................................................ 12 4.2.1 The GetRequest-PDU .......................................... 13 4.2.2 The GetNextRequest-PDU ...................................... 14 4.2.2.1 Example of Table Traversal ................................ 16 4.2.3 The GetBulkRequest-PDU ...................................... 18 4.2.3.1 Another Example of Table Traversal ........................ 20 4.2.4 The Response-PDU ............................................ 22 4.2.5 The SetRequest-PDU .......................................... 22 4.2.6 The SNMPv2-Trap-PDU ......................................... 26 4.2.7 The InformRequest-PDU ....................................... 27 4.2.8 Report-PDU .................................................. 28 5 Acknowledgements ................................................ 30 6 References ...................................................... 30 7 Security Considerations ......................................... 31 8 Authors' Addresses .............................................. 31 Expires January 1996 [Page 32] provisions for access control. The enforcement of access rights requires the means to identify the entity on whose behalf a request is generated. That is, authentication is a functional prerequisite to access control. The SNMPv2 security services described herein identify an entity on whose behalf an SNMPv2 message is generated as a "user". For the purpose of exposition, the original Internet-standard Network Management Framework, as described in RFCs 1155, 1157, and 1212, is termed the SNMP version 1 framework (SNMPv1). This document is a part