Draft Protocol Operations for SMP Jul 92 Protocol Operations for the Simple Management Protocol (SMP) Framework Sat Jul 4 17:76:04 1992 Jeffrey D. Case SNMP Research, Inc. University of Tennessee, Knoxville case@cs.utk.edu Keith McCloghrie Hughes LAN Systems kzm@hls.com Marshall T. Rose Dover Beach Consulting, Inc. mrose@dbc.mtview.ca.us Steven L. Waldbusser Carnegie Mellon University waldbusser@andrew.cmu.edu 1. 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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in Expires January 4, 1993 [Page 1] Draft Protocol Operations for SMP Jul 92 progress". Please check the 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the current status of any Internet Draft. Please send comments to the SNMP discussion group, . Expires January 4, 1993 [Page 2] Draft Protocol Operations for SMP Jul 92 2. Introduction A network management system contains: several (potentially, many) network elements, each with an associated processing entity, termed an agent, which has access to management instrumentation; at least one management station; and, a management protocol, used to convey management information between the agents and the management stations. Operations of the protocol are carried out under an administrative framework which defines both authentication and authorization policies. Network management stations execute management applications which monitor and control network elements through access to their management information. Network elements are devices such as hosts, routers, terminal servers, network monitors, etc., which are monitored and controlled through 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) [1]. The management protocol, termed the Simple Management Protocol (SMP), 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 the SMP, to define the operations of the protocol with respect to the sending and receiving of the PDUs. Expires January 4, 1993 [Page 3] Draft Protocol Operations for SMP Jul 92 3. Overview 3.1. Roles of Protocol Entities A SMP entity may operate in a manager role or an agent role. A SMP entity acts in an agent role when it performs SMP management operations in response to received SMP protocol messages (other than an inform notification) or when it sends trap notifications. A SMP entity acts in a manager role when it initiates SMP management operations by the generation of SMP protocol messages or when it performs SMP management operations in response to received trap or inform notifications. A SMP entity may support either or both roles, as dictated by its implementation and configuration. Further, a SMP 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 [2]. 3.2. 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 [3] or the textual conventions based on the SMI [4]. 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 4, 1993 [Page 4] Draft Protocol Operations for SMP Jul 92 3.3. 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 SMP entity, acting in a manager role, sends a request to a SMP entity, acting in an agent role, and the latter SMP 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 SMP entity, acting in a manager role, sends a request to a SMP entity, also acting in a manager role, and the latter SMP entity then responds to the request. This type is used to notify a SMP entity, acting in a manager role, of management information associated with another SMP entity, also acting in a manager role. The third type of access is an unconfirmed interaction, in which a SMP entity, acting in an agent role, sends a unsolicited message, termed a trap, to a SMP entity, acting in a manager role, and no response is returned. This type is used to notify a SMP entity, acting in a manager role, of an exceptional event which has resulted in changes to management information associated with the managed device. 3.4. Retransmission of Requests For all types of request 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. 3.5. Message Sizes The maximum size of an SMP message is limited the minimum of: Expires January 4, 1993 [Page 5] Draft Protocol Operations for SMP Jul 92 (1) the maximum message size which the destination SMP entity can accept; and, (2) the maximum message size which the source SMP entity can generate. The former is indicated by partyMaxMessageSize[5] of the destination party. The latter is imposed by implementation-specific local constraints. Each transport mapping for the SMP indicates the mimimum message size which a SMP 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 SMP 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 SMP 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 SMP entity acting in an agent role can generate, and the SMP 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 [6], since among other problems, it leads to a decrease in the reliability of the transfer of the messages. Thus, a SMP protocol 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. 3.6. Transport Mappings It is important to note that the exchange of SMP 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 Expires January 4, 1993 [Page 6] Draft Protocol Operations for SMP Jul 92 rules are specified elsewhere [7]. However, the preferred mapping is the use of the User Datagram Protocol [8]. Expires January 4, 1993 [Page 7] Draft Protocol Operations for SMP Jul 92 4. Definitions SMP-PDU DEFINITIONS ::= BEGIN IMPORTS ObjectName, ObjectSyntax, Integer32 FROM SMP-SMI; -- protocol data units 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, trap SMP-Trap-PDU } Expires January 4, 1993 [Page 8] Draft Protocol Operations for SMP Jul 92 -- PDUs GetRequest-PDU ::= [0] IMPLICIT PDU GetNextRequest-PDU ::= [1] IMPLICIT PDU GetBulkRequest-PDU ::= [5] IMPLICIT BulkPDU Response-PDU ::= [2] IMPLICIT PDU SetRequest-PDU ::= [3] IMPLICIT PDU -- [4] is obsolete InformRequest-PDU ::= [6] IMPLICIT PDU SMP-Trap-PDU ::= [7] IMPLICIT PDU Expires January 4, 1993 [Page 9] Draft Protocol Operations for SMP Jul 92 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) }, error-index -- sometimes ignored INTEGER (0..max-bindings), variable-bindings -- values are sometimes ignored VarBindList } Expires January 4, 1993 [Page 10] Draft Protocol Operations for SMP Jul 92 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 4, 1993 [Page 11] Draft Protocol Operations for SMP Jul 92 -- 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 4, 1993 [Page 12] Draft Protocol Operations for SMP Jul 92 5. Protocol Specification 5.1. 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 SMP 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 SMP 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. SMP limits OBJECT IDENTIFIER values to a maximum of 128 sub- identifiers, where each sub-identifier has a maximum value of 2**32-1. 5.2. PDU Processing It is mandatory that all SMP entities acting in an agent role be able to generate the following PDU types: Response-PDU and SMP-Trap-PDU; further, all such implementations must be able to receive the following PDU types: GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU, and SetRequest-PDU. Expires January 4, 1993 [Page 13] Draft Protocol Operations for SMP Jul 92 It is mandatory that all SMP entities acting in a manager role be able to generate the following PDU types: GetRequest-PDU, GetNextRequest-PDU, GetBulkRequest-PDU, SetRequest-PDU, InformRequest-PDU, and Response-PDU; further, all such implementations must be able to receive the following PDU types: Response-PDU, SMP-Trap-PDU, InformRequest-PDU; In the elements of procedure below, any field of a PDU which is not referenced by the relevant procedure is ignored by the receiving SMP entity. However, all components of a PDU, including those whose values are ignored by the receiving SMP 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 SMP 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 and transmitted as specified in [2] (as modified in [9]). The size of a message is limited only by constraints on the maximum message size, either a local limitation or the limit associated with the message's destination party, i.e., it is not limited by the number of variable bindings. On receiving a PDU, a SMP entity parses the encoded PDU. If a parse error is detected, the PDU is discarded and the relevant error counter is incremented. Otherwise, the PDU is processed according to its PDU type, in the authorization context of the source and destination parties given by the message "wrapper" which encapsulated the PDU. By definition, this authorization context indicates whether the PDU type is authorized, and determines which variables are accessible by this request. For PDU types which are not authorized, either due to policy (e.g., a SetRequest-PDU in a read-only authorization context), or due to implementation constraints (e.g., a Response-PDU received by a SMP entity acting in an agent role), the PDU is discarded and the relevant error counter is incremented. If the discarded PDU was one of following PDU types: GetRequest- PDU, GetNextRequest-PDU, GetBulkRequest-PDU, SetRequest-PDU, or InformRequest-PDU, then a Response-PDU is generated and transmitted to the originator of the request. This Response- PDU is formatted with the same values in its request-id and variable-bindings fields as the discarded PDU, with the value Expires January 4, 1993 [Page 14] Draft Protocol Operations for SMP Jul 92 of its error-status field set to `authorizationError', and the value of its error-index field set to zero. 5.2.1. The GetRequest-PDU A GetRequest-PDU is generated and transmitted at the request of a SMP application. Upon receipt of a GetRequest-PDU, the receiving SMP 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 does not have an OBJECT IDENTIFIER prefix which exactly matches the OBJECT IDENTIFIER prefix of any variable accessible by this request, then its value field is set to `noSuchObject'. (2) Otherwise, if the variable binding's name does not exactly match the name of a variable accessible by this request, then its value field is set to `noSuchInstance'. (3) Otherwise, the variable binding's value field is set to the value of the named variable. 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 request's source party, it is transmitted to the originator of the GetRequest-PDU. Expires January 4, 1993 [Page 15] Draft Protocol Operations for SMP Jul 92 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 request's source party, it is transmitted to the originator of the GetRequest-PDU. Otherwise, the resultant message is discarded. 5.2.2. The GetNextRequest-PDU A GetNextRequest-PDU is generated and transmitted at the request of a SMP application. Upon receipt of a GetNextRequest-PDU, the receiving SMP 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) 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 Expires January 4, 1993 [Page 16] Draft Protocol Operations for SMP Jul 92 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 request's source party, 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 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 request's source party, it is transmitted to the originator of the GetNextRequest-PDU. Otherwise, the resultant message is discarded. 5.2.2.1. 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 SMP application retrieves the media-dependent physical address and the address-mapping type for each entry in the IP net-to-media Address Translation Table [10] of a particular network element. It also retrieves the value of sysUpTime [10], at which the mappings existed. Suppose that the agent's IP net- to-media table has three entries: Expires January 4, 1993 [Page 17] Draft Protocol Operations for SMP Jul 92 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 SMP 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 SMP 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 SMP entity acting in a manager role continues with: GetNextRequest ( sysUpTime, ipNetToMediaPhysAddress.1.9.2.3.4, ipNetToMediaType.1.9.2.3.4 ) The SMP 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 SMP entity acting in a manager role continues with: GetNextRequest ( sysUpTime, ipNetToMediaPhysAddress.1.10.0.0.51, ipNetToMediaType.1.10.0.0.51 ) Expires January 4, 1993 [Page 18] Draft Protocol Operations for SMP Jul 92 The SMP 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 SMP 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 SMP 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 SMP entity acting in a manager role. 5.2.3. The GetBulkRequest-PDU A GetBulkRequest-PDU is generated and transmitted at the request of a SMP 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 SMP 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. Expires January 4, 1993 [Page 19] Draft Protocol Operations for SMP Jul 92 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 SMP 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 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 Expires January 4, 1993 [Page 20] Draft Protocol Operations for SMP Jul 92 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. It should be noted that this algorithm allows at least two implementation strategies, so long as the variable bindings in the Response-PDU are ordered as specified above in all cases. First, an agent might attempt to locate one variable for the first N variables followed by attempts to locate one variable for each of the remaining R variable bindings, repeating M times. An alternate strategy is to attempt to locate one variable for the first N variable bindings and to attempt to locate M variables for the remaining R variable bindings. That is, an implementer might choose to iterate within repetitions or to repeat within iterations. 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 two reasons. (1) If the size of the message encapsulating the Response-PDU containing the requested number of variable bindings Expires January 4, 1993 [Page 21] Draft Protocol Operations for SMP Jul 92 would be greater than either a local constraint or the maximum message size of the request's source party, 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 the minimum of the local constraint and the maximum message size of the request's source party. 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. 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 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 request's source party, it is transmitted to the originator of the GetBulkRequest-PDU. Otherwise, the resultant message is discarded. 5.2.3.1. Another Example of Table Traversal This example demonstrates how the GetBulkRequest-PDU can be used as an alternative to the GetNextRequest-PDU. The same Expires January 4, 1993 [Page 22] Draft Protocol Operations for SMP Jul 92 traversal of the IP net-to-media table as shown in Section 5.2.2.1 is achieved with fewer exchanges. The SMP 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 SMP 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 SMP 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 SMP 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 SMP entity acting in a manager role. Expires January 4, 1993 [Page 23] Draft Protocol Operations for SMP Jul 92 5.2.4. The Response-PDU The Response-PDU is generated by a SMP 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. Upon receipt of a Response-PDU, the receiving SMP entity presents its contents to the SMP application which generated the request with the same request-id value. 5.2.5. The SetRequest-PDU A SetRequest-PDU is generated and transmitted at the request of a SMP application. Upon receipt of a SetRequest-PDU, the receiving SMP 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 SetRequest-PDU. If the determined message size is greater than either a local constraint or the maximum message size of the request's source party, 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 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 Expires January 4, 1993 [Page 24] Draft Protocol Operations for SMP Jul 92 constraint and the maximum message size of the request's source party, it is transmitted to the originator of the SetRequest-PDU. Otherwise, the resultant message is discarded. Regardless, processing of the SetRequest-PDU terminates. Otherwise, the receiving SMP 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. 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 a variable which is not accessible by this request, 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 the variable binding's name specifies a variable which does not exist and could not ever 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. (3) 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. (4) Otherwise, if the variable binding's value field specifies, according to the ASN.1 language, a type which is inconsistent with that required for the variable, then the value of the Response-PDU's error-status field is set Expires January 4, 1993 [Page 25] Draft Protocol Operations for SMP Jul 92 to `wrongType', 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 specifies, according to the ASN.1 language, a length which is inconsistent with that required for the variable, 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. (6) 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. (7) 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. (8) Otherwise, if the variable binding's value field specifies a value that could under other circumstances be assigned to the variable, but is presently inconsistent, 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. (9) Otherwise, if 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. (10) 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 Expires January 4, 1993 [Page 26] Draft Protocol Operations for SMP Jul 92 the failed variable binding. (11) 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. 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 set to the index of the (first) variable binding for which the assignment couldn't be undone. Note that implementations are strongly encouraged to take all possible measures to avoid use of this error-status. Finally, the generated Response-PDU is encapsulated into a message, and transmitted to the originator of the SetRequest- PDU. 5.2.6. The SMP-Trap-PDU A SMP-Trap-PDU is generated and transmitted by a SMP entity acting in an agent role when an unusual event occurs. Expires January 4, 1993 [Page 27] Draft Protocol Operations for SMP Jul 92 Section 6.4 of [3] describes how the request-id and variable- bindings fields of the SMP-Trap-PDU are constructed, and also how the destinations for the SMP-Trap-PDU are determined. 5.2.7. The InformRequest-PDU An InformRequest-PDU is generated and transmitted at the request an application in a SMP entity acting in a manager role, that wishes to notify another application (in a SMP entity also acting in a manager role) of information in the MIB View of a party local to the sending application. Upon receipt of an InformRequest-PDU, the receiving SMP 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 request's source party, 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 request's source party, it is transmitted to the originator of the InformRequest-PDU. Otherwise, the resultant message is discarded. Regardless, processing of the InformRequest-PDU terminates. Otherwise, the receiving SMP entity: (1) presents its contents to the appropriate SMP 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 Expires January 4, 1993 [Page 28] Draft Protocol Operations for SMP Jul 92 (3) transmits the generated Response-PDU to the originator of the InformRequest-PDU. The destination(s) to which an InformRequest-PDU is sent is determined by inspecting the smpEventNotifyTable [11], or as specified by the requesting application. The first two variable bindings in the variable binding list of an InformRequest-PDU are sysUpTime.0 [10] and smpEventID.i [11] respectively. The other variable bindings to be included in the variable binding list are specified by the requesting application. Expires January 4, 1993 [Page 29] Draft Protocol Operations for SMP Jul 92 6. Acknowledgements This document is based, in part, on RFC 1157. The mechanism for bulk retrieval is influenced by many experiments, including RFC1187 and also Greg Satz's work on SNMP over TCP. Expires January 4, 1993 [Page 30] Draft Protocol Operations for SMP Jul 92 7. References [1] Information processing systems - Open Systems Interconnection - Specification of Abstract Syntax Notation One (ASN.1), International Organization for Standardization. International Standard 8824, (December, 1987). [2] J.R. Davin, J.M. Galvin, K. McCloghrie, SNMP Administrative Model. Request for Comments 1351, (July, 1992). [3] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, Structure of Management Information for the Simple Management Protocol (SMP) Framework, (July, 1992). [4] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, Textual Conventions for the Simple Management Protocol (SMP) Framework, (July, 1992). [5] K. McCloghrie, J.R. Davin, J.M. Galvin, Definitions of Managed Objects for Administration of SNMP Parties. Request for Comments 1353, (July, 1992). [6] C. Kent, J. Mogul, Fragmentation Considered Harmful, Proceedings, ACM SIGCOMM '87, Stowe, VT, (August 1987). [7] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, Transport Mappings for the Simple Management Protocol (SMP) Framework, (July, 1992). [8] J. Postel, User Datagram Protocol. Request for Comments 768, (November 1980). [9] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, Introduction to the Simple Management Protocol (SMP) Framework, (July, 1992). [10] K. McCloghrie and M.T. Rose, Management Information Base for Network Management of TCP/IP-based internets: MIB- II. Request for Comments 1213, (March, 1991). [11] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, Manager to Manager Management Information Base for the Simple Management Protocol (SMP) Framework, (July, 1992). Expires January 4, 1993 [Page 31] Draft Protocol Operations for SMP Jul 92 Table of Contents 1 Status of this Memo ................................... 1 2 Introduction .......................................... 3 3 Overview .............................................. 4 3.1 Roles of Protocol Entities .......................... 4 3.2 Management Information .............................. 4 3.3 Access to Management Information .................... 5 3.4 Retransmission of Requests .......................... 5 3.5 Message Sizes ....................................... 5 3.6 Transport Mappings .................................. 6 4 Definitions ........................................... 8 5 Protocol Specification ................................ 13 5.1 Common Constructs ................................... 13 5.2 PDU Processing ...................................... 13 5.2.1 The GetRequest-PDU ................................ 15 5.2.2 The GetNextRequest-PDU ............................ 16 5.2.2.1 Example of Table Traversal ...................... 17 5.2.3 The GetBulkRequest-PDU ............................ 19 5.2.3.1 Another Example of Table Traversal .............. 22 5.2.4 The Response-PDU .................................. 24 5.2.5 The SetRequest-PDU ................................ 24 5.2.6 The SMP-Trap-PDU .................................. 27 5.2.7 The InformRequest-PDU ............................. 28 6 Acknowledgements ...................................... 30 7 References ............................................ 31 Expires January 4, 1993 [Page 32]