RFC 2741 (rfc2741) - Agent Extensibility (AgentX) Protocol Version 1@import 'http://faqs.org/abstracts/css/default.css';@import 'http://faqs.org/search.css';function erfc(s){document.write("[ RFC Index | RFC Search | Usenet FAQs | Web FAQs | Documents | Cities ]Alternate Formats: rfc2741.txt | rfc2741.txt.pdfRFC 2741 - Agent Extensibility (AgentX) Protocol Version 1Search the Archives  Display RFC by number RFC2741 - Agent Extensibility (AgentX) Protocol Version 1Network Working Group M. DanieleRequest for Comments: 2741 Compaq Computer CorporationObsoletes: 2257 B. WijnenCategory: Standards Track T.J. Watson Research Center, IBM Corp. M. Ellison, Ed. Ellison Software Consulting, Inc. D. Francisco. Ed. Cisco Systems, Inc. January 2000 Agent Extensibility (AgentX) Protocol Version 1Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved.Abstract This memo defines a standardized framework for extensible SNMP agents. It defines processing entities called master agents and subagents, a protocol (AgentX) used to communicate between them, and the elements of procedure by which the extensible agent processes SNMP protocol messages. This memo obsoletes RFC 2257.Table of Contents 1. Introduction.....................................................4 2. The SNMP Management Framework....................................4 2.1. A Note on Terminology........................................5 3. Extending the MIB................................................5 3.1. Motivation for AgentX........................................6 4. AgentX Framework.................................................6 4.1. AgentX Roles.................................................7 4.2. Applicability................................................8 4.3. Design Features of AgentX....................................9 4.4. Non-Goals...................................................10 5. AgentX Encodings................................................11 5.1. Object Identifier...........................................11 5.2. SearchRange.................................................13 5.3. Octet String................................................14 5.4. Value Representation........................................15 6. Protocol Definitions............................................17 6.1. AgentX PDU Header...........................................17 6.1.1. Context.................................................20 6.2. AgentX PDUs.................................................20 6.2.1. The agentx-Open-PDU.....................................20 6.2.2. The agentx-Close-PDU....................................22 6.2.3. The agentx-Register-PDU.................................23 6.2.4. The agentx-Unregister-PDU...............................27 6.2.5. The agentx-Get-PDU......................................29 6.2.6. The agentx-GetNext-PDU..................................30 6.2.7. The agentx-GetBulk-PDU..................................32 6.2.8. The agentx-TestSet-PDU..................................34 6.2.9. The agentx-CommitSet, -UndoSet, -CleanupSet PDUs........35 6.2.10. The agentx-Notify-PDU..................................36 6.2.11. The agentx-Ping-PDU....................................37 6.2.12. The agentx-IndexAllocate-PDU...........................37 6.2.13. The agentx-IndexDeallocate-PDU.........................38 6.2.14. The agentx-AddAgentCaps-PDU............................39 6.2.15. The agentx-RemoveAgentCaps-PDU.........................41 6.2.16. The agentx-Response-PDU................................43 7. Elements of Procedure...........................................45 7.1. Processing AgentX Administrative Messages...................45 7.1.1. Processing the agentx-Open-PDU..........................46 7.1.2. Processing the agentx-IndexAllocate-PDU.................47 7.1.3. Processing the agentx-IndexDeallocate-PDU...............49 7.1.4. Processing the agentx-Register-PDU......................50 7.1.4.1. Handling Duplicate and Overlapping Subtrees.........50 7.1.4.2. Registering Stuff...................................51 7.1.4.2.1. Registration Priority...........................51 7.1.4.2.2. Index Allocation................................51 7.1.4.2.3. Examples........................................53 7.1.5. Processing the agentx-Unregister-PDU....................55 7.1.6. Processing the agentx-AddAgentCaps-PDU..................55 7.1.7. Processing the agentx-RemoveAgentCaps-PDU...............55 7.1.8. Processing the agentx-Close-PDU.........................56 7.1.9. Detecting Connection Loss...............................56 7.1.10. Processing the agentx-Notify-PDU.......................56 7.1.11. Processing the agentx-Ping-PDU.........................57 7.2. Processing Received SNMP Protocol Messages..................58 7.2.1. Dispatching AgentX PDUs.................................58 7.2.1.1. agentx-Get-PDU......................................61 7.2.1.2. agentx-GetNext-PDU..................................61 7.2.1.3. agentx-GetBulk-PDU..................................62 7.2.1.4. agentx-TestSet-PDU..................................63 7.2.1.5. Dispatch............................................64 7.2.2. Subagent Processing.....................................64 7.2.3. Subagent Processing of agentx-Get, GetNext, GetBulk-PDUs65 7.2.3.1. Subagent Processing of the agentx-Get-PDU...........65 7.2.3.2. Subagent Processing of the agentx-GetNext-PDU.......66 7.2.3.3. Subagent Processing of the agentx-GetBulk-PDU.......66 7.2.4. Subagent Processing of agentx-TestSet, -CommitSet, -UndoSet, -CleanupSet-PDUs..............................67 7.2.4.1. Subagent Processing of the agentx-TestSet-PDU.......68 7.2.4.2. Subagent Processing of the agentx-CommitSet-PDU.....69 7.2.4.3. Subagent Processing of the agentx-UndoSet-PDU.......69 7.2.4.4. Subagent Processing of the agentx-CleanupSet-PDU....70 7.2.5. Master Agent Processing of AgentX Responses.............70 7.2.5.1. Common Processing of All AgentX Response PDUs.......70 7.2.5.2. Processing of Responses to agentx-Get-PDUs..........70 7.2.5.3. Processing of Responses to agentx-GetNext-PDU and agentx-GetBulk-PDU..................................71 7.2.5.4. Processing of Responses to agentx-TestSet-PDUs......72 7.2.5.5. Processing of Responses to agentx-CommitSet-PDUs....73 7.2.5.6. Processing of Responses to agentx-UndoSet-PDUs......74 7.2.6. Sending the SNMP Response-PDU...........................74 7.2.7. MIB Views...............................................74 7.3. State Transitions...........................................75 7.3.1. Set Transaction States..................................75 7.3.2. Transport Connection States.............................77 7.3.3. Session States..........................................78 8. Transport Mappings..............................................79 8.1. AgentX over TCP.............................................79 8.1.1. Well-known Values.......................................79 8.1.2. Operation...............................................79 8.2. AgentX over UNIX-domain Sockets.............................80 8.2.1. Well-known Values.......................................80 8.2.2. Operation...............................................80 9. Security Considerations.........................................81 10. Acknowledgements...............................................82 11. Authors' and Editor's Addresses................................83 12. References.....................................................84 13. Notices........................................................86 Appendix A. Changes relative to RFC 2257 ..........................87 Full Copyright Statement ..........................................911. Introduction This memo defines a standardized framework for extensible SNMP agents. It defines processing entities called master agents and subagents, a protocol (AgentX) used to communicate between them, and the elements of procedure by which the extensible agent processes SNMP protocol messages. This memo obsoletes RFC 2257. It is worth noting that most of the changes are for the purpose of clarification. The only changes affecting AgentX protocol messages on the wire are: - The agentx-Notify-PDU and agentx-Close-PDU now generate an agentx-Response-PDU - Three new error codes are available: parseFailed(266), requestDenied(267), and processingError(268) Appendix A provides a detailed list of changes relative to RFC 2257. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [27].2. The SNMP Management Framework The SNMP Management Framework presently consists of five major components: An overall architecture, described in RFC 2571 [1]. Mechanisms for describing and naming objects and events for the purpose of management. The first version of this Structure of Management Information (SMI) is called SMIv1 and described in STD 16, RFC 1155 [2], STD 16, RFC 1212 [3] and RFC 1215 [4]. The second version, called SMIv2, is described in STD 58, RFC 2578 [5], STD 58, RFC 2579 [6] and STD 58, RFC 2580 [7]. Message protocols for transferring management information. The first version of the SNMP message protocol is called SNMPv1 and described in STD 15, RFC 1157 [8]. A second version of the SNMP message protocol, which is not an Internet standards track protocol, is called SNMPv2c and described in RFC 1901 [9] and RFC 1906 [10]. The third version of the message protocol is called SNMPv3 and described in RFC 1906 [10], RFC 2572 [11] and RFC 2574 [12]. Protocol operations for accessing management information. The first set of protocol operations and associated PDU formats is described in STD 15, RFC 1157 [8]. A second set of protocol operations and associated PDU formats is described in RFC 1905 [13]. A set of fundamental applications described in RFC 2573 [14] and the view-based access control mechanism described in RFC 2575 [15]. A more detailed introduction to the current SNMP Management Framework can be found in RFC 2570 [16]. Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. Objects in the MIB are defined using the mechanisms defined in the SMI.2.1. A Note on Terminology The term "variable" refers to an instance of a non-aggregate object type defined according to the conventions set forth in the SMIv2 (STD 58, RFC 2578, [5]) or the textual conventions based on the SMIv2 (STD 58, RFC 2579 [6]). 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.3. Extending the MIB New MIB modules that extend the Internet-standard MIB are continuously being defined by various IETF working groups. It is also common for enterprises or individuals to create or extend enterprise-specific or experimental MIBs. As a result, managed devices are frequently complex collections of manageable components that have been independently installed on a managed node. Each component provides instrumentation for the managed objects defined in the MIB module(s) it implements. The SNMP framework does not describe how the set of managed objects supported by a particular agent may be changed dynamically.3.1. Motivation for AgentX This very real need to dynamically extend the management objects within a node has given rise to a variety of "extensible agents", which typically comprise - a "master" agent that is available on the standard transport address and that accepts SNMP protocol messages - a set of "subagents" that each contain management instrumentation - a protocol that operates between the master agent and subagents, permitting subagents to "connect" to the master agent, and the master agent to multiplex received SNMP protocol messages amongst the subagents. - a set of tools to aid subagent development, and a runtime (API) environment that hides much of the protocol operation between a subagent and the master agent. The wide deployment of extensible SNMP agents, coupled with the lack of Internet standards in this area, makes it difficult to field SNMP-manageable applications. A vendor may have to support several different subagent environments (APIs) in order to support different target platforms. It can also become quite cumbersome to configure subagents and (possibly multiple) master agents on a particular managed node. Specifying a standard protocol for agent extensibility (AgentX) provides the technical foundation required to solve both of these problems. Independently developed AgentX-capable master agents and subagents will be able to interoperate at the protocol level. Vendors can continue to differentiate their products in all other respects.4. AgentX Framework Within the SNMP framework, a managed node contains a processing entity, called an agent, which has access to management information. Within the AgentX framework, an agent is further defined to consist of: - a single processing entity called the master agent, which sends and receives SNMP protocol messages in an agent role (as specified by the SNMP framework documents) but typically has little or no direct access to management information. - zero or more processing entities called subagents, which are "shielded" from the SNMP protocol messages processed by the master agent, but which have access to management information. The master and subagent entities communicate via AgentX protocol messages, as specified in this memo. Other interfaces (if any) on these entities, and their associated protocols, are outside the scope of this document. While some of the AgentX protocol messages appear similar in syntax and semantics to the SNMP, bear in mind that AgentX is not SNMP. The internal operations of AgentX are invisible to an SNMP entity operating in a manager role. From a manager's point of view, an extensible agent behaves exactly as would a non-extensible (monolithic) agent that has access to the same management instrumentation. This transparency to managers is a fundamental requirement of AgentX, and is what differentiates AgentX subagents from SNMP proxy agents.4.1. AgentX Roles An entity acting in a master agent role performs the following functions: - Accepts AgentX session establishment requests from subagents. - Accepts registration of MIB regions by subagents. - Sends and accepts SNMP protocol messages on the agent's specified transport addresses. - Implements the agent role Elements of Procedure specified for the administrative framework applicable to the SNMP protocol message, except where they specify performing management operations. (The application of MIB views, and the access control policy for the managed node, are implemented by the master agent.) - Provides instrumentation for the MIB objects defined in RFC 1907 [17], and for any MIB objects relevant to any administrative framework it supports. - Sends and receives AgentX protocol messages to access management information, based on the current registry of MIB regions. - Forwards notifications on behalf of subagents. An entity acting in a subagent role performs the following functions: - Initiates AgentX sessions with the master agent. - Registers MIB regions with the master agent. - Instantiates managed objects. - Binds OIDs within its registered MIB regions to actual variables. - Performs management operations on variables. - Initiates notifications.4.2. Applicability It is intended that this memo specify the smallest amount of required behavior necessary to achieve the largest benefit, that is, to cover a very large number of possible MIB implementations and configurations with minimum complexity and low "cost of entry". This section discusses several typical usage scenarios. 1) Subagents implement separate MIB modules -- for example, subagent `A' implements "mib-2", subagent `B' implements "host-resources". It is anticipated that this will be the most common subagent configuration. 2) Subagents implement rows in a "simple table". A simple table is one in which row creation is not specified, and for which the MIB does not define an object that counts entries in the table. Examples of simple tables are rdbmsDbTable, udpTable, and hrSWRunTable. This is the most commonly defined type of MIB table, and probably represents the next most typical configuration that AgentX would support. 3) Subagents share MIBs along non-row partitions. Subagents register "chunks" of the MIB that represent multiple rows, due to the nature of the MIB's index structure. Examples include registering ipNetToMediaEntry.n, where n represents the ifIndex value for an interface implemented by the subagent, and tcpConnEntry.a.b.c.d, where a.b.c.d represents an IP address on an interface implemented by the subagent. AgentX supports these three common configurations, and all permutations of them, completely. The consensus is that they comprise a very large majority of current and likely future uses of multi-vendor extensible agent configurations. 4) Subagents implement rows in tables that permit row creation, for example, the RMON historyControlTable. To implement row creation in such tables, at least one AgentX subagent must register at a point "higher" in the OID tree than an individual row (per AgentX's dispatching procedure). 5) Subagents implement rows in tables whose MIB also defines an object that counts entries in the table, for example the MIB-2 ifTable (due to ifNumber). The subagent that implements such a counter object (like ifNumber) must go beyond AgentX to correctly implement it. This is an implementation issue (and most new MIB designs no longer include such objects). Scenarios in these latter 2 categories were thought to occur somewhat rarely in configurations where subagents are independently implemented by different vendors. The focus of a standard protocol, however, must be in just those areas where multi-vendor interoperability must be assured. Note that it would be inefficient (due to AgentX registration overhead) to share a table among AgentX subagents if the table contains very dynamic instances, and each subagent registers fully qualified instances. ipRouteTable could be an example of such a table in some environments.4.3. Design Features of AgentX The primary features of the design described in this memo are: 1) A general architectural division of labor between master agent and subagent: The master agent is MIB ignorant and SNMP omniscient, while the subagent is SNMP ignorant and MIB omniscient (for the MIB variables it instantiates). That is, master agents, exclusively, are concerned with SNMP protocol operations and the translations to and from AgentX protocol operations needed to carry them out; subagents are exclusively concerned with management instrumentation; and neither should intrude on the other's territory. 2) A standard protocol and "rules of engagement" to enable interoperability between management instrumentation and extensible agents. 3) Mechanisms for independently developed subagents to integrate into the extensible agent on a particular managed node in such a way that they need not be aware of any other existing subagents. 4) A simple, deterministic registry and dispatching algorithm. For a given extensible agent configuration, there is a single subagent who is "authoritative" for any particular region of the MIB (where "region" may extend from an entire MIB down to a single object- instance). 5) Performance considerations. It is likely that the master agent and all subagents will reside on the same host, and in such cases AgentX is more a form of inter-process communication than a traditional communications protocol. Some of the design decisions made with this in mind include: - 32-bit alignment of data within PDUs - Native byte-order encoding by subagents - Large AgentX PDU payload sizes.4.4. Non-Goals 1) Subagent-to-subagent communication. This is out of scope, due to the security ramifications and complexity involved. 2) Subagent access (via the master agent) to MIB variables. This is not addressed, since various other mechanisms are available and it was not a fundamental requirement. 3) The ability to accommodate every conceivable extensible agent configuration option. This was the most contentious aspect in the development of this protocol. In essence, certain features currently available in some commercial extensible agent products are not included in AgentX. Although useful or even vital in some implementation strategies, the rough consensus was that these features were not appropriate for an Internet Standard, or not typically required for independently developed subagents to coexist. The set of supported extensible agent configurations is described above, in Section 4.2, "Applicability". Some possible future version of the AgentX protocol may provide coverage for one or more of these "non-goals" or for new goals that might be identified after greater deployment experience.5. AgentX Encodings AgentX PDUs consist of a common header, followed by PDU-specific data of variable length. Unlike SNMP PDUs, AgentX PDUs are not encoded using the BER (as specified in ISO 8824 [18]), but are transmitted as a contiguous byte stream. The data within this stream is organized to provide natural alignment with respect to the start of the PDU, permitting direct (integer) access by the processing entities. The first four fields in the header are single-byte values. A bit (NETWORK_BYTE_ORDER) in the third field (h.flags) is used to indicate the byte ordering of all multi-byte integer values in the PDU, including those which follow in the header itself. This is described in more detail in Section 6.1, "AgentX PDU Header", below. PDUs are depicted in this memo using the following convention (where byte 1 is the first transmitted byte): +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | byte 1 | byte 2 | byte 3 | byte 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | byte 5 | byte 6 | byte 7 | byte 8 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fields marked "<reserved>" are reserved for future use and must be zero-filled.5.1. Object Identifier An object identifier is encoded as a 4-byte header, followed by a variable number of contiguous 4-byte fields representing sub- identifiers. This representation (termed Object Identifier) is as follows: Object Identifier +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | include | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Object Identifier header fields: n_subid The number (0-128) of sub-identifiers in the object identifier. An ordered list of "n_subid" 4-byte sub-identifiers follows the 4-byte header. prefix An unsigned value used to reduce the length of object identifier encodings. A non-zero value "x" is interpreted as the first sub-identifier after "internet" (1.3.6.1), and indicates an implicit prefix "internet.x" to the actual sub- identifiers encoded in the Object Identifier. For example, a prefix field value 2 indicates an implicit prefix "1.3.6.1.2". A value of 0 in the prefix field indicates there is no prefix to the sub-identifiers. include Used only when the Object Identifier is the start of a SearchRange, as described in section 5.2, "SearchRange". sub-identifier 1, 2, ... n_subid A 4-byte unsigned integer, encoded according to the header's NETWORK_BYTE_ORDER bit. A null Object Identifier consists of the 4-byte header with all bytes set to 0. Examples: sysDescr.0 (1.3.6.1.2.1.1.1.0) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4 | 2 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1.2.3.4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4 | 0 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+5.2. SearchRange A SearchRange consists of two Object Identifiers. In its communication with a subagent, the master agent uses a SearchRange to identify a requested variable binding, and, in GetNext and GetBulk operations, to set an upper bound on the names of managed object instances the subagent may send in reply. The first Object Identifier in a SearchRange (called the starting OID) indicates the beginning of the range. It is frequently (but not necessarily) the name of a requested variable binding. The "include" field in this OID's header is a boolean value (0 or 1) indicating whether or not the starting OID is included in the range. The second object identifier (ending OID) indicates the non-inclusive end of the range, and its "include" field is always 0. A null value for ending OID indicates an unbounded SearchRange. Example: To indicate a search range from 1.3.6.1.2.1.25.2 (inclusive) to 1.3.6.1.2.1.25.2.1 (exclusive), the SearchRange would be: (start) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 3 | 2 | 1 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 25 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (end) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 4 | 2 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 25 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A SearchRangeList is a contiguous list of SearchRanges.5.3. Octet String An octet string is represented by a contiguous series of bytes, beginning with a 4-byte integer (encoded according to the header's NETWORK_BYTE_ORDER bit) whose value is the number of octets in the octet string, followed by the octets themselves. This representation is termed an Octet String. If the last octet does not end on a 4- byte offset from the start of the Octet String, padding bytes are appended to achieve alignment of following data. This padding must be added even if the Octet String is the last item in the PDU. Padding bytes must be zero filled. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A null Octet String consists of a 4-byte length field set to 0.5.4. Value Representation Variable bindings may be encoded within the variable-length portion of some PDUs. The representation of a variable binding (termed a VarBind) consists of a 2-byte type field, a name (Object Identifier), and the actual value data. VarBind +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | v.type | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (v.name) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (v.data) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ VarBind fields: v.type Indicates the variable binding's syntax, and must be one of the following values: Integer (2), Octet String (4), Null (5), Object Identifier (6), IpAddress (64), Counter32 (65), Gauge32 (66), TimeTicks (67), Opaque (68), Counter64 (70), noSuchObject (128), noSuchInstance (129), endOfMibView (130) v.name The Object Identifier which names the variable. v.data The actual value, encoded as follows: - Integer, Counter32, Gauge32, and TimeTicks are encoded as 4 contiguous bytes, according to the header's NETWORK_BYTE_ORDER bit. - Counter64 is encoded as 8 contiguous bytes, according to the header's NETWORK_BYTE_ORDER bit. - Object Identifiers are encoded as described in section 5.1, Object Identifier. - IpAddress, Opaque, and Octet String are all octet strings and are encoded as described in section 5.3, "Octet String", Octet String. Note that the octets used to represent IpAddress are always ordered most significant to least significant. Value data always follows v.name whenever v.type is one of the above types. These data bytes are present even if they will not be used (as, for example, in certain types of index allocation). - Null, noSuchObject, noSuchInstance, and endOfMibView do not contain any encoded value. Value data never follows v.name in these cases. Note that the VarBind itself does not contain the value size. That information is implied for the fixed-length types, and explicitly contained in the encodings of variable-length types Object Identifier and Octet String). A VarBindList is a contiguous list of VarBinds. Within a VarBindList, a particular VarBind is identified by an index value. The first VarBind in a VarBindList has index value 1, the second has index value 2, and so on.6. Protocol Definitions6.1. AgentX PDU Header The AgentX PDU header is a fixed-format, 20-octet structure: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version | h.type | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An AgentX PDU header contains the following fields: h.version The version of the AgentX protocol (1 for this memo). h.type The PDU type; one of the following values: agentx-Open-PDU (1), agentx-Close-PDU (2), agentx-Register-PDU (3), agentx-Unregister-PDU (4), agentx-Get-PDU (5), agentx-GetNext-PDU (6), agentx-GetBulk-PDU (7), agentx-TestSet-PDU (8), agentx-CommitSet-PDU (9), agentx-UndoSet-PDU (10), agentx-CleanupSet-PDU (11), agentx-Notify-PDU (12), agentx-Ping-PDU (13), agentx-IndexAllocate-PDU (14), agentx-IndexDeallocate-PDU (15), agentx-AddAgentCaps-PDU (16), agentx-RemoveAgentCaps-PDU (17), agentx-Response-PDU (18) The set of PDU types for "administrative processing" are 1-4 and 12-17. The set of PDU types for "SNMP request processing" are 5-11. h.flags A bitmask, with bit 0 the least significant bit. The bit definitions are as follows: Bit Definition --- ---------- 0 INSTANCE_REGISTRATION 1 NEW_INDEX 2 ANY_INDEX 3 NON_DEFAULT_CONTEXT 4 NETWORK_BYTE_ORDER 5-7 (reserved) The NETWORK_BYTE_ORDER bit applies to all multi-byte integer values in the entire AgentX packet, including the remaining header fields. If set, then network byte order (most significant byte first; "big endian") is used. If not set, then least significant byte first ("little endian") is used. The NETWORK_BYTE_ORDER bit applies to all AgentX PDUs. The NON_DEFAULT_CONTEXT bit is used only in the AgentX PDUs described in section 6.1.1, "Context". The NEW_INDEX and ANY_INDEX bits are used only within the agentx-IndexAllocate-, and -IndexDeallocate-PDUs. The INSTANCE_REGISTRATION bit is used only within the agentx-Register-PDU. h.sessionID The session ID uniquely identifies a session over which AgentX PDUs are exchanged between a subagent and the master agent. The session ID has no significance and no defined value in the agentx-Open-PDU sent by a subagent to open a session with the master agent; in this case, the master agent will assign a unique session ID that it will pass back in the corresponding agentx-Response-PDU. From that point on, that same session ID will appear in every AgentX PDU exchanged over that session between the master and the subagent. A subagent may establish multiple AgentX sessions by sending multiple agentx-Open-PDUs to the master agent. In master agents that support multiple transport protocols, the sessionID should be globally unique rather than unique just to a particular transport. h.transactionID The transaction ID uniquely identifies, for a given session, the single SNMP management request (and single SNMP PDU) with which an AgentX PDU is associated. If a single SNMP management request results in multiple AgentX PDUs being sent by the master agent with the same session ID, each of these AgentX PDUs must contain the same transaction ID; conversely, AgentX PDUs sent during a particular session, that result from distinct SNMP management requests, must have distinct transaction IDs within the limits of the 32- bit field). Note that the transaction ID is not the same as the SNMP PDU's request-id (as described in section 4.1 of RFC 1905 [13], nor is it the same as the SNMP Message's msgID (as described in section 6.2 of RFC 2572 [11]), nor can it be, since a master agent might receive SNMP requests with the same request-ids or msgIDs from different managers. The transaction ID has no significance and no defined value in AgentX administrative PDUs, i.e., AgentX PDUs that are not associated with an SNMP management request. h.packetID A packet ID generated by the sender for all AgentX PDUs except the agentx-Response-PDU. In an agentx-Response-PDU, the packet ID must be the same as that in the received AgentX PDU to which it is a response. A master agent might use this field to associate subagent response PDUs with their corresponding request PDUs. A subagent might use this field to correlate responses to multiple (batched) registrations. h.payload_length The size in octets of the PDU contents, excluding the 20- byte header. As a result of the encoding schemes and PDU layouts, this value will always be either 0, or a multiple of 4.6.1.1. Context In the SNMPv1 or SNMPv2c, the community string may be used as an index into a local repository of configuration information that may include community profiles or more complex context information. In SNMPv3 this notion of "context" is formalized (see section 3.3.1 in RFC 2571 [1]. AgentX provides a mechanism for transmitting a context specification within relevant PDUs, but does not place any constraints on the content of that specification. An optional context field may be present in the agentx-Register-, UnRegister-, AddAgentCaps-, RemoveAgentCaps-, Get-, GetNext-, GetBulk-, IndexAllocate-, IndexDeallocate-, Notify-, TestSet-, and Ping- PDUs. If the NON_DEFAULT_CONTEXT bit in the AgentX header field h.flags is clear, then there is no context field in the PDU, and the operation refers to the default context. (This does not mean there is a zero- length Octet String, it means there is no Octet String present.) If the NON_DEFAULT_CONTEXT bit is set, then a context field immediately follows the AgentX header, and the operation refers to that specific context. The context is represented as an Octet String. There are no constraints on its length or contents. Thus, all of these AgentX PDUs (that is, those listed immediately above) refer to, or "indicate" a context, which is either the default context, or a non-default context explicitly named in the PDU.6.2. AgentX PDUs6.2.1. The agentx-Open-PDU An agentx-Open-PDU is generated by a subagent to request establishment of an AgentX session with the master agent. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (1) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | o.timeout | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (o.id) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | subidentifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | subidentifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (o.descr) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-Open-PDU contains the following fields: o.timeout The length of time, in seconds, that a master agent should allow to elapse after dispatching a message on a session before it regards the subagent as not responding. This is the default value for the session, and may be overridden by values associated with specific registered MIB regions. The default value of 0 indicates that there is no session-wide default value. o.id An Object Identifier that identifies the subagent. Subagents that do not support such an notion may send a null Object Identifier. o.descr An Octet String containing a DisplayString describing the subagent.6.2.2. The agentx-Close-PDU An agentx-Close-PDU issued by either a subagent or the master agent terminates an AgentX session. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (2) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | c.reason | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-Close-PDU contains the following field: c.reason An enumerated value that gives the reason that the master agent or subagent closed the AgentX session. This field may take one of the following values: reasonOther(1) None of the following reasons reasonParseError(2) Too many AgentX parse errors from peer reasonProtocolError(3) Too many AgentX protocol errors from peer reasonTimeouts(4) Too many timeouts waiting for peer reasonShutdown(5) Sending entity is shutting down reasonByManager(6) Due to Set operation; this reason code can be used only by the master agent, in response to an SNMP management request.6.2.3. The agentx-Register-PDU An agentx-Register-PDU is generated by a subagent for each region of the MIB variable naming tree (within one or more contexts) that it wishes to support. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (3) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (r.context) (OPTIONAL) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | r.timeout | r.priority | r.range_subid | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (r.subtree) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (r.upper_bound) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | optional upper-bound sub-identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-Register-PDU contains the following fields: r.context An optional non-default context. r.timeout The length of time, in seconds, that a master agent should allow to elapse after dispatching a message on a session before it regards the subagent as not responding. r.timeout applies only to messages that concern MIB objects within r.subtree. It overrides both the session's default value (if any) indicated when the AgentX session with the master agent was established, and the master agent's default timeout. The default value for r.timeout is 0 (no override). r.priority A value between 1 and 255, used to achieve a desired configuration when different sessions register identical or overlapping regions. Subagents with no particular knowledge of priority should register with the default value of 127. In the master agent's dispatching algorithm, smaller values of r.priority take precedence over larger values, as described in section 7.1.4.1, "Handling Duplicate and Overlapping Subtrees". r.subtree An Object Identifier that names the basic subtree of a MIB region for which a subagent indicates its support. The term "subtree" is used generically here, it may represent a fully-qualified instance name, a partial instance name, a MIB table, an entire MIB, etc. The choice of what to register is implementation-specific; this memo does not specify permissible values. Standard practice however is for a subagent to register at the highest level of the naming tree that makes sense. Registration of fully- qualified instances is typically done only when a subagent can perform management operations only on particular rows of a conceptual table. If r.subtree is in fact a fully qualified instance name, the INSTANCE_REGISTRATION bit in h.flags must be set, otherwise it must be cleared. The master agent may save this information to optimize subsequent operational dispatching. r.range_subid Permits specifying a range in place of one of r.subtree's sub-identifiers. If this value is 0, no range is being specified and there is no r.upper_bound field present in the PDU. In this case the MIB region being registered is the single subtree named by r.subtree. Otherwise the "r.range_subid"-th sub-identifier in r.subtree is a range lower bound, and the range upper bound sub- identifier (r.upper_bound) immediately follows r.subtree. In this case the MIB region being registered is the union of the subtrees formed by enumerating this range. Note that r.range_subid indicates the (1-based) index of this sub-identifier within the OID represented by r.subtree, regardless of whether or not r.subtree is encoded using a prefix. (See the example below.) r.upper_bound The upper bound of a sub-identifier's range. This field is present only if r.range_subid is not 0. The use of r.range_subid and r.upper_bound provide a general shorthand mechanism for specifying a MIB region. For example, if r.subtree is the OID 1.3.6.1.2.1.2.2.1.1.7, r.range_subid is 10, and r.upper_bound is 22, the specified MIB region can be denoted 1.3.6.1.2.1.2.2.1.[1-22].7. Registering this region is equivalent to registering the union of subtrees 1.3.6.1.2.1.2.2.1.1.7 1.3.6.1.2.1.2.2.1.2.7 1.3.6.1.2.1.2.2.1.3.7 ... 1.3.6.1.2.1.2.2.1.22.7 One expected use of this mechanism is registering a conceptual row with a single PDU. In the example above, the MIB region happens to be row 7 of the RFC 1573 ifTable. The actual PDU would be: (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (3) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | r.timeout | r.priority | 10 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (r.subtree) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 6 | 2 | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 7 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (r.upper_bound) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 22 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Note again that here r.range_subid is 10, even though n_subid in r.subtree is only 6. r.range_subid may be used at any level within a subtree, it need not represent row-level registration. This mechanism may be used in any way that is convenient for a subagent to achieve its registrations.6.2.4. The agentx-Unregister-PDU The agentx-Unregister-PDU is sent by a subagent to remove a MIB region that was previously registered on this session. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (4) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (u.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | <reserved> | u.priority | u.range_subid | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (u.subtree) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (u.upper_bound) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | optional upper-bound sub-identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-Unregister-PDU contains the following fields: u.context An optional non-default context. u.priority The priority at which this region was originally registered. u.subtree Indicates a previously-registered region of the MIB that a subagent no longer wishes to support. u.range_subid Indicates a sub-identifier in u.subtree is a range lower bound. u.upper_bound The upper bound of the range sub-identifier. This field is present in the PDU only if u.range_subid is not 0.6.2.5. The agentx-Get-PDU (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (5) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (g.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (g.sr) (start 1) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | include | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (end 1) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | 0 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... (start n) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | include | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (end n) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0 | 0 | 0 | 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-Get-PDU contains the following fields: g.context An optional non-default context. g.sr A SearchRangeList containing the requested variables for this session. Within the agentx-Get-PDU, the Ending OIDs within SearchRanges are null-valued Object Identifiers.6.2.6. The agentx-GetNext-PDU (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (6) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (g.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (g.sr) (start 1) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | include | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (end 1) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... (start n) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | include | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (end n) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... An agentx-GetNext-PDU contains the following fields: g.context An optional non-default context. g.sr A SearchRangeList containing the requested variables for this session.6.2.7. The agentx-GetBulk-PDU (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (7) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (g.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | g.non_repeaters | g.max_repetitions | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (g.sr) ... An agentx-GetBulk-PDU contains the following fields: g.context An optional non-default context. g.non_repeaters The number of variables in the SearchRangeList that are not repeaters. g.max_repetitions The maximum number of repetitions requested for repeating variables. g.sr A SearchRangeList containing the requested variables for this session.6.2.8. The agentx-TestSet-PDU (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (8) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (t.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (t.vb) (VarBind 1) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | v.type | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... (VarBind n) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | v.type | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-TestSet-PDU contains the following fields: t.context An optional non-default context. t.vb A VarBindList containing the requested VarBinds for this subagent.6.2.9. The agentx-CommitSet, -UndoSet, -CleanupSet PDUs These PDUs consist of the AgentX header only. The agentx-CommitSet-, -UndoSet-, and -Cleanup-PDUs are used in processing an SNMP SetRequest operation.6.2.10. The agentx-Notify-PDU An agentx-Notify-PDU is sent by a subagent to cause the master agent to forward a notification. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (12) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (n.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (n.vb) ... An agentx-Notify-PDU contains the following fields: n.context An optional non-default context. n.vb A VarBindList whose contents define the actual PDU to be sent. This memo places the following restrictions on its contents: - If the subagent supplies sysUpTime.0, it must be present as the first varbind. - snmpTrapOID.0 must be present, as the second varbind if sysUpTime.0 was supplied, as the first if it was not.6.2.11. The agentx-Ping-PDU The agentx-Ping-PDU is sent by a subagent to the master agent to monitor the master agent's ability to receive and send AgentX PDUs over their AgentX session. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (13) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (p.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-Ping-PDU may contain the following field: p.context An optional non-default context. Using p.context a subagent can retrieve the sysUpTime value for a specific context, if required.6.2.12. The agentx-IndexAllocate-PDU An agentx-IndexAllocate-PDU is sent by a subagent to request allocation of a value for specific index objects. Refer to section 7.1.4.2, "Registering Stuff", for suggested usage. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (14) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (i.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (i.vb) ... An agentx-IndexAllocate-PDU contains the following fields: i.context An optional non-default context. i.vb A VarBindList containing the index names and values requested for allocation.6.2.13. The agentx-IndexDeallocate-PDU An agentx-IndexDeallocate-PDU is sent by a subagent to release previously allocated index values. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (15) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (i.context) OPTIONAL +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Padding (as required) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (i.vb) ... An agentx-IndexDeallocate-PDU contains the following fields: i.context An optional non-default context. i.vb A VarBindList containing the index names and values to be released.6.2.14. The agentx-AddAgentCaps-PDU An agentx-AddAgentCaps-PDU is generated by a subagent to inform the master agent of agent capabilities for the specified session. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (16) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (a.context) (OPTIONAL) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Optional Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (a.id) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (a.descr) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Optional Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-AddAgentCaps-PDU contains the following fields: a.context An optional non-default context. a.id An Object Identifier containing the value of an invocation of the AGENT-CAPABILITIES macro, which the master agent exports as a value of sysORID for the indicated context. (Recall that the value of an invocation of an AGENT- CAPABILITIES macro is an object identifier that describes a precise level of support with respect to implemented MIB modules. A more complete discussion of the AGENT- CAPABILITIES macro and related sysORID values can be found in section 6 of STD 58, RFC 2580 [7].) a.descr An Octet String containing a DisplayString to be used as the value of sysORDescr corresponding to the sysORID value above.6.2.15. The agentx-RemoveAgentCaps-PDU An agentx-RemoveAgentCaps-PDU is generated by a subagent to request that the master agent stop exporting a particular value of sysORID. This value must have previously been advertised by the subagent in an agentx-AddAgentCaps-PDU for this session. (AgentX header) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (17) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (a.context) (OPTIONAL) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet String Length (L) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet 1 | Octet 2 | Octet 3 | Octet 4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Octet L - 1 | Octet L | Optional Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (a.id) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | n_subid | prefix | 0 | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-identifier #n_subid | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ An agentx-RemoveAgentCaps-PDU contains the following fields: a.context An optional non-default context. a.id An ObjectIdentifier containing the value of sysORID that should no longer be exported.6.2.16. The agentx-Response-PDU +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.version (1) | h.type (18) | h.flags | <reserved> | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.sessionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.transactionID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.packetID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | h.payload_length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | res.sysUpTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | res.error | res.index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... An agentx-Response-PDU contains the following fields: h.sessionID If this is a response to an agentx-Open-PDU, then it contains the new and unique sessionID (as assigned by the master agent) for this session. Otherwise it must be identical to the h.sessionID value in the PDU to which this PDU is a response. h.transactionID Must be identical to the h.transactionID value in the PDU to which this PDU is a response. In an agentx response PDU from the master agent to the subagent, the value of h.transactionID has no significance and can be ignored by the subagent. h.packetID Must be identical to the h.packetID value in the PDU to which this PDU is a response. res.sysUpTime This field contains the current value of sysUpTime for the context indicated within the PDU to which this PDU is a response. It is relevant only in agentx response PDUs sent from the master agent to a subagent in response to the set of administrative PDUs listed in section 6.1, "AgentX PDU Header". In an agentx response PDU from the subagent to the master agent, the value of res.sysUpTime has no significance and is ignored by the master agent. res.error Indicates error status. Within responses to the set of "administrative" PDU types listed in section 6.1, "AgentX PDU Header", values are limited to the following: noAgentXError (0), openFailed (256), notOpen (257), indexWrongType (258), indexAlreadyAllocated (259), indexNoneAvailable (260), indexNotAllocated (261), unsupportedContext (262), duplicateRegistration (263), unknownRegistration (264), unknownAgentCaps (265), parseError (266), requestDenied (267), processingError (268) Within responses to the set of "SNMP request processing" PDU types listed in section 6.1, "AgentX PDU Header", values may also include those defined for errors in the SNMPv2 PDU (RFC 1905 [13]). res.index In error cases, this is the index of the failed variable binding within a received request PDU. (Note: As explained in section 5.4, "Value Representation", the index values of variable bindings within a variable binding list are 1- based.) A VarBindList may follow res.index, depending on which AgentX PDU is being responded to. These data are specified in the subsequent elements of procedure.7. Elements of Procedure This section describes the actions of protocol entities (master agents and subagents) implementing the AgentX protocol. Note, however, that it is not intended to constrain the internal architecture of any conformant implementation. The actions of AgentX protocol entities can be broadly categorized under two headings, each of which is described separately: (1) processing AgentX administrative messages (e.g., registration requests from a subagent to a master agent); and (2) processing SNMP messages (the coordinated actions of a master agent and one or more subagents in processing, for example, a received SNMP GetRequest-PDU).7.1. Processing AgentX Administrative Messages This subsection describes the actions of AgentX protocol entities in processing AgentX administrative messages. Such messages include those involved in establishing and terminating an AgentX session between a subagent and a master agent, those by which a subagent requests allocation of instance index values, and those by which a subagent communicates to a master agent which MIB regions it supports. Processing is defined specifically for each PDU type in its own section. For the master agent, many of these PDU types require the same initial processing steps. This common processing is defined here, and referenced as needed in the PDU type-specific descriptions. Common Processing: The master agent initially processes a received AgentX PDU as follows: 1) An agentx-Response-PDU is created, res.sysUpTime is set to the value of sysUpTime.0 for the default context, res.error is set to `noAgentXError', and res.index is set to 0. 2) If the received PDU cannot be parsed, res.error is set to ` parseError'. Examples of a parse error are: - PDU length (h.payload) too short to contain current construct (Object Identifier header indicates more sub- identifiers, VarBind v.type indicates data follows, etc) - An unrecognized value is encountered for h.type, v.type, etc. 3) Otherwise, if h.sessionID does not correspond to a currently established session with this subagent, res.error is set to `notOpen'. 4) Otherwise, if the NON_DEFAULT_CONTEXT bit is set and the master agent does not support the indicated context, res.error is set to `unsupportedContext'. If the master agent does support the indicated context, the value of res.sysUpTime is set to the value of sysUpTime.0 for that context. Note: Non-default contexts might be added on the fly by the master agent, or the master agent might require such non-default contexts to be pre-configured. The choice is implementation-specific. 5) If resources cannot be allocated or some other condition prevents processing, res.error is set to `processingError'. 6) At this point, if res.error is not `noAgentXError', the received PDU is not processed further. If the received PDU's header was successfully parsed, the AgentX-Response-PDU is sent in reply. If the received PDU contained a VarBindList which was successfully parsed, the AgentX-Response-PDU contains the identical VarBindList. If the received PDU's header was not successfully parsed or for some other reason the master agent cannot send a reply, processing is complete.7.1.1. Processing the agentx-Open-PDU When the master agent receives an agentx-Open-PDU, it processes it as follows: 1) An agentx-Response-PDU is created, res.sysUpTime is set to the value of sysUpTime.0 for the default context, res.error is set to `noAgentXError', and res.index is set to 0. 2) If the received PDU cannot be parsed, res.error is set to `parseError'. 3) Otherwise, if the master agent is unable to open an AgentX session for any reason, res.error is set to `openFailed'. 4) Otherwise: The master agent assigns a sessionID to the new session and puts the value in the h.sessionID field of the agentx-Response-PDU. This value must be unique among all existing open sessions. The master agent retains session-specific information from the PDU for this session: - The NETWORK_BYTE_ORDER value in h.flags is retained. All subsequent AgentX protocol operations initiated by the master agent for this session must use this byte ordering and set this bit accordingly. The subagent typically sets this bit to correspond to its native byte ordering, and typically does not vary byte ordering for an initiated session. The master agent must be able to decode each PDU according to the h.flag NETWORK_BYTE_ORDER bit in the PDU, but does not need to toggle its retained value for the session if the subagent varies its byte ordering. - The o.timeout value is used in calculating response timeout conditions for this session. This field is also referenced in the AgentX MIB (a work-in-progress) by the agentxSessionTimeout object. - The o.id and o.descr fields are used for informational purposes. These two fields are also referenced in the AgentX MIB (a work-in-progress) by the agentxSessionObjectID object, and by the agentxSessionDescr object. 5) The agentx-Response-PDU is sent with the res.error field indicating the result of the session initiation. If processing was successful, an AgentX session is considered established between the master agent and the subagent. An AgentX session is a distinct channel for the exchange of AgentX protocol messages between a master agent and one subagent, qualified by the session-specific attributes listed in 4) above. AgentX session establishment is initiated by the subagent. An AgentX session can be terminated by either the master agent or the subagent.7.1.2. Processing the agentx-IndexAllocate-PDU When the master agent receives an agentx-IndexAllocate-PDU, it performs the common processing described in section 7.1, "Processing AgentX Administrative Messages". If as a result res.error is `noAgentXError', processing continues as follows: 1) Each VarBind in the VarBindList is processed until either all are successful, or one fails. If any VarBind fails, the agentx- Response-PDU is sent in reply containing the original VarBindList, with res.index set to indicate the failed VarBind, and with res.error set as described subsequently. All other VarBinds are ignored; no index values are allocated. VarBinds are processed as follows: - v.name is the OID prefix of the MIB OBJECT-TYPE for which a value is to be allocated. - v.type is the syntax of the MIB OBJECT-TYPE for which a value is to be allocated. - v.data indicates the specific index value requested. If the NEW_INDEX or the ANY_INDEX bit is set, the actual value in v.data is ignored and an appropriate index value is generated. a) If there are no currently allocated index values for v.name in the indicated context, and v.type does not correspond to a valid index type value, the VarBind fails and res.error is set to `indexWrongType'. b) If there are currently allocated index values for v.name in the indicated context, but the syntax of those values does not match v.type, the VarBind fails and res.error is set to `indexWrongType'. c) Otherwise, if both the NEW_INDEX and ANY_INDEX bits are clear, allocation of a specific index value is being requested. If the requested index is already allocated for v.name in the indicated context, the VarBind fails and res.error is set to `indexAlreadyAllocated'. d) Otherwise, if the NEW_INDEX bit is set, the master agent should generate the next available index value for v.name in the indicated context, with the constraint that this value must not have been allocated (even if subsequently released) to any subagent since the last re-initialization of the master agent. If no such value can be generated, the VarBind fails and res.error is set to `indexNoneAvailable'. e) Otherwise, if the ANY_INDEX bit is set, the master agent should generate an index value for v.name in the indicated context, with the constraint that this value is not currently allocated to any subagent. If no such value can be generated, then the VarBind fails and res.error is set to `indexNoneAvailable'. 2) If all VarBinds are processed successfully, the agentx-Response- PDU is sent in reply with res.error set to `noAgentXError'. A VarBindList is included that is identical to the one sent in the agentx-IndexAllocate-PDU, except that VarBinds requesting a NEW_INDEX or ANY_INDEX value are generated with an appropriate value. See section 7.1.4.2, "Registering Stuff" for more information on how subagents should perform index allocations.7.1.3. Processing the agentx-IndexDeallocate-PDU When the master agent receives an agentx-IndexDeallocate-PDU, it performs the common processing described in section 7.1, "Processing AgentX Administrative Messages". If as a result res.error is `noAgentXError', processing continues as follows: 1) Each VarBind in the VarBindList is processed until either all are successful, or one fails. If any VarBind fails, the agentx- Response-PDU is sent in reply, containing the original VarBindList, with res.index set to indicate the failed VarBind, and with res.error set as described subsequently. All other VarBinds are ignored; no index values are released. VarBinds are processed as follows: - v.name is the name of the index for which a value is to be released - v.type is the syntax of the index object - v.data indicates the specific index value to be released. The NEW_INDEX and ANY_INDEX bits are ignored. a) If the index value for the named index is not currently allocated to this session, the VarBind fails and res.error is set to `indexNotAllocated'. 2) If all VarBinds are processed successfully, res.error is set to `noAgentXError' and the agentx-Response-PDU is sent. A VarBindList is included which is identical to the one sent in the agentx-IndexDeallocate-PDU. All released index values are now available, and may be used in response to subsequent allocation requests for ANY_INDEX values and in response to subsequent allocation requests for the particular index value.7.1.4. Processing the agentx-Register-PDU When the master agent receives an agentx-Register-PDU, it performs the common processing described in section 7.1, "Processing AgentX Administrative Messages". If as a result res.error is `noAgentXError', processing continues as follows: If any of the union of subtrees defined by this MIB region is exactly the same as any subtree defined by a MIB region currently registered within the indicated context, those subtrees are termed "duplicate subtrees". If any of the union of subtrees defined by this MIB region overlaps, or is itself overlapped by, any subtree defined by a MIB region currently registered within the indicated context, those subtrees are termed "overlapping subtrees". 1) If this registration would result in duplicate subtrees registered with the same value of r.priority, the request fails and an agentx-Response-PDU is returned with res.error set to `duplicateRegistration'. 2) Otherwise, if the master agent does not wish to permit this registration for implementation-specific reasons, the request fails and an agentx-Response-PDU is returned with res.error set to `requestDenied'. 3) Otherwise, the agentx-Response-PDU is returned with res.error set to `noAgentXError'. The master agent adds this MIB region to its registration data store for the indicated context, to be considered during the dispatching phase for subsequently received SNMP protocol messages.7.1.4.1. Handling Duplicate and Overlapping Subtrees As a result of this registration algorithm there are likely to be duplicate and/or overlapping subtrees within the registration data store of the master agent. Whenever the master agent's dispatching algorithm (see section 7.2.1, "Dispatching AgentX PDUs") determines that there are multiple subtrees that could potentially contain the same MIB object instances, the master agent selects one to use, termed the 'authoritative region', as follows: 1) Choose the one whose original agentx-Register-PDU r.subtree contained the most subids, i.e., the most specific r.subtree. Note: The presence or absence of a range subid has no bearing on how "specific" one object identifier is compared to another. 2) If still ambiguous, there were duplicate subtrees. Choose the one whose original agentx-Register-PDU specified the smaller value of r.priority.7.1.4.2. Registering Stuff This section describes more fully how AgentX subagents use the agentx-IndexAllocate-PDU and agentx-Register-PDU to achieve desired configurations.7.1.4.2.1. Registration Priority The r.priority field in the agentx-Register-PDU is intended to be manipulated by human administrators to achieve a desired subagent configuration. Typically this would be needed where a legacy application registers a specific subtree, and a different (configurable) application may need to become authoritative for the identical subtree. The result of this configuration (the same subtree registered on different sessions with different priorities) is that the session using the better priority (see section 7.1.4.1, "Handling Duplicate and Overlapping Subtrees") will be authoritative. The other session will simply never be dispatched to. This is useful in the case described above, but is NOT useful in other cases, particularly when subagents share tables indexed by arbitrary values (see below). In general, subagents should register using the default priority (127).7.1.4.2.2. Index Allocation Index allocation is a service provided by an AgentX master agent. It provides generic support for sharing MIB conceptual tables among subagents who are assumed to have no knowledge of each other. The master agent maintains a database of index objects (OIDs), and, for each index, the values that have been allocated for it. It is unaware of what MIB variables (if any) the index objects represent. By convention, subagents use the MIB variable listed in the INDEX clause as the index object for which values must be allocated. For tables indexed by multiple variables, values may be allocated for each index (although this is frequently unnecessary; see example 2 below). The subagent may request allocation of a) a specific index value b) an index value that is not currently allocated c) an index value that has never been allocated The last two alternatives reflect the uniqueness and constancy requirements present in many MIB specifications for arbitrary integer indexes (e.g., ifIndex in the IF-MIB (RFC 2233 [19]), snmpFddiSMTIndex in the FDDI MIB (RFC 1285 [20]), or sysApplInstallPkgIndex in the System Application MIB (RFC 2287 [21])). The need for subagents to share tables using such indexes is the main motivation for index allocation in AgentX. It is important to note that index allocation and MIB region registration are not coupled in the master agent. The current state of index allocations is not considered when processing registration requests, and the current registry is not considered when processing index allocation requests. (This is mainly to accommodate non-AgentX subagents.) AgentX subagents should follow the model of "first request allocation of an index, then register the corresponding region". Then a successful index allocation request gives a subagent a good hint (but no guarantee) of what it should be able to register. The registration may fail (with `duplicateRegistration') because some other subagent session has already registered that row of the table. The recommended mechanism for subagents to register conceptual rows in a shared table is 1) Successfully allocate an index value. 2) Use that value to fully qualify the MIB region(s), and attempt to register using the default priority. 3) If the registration fails with `duplicateRegistration' deallocate the previously allocated index value(s) for this row and go to step 1). Note that index allocation is necessary only when the index in question is an arbitrary value, and hence the subagent has no other reasonable way to determine which index values to use. When index values have intrinsic meaning it is not expected that subagents will allocate their index values. For example, RFC 1514's table of running software processes (hrSWRunTable) is indexed by the system's native process identifier (pid). A subagent implementing the row of hrSWRunTable corresponding to its own process would simply register the region defining that row's object instances without allocating index values.7.1.4.2.3. Examples Example 1: A subagent implements an interface, and wishes to register a single row of the RFC 2233 ifTable. It requests an allocation for the index object "ifIndex", for a value that has never been allocated (since ifIndex values must be unique). The master agent returns the value "7". The subagent now attempts to register row 7 of ifTable, by specifying a MIB region in the agentx-Register-PDU of 1.3.6.1.2.1.2.2.1.[1-22].7. If the registration succeeds, no further processing is required. The master agent will dispatch to this subagent correctly. If the registration failed with `duplicateRegistration', the subagent should deallocate the failed index, request allocation of a new index i, and attempt to register ifTable.[1-22].i, until successful. Example 2: This same subagent wishes to register ipNetToMediaTable rows corresponding to its interface (ifIndex i). Due to the structure of this table, no further index allocation need be done. The subagent can register the MIB region ipNetToMediaTable.[1-4].i, It is claiming responsibility for all rows of the table whose value of ipNetToMediaIfIndex is i. Example 3: A network device consists of a set of processors, each of which accepts network connections for a unique set of IP addresses. Further, each processor contains a subagent that implements tcpConnTable. In order to represent tcpConnTable for the entire managed device, the subagents need to share tcpConnTable. In this case, no index allocation need be done at all. Each subagent can register a MIB region of tcpConnTable.[1-5].a.b.c.d, where a.b.c.d represents an unique IP address of the individual processor. Each subagent is claiming responsibility for the region of tcpConnTable where the value of tcpConnLocalAddress is a.b.c.d. Example 4: The Application Management MIB (RFC 2564 [22]) uses two objects to index several tables. A partial description of them is: applSrvIndex OBJECT-TYPE SYNTAX Unsigned32 (1..'ffffffff'h) MAX-ACCESS read-only STATUS current DESCRIPTION "An applSrvIndex is the system-unique identifier of an instance of a service. The value is unique not only across all instances of a given service, but also across all services in a system." applSrvName OBJECT-TYPE SYNTAX SnmpAdminString MAX-ACCESS read-only STATUS current DESCRIPTION "The human-readable name of a service. Where appropriate, as in the case where a service can be identified in terms of a single protocol, the strings should be established names such as those assigned by IANA and found in STD 2 [23], or defined by some other authority. In some cases private conventions apply and the string should in these cases be consistent with these non-standard conventions. An applicability statement may specify the service name(s) to be used." Since applSrvIndex is an arbitrary value, it would be reasonable for subagents to allocate values for this index. applSrvName however has intrinsic meaning and any values a subagent would use should be known a priori, hence it is not reasonable for subagents to allocate values of this index.7.1.5. Processing the agentx-Unregister-PDU When the master agent receives an agentx-Unregister-PDU, it performs the common processing described in section 7.1, "Processing AgentX Administrative Messages". If as a result res.error is ` noAgentXError', processing continues as follows: 1) If u.subtree, u.priority, u.range_subid (and if u.range_subid is not 0, u.upper_bound), and the indicated context do not match an existing registration made during this session, the agentx- Response-PDU is returned with res.error set to ` unknownRegistration'. 2) Otherwise, the agentx-Response-PDU is sent in reply with res.error set to `noAgentXError', and the previous registration is removed from the registration data store.7.1.6. Processing the agentx-AddAgentCaps-PDU When the master agent receives an agentx-AddAgentCaps-PDU, it performs the common processing described in section 7.1, "Processing AgentX Administrative Messages". If as a result res.error is ` noAgentXError', processing continues as follows: 1) The master agent adds this agent capabilities information to the sysORTable for the indicated context. An agentx-Response-PDU is sent in reply with res.error set to `noAgentXError'.7.1.7. Processing the agentx-RemoveAgentCaps-PDU When the master agent receives an agentx-RemoveAgentCaps-PDU, it performs the common processing described in section 7.1, "Processing AgentX Administrative Messages". If as a result res.error is `noAgentXError', processing continues as follows: 1) If the combination of a.id and the optional a.context does not represent a sysORTable entry that was added by this subagent during this session, the agentx-Response-PDU is returned with res.error set to `unknownAgentCaps'. 2) Otherwise the master agent deletes the corresponding sysORTable entry and sends in reply the agentx-Response-PDU, with res.error set to `noAgentXError'.7.1.8. Processing the agentx-Close-PDU When the master agent receives an agentx-Close-PDU, it performs the common processing described in section 7.1, "Processing AgentX Administrative Messages", with the exception that step 4) is not performed since the agentx-Close-PDU does may not contain a context field. If as a result res.error is `noAgentXError', processing continues as follows: 1) The master | |
