Network Working Group D. Harrington Internet-Draft Huawei Technologies (USA) Intended status: Standards Track May 1, 2007 Expires: November 2, 2007 Transport Security Model for SNMP draft-ietf-isms-transport-security-model-04 Status of This Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 2, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This memo describes a Transport Security Model for the Simple Network Management Protocol. This memo also defines a portion of the Management Information Base (MIB) for use with network management protocols in TCP/IP based internets. In particular it defines objects for monitoring and managing the Transport Security Model for SNMP. Harrington Expires November 2, 2007 [Page 1] Internet-Draft Transport Security Model for SNMP May 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. The Internet-Standard Management Framework . . . . . . . . 3 1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Modularity . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4 1.5. Constraints . . . . . . . . . . . . . . . . . . . . . . . 4 2. How the Transport Security Model Fits in the Architecture . . 5 2.1. Security Capabilities of this Model . . . . . . . . . . . 6 2.1.1. Threats . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.2. Security Levels . . . . . . . . . . . . . . . . . . . 6 2.2. No Sessions . . . . . . . . . . . . . . . . . . . . . . . 7 2.3. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 7 2.4. Security Parameter Passing . . . . . . . . . . . . . . . . 8 2.5. Notifications and Proxy . . . . . . . . . . . . . . . . . 8 3. Cached Information and References . . . . . . . . . . . . . . 9 3.1. securityStateReference . . . . . . . . . . . . . . . . . . 9 3.2. tmStateReference . . . . . . . . . . . . . . . . . . . . . 9 4. Processing an Outgoing Message . . . . . . . . . . . . . . . . 10 4.1. Security Processing for an Outgoing Message . . . . . . . 10 4.2. securityLevel . . . . . . . . . . . . . . . . . . . . . . 11 4.3. Elements of Procedure for Outgoing Messages . . . . . . . 11 5. Processing an Incoming SNMP Message . . . . . . . . . . . . . 12 5.1. Security Processing for an Incoming Message . . . . . . . 12 5.2. Elements of Procedure for Incoming Messages . . . . . . . 12 6. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. Structure of the MIB Module . . . . . . . . . . . . . . . 13 6.2. The tsmStats Subtree . . . . . . . . . . . . . . . . . . . 14 6.3. Relationship to Other MIB Modules . . . . . . . . . . . . 14 6.3.1. Relationship to the SNMPv2-MIB . . . . . . . . . . . . 14 6.3.2. Relationship to the SNMP-FRAMEWORK-MIB . . . . . . . . 14 6.3.3. MIB Modules Required for IMPORTS . . . . . . . . . . . 14 7. MIB module definition . . . . . . . . . . . . . . . . . . . . 14 8. Security Considerations . . . . . . . . . . . . . . . . . . . 17 8.1. MIB module security . . . . . . . . . . . . . . . . . . . 18 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 10.1. Normative References . . . . . . . . . . . . . . . . . . . 19 10.2. Informative References . . . . . . . . . . . . . . . . . . 20 Appendix A. Notification Tables Configuration . . . . . . . . . . 20 A.1. Transport Security Model Processing . . . . . . . . . . . 22 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 22 Harrington Expires November 2, 2007 [Page 2] Internet-Draft Transport Security Model for SNMP May 2007 1. Introduction This memo describes a Transport Security Model for the Simple Network Management Protocol, for use with secure Transport Models in the Transport Subsystem [I-D.ietf-isms-tmsm]. This memo also defines a portion of the Management Information Base (MIB) for use with network management protocols in TCP/IP based internets. In particular it defines objects for monitoring and managing the Transport Security Model for SNMP. It is important to understand the SNMP architecture and the terminology of the architecture to understand where the Transport Security Model described in this memo fits into the architecture and interacts with other subsystems and models within the architecture. It is expected that reader will have also read and understood RFC3411 [RFC3411], RFC3412 [RFC3412], RFC3413 [RFC3413], and RFC3418 [RFC3418]. 1.1. The Internet-Standard Management Framework For a detailed overview of the documents that describe the current Internet-Standard Management Framework, please refer to section 7 of RFC 3410 [RFC3410]. Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. MIB objects are generally accessed through the Simple Network Management Protocol (SNMP). Objects in the MIB are defined using the mechanisms defined in the Structure of Management Information (SMI). This memo specifies a MIB module that is compliant to the SMIv2, which is described in STD 58, RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580 [RFC2580]. 1.2. Conventions The terms "manager" and "agent" are not used in this document, because in the RFC 3411 architecture, all SNMP entities have the capability of acting as either manager or agent or both depending on the SNMP applications included in the engine. Where distinction is required, the application names of Command Generator, Command Responder, Notification Originator, Notification Receiver, and Proxy Forwarder are used. See "SNMP Applications" [RFC3413] for further information. While security protocols frequently refer to a user, the terminology used in RFC3411 [RFC3411] and in this memo is "principal". A principal is the "who" on whose behalf services are provided or Harrington Expires November 2, 2007 [Page 3] Internet-Draft Transport Security Model for SNMP May 2007 processing takes place. A principal can be, among other things, an individual acting in a particular role; a set of individuals, with each acting in a particular role; an application or a set of applications, or a combination of these within an administrative domain. 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 [RFC2119]. 1.3. Modularity The reader is expected to have read and understood the description of the SNMP architecture, as defined in [RFC3411], and the architecture extension specified in "Transport Subsystem for the Simple Network Management Protocol" [I-D.ietf-isms-tmsm], which enables the use of external "lower layer transport" protocols to provide message security, tied into the SNMP architecture through the Transport Subsystem. The Transport Security Model is designed to work with such lower-layer secure Transport Models. In keeping with the RFC 3411 design decisions to use self-contained documents, this memo includes the elements of procedure plus associated MIB objects which are needed for processing the Transport Security Model for SNMP. These MIB objects SHOULD not be referenced in other documents. This allows the Transport Security Model to be designed and documented as independent and self-contained, having no direct impact on other modules, and allowing this module to be upgraded and supplemented as the need arises, and to move along the standards track on different time-lines from other modules. This modularity of specification is not meant to be interpreted as imposing any specific requirements on implementation. 1.4. Motivation This memo describes a Security Model to make use of Transport Models that use lower layer secure transports and existing and commonly deployed security infrastructures. This Security Model is designed to meet the security and operational needs of network administrators, maximize usability in operational environments to achieve high deployment success and at the same time minimize implementation and deployment costs to minimize the time until deployment is possible. 1.5. Constraints The design of this SNMP Security Model is also influenced by the following constraints: Harrington Expires November 2, 2007 [Page 4] Internet-Draft Transport Security Model for SNMP May 2007 1. In times of network stress, the security protocol and its underlying security mechanisms SHOULD NOT depend solely upon the ready availability of other network services (e.g., Network Time Protocol (NTP) or Authentication, Authorization, and Accounting (AAA) protocols). 2. When the network is not under stress, the Security Model and its underlying security mechanisms MAY depend upon the ready availability of other network services. 3. It may not be possible for the Security Model to determine when the network is under stress. 4. A Security Model should require no changes to the SNMP architecture. 5. A Security Model should require no changes to the underlying security protocol. 2. How the Transport Security Model Fits in the Architecture The Transport Security Model is designed to fit into the RFC3411 architecture as a Security Model in the Security Subsystem, and to utilize the services of a secure Transport Model. A cache, referenced by tmStateReference, is used to pass information between the Transport Security Model and a Transport Model, and vice versa. If the Transport Security Model is used with an insecure Transport Model, then the cache is unlikely to be populated with security parameters, which will cause the Transport Security Model to return an error (see section 5.2) If another Security Model (eg Community-based Security Model) is used with a secure Transport Model, then the cache may be populated but the other Security Model may be unaware of the cache and ignore its contents (eg deriving the securityName from the Community name in the message instead of deriving it from the cache). When the Transport Security Model is used with a secure Transport Model, the information in the cache is used by the Transport Security Model to translate between the security model-independent securityName and any identity used by the secure transport; and to record the tmSecurityLevel provided for the message by the transport (a level of security which may exceed the securityLevel requested for the message by the application). The Transport Model of an SNMP engine will perform the translation between transport-specific security parameters and the SNMP-specific, model-independent parameters securityName and securityLevel. To maintain the RFC3411 modularity, the Transport Model does not know which securityModel will be used for an incoming message; the Message Harrington Expires November 2, 2007 [Page 5] Internet-Draft Transport Security Model for SNMP May 2007 Processing Model will determine the securityModel to be used, in a Message Processing Model dependent manner. 2.1. Security Capabilities of this Model 2.1.1. Threats The Transport Security Model, when used with suitable secure Transport Models, provides protection against the threats identified by the RFC 3411 architecture [RFC3411]. Which threats are addressed depends on the Transport Model. The Transport Security Model does not address any threats itself, but delegates that responsibility to a secure Transport Model. The Transport Security Model is called a Security Model to be compatible with the RFC3411 architecture. However, this Security Model does not provide security mechanisms such as authentication and encryption itself, so it SHOULD always be used with a Transport Model that provides appropriate security. 2.1.2. Security Levels The RFC 3411 architecture recognizes three levels of security: - without authentication and without privacy (noAuthNoPriv) - with authentication but without privacy (authNoPriv) - with authentication and with privacy (authPriv) The model-independent securityLevel parameter is used to request specific levels of security for outgoing messages, and to assert that specific levels of security were applied during the transport and processing of incoming messages. The transport layer algorithms used to provide security SHOULD NOT be exposed to the Transport Security Model, as the Transport Security Model has no mechanisms by which it can test whether an assertion made by a Transport Model is accurate. The Transport Security Model trusts that the underlying secure transport connection has been properly configured to support security characteristics at least as strong as requested in securityLevel. Harrington Expires November 2, 2007 [Page 6] Internet-Draft Transport Security Model for SNMP May 2007 2.2. No Sessions The Transport Security Model will associate state regarding each message and each known remote engine with a single combination of transportDomain, transportAddress, securityName, securityModel, and securityLevel. Some Transport Models will utilize sessions to maintain long-lived state; others will use stateless transport. For reasons of module independence, the Transport Security Model will make no assumptions about there being a session of any kind. Each message may be totally independent of other messages. Any binding of multiples messages into a session is specific to the Transport Model. There may be circumstances where having an SNMP-specific session provided by a Security Model is useful; such functionality is left to future Security Models. 2.3. Coexistence There are two primary factors which determine whether Security Models can coexist. First, there must be a mechanism to select different Security Models at run-time. Second, the processing of one Security Model should not impact the processing of another Security Model. In the RFC3411 architecture, a Message Processing Model determines which Security Model should be called. As of this writing, IANA has registered four Message Processing Models (SNMPv1, SNMPv2c, SNMPv2u/ SNMPv2*, and SNMPv3) and three other Security Models (SNMPv1, SNMPv2c, and the User-based Security Model). The SNMPv1 and SNMPv2c message processing described in RFC3584 (BCP 74) [RFC3584] always selects the SNMPv1(1) Security Model for an SNMPv1 message, or the SNMPv2c(2) Security Model for an SNMPv2c message. Since there is no field in the message format that permits specifying a Security Model, RFC3584 message processing does not permit the selection of Security Models other than SNMPv1 or SNMPv2. Therefore, SNMPv1 or SNMPv2c messages that go through the SNMPv1 or SNMPv2 Message Processing Models **as defined in RFC3584** cannot use the Transport Security Model. (This does not mean an SNMPv1 or SNMPv2 message cannot use a secure transport model, only that the RFC3584 MPM will not invoke this security model.) The SNMPv2u/SNMPv2* Message Processing Model is a historic artifact for which there is no existing IETF specification. The SNMPv3 message processing defined in RFC3412 [RFC3412], extracts the securityModel from the msgSecurityModel field of an incoming SNMPv3Message. When the extracted value of msgSecurityModel is Harrington Expires November 2, 2007 [Page 7] Internet-Draft Transport Security Model for SNMP May 2007 transportSecurityModel(YY), security processing is directed to the Transport Security Model. For an outgoing message to be secured using the Transport Security Model, msgSecurityModel should be set to transportSecurityModel(YY). The Transport Security Model uses its own MIB module for processing to maintain independence from other Security Models. This allows the Transport Security Model to coexist with other Security Models, such as the User-based Security Model. Note that the Transport Security Model may work with multiple Transport Models, but the isAccessAllowed() primitive only accepts a value for the Security Model, not for Transport Models. As a result, it is not possible to have different access control rules for different Transport Models that use the Transport Security Model. 2.4. Security Parameter Passing For outgoing messages, Transport Security Model takes input provided by the SNMP application, converts that information into suitable transport and security parameters in a cache referenced by tmStateReference. The wholeMsg and the tmStateReference are passed to the appropriate Transport Model through a series of APIs, as described in "Transport Subsystem for the Simple Network Management Protocol" [I-D.ietf-isms-tmsm]. For incoming messages, the Transport Model accepts messages from the lower layer transport, and records the transport-related information and security-related information, including a securityName that represents the authenticated identity, and a securityLevel that represents the security features provided during transport, in a cache referenced by tmStateReference. The wholeMsg and the tmStateReference are passed to the appropriate Security Model through a series of APIs, as described in "Transport Subsystem for the Simple Network Management Protocol" [I-D.ietf-isms-tmsm]. 2.5. Notifications and Proxy The SNMP-TARGET-MIB module [RFC3413] contains objects for defining management targets, including transportDomain, transportAddress, securityName, securityModel, and securityLevel parameters, for applications such as notifications and proxy. For the Transport Security Model, transport type and address are configured in the snmpTargetAddrTable, and the securityModel, securityName, and securityLevel parameters are configured in the snmpTargetParamsTable. The default approach is for an administrator to statically configure this information to identify the targets authorized to receive Harrington Expires November 2, 2007 [Page 8] Internet-Draft Transport Security Model for SNMP May 2007 notifications or perform proxy. 3. Cached Information and References The RFC3411 architecture uses caches to store dynamic model-specific information, and uses references in the ASIs to indicate in a model- independent manner which cached information must flow between subsystems. There are two levels of state that may need to be maintained: the security state in a request-response pair, and potentially long-term state relating to transport and security. This document describes caches, and differentiates the tmStateReference from the securityStateReference, but how this is represented internally is an implementation decision. As a general rule, if state information is available when a message being processed gets discarded, the state related to that message should also be discarded, and if state information is available when a relationship between engines is severed, such as the closing of a transport session, the state information for that relationship might also be discarded. 3.1. securityStateReference The securityStateReference parameter is defined in RFC3411. A sample model-specific cache can be found in RFC3414 [RFC3414]. 3.2. tmStateReference For each transport session, information about the message security is stored in a cache to pass model- and mechanism-specific parameters. The state referenced by tmStateReference may be saved across multiple messages, in a Local Configuration Datastore (LCD), as compared to securityStateReference which is usually only saved for the life of a request-response pair of messages. For security reasons, if a secure transport session is closed between the time a request message is received and the corresponding response message is sent, then the response message MUST be discarded, even if a new session has been established. Each Security Model SHOULD pass a tmSameSession parameter in the tmStateReference cache for outgoing messages to indicate whether the same session must be used for the outgoing message as was used for the corresponding incoming message. The format of the cache and the LCD are implementation-specific. Harrington Expires November 2, 2007 [Page 9] Internet-Draft Transport Security Model for SNMP May 2007 4. Processing an Outgoing Message An error indication may return an OID and value for an incremented counter and a value for securityLevel, and values for contextEngineID and contextName for the counter, and the securityStateReference if the information is available at the point where the error is detected. 4.1. Security Processing for an Outgoing Message This section describes the procedure followed by the Transport Security Model. The parameters needed for generating a message are supplied to the Security Model by the Message Processing Model via the generateRequestMsg() or the generateResponseMsg() ASI. The Transport Subsystem architectural extension has added the transportDomain, transportAddress, and tmStateReference parameters to the original RFC3411 ASIs. statusInformation = -- success or errorIndication generateRequestMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN transportDomain -- (NEW) specified by application IN transportAddress -- (NEW) specified by application IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN scopedPDU -- message (plaintext) payload OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of generated message OUT tmStateReference -- (NEW) transport info ) Harrington Expires November 2, 2007 [Page 10] Internet-Draft Transport Security Model for SNMP May 2007 statusInformation = -- success or errorIndication generateResponseMsg( IN messageProcessingModel -- typically, SNMP version IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN transportDomain -- (NEW) specified by application IN transportAddress -- (NEW) specified by application IN securityModel -- for the outgoing message IN securityEngineID -- authoritative SNMP entity IN securityName -- on behalf of this principal IN securityLevel -- Level of Security requested IN scopedPDU -- message (plaintext) payload IN securityStateReference -- reference to security state -- information from original -- request OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of generated message OUT tmStateReference -- (NEW) transport info ) 4.2. securityLevel For an incoming message, the Message Processing Model specifies the requested securityLevel to the Security Model. When the Transport Security Model processes an incoming message, if the securityLevel reported by the Transport Model in the cache is less than the securityLevel requested via the processIncomingMsg ASI, it discards the message, and notifies the Message Processing Model. 4.3. Elements of Procedure for Outgoing Messages 1) If there is a securityStateReference, then this is a response message. Extract transportDomain, transportAddress, securityName, securityLevel, securityModel, and tmStateReference from the cache. The cachedSecurityData for this message can now be discarded. Set the tmSameSession parameter in the tmStateReference cache to true. 2) If there is no securityStateReference, then find or create an entry in a Local Configuration Datastore containing the provided transportDomain, transportAddress, securityName, securityLevel, and securityModel, create a tmStateReference to reference the entry. 3) Fill in the securityParameters with a zero-length OCTET STRING ('0400'). 4) Combine the message parts into a wholeMsg and calculate wholeMsgLength. Harrington Expires November 2, 2007 [Page 11] Internet-Draft Transport Security Model for SNMP May 2007 5) The wholeMsg, wholeMsgLength, securityParameters and tmStateReference are returned to the calling Message Processing Model with the statusInformation set to success. 5. Processing an Incoming SNMP Message An error indication may return an OID and value for an incremented counter and a value for securityLevel, and values for contextEngineID and contextName for the counter, and the securityStateReference if the information is available at the point where the error is detected. 5.1. Security Processing for an Incoming Message This section describes the procedure followed by the Transport Security Model whenever it receives an incoming message from a Message Processing Model. The abstract service primitive from a Message Processing Model to the Security Subsystem for a received message is: statusInformation = -- errorIndication or success -- error counter OID/value if error processIncomingMsg( IN messageProcessingModel -- typically, SNMP version IN maxMessageSize -- from the received message IN securityParameters -- from the received message IN securityModel -- from the received message IN securityLevel -- from the received message IN wholeMsg -- as received on the wire IN wholeMsgLength -- length as received on the wire IN tmStateReference -- (NEW) from the Transport Model OUT securityEngineID -- authoritative SNMP entity OUT securityName -- identification of the principal OUT scopedPDU, -- message (plaintext) payload OUT maxSizeResponseScopedPDU -- maximum size sender can handle OUT securityStateReference -- reference to security state ) -- information, needed for response 5.2. Elements of Procedure for Incoming Messages 1) Set the securityEngineID to the local snmpEngineID. 2) If the received securityParameters is not a zero-length OCTET STRING, then the snmpInASNParseErrs counter [RFC3418] is incremented, and an error indication (parseError) is returned to the calling module, and Security Model processing stops for this message. 3) If tmStateReference does not refer to a cache containing values Harrington Expires November 2, 2007 [Page 12] Internet-Draft Transport Security Model for SNMP May 2007 for securityName and securityLevel, then the tsmInvalidCache counter is incremented, an error indication is returned to the calling module, and Security Model processing stops for this message. 4) Extract the value of securityName from the cache referenced by tmStateReference. 5) The scopedPDU component is extracted from the wholeMsg. 6) The maxSizeResponseScopedPDU is calculated. This is the maximum size allowed for a scopedPDU for a possible Response message. 7) Compare the value of securityLevel in the cache referenced by tmStateReference to the value of the securityLevel parameter passed in the processIncomingMsg service primitive. If the parameter specifies privacy (Priv), and the cache specifies no privacy (noPriv) was provided by the Transport Model, or the parameter specifies authentication (auth) and the cache specifies no authentication (noAuth) was provided by the Transport Model, then the tsmInadequateSecurity counter is incremented, and an error indication (unsupportedSecurityLevel) together with the OID and value of the incremented counter is returned to the calling module. 8) The information in the tmStateReference may be saved, in an implementation-dependent manner, in a Local Configuration Datastore (LCD) for subsequent usage. 9)The security data is cached as cachedSecurityData, so that a possible response to this message can use the same security parameters. Then securityStateReference is set for subsequent reference to this cached data. For Transport Security Model, the securityStateReference should include a reference to the tmStateReference cache. 10) The statusInformation is set to success and a return is made to the calling module passing back the OUT parameters as specified in the processIncomingMsg primitive. 6. Overview This MIB module provides management of the Transport Security Model. It defines some needed textual conventions, and some statistics. 6.1. Structure of the MIB Module Objects in this MIB module are arranged into subtrees. Each subtree is organized as a set of related objects. The overall structure and assignment of objects to their subtrees, and the intended purpose of Harrington Expires November 2, 2007 [Page 13] Internet-Draft Transport Security Model for SNMP May 2007 each subtree, is shown below. 6.2. The tsmStats Subtree This subtree contains counters specific to the Transport Security Model, that provide information for identifying fault conditions. 6.3. Relationship to Other MIB Modules Some management objects defined in other MIB modules are applicable to an entity implementing the Transport Security Model In particular, it is assumed that an entity implementing the Transport Security Model will implement the SNMPv2-MIB [RFC3418] and the SNMP-FRAMEWORK- MIB [RFC3411]. 6.3.1. Relationship to the SNMPv2-MIB The 'system' group in the SNMPv2-MIB [RFC3418] is defined as being mandatory for all systems, and the objects apply to the entity as a whole. The 'system' group provides identification of the management entity and certain other system-wide data. The snmpInASNParseErrs counter is incremented during the elements of procedure. The SNMP- TRANSPORT-SM-MIB does not duplicate those objects. 6.3.2. Relationship to the SNMP-FRAMEWORK-MIB The SNMP-FRAMEWORK-MIB provides definitions for the concepts of SnmpEngineID, enumeration of Message Processing Models, Security Models and Security Levels, and object definitions for snmpEngineID These are important for implementing the Transport Security Model, but are not needed to implement the SNMP-TRANSPORT-SM-MIB. 6.3.3. MIB Modules Required for IMPORTS The following MIB module imports items from [RFC2578] and [RFC2580]. 7. MIB module definition SNMP-TRANSPORT-SM-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, snmpModules, Counter32 FROM SNMPv2-SMI MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF ; Harrington Expires November 2, 2007 [Page 14] Internet-Draft Transport Security Model for SNMP May 2007 tsmMIB MODULE-IDENTITY LAST-UPDATED "200701250000Z" ORGANIZATION "ISMS Working Group" CONTACT-INFO "WG-EMail: isms@lists.ietf.org Subscribe: isms-request@lists.ietf.org Chairs: Juergen Quittek NEC Europe Ltd. Network Laboratories Kurfuersten-Anlage 36 69115 Heidelberg Germany +49 6221 90511-15 quittek@netlab.nec.de Juergen Schoenwaelder International University Bremen Campus Ring 1 28725 Bremen Germany +49 421 200-3587 j.schoenwaelder@iu-bremen.de Editor: David Harrington Huawei Technologies USA 1700 Alma Dr. Plano TX 75075 USA +1 603-436-8634 ietfdbh@comcast.net " DESCRIPTION "The Transport Security Model MIB Copyright (C) The IETF Trust (2007). This version of this MIB module is part of RFC XXXX; see the RFC itself for full legal notices. -- NOTE to RFC editor: replace XXXX with actual RFC number -- for this document and remove this note " REVISION "200701250000Z" DESCRIPTION "The initial version, published in RFC XXXX. -- NOTE to RFC editor: replace XXXX with actual RFC number -- for this document and remove this note " Harrington Expires November 2, 2007 [Page 15] Internet-Draft Transport Security Model for SNMP May 2007 ::= { snmpModules xxxx } -- RFC Ed.: replace xxxx with IANA-assigned number and -- remove this note -- ---------------------------------------------------------- -- -- subtrees in the SNMP-TRANSPORT-SM-MIB -- ---------------------------------------------------------- -- tsmNotifications OBJECT IDENTIFIER ::= { tsmMIB 0 } tsmMIBObjects OBJECT IDENTIFIER ::= { tsmMIB 1 } tsmConformance OBJECT IDENTIFIER ::= { tsmMIB 2 } -- ------------------------------------------------------------- -- Objects -- ------------------------------------------------------------- -- Statistics for the Transport Security Model tsmStats OBJECT IDENTIFIER ::= { tsmMIBObjects 1 } tsmInvalidCache OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of messages dropped because the tmStateReference referred to an invalid cache. This value is not persistent across reboots. " ::= { tsmStats 1 } tsmInadequateSecurity OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of incoming messages dropped because the actual securityLevel provided was less than the requested securityLevel. This value is not persistent across reboots. " ::= { tsmStats 2 } -- ------------------------------------------------------------- -- tsmMIB - Conformance Information -- ------------------------------------------------------------- Harrington Expires November 2, 2007 [Page 16] Internet-Draft Transport Security Model for SNMP May 2007 tsmGroups OBJECT IDENTIFIER ::= { tsmConformance 1 } tsmCompliances OBJECT IDENTIFIER ::= { tsmConformance 2 } -- ------------------------------------------------------------- -- Units of conformance -- ------------------------------------------------------------- tsmGroup OBJECT-GROUP OBJECTS { tsmInvalidCache, tsmInadequateSecurity } STATUS current DESCRIPTION "A collection of objects for maintaining information of an SNMP engine which implements the SNMP Transport Security Model. " ::= { tsmGroups 2 } -- ------------------------------------------------------------- -- Compliance statements -- ------------------------------------------------------------- tsmCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP engines that support the SNMP-TRANSPORT-SM-MIB" MODULE MANDATORY-GROUPS { tsmGroup } ::= { tsmCompliances 1 } END 8. Security Considerations This document describes a Security Model that permits SNMP to utilize security services provided through an SNMP Transport Model. The Transport Security Model relies on Transport Models for mutual authentication, binding of keys, confidentiality and integrity. The security threats and how those threats are mitigated should be covered in detail in the specification of the Transport Model and the underlying secure transport. Transport Security Model relies on a Transport Model to provide an authenticated principal for mapping to securityName, and an assertion Harrington Expires November 2, 2007 [Page 17] Internet-Draft Transport Security Model for SNMP May 2007 for mapping to securityLevel. The Transport Security Model is called a Security Model to be compatible with the RFC3411 architecture. However, this Security Model provides no security itself. It SHOULD always be used with a Transport Model that provides security, but this is a run-time decision of the operator or management application, or a configuration decision of an operator. 8.1. MIB module security There are no management objects defined in this MIB module that have a MAX-ACCESS clause of read-write and/or read-create. So, if this MIB module is implemented correctly, then there is no risk that an intruder can alter or create any management objects of this MIB module via direct SNMP SET operations. Some of the readable objects in this MIB module (i.e., objects with a MAX-ACCESS other than not-accessible) may be considered sensitive or vulnerable in some network environments. It is thus important to control even GET and/or NOTIFY access to these objects and possibly to even encrypt the values of these objects when sending them over the network via SNMP. These are the tables and objects and their sensitivity/vulnerability: o tsmInvalidCache and tsmInadequateSecurity may make it easier for an attacker to detect vulnerabilities. SNMP versions prior to SNMPv3 did not include adequate security. Even if the network itself is secure (for example by using IPsec), even then, there is no control as to who on the secure network is allowed to access and GET/SET (read/change/create/delete) the objects in this MIB module. It is RECOMMENDED that implementers consider the security features as provided by the SNMPv3 framework (see [RFC3410] section 8), including full support for the USM and Transport Security Model cryptographic mechanisms (for authentication and privacy). Further, deployment of SNMP versions prior to SNMPv3 is NOT RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to enable cryptographic security. It is then a customer/operator responsibility to ensure that the SNMP entity giving access to an instance of this MIB module is properly configured to give access to the objects only to those principals (users) that have legitimate rights to indeed GET or SET (change/create/delete) them. Harrington Expires November 2, 2007 [Page 18] Internet-Draft Transport Security Model for SNMP May 2007 9. IANA Considerations IANA is requested to assign: 1. an SMI number under snmpModules, for the MIB module in this document, 2. a value, preferably 4, to identify the Transport Security Model, in the Security Models registry at http://www.iana.org/assignments/snmp-number-spaces. This should result in the following table of values: Value Description References ----- ----------- ---------- 0 reserved for 'any' [RFC2571, RFC3411] 1 reserved for SNMPv1 [RFC2571, RFC3411] 2 reserved for SNMPv2c [RFC2571, RFC3411] 3 User-Based Security Model (USM) [RFC2571, RFC3411] YY Transport Security Model (TSM) [RFCXXXX] -- NOTE to RFC editor: replace XXXX with actual RFC number -- for this document and remove this note -- NOTE to RFC editor: replace YY with actual IANA-assigned number, throughout this document and remove this note. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999. [RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999. [RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture for Describing Simple Network Harrington Expires November 2, 2007 [Page 19] Internet-Draft Transport Security Model for SNMP May 2007 Management Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, December 2002. [RFC3412] Case, J., Harrington, D., Presuhn, R., and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3412, December 2002. [RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network Management Protocol (SNMP) Applications", STD 62, RFC 3413, December 2002. [RFC3418] Presuhn, R., "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3418, December 2002. [I-D.ietf-isms-tmsm] Harrington, D. and J. Schoenwaelder, "Transport Subsystem for the Simple Network Management Protocol (SNMP)", draft-ietf-isms-tmsm-07 (work in progress), March 2007. 10.2. Informative References [RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart, "Introduction and Applicability Statements for Internet-Standard Management Framework", RFC 3410, December 2002. [RFC3414] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", STD 62, RFC 3414, December 2002. [RFC3584] Frye, R., Levi, D., Routhier, S., and B. Wijnen, "Coexistence between Version 1, Version 2, and Version 3 of the Internet-standard Network Management Framework", BCP 74, RFC 3584, August 2003. Appendix A. Notification Tables Configuration The SNMP-TARGET-MIB and SNMP-NOTIFICATION-MIB [RFC3413] are used to configure notification originators with the destinations to which notifications should be sent. Most of the configuration is security-model-independent and transport-model-independent. Harrington Expires November 2, 2007 [Page 20] Internet-Draft Transport Security Model for SNMP May 2007 The values we will use in the examples for the five model-independent security and transport parameters are: transportDomain = snmpSSHDomain transportAddress = 192.0.2.1:162 securityModel = Transport Security Model securityName = sampleUser securityLevel = authPriv The following example will configure the Notification Originator to send informs to a Notification Receiver at host 192.0.2.1 port 162 using the securityName "sampleUser". The columns marked with a "*" are the items that are Security Model or Transport Model specific. The configuration for the "sampleUser" settings in the SNMP-VIEW- BASED-ACM-MIB objects are not shown here for brevity. First we configure which type of notification should be sent for this taglist (toCRTag). In this example, we choose to send an Inform. snmpNotifyTable row: snmpNotifyName CRNotif snmpNotifyTag toCRTag snmpNotifyType inform snmpNotifyStorageType nonVolatile snmpNotifyColumnStatus createAndGo Then we configure a transport address to which notifications associated with this taglist should be sent, and we specify which snmpTargetParamsEntry should be used (toCR) when sending to this transport address. snmpTargetAddrTable row: snmpTargetAddrName toCRAddr * snmpTargetAddrTDomain snmpSSHDomain snmpTargetAddrTAddress 192.0.2.1:162 snmpTargetAddrTimeout 1500 snmpTargetAddrRetryCount 3 snmpTargetAddrTagList toCRTag snmpTargetAddrParams toCR (must match below) snmpTargetAddrStorageType nonVolatile snmpTargetAddrColumnStatus createAndGo Then we configure which principal at the host should receive the notifications associated with this taglist. Here we choose "sampleUser", who uses the Transport Security Model. Harrington Expires November 2, 2007 [Page 21] Internet-Draft Transport Security Model for SNMP May 2007 snmpTargetParamsTable row: snmpTargetParamsName toCR snmpTargetParamsMPModel SNMPv3 * snmpTargetParamsSecurityModel TransportSecurityModel snmpTargetParamsSecurityName "sampleUser" snmpTargetParamsSecurityLevel authPriv snmpTargetParamsStorageType nonVolatile snmpTargetParamsRowStatus createAndGo A.1. Transport Security Model Processing The Transport Security Model is called using the generateRequestMsg() ASI, with the following parameters (* are from the above tables): statusInformation = -- success or errorIndication generateRequestMsg( IN messageProcessingModel -- *snmpTargetParamsMPModel IN globalData -- message header, admin data IN maxMessageSize -- of the sending SNMP entity IN transportDomain -- *snmpTargetAddrTDomain IN transportAddress -- *snmpTargetAddrTAddress IN securityModel -- *snmpTargetParamsSecurityModel IN securityEngineID -- immaterial; TSM will ignore. IN securityName -- snmpTargetParamsSecurityName IN securityLevel -- *snmpTargetParamsSecurityLevel IN scopedPDU -- message (plaintext) payload OUT securityParameters -- filled in by Security Module OUT wholeMsg -- complete generated message OUT wholeMsgLength -- length of generated message OUT tmStateReference -- reference to transport info ) The Transport Security Model will determine the Transport Model based on the snmpTargetAddrTDomain. The selected Transport Model will select the appropriate transport "session" using the snmpTargetAddrTAddress, snmpTargetParamsSecurityName, and snmpTargetParamsSecurityLevel. Appendix B. Change Log From -03- to -04- Editorial changes requested by Tom Petch, to clarify behavior with SNMPv1/v2c Added early discussion of how TSM fits into the architecture to clarify behavior when RFC3584 security models are co-resident. Harrington Expires November 2, 2007 [Page 22] Internet-Draft Transport Security Model for SNMP May 2007 Editorial changes requested by Bert Wijnen, to eliminate version- specific discussions. Removed sections on version-specific message formats. Removed discussion of SNMPv3 in Motivation section. Added discussion of request/response session matching. From -02- to -03- Editorial changes suggested by Juergen Schoenwaelder Capitalized Transport Models, Security Models, and Message Processing Models, to be consistent with RFC341x conventions. Eliminated some text that duplicated RFC3412, especially in Elements of Procedure. Changed the encoding of msgSecurityParameters Marked the (NEW) fields added to existing ASIs Modified text intro discussing relationships to other MIB modules. From -01- to -02- Changed transportSecurityModel(4) to transportSecurityModel(YY), waiting for assignment cleaned up elements of procedure [todo]s use the same errorIndication as USM for unsupportedSecurityLevel fixed syntax of tsmInadequateSecurity counter changed the "can and will use" the same security parameters to "can use", to allow responses that have different security parameters than the request. removed "Relationship to the SNMP-FRAMEWORK-MIB" cleaned up "MIB Modules Required for IMPORTS" Harrington Expires November 2, 2007 [Page 23] Internet-Draft Transport Security Model for SNMP May 2007 From -00- to -01- made the Transport Model not know anything about the Security Model. modified the elements of procedure sections, given the implications of this change. simplified elements of procedure, removing most info specified in architecture/subsystem definitions. rethought the coexistence section noted the implications of the Transport Security Model on isAccessAllowed() modified all text related to the LCD. removed most of the MIB (now the TSM has no configuration parameters). added counters needed to support elements of procedure renamed MIB module, and registered under snmpModules updated IANA and Security Considerations updated references. modified the notification configurations. From SSHSM-04- to Transport-security-model-00 added tsmUserTable updated Appendix - Notification Tables Configuration remove open/closed issue appendices changed tmSessionReference to tmStateReference Harrington Expires November 2, 2007 [Page 24] Internet-Draft Transport Security Model for SNMP May 2007 Author's Address David Harrington Huawei Technologies (USA) 1700 Alma Dr. Suite 100 Plano, TX 75075 USA Phone: +1 603 436 8634 EMail: dharrington@huawei.com Harrington Expires November 2, 2007 [Page 25] Internet-Draft Transport Security Model for SNMP May 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Harrington Expires November 2, 2007 [Page 26]