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RFC 5953: Transport Layer Security (TLS) Transport Model for the Simple Network Management Protocol (SNMP)
- W. Hardaker
Proposed Standard
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Internet Engineering Task Force (IETF) W. Hardaker Request for Comments: 5953 SPARTA, Inc. Category: Standards Track August 2010 ISSN: 2070-1721 Transport Layer Security (TLS) Transport Model for the Simple Network Management Protocol (SNMP) Abstract This document describes a Transport Model for the Simple Network Management Protocol (SNMP), that uses either the Transport Layer Security protocol or the Datagram Transport Layer Security (DTLS) protocol. The TLS and DTLS protocols provide authentication and privacy services for SNMP applications. This document describes how the TLS Transport Model (TLSTM) implements the needed features of a SNMP Transport Subsystem to make this protection possible in an interoperable way. This Transport Model is designed to meet the security and operational needs of network administrators. It supports the sending of SNMP messages over TLS/TCP and DTLS/UDP. The TLS mode can make use of TCP's improved support for larger packet sizes and the DTLS mode provides potentially superior operation in environments where a connectionless (e.g., UDP) transport is preferred. Both TLS and DTLS integrate well into existing public keying infrastructures. This document also defines a portion of the Management Information Base (MIB) for use with network management protocols. In particular, it defines objects for managing the TLS Transport Model for SNMP. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5953. Hardaker Standards Track [Page 1]
RFC 5953 TLS Transport Model for SNMP August 2010 Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction ....................................................4 1.1. Conventions ................................................7 2. The Transport Layer Security Protocol ...........................8 3. How the TLSTM Fits into the Transport Subsystem .................8 3.1. Security Capabilities of this Model .......................10 3.1.1. Threats ............................................10 3.1.2. Message Protection .................................11 3.1.3. (D)TLS Connections .................................12 3.2. Security Parameter Passing ................................13 3.3. Notifications and Proxy ...................................13 4. Elements of the Model ..........................................14 4.1. X.509 Certificates ........................................14 4.1.1. Provisioning for the Certificate ...................14 4.2. (D)TLS Usage ..............................................16 4.3. SNMP Services .............................................17 4.3.1. SNMP Services for an Outgoing Message ..............17 4.3.2. SNMP Services for an Incoming Message ..............18 4.4. Cached Information and References .........................19 4.4.1. TLS Transport Model Cached Information .............19 Hardaker Standards Track [Page 2]
RFC 5953 TLS Transport Model for SNMP August 2010 4.4.1.1. tmSecurityName ............................19 4.4.1.2. tmSessionID ...............................20 4.4.1.3. Session State .............................20 5. Elements of Procedure ..........................................20 5.1. Procedures for an Incoming Message ........................20 5.1.1. DTLS over UDP Processing for Incoming Messages .....21 5.1.2. Transport Processing for Incoming SNMP Messages ....22 5.2. Procedures for an Outgoing SNMP Message ...................24 5.3. Establishing or Accepting a Session .......................25 5.3.1. Establishing a Session as a Client .................25 5.3.2. Accepting a Session as a Server ....................27 5.4. Closing a Session .........................................28 6. MIB Module Overview ............................................29 6.1. Structure of the MIB Module ...............................29 6.2. Textual Conventions .......................................29 6.3. Statistical Counters ......................................29 6.4. Configuration Tables ......................................29 6.4.1. Notifications ......................................30 6.5. Relationship to Other MIB Modules .........................30 6.5.1. MIB Modules Required for IMPORTS ...................30 7. MIB Module Definition ..........................................30 8. Operational Considerations .....................................53 8.1. Sessions ..................................................53 8.2. Notification Receiver Credential Selection ................54 8.3. contextEngineID Discovery .................................54 8.4. Transport Considerations ..................................55 9. Security Considerations ........................................55 9.1. Certificates, Authentication, and Authorization ...........55 9.2. (D)TLS Security Considerations ............................56 9.2.1. TLS Version Requirements ...........................56 9.2.2. Perfect Forward Secrecy ............................56 9.3. Use with SNMPv1/SNMPv2c Messages ..........................56 9.4. MIB Module Security .......................................57 10. IANA Considerations ...........................................58 11. Acknowledgements ..............................................59 12. References ....................................................60 12.1. Normative References .....................................60 12.2. Informative References ...................................61 Appendix A. Target and Notification Configuration Example ........63 A.1. Configuring a Notification Originator .....................63 A.2. Configuring TLSTM to Utilize a Simple Derivation of tmSecurityName ............................................64 A.3. Configuring TLSTM to Utilize Table-Driven Certificate Mapping ...................................................64 Hardaker Standards Track [Page 3]
RFC 5953 TLS Transport Model for SNMP August 2010 1. Introduction It is important to understand the modular SNMPv3 architecture as defined by [RFC3411] and enhanced by the Transport Subsystem [RFC5590]. It is also important to understand the terminology of the SNMPv3 architecture in order to understand where the Transport Model described in this document fits into the architecture and how it interacts with the other architecture subsystems. For a detailed overview of the documents that describe the current Internet-Standard Management Framework, please refer to Section 7 of [RFC3410]. This document describes a Transport Model that makes use of the Transport Layer Security (TLS) [RFC5246] and the Datagram Transport Layer Security (DTLS) Protocol [RFC4347], within a Transport Subsystem [RFC5590]. DTLS is the datagram variant of the Transport Layer Security (TLS) protocol [RFC5246]. The Transport Model in this document is referred to as the Transport Layer Security Transport Model (TLSTM). TLS and DTLS take advantage of the X.509 public keying infrastructure [RFC5280]. While (D)TLS supports multiple authentication mechanisms, this document only discusses X.509 certificate-based authentication. Although other forms of authentication are possible, they are outside the scope of this specification. This transport model is designed to meet the security and operational needs of network administrators, operating in both environments where a connectionless (e.g., UDP) transport is preferred and in environments where large quantities of data need to be sent (e.g., over a TCP-based stream). Both TLS and DTLS integrate well into existing public keying infrastructures. This document supports sending of SNMP messages over TLS/TCP and DTLS/UDP. This document also defines a portion of the Management Information Base (MIB) for use with network management protocols. In particular, it defines objects for managing the TLS Transport Model for SNMP. 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: [RFC2578], [RFC2579], and [RFC2580]. Hardaker Standards Track [Page 4]
RFC 5953 TLS Transport Model for SNMP August 2010 The diagram shown below gives a conceptual overview of two SNMP entities communicating using the TLS Transport Model (shown as "TLSTM"). One entity contains a command responder and notification originator application, and the other a command generator and notification receiver application. It should be understood that this particular mix of application types is an example only and other combinations are equally valid. Note: this diagram shows the Transport Security Model (TSM) being used as the security model that is defined in [RFC5591]. Hardaker Standards Track [Page 5]
RFC 5953 TLS Transport Model for SNMP August 2010 +---------------------------------------------------------------------+ | Network | +---------------------------------------------------------------------+ ^ | ^ | |Notifications |Commands |Commands |Notifications +---|---------------------|-------+ +--|---------------|--------------+ | | V | | | V | | +------------+ +------------+ | | +-----------+ +----------+ | | | (D)TLS | | (D)TLS | | | | (D)TLS | | (D)TLS | | | | (Client) | | (Server) | | | | (Client) | | (Server) | | | +------------+ +------------+ | | +-----------+ +----------+ | | ^ ^ | | ^ ^ | | | | | | | | | | +-------------+ | | +--------------+ | | +-----|------------+ | | +-----|------------+ | | | V | | | | V | | | | +--------+ | +-----+ | | | +--------+ | +-----+ | | | | TLS TM |<--------->|Cache| | | | | TLS TM |<--------->|Cache| | | | +--------+ | +-----+ | | | +--------+ | +-----+ | | |Transport Subsys. | ^ | | |Transport Subsys. | ^ | | +------------------+ | | | +------------------+ | | | ^ | | | ^ | | | | +--+ | | | +--+ | | v | | | V | | | +-----+ +--------+ +-------+ | | | +-----+ +--------+ +-------+ | | | | | |Message | |Securi.| | | | | | |Message | |Securi.| | | | |Disp.| |Proc. | |Subsys.| | | | |Disp.| |Proc. | |Subsys.| | | | | | |Subsys. | | | | | | | | |Subsys. | | | | | | | | | | | | | | | | | | | | | | | | | | | +----+ | | +---+ | | | | | | | +----+ | | +---+ | | | | | <--->|v3MP|<--> |TSM|<--+ | | | <--->|v3MP|<--->|TSM|<--+ | | | | | +----+ | | +---+ | | | | | | +----+ | | +---+ | | | | | | | | | | | | | | | | | | | +-----+ +--------+ +-------+ | | +-----+ +--------+ +-------+ | | ^ | | ^ | | | | | | | | +-+------------+ | | +-+----------+ | | | | | | | | | | v v | | v V | | +-------------+ +-------------+ | | +-------------+ +-------------+ | | | COMMAND | | NOTIFICAT. | | | | COMMAND | | NOTIFICAT. | | | | RESPONDER | | ORIGINATOR | | | | GENERATOR | | RECEIVER | | | | application | | application | | | | application | | application | | | +-------------+ +-------------+ | | +-------------+ +-------------+ | | SNMP entity | | SNMP entity | +---------------------------------+ +---------------------------------+ Hardaker Standards Track [Page 6]
RFC 5953 TLS Transport Model for SNMP August 2010 1.1. Conventions For consistency with SNMP-related specifications, this document favors terminology as defined in STD 62, rather than favoring terminology that is consistent with non-SNMP specifications. This is consistent with the IESG decision to not require the SNMPv3 terminology be modified to match the usage of other non-SNMP specifications when SNMPv3 was advanced to a Full Standard. "Authentication" in this document typically refers to the English meaning of "serving to prove the authenticity of" the message, not data source authentication or peer identity authentication. The terms "manager" and "agent" are not used in this document because, in the [RFC3411] architecture, all SNMP entities have the capability of acting as manager, agent, or both depending on the SNMP application types supported in the implementation. 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. Large portions of this document simultaneously refer to both TLS and DTLS when discussing TLSTM components that function equally with either protocol. "(D)TLS" is used in these places to indicate that the statement applies to either or both protocols as appropriate. When a distinction between the protocols is needed, they are referred to independently through the use of "TLS" or "DTLS". The Transport Model, however, is named "TLS Transport Model" and refers not to the TLS or DTLS protocol but to the specification in this document, which includes support for both TLS and DTLS. Throughout this document, the terms "client" and "server" are used to refer to the two ends of the (D)TLS transport connection. The client actively opens the (D)TLS connection, and the server passively listens for the incoming (D)TLS connection. An SNMP entity may act as a (D)TLS client or server or both, depending on the SNMP applications supported. The User-Based Security Model (USM) [RFC3414] is a mandatory-to- implement Security Model in STD 62. While (D)TLS and USM frequently refer to a user, the terminology preferred in RFC 3411 and in this memo is "principal". A principal is the "who" on whose behalf services are provided or 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. Hardaker Standards Track [Page 7]
RFC 5953 TLS Transport Model for SNMP August 2010 Throughout this document, the term "session" is used to refer to a secure association between two TLS Transport Models that permits the transmission of one or more SNMP messages within the lifetime of the session. The (D)TLS protocols also have an internal notion of a session and although these two concepts of a session are related, when the term "session" is used this document is referring to the TLSTM's specific session and not directly to the (D)TLS protocol's session. 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]. 2. The Transport Layer Security Protocol (D)TLS provides authentication, data message integrity, and privacy at the transport layer (see [RFC4347]). The primary goals of the TLS Transport Model are to provide privacy, peer identity authentication and data integrity between two communicating SNMP entities. The TLS and DTLS protocols provide a secure transport upon which the TLSTM is based. Please refer to [RFC5246] and [RFC4347] for complete descriptions of the protocols. 3. How the TLSTM Fits into the Transport Subsystem A transport model is a component of the Transport Subsystem. The TLS Transport Model thus fits between the underlying (D)TLS transport layer and the Message Dispatcher [RFC3411] component of the SNMP engine. The TLS Transport Model will establish a session between itself and the TLS Transport Model of another SNMP engine. The sending transport model passes unencrypted and unauthenticated messages from the Dispatcher to (D)TLS to be encrypted and authenticated, and the receiving transport model accepts decrypted and authenticated/ integrity-checked incoming messages from (D)TLS and passes them to the Dispatcher. After a TLS Transport Model session is established, SNMP messages can conceptually be sent through the session from one SNMP message Dispatcher to another SNMP Message Dispatcher. If multiple SNMP messages are needed to be passed between two SNMP applications they MAY be passed through the same session. A TLSTM implementation engine MAY choose to close the session to conserve resources. Hardaker Standards Track [Page 8]
RFC 5953 TLS Transport Model for SNMP August 2010 The TLS Transport Model of an SNMP engine will perform the translation between (D)TLS-specific security parameters and SNMP- specific, model-independent parameters. The diagram below depicts where the TLS Transport Model (shown as "(D)TLS TM") fits into the architecture described in RFC 3411 and the Transport Subsystem: +------------------------------+ | Network | +------------------------------+ ^ ^ ^ | | | v v v +-------------------------------------------------------------------+ | +--------------------------------------------------+ | | | Transport Subsystem | +--------+ | | | +-----+ +-----+ +-------+ +-------+ | | | | | | | UDP | | SSH | |(D)TLS | . . . | other |<--->| Cache | | | | | | | TM | | TM | | | | | | | | | +-----+ +-----+ +-------+ +-------+ | +--------+ | | +--------------------------------------------------+ ^ | | ^ | | | | | | | Dispatcher v | | | +--------------+ +---------------------+ +----------------+ | | | | Transport | | Message Processing | | Security | | | | | Dispatch | | Subsystem | | Subsystem | | | | | | | +------------+ | | +------------+ | | | | | | | +->| v1MP |<--->| | USM | | | | | | | | | +------------+ | | +------------+ | | | | | | | | +------------+ | | +------------+ | | | | | | | +->| v2cMP |<--->| | Transport | | | | | | Message | | | +------------+ | | | Security |<--+ | | | Dispatch <---->| +------------+ | | | Model | | | | | | | +->| v3MP |<--->| +------------+ | | | | | | | +------------+ | | +------------+ | | | | PDU Dispatch | | | +------------+ | | | Other | | | | +--------------+ | +->| otherMP |<--->| | Model(s) | | | | ^ | +------------+ | | +------------+ | | | | +---------------------+ +----------------+ | | v | | +-------+-------------------------+---------------+ | | ^ ^ ^ | | | | | | | v v v | Hardaker Standards Track [Page 9]
RFC 5953 TLS Transport Model for SNMP August 2010 | +-------------+ +---------+ +--------------+ +-------------+ | | | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | | | | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | | | | application | | | | applications | | application | | | +-------------+ +---------+ +--------------+ +-------------+ | | ^ ^ | | | | | | v v | | +----------------------------------------------+ | | | MIB instrumentation | SNMP entity | +-------------------------------------------------------------------+ 3.1. Security Capabilities of this Model 3.1.1. Threats The TLS Transport Model provides protection against the threats identified by the RFC 3411 architecture [RFC3411]: 1. Modification of Information - The modification threat is the danger that an unauthorized entity may alter in-transit SNMP messages generated on behalf of an authorized principal in such a way as to effect unauthorized management operations, including falsifying the value of an object. (D)TLS provides verification that the content of each received message has not been modified during its transmission through the network, data has not been altered or destroyed in an unauthorized manner, and data sequences have not been altered to an extent greater than can occur non-maliciously. 2. Masquerade - The masquerade threat is the danger that management operations unauthorized for a given principal may be attempted by assuming the identity of another principal that has the appropriate authorizations. The TLSTM verifies the identity of the (D)TLS server through the use of the (D)TLS protocol and X.509 certificates. A TLS Transport Model implementation MUST support the authentication of both the server and the client. 3. Message stream modification - The re-ordering, delay, or replay of messages can and does occur through the natural operation of many connectionless transport services. The message stream modification threat is the danger that messages may be maliciously re-ordered, delayed or replayed to an extent that is Hardaker Standards Track [Page 10]
RFC 5953 TLS Transport Model for SNMP August 2010 greater than can occur through the natural operation of connectionless transport services, in order to effect unauthorized management operations. (D)TLS provides replay protection with a Message Authentication Code (MAC) that includes a sequence number. Since UDP provides no sequencing ability, DTLS uses a sliding window protocol with the sequence number used for replay protection (see [RFC4347]). 4. Disclosure - The disclosure threat is the danger of eavesdropping on the exchanges between SNMP engines. (D)TLS provides protection against the disclosure of information to unauthorized recipients or eavesdroppers by allowing for encryption of all traffic between SNMP engines. A TLS Transport Model implementation MUST support message encryption to protect sensitive data from eavesdropping attacks. 5. Denial of Service - the RFC 3411 architecture [RFC3411] states that denial-of-service (DoS) attacks need not be addressed by an SNMP security protocol. However, connectionless transports (like DTLS over UDP) are susceptible to a variety of DoS attacks because they are more vulnerable to spoofed IP addresses. See Section 4.2 for details on how the cookie mechanism is used. Note, however, that this mechanism does not provide any defense against DoS attacks mounted from valid IP addresses. See Section 9 for more detail on the security considerations associated with the TLSTM and these security threats. 3.1.2. Message Protection The RFC 3411 architecture recognizes three levels of security: o without authentication and without privacy (noAuthNoPriv) o with authentication but without privacy (authNoPriv) o with authentication and with privacy (authPriv) The TLS Transport Model determines from (D)TLS the identity of the authenticated principal, the transport type and the transport address associated with an incoming message. The TLS Transport Model provides the identity and destination type and address to (D)TLS for outgoing messages. Hardaker Standards Track [Page 11]
RFC 5953 TLS Transport Model for SNMP August 2010 When an application requests a session for a message, it also requests a security level for that session. The TLS Transport Model MUST ensure that the (D)TLS connection provides security at least as high as the requested level of security. How the security level is translated into the algorithms used to provide data integrity and privacy is implementation dependent. However, the NULL integrity and encryption algorithms MUST NOT be used to fulfill security level requests for authentication or privacy. Implementations MAY choose to force (D)TLS to only allow cipher_suites that provide both authentication and privacy to guarantee this assertion. If a suitable interface between the TLS Transport Model and the (D)TLS Handshake Protocol is implemented to allow the selection of security-level-dependent algorithms (for example, a security level to cipher_suites mapping table), then different security levels may be utilized by the application. The authentication, integrity, and privacy algorithms used by the (D)TLS Protocols may vary over time as the science of cryptography continues to evolve and the development of (D)TLS continues over time. Implementers are encouraged to plan for changes in operator trust of particular algorithms. Implementations SHOULD offer configuration settings for mapping algorithms to SNMPv3 security levels. 3.1.3. (D)TLS Connections (D)TLS connections are opened by the TLS Transport Model during the elements of procedure for an outgoing SNMP message. Since the sender of a message initiates the creation of a (D)TLS connection if needed, the (D)TLS connection will already exist for an incoming message. Implementations MAY choose to instantiate (D)TLS connections in anticipation of outgoing messages. This approach might be useful to ensure that a (D)TLS connection to a given target can be established before it becomes important to send a message over the (D)TLS connection. Of course, there is no guarantee that a pre-established session will still be valid when needed. DTLS connections, when used over UDP, are uniquely identified within the TLS Transport Model by the combination of transportDomain, transportAddress, tmSecurityName, and requestedSecurityLevel associated with each session. Each unique combination of these parameters MUST have a locally chosen unique tlstmSessionID for each active session. For further information, see Section 5. TLS over TCP sessions, on the other hand, do not require a unique pairing of Hardaker Standards Track [Page 12]
RFC 5953 TLS Transport Model for SNMP August 2010 address and port attributes since their lower-layer protocols (TCP) already provide adequate session framing. But they must still provide a unique tlstmSessionID for referencing the session. The tlstmSessionID MUST NOT change during the entire duration of the session from the TLSTM's perspective, and MUST uniquely identify a single session. As an implementation hint: note that the (D)TLS internal SessionID does not meet these requirements, since it can change over the life of the connection as seen by the TLSTM (for example, during renegotiation), and does not necessarily uniquely identify a TLSTM session (there can be multiple TLSTM sessions sharing the same D(TLS) internal SessionID). 3.2. Security Parameter Passing For the (D)TLS server-side, (D)TLS-specific security parameters (i.e., cipher_suites, X.509 certificate fields, IP addresses, and ports) are translated by the TLS Transport Model into security parameters for the TLS Transport Model and security model (e.g., tmSecurityLevel, tmSecurityName, transportDomain, transportAddress). The transport-related and (D)TLS-security-related information, including the authenticated identity, are stored in a cache referenced by tmStateReference. For the (D)TLS client side, the TLS Transport Model takes input provided by the Dispatcher in the sendMessage() Abstract Service Interface (ASI) and input from the tmStateReference cache. The (D)TLS Transport Model converts that information into suitable security parameters for (D)TLS and establishes sessions as needed. The elements of procedure in Section 5 discuss these concepts in much greater detail. 3.3. Notifications and Proxy (D)TLS connections may be initiated by (D)TLS clients on behalf of SNMP applications that initiate communications, such as command generators, notification originators, proxy forwarders. Command generators are frequently operated by a human, but notification originators and proxy forwarders are usually unmanned automated processes. The targets to whom notifications and proxied requests should be sent is typically determined and configured by a network administrator. The SNMP-TARGET-MIB module [RFC3413] contains objects for defining management targets, including transportDomain, transportAddress, securityName, securityModel, and securityLevel parameters, for notification originator, proxy forwarder, and SNMP-controllable Hardaker Standards Track [Page 13]
RFC 5953 TLS Transport Model for SNMP August 2010 command generator applications. Transport domains and transport addresses are configured in the snmpTargetAddrTable, and the securityModel, securityName, and securityLevel parameters are configured in the snmpTargetParamsTable. This document defines a MIB module that extends the SNMP-TARGET-MIB's snmpTargetParamsTable to specify a (D)TLS client-side certificate to use for the connection. When configuring a (D)TLS target, the snmpTargetAddrTDomain and snmpTargetAddrTAddress parameters in snmpTargetAddrTable SHOULD be set to the snmpTLSTCPDomain or snmpDTLSUDPDomain object and an appropriate snmpTLSAddress value. When used with the SNMPv3 message processing model, the snmpTargetParamsMPModel column of the snmpTargetParamsTable SHOULD be set to a value of 3. The snmpTargetParamsSecurityName SHOULD be set to an appropriate securityName value and the snmpTlstmParamsClientFingerprint parameter of the snmpTlstmParamsTable SHOULD be set a value that refers to a locally held certificate (and the corresponding private key) to be used. Other parameters, for example, cryptographic configuration such as which cipher_suites to use, must come from configuration mechanisms not defined in this document. The securityName defined in the snmpTargetParamsSecurityName column will be used by the access control model to authorize any notifications that need to be sent. 4. Elements of the Model This section contains definitions required to realize the (D)TLS Transport Model defined by this document. 4.1. X.509 Certificates (D)TLS can make use of X.509 certificates for authentication of both sides of the transport. This section discusses the use of X.509 certificates in the TLSTM. While (D)TLS supports multiple authentication mechanisms, this document only discusses X.509-certificate-based authentication; other forms of authentication are outside the scope of this specification. TLSTM implementations are REQUIRED to support X.509 certificates. 4.1.1. Provisioning for the Certificate Authentication using (D)TLS will require that SNMP entities have certificates, either signed by trusted Certification Authorities (CAs), or self signed. Furthermore, SNMP entities will most commonly need to be provisioned with root certificates that represent the list of trusted CAs that an SNMP entity can use for certificate Hardaker Standards Track [Page 14]
RFC 5953 TLS Transport Model for SNMP August 2010 verification. SNMP entities SHOULD also be provisioned with a X.509 certificate revocation mechanism which can be used to verify that a certificate has not been revoked. Trusted public keys from either CA certificates and/or self-signed certificates MUST be installed into the server through a trusted out-of-band mechanism and their authenticity MUST be verified before access is granted. Having received a certificate from a connecting TLSTM client, the authenticated tmSecurityName of the principal is derived using the snmpTlstmCertToTSNTable. This table allows mapping of incoming connections to tmSecurityNames through defined transformations. The transformations defined in the SNMP-TLS-TM-MIB include: o Mapping a certificate's subjectAltName or CommonName components to a tmSecurityName, or o Mapping a certificate's fingerprint value to a directly specified tmSecurityName As an implementation hint: implementations may choose to discard any connections for which no potential snmpTlstmCertToTSNTable mapping exists before performing certificate verification to avoid expending computational resources associated with certificate verification. Deployments SHOULD map the "subjectAltName" component of X.509 certificates to the TLSTM specific tmSecurityNames. The authenticated identity can be obtained by the TLS Transport Model by extracting the subjectAltName(s) from the peer's certificate. The receiving application will then have an appropriate tmSecurityName for use by other SNMPv3 components like an access control model. An example of this type of mapping setup can be found in Appendix A. This tmSecurityName may be later translated from a TLSTM specific tmSecurityName to a SNMP engine securityName by the security model. A security model, like the TSM security model [RFC5591], may perform an identity mapping or a more complex mapping to derive the securityName from the tmSecurityName offered by the TLS Transport Model. The standard View-Based Access Control Model (VACM) access control model constrains securityNames to be 32 octets or less in length. A TLSTM generated tmSecurityName, possibly in combination with a messaging or security model that increases the length of the securityName, might cause the securityName length to exceed 32 octets. For example, a 32-octet tmSecurityName derived from an IPv6 address, paired with a TSM prefix, will generate a 36-octet Hardaker Standards Track [Page 15]
RFC 5953 TLS Transport Model for SNMP August 2010 securityName. Such a securityName will not be able to be used with standard VACM or TARGET MIB modules. Operators should be careful to select algorithms and subjectAltNames to avoid this situation. A pictorial view of the complete transformation process (using the TSM security model for the example) is shown below: +-------------+ +-------+ +-----+ | Certificate | | | | | | Path | | TLSTM | tmSecurityName | TSM | | Validation | --> | | ----------------->| | +-------------+ +-------+ +-----+ | | securityName V +-------------+ | application | +-------------+ 4.2. (D)TLS Usage (D)TLS MUST negotiate a cipher_suite that uses X.509 certificates for authentication, and MUST authenticate both the client and the server. The mandatory-to-implement cipher_suite is specified in the TLS specification [RFC5246]. TLSTM verifies the certificates when the connection is opened (see Section 5.3). For this reason, TLS renegotiation with different certificates MUST NOT be done. That is, implementations MUST either disable renegotiation completely (RECOMMENDED), or they MUST present the same certificate during renegotiation (and MUST verify that the other end presented the same certificate). For DTLS over UDP, each SNMP message MUST be placed in a single UDP datagram; it MAY be split to multiple DTLS records. In other words, if a single datagram contains multiple DTLS application_data records, they are concatenated when received. The TLSTM implementation SHOULD return an error if the SNMP message does not fit in the UDP datagram, and thus cannot be sent. For DTLS over UDP, the DTLS server implementation MUST support DTLS cookies ([RFC4347] already requires that clients support DTLS cookies). Implementations are not required to perform the cookie exchange for every DTLS handshake; however, enabling it by default is RECOMMENDED. For DTLS, replay protection MUST be used. Hardaker Standards Track [Page 16]
RFC 5953 TLS Transport Model for SNMP August 2010 4.3. SNMP Services This section describes the services provided by the TLS Transport Model with their inputs and outputs. The services are between the Transport Model and the Dispatcher. The services are described as primitives of an abstract service interface (ASI) and the inputs and outputs are described as abstract data elements as they are passed in these abstract service primitives. 4.3.1. SNMP Services for an Outgoing Message The Dispatcher passes the information to the TLS Transport Model using the ASI defined in the Transport Subsystem: statusInformation = sendMessage( IN destTransportDomain -- transport domain to be used IN destTransportAddress -- transport address to be used IN outgoingMessage -- the message to send IN outgoingMessageLength -- its length IN tmStateReference -- reference to transport state ) The abstract data elements returned from or passed as parameters into the abstract service primitives are as follows: statusInformation: An indication of whether the sending of the message was successful. If not, it is an indication of the problem. destTransportDomain: The transport domain for the associated destTransportAddress. The Transport Model uses this parameter to determine the transport type of the associated destTransportAddress. This document specifies the snmpTLSTCPDomain and the snmpDTLSUDPDomain transport domains. destTransportAddress: The transport address of the destination TLS Transport Model in a format specified by the SnmpTLSAddress TEXTUAL-CONVENTION. outgoingMessage: The outgoing message to send to (D)TLS for encapsulation and transmission. outgoingMessageLength: The length of the outgoingMessage. Hardaker Standards Track [Page 17]
RFC 5953 TLS Transport Model for SNMP August 2010 tmStateReference: A reference used to pass model-specific and mechanism-specific parameters between the Transport Subsystem and transport-aware Security Models. 4.3.2. SNMP Services for an Incoming Message The TLS Transport Model processes the received message from the network using the (D)TLS service and then passes it to the Dispatcher using the following ASI: statusInformation = receiveMessage( IN transportDomain -- origin transport domain IN transportAddress -- origin transport address IN incomingMessage -- the message received IN incomingMessageLength -- its length IN tmStateReference -- reference to transport state ) The abstract data elements returned from or passed as parameters into the abstract service primitives are as follows: statusInformation: An indication of whether the passing of the message was successful. If not, it is an indication of the problem. transportDomain: The transport domain for the associated transportAddress. This document specifies the snmpTLSTCPDomain and the snmpDTLSUDPDomain transport domains. transportAddress: The transport address of the source of the received message in a format specified by the SnmpTLSAddress TEXTUAL-CONVENTION. incomingMessage: The whole SNMP message after being processed by (D)TLS. incomingMessageLength: The length of the incomingMessage. tmStateReference: A reference used to pass model-specific and mechanism-specific parameters between the Transport Subsystem and transport-aware Security Models. Hardaker Standards Track [Page 18]
RFC 5953 TLS Transport Model for SNMP August 2010 4.4. Cached Information and References When performing SNMP processing, there are two levels of state information that may need to be retained: the immediate state linking a request-response pair, and potentially longer-term state relating to transport and security. "Transport Subsystem for the Simple Network Management Protocol (SNMP)" [RFC5590] defines general requirements for caches and references. 4.4.1. TLS Transport Model Cached Information The TLS Transport Model has specific responsibilities regarding the cached information. See the Elements of Procedure in Section 5 for detailed processing instructions on the use of the tmStateReference fields by the TLS Transport Model. 4.4.1.1. tmSecurityName The tmSecurityName MUST be a human-readable name (in snmpAdminString format) representing the identity that has been set according to the procedures in Section 5. The tmSecurityName MUST be constant for all traffic passing through a single TLSTM session. Messages MUST NOT be sent through an existing (D)TLS connection that was established using a different tmSecurityName. On the (D)TLS server side of a connection, the tmSecurityName is derived using the procedures described in Section 5.3.2 and the SNMP- TLS-TM-MIB's snmpTlstmCertToTSNTable DESCRIPTION clause. On the (D)TLS client side of a connection, the tmSecurityName is presented to the TLS Transport Model by the security model through the tmStateReference. This tmSecurityName is typically a copy of or is derived from the securityName that was passed by application (possibly because of configuration specified in the SNMP-TARGET-MIB). The Security Model likely derived the tmSecurityName from the securityName presented to the Security Model by the application (possibly because of configuration specified in the SNMP-TARGET-MIB). Transport-Model-aware security models derive tmSecurityName from a securityName, possibly configured in MIB modules for notifications and access controls. Transport Models SHOULD use predictable tmSecurityNames so operators will know what to use when configuring MIB modules that use securityNames derived from tmSecurityNames. The TLSTM generates predictable tmSecurityNames based on the configuration found in the SNMP-TLS-TM-MIB's snmpTlstmCertToTSNTable and relies on the network operators to have configured this table appropriately. Hardaker Standards Track [Page 19]
RFC 5953 TLS Transport Model for SNMP August 2010 4.4.1.2. tmSessionID The tmSessionID MUST be recorded per message at the time of receipt. When tmSameSecurity is set, the recorded tmSessionID can be used to determine whether the (D)TLS connection available for sending a corresponding outgoing message is the same (D)TLS connection as was used when receiving the incoming message (e.g., a response to a request). 4.4.1.3. Session State The per-session state that is referenced by tmStateReference may be saved across multiple messages in a Local Configuration Datastore. Additional session/connection state information might also be stored in a Local Configuration Datastore. 5. Elements of Procedure Abstract service interfaces have been defined by [RFC3411] and further augmented by [RFC5590] to describe the conceptual data flows between the various subsystems within an SNMP entity. The TLSTM uses some of these conceptual data flows when communicating between subsystems. To simplify the elements of procedure, the release of state information is not always explicitly specified. As a general rule, if state information is available when a message gets discarded, the message-state information should also be released. If state information is available when a session is closed, the session state information should also be released. Sensitive information, like cryptographic keys, should be overwritten appropriately prior to being released. An error indication in statusInformation will typically include the Object Identifier (OID) and value for an incremented error counter. This may be accompanied by the requested securityLevel and the tmStateReference. Per-message context information is not accessible to Transport Models, so for the returned counter OID and value, contextEngine would be set to the local value of snmpEngineID and contextName to the default context for error counters. 5.1. Procedures for an Incoming Message This section describes the procedures followed by the (D)TLS Transport Model when it receives a (D)TLS protected packet. The required functionality is broken into two different sections. Hardaker Standards Track [Page 20]
RFC 5953 TLS Transport Model for SNMP August 2010 Section 5.1.1 describes the processing required for de-multiplexing multiple DTLS connections, which is specifically needed for DTLS over UDP sessions. It is assumed that TLS protocol implementations already provide appropriate message demultiplexing. Section 5.1.2 describes the transport processing required once the (D)TLS processing has been completed. This will be needed for all (D)TLS-based connections. 5.1.1. DTLS over UDP Processing for Incoming Messages Demultiplexing of incoming packets into separate DTLS sessions MUST be implemented. For connection-oriented transport protocols, such as TCP, the transport protocol takes care of demultiplexing incoming packets to the right connection. For DTLS over UDP, this demultiplexing will either need to be done within the DTLS implementation, if supported, or by the TLSTM implementation. Like TCP, DTLS over UDP uses the four-tuple <source IP, destination IP, source port, destination port> for identifying the connection (and relevant DTLS connection state). This means that when establishing a new session, implementations MUST use a different UDP source port number for each active connection to a remote destination IP-address/port-number combination to ensure the remote entity can disambiguate between multiple connections. If demultiplexing received UDP datagrams to DTLS connection state is done by the TLSTM implementation (instead of the DTLS implementation), the steps below describe one possible method to accomplish this. The important output results from the steps in this process are the remote transport address, incomingMessage, incomingMessageLength, and the tlstmSessionID. 1) The TLS Transport Model examines the raw UDP message, in an implementation-dependent manner. 2) The TLS Transport Model queries the Local Configuration Datastore (LCD) (see [RFC3411] Section 3.4.2) using the transport parameters (source and destination IP addresses and ports) to determine if a session already exists. 2a) If a matching entry in the LCD does not exist, then the UDP packet is passed to the DTLS implementation for processing. If the DTLS implementation decides to continue with the connection and allocate state for it, it returns a new DTLS connection handle (an implementation dependent detail). In Hardaker Standards Track [Page 21]
RFC 5953 TLS Transport Model for SNMP August 2010 this case, TLSTM selects a new tlstmSessionId, and caches this and the DTLS connection handle as a new entry in the LCD (indexed by the transport parameters). If the DTLS implementation returns an error or does not allocate connection state (which can happen with the stateless cookie exchange), processing stops. 2b) If a session does exist in the LCD, then its DTLS connection handle (an implementation dependent detail) and its tlstmSessionId is extracted from the LCD. The UDP packet and the connection handle is passed to the DTLS implementation. If the DTLS implementation returns success but does not return an incomingMessage and an incomingMessageLength then processing stops (this is the case when the UDP datagram contained DTLS handshake messages, for example). If the DTLS implementation returns an error then processing stops. 3) Retrieve the incomingMessage and an incomingMessageLength from DTLS. These results and the tlstmSessionID are used below in Section 5.1.2 to complete the processing of the incoming message. 5.1.2. Transport Processing for Incoming SNMP Messages The procedures in this section describe how the TLS Transport Model should process messages that have already been properly extracted from the (D)TLS stream. Note that care must be taken when processing messages originating from either TLS or DTLS to ensure they're complete and single. For example, multiple SNMP messages can be passed through a single DTLS message and partial SNMP messages may be received from a TLS stream. These steps describe the processing of a singular SNMP message after it has been delivered from the (D)TLS stream. 1) Determine the tlstmSessionID for the incoming message. The tlstmSessionID MUST be a unique session identifier for this (D)TLS connection. The contents and format of this identifier are implementation dependent as long as it is unique to the session. A session identifier MUST NOT be reused until all references to it are no longer in use. The tmSessionID is equal to the tlstmSessionID discussed in Section 5.1.1. tmSessionID refers to the session identifier when stored in the tmStateReference and tlstmSessionID refers to the session identifier when stored in the LCD. They MUST always be equal when processing a given session's traffic. Hardaker Standards Track [Page 22]
RFC 5953 TLS Transport Model for SNMP August 2010 If this is the first message received through this session, and the session does not have an assigned tlstmSessionID yet, then the snmpTlstmSessionAccepts counter is incremented and a tlstmSessionID for the session is created. This will only happen on the server side of a connection because a client would have already assigned a tlstmSessionID during the openSession() invocation. Implementations may have performed the procedures described in Section 5.3.2 prior to this point or they may perform them now, but the procedures described in Section 5.3.2 MUST be performed before continuing beyond this point. 2) Create a tmStateReference cache for the subsequent reference and assign the following values within it: tmTransportDomain = snmpTLSTCPDomain or snmpDTLSUDPDomain as appropriate. tmTransportAddress = The address from which the message originated. tmSecurityLevel = The derived tmSecurityLevel for the session, as discussed in Sections 3.1.2 and 5.3. tmSecurityName = The derived tmSecurityName for the session as discussed in Section 5.3. This value MUST be constant during the lifetime of the session. tmSessionID = The tlstmSessionID described in step 1 above. 3) The incomingMessage and incomingMessageLength are assigned values from the (D)TLS processing. 4) The TLS Transport Model passes the transportDomain, transportAddress, incomingMessage, and incomingMessageLength to the Dispatcher using the receiveMessage ASI: statusInformation = receiveMessage( IN transportDomain -- snmpTLSTCPDomain or snmpDTLSUDPDomain, IN transportAddress -- address for the received message IN incomingMessage -- the whole SNMP message from (D)TLS IN incomingMessageLength -- the length of the SNMP message IN tmStateReference -- transport info ) Hardaker Standards Track [Page 23]
RFC 5953 TLS Transport Model for SNMP August 2010 5.2. Procedures for an Outgoing SNMP Message The Dispatcher sends a message to the TLS Transport Model using the following ASI: statusInformation = sendMessage( IN destTransportDomain -- transport domain to be used IN destTransportAddress -- transport address to be used IN outgoingMessage -- the message to send IN outgoingMessageLength -- its length IN tmStateReference -- transport info ) This section describes the procedure followed by the TLS Transport Model whenever it is requested through this ASI to send a message. 1) If tmStateReference does not refer to a cache containing values for tmTransportDomain, tmTransportAddress, tmSecurityName, tmRequestedSecurityLevel, and tmSameSecurity, then increment the snmpTlstmSessionInvalidCaches counter, discard the message, and return the error indication in the statusInformation. Processing of this message stops. 2) Extract the tmSessionID, tmTransportDomain, tmTransportAddress, tmSecurityName, tmRequestedSecurityLevel, and tmSameSecurity values from the tmStateReference. Note: the tmSessionID value may be undefined if no session exists yet over which the message can be sent. 3) If tmSameSecurity is true and tmSessionID is either undefined or refers to a session that is no longer open, then increment the snmpTlstmSessionNoSessions counter, discard the message, and return the error indication in the statusInformation. Processing of this message stops. 4) If tmSameSecurity is false and tmSessionID refers to a session that is no longer available, then an implementation SHOULD open a new session, using the openSession() ASI (described in greater detail in step 5b). Instead of opening a new session an implementation MAY return a snmpTlstmSessionNoSessions error to the calling module and stop the processing of the message. 5) If tmSessionID is undefined, then use tmTransportDomain, tmTransportAddress, tmSecurityName, and tmRequestedSecurityLevel to see if there is a corresponding entry in the LCD suitable to send the message over. Hardaker Standards Track [Page 24]
RFC 5953 TLS Transport Model for SNMP August 2010 5a) If there is a corresponding LCD entry, then this session will be used to send the message. 5b) If there is no corresponding LCD entry, then open a session using the openSession() ASI (discussed further in Section 5.3.1). Implementations MAY wish to offer message buffering to prevent redundant openSession() calls for the same cache entry. If an error is returned from openSession(), then discard the message, discard the tmStateReference, increment the snmpTlstmSessionOpenErrors, return an error indication to the calling module, and stop the processing of the message. 6) Using either the session indicated by the tmSessionID (if there was one) or the session resulting from a previous step (4 or 5), pass the outgoingMessage to (D)TLS for encapsulation and transmission. 5.3. Establishing or Accepting a Session Establishing a (D)TLS connection as either a client or a server requires slightly different processing. The following two sections describe the necessary processing steps. 5.3.1. Establishing a Session as a Client The TLS Transport Model provides the following primitive for use by a client to establish a new (D)TLS connection: statusInformation = -- errorIndication or success openSession( IN tmStateReference -- transport information to be used OUT tmStateReference -- transport information to be used IN maxMessageSize -- of the sending SNMP entity ) The following describes the procedure to follow when establishing an SNMP over a (D)TLS connection between SNMP engines for exchanging SNMP messages. This process is followed by any SNMP client's engine when establishing a session for subsequent use. This procedure MAY be done automatically for an SNMP application that initiates a transaction, such as a command generator, a notification originator, or a proxy forwarder. 1) The snmpTlstmSessionOpens counter is incremented. Hardaker Standards Track [Page 25]
RFC 5953 TLS Transport Model for SNMP August 2010 2) The client selects the appropriate certificate and cipher_suites for the key agreement based on the tmSecurityName and the tmRequestedSecurityLevel for the session. For sessions being established as a result of an SNMP-TARGET-MIB based operation, the certificate will potentially have been identified via the snmpTlstmParamsTable mapping and the cipher_suites will have to be taken from a system-wide or implementation-specific configuration. If no row in the snmpTlstmParamsTable exists, then implementations MAY choose to establish the connection using a default client certificate available to the application. Otherwise, the certificate and appropriate cipher_suites will need to be passed to the openSession() ASI as supplemental information or configured through an implementation-dependent mechanism. It is also implementation-dependent and possibly policy-dependent how tmRequestedSecurityLevel will be used to influence the security capabilities provided by the (D)TLS connection. However this is done, the security capabilities provided by (D)TLS MUST be at least as high as the level of security indicated by the tmRequestedSecurityLevel parameter. The actual security level of the session is reported in the tmStateReference cache as tmSecurityLevel. For (D)TLS to provide strong authentication, each principal acting as a command generator SHOULD have its own certificate. 3) Using the destTransportDomain and destTransportAddress values, the client will initiate the (D)TLS handshake protocol to establish session keys for message integrity and encryption. If the attempt to establish a session is unsuccessful, then snmpTlstmSessionOpenErrors is incremented, an error indication is returned, and processing stops. If the session failed to open because the presented server certificate was unknown or invalid, then the snmpTlstmSessionUnknownServerCertificate or snmpTlstmSessionInvalidServerCertificates MUST be incremented and an snmpTlstmServerCertificateUnknown or snmpTlstmServerInvalidCertificate notification SHOULD be sent as appropriate. Reasons for server certificate invalidation includes, but is not limited to, cryptographic validation failures and an unexpected presented certificate identity. 4) The (D)TLS client MUST then verify that the (D)TLS server's presented certificate is the expected certificate. The (D)TLS client MUST NOT transmit SNMP messages until the server certificate has been authenticated, the client certificate has been transmitted and the TLS connection has been fully established. Hardaker Standards Track [Page 26]
RFC 5953 TLS Transport Model for SNMP August 2010 If the connection is being established from a configuration based on SNMP-TARGET-MIB configuration, then the snmpTlstmAddrTable DESCRIPTION clause describes how the verification is done (using either a certificate fingerprint, or an identity authenticated via certification path validation). If the connection is being established for reasons other than configuration found in the SNMP-TARGET-MIB, then configuration and procedures outside the scope of this document should be followed. Configuration mechanisms SHOULD be similar in nature to those defined in the snmpTlstmAddrTable to ensure consistency across management configuration systems. For example, a command- line tool for generating SNMP GETs might support specifying either the server's certificate fingerprint or the expected host name as a command-line argument. 5) (D)TLS provides assurance that the authenticated identity has been signed by a trusted configured Certification Authority. If verification of the server's certificate fails in any way (for example, because of failures in cryptographic verification or the presented identity did not match the expected named entity) then the session establishment MUST fail, the snmpTlstmSessionInvalidServerCertificates object is incremented. If the session cannot be opened for any reason at all, including cryptographic verification failures and snmpTlstmCertToTSNTable lookup failures, then the snmpTlstmSessionOpenErrors counter is incremented and processing stops. 6) The TLSTM-specific session identifier (tlstmSessionID) is set in the tmSessionID of the tmStateReference passed to the TLS Transport Model to indicate that the session has been established successfully and to point to a specific (D)TLS connection for future use. The tlstmSessionID is also stored in the LCD for later lookup during processing of incoming messages (Section 5.1.2). 5.3.2. Accepting a Session as a Server A (D)TLS server should accept new session connections from any client for which it is able to verify the client's credentials. This is done by authenticating the client's presented certificate through a certificate path validation process (e.g., [RFC5280]) or through certificate fingerprint verification using fingerprints configured in the snmpTlstmCertToTSNTable. Afterward, the server will determine the identity of the remote entity using the following procedures. Hardaker Standards Track [Page 27]
RFC 5953 TLS Transport Model for SNMP August 2010 The (D)TLS server identifies the authenticated identity from the (D)TLS client's principal certificate using configuration information from the snmpTlstmCertToTSNTable mapping table. The (D)TLS server MUST request and expect a certificate from the client and MUST NOT accept SNMP messages over the (D)TLS connection until the client has sent a certificate and it has been authenticated. The resulting derived tmSecurityName is recorded in the tmStateReference cache as tmSecurityName. The details of the lookup process are fully described in the DESCRIPTION clause of the snmpTlstmCertToTSNTable MIB object. If any verification fails in any way (for example, because of failures in cryptographic verification or because of the lack of an appropriate row in the snmpTlstmCertToTSNTable), then the session establishment MUST fail, and the snmpTlstmSessionInvalidClientCertificates object is incremented. If the session cannot be opened for any reason at all, including cryptographic verification failures, then the snmpTlstmSessionOpenErrors counter is incremented and processing stops. Servers that wish to support multiple principals at a particular port SHOULD make use of a (D)TLS extension that allows server-side principal selection like the Server Name Indication extension defined in Section 3.1 of [RFC4366]. Supporting this will allow, for example, sending notifications to a specific principal at a given TCP or UDP port. 5.4. Closing a Session The TLS Transport Model provides the following primitive to close a session: statusInformation = closeSession( IN tmSessionID -- session ID of the session to be closed ) The following describes the procedure to follow to close a session between a client and server. This process is followed by any SNMP engine closing the corresponding SNMP session. 1) Increment either the snmpTlstmSessionClientCloses or the snmpTlstmSessionServerCloses counter as appropriate. 2) Look up the session using the tmSessionID. 3) If there is no open session associated with the tmSessionID, then closeSession processing is completed. Hardaker Standards Track [Page 28]
RFC 5953 TLS Transport Model for SNMP August 2010 4) Have (D)TLS close the specified connection. This MUST include sending a close_notify TLS Alert to inform the other side that session cleanup may be performed. 6. MIB Module Overview This MIB module provides management of the TLS Transport Model. It defines needed textual conventions, statistical counters, notifications, and configuration infrastructure necessary for session establishment. Example usage of the configuration tables can be found in Appendix A. 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 each subtree, is shown below. 6.2. Textual Conventions Generic and Common Textual Conventions used in this module can be found summarized at http://www.ops.ietf.org/mib-common-tcs.html. This module defines the following new Textual Conventions: o A new TransportAddress format for describing (D)TLS connection addressing requirements. o A certificate fingerprint allowing MIB module objects to generically refer to a stored X.509 certificate using a cryptographic hash as a reference pointer. 6.3. Statistical Counters The SNMP-TLS-TM-MIB defines counters that provide network management stations with information about session usage and potential errors that a device may be experiencing. 6.4. Configuration Tables The SNMP-TLS-TM-MIB defines configuration tables that an administrator can use for configuring a device for sending and receiving SNMP messages over (D)TLS. In particular, there are MIB tables that extend the SNMP-TARGET-MIB for configuring (D)TLS certificate usage and a MIB table for mapping incoming (D)TLS client certificates to SNMPv3 tmSecurityNames. Hardaker Standards Track [Page 29]
RFC 5953 TLS Transport Model for SNMP August 2010 6.4.1. Notifications The SNMP-TLS-TM-MIB defines notifications to alert management stations when a (D)TLS connection fails because a server's presented certificate did not meet an expected value (snmpTlstmServerCertificateUnknown) or because cryptographic validation failed (snmpTlstmServerInvalidCertificate). 6.5. Relationship to Other MIB Modules Some management objects defined in other MIB modules are applicable to an entity implementing the TLS Transport Model. In particular, it is assumed that an entity implementing the SNMP-TLS-TM-MIB will implement the SNMPv2-MIB [RFC3418], the SNMP-FRAMEWORK-MIB [RFC3411], the SNMP-TARGET-MIB [RFC3413], the SNMP-NOTIFICATION-MIB [RFC3413], and the SNMP-VIEW-BASED-ACM-MIB [RFC3415]. The SNMP-TLS-TM-MIB module contained in this document is for managing TLS Transport Model information. 6.5.1. MIB Modules Required for IMPORTS The SNMP-TLS-TM-MIB module imports items from SNMPv2-SMI [RFC2578], SNMPv2-TC [RFC2579], SNMP-FRAMEWORK-MIB [RFC3411], SNMP-TARGET-MIB [RFC3413], and SNMPv2-CONF [RFC2580]. 7. MIB Module Definition SNMP-TLS-TM-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, OBJECT-IDENTITY, mib-2, snmpDomains, Counter32, Unsigned32, Gauge32, NOTIFICATION-TYPE FROM SNMPv2-SMI -- RFC 2578 or any update thereof TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType, AutonomousType FROM SNMPv2-TC -- RFC 2579 or any update thereof MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP FROM SNMPv2-CONF -- RFC 2580 or any update thereof SnmpAdminString FROM SNMP-FRAMEWORK-MIB -- RFC 3411 or any update thereof snmpTargetParamsName, snmpTargetAddrName FROM SNMP-TARGET-MIB -- RFC 3413 or any update thereof ; Hardaker Standards Track [Page 30]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmMIB MODULE-IDENTITY LAST-UPDATED "201005070000Z" ORGANIZATION "ISMS Working Group" CONTACT-INFO "WG-EMail: isms@lists.ietf.org Subscribe: isms-request@lists.ietf.org Chairs: Juergen Schoenwaelder Jacobs University Bremen Campus Ring 1 28725 Bremen Germany +49 421 200-3587 j.schoenwaelder@jacobs-university.de Russ Mundy SPARTA, Inc. 7110 Samuel Morse Drive Columbia, MD 21046 USA Editor: Wes Hardaker SPARTA, Inc. P.O. Box 382 Davis, CA 95617 USA ietf@hardakers.net " DESCRIPTION " The TLS Transport Model MIB Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info)." REVISION "201005070000Z" DESCRIPTION "This version of this MIB module is part of RFC 5953; see the RFC itself for full legal notices." Hardaker Standards Track [Page 31]
RFC 5953 TLS Transport Model for SNMP August 2010 ::= { mib-2 198 } -- ************************************************ -- subtrees of the SNMP-TLS-TM-MIB -- ************************************************ snmpTlstmNotifications OBJECT IDENTIFIER ::= { snmpTlstmMIB 0 } snmpTlstmIdentities OBJECT IDENTIFIER ::= { snmpTlstmMIB 1 } snmpTlstmObjects OBJECT IDENTIFIER ::= { snmpTlstmMIB 2 } snmpTlstmConformance OBJECT IDENTIFIER ::= { snmpTlstmMIB 3 } -- ************************************************ -- snmpTlstmObjects - Objects -- ************************************************ snmpTLSTCPDomain OBJECT-IDENTITY STATUS current DESCRIPTION "The SNMP over TLS via TCP transport domain. The corresponding transport address is of type SnmpTLSAddress. The securityName prefix to be associated with the snmpTLSTCPDomain is 'tls'. This prefix may be used by security models or other components to identify which secure transport infrastructure authenticated a securityName." REFERENCE "RFC 2579: Textual Conventions for SMIv2" ::= { snmpDomains 8 } snmpDTLSUDPDomain OBJECT-IDENTITY STATUS current DESCRIPTION "The SNMP over DTLS via UDP transport domain. The corresponding transport address is of type SnmpTLSAddress. The securityName prefix to be associated with the snmpDTLSUDPDomain is 'dtls'. This prefix may be used by security models or other components to identify which secure transport infrastructure authenticated a securityName." REFERENCE "RFC 2579: Textual Conventions for SMIv2" ::= { snmpDomains 9 } Hardaker Standards Track [Page 32]
RFC 5953 TLS Transport Model for SNMP August 2010 SnmpTLSAddress ::= TEXTUAL-CONVENTION DISPLAY-HINT "1a" STATUS current DESCRIPTION "Represents an IPv4 address, an IPv6 address, or a US-ASCII-encoded hostname and port number. An IPv4 address must be in dotted decimal format followed by a colon ':' (US-ASCII character 0x3A) and a decimal port number in US-ASCII. An IPv6 address must be a colon-separated format (as described in RFC 5952), surrounded by square brackets ('[', US-ASCII character 0x5B, and ']', US-ASCII character 0x5D), followed by a colon ':' (US-ASCII character 0x3A) and a decimal port number in US-ASCII. A hostname is always in US-ASCII (as per [RFC1033]); internationalized hostnames are encoded in US-ASCII as domain names after transformation via the ToASCII operation specified in [RFC3490]. The ToASCII operation MUST be performed with the UseSTD3ASCIIRules flag set. The hostname is followed by a colon ':' (US-ASCII character 0x3A) and a decimal port number in US-ASCII. The name SHOULD be fully qualified whenever possible. Values of this textual convention may not be directly usable as transport-layer addressing information, and may require run-time resolution. As such, applications that write them must be prepared for handling errors if such values are not supported, or cannot be resolved (if resolution occurs at the time of the management operation). The DESCRIPTION clause of TransportAddress objects that may have SnmpTLSAddress values must fully describe how (and when) such names are to be resolved to IP addresses and vice versa. This textual convention SHOULD NOT be used directly in object definitions since it restricts addresses to a specific format. However, if it is used, it MAY be used either on its own or in conjunction with TransportAddressType or TransportDomain as a pair. When this textual convention is used as a syntax of an index object, there may be issues with the limit of 128 sub-identifiers specified in SMIv2 (STD 58). It is RECOMMENDED that all MIB documents using this textual convention make Hardaker Standards Track [Page 33]
RFC 5953 TLS Transport Model for SNMP August 2010 explicit any limitations on index component lengths that management software must observe. This may be done either by including SIZE constraints on the index components or by specifying applicable constraints in the conceptual row DESCRIPTION clause or in the surrounding documentation." REFERENCE "RFC 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE RFC 3490: Internationalizing Domain Names in Applications RFC 5952: A Recommendation for IPv6 Address Text Representation " SYNTAX OCTET STRING (SIZE (1..255)) SnmpTLSFingerprint ::= TEXTUAL-CONVENTION DISPLAY-HINT "1x:1x" STATUS current DESCRIPTION "A fingerprint value that can be used to uniquely reference other data of potentially arbitrary length. An SnmpTLSFingerprint value is composed of a 1-octet hashing algorithm identifier followed by the fingerprint value. The octet value encoded is taken from the IANA TLS HashAlgorithm Registry (RFC 5246). The remaining octets are filled using the results of the hashing algorithm. This TEXTUAL-CONVENTION allows for a zero-length (blank) SnmpTLSFingerprint value for use in tables where the fingerprint value may be optional. MIB definitions or implementations may refuse to accept a zero-length value as appropriate." REFERENCE "RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2 http://www.iana.org/assignments/tls-parameters/ " SYNTAX OCTET STRING (SIZE (0..255)) -- Identities for use in the snmpTlstmCertToTSNTable snmpTlstmCertToTSNMIdentities OBJECT IDENTIFIER ::= { snmpTlstmIdentities 1 } snmpTlstmCertSpecified OBJECT-IDENTITY STATUS current DESCRIPTION "Directly specifies the tmSecurityName to be used for this certificate. The value of the tmSecurityName to use is specified in the snmpTlstmCertToTSNData column. The snmpTlstmCertToTSNData column must Hardaker Standards Track [Page 34]
RFC 5953 TLS Transport Model for SNMP August 2010 contain a non-zero length SnmpAdminString compliant value or the mapping described in this row must be considered a failure." ::= { snmpTlstmCertToTSNMIdentities 1 } snmpTlstmCertSANRFC822Name OBJECT-IDENTITY STATUS current DESCRIPTION "Maps a subjectAltName's rfc822Name to a tmSecurityName. The local part of the rfc822Name is passed unaltered but the host-part of the name must be passed in lowercase. This mapping results in a 1:1 correspondence between equivalent subjectAltName rfc822Name values and tmSecurityName values except that the host-part of the name MUST be passed in lowercase. Example rfc822Name Field: FooBar@Example.COM is mapped to tmSecurityName: FooBar@example.com." ::= { snmpTlstmCertToTSNMIdentities 2 } snmpTlstmCertSANDNSName OBJECT-IDENTITY STATUS current DESCRIPTION "Maps a subjectAltName's dNSName to a tmSecurityName after first converting it to all lowercase (RFC 5280 does not specify converting to lowercase so this involves an extra step). This mapping results in a 1:1 correspondence between subjectAltName dNSName values and the tmSecurityName values." REFERENCE "RFC 5280 - Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile." ::= { snmpTlstmCertToTSNMIdentities 3 } snmpTlstmCertSANIpAddress OBJECT-IDENTITY STATUS current DESCRIPTION "Maps a subjectAltName's iPAddress to a tmSecurityName by transforming the binary encoded address as follows: 1) for IPv4, the value is converted into a decimal-dotted quad address (e.g., '192.0.2.1'). 2) for IPv6 addresses, the value is converted into a 32-character all lowercase hexadecimal string without any colon separators. Hardaker Standards Track [Page 35]
RFC 5953 TLS Transport Model for SNMP August 2010 This mapping results in a 1:1 correspondence between subjectAltName iPAddress values and the tmSecurityName values. The resulting length of an encoded IPv6 address is the maximum length supported by the View-Based Access Control Model (VACM). Using both the Transport Security Model's support for transport prefixes (see the SNMP-TSM-MIB's snmpTsmConfigurationUsePrefix object for details) will result in securityName lengths that exceed what VACM can handle." ::= { snmpTlstmCertToTSNMIdentities 4 } snmpTlstmCertSANAny OBJECT-IDENTITY STATUS current DESCRIPTION "Maps any of the following fields using the corresponding mapping algorithms: |------------+----------------------------| | Type | Algorithm | |------------+----------------------------| | rfc822Name | snmpTlstmCertSANRFC822Name | | dNSName | snmpTlstmCertSANDNSName | | iPAddress | snmpTlstmCertSANIpAddress | |------------+----------------------------| The first matching subjectAltName value found in the certificate of the above types MUST be used when deriving the tmSecurityName. The mapping algorithm specified in the 'Algorithm' column MUST be used to derive the tmSecurityName. This mapping results in a 1:1 correspondence between subjectAltName values and tmSecurityName values. The three sub-mapping algorithms produced by this combined algorithm cannot produce conflicting results between themselves." ::= { snmpTlstmCertToTSNMIdentities 5 } snmpTlstmCertCommonName OBJECT-IDENTITY STATUS current DESCRIPTION "Maps a certificate's CommonName to a tmSecurityName after converting it to a UTF-8 encoding. The usage of CommonNames is deprecated and users are encouraged to use subjectAltName mapping methods Hardaker Standards Track [Page 36]
RFC 5953 TLS Transport Model for SNMP August 2010 instead. This mapping results in a 1:1 correspondence between certificate CommonName values and tmSecurityName values." ::= { snmpTlstmCertToTSNMIdentities 6 } -- The snmpTlstmSession Group snmpTlstmSession OBJECT IDENTIFIER ::= { snmpTlstmObjects 1 } snmpTlstmSessionOpens OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times an openSession() request has been executed as a (D)TLS client, regardless of whether it succeeded or failed." ::= { snmpTlstmSession 1 } snmpTlstmSessionClientCloses OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a closeSession() request has been executed as an (D)TLS client, regardless of whether it succeeded or failed." ::= { snmpTlstmSession 2 } snmpTlstmSessionOpenErrors OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times an openSession() request failed to open a session as a (D)TLS client, for any reason." ::= { snmpTlstmSession 3 } snmpTlstmSessionAccepts OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a (D)TLS server has accepted a new connection from a client and has received at least one SNMP message through it." ::= { snmpTlstmSession 4 } Hardaker Standards Track [Page 37]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmSessionServerCloses OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times a closeSession() request has been executed as an (D)TLS server, regardless of whether it succeeded or failed." ::= { snmpTlstmSession 5 } snmpTlstmSessionNoSessions OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times an outgoing message was dropped because the session associated with the passed tmStateReference was no longer (or was never) available." ::= { snmpTlstmSession 6 } snmpTlstmSessionInvalidClientCertificates OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times an incoming session was not established on an (D)TLS server because the presented client certificate was invalid. Reasons for invalidation include, but are not limited to, cryptographic validation failures or lack of a suitable mapping row in the snmpTlstmCertToTSNTable." ::= { snmpTlstmSession 7 } snmpTlstmSessionUnknownServerCertificate OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times an outgoing session was not established on an (D)TLS client because the server certificate presented by an SNMP over (D)TLS server was invalid because no configured fingerprint or Certification Authority (CA) was acceptable to validate it. This may result because there was no entry in the snmpTlstmAddrTable or because no path could be found to a known CA." ::= { snmpTlstmSession 8 } Hardaker Standards Track [Page 38]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmSessionInvalidServerCertificates OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of times an outgoing session was not established on an (D)TLS client because the server certificate presented by an SNMP over (D)TLS server could not be validated even if the fingerprint or expected validation path was known. That is, a cryptographic validation error occurred during certificate validation processing. Reasons for invalidation include, but are not limited to, cryptographic validation failures." ::= { snmpTlstmSession 9 } snmpTlstmSessionInvalidCaches OBJECT-TYPE SYNTAX Counter32 MAX-ACCESS read-only STATUS current DESCRIPTION "The number of outgoing messages dropped because the tmStateReference referred to an invalid cache." ::= { snmpTlstmSession 10 } -- Configuration Objects snmpTlstmConfig OBJECT IDENTIFIER ::= { snmpTlstmObjects 2 } -- Certificate mapping snmpTlstmCertificateMapping OBJECT IDENTIFIER ::= { snmpTlstmConfig 1 } snmpTlstmCertToTSNCount OBJECT-TYPE SYNTAX Gauge32 MAX-ACCESS read-only STATUS current DESCRIPTION "A count of the number of entries in the snmpTlstmCertToTSNTable." ::= { snmpTlstmCertificateMapping 1 } Hardaker Standards Track [Page 39]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmCertToTSNTableLastChanged OBJECT-TYPE SYNTAX TimeStamp MAX-ACCESS read-only STATUS current DESCRIPTION "The value of sysUpTime.0 when the snmpTlstmCertToTSNTable was last modified through any means, or 0 if it has not been modified since the command responder was started." ::= { snmpTlstmCertificateMapping 2 } snmpTlstmCertToTSNTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpTlstmCertToTSNEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "This table is used by a (D)TLS server to map the (D)TLS client's presented X.509 certificate to a tmSecurityName. On an incoming (D)TLS/SNMP connection, the client's presented certificate must either be validated based on an established trust anchor, or it must directly match a fingerprint in this table. This table does not provide any mechanisms for configuring the trust anchors; the transfer of any needed trusted certificates for path validation is expected to occur through an out-of-band transfer. Once the certificate has been found acceptable (either by path validation or directly matching a fingerprint in this table), this table is consulted to determine the appropriate tmSecurityName to identify with the remote connection. This is done by considering each active row from this table in prioritized order according to its snmpTlstmCertToTSNID value. Each row's snmpTlstmCertToTSNFingerprint value determines whether the row is a match for the incoming connection: 1) If the row's snmpTlstmCertToTSNFingerprint value identifies the presented certificate, then consider the row as a successful match. 2) If the row's snmpTlstmCertToTSNFingerprint value identifies a locally held copy of a trusted CA certificate and that CA certificate was used to validate the path to the presented certificate, then consider the row as a successful match. Once a matching row has been found, the snmpTlstmCertToTSNMapType value can be used to determine how the tmSecurityName to associate with the session should be Hardaker Standards Track [Page 40]
RFC 5953 TLS Transport Model for SNMP August 2010 determined. See the snmpTlstmCertToTSNMapType column's DESCRIPTION for details on determining the tmSecurityName value. If it is impossible to determine a tmSecurityName from the row's data combined with the data presented in the certificate, then additional rows MUST be searched looking for another potential match. If a resulting tmSecurityName mapped from a given row is not compatible with the needed requirements of a tmSecurityName (e.g., VACM imposes a 32-octet-maximum length and the certificate derived securityName could be longer), then it must be considered an invalid match and additional rows MUST be searched looking for another potential match. If no matching and valid row can be found, the connection MUST be closed and SNMP messages MUST NOT be accepted over it. Missing values of snmpTlstmCertToTSNID are acceptable and implementations should continue to the next highest numbered row. It is recommended that administrators skip index values to leave room for the insertion of future rows (for example, use values of 10 and 20 when creating initial rows). Users are encouraged to make use of certificates with subjectAltName fields that can be used as tmSecurityNames so that a single root CA certificate can allow all child certificate's subjectAltName to map directly to a tmSecurityName via a 1:1 transformation. However, this table is flexible to allow for situations where existing deployed certificate infrastructures do not provide adequate subjectAltName values for use as tmSecurityNames. Certificates may also be mapped to tmSecurityNames using the CommonName portion of the Subject field. However, the usage of the CommonName field is deprecated and thus this usage is NOT RECOMMENDED. Direct mapping from each individual certificate fingerprint to a tmSecurityName is also possible but requires one entry in the table per tmSecurityName and requires more management operations to completely configure a device." ::= { snmpTlstmCertificateMapping 3 } snmpTlstmCertToTSNEntry OBJECT-TYPE SYNTAX SnmpTlstmCertToTSNEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A row in the snmpTlstmCertToTSNTable that specifies a mapping for an incoming (D)TLS certificate to a tmSecurityName to use for a connection." Hardaker Standards Track [Page 41]
RFC 5953 TLS Transport Model for SNMP August 2010 INDEX { snmpTlstmCertToTSNID } ::= { snmpTlstmCertToTSNTable 1 } SnmpTlstmCertToTSNEntry ::= SEQUENCE { snmpTlstmCertToTSNID Unsigned32, snmpTlstmCertToTSNFingerprint SnmpTLSFingerprint, snmpTlstmCertToTSNMapType AutonomousType, snmpTlstmCertToTSNData OCTET STRING, snmpTlstmCertToTSNStorageType StorageType, snmpTlstmCertToTSNRowStatus RowStatus } snmpTlstmCertToTSNID OBJECT-TYPE SYNTAX Unsigned32 (1..4294967295) MAX-ACCESS not-accessible STATUS current DESCRIPTION "A unique, prioritized index for the given entry. Lower numbers indicate a higher priority." ::= { snmpTlstmCertToTSNEntry 1 } snmpTlstmCertToTSNFingerprint OBJECT-TYPE SYNTAX SnmpTLSFingerprint (SIZE(1..255)) MAX-ACCESS read-create STATUS current DESCRIPTION "A cryptographic hash of a X.509 certificate. The results of a successful matching fingerprint to either the trusted CA in the certificate validation path or to the certificate itself is dictated by the snmpTlstmCertToTSNMapType column." ::= { snmpTlstmCertToTSNEntry 2 } snmpTlstmCertToTSNMapType OBJECT-TYPE SYNTAX AutonomousType MAX-ACCESS read-create STATUS current DESCRIPTION "Specifies the mapping type for deriving a tmSecurityName from a certificate. Details for mapping of a particular type SHALL be specified in the DESCRIPTION clause of the OBJECT-IDENTITY that describes the mapping. If a mapping succeeds it will return a tmSecurityName for use by the TLSTM model and processing stops. If the resulting mapped value is not compatible with the needed requirements of a tmSecurityName (e.g., VACM imposes a 32-octet-maximum length and the certificate derived Hardaker Standards Track [Page 42]
RFC 5953 TLS Transport Model for SNMP August 2010 securityName could be longer), then future rows MUST be searched for additional snmpTlstmCertToTSNFingerprint matches to look for a mapping that succeeds. Suitable values for assigning to this object that are defined within the SNMP-TLS-TM-MIB can be found in the snmpTlstmCertToTSNMIdentities portion of the MIB tree." DEFVAL { snmpTlstmCertSpecified } ::= { snmpTlstmCertToTSNEntry 3 } snmpTlstmCertToTSNData OBJECT-TYPE SYNTAX OCTET STRING (SIZE(0..1024)) MAX-ACCESS read-create STATUS current DESCRIPTION "Auxiliary data used as optional configuration information for a given mapping specified by the snmpTlstmCertToTSNMapType column. Only some mapping systems will make use of this column. The value in this column MUST be ignored for any mapping type that does not require data present in this column." DEFVAL { "" } ::= { snmpTlstmCertToTSNEntry 4 } snmpTlstmCertToTSNStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpTlstmCertToTSNEntry 5 } snmpTlstmCertToTSNRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. This object may be used to create or remove rows from this table. To create a row in this table, an administrator must set this object to either createAndGo(4) or createAndWait(5). Hardaker Standards Track [Page 43]
RFC 5953 TLS Transport Model for SNMP August 2010 Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the snmpTlstmParamsRowStatus column is notReady(3). In particular, a newly created row cannot be made active until the corresponding snmpTlstmCertToTSNFingerprint, snmpTlstmCertToTSNMapType, and snmpTlstmCertToTSNData columns have been set. The following objects may not be modified while the value of this object is active(1): - snmpTlstmCertToTSNFingerprint - snmpTlstmCertToTSNMapType - snmpTlstmCertToTSNData An attempt to set these objects while the value of snmpTlstmParamsRowStatus is active(1) will result in an inconsistentValue error." ::= { snmpTlstmCertToTSNEntry 6 } -- Maps tmSecurityNames to certificates for use by the SNMP-TARGET-MIB snmpTlstmParamsCount OBJECT-TYPE SYNTAX Gauge32 MAX-ACCESS read-only STATUS current DESCRIPTION "A count of the number of entries in the snmpTlstmParamsTable." ::= { snmpTlstmCertificateMapping 4 } snmpTlstmParamsTableLastChanged OBJECT-TYPE SYNTAX TimeStamp MAX-ACCESS read-only STATUS current DESCRIPTION "The value of sysUpTime.0 when the snmpTlstmParamsTable was last modified through any means, or 0 if it has not been modified since the command responder was started." ::= { snmpTlstmCertificateMapping 5 } Hardaker Standards Track [Page 44]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmParamsTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpTlstmParamsEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "This table is used by a (D)TLS client when a (D)TLS connection is being set up using an entry in the SNMP-TARGET-MIB. It extends the SNMP-TARGET-MIB's snmpTargetParamsTable with a fingerprint of a certificate to use when establishing such a (D)TLS connection." ::= { snmpTlstmCertificateMapping 6 } snmpTlstmParamsEntry OBJECT-TYPE SYNTAX SnmpTlstmParamsEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A conceptual row containing a fingerprint hash of a locally held certificate for a given snmpTargetParamsEntry. The values in this row should be ignored if the connection that needs to be established, as indicated by the SNMP-TARGET-MIB infrastructure, is not a certificate and (D)TLS based connection. The connection SHOULD NOT be established if the certificate fingerprint stored in this entry does not point to a valid locally held certificate or if it points to an unusable certificate (such as might happen when the certificate's expiration date has been reached)." INDEX { IMPLIED snmpTargetParamsName } ::= { snmpTlstmParamsTable 1 } SnmpTlstmParamsEntry ::= SEQUENCE { snmpTlstmParamsClientFingerprint SnmpTLSFingerprint, snmpTlstmParamsStorageType StorageType, snmpTlstmParamsRowStatus RowStatus } snmpTlstmParamsClientFingerprint OBJECT-TYPE SYNTAX SnmpTLSFingerprint MAX-ACCESS read-create STATUS current DESCRIPTION "This object stores the hash of the public portion of a locally held X.509 certificate. The X.509 certificate, its public key, and the corresponding private key will be used when initiating a (D)TLS connection as a (D)TLS client." ::= { snmpTlstmParamsEntry 1 } Hardaker Standards Track [Page 45]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmParamsStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpTlstmParamsEntry 2 } snmpTlstmParamsRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current DESCRIPTION "The status of this conceptual row. This object may be used to create or remove rows from this table. To create a row in this table, an administrator must set this object to either createAndGo(4) or createAndWait(5). Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the snmpTlstmParamsRowStatus column is notReady(3). In particular, a newly created row cannot be made active until the corresponding snmpTlstmParamsClientFingerprint column has been set. The snmpTlstmParamsClientFingerprint object may not be modified while the value of this object is active(1). An attempt to set these objects while the value of snmpTlstmParamsRowStatus is active(1) will result in an inconsistentValue error." ::= { snmpTlstmParamsEntry 3 } snmpTlstmAddrCount OBJECT-TYPE SYNTAX Gauge32 MAX-ACCESS read-only STATUS current DESCRIPTION "A count of the number of entries in the snmpTlstmAddrTable." ::= { snmpTlstmCertificateMapping 7 } Hardaker Standards Track [Page 46]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmAddrTableLastChanged OBJECT-TYPE SYNTAX TimeStamp MAX-ACCESS read-only STATUS current DESCRIPTION "The value of sysUpTime.0 when the snmpTlstmAddrTable was last modified through any means, or 0 if it has not been modified since the command responder was started." ::= { snmpTlstmCertificateMapping 8 } snmpTlstmAddrTable OBJECT-TYPE SYNTAX SEQUENCE OF SnmpTlstmAddrEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "This table is used by a (D)TLS client when a (D)TLS connection is being set up using an entry in the SNMP-TARGET-MIB. It extends the SNMP-TARGET-MIB's snmpTargetAddrTable so that the client can verify that the correct server has been reached. This verification can use either a certificate fingerprint, or an identity authenticated via certification path validation. If there is an active row in this table corresponding to the entry in the SNMP-TARGET-MIB that was used to establish the connection, and the row's snmpTlstmAddrServerFingerprint column has non-empty value, then the server's presented certificate is compared with the snmpTlstmAddrServerFingerprint value (and the snmpTlstmAddrServerIdentity column is ignored). If the fingerprint matches, the verification has succeeded. If the fingerprint does not match, then the connection MUST be closed. If the server's presented certificate has passed certification path validation [RFC5280] to a configured trust anchor, and an active row exists with a zero-length snmpTlstmAddrServerFingerprint value, then the snmpTlstmAddrServerIdentity column contains the expected host name. This expected host name is then compared against the server's certificate as follows: - Implementations MUST support matching the expected host name against a dNSName in the subjectAltName extension field and MAY support checking the name against the CommonName portion of the subject distinguished name. Hardaker Standards Track [Page 47]
RFC 5953 TLS Transport Model for SNMP August 2010 - The '*' (ASCII 0x2a) wildcard character is allowed in the dNSName of the subjectAltName extension (and in common name, if used to store the host name), but only as the left-most (least significant) DNS label in that value. This wildcard matches any left-most DNS label in the server name. That is, the subject *.example.com matches the server names a.example.com and b.example.com, but does not match example.com or a.b.example.com. Implementations MUST support wildcards in certificates as specified above, but MAY provide a configuration option to disable them. - If the locally configured name is an internationalized domain name, conforming implementations MUST convert it to the ASCII Compatible Encoding (ACE) format for performing comparisons, as specified in Section 7 of [RFC5280]. If the expected host name fails these conditions then the connection MUST be closed. If there is no row in this table corresponding to the entry in the SNMP-TARGET-MIB and the server can be authorized by another, implementation-dependent means, then the connection MAY still proceed." ::= { snmpTlstmCertificateMapping 9 } snmpTlstmAddrEntry OBJECT-TYPE SYNTAX SnmpTlstmAddrEntry MAX-ACCESS not-accessible STATUS current DESCRIPTION "A conceptual row containing a copy of a certificate's fingerprint for a given snmpTargetAddrEntry. The values in this row should be ignored if the connection that needs to be established, as indicated by the SNMP-TARGET-MIB infrastructure, is not a (D)TLS based connection. If an snmpTlstmAddrEntry exists for a given snmpTargetAddrEntry, then the presented server certificate MUST match or the connection MUST NOT be established. If a row in this table does not exist to match an snmpTargetAddrEntry row, then the connection SHOULD still proceed if some other certificate validation path algorithm (e.g., RFC 5280) can be used." INDEX { IMPLIED snmpTargetAddrName } ::= { snmpTlstmAddrTable 1 } Hardaker Standards Track [Page 48]
RFC 5953 TLS Transport Model for SNMP August 2010 SnmpTlstmAddrEntry ::= SEQUENCE { snmpTlstmAddrServerFingerprint SnmpTLSFingerprint, snmpTlstmAddrServerIdentity SnmpAdminString, snmpTlstmAddrStorageType StorageType, snmpTlstmAddrRowStatus RowStatus } snmpTlstmAddrServerFingerprint OBJECT-TYPE SYNTAX SnmpTLSFingerprint MAX-ACCESS read-create STATUS current DESCRIPTION "A cryptographic hash of a public X.509 certificate. This object should store the hash of the public X.509 certificate that the remote server should present during the (D)TLS connection setup. The fingerprint of the presented certificate and this hash value MUST match exactly or the connection MUST NOT be established." DEFVAL { "" } ::= { snmpTlstmAddrEntry 1 } snmpTlstmAddrServerIdentity OBJECT-TYPE SYNTAX SnmpAdminString MAX-ACCESS read-create STATUS current DESCRIPTION "The reference identity to check against the identity presented by the remote system." DEFVAL { "" } ::= { snmpTlstmAddrEntry 2 } snmpTlstmAddrStorageType OBJECT-TYPE SYNTAX StorageType MAX-ACCESS read-create STATUS current DESCRIPTION "The storage type for this conceptual row. Conceptual rows having the value 'permanent' need not allow write-access to any columnar objects in the row." DEFVAL { nonVolatile } ::= { snmpTlstmAddrEntry 3 } snmpTlstmAddrRowStatus OBJECT-TYPE SYNTAX RowStatus MAX-ACCESS read-create STATUS current Hardaker Standards Track [Page 49]
RFC 5953 TLS Transport Model for SNMP August 2010 DESCRIPTION "The status of this conceptual row. This object may be used to create or remove rows from this table. To create a row in this table, an administrator must set this object to either createAndGo(4) or createAndWait(5). Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the snmpTlstmAddrRowStatus column is notReady(3). In particular, a newly created row cannot be made active until the corresponding snmpTlstmAddrServerFingerprint column has been set. Rows MUST NOT be active if the snmpTlstmAddrServerFingerprint column is blank and the snmpTlstmAddrServerIdentity is set to '*' since this would insecurely accept any presented certificate. The snmpTlstmAddrServerFingerprint object may not be modified while the value of this object is active(1). An attempt to set these objects while the value of snmpTlstmAddrRowStatus is active(1) will result in an inconsistentValue error." ::= { snmpTlstmAddrEntry 4 } -- ************************************************ -- snmpTlstmNotifications - Notifications Information -- ************************************************ snmpTlstmServerCertificateUnknown NOTIFICATION-TYPE OBJECTS { snmpTlstmSessionUnknownServerCertificate } STATUS current DESCRIPTION "Notification that the server certificate presented by an SNMP over (D)TLS server was invalid because no configured fingerprint or CA was acceptable to validate it. This may be because there was no entry in the snmpTlstmAddrTable or because no path could be found to known Certification Authority. Hardaker Standards Track [Page 50]
RFC 5953 TLS Transport Model for SNMP August 2010 To avoid notification loops, this notification MUST NOT be sent to servers that themselves have triggered the notification." ::= { snmpTlstmNotifications 1 } snmpTlstmServerInvalidCertificate NOTIFICATION-TYPE OBJECTS { snmpTlstmAddrServerFingerprint, snmpTlstmSessionInvalidServerCertificates} STATUS current DESCRIPTION "Notification that the server certificate presented by an SNMP over (D)TLS server could not be validated even if the fingerprint or expected validation path was known. That is, a cryptographic validation error occurred during certificate validation processing. To avoid notification loops, this notification MUST NOT be sent to servers that themselves have triggered the notification." ::= { snmpTlstmNotifications 2 } -- ************************************************ -- snmpTlstmCompliances - Conformance Information -- ************************************************ snmpTlstmCompliances OBJECT IDENTIFIER ::= { snmpTlstmConformance 1 } snmpTlstmGroups OBJECT IDENTIFIER ::= { snmpTlstmConformance 2 } -- ************************************************ -- Compliance statements -- ************************************************ snmpTlstmCompliance MODULE-COMPLIANCE STATUS current DESCRIPTION "The compliance statement for SNMP engines that support the SNMP-TLS-TM-MIB" MODULE MANDATORY-GROUPS { snmpTlstmStatsGroup, snmpTlstmIncomingGroup, snmpTlstmOutgoingGroup, snmpTlstmNotificationGroup } ::= { snmpTlstmCompliances 1 } Hardaker Standards Track [Page 51]
RFC 5953 TLS Transport Model for SNMP August 2010 -- ************************************************ -- Units of conformance -- ************************************************ snmpTlstmStatsGroup OBJECT-GROUP OBJECTS { snmpTlstmSessionOpens, snmpTlstmSessionClientCloses, snmpTlstmSessionOpenErrors, snmpTlstmSessionAccepts, snmpTlstmSessionServerCloses, snmpTlstmSessionNoSessions, snmpTlstmSessionInvalidClientCertificates, snmpTlstmSessionUnknownServerCertificate, snmpTlstmSessionInvalidServerCertificates, snmpTlstmSessionInvalidCaches } STATUS current DESCRIPTION "A collection of objects for maintaining statistical information of an SNMP engine that implements the SNMP TLS Transport Model." ::= { snmpTlstmGroups 1 } snmpTlstmIncomingGroup OBJECT-GROUP OBJECTS { snmpTlstmCertToTSNCount, snmpTlstmCertToTSNTableLastChanged, snmpTlstmCertToTSNFingerprint, snmpTlstmCertToTSNMapType, snmpTlstmCertToTSNData, snmpTlstmCertToTSNStorageType, snmpTlstmCertToTSNRowStatus } STATUS current DESCRIPTION "A collection of objects for maintaining incoming connection certificate mappings to tmSecurityNames of an SNMP engine that implements the SNMP TLS Transport Model." ::= { snmpTlstmGroups 2 } snmpTlstmOutgoingGroup OBJECT-GROUP OBJECTS { snmpTlstmParamsCount, snmpTlstmParamsTableLastChanged, snmpTlstmParamsClientFingerprint, snmpTlstmParamsStorageType, snmpTlstmParamsRowStatus, Hardaker Standards Track [Page 52]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTlstmAddrCount, snmpTlstmAddrTableLastChanged, snmpTlstmAddrServerFingerprint, snmpTlstmAddrServerIdentity, snmpTlstmAddrStorageType, snmpTlstmAddrRowStatus } STATUS current DESCRIPTION "A collection of objects for maintaining outgoing connection certificates to use when opening connections as a result of SNMP-TARGET-MIB settings." ::= { snmpTlstmGroups 3 } snmpTlstmNotificationGroup NOTIFICATION-GROUP NOTIFICATIONS { snmpTlstmServerCertificateUnknown, snmpTlstmServerInvalidCertificate } STATUS current DESCRIPTION "Notifications" ::= { snmpTlstmGroups 4 } END 8. Operational Considerations This section discusses various operational aspects of deploying TLSTM. 8.1. Sessions A session is discussed throughout this document as meaning a security association between two TLSTM instances. State information for the sessions are maintained in each TLSTM implementation and this information is created and destroyed as sessions are opened and closed. A "broken" session (one side up and one side down) can result if one side of a session is brought down abruptly (i.e., reboot, power outage, etc.). Whenever possible, implementations SHOULD provide graceful session termination through the use of TLS disconnect messages. Implementations SHOULD also have a system in place for detecting "broken" sessions through the use of heartbeats [HEARTBEAT] or other detection mechanisms. Hardaker Standards Track [Page 53]
RFC 5953 TLS Transport Model for SNMP August 2010 Implementations SHOULD limit the lifetime of established sessions depending on the algorithms used for generation of the master session secret, the privacy and integrity algorithms used to protect messages, the environment of the session, the amount of data transferred, and the sensitivity of the data. 8.2. Notification Receiver Credential Selection When an SNMP engine needs to establish an outgoing session for notifications, the snmpTargetParamsTable includes an entry for the snmpTargetParamsSecurityName of the target. Servers that wish to support multiple principals at a particular port SHOULD make use of the Server Name Indication extension defined in Section 3.1 of [RFC4366]. Without the Server Name Indication the receiving SNMP engine (server) will not know which (D)TLS certificate to offer to the client so that the tmSecurityName identity-authentication will be successful. Another solution is to maintain a one-to-one mapping between certificates and incoming ports for notification receivers. This can be handled at the notification originator by configuring the snmpTargetAddrTable (snmpTargetAddrTDomain and snmpTargetAddrTAddress) and requiring the receiving SNMP engine to monitor multiple incoming static ports based on which principals are capable of receiving notifications. Implementations MAY also choose to designate a single Notification Receiver Principal to receive all incoming notifications or select an implementation specific method of selecting a server certificate to present to clients. 8.3. contextEngineID Discovery SNMPv3 requires that an application know the identifier (snmpEngineID) of the remote SNMP protocol engine in order to retrieve or manipulate objects maintained on the remote SNMP entity. [] introduces a well-known localEngineID and a discovery mechanism that can be used to learn the snmpEngineID of a remote SNMP protocol engine. Implementations are RECOMMENDED to support and use the contextEngineID discovery mechanism defined in [RFC5343]. Hardaker Standards Track [Page 54]
RFC 5953 TLS Transport Model for SNMP August 2010 8.4. Transport Considerations This document defines how SNMP messages can be transmitted over the TLS- and DTLS-based protocols. Each of these protocols are additionally based on other transports (TCP and UDP). These two base protocols also have operational considerations that must be taken into consideration when selecting a (D)TLS-based protocol to use such as its performance in degraded or limited networks. It is beyond the scope of this document to summarize the characteristics of these transport mechanisms. Please refer to the base protocol documents for details on messaging considerations with respect to MTU size, fragmentation, performance in lossy networks, etc. 9. Security Considerations This document describes a transport model that permits SNMP to utilize (D)TLS security services. The security threats and how the (D)TLS transport model mitigates these threats are covered in detail throughout this document. Security considerations for DTLS are covered in [RFC4347] and security considerations for TLS are described in Section 11 and Appendices D, E, and F of TLS 1.2 [RFC5246]. When run over a connectionless transport such as UDP, DTLS is more vulnerable to denial-of-service attacks from spoofed IP addresses; see Section 4.2 for details how the cookie exchange is used to address this issue. 9.1. Certificates, Authentication, and Authorization Implementations are responsible for providing a security certificate installation and configuration mechanism. Implementations SHOULD support certificate revocation lists. (D)TLS provides for authentication of the identity of both the (D)TLS server and the (D)TLS client. Access to MIB objects for the authenticated principal MUST be enforced by an access control subsystem (e.g., the VACM). Authentication of the command generator principal's identity is important for use with the SNMP access control subsystem to ensure that only authorized principals have access to potentially sensitive data. The authenticated identity of the command generator principal's certificate is mapped to an SNMP model-independent securityName for use with SNMP access control. The (D)TLS handshake only provides assurance that the certificate of the authenticated identity has been signed by a configured accepted Certification Authority. (D)TLS has no way to further authorize or reject access based on the authenticated identity. An Access Control Hardaker Standards Track [Page 55]
RFC 5953 TLS Transport Model for SNMP August 2010 Model (such as the VACM) provides access control and authorization of a command generator's requests to a command responder and a notification receiver's authorization to receive Notifications from a notification originator. However, to avoid man-in-the-middle attacks, both ends of the (D)TLS-based connection MUST check the certificate presented by the other side against what was expected. For example, command generators must check that the command responder presented and authenticated itself with a X.509 certificate that was expected. Not doing so would allow an impostor, at a minimum, to present false data, receive sensitive information and/or provide a false belief that configuration was actually received and acted upon. Authenticating and verifying the identity of the (D)TLS server and the (D)TLS client for all operations ensures the authenticity of the SNMP engine that provides MIB data. The instructions found in the DESCRIPTION clause of the snmpTlstmCertToTSNTable object must be followed exactly. It is also important that the rows of the table be searched in prioritized order starting with the row containing the lowest numbered snmpTlstmCertToTSNID value. 9.2. (D)TLS Security Considerations This section discusses security considerations specific to the usage of (D)TLS. 9.2.1. TLS Version Requirements Implementations of TLS typically support multiple versions of the Transport Layer Security protocol as well as the older Secure Sockets Layer (SSL) protocol. Because of known security vulnerabilities, TLSTM clients and servers MUST NOT request, offer, or use SSL 2.0. See Appendix E.2 of [RFC5246] for further details. 9.2.2. Perfect Forward Secrecy The use of Perfect Forward Secrecy is RECOMMENDED and can be provided by (D)TLS with appropriately selected cipher_suites, as discussed in Appendix F of [RFC5246]. 9.3. Use with SNMPv1/SNMPv2c Messages The SNMPv1 and SNMPv2c message processing described in [RFC3584] (BCP 74) always selects the SNMPv1 or SNMPv2c Security Models, respectively. Both of these and the User-based Security Model typically used with SNMPv3 derive the securityName and securityLevel from the SNMP message received, even when the message was received over a secure transport. Access control decisions are therefore made Hardaker Standards Track [Page 56]
RFC 5953 TLS Transport Model for SNMP August 2010 based on the contents of the SNMP message, rather than using the authenticated identity and securityLevel provided by the TLS Transport Model. It is RECOMMENDED that only SNMPv3 messages using the Transport Security Model (TSM) or another secure-transport aware security model be sent over the TLSTM transport. Using a non-transport-aware Security Model with a secure Transport Model is NOT RECOMMENDED. See [RFC5590] Section 7.1 for additional details on the coexistence of security-aware transports and non- transport-aware security models. 9.4. MIB Module Security There are a number of management objects defined in this MIB module with a MAX-ACCESS clause of read-write and/or read-create. Such objects may be considered sensitive or vulnerable in some network environments. The support for SET operations in a non-secure environment without proper protection can have a negative effect on network operations. These are the tables and objects and their sensitivity/vulnerability: o The snmpTlstmParamsTable can be used to change the outgoing X.509 certificate used to establish a (D)TLS connection. Modification to objects in this table need to be adequately authenticated since modification to values in this table will have profound impacts to the security of outbound connections from the device. Since knowledge of authorization rules and certificate usage mechanisms may be considered sensitive, protection from disclosure of the SNMP traffic via encryption is also highly recommended. o The snmpTlstmAddrTable can be used to change the expectations of the certificates presented by a remote (D)TLS server. Modification to objects in this table need to be adequately authenticated since modification to values in this table will have profound impacts to the security of outbound connections from the device. Since knowledge of authorization rules and certificate usage mechanisms may be considered sensitive, protection from disclosure of the SNMP traffic via encryption is also highly recommended. o The snmpTlstmCertToTSNTable is used to specify the mapping of incoming X.509 certificates to tmSecurityNames, which eventually get mapped to a SNMPv3 securityName. Modification to objects in this table need to be adequately authenticated since modification to values in this table will have profound impacts to the security of incoming connections to the device. Since knowledge of authorization rules and certificate usage mechanisms may be considered sensitive, protection from disclosure of the SNMP Hardaker Standards Track [Page 57]
RFC 5953 TLS Transport Model for SNMP August 2010 traffic via encryption is also highly recommended. When this table contains a significant number of rows it may affect the system performance when accepting new (D)TLS connections. 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 This MIB contains a collection of counters that monitor the (D)TLS connections being established with a device. Since knowledge of connection and certificate usage mechanisms may be considered sensitive, protection from disclosure of the SNMP traffic via encryption is highly recommended. 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 SNMPv3 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. 10. IANA Considerations IANA has assigned: 1. Two TCP/UDP port numbers from the "Registered Ports" range of the Port Numbers registry, with the following keywords: Hardaker Standards Track [Page 58]
RFC 5953 TLS Transport Model for SNMP August 2010 Keyword Decimal Description References ------- ------- ----------- ---------- snmptls 10161/tcp SNMP-TLS [RFC5953] snmpdtls 10161/udp SNMP-DTLS [RFC5953] snmptls-trap 10162/tcp SNMP-Trap-TLS [RFC5953] snmpdtls-trap 10162/udp SNMP-Trap-DTLS [RFC5953] These are the default ports for receipt of SNMP command messages (snmptls and snmpdtls) and SNMP notification messages (snmptls- trap and snmpdtls-trap) over a TLS Transport Model as defined in this document. 2. An SMI number (8) under snmpDomains for the snmpTLSTCPDomain object identifier 3. An SMI number (9) under snmpDomains for the snmpDTLSUDPDomain object identifier 4. An SMI number (198) under mib-2, for the MIB module in this document 5. "tls" as the corresponding prefix for the snmpTLSTCPDomain in the SNMP Transport Domains registry 6. "dtls" as the corresponding prefix for the snmpDTLSUDPDomain in the SNMP Transport Domains registry 11. Acknowledgements This document closely follows and copies the Secure Shell Transport Model for SNMP documented by David Harrington and Joseph Salowey in [RFC5592]. This document was reviewed by the following people who helped provide useful comments (in alphabetical order): Andy Donati, Pasi Eronen, David Harrington, Jeffrey Hutzelman, Alan Luchuk, Michael Peck, Tom Petch, Randy Presuhn, Ray Purvis, Peter Saint-Andre, Joseph Salowey, Juergen Schoenwaelder, Dave Shield, and Robert Story. This work was supported in part by the United States Department of Defense. Large portions of this document are based on work by General Dynamics C4 Systems and the following individuals: Brian Baril, Kim Bryant, Dana Deluca, Dan Hanson, Tim Huemiller, John Holzhauer, Colin Hoogeboom, Dave Kornbau, Chris Knaian, Dan Knaul, Charles Limoges, Steve Moccaldi, Gerardo Orlando, and Brandon Yip. Hardaker Standards Track [Page 59]
RFC 5953 TLS Transport Model for SNMP August 2010 12. References 12.1. Normative References [] Lottor, M., "Domain administrators operations guide", RFC 1033, November 1987. [] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999. [] McCloghrie, K., Ed., Perkins, D., Ed., and J. Schoenwaelder, Ed., "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999. [] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999. [] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, December 2002. [] Levi, D., Meyer, P., and B. Stewart, "Simple Network Management Protocol (SNMP) Applications", STD 62, RFC 3413, December 2002. [] 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. [] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3415, December 2002. [] Presuhn, R., "Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)", STD 62, RFC 3418, December 2002. [] Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing Domain Names in Applications (IDNA)", RFC 3490, March 2003. Hardaker Standards Track [Page 60]
RFC 5953 TLS Transport Model for SNMP August 2010 [] 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. [] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security", RFC 4347, April 2006. [] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and T. Wright, "Transport Layer Security (TLS) Extensions", RFC 4366, April 2006. [] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. [] Harrington, D. and J. Schoenwaelder, "Transport Subsystem for the Simple Network Management Protocol (SNMP)", RFC 5590, June 2009. [] Harrington, D. and W. Hardaker, "Transport Security Model for the Simple Network Management Protocol (SNMP)", RFC 5591, June 2009. [] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, August 2010. 12.2. Informative References [] Case, J., Mundy, R., Partain, D., and B. Stewart, "Introduction and Applicability Statements for Internet- Standard Management Framework", RFC 3410, December 2002. [] Schoenwaelder, J., "Simple Network Management Protocol (SNMP) Context EngineID Discovery", RFC 5343, September 2008. [] Harrington, D., Salowey, J., and W. Hardaker, "Secure Shell Transport Model for the Simple Network Management Protocol (SNMP)", RFC 5592, June 2009. Hardaker Standards Track [Page 61]
RFC 5953 TLS Transport Model for SNMP August 2010 [] Seggelmann, R., Tuexen, M., and M. Williams, "Transport Layer Security and Datagram Transport Layer Security Heartbeat Extension", Work in Progress, February 2010. Hardaker Standards Track [Page 62]
RFC 5953 TLS Transport Model for SNMP August 2010 Appendix A. Target and Notification Configuration Example The following sections describe example configuration for the SNMP- TLS-TM-MIB, the SNMP-TARGET-MIB, the NOTIFICATION-MIB, and the SNMP- VIEW-BASED-ACM-MIB. A.1. Configuring a Notification Originator The following row adds the "Joe Cool" user to the "administrators" group: vacmSecurityModel = 4 (TSM) vacmSecurityName = "Joe Cool" vacmGroupName = "administrators" vacmSecurityToGroupStorageType = 3 (nonVolatile) vacmSecurityToGroupStatus = 4 (createAndGo) The following row configures the snmpTlstmAddrTable to use certificate path validation and to require the remote notification receiver to present a certificate for the "server.example.org" identity. snmpTargetAddrName = "toNRAddr" snmpTlstmAddrServerFingerprint = "" snmpTlstmAddrServerIdentity = "server.example.org" snmpTlstmAddrStorageType = 3 (nonVolatile) snmpTlstmAddrRowStatus = 4 (createAndGo) The following row configures the snmpTargetAddrTable to send notifications using TLS/TCP to the snmptls-trap port at 192.0.2.1: snmpTargetAddrName = "toNRAddr" snmpTargetAddrTDomain = snmpTLSTCPDomain snmpTargetAddrTAddress = "192.0.2.1:10162" snmpTargetAddrTimeout = 1500 snmpTargetAddrRetryCount = 3 snmpTargetAddrTagList = "toNRTag" snmpTargetAddrParams = "toNR" (MUST match below) snmpTargetAddrStorageType = 3 (nonVolatile) snmpTargetAddrColumnStatus = 4 (createAndGo) The following row configures the snmpTargetParamsTable to send the notifications to "Joe Cool", using authPriv SNMPv3 notifications through the TransportSecurityModel [RFC5591]: Hardaker Standards Track [Page 63]
RFC 5953 TLS Transport Model for SNMP August 2010 snmpTargetParamsName = "toNR" (must match above) snmpTargetParamsMPModel = 3 (SNMPv3) snmpTargetParamsSecurityModel = 4 (TransportSecurityModel) snmpTargetParamsSecurityName = "Joe Cool" snmpTargetParamsSecurityLevel = 3 (authPriv) snmpTargetParamsStorageType = 3 (nonVolatile) snmpTargetParamsRowStatus = 4 (createAndGo0 A.2. Configuring TLSTM to Utilize a Simple Derivation of tmSecurityName The following row configures the snmpTlstmCertToTSNTable to map a validated client certificate, referenced by the client's public X.509 hash fingerprint, to a tmSecurityName using the subjectAltName component of the certificate. snmpTlstmCertToTSNID = 1 (chosen by ordering preference) snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint) snmpTlstmCertToTSNMapType = snmpTlstmCertSANAny snmpTlstmCertToTSNData = "" (not used) snmpTlstmCertToTSNStorageType = 3 (nonVolatile) snmpTlstmCertToTSNRowStatus = 4 (createAndGo) This type of configuration should only be used when the naming conventions of the (possibly multiple) Certification Authorities are well understood, so two different principals cannot inadvertently be identified by the same derived tmSecurityName. A.3. Configuring TLSTM to Utilize Table-Driven Certificate Mapping The following row configures the snmpTlstmCertToTSNTable to map a validated client certificate, referenced by the client's public X.509 hash fingerprint, to the directly specified tmSecurityName of "Joe Cool". snmpTlstmCertToTSNID = 2 (chosen by ordering preference) snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint) snmpTlstmCertToTSNMapType = snmpTlstmCertSpecified snmpTlstmCertToTSNSecurityName = "Joe Cool" snmpTlstmCertToTSNStorageType = 3 (nonVolatile) snmpTlstmCertToTSNRowStatus = 4 (createAndGo) Hardaker Standards Track [Page 64]
RFC 5953 TLS Transport Model for SNMP August 2010
Author's Address
Wes Hardaker
SPARTA, Inc.
P.O. Box 382
Davis, CA 95617
USA
Phone: +1 530 792 1913
EMail: ietf@hardakers.net
Hardaker Standards Track [Page 65]
RFC 5953: Transport Layer Security (TLS) Transport Model for the Simple Network Management Protocol (SNMP)
Proposed Standard