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Security ISMS Network Management Management Information Base MIB SMIv2 TLS DTLS SNMP 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 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.

It is important to understand the modular SNMPv3 architecture as defined by and enhanced by the Transport Subsystem . 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 . This document describes a Transport Model that makes use of the Transport Layer Security (TLS) and the Datagram Transport Layer Security (DTLS) Protocol , within a transport subsystem . DTLS is the datagram variant of the Transport Layer Security (TLS) protocol . 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 . 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: , and . The diagram shown below gives a conceptual overview of two SNMP entities communicating using the TLS Transport Model (shown as "TLS TM"). One entity contains a command responder and notification originator application, and the other a command generator and notification responder 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 which is defined in .

+---------------------------------------------------------------------+ | 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 | +---------------------------------+ +---------------------------------+

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 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 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" 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 standard defined 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) is a mandatory-to-implement Security Model in STD 62. While (D)TLS and USM frequently refer to a user, the terminology preferred in RFC3411 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. 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 .

(D)TLS provides authentication, data message integrity, and privacy at the transport layer. (See ) 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 and for complete descriptions of the protocols.

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 component of the SNMP engine and the Transport Subsystem. 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. 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 RFC3411 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 | | +-------------+ +---------+ +--------------+ +-------------+ | | | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | | | | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | | | | application | | | | applications | | application | | | +-------------+ +---------+ +--------------+ +-------------+ | | ^ ^ | | | | | | v v | | +----------------------------------------------+ | | | MIB instrumentation | SNMP entity | +-------------------------------------------------------------------+

The TLS Transport Model provides protection against the threats identified by the RFC 3411 architecture : 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. 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 of 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 authentication of both the server and the client. 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 which is 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 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 ). 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 SHOULD support message encryption to protect sensitive data from eavesdropping attacks. Denial of Service - the RFC 3411 architecture 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 denial of service attacks because they are more vulnerable to spoofed IP addresses. See for details how the cookie mechanism is used. Note, however, that this mechanism does not provide any defense against denial of service attacks mounted from valid IP addresses. See for more detail on the security considerations associated with the TLSTM and these security threats.

The RFC 3411 architecture recognizes three levels of security: without authentication and without privacy (noAuthNoPriv) with authentication but without privacy (authNoPriv) with authentication and with privacy (authPriv) The 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. 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.

(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 . TLS over TCP sessions, on the other hand, do not require a unique pairing of 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 identifier 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 idenfify a TLSTM session (there can be multiple TLSTM sessions sharing the same D(TLS) internal SessionID).

For the (D)TLS server-side, (D)TLS-specific security parameters (i.e., cipher_suites, X.509 certificate fields, IP address and port) 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 discuss these concepts in much greater detail.

(D)TLS connections may be initiated by (D)TLS clients on behalf of SNMP appplications 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 contains objects for defining management targets, including transportDomain, transportAddress, securityName, securityModel, and securityLevel parameters, for notification originator, proxy forwarder, and SNMP-controllable 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.

This section contains definitions required to realize the (D)TLS Transport Model defined by this document.

(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 are outside the scope of this specification. TLSTM implementations are REQUIRED to support X.509 certificates.

Authentication using (D)TLS will require that SNMP entities have certificates, either signed by trusted certification authorities, or self-signed. Furthermore, SNMP entities will most commonly need to be provisioned with root certificates which represent the list of trusted certificate authorities that an SNMP entity can use for certificate 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: Mapping a certificate's subjectAltName or CommonName components to a tmSecurityName, or 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. Enterprise configurations are encouraged to map a "subjectAltName" component of the X.509 certificate to the TLSTM specific tmSecurityName. 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 . 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 , may perform an identity mapping or a more complex mapping to derive the securityName from the tmSecurityName offered by the TLS Transport Model. 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 | +-------------+

(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 . 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 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 ( 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.

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.

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: An indication of whether the sending of the message was successful. If not, it is an indication of the problem. 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. The transport address of the destination TLS Transport Model in a format specified by the SnmpTLSAddress TEXTUAL-CONVENTION. The outgoing message to send to (D)TLS for encapsulation and transmission. The length of the outgoingMessage field. A reference to tmState to be used when securing outgoing messages.

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: An indication of whether the passing of the message was successful. If not, it is an indication of the problem. The transport domain for the associated transportAddress. This document specifies the snmpTLSTCPDomain and the snmpDTLSUDPDomain transport domains. The transport address of the source of the received message in a format specified by the SnmpTLSAddress TEXTUAL-CONVENTION. The whole SNMP message after being processed by (D)TLS and the (D)TLS transport layer data has been removed. The length of the incomingMessage field. A reference to tmSecurityData to be used by the security model.

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" defines general requirements for caches and references.

The TLS Transport Model has specific responsibilities regarding the cached information. See the Elements of Procedure in for detailed processing instructions on the use of the tmStateReference fields by the TLS Transport Model.

The tmSecurityName MUST be a human-readable name (in snmpAdminString format) representing the identity that has been set according to the procedures in . The tmSecurityName MUST be constant for all traffic passing through an 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 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 application (possibly because of configuration specified in the SNMP-TARGET-MIB). The securityName MAY be derived from the tmSecurityName by a Security Model and MAY be used to configure notifications and access controls in MIB modules. Transport Models SHOULD generate a predictable tmSecurityName 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.

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).

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.

Abstract service interfaces have been defined by and further augmented by 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.

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. 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. describes the transport processing required once the (D)TLS processing has been completed. This will be needed for all (D)TLS-based connections.

For connection-oriented transport protocols, such as TCP, the transport protocol takes care of demultiplexing incoming packets to the right connection. Depending on the DTLS implementation, for DTLS over UDP, this demultiplexing may need to be done 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. The TLS Transport Model examines the raw UDP message, in an implementation-dependent manner. The TLS Transport Model queries the LCD using the transport parameters (source and destination IP addresses and ports) to determine if a session already exists. 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 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. 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. Retrieve the incomingMessage and an incomingMessageLength from DTLS. These results and the tlstmSessionID are used below in to complete the processing of the incoming message.

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. 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 . 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. 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 prior to this point or they may perform them now, but the procedures described in MUST be performed before continuing beyond this point. Create a tmStateReference cache for the subsequent reference and assign the following values within it: = snmpTLSTCPDomain or snmpDTLSUDPDomain as appropriate. = The address the message originated from. = The derived tmSecurityLevel for the session, as discussed in and . = The derived tmSecurityName for the session as discussed in . This value MUST be constant during the lifetime of the session. = The tlstmSessionID described in step 1 above. The incomingMessage and incomingMessageLength are assigned values from the (D)TLS processing. The TLS Transport Model passes the transportDomain, transportAddress, incomingMessage, and incomingMessageLength to the Dispatcher using the receiveMessage ASI:

The Dispatcher sends a message to the TLS Transport Model using the following ASI:

This section describes the procedure followed by the TLS Transport Model whenever it is requested through this ASI to send a message. 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. 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. If tmSameSecurity is true and either tmSessionID is 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. 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 processing of the message. 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. If there is a corresponding LCD entry, then this session will be used to send the message. If there is not a corresponding LCD entry, then open a session using the openSession() ASI (discussed further in ). 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 processing of the message. 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.

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.

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 a SNMP over (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. The snmpTlstmSessionOpens counter is incremented. 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 a 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 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. 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 a 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. 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. If the connection is being established from 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. (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 can not be opened for any reason at all, including cryptographic verification failures, then the snmpTlstmSessionOpenErrors counter is incremented and processing stops. 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 ().

A (D)TLS server should accept new session connections from any client that it is able to verify the client's credentials for. This is done by authenticating the client's presented certificate through a certificate path validation process (e.g. ) 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. 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 can not 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 . Supporting this will allow, for example, sending notifications to a specific principal at a given TCP or UDP port.

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. Increment either the snmpTlstmSessionClientCloses or the snmpTlstmSessionServerCloses counter as appropriate. Look up the session using the tmSessionID. If there is no open session associated with the tmSessionID, then closeSession processing is completed. Have (D)TLS close the specified connection. This SHOULD include sending a close_notify TLS Alert to inform the other side that session cleanup may be performed.

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 .

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.

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: A new TransportAddress format for describing (D)TLS connection addressing requirements. A certificate fingerprint allowing MIB module objects to generically refer to a stored X.509 certificate using a cryptographic hash as a reference pointer.

The SNMP-TLS-TM-MIB defines some counters that can provide network management stations with information about session usage and potential errors that a MIB-instrumented device may be experiencing.

The SNMP-TLS-TM-MIB defines configuration tables that an administrator can use for configuring a MIB-instrumented 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 securityNames.

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).

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 , the SNMP-FRAMEWORK-MIB , the SNMP-TARGET-MIB , the SNMP-NOTIFICATION-MIB and the SNMP-VIEW-BASED-ACM-MIB . The SNMP-TLS-TM-MIB module contained in this document is for managing TLS Transport Model information.

The SNMP-TLS-TM-MIB module imports items from SNMPv2-SMI , SNMPv2-TC , SNMP-FRAMEWORK-MIB , SNMP-TARGET-MIB and SNMPv2-CONF .

SNMP-TLS-TM-MIB DEFINITIONS ::= BEGIN IMPORTS MODULE-IDENTITY, OBJECT-TYPE, OBJECT-IDENTITY, mib-2, snmpDomains, Counter32, Unsigned32, Gauge32, NOTIFICATION-TYPE FROM SNMPv2-SMI TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType, AutonomousType FROM SNMPv2-TC MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP FROM SNMPv2-CONF SnmpAdminString FROM SNMP-FRAMEWORK-MIB snmpTargetParamsName, snmpTargetAddrName FROM SNMP-TARGET-MIB ; snmpTlstmMIB MODULE-IDENTITY LAST-UPDATED "MIBDATE0000Z" 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) FILLYEAR 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 "MIBDATE0000Z" DESCRIPTION "This version of this MIB module is part of RFC XXXX; see the RFC itself for full legal notices." -- NOTE to RFC editor: replace XXXX with actual RFC number -- for this document and change the date to the -- current date and remove this note ::= { mib-2 www } -- RFC Ed.: replace www with IANA-assigned number under the mib-2 -- SNMP OID tree and remove this note -- ************************************************ -- 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 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." ::= { snmpDomains xx } -- RFC Ed.: replace xx with IANA-assigned number and -- remove this note -- RFC Ed.: replace 'tls' with the actual IANA assigned prefix string -- if 'tls' is not assigned to this document. snmpDTLSUDPDomain OBJECT-IDENTITY STATUS current DESCRIPTION "The SNMP over DTLS/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." ::= { snmpDomains yy } -- RFC Ed.: replace yy with IANA-assigned number and -- remove this note -- RFC Ed.: replace 'dtls' with the actual IANA assigned prefix string -- if 'dtls' is not assigned to this document. SnmpTLSAddress ::= TEXTUAL-CONVENTION DISPLAY-HINT "1a" STATUS current DESCRIPTION "Represents a IPv4 address, an IPv6 address or an 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, 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 specified in RFC 3490. 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 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 3986: Uniform Resource Identifier (URI): Generic Syntax RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2 " SYNTAX OCTET STRING (SIZE (1..255)) Fingerprint ::= TEXTUAL-CONVENTION DISPLAY-HINT "1x:254x" STATUS current DESCRIPTION "A Fingerprint value that can be used to uniquely reference other data of potentially arbitrary length. A Fingerprint 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 (RFC5246). The remaining octets are filled using the results of the hashing algorithm. This TEXTUAL-CONVENTION allows for a zero-length (blank) Fingerprint 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 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 lower case. 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 lower case." ::= { 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. Note that the resulting length is the maximum length supported by the View-Based Access Control Model (VACM). Note that 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." ::= { snmpTlstmCertToTSNMIdentities 5 } snmpTlstmCertCommonName OBJECT-IDENTITY STATUS current DESCRIPTION "Maps a certificate's CommonName to a tmSecurityName after converting it to a UTF-8 encoding." ::= { 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 an (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 } 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 a SNMP over (D)TLS server was invalid because no configured fingerprint or 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 certification authority." ::= { snmpTlstmSession 8 } 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. I.E., 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 } 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 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. Missing values of snmpTlstmCertToTSNID are acceptable and implementations should continue to the next highest numbered row. E.G., the table may legally contain only two rows with snmpTlstmCertToTSNID values of 10 and 20. 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." INDEX { snmpTlstmCertToTSNID } ::= { snmpTlstmCertToTSNTable 1 } SnmpTlstmCertToTSNEntry ::= SEQUENCE { snmpTlstmCertToTSNID Unsigned32, snmpTlstmCertToTSNFingerprint Fingerprint, 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 Fingerprint (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 securityName could be longer) then future rows MUST be searched for additional snmpTlstmCertToTSNFingerprint matches to look for a mapping that succeeds." 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). Until instances of all corresponding columns are appropriately configured, the value of the corresponding instance of the snmpTlstmParamsRowStatus column is 'notReady'. 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 } 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 Fingerprint, snmpTlstmParamsStorageType StorageType, snmpTlstmParamsRowStatus RowStatus } snmpTlstmParamsClientFingerprint OBJECT-TYPE SYNTAX Fingerprint MAX-ACCESS read-create STATUS current DESCRIPTION "A cryptographic hash of a X.509 certificate. This object should store the hash of a locally held X.509 certificate that should be used (along with the corresponding private key) when initiating a (D)TLS connection as a (D)TLS client." ::= { snmpTlstmParamsEntry 1 } 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'. 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 } 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 SHOULD support checking the name against the common name portion of the subject distinguished name. - 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 a snmpTargetAddrEntry row then the connection SHOULD still proceed if some other certificate validation path algorithm (e.g. RFC5280) can be used." INDEX { IMPLIED snmpTargetAddrName } ::= { snmpTlstmAddrTable 1 } SnmpTlstmAddrEntry ::= SEQUENCE { snmpTlstmAddrServerFingerprint Fingerprint, snmpTlstmAddrServerIdentity SnmpAdminString, snmpTlstmAddrStorageType StorageType, snmpTlstmAddrRowStatus RowStatus } snmpTlstmAddrServerFingerprint OBJECT-TYPE SYNTAX Fingerprint 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 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'. 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 a 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 certificate authority. 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. I.E., a cryptographic validation 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 } -- ************************************************ -- 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 which 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 which implements the SNMP TLS Transport Model." ::= { snmpTlstmGroups 2 } snmpTlstmOutgoingGroup OBJECT-GROUP OBJECTS { snmpTlstmParamsCount, snmpTlstmParamsTableLastChanged, snmpTlstmParamsClientFingerprint, snmpTlstmParamsStorageType, snmpTlstmParamsRowStatus, 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

This section discusses various operational aspects of deploying TLSTM.

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 disconnect messages. Implementations SHOULD also have a system in place for detecting "broken" sessions through the use of heartbeats or other detection mechanisms. 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.

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 . 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.

Most command responders have contextEngineIDs that are identical to the USM securityEngineID. USM provides a discovery service that allows command generators to determine a securityEngineID and thus a default contextEngineID to use. Because the TLS Transport Model does not make use of a securityEngineID, it may be difficult for command generators to discover a suitable default contextEngineID. Implementations should consider offering another engineID discovery mechanism to continue providing Command Generators with a suitable contextEngineID mechanism. A recommended discovery solution is documented in .

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.

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 and security considerations for TLS are described in Section 11 and Appendices D, E, and F of TLS 1.2 . 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.

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 an configured accepted certification authority. (D)TLS has no way to further authorize or reject access based on the authenticated identity. An Access Control Model (such as the VACM) provides access control and authorization of a command generator's requests to a command responder and a notification responder'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.

The SNMPv1 and SNMPv2c message processing described in (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 based on the contents of the SNMP message, rather than using the authenticated identity and securityLevel provided by the TLS Transport Model.

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: 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. 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. 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 traffic via encryption is also highly recommended. 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: 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 also 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 , 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.

IANA is requested to assign: Two TCP/UDP port numbers from the "Registered Ports" range of the Port Numbers registry, with the following keywords (where TBD1 and TBD2 correspond to the assigned port numbers):

Keyword Decimal Description References ------- ------- ----------- ---------- snmptls TBD1/tcp SNMPv3-TLS [RFC-isms-dtls-tm] snmpdtls TBD1/udp SNMPv3-DTLS [RFC-isms-dtls-tm] snmptls-trap TBD2/tcp SNMPv3-Trap-TLS [RFC-isms-dtls-tm] snmpdtls-trap TBD2/udp SNMPv3-Trap-DTLS [RFC-isms-dtls-tm]

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. An SMI number under snmpDomains for the snmpTLSTCPDomain object identifier, An SMI number under snmpDomains for the snmpDTLSUDPDomain object identifier, A SMI number under mib-2, for the MIB module in this document, "tls" as the corresponding prefix for the snmpTLSTCPDomain in the SNMP Transport Model registry, "dtls" as the corresponding prefix for the snmpDTLSUDPDomain in the SNMP Transport Model registry, RFC Editor's note: this section should be replaced with appropriate descriptive assignment text after IANA assignments are made and prior to publication.

This document closely follows and copies the Secure Shell Transport Model for SNMP defined by David Harrington and Joseph Salowey in . 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, Jurgen Schonwalder, Dave Shield, 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.

&rfc2119; &rfc2578; &rfc2579; &rfc2580; &rfc3411; &rfc3413; &rfc3414; &rfc3415; &rfc3418; &rfc3584; &rfc4347; &rfc5246; &rfc5280; &rfc5590; &rfc5591; &rfc3410; &rfc4366; &rfc5292; &rfc5343; Muenster Univ. of Applied Sciences Muenster Univ. of Applied Sciences

Configuring the SNMP-TARGET-MIB and NOTIFICATION-MIB along with access control settings for the SNMP-VIEW-BASED-ACM-MIB can be a daunting task without an example to follow. The following section describes an example of what pieces must be in place to accomplish this configuration. The isAccessAllowed() ASI requires configuration to exist in the following SNMP-VIEW-BASED-ACM-MIB tables:

vacmSecurityToGroupTable vacmAccessTable vacmViewTreeFamilyTable

The only table that needs to be discussed as particularly different here is the vacmSecurityToGroupTable. This table is indexed by both the SNMPv3 security model and the security name. The security model, when TLSTM is in use, should be set to the value of 4, corresponding to the TSM . An example vacmSecurityToGroupTable row might be filled out as follows (using a single SNMP SET request):

vacmSecurityModel = 4 (TSM) vacmSecurityName = "blueberry" vacmGroupName = "administrators" vacmSecurityToGroupStorageType = 3 (nonVolatile) vacmSecurityToGroupStatus = 4 (createAndGo)

This example will assume that the "administrators" group has been given proper permissions via rows in the vacmAccessTable and vacmViewTreeFamilyTable. Depending on whether this VACM configuration is for a Command Responder or a command generator the security name "blueberry" will come from a few different locations.

For notification originators performing authorization checks, the server's certificate must be verified against the expected certificate before proceeding to send the notification. The expected certificate from the server may be listed in the snmpTlstmAddrTable or may be determined through other X.509 path validation mechanisms. The securityName to use for VACM authorization checks is set by the SNMP-TARGET-MIB's snmpTargetParamsSecurityName column. The certificate that the notification originator should present to the server is taken from the snmpTlstmParamsClientFingerprint column from the appropriate entry in the snmpTlstmParamsTable table. (Or else a default certificate may be used if available.) To configure a notification originator to open a TLS over TCP connection to a notification receiver it must be configured so the server's presented certificate can be verified against the expected certificate before proceeding to send the notification. This is done by configuring the snmpTlstmAddrTable accordingly. For example, if the verification is done via certification path validation (to a trust anchor configured in implementation dependent manner), then the table entries could look like:

snmpTargetAddrTable row: snmpTargetAddrName = "toNRAddr" snmpTargetAddrTDomain = snmpTLSTCPDomain snmpTargetAddrTAddress = "192.0.2.1:XXXTLSTCPTRAPPORT" snmpTargetAddrTimeout = 1500 snmpTargetAddrRetryCount = 3 snmpTargetAddrTagList = "toNRTag" snmpTargetAddrParams = "toNR" (MUST match below) snmpTargetAddrStorageType = 3 (nonVolatile) snmpTargetAddrColumnStatus = 4 (createAndGo) snmpTargetParamsTable row: snmpTargetParamsName = toNR snmpTargetParamsMPModel = SNMPv3 snmpTargetParamsSecurityModel = 4 (TransportSecurityModel) snmpTargetParamsSecurityName = "blueberry" snmpTargetParamsSecurityLevel = 3 (authPriv) snmpTargetParamsStorageType = 3 (nonVolatile) snmpTargetParamsRowStatus = 4 (createAndGo0 snmpTlstmAddrTable row: snmpTargetAddrName = "toNRAddr" snmpTlstmAddrServerFingerprint = "" snmpTlstmAddrServerIdentity = "server.example.org" snmpTlstmAddrStorageType = 3 (nonVolatile) snmpTlstmAddrRowStatus = 4 (createAndGo)

Editor's note: replace the string "XXXTLSTCPTRAPPORT" above with the appropriately assigned "snmptls-trap" port.

For command responder applications, the vacmSecurityName "blueberry" value is a value that derived from an incoming (D)TLS connection. The mapping from a recevied (D)TLS client certificate to a tmSecurityName is done with the snmpTlstmCertToTSNTable. The certificates must be loaded into the device so that a snmpTlstmCertToTSNEntry may refer to it. As an example, consider the following entry which will provide a mapping from a client's public X.509's hash fingerprint directly to the "blueberry" tmSecurityName:

snmpTlstmCertToTSNID = 1 (chosen by ordering preference) snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint) snmpTlstmCertToTSNMapType = snmpTlstmCertSpecified snmpTlstmCertToTSNSecurityName = "blueberry" snmpTlstmCertToTSNStorageType = 3 (nonVolatile) snmpTlstmCertToTSNRowStatus = 4 (createAndGo)

The above is an example of how to map a particular certificate to a particular tmSecurityName. It is recommended, however, that users make use of direct subjectAltName or CommonName mappings where possible as it provides a more scalable approach to certificate management. This entry provides an example of using a subjectAltName mapping:

snmpTlstmCertToTSNID = 1 (chosen by ordering preference) snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint) snmpTlstmCertToTSNMapType = snmpTlstmCertSANAny snmpTlstmCertToTSNData = "" (not used) snmpTlstmCertToTSNStorageType = 3 (nonVolatile) snmpTlstmCertToTSNRowStatus = 4 (createAndGo)

The above entry indicates the subjectAltName field for certificates created by an issuing certificate with a corresponding fingerprint will be trusted to always produce common names that are directly one-to-one mappable into tmSecurityNames. This type of configuration should only be used when the certificate authorities naming conventions are carefully controlled. In the example, if the incoming (D)TLS client provided certificate contained a subjectAltName where the first listed subjectAltName in the extension is the rfc822Name of "blueberry@example.com", the certificate was signed by a certificate matching the snmpTlstmCertToTSNFingerprint value and the CA's certificate was properly installed on the device then the string "blueberry@example.com" would be used as the tmSecurityName for the session.