RFC 5953
Transport Layer Security (TLS) Transport Model for the Simple Network Management Protocol (SNMP)
Transport Layer Security (TLS) Transport Model for the Simple Network Management Protocol (SNMP) 🎀
Bestie, this is RFC 5953! 💖 It's a Standards Track doc from the IETF, written by W. Hardaker at SPARTA, Inc., and it dropped in August 2010 📅. The ISSN is 2070-1721. ✨ The title block has no Obsoletes or Updates line, so this doc doesn't replace or change any older RFC, and that's a clean start 🧚.
Abstract ✨
okay so this doc describes a Transport Model for SNMP that runs on either Transport Layer Security or Datagram Transport Layer Security (DTLS) 🔐. Both TLS and DTLS give SNMP applications authentication and privacy, which is literally the whole point 💅. It explains how the TLS Transport Model (TLSTM) fills in the features a SNMP Transport Subsystem needs so all this protection works in an interoperable way 🦋.
The model is built for the security and operational needs of network admins 👑. It sends SNMP messages over TLS/TCP and DTLS/UDP. TLS mode can use TCP's better support for larger packet sizes 📦, and DTLS mode is the move when you'd rather use a connectionless transport like UDP 🌸. Both of them plug nicely into existing public keying infrastructures 🔑, no cap.
The doc also defines a chunk of the Management Information Base (MIB) for network management protocols 🧠. Specifically, it defines objects for managing the TLS Transport Model for SNMP 🍓.
Status of This Memo ✨
This is an Internet Standards Track document 🌈.
It's a product of the Internet Engineering Task Force (IETF) and represents the consensus of the IETF community 🫶. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG) ✅. For more on Internet Standards, check Section 2 of RFC 5741 📚.
Info about the current status of this doc, any errata, and how to give feedback can be found at http://www.rfc-editor.org/info/rfc5953 💜.
Copyright Notice 💅
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved 🎀.
This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info), as they stood on the publication date 📜. Please read these carefully, bestie, because they spell out your rights and restrictions for this doc 🙈. Code Components pulled out of this doc must include the Simplified BSD License text described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, just like the Simplified BSD License says 💀.
This doc may include material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008 🕰️. The people who control the copyright in some of that material may not have given the IETF Trust permission to allow modifications outside the IETF Standards Process 😭. Without an adequate license from those copyright holders, this doc may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process 🚫. The exceptions are formatting it for publication as an RFC or translating it into languages other than English 🌍.
Table of Contents 🧚
1. Introduction ....................................................4
1.1. Conventions ................................................7
2. The Transport Layer Security Protocol ...........................8
3. How the TLSTM Fits into the Transport Subsystem .................8
3.1. Security Capabilities of this Model .......................10
3.1.1. Threats ............................................10
3.1.2. Message Protection .................................11
3.1.3. (D)TLS Connections .................................12
3.2. Security Parameter Passing ................................13
3.3. Notifications and Proxy ...................................13
4. Elements of the Model ..........................................14
4.1. X.509 Certificates ........................................14
4.1.1. Provisioning for the Certificate ...................14
4.2. (D)TLS Usage ..............................................16
4.3. SNMP Services .............................................17
4.3.1. SNMP Services for an Outgoing Message ..............17
4.3.2. SNMP Services for an Incoming Message ..............18
4.4. Cached Information and References .........................19
4.4.1. TLS Transport Model Cached Information .............19
4.4.1.1. tmSecurityName ............................19
4.4.1.2. tmSessionID ...............................20
4.4.1.3. Session State .............................20
5. Elements of Procedure ..........................................20
5.1. Procedures for an Incoming Message ........................20
5.1.1. DTLS over UDP Processing for Incoming Messages .....21
5.1.2. Transport Processing for Incoming SNMP Messages ....22
5.2. Procedures for an Outgoing SNMP Message ...................24
5.3. Establishing or Accepting a Session .......................25
5.3.1. Establishing a Session as a Client .................25
5.3.2. Accepting a Session as a Server ....................27
5.4. Closing a Session .........................................28
6. MIB Module Overview ............................................29
6.1. Structure of the MIB Module ...............................29
6.2. Textual Conventions .......................................29
6.3. Statistical Counters ......................................29
6.4. Configuration Tables ......................................29
6.4.1. Notifications ......................................30
6.5. Relationship to Other MIB Modules .........................30
6.5.1. MIB Modules Required for IMPORTS ...................30
7. MIB Module Definition ..........................................30
8. Operational Considerations .....................................53
8.1. Sessions ..................................................53
8.2. Notification Receiver Credential Selection ................54
8.3. contextEngineID Discovery .................................54
8.4. Transport Considerations ..................................55
9. Security Considerations ........................................55
9.1. Certificates, Authentication, and Authorization ...........55
9.2. (D)TLS Security Considerations ............................56
9.2.1. TLS Version Requirements ...........................56
9.2.2. Perfect Forward Secrecy ............................56
9.3. Use with SNMPv1/SNMPv2c Messages ..........................56
9.4. MIB Module Security .......................................57
10. IANA Considerations ...........................................58
11. Acknowledgements ..............................................59
12. References ....................................................60
12.1. Normative References .....................................60
12.2. Informative References ...................................61
Appendix A. Target and Notification Configuration Example ........63
A.1. Configuring a Notification Originator .....................63
A.2. Configuring TLSTM to Utilize a Simple Derivation of
tmSecurityName ............................................64
A.3. Configuring TLSTM to Utilize Table-Driven Certificate
Mapping ...................................................641. Introduction ✨
okay so bestie, this is the intro and it's giving "the foundation everything else is built on" 💅. First, the modular SNMPv3 architecture is defined in [RFC3411] and then enhanced by the Transport Subsystem [RFC5590]. You need that picture to see where the Transport Model in this doc fits and how it talks to the other subsystems 🧚. For the full tea on the documents that make up the current Internet-Standard Management Framework, check out Section 7 of [RFC3410] 📚.
So this doc describes a Transport Model that uses Transport Layer Security (TLS) [RFC5246] and the Datagram Transport Layer Security (DTLS) Protocol [RFC4347], inside a Transport Subsystem [RFC5590]. DTLS is basically the datagram version of TLS [RFC5246], so it's the one for UDP-style vibes 🦋. This Transport Model is called the Transport Layer Security Transport Model, or TLSTM for short 💜. TLS and DTLS both lean on the X.509 public keying infrastructure [RFC5280] 🔐. (D)TLS supports multiple authentication mechanisms, but this doc only talks about X.509 certificate-based authentication. Other forms of authentication are possible, but they're out of scope for this spec, so don't come for me about it 🙈.
The design goal is to meet the security and operational needs of network admins in two very different worlds: places where a connectionless transport like UDP is preferred, and places where big piles of data need to get sent, like over a TCP-based stream 🌊. Both TLS and DTLS plug nicely into existing public keying infrastructures, which is so convenient ✨. This doc supports sending SNMP messages over TLS/TCP and DTLS/UDP, so both lanes are open 🛣️🌸.
This document also defines a chunk of the Management Information Base (MIB) for use with network management protocols. Specifically, it defines objects for managing the TLS Transport Model for SNMP 🎀.
Managed objects live in a virtual information store called the Management Information Base, or MIB 🗂️. MIB objects are usually accessed through the Simple Network Management Protocol (SNMP). The objects in the MIB are defined using the mechanisms in the Structure of Management Information (SMI) 🧠. This memo specifies a MIB module that's compliant with SMIv2, which is described in STD 58: [RFC2578], [RFC2579], and [RFC2580] 💅.
Here's a diagram giving a conceptual overview of two SNMP entities chatting over the TLS Transport Model (shown as "TLSTM") 🦋. One entity has a command responder and a notification originator application, and the other has a command generator and a notification receiver application. Quick reminder that this particular mix of application types is just an example, and other combinations are equally valid 💖.
Note: this diagram shows the Transport Security Model (TSM) being used as the security model that is defined in [RFC5591] 🔥.
+---------------------------------------------------------------------+
| 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 |
+---------------------------------+ +---------------------------------+1.1. Conventions
Okay, terminology time 🤓. For consistency with SNMP-related specs, this doc goes with the terms defined in STD 62, instead of the terms used by non-SNMP specs. This lines up with the IESG decision not to make SNMPv3 terminology change to match non-SNMP specs when SNMPv3 became a Full Standard 🎓.
"Authentication" in this doc usually means the everyday English sense of "serving to prove the authenticity of" the message. It does not mean data source authentication or peer identity authentication 🙃.
The terms "manager" and "agent" aren't used here, because in the [RFC3411] architecture every SNMP entity can act as a manager, an agent, or both, depending on which SNMP application types its implementation supports 🦋. When you need to make a distinction, the doc uses the application names: command generator, command responder, notification originator, notification receiver, and proxy forwarder. Check out "SNMP Applications" [RFC3413] for more info 💜.
A lot of this doc talks about TLS and DTLS together, for TLSTM parts that work the same with either protocol. "(D)TLS" is used in those spots to mean the statement applies to either or both protocols, as appropriate 🌈. When a difference between the protocols matters, they get referred to on their own as "TLS" or "DTLS". The Transport Model itself is named "TLS Transport Model", but it doesn't refer to the TLS or DTLS protocol. It refers to the spec in this doc, which supports both TLS and DTLS ✨.
Throughout this doc, "client" and "server" 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 which SNMP applications it supports.
The User-Based Security Model (USM) [RFC3414] is a mandatory-to-implement Security Model in STD 62 💅. While (D)TLS and USM often talk about a "user", the term this doc (and RFC 3411) prefers is "principal" 👑. A principal is the "who" on whose behalf services are provided or processing takes place. A principal can be lots of things: an individual acting in a particular role, a set of individuals each acting in a particular role, an application or a set of applications, or a combination of these within an administrative domain 🧚.
Throughout this doc, "session" means a secure association between two TLS Transport Models that lets one or more SNMP messages get sent within the session's lifetime 🔐. The (D)TLS protocols have their own internal idea of a session too. These two concepts are related, but when this doc says "session", it means the TLSTM's specific session, not the (D)TLS protocol's session 💖.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] 🎀.
2. The Transport Layer Security Protocol
(D)TLS gives you authentication, data message integrity, and privacy at the transport layer (see [RFC4347]) 🔒✨.
The main 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 give a secure transport that the TLSTM is built on. For the complete descriptions of the protocols, go check [RFC5246] and [RFC4347] 📚💅.
3. How the TLSTM Fits into the Transport Subsystem ✨
Okay bestie, so the TLS Transport Model is a component of the Transport Subsystem 🦋 That means it sits right between the underlying (D)TLS transport layer and the Message Dispatcher [RFC3411] component of the SNMP engine. Main character placement, honestly 💅
The TLS Transport Model will establish a session with the TLS Transport Model of another SNMP engine 🫶 On the sending side, the transport model takes unencrypted and unauthenticated messages from the Dispatcher and hands them to (D)TLS so they can get encrypted and authenticated. On the receiving side, the transport model gets decrypted and authenticated/integrity-checked messages back from (D)TLS and passes them up to the Dispatcher. It's giving tag-team energy 👯♀️
Once a TLS Transport Model session is up, SNMP messages can conceptually travel through that session from one SNMP message Dispatcher to another SNMP Message Dispatcher 🌸 If multiple SNMP messages need to pass between two SNMP applications, they MAY be passed through the same session. And a TLSTM implementation engine MAY choose to close the session to conserve resources, which is a very responsible move 🧚
The TLS Transport Model of an SNMP engine handles the translation between (D)TLS-specific security parameters and SNMP-specific, model-independent parameters. It's the translator in the group chat, no cap 🎀
The diagram below shows where the TLS Transport Model (labelled "(D)TLS TM") fits into the architecture described in RFC 3411 and the Transport Subsystem 🦋
+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Subsystem | +--------+ |
| | +-----+ +-----+ +-------+ +-------+ | | | |
| | | UDP | | SSH | |(D)TLS | . . . | other |<--->| Cache | |
| | | | | TM | | TM | | | | | | |
| | +-----+ +-----+ +-------+ +-------+ | +--------+ |
| +--------------------------------------------------+ ^ |
| ^ | |
| | | |
| Dispatcher v | |
| +--------------+ +---------------------+ +----------------+ | |
| | Transport | | Message Processing | | Security | | |
| | Dispatch | | Subsystem | | Subsystem | | |
| | | | +------------+ | | +------------+ | | |
| | | | +->| v1MP |<--->| | USM | | | |
| | | | | +------------+ | | +------------+ | | |
| | | | | +------------+ | | +------------+ | | |
| | | | +->| v2cMP |<--->| | Transport | | | |
| | Message | | | +------------+ | | | Security |<--+ |
| | Dispatch <---->| +------------+ | | | Model | | |
| | | | +->| v3MP |<--->| +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | | | | +------------+ | | | Other | | |
| | PDU Dispatch | | | +------------+ | | | Model(s) | | |
| +--------------+ | +->| otherMP |<--->| | Model(s) | | |
| ^ | +------------+ | | +------------+ | |
| | +---------------------+ +----------------+ |
| v |
| +-------+-------------------------+---------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v |
| +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+3.1. Security Capabilities of this Model 🛡️
3.1.1. Threats 💀
The TLS Transport Model protects against the threats identified by the RFC 3411 architecture [RFC3411]. Let's go through them, bestie 🙈
- 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. Verified, locked in 🔒
- Masquerade - The masquerade threat is the danger that management operations unauthorized for a given principal may be attempted by assuming the identity of another principal that has the appropriate authorizations.
The TLSTM verifies the identity of the (D)TLS server through the use of the (D)TLS protocol and X.509 certificates. A TLS Transport Model implementation MUST support the authentication of both the server and the client. Both sides get checked, no sneaking in 🕵️♀️
- Message stream modification - The re-ordering, delay, or replay of messages can and does occur through the natural operation of many connectionless transport services. The message stream modification threat is the danger that messages may be maliciously re-ordered, delayed or replayed to an extent that is greater than can occur through the natural operation of connectionless transport services, in order to effect unauthorized management operations.
(D)TLS provides replay protection with a Message Authentication Code (MAC) that includes a sequence number. Since UDP provides no sequencing ability, DTLS uses a sliding window protocol with the sequence number used for replay protection (see [RFC4347]). Replay? Not on my watch 🔁
- Disclosure - The disclosure threat is the danger of eavesdropping on the exchanges between SNMP engines.
(D)TLS provides protection against the disclosure of information to unauthorized recipients or eavesdroppers by allowing for encryption of all traffic between SNMP engines. A TLS Transport Model implementation MUST support message encryption to protect sensitive data from eavesdropping attacks. Nobody's peeking at the tea ☕🤫
- Denial of Service - the RFC 3411 architecture [RFC3411] states that denial-of-service (DoS) attacks need not be addressed by an SNMP security protocol. However, connectionless transports (like DTLS over UDP) are susceptible to a variety of DoS attacks because they are more vulnerable to spoofed IP addresses. See Section 4.2 for details on how the cookie mechanism is used. Note, however, that this mechanism does not provide any defense against DoS attacks mounted from valid IP addresses.
See Section 9 for more detail on the security considerations associated with the TLSTM and these security threats. Read it, it's serious 😭
3.1.2. Message Protection 🔐
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 works out from (D)TLS the identity of the authenticated principal, the transport type and the transport address associated with an incoming message 🦋 For outgoing messages, it hands the identity and destination type and address to (D)TLS.
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 that security level gets turned into the algorithms for 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. Guarantee secured, periodt 💖
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. Mix and match, it's giving flexibility 🌈
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. Keep your settings flexible, bestie ⭐
3.1.3. (D)TLS Connections 🧚♀️
(D)TLS connections are opened by the TLS Transport Model during the elements of procedure for an outgoing SNMP message. Since the sender of a message starts creating a (D)TLS connection if one is needed, the (D)TLS connection will already exist for an incoming message. The sender always goes first, iykyk 🫶
Implementations MAY choose to instantiate (D)TLS connections in anticipation of outgoing messages. This approach might be useful to make sure that a (D)TLS connection to a given target can be established before it becomes important to send a message over that connection. Of course, there is no guarantee that a pre-established session will still be valid when it's needed 🙃
DTLS connections, when used over UDP, are uniquely identified within the TLS Transport Model by the combination of transportDomain, transportAddress, tmSecurityName, and requestedSecurityLevel associated with each session. Each unique combination of these parameters MUST have a locally chosen unique tlstmSessionID for each active session. For further information, see Section 5. TLS over TCP sessions, on the other hand, do not need a unique pairing of address and port attributes, since their lower-layer protocol (TCP) already provides adequate session framing. But they must still provide a unique tlstmSessionID for referencing the session 🎀
The tlstmSessionID MUST NOT change during the entire duration of the session from the TLSTM's perspective, and MUST uniquely identify a single session. As an implementation hint: 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 it does not necessarily uniquely identify a TLSTM session (there can be multiple TLSTM sessions sharing the same D(TLS) internal SessionID). Don't mix up your IDs, bestie 👑
3.2. Security Parameter Passing 🎀
okay so on the (D)TLS server side, the (D)TLS-specific stuff (cipher_suites, X.509 certificate fields, IP addresses, and ports) gets translated by the TLS Transport Model into security parameters for the TLS Transport Model and the security model, like tmSecurityLevel, tmSecurityName, transportDomain, and transportAddress. The transport info and the (D)TLS security info, including the authenticated identity, get stashed in a cache that tmStateReference points to. bestie, that's so organized 🗂️✨
On the (D)TLS client side, the TLS Transport Model takes the input the Dispatcher hands over in the sendMessage() ASI, and it also reads from the tmStateReference cache. Then it converts all of that into suitable security parameters for (D)TLS and sets up sessions as needed. the vibe is basically "gather everything, translate it, go" 💅
The elements of procedure in Section 5 go way deeper into all of this, so check there if you want the full tea 🫖
3.3. Notifications and Proxy 🦋
(D)TLS connections can be started by (D)TLS clients on behalf of SNMP applications that kick off communications, like command generators, notification originators, and proxy forwarders. Command generators are often run by a human 🧑💻, but notification originators and proxy forwarders are usually unmanned automated processes 🤖. The targets that notifications and proxied requests should be sent to are typically decided and set up by a network administrator.
The SNMP-TARGET-MIB module [RFC3413] has objects for defining management targets, including the 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 so you can specify a (D)TLS client-side certificate to use for the connection 🎀
When you configure 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 it's 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 to a value that refers to a locally held certificate (and the corresponding private key) to be used. Other parameters, for example cryptographic configuration like which cipher_suites to use, must come from configuration mechanisms not defined in this document. so those live somewhere else, babe 🙈
The securityName defined in the snmpTargetParamsSecurityName column will be used by the access control model to authorize any notifications that need to be sent 🔐
4. Elements of the Model ✨
This section has the definitions you need to actually realize the (D)TLS Transport Model defined by this document 🧩
4.1. X.509 Certificates 🪪
(D)TLS can use X.509 certificates to authenticate both sides of the transport. This section talks about how X.509 certificates get used in the TLSTM.
(D)TLS supports multiple authentication mechanisms, but this document only covers X.509-certificate-based authentication. Other forms of authentication are outside the scope of this specification. TLSTM implementations are REQUIRED to support X.509 certificates. no skipping this one, it's non-negotiable 💅
4.1.1. Provisioning for the Certificate 📜
Authentication using (D)TLS means SNMP entities need certificates, either signed by trusted Certification Authorities (CAs) or self-signed. SNMP entities will also most commonly need to be provisioned with root certificates that represent the list of trusted CAs an SNMP entity can use for certificate verification. SNMP entities SHOULD also be provisioned with an X.509 certificate revocation mechanism that can be used to verify that a certificate has not been revoked. Trusted public keys from 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. the vibe is "verify everything, trust nothing" 🫣
Once a TLSTM client has sent a certificate, the authenticated tmSecurityName of the principal is derived using the snmpTlstmCertToTSNTable. This table lets incoming connections get mapped 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, so they don't waste computational resources on certificate verification 💡
Deployments SHOULD map the "subjectAltName" component of X.509 certificates to the TLSTM-specific tmSecurityNames. The authenticated identity can be obtained by the TLS Transport Model by extracting the subjectAltName(s) from the peer's certificate. The receiving application then has an appropriate tmSecurityName to use with other SNMPv3 components, like an access control model 🎯
An example of this type of mapping setup can be found in Appendix A 📖
This tmSecurityName may later get translated from a TLSTM-specific tmSecurityName into an SNMP engine securityName by the security model. A security model, like the TSM security model [RFC5591], may do an identity mapping or a more complex mapping to derive the securityName from the tmSecurityName the TLS Transport Model offered 🔄
The standard View-Based Access Control Model (VACM) constrains securityNames to be 32 octets or less in length. A TLSTM-generated tmSecurityName, possibly combined with a messaging or security model that makes the securityName longer, might push the securityName length past 32 octets. For example, a 32-octet tmSecurityName derived from an IPv6 address, paired with a TSM prefix, will generate a 36-octet securityName. A securityName like that won't work with standard VACM or TARGET MIB modules. Operators should be careful to select algorithms and subjectAltNames that avoid this situation 🚨
A pictorial view of the complete transformation process (using the TSM security model as the example) is shown below 👀
+-------------+ +-------+ +-----+
| Certificate | | | | |
| Path | | TLSTM | tmSecurityName | TSM |
| Validation | --> | | ----------------->| |
+-------------+ +-------+ +-----+
|
| securityName
V
+-------------+
| application |
+-------------+4.2. (D)TLS Usage 🔒
(D)TLS MUST negotiate a cipher_suite that uses X.509 certificates for authentication, and it MUST authenticate both the client and the server. The mandatory-to-implement cipher_suite is specified in the TLS specification [RFC5246].
TLSTM verifies the certificates when the connection is opened (see Section 5.3). For this reason, TLS renegotiation with different certificates MUST NOT be done. Implementations MUST either disable renegotiation completely (RECOMMENDED), or they MUST present the same certificate during renegotiation (and MUST verify that the other end presented the same certificate). the renegotiation rules are a whole mood 😤
For DTLS over UDP, each SNMP message MUST be placed in a single UDP datagram. It MAY be split into multiple DTLS records. In other words, if a single datagram contains multiple DTLS application_data records, they are concatenated when received. The TLSTM implementation SHOULD return an error if the SNMP message does not fit in the UDP datagram and thus cannot be sent 📦
For DTLS over UDP, the DTLS server implementation MUST support DTLS cookies ([RFC4347] already requires that clients support DTLS cookies). Implementations are not required to perform the cookie exchange for every DTLS handshake; however, enabling it by default is RECOMMENDED 🍪
For DTLS, replay protection MUST be used. no replay attacks on my watch 🚫🔁
4.3. SNMP Services 🛎️
This section describes the services the TLS Transport Model provides, along with their inputs and outputs. The services sit 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 get passed in these abstract service primitives.
4.3.1. SNMP Services for an Outgoing Message 📤
The Dispatcher passes the information to the TLS Transport Model using the ASI defined in the Transport Subsystem:
statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- reference to transport state
)The abstract data elements returned from, or passed as parameters into, the abstract service primitives are as follows:
statusInformation: An indication of whether the sending of the message was successful. If not, it is an indication of the problem.destTransportDomain: The transport domain for the associateddestTransportAddress. The Transport Model uses this parameter to determine the transport type of the associateddestTransportAddress. This document specifies thesnmpTLSTCPDomainand thesnmpDTLSUDPDomaintransport domains.destTransportAddress: The transport address of the destination TLS Transport Model, in a format specified by theSnmpTLSAddressTEXTUAL-CONVENTION.outgoingMessage: The outgoing message to send to (D)TLS for encapsulation and transmission.outgoingMessageLength: The length of theoutgoingMessage.tmStateReference: A reference used to pass model-specific and mechanism-specific parameters between the Transport Subsystem and transport-aware Security Models. ✨
4.3.2. SNMP Services for an Incoming Message ✨
Okay so the TLS Transport Model grabs the message off the network using the (D)TLS service, then passes it up to the Dispatcher with this 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
)Here's what the abstract data elements returned from or passed into these primitives mean 🦋:
statusInformation: says whether passing the message along worked. If it didn't, it tells you what the problem was 😭transportDomain: the transport domain for the matchingtransportAddress. This document specifies thesnmpTLSTCPDomainandsnmpDTLSUDPDomaintransport domains 🌸transportAddress: the transport address of whoever sent the message, in a format defined by theSnmpTLSAddressTEXTUAL-CONVENTION 🎀incomingMessage: the whole SNMP message after (D)TLS is done with it 🧚incomingMessageLength: the length of theincomingMessage📏tmStateReference: a reference used to pass model-specific and mechanism-specific parameters between the Transport Subsystem and transport-aware Security Models 💜
4.4. Cached Information and References
Okay, this part is lowkey important. When SNMP is processing stuff, there are two levels of state info that might need to stick around: the immediate state linking a request and its response, and possibly longer-term state about transport and security 🧠. "Transport Subsystem for the Simple Network Management Protocol (SNMP)" [RFC5590] is where the general requirements for caches and references live, so go check that out too 🔥.
4.4.1. TLS Transport Model Cached Information
The TLS Transport Model has its own specific responsibilities when it comes to cached information 🍓. For detailed processing instructions on how the TLS Transport Model uses the tmStateReference fields, see the Elements of Procedure in Section 5 ✨.
4.4.1.1. tmSecurityName
Main character energy: the tmSecurityName MUST be a human-readable name (in snmpAdminString format) representing the identity that has been set according to the procedures in Section 5 💖. It MUST be constant for all traffic passing through a single TLSTM session 🔒. Messages MUST NOT be sent through an existing (D)TLS connection that was established using a different tmSecurityName 🙅♀️.
On the (D)TLS server side of a connection, the tmSecurityName is derived using the procedures described in Section 5.3.2 and the SNMP-TLS-TM-MIB's snmpTlstmCertToTSNTable DESCRIPTION clause 🧚.
On the (D)TLS client side, it's a little different 👀. The security model hands the tmSecurityName to the TLS Transport Model through the tmStateReference. This tmSecurityName is typically a copy of, or derived from, the securityName that the application passed in (possibly because of configuration specified in the SNMP-TARGET-MIB). The Security Model likely derived the tmSecurityName from the securityName the application gave it, again possibly because of SNMP-TARGET-MIB configuration 🫶.
Transport-Model-aware security models derive tmSecurityName from a securityName, which might be configured in MIB modules for notifications and access controls 🌈. Transport Models SHOULD use predictable tmSecurityNames so operators know what to use when they configure MIB modules that use securityNames derived from tmSecurityNames 💅. The TLSTM generates predictable tmSecurityNames based on the configuration in the SNMP-TLS-TM-MIB's snmpTlstmCertToTSNTable, and it relies on network operators to have configured that table appropriately 🎀.
4.4.1.2. tmSessionID
The tmSessionID MUST be recorded per message at the time of receipt 📝. When tmSameSecurity is set, the recorded tmSessionID can be used to figure out whether the (D)TLS connection available for sending a corresponding outgoing message is the same (D)TLS connection that was used to receive the incoming message (for example, a response to a request) 🦋.
4.4.1.3. Session State
The per-session state that tmStateReference points to may be saved across multiple messages in a Local Configuration Datastore 💾. Additional session or connection state info might also be stored in a Local Configuration Datastore 🌸.
5. Elements of Procedure
Okay, so [RFC3411] and [RFC5590] defined abstract service interfaces to describe the conceptual data flows between the various subsystems inside an SNMP entity 🧚. The TLSTM uses some of those conceptual data flows when it talks to other subsystems 💜.
To keep the elements of procedure simple, the release of state info isn't always spelled out explicitly 🙈. As a general rule, if state info is available when a message gets discarded, the message-state info should also be released. If state info is available when a session is closed, the session state info should also be released. Sensitive info, like cryptographic keys, should be overwritten appropriately before it's released 🔐.
An error indication in statusInformation will typically include the Object Identifier (OID) and value for an incremented error counter 🔥. It may be accompanied by the requested securityLevel and the tmStateReference. Per-message context info isn't accessible to Transport Models, so for the returned counter OID and value, contextEngine would be set to the local value of snmpEngineID, and contextName to the default context for error counters 🍓.
5.1. Procedures for an Incoming Message
This section covers the steps the (D)TLS Transport Model follows when it receives a (D)TLS protected packet 📦. The required functionality is split into two sections ✨.
Section 5.1.1 covers the processing needed to de-multiplex multiple DTLS connections, which is specifically needed for DTLS over UDP sessions. It's assumed that TLS protocol implementations already handle the message demultiplexing 🎀.
Section 5.1.2 covers the transport processing needed once (D)TLS processing is complete. This is needed for all (D)TLS-based connections 💖.
5.1.1. DTLS over UDP Processing for Incoming Messages
Demultiplexing incoming packets into separate DTLS sessions MUST be implemented 🚨. For connection-oriented transport protocols, like TCP, the transport protocol takes care of routing incoming packets to the right connection 🫶. For DTLS over UDP, that demultiplexing will either need to be done inside the DTLS implementation (if it's supported) or by the TLSTM implementation 🦋.
Just like TCP, DTLS over UDP uses the four-tuple <source IP, destination IP, source port, destination port> to identify the connection (and the relevant DTLS connection state) 🌈. That means when a new session is being established, implementations MUST use a different UDP source port number for each active connection to a remote destination IP-address/port-number combination, so the remote entity can tell the multiple connections apart 👑.
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 for doing it 🧚. The important outputs of these steps 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 Local Configuration Datastore (LCD) (see [RFC3411] Section 3.4.2) using the transport parameters (source and destination IP addresses and ports) to find out whether a session already exists 🕵️♀️.
- 2a) If a matching entry in the LCD does not exist, 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 doesn't allocate connection state (which can happen with the stateless cookie exchange), processing stops 🛑. - 2b) If a session does exist in the LCD, its DTLS connection handle (an implementation-dependent detail) and its
tlstmSessionIdare extracted from the LCD. The UDP packet and the connection handle are passed to the DTLS implementation. If the DTLS implementation returns success but doesn't return anincomingMessageand anincomingMessageLength, processing stops (this happens when the UDP datagram contained DTLS handshake messages, for example) 🤝. If the DTLS implementation returns an error, processing stops 🙅♀️.
- 2a) If a matching entry in the LCD does not exist, 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
- Retrieve the
incomingMessageand anincomingMessageLengthfrom DTLS. These results and thetlstmSessionIDare used below in Section 5.1.2 to finish processing the incoming message 🎉.
5.1.2. Transport Processing for Incoming SNMP Messages ✨
okay so this section is about what the TLS Transport Model does once a message has already been pulled out of the (D)TLS stream 🌸 the procedures here assume that part is done. ngl, you have to be careful with messages from TLS or DTLS. they need to be complete and single, bestie. like, one DTLS message can carry several SNMP messages 💀 and a TLS stream can hand you only part of one. these steps handle one SNMP message at a time, right after it's been delivered from the (D)TLS stream 🦋
- Work out the tlstmSessionID for the incoming message. The tlstmSessionID MUST be a unique session identifier for this (D)TLS connection 🔑 how it's built and what it looks like is up to the implementation, as long as it's unique to the session. A session identifier MUST NOT be reused until every reference to it is no longer in use 🙅♀️ The tmSessionID is the same thing as the tlstmSessionID from Section 5.1.1. tmSessionID is the name when it's stored in the tmStateReference, and tlstmSessionID is the name when it's stored in the LCD. They MUST always be equal while you're processing a given session's traffic, no exceptions 💜
If this is the first message through this session and the session doesn't have a tlstmSessionID assigned yet, then the snmpTlstmSessionAccepts counter goes up by one and a tlstmSessionID gets created for the session 🎀 This only happens on the server side, since a client already assigned one during the openSession() call. Implementations may have done the procedures in Section 5.3.2 before this point, or they can do them now, but the procedures in Section 5.3.2 MUST be performed before you go any further than this point 🫶
- Make a tmStateReference cache for the next reference and fill in these values: 🧁
tmTransportDomain=snmpTLSTCPDomainorsnmpDTLSUDPDomain, whichever fits.tmTransportAddress= the address the message came from.tmSecurityLevel= the derived tmSecurityLevel for the session, as covered in Sections 3.1.2 and 5.3.tmSecurityName= the derived tmSecurityName for the session, as covered in Section 5.3. This value MUST be constant for the whole lifetime of the session 🔒tmSessionID= the tlstmSessionID from step 1 above.
- The
incomingMessageandincomingMessageLengthget their values from the (D)TLS processing 📦 - The TLS Transport Model passes the transportDomain, transportAddress, incomingMessage, and incomingMessageLength to the Dispatcher using the receiveMessage ASI 🚀
statusInformation =
receiveMessage(
IN transportDomain -- snmpTLSTCPDomain or snmpDTLSUDPDomain,
IN transportAddress -- address for the received message
IN incomingMessage -- the whole SNMP message from (D)TLS
IN incomingMessageLength -- the length of the SNMP message
IN tmStateReference -- transport info
)5.2. Procedures for an Outgoing SNMP Message 💌
the Dispatcher sends a message to the TLS Transport Model using this ASI:
statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- transport info
)this part walks through what the TLS Transport Model does every time it gets asked to send something through that ASI 🦋
- If tmStateReference doesn't point to a cache that has values for tmTransportDomain, tmTransportAddress, tmSecurityName, tmRequestedSecurityLevel, and tmSameSecurity, then the
snmpTlstmSessionInvalidCachescounter goes up, the message gets discarded, and the error indication goes back in the statusInformation 🙅♀️ Processing of this message stops right there. - Pull out the tmSessionID, tmTransportDomain, tmTransportAddress, tmSecurityName, tmRequestedSecurityLevel, and tmSameSecurity values from the tmStateReference. Note: the tmSessionID might be undefined if there's no session yet that the message can go over 👀
- If tmSameSecurity is true and tmSessionID is either undefined or points to a session that's no longer open, then the
snmpTlstmSessionNoSessionscounter goes up, the message gets discarded, and the error indication goes back in the statusInformation 💀 Processing of this message stops. - If tmSameSecurity is false and tmSessionID points to a session that's no longer available, then an implementation SHOULD open a new session using the openSession() ASI (more on that in step 5b) ✨ Instead of opening a new session, an implementation MAY return a
snmpTlstmSessionNoSessionserror to the calling module and stop processing the message. - If tmSessionID is undefined, then use tmTransportDomain, tmTransportAddress, tmSecurityName, and tmRequestedSecurityLevel to check whether there's a matching entry in the LCD that's suitable for sending the message 🔍
- 5a) If there's a matching LCD entry, then that session gets used to send the message 🎀
- 5b) If there's no matching LCD entry, then open a session using the openSession() ASI (discussed further in Section 5.3.1). Implementations MAY wish to offer message buffering so they don't make redundant openSession() calls for the same cache entry 🧺 If openSession() returns an error, then discard the message, discard the tmStateReference, increment
snmpTlstmSessionOpenErrors, return an error indication to the calling module, and stop processing the message 😭
- Using either the session named by the tmSessionID (if there was one) or the session from an earlier step (4 or 5), pass the outgoingMessage to (D)TLS for encapsulation and transmission 🚀
5.3. Establishing or Accepting a Session 🤝
okay so setting up a (D)TLS connection is a little different depending on whether you're the client or the server 🌈 the next two sections walk through the steps for each one, so get ready 💅
5.3.1. Establishing a Session as a Client ✨
Okay bestie, let's talk about the client side 💖 The TLS Transport Model gives you this primitive for a client to set up a brand 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
)Every SNMP client's engine follows this procedure when it sets up an SNMP over (D)TLS session between SNMP engines, so it can swap SNMP messages later 🦋 Here's how it goes:
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
snmpTlstmSessionOpenscounter gets incremented 🔢 - The client picks the right certificate and
cipher_suitesfor the key agreement, based on thetmSecurityNameand thetmRequestedSecurityLevelfor the session. For sessions being set up because of an SNMP-TARGET-MIB based operation, the certificate could potentially already be identified through thesnmpTlstmParamsTablemapping, and thecipher_suiteshave to come from a system-wide or implementation-specific configuration. If there's no row in thesnmpTlstmParamsTable, implementations MAY choose to establish the connection using a default client certificate available to the application. Otherwise, the certificate and the appropriatecipher_suitesneed to be passed to theopenSession()ASI as supplemental information, or configured through an implementation-dependent mechanism. HowtmRequestedSecurityLevelgets used to shape the security capabilities of the (D)TLS connection is implementation-dependent and possibly policy-dependent too. However you do it, the security capabilities provided by (D)TLS MUST be at least as high as the level of security indicated by thetmRequestedSecurityLevelparameter. The actual security level of the session gets reported in thetmStateReferencecache astmSecurityLevel. For (D)TLS to provide strong authentication, each principal acting as a command generator SHOULD have its own certificate 🔐 - Using the
destTransportDomainanddestTransportAddressvalues, the client starts the (D)TLS handshake protocol to set up 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 snmpTlstmSessionUnknownServerCertificate or snmpTlstmSessionInvalidServerCertificates MUST be incremented, and an snmpTlstmServerCertificateUnknown or snmpTlstmServerInvalidCertificate notification SHOULD be sent as appropriate. Reasons for server certificate invalidation include, but aren't 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. No sending anything early, bestie 🙅♀️
If the connection is being established from a configuration based on SNMP-TARGET-MIB configuration, then the snmpTlstmAddrTable DESCRIPTION clause describes how the verification is done (using either a certificate fingerprint, or an identity authenticated via certification path validation).
If the connection is being established for reasons other than configuration found in the SNMP-TARGET-MIB, then configuration and procedures outside the scope of this document should be followed. Configuration mechanisms SHOULD be similar in nature to those defined in the snmpTlstmAddrTable so everything stays consistent 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 because the presented identity did not match the expected named entity), then the session establishment MUST fail, and the
snmpTlstmSessionInvalidServerCertificatesobject is incremented. If the session cannot be opened for any reason at all, including cryptographic verification failures andsnmpTlstmCertToTSNTablelookup failures, then thesnmpTlstmSessionOpenErrorscounter is incremented and processing stops 🚫 - The TLSTM-specific session identifier (
tlstmSessionID) is set in thetmSessionIDof thetmStateReferencepassed to the TLS Transport Model. This marks the session as established successfully and points to a specific (D)TLS connection for future use 🎉 ThetlstmSessionIDis also stored in the LCD for later lookup during processing of incoming messages (Section 5.1.2).
5.3.2. Accepting a Session as a Server
A (D)TLS server should accept new session connections from any client for which it is able to verify the client's credentials 🛡️ This happens by authenticating the client's presented certificate through a certificate path validation process (e.g., [RFC5280]) or through certificate fingerprint verification using fingerprints configured in the snmpTlstmCertToTSNTable. Afterward, the server figures out 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 it MUST NOT accept SNMP messages over the (D)TLS connection until the client has sent a certificate and it has been authenticated. The resulting derived tmSecurityName is recorded in the tmStateReference cache as tmSecurityName. The details of the lookup process are fully described in the DESCRIPTION clause of the snmpTlstmCertToTSNTable MIB object. If any verification fails in any way (for example, because of failures in cryptographic verification or because of the lack of an appropriate row in the snmpTlstmCertToTSNTable), then the session establishment MUST fail, and the snmpTlstmSessionInvalidClientCertificates object is incremented. If the session cannot be opened for any reason at all, including cryptographic verification failures, then the snmpTlstmSessionOpenErrors counter is incremented and processing stops 😤
Servers that wish to support multiple principals at a particular port SHOULD make use of a (D)TLS extension that allows server-side principal selection, like the Server Name Indication extension defined in Section 3.1 of [RFC4366] ✨ Supporting this will allow, for example, sending notifications to a specific principal at a given TCP or UDP port 📬
5.4. Closing a Session
The TLS Transport Model provides the following primitive to close a session 👋
statusInformation =
closeSession(
IN tmSessionID -- session ID of the session to be closed
)Here's the procedure to follow to close a session between a client and server. Any SNMP engine closing the corresponding SNMP session follows this process too 🌸
- Increment either the
snmpTlstmSessionClientClosesor thesnmpTlstmSessionServerClosescounter, as appropriate. - Look up the session using the
tmSessionID. - If there is no open session associated with the
tmSessionID, thencloseSessionprocessing is completed ✅ - Have (D)TLS close the specified connection. This MUST include sending a
close_notifyTLS Alert to tell the other side that session cleanup may be performed 🧹
6. MIB Module Overview 🦋
This MIB module provides management of the TLS Transport Model 💜 It defines the textual conventions, statistical counters, notifications, and configuration infrastructure needed for session establishment. Example usage of the configuration tables can be found in Appendix A.
6.1. Structure of the MIB Module
Objects in this MIB module are arranged into subtrees. Each subtree is organized as a set of related objects. The overall structure, the way objects are assigned to their subtrees, and the intended purpose of each subtree are shown below 🌳
6.2. Textual Conventions
Generic and Common Textual Conventions used in this module can be found summarized at http://www.ops.ietf.org/mib-common-tcs.html.
This module defines the following new Textual Conventions:
- 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 🔏
6.3. Statistical Counters
The SNMP-TLS-TM-MIB defines counters that give network management stations info about session usage and the potential errors a device might be experiencing 📊
6.4. Configuration Tables
The SNMP-TLS-TM-MIB defines configuration tables that an administrator can use to set up a device for sending and receiving SNMP messages over (D)TLS 🛠️ In particular, there are MIB tables that extend the SNMP-TARGET-MIB for configuring (D)TLS certificate usage, and a MIB table for mapping incoming (D)TLS client certificates to SNMPv3 tmSecurityNames.
6.4.1. Notifications
The SNMP-TLS-TM-MIB defines notifications to alert management stations when a (D)TLS connection fails. That happens when a server's presented certificate didn't meet an expected value (snmpTlstmServerCertificateUnknown) or when cryptographic validation failed (snmpTlstmServerInvalidCertificate) 🚨
6.5. Relationship to Other MIB Modules
Some management objects defined in other MIB modules apply to an entity implementing the TLS Transport Model 🤓 In particular, it is assumed that an entity implementing the SNMP-TLS-TM-MIB will implement the SNMPv2-MIB [RFC3418], the SNMP-FRAMEWORK-MIB [RFC3411], the SNMP-TARGET-MIB [RFC3413], the SNMP-NOTIFICATION-MIB [RFC3413], and the SNMP-VIEW-BASED-ACM-MIB [RFC3415].
The SNMP-TLS-TM-MIB module contained in this document is for managing TLS Transport Model information 💅
6.5.1. MIB Modules Required for IMPORTS
The SNMP-TLS-TM-MIB module imports items from SNMPv2-SMI [RFC2578], SNMPv2-TC [RFC2579], SNMP-FRAMEWORK-MIB [RFC3411], SNMP-TARGET-MIB [RFC3413], and SNMPv2-CONF [RFC2580] 📥
7. MIB Module Definition 🔥
SNMP-TLS-TM-MIB DEFINITIONS ::= BEGINOkay so the IMPORTS block is basically the module going "here's everything I borrowed from my besties" 🧚💖
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY, mib-2, snmpDomains,
Counter32, Unsigned32, Gauge32, NOTIFICATION-TYPE
FROM SNMPv2-SMI -- RFC 2578 or any update thereof
TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType,
AutonomousType
FROM SNMPv2-TC -- RFC 2579 or any update thereof
MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
FROM SNMPv2-CONF -- RFC 2580 or any update thereof
SnmpAdminString
FROM SNMP-FRAMEWORK-MIB -- RFC 3411 or any update thereof
snmpTargetParamsName, snmpTargetAddrName
FROM SNMP-TARGET-MIB -- RFC 3413 or any update thereof
;
snmpTlstmMIB MODULE-IDENTITY
LAST-UPDATED "201005070000Z"
ORGANIZATION "ISMS Working Group"
CONTACT-INFO "WG-EMail: isms@lists.ietf.org
Subscribe: isms-request@lists.ietf.org
Chairs:
Juergen Schoenwaelder
Jacobs University Bremen
Campus Ring 1
28725 Bremen
Germany
+49 421 200-3587
j.schoenwaelder@jacobs-university.de
Russ Mundy
SPARTA, Inc.
7110 Samuel Morse Drive
Columbia, MD 21046
USA
Editor:
Wes Hardaker
SPARTA, Inc.
P.O. Box 382
Davis, CA 95617
USA
ietf@hardakers.net
"
DESCRIPTION "
The TLS Transport Model MIB
Copyright (c) 2010 IETF Trust and the persons identified as
the document authors. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info)."
REVISION "201005070000Z"
DESCRIPTION "This version of this MIB module is part of
RFC 5953; see the RFC itself for full legal
notices."
::= { mib-2 198 }The subtree block is the module's little family tree, with the notifications, identities, objects and conformance branches all hanging off snmpTlstmMIB 🌳🎀
-- ************************************************
-- subtrees of the SNMP-TLS-TM-MIB
-- ************************************************
snmpTlstmNotifications OBJECT IDENTIFIER ::= { snmpTlstmMIB 0 }
snmpTlstmIdentities OBJECT IDENTIFIER ::= { snmpTlstmMIB 1 }
snmpTlstmObjects OBJECT IDENTIFIER ::= { snmpTlstmMIB 2 }
snmpTlstmConformance OBJECT IDENTIFIER ::= { snmpTlstmMIB 3 }
-- ************************************************
-- snmpTlstmObjects - Objects
-- ************************************************
snmpTLSTCPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over TLS via TCP transport domain. The
corresponding transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpTLSTCPDomain is 'tls'. This prefix may be used by
security models or other components to identify which secure
transport infrastructure authenticated a securityName."
REFERENCE
"RFC 2579: Textual Conventions for SMIv2"
::= { snmpDomains 8 }
snmpDTLSUDPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over DTLS via UDP transport domain. The
corresponding transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpDTLSUDPDomain is 'dtls'. This prefix may be used by
security models or other components to identify which secure
transport infrastructure authenticated a securityName."
REFERENCE
"RFC 2579: Textual Conventions for SMIv2"
::= { snmpDomains 9 }Now the big one: SnmpTLSAddress 👑 It's the textual convention for addresses, and it has a LOT of rules, so read the bits in caps extra carefully, bestie 🙈
SnmpTLSAddress ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1a"
STATUS current
DESCRIPTION
"Represents an IPv4 address, an IPv6 address, or a
US-ASCII-encoded hostname and port number.
An IPv4 address must be in dotted decimal format followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number
in US-ASCII.
An IPv6 address must be a colon-separated format (as described
in RFC 5952), surrounded by square brackets ('[', US-ASCII
character 0x5B, and ']', US-ASCII character 0x5D), followed by
a colon ':' (US-ASCII character 0x3A) and a decimal port number
in US-ASCII.
A hostname is always in US-ASCII (as per [RFC1033]);
internationalized hostnames are encoded in US-ASCII as domain
names after transformation via the ToASCII operation specified
in [RFC3490]. The ToASCII operation MUST be performed with the
UseSTD3ASCIIRules flag set. The hostname is followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number
in US-ASCII. The name SHOULD be fully qualified whenever
possible.
Values of this textual convention may not be directly usable
as transport-layer addressing information, and may require
run-time resolution. As such, applications that write them
must be prepared for handling errors if such values are not
supported, or cannot be resolved (if resolution occurs at the
time of the management operation).
The DESCRIPTION clause of TransportAddress objects that may
have SnmpTLSAddress values must fully describe how (and
when) such names are to be resolved to IP addresses and vice
versa.
This textual convention SHOULD NOT be used directly in object
definitions since it restricts addresses to a specific
format. However, if it is used, it MAY be used either on its
own or in conjunction with TransportAddressType or
TransportDomain as a pair.
When this textual convention is used as a syntax of an index
object, there may be issues with the limit of 128
sub-identifiers specified in SMIv2 (STD 58). It is RECOMMENDED
that all MIB documents using this textual convention make
explicit any limitations on index component lengths that
management software must observe. This may be done either by
including SIZE constraints on the index components or by
specifying applicable constraints in the conceptual row
DESCRIPTION clause or in the surrounding documentation."
REFERENCE
"RFC 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE
RFC 3490: Internationalizing Domain Names in Applications
RFC 5952: A Recommendation for IPv6 Address Text Representation
"
SYNTAX OCTET STRING (SIZE (1..255))Next up is SnmpTLSFingerprint, which is basically a hash with a little algorithm ID stuck on the front 🔐✨
SnmpTLSFingerprint ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1x:1x"
STATUS current
DESCRIPTION
"A fingerprint value that can be used to uniquely reference
other data of potentially arbitrary length.
An SnmpTLSFingerprint value is composed of a 1-octet hashing
algorithm identifier followed by the fingerprint value. The
octet value encoded is taken from the IANA TLS HashAlgorithm
Registry (RFC 5246). The remaining octets are filled using the
results of the hashing algorithm.
This TEXTUAL-CONVENTION allows for a zero-length (blank)
SnmpTLSFingerprint value for use in tables where the
fingerprint value may be optional. MIB definitions or
implementations may refuse to accept a zero-length value as
appropriate."
REFERENCE "RFC 5246: The Transport Layer
Security (TLS) Protocol Version 1.2
http://www.iana.org/assignments/tls-parameters/
"
SYNTAX OCTET STRING (SIZE (0..255))Then the identities for the certificate-to-tmSecurityName table. These are the mapping rules, and they're giving very "one input, one output, no drama" energy 🦋
-- 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 lowercase. This mapping results in a
1:1 correspondence between equivalent subjectAltName
rfc822Name values and tmSecurityName values except
that the host-part of the name MUST be passed in
lowercase.
Example rfc822Name Field: FooBar@Example.COM
is mapped to tmSecurityName: FooBar@example.com."
::= { snmpTlstmCertToTSNMIdentities 2 }
snmpTlstmCertSANDNSName OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a subjectAltName's dNSName to a
tmSecurityName after first converting it to all
lowercase (RFC 5280 does not specify converting to
lowercase so this involves an extra step). This
mapping results in a 1:1 correspondence between
subjectAltName dNSName values and the tmSecurityName
values."
REFERENCE "RFC 5280 - Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation
List (CRL) Profile."
::= { snmpTlstmCertToTSNMIdentities 3 }
snmpTlstmCertSANIpAddress OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a subjectAltName's iPAddress to a
tmSecurityName by transforming the binary encoded
address as follows:
1) for IPv4, the value is converted into a
decimal-dotted quad address (e.g., '192.0.2.1').
2) for IPv6 addresses, the value is converted into a
32-character all lowercase hexadecimal string
without any colon separators.
This mapping results in a 1:1 correspondence between
subjectAltName iPAddress values and the
tmSecurityName values.
The resulting length of an encoded IPv6 address is
the maximum length supported by the View-Based
Access Control Model (VACM). Using both the
Transport Security Model's support for transport
prefixes (see the SNMP-TSM-MIB's
snmpTsmConfigurationUsePrefix object for details)
will result in securityName lengths that exceed what
VACM can handle."
::= { snmpTlstmCertToTSNMIdentities 4 }Okay bestie, the subjectAltName mapping is the main character of this part 🎀✨ It checks three fields and it's giving 1:1 correspondence 💅
snmpTlstmCertSANAny OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps any of the following fields using the
corresponding mapping algorithms:
|------------+----------------------------|
| Type | Algorithm |
|------------+----------------------------|
| rfc822Name | snmpTlstmCertSANRFC822Name |
| dNSName | snmpTlstmCertSANDNSName |
| iPAddress | snmpTlstmCertSANIpAddress |
|------------+----------------------------|
The first matching subjectAltName value found in the
certificate of the above types MUST be used when
deriving the tmSecurityName. The mapping algorithm
specified in the 'Algorithm' column MUST be used to
derive the tmSecurityName.
This mapping results in a 1:1 correspondence between
subjectAltName values and tmSecurityName values. The
three sub-mapping algorithms produced by this
combined algorithm cannot produce conflicting
results between themselves."
::= { snmpTlstmCertToTSNMIdentities 5 }
snmpTlstmCertCommonName OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a certificate's CommonName to a tmSecurityName
after converting it to a UTF-8 encoding. The usage
of CommonNames is deprecated and users are
encouraged to use subjectAltName mapping methods
instead. This mapping results in a 1:1
correspondence between certificate CommonName values
and tmSecurityName values."
::= { snmpTlstmCertToTSNMIdentities 6 }Next up is the session group 🦋 It's basically a scoreboard of every time a session gets opened, closed, accepted, or goes sideways. Counters only, so no drama on the write side 📊
-- The snmpTlstmSession Group
snmpTlstmSession OBJECT IDENTIFIER ::= { snmpTlstmObjects 1 }
snmpTlstmSessionOpens OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request has been executed
as a (D)TLS client, regardless of whether it succeeded or
failed."
::= { snmpTlstmSession 1 }
snmpTlstmSessionClientCloses OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times a closeSession() request has been
executed as an (D)TLS client, regardless of whether it
succeeded or failed."
::= { snmpTlstmSession 2 }
snmpTlstmSessionOpenErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request failed to open a
session as a (D)TLS client, for any reason."
::= { snmpTlstmSession 3 }
snmpTlstmSessionAccepts OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times a (D)TLS server has accepted a new
connection from a client and has received at least one SNMP
message through it."
::= { snmpTlstmSession 4 }
snmpTlstmSessionServerCloses OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times a closeSession() request has been
executed as an (D)TLS server, regardless of whether it
succeeded or failed."
::= { snmpTlstmSession 5 }
snmpTlstmSessionNoSessions OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing message was dropped because
the session associated with the passed tmStateReference was no
longer (or was never) available."
::= { snmpTlstmSession 6 }
snmpTlstmSessionInvalidClientCertificates OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an incoming session was not established
on an (D)TLS server because the presented client certificate
was invalid. Reasons for invalidation include, but are not
limited to, cryptographic validation failures or lack of a
suitable mapping row in the snmpTlstmCertToTSNTable."
::= { snmpTlstmSession 7 }
snmpTlstmSessionUnknownServerCertificate OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing session was not established
on an (D)TLS client because the server certificate presented
by an SNMP over (D)TLS server was invalid because no
configured fingerprint or Certification Authority (CA) was
acceptable to validate it.
This may result because there was no entry in the
snmpTlstmAddrTable or because no path could be found to a
known CA."
::= { snmpTlstmSession 8 }
snmpTlstmSessionInvalidServerCertificates OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing session was not established
on an (D)TLS client because the server certificate presented
by an SNMP over (D)TLS server could not be validated even if
the fingerprint or expected validation path was known. That
is, a cryptographic validation error occurred during
certificate validation processing.
Reasons for invalidation include, but are not
limited to, cryptographic validation failures."
::= { snmpTlstmSession 9 }
snmpTlstmSessionInvalidCaches OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of outgoing messages dropped because the
tmStateReference referred to an invalid cache."
::= { snmpTlstmSession 10 }Now we're on to the configuration objects ⚙️🌸 The certificate mapping table is where the magic happens. It decides which tmSecurityName a client's certificate gets, and the rules are strict, so read closely 🧐
-- 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.
If no matching and valid row can be found, the connection MUST
be closed and SNMP messages MUST NOT be accepted over it.
Missing values of snmpTlstmCertToTSNID are acceptable and
implementations should continue to the next highest numbered
row. It is recommended that administrators skip index values
to leave room for the insertion of future rows (for example,
use values of 10 and 20 when creating initial rows).
Users are encouraged to make use of certificates with
subjectAltName fields that can be used as tmSecurityNames so
that a single root CA certificate can allow all child
certificate's subjectAltName to map directly to a
tmSecurityName via a 1:1 transformation. However, this table
is flexible to allow for situations where existing deployed
certificate infrastructures do not provide adequate
subjectAltName values for use as tmSecurityNames.
Certificates may also be mapped to tmSecurityNames using the
CommonName portion of the Subject field. However, the usage
of the CommonName field is deprecated and thus this usage is
NOT RECOMMENDED. Direct mapping from each individual
certificate fingerprint to a tmSecurityName is also possible
but requires one entry in the table per tmSecurityName and
requires more management operations to completely configure a
device."
::= { snmpTlstmCertificateMapping 3 }
snmpTlstmCertToTSNEntry OBJECT-TYPE
SYNTAX SnmpTlstmCertToTSNEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A row in the snmpTlstmCertToTSNTable that specifies a mapping
for an incoming (D)TLS certificate to a tmSecurityName to use
for a connection."
INDEX { snmpTlstmCertToTSNID }
::= { snmpTlstmCertToTSNTable 1 }
SnmpTlstmCertToTSNEntry ::= SEQUENCE {
snmpTlstmCertToTSNID Unsigned32,
snmpTlstmCertToTSNFingerprint SnmpTLSFingerprint,
snmpTlstmCertToTSNMapType AutonomousType,
snmpTlstmCertToTSNData OCTET STRING,
snmpTlstmCertToTSNStorageType StorageType,
snmpTlstmCertToTSNRowStatus RowStatus
}Okay bestie, this part is all about the cert-to-name mapping table, the params table, and the addr table. 🦋 Every bit of this is a literal MIB definition, so it's shown exactly as the original has it. I just get to hype it up around the edges. 💖
snmpTlstmCertToTSNID OBJECT-TYPE
SYNTAX Unsigned32 (1..4294967295)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A unique, prioritized index for the given entry. Lower
numbers indicate a higher priority."
::= { snmpTlstmCertToTSNEntry 1 }
snmpTlstmCertToTSNFingerprint OBJECT-TYPE
SYNTAX SnmpTLSFingerprint (SIZE(1..255))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a X.509 certificate. The results of
a successful matching fingerprint to either the trusted CA in
the certificate validation path or to the certificate itself
is dictated by the snmpTlstmCertToTSNMapType column."
::= { snmpTlstmCertToTSNEntry 2 }
snmpTlstmCertToTSNMapType OBJECT-TYPE
SYNTAX AutonomousType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"Specifies the mapping type for deriving a tmSecurityName from
a certificate. Details for mapping of a particular type SHALL
be specified in the DESCRIPTION clause of the OBJECT-IDENTITY
that describes the mapping. If a mapping succeeds it will
return a tmSecurityName for use by the TLSTM model and
processing stops.
If the resulting mapped value is not compatible with the
needed requirements of a tmSecurityName (e.g., VACM imposes a
32-octet-maximum length and the certificate derived
securityName could be longer), then future rows MUST be
searched for additional snmpTlstmCertToTSNFingerprint matches
to look for a mapping that succeeds.
Suitable values for assigning to this object that are defined
within the SNMP-TLS-TM-MIB can be found in the
snmpTlstmCertToTSNMIdentities portion of the MIB tree."
DEFVAL { snmpTlstmCertSpecified }
::= { snmpTlstmCertToTSNEntry 3 }
snmpTlstmCertToTSNData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"Auxiliary data used as optional configuration information for
a given mapping specified by the snmpTlstmCertToTSNMapType
column. Only some mapping systems will make use of this
column. The value in this column MUST be ignored for any
mapping type that does not require data present in this
column."
DEFVAL { "" }
::= { snmpTlstmCertToTSNEntry 4 }
snmpTlstmCertToTSNStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { snmpTlstmCertToTSNEntry 5 }
snmpTlstmCertToTSNRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, an administrator must set this
object to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are appropriately
configured, the value of the corresponding instance of the
snmpTlstmParamsRowStatus column is notReady(3).
In particular, a newly created row cannot be made active until
the corresponding snmpTlstmCertToTSNFingerprint,
snmpTlstmCertToTSNMapType, and snmpTlstmCertToTSNData columns
have been set.
The following objects may not be modified while the
value of this object is active(1):
- snmpTlstmCertToTSNFingerprint
- snmpTlstmCertToTSNMapType
- snmpTlstmCertToTSNData
An attempt to set these objects while the value of
snmpTlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { snmpTlstmCertToTSNEntry 6 }Next up is the params table, which maps tmSecurityNames to certificates for the SNMP-TARGET-MIB. ✨ Wait till you see how many little rules hide in these descriptions. 🙈
-- 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 SnmpTLSFingerprint,
snmpTlstmParamsStorageType StorageType,
snmpTlstmParamsRowStatus RowStatus
}
snmpTlstmParamsClientFingerprint OBJECT-TYPE
SYNTAX SnmpTLSFingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"This object stores the hash of the public portion of a
locally held X.509 certificate. The X.509 certificate, its
public key, and the corresponding private key will be used
when initiating a (D)TLS connection as a (D)TLS client."
::= { snmpTlstmParamsEntry 1 }
snmpTlstmParamsStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { snmpTlstmParamsEntry 2 }
snmpTlstmParamsRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, an administrator must set this
object to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are appropriately
configured, the value of the corresponding instance of the
snmpTlstmParamsRowStatus column is notReady(3).
In particular, a newly created row cannot be made active until
the corresponding snmpTlstmParamsClientFingerprint column has
been set.
The snmpTlstmParamsClientFingerprint object may not be modified
while the value of this object is active(1).
An attempt to set these objects while the value of
snmpTlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { snmpTlstmParamsEntry 3 }Last stop is the addr table, and this is where the big verification rules live. 🌸 Read the wildcard bit slowly, it's iconic. 💅
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 MAY support checking the name against the
CommonName 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 }Okay bestie, the snmpTlstmAddr table is where the cert pinning really lives 🔐✨ Here's the entry, the row fields, and the notifications, all copied exactly 💅
snmpTlstmAddrEntry OBJECT-TYPE
SYNTAX SnmpTlstmAddrEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A conceptual row containing a copy of a certificate's
fingerprint for a given snmpTargetAddrEntry. The values in
this row should be ignored if the connection that needs to be
established, as indicated by the SNMP-TARGET-MIB
infrastructure, is not a (D)TLS based connection. If an
snmpTlstmAddrEntry exists for a given snmpTargetAddrEntry, then
the presented server certificate MUST match or the connection
MUST NOT be established. If a row in this table does not
exist to match an snmpTargetAddrEntry row, then the connection
SHOULD still proceed if some other certificate validation path
algorithm (e.g., RFC 5280) can be used."
INDEX { IMPLIED snmpTargetAddrName }
::= { snmpTlstmAddrTable 1 }
SnmpTlstmAddrEntry ::= SEQUENCE {
snmpTlstmAddrServerFingerprint SnmpTLSFingerprint,
snmpTlstmAddrServerIdentity SnmpAdminString,
snmpTlstmAddrStorageType StorageType,
snmpTlstmAddrRowStatus RowStatus
}
snmpTlstmAddrServerFingerprint OBJECT-TYPE
SYNTAX SnmpTLSFingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a public X.509 certificate. This
object should store the hash of the public X.509 certificate
that the remote server should present during the (D)TLS
connection setup. The fingerprint of the presented
certificate and this hash value MUST match exactly or the
connection MUST NOT be established."
DEFVAL { "" }
::= { snmpTlstmAddrEntry 1 }
snmpTlstmAddrServerIdentity OBJECT-TYPE
SYNTAX SnmpAdminString
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The reference identity to check against the identity
presented by the remote system."
DEFVAL { "" }
::= { snmpTlstmAddrEntry 2 }
snmpTlstmAddrStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { snmpTlstmAddrEntry 3 }
snmpTlstmAddrRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, an administrator must set this
object to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are
appropriately configured, the value of the
corresponding instance of the snmpTlstmAddrRowStatus
column is notReady(3).
In particular, a newly created row cannot be made active until
the corresponding snmpTlstmAddrServerFingerprint column has been
set.
Rows MUST NOT be active if the snmpTlstmAddrServerFingerprint
column is blank and the snmpTlstmAddrServerIdentity is set to
'*' since this would insecurely accept any presented
certificate.
The snmpTlstmAddrServerFingerprint object may not be modified
while the value of this object is active(1).
An attempt to set these objects while the value of
snmpTlstmAddrRowStatus is active(1) will result in
an inconsistentValue error."
::= { snmpTlstmAddrEntry 4 }Now the notifications, the fun part where the engines tell each other when something's sus 🚨
-- ************************************************
-- snmpTlstmNotifications - Notifications Information
-- ************************************************
snmpTlstmServerCertificateUnknown NOTIFICATION-TYPE
OBJECTS { snmpTlstmSessionUnknownServerCertificate }
STATUS current
DESCRIPTION
"Notification that the server certificate presented by an SNMP
over (D)TLS server was invalid because no configured
fingerprint or CA was acceptable to validate it. This may be
because there was no entry in the snmpTlstmAddrTable or
because no path could be found to known Certification
Authority.
To avoid notification loops, this notification MUST NOT be
sent to servers that themselves have triggered the
notification."
::= { snmpTlstmNotifications 1 }
snmpTlstmServerInvalidCertificate NOTIFICATION-TYPE
OBJECTS { snmpTlstmAddrServerFingerprint,
snmpTlstmSessionInvalidServerCertificates}
STATUS current
DESCRIPTION
"Notification that the server certificate presented by an SNMP
over (D)TLS server could not be validated even if the
fingerprint or expected validation path was known. That is, a
cryptographic validation error occurred during certificate
validation processing.
To avoid notification loops, this notification MUST NOT be
sent to servers that themselves have triggered the
notification."
::= { snmpTlstmNotifications 2 }
-- ************************************************
-- snmpTlstmCompliances - Conformance Information
-- ************************************************
snmpTlstmCompliances OBJECT IDENTIFIER ::= { snmpTlstmConformance 1 }
snmpTlstmGroups OBJECT IDENTIFIER ::= { snmpTlstmConformance 2 }
-- ************************************************
-- Compliance statements
-- ************************************************
snmpTlstmCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines that support the
SNMP-TLS-TM-MIB"
MODULE
MANDATORY-GROUPS { snmpTlstmStatsGroup,
snmpTlstmIncomingGroup,
snmpTlstmOutgoingGroup,
snmpTlstmNotificationGroup }
::= { snmpTlstmCompliances 1 }
-- ************************************************
-- Units of conformance
-- ************************************************
snmpTlstmStatsGroup OBJECT-GROUP
OBJECTS {
snmpTlstmSessionOpens,
snmpTlstmSessionClientCloses,
snmpTlstmSessionOpenErrors,
snmpTlstmSessionAccepts,
snmpTlstmSessionServerCloses,
snmpTlstmSessionNoSessions,
snmpTlstmSessionInvalidClientCertificates,
snmpTlstmSessionUnknownServerCertificate,
snmpTlstmSessionInvalidServerCertificates,
snmpTlstmSessionInvalidCaches
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
statistical information of an SNMP engine that
implements the SNMP TLS Transport Model."
::= { snmpTlstmGroups 1 }
snmpTlstmIncomingGroup OBJECT-GROUP
OBJECTS {
snmpTlstmCertToTSNCount,
snmpTlstmCertToTSNTableLastChanged,
snmpTlstmCertToTSNFingerprint,
snmpTlstmCertToTSNMapType,
snmpTlstmCertToTSNData,
snmpTlstmCertToTSNStorageType,
snmpTlstmCertToTSNRowStatus
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
incoming connection certificate mappings to
tmSecurityNames of an SNMP engine that implements the
SNMP TLS Transport Model."
::= { snmpTlstmGroups 2 }
snmpTlstmOutgoingGroup OBJECT-GROUP
OBJECTS {
snmpTlstmParamsCount,
snmpTlstmParamsTableLastChanged,
snmpTlstmParamsClientFingerprint,
snmpTlstmParamsStorageType,
snmpTlstmParamsRowStatus,
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 }
END8. Operational Considerations ✨
This section is all about what it's like to actually run TLSTM in the real world, so pay attention, it's giving practical 🧠🎀
8.1. Sessions
A session is a security association between two TLSTM instances, and that's how we use the word all the way through this doc 🦋 Each TLSTM implementation keeps state for its sessions, and that state gets created and destroyed as sessions open and close. Now, a "broken" session (one side up and one side down) can happen if one side goes down abruptly, like a reboot or a power outage 😭 Whenever possible, implementations SHOULD provide graceful session termination through the use of TLS disconnect messages. They SHOULD also have a way of detecting "broken" sessions using heartbeats [HEARTBEAT] or other detection mechanisms, bestie 💜
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. Lots of factors, no cap 🍓
8.2. Notification Receiver Credential Selection
When an SNMP engine needs to set up an outgoing session for notifications, the snmpTargetParamsTable has an entry for the snmpTargetParamsSecurityName of the target 🎯 Servers that want to support multiple principals at one particular port SHOULD make use of the Server Name Indication extension defined in Section 3.1 of [RFC4366]. Without Server Name Indication, the receiving SNMP engine (the server) won't know which (D)TLS certificate to offer the client, so the tmSecurityName identity-authentication won't succeed. Big oof 🙈
Another option is a one-to-one mapping between certificates and incoming ports for notification receivers. The notification originator can set this up by configuring the snmpTargetAddrTable (snmpTargetAddrTDomain and snmpTargetAddrTAddress), and then the receiving SNMP engine has to monitor multiple incoming static ports based on which principals are able to receive notifications 🌸
Implementations MAY also choose to designate a single Notification Receiver Principal to receive all incoming notifications, or select an implementation-specific method of picking the server certificate to present to clients. Options, options 💅
8.3. contextEngineID Discovery
SNMPv3 requires that an application know the identifier (snmpEngineID) of the remote SNMP protocol engine in order to retrieve or manipulate objects maintained on the remote SNMP entity 🧚
[RFC5343] brings in a well-known localEngineID and a discovery mechanism that can be used to learn the snmpEngineID of a remote SNMP protocol engine. Implementations are RECOMMENDED to support and use the contextEngineID discovery mechanism defined in [RFC5343]. The vibe is clearly "find the engine, then talk to it" 🫶
8.4. Transport Considerations ✨
okay so this section is about how SNMP messages can ride over the TLS- and DTLS-based protocols 🚀 these protocols are built on top of other transports (TCP and UDP), and those base protocols have their own operational stuff you must take into consideration when you pick a (D)TLS-based protocol, like how they perform in degraded or limited networks 🌧️ the spec is NOT going to summarize how those transports work tho. for MTU size, fragmentation, performance in lossy networks, etc., go check the base protocol docs bestie 📚💅
9. Security Considerations 🔐
this document describes a transport model that lets SNMP use (D)TLS security services 🫶 the threats and how the (D)TLS transport model handles them get covered in detail all throughout the doc. for DTLS security stuff, see [RFC4347]. for TLS, see Section 11 and Appendices D, E, and F of TLS 1.2 [RFC5246]. when you run over a connectionless transport like UDP, DTLS is more open to denial-of-service attacks from spoofed IP addresses 😭 check Section 4.2 for how the cookie exchange is used to deal with that.
9.1. Certificates, Authentication, and Authorization 🎀
implementations are responsible for providing a security certificate installation and configuration mechanism 🛠️ and implementations SHOULD support certificate revocation lists 📜
(D)TLS gives you 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) 👑
authenticating the command generator principal's identity matters a LOT when you're using the SNMP access control subsystem, so only authorized principals can get at potentially sensitive data 🥺 the authenticated identity from the command generator principal's certificate gets mapped to an SNMP model-independent securityName for SNMP access control 🔑
heads up: the (D)TLS handshake only proves that the certificate of the authenticated identity was signed by a configured accepted Certification Authority 💀 (D)TLS can't go further and authorize or reject access based on that identity. an Access Control Model (like the VACM) handles access control and authorization for a command generator's requests to a command responder, and for a notification receiver's authorization to get Notifications from a notification originator 💅 but to avoid man-in-the-middle attacks, both ends of the (D)TLS-based connection MUST check the certificate the other side presents against what was expected 🚨 for example, command generators must check that the command responder presented and authenticated itself with an X.509 certificate that was expected. skipping this would let an impostor, at a minimum, present false data, receive sensitive information, and/or make you believe config was received and acted on when it wasn't 😱 authenticating and verifying the identity of the (D)TLS server and the (D)TLS client for all operations is what keeps the SNMP engine providing MIB data authentic ✨
the instructions in the DESCRIPTION clause of the snmpTlstmCertToTSNTable object must be followed exactly 📖 it's also important that the rows of that table get searched in prioritized order, starting with the row that has the lowest numbered snmpTlstmCertToTSNID value 🔢
9.2. (D)TLS Security Considerations 🦋
this section talks about security considerations that are specific to using (D)TLS 🫧
9.2.1. TLS Version Requirements 🚫
implementations of TLS usually support multiple versions of the Transport Layer Security protocol, plus the older Secure Sockets Layer (SSL) protocol 🙈 because of known security vulnerabilities, TLSTM clients and servers MUST NOT request, offer, or use SSL 2.0. see Appendix E.2 of [RFC5246] for the full details 📚
9.2.2. Perfect Forward Secrecy 🌸
using Perfect Forward Secrecy is RECOMMENDED 💜 (D)TLS can provide it with appropriately selected cipher_suites, as discussed in Appendix F of [RFC5246] ✨
9.3. Use with SNMPv1/SNMPv2c Messages 🍓
the SNMPv1 and SNMPv2c message processing described in [RFC3584] (BCP 74) always selects the SNMPv1 or SNMPv2c Security Models, respectively 🧚 both of those, plus the User-based Security Model that usually goes with SNMPv3, derive the securityName and securityLevel from the SNMP message that was received, even when the message came in over a secure transport 😤 so access control decisions are based on the contents of the SNMP message, NOT on the authenticated identity and securityLevel the TLS Transport Model gives you 🙃 it is RECOMMENDED that only SNMPv3 messages using the Transport Security Model (TSM) or another secure-transport aware security model get sent over the TLSTM transport 🔐
using a non-transport-aware Security Model with a secure Transport Model is NOT RECOMMENDED 🙅♀️ check [RFC5590] Section 7.1 for more details on how security-aware transports and non-transport-aware security models coexist 💅
9.4. MIB Module Security 🛡️
a bunch of management objects in this MIB module have a MAX-ACCESS clause of read-write and/or read-create 👀 those objects can be seen as sensitive or vulnerable in some network environments. supporting SET operations in a non-secure environment without proper protection can really mess with network operations 😭 here are the tables and objects, plus their sensitivity/vulnerability:
- The snmpTlstmParamsTable can be used to change the outgoing X.509 certificate used to establish a (D)TLS connection. modifications to objects in this table need to be adequately authenticated, since changing values here has profound impacts on the security of outbound connections from the device 🚨 knowledge of authorization rules and certificate usage mechanisms may be considered sensitive, so protecting the SNMP traffic from disclosure with encryption is also highly recommended 🔒
- The snmpTlstmAddrTable can be used to change the expectations of the certificates presented by a remote (D)TLS server. modifications to objects in this table need to be adequately authenticated, since changing values here has profound impacts on the security of outbound connections from the device 🚨 knowledge of authorization rules and certificate usage mechanisms may be considered sensitive, so protecting the SNMP traffic from disclosure with 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 an SNMPv3 securityName. modifications to objects in this table need to be adequately authenticated, since changing values here has profound impacts on the security of incoming connections to the device 🚨 knowledge of authorization rules and certificate usage mechanisms may be considered sensitive, so protecting the SNMP traffic from disclosure with encryption is also highly recommended 🔒 and when this table has a significant number of rows, it may affect system performance when accepting new (D)TLS connections 🐢
some of the readable objects in this MIB module (the ones with a MAX-ACCESS other than not-accessible) may also be considered sensitive or vulnerable in some network environments 👁️ so it's important to control even GET and/or NOTIFY access to them, and possibly even encrypt their values when sending them over the network via SNMP 🫣 here they are:
- 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, protecting the SNMP traffic from disclosure with encryption is highly recommended 🔒
SNMP versions before SNMPv3 didn't include adequate security 💀 even if the network itself is secure (for example, by using IPsec), there's still no control over who on that 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 provided by the SNMPv3 framework (see [RFC3410], Section 8), including full support for the SNMPv3 cryptographic mechanisms (for authentication and privacy) 🔐
deploying SNMP versions prior to SNMPv3 is NOT RECOMMENDED 🙅♀️ instead, it is RECOMMENDED to deploy SNMPv3 and enable cryptographic security 🎀 then it's a customer/operator responsibility to make sure the SNMP entity giving access to an instance of this MIB module is configured properly, so the objects are only given to principals (users) who have legitimate rights to GET or SET (change/create/delete) them 👑
10. IANA Considerations 🧾
IANA has assigned:
- Two TCP/UDP port numbers from the "Registered Ports" range of the Port Numbers registry, with the following keywords:
Keyword Decimal Description References
------- ------- ----------- ----------
snmptls 10161/tcp SNMP-TLS [RFC5953]
snmpdtls 10161/udp SNMP-DTLS [RFC5953]
snmptls-trap 10162/tcp SNMP-Trap-TLS [RFC5953]
snmpdtls-trap 10162/udp SNMP-Trap-DTLS [RFC5953]these are the default ports for receiving 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 (8) under snmpDomains for the snmpTLSTCPDomain object identifier 🔢
- An SMI number (9) under snmpDomains for the snmpDTLSUDPDomain object identifier 🔢
- An SMI number (198) under mib-2, for the MIB module in this document 🔢
- "tls" as the corresponding prefix for the snmpTLSTCPDomain in the SNMP Transport Domains registry 🏷️
- "dtls" as the corresponding prefix for the snmpDTLSUDPDomain in the SNMP Transport Domains registry 🏷️
11. Acknowledgements 🫶
this document closely follows and copies the Secure Shell Transport Model for SNMP documented by David Harrington and Joseph Salowey in [RFC5592] 🙌
this document was reviewed by the following people, who gave useful comments (in alphabetical order): Andy Donati, Pasi Eronen, David Harrington, Jeffrey Hutzelman, Alan Luchuk, Michael Peck, Tom Petch, Randy Presuhn, Ray Purvis, Peter Saint-Andre, Joseph Salowey, Juergen Schoenwaelder, Dave Shield, and Robert Story 🌟
this work was supported in part by the United States Department of Defense 🇺🇸 large portions of this document are based on work by General Dynamics C4 Systems and the following individuals: Brian Baril, Kim Bryant, Dana Deluca, Dan Hanson, Tim Huemiller, John Holzhauer, Colin Hoogeboom, Dave Kornbau, Chris Knaian, Dan Knaul, Charles Limoges, Steve Moccaldi, Gerardo Orlando, and Brandon Yip 💖
12. References 📚
12.1. Normative References 📚
Okay bestie, these are the docs this RFC leans on hard. Here's the full list, exactly as written 🫶
[RFC1033] Lottor, M., "Domain administrators operations guide",
RFC 1033, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580,
April 1999.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62,
RFC 3411, December 2002.
[RFC3413] Levi, D., Meyer, P., and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62,
RFC 3413, December 2002.
[RFC3414] Blumenthal, U. and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management
Protocol (SNMPv3)", STD 62, RFC 3414, December 2002.
[RFC3415] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3415,
December 2002.
[RFC3418] Presuhn, R., "Management Information Base (MIB) for the
Simple Network Management Protocol (SNMP)", STD 62,
RFC 3418, December 2002.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications
(IDNA)", RFC 3490, March 2003.
[RFC3584] Frye, R., Levi, D., Routhier, S., and B. Wijnen,
"Coexistence between Version 1, Version 2, and Version 3
of the Internet-standard Network Management Framework",
BCP 74, RFC 3584, August 2003.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen,
J., and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC5590] Harrington, D. and J. Schoenwaelder, "Transport
Subsystem for the Simple Network Management Protocol
(SNMP)", RFC 5590, June 2009.
[RFC5591] Harrington, D. and W. Hardaker, "Transport Security
Model for the Simple Network Management Protocol
(SNMP)", RFC 5591, June 2009.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for
IPv6 Address Text Representation", RFC 5952,
August 2010.12.2. Informative References 💡
These ones are the helpful background reads, the lore that gives you the full picture 🌸
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC5343] Schoenwaelder, J., "Simple Network Management Protocol
(SNMP) Context EngineID Discovery", RFC 5343,
September 2008.
[RFC5592] Harrington, D., Salowey, J., and W. Hardaker, "Secure
Shell Transport Model for the Simple Network Management
Protocol (SNMP)", RFC 5592, June 2009.
[HEARTBEAT] Seggelmann, R., Tuexen, M., and M. Williams, "Transport
Layer Security and Datagram Transport Layer Security
Heartbeat Extension", Work in Progress, February 2010.Appendix A. Target and Notification Configuration Example ✨
Now for the fun part, the examples 🎀 These sections show example configuration for the SNMP-TLS-TM-MIB, the SNMP-TARGET-MIB, the NOTIFICATION-MIB, and the SNMP-VIEW-BASED-ACM-MIB. Iconic, honestly 💅
A.1. Configuring a Notification Originator 📣
Here's a row that adds the "Joe Cool" user to the "administrators" group:
vacmSecurityModel = 4 (TSM)
vacmSecurityName = "Joe Cool"
vacmGroupName = "administrators"
vacmSecurityToGroupStorageType = 3 (nonVolatile)
vacmSecurityToGroupStatus = 4 (createAndGo)Next, this row sets up the snmpTlstmAddrTable to use certificate path validation, and to require the remote notification receiver to present a certificate for the "server.example.org" identity. Very strict, very cute 🔒
snmpTargetAddrName = "toNRAddr"
snmpTlstmAddrServerFingerprint = ""
snmpTlstmAddrServerIdentity = "server.example.org"
snmpTlstmAddrStorageType = 3 (nonVolatile)
snmpTlstmAddrRowStatus = 4 (createAndGo)This row configures the snmpTargetAddrTable to send notifications using TLS/TCP to the snmptls-trap port at 192.0.2.1 🦋
snmpTargetAddrName = "toNRAddr"
snmpTargetAddrTDomain = snmpTLSTCPDomain
snmpTargetAddrTAddress = "192.0.2.1:10162"
snmpTargetAddrTimeout = 1500
snmpTargetAddrRetryCount = 3
snmpTargetAddrTagList = "toNRTag"
snmpTargetAddrParams = "toNR" (MUST match below)
snmpTargetAddrStorageType = 3 (nonVolatile)
snmpTargetAddrColumnStatus = 4 (createAndGo)Then this row configures the snmpTargetParamsTable to send the notifications to "Joe Cool", using authPriv SNMPv3 notifications through the TransportSecurityModel [RFC5591] 🔐
snmpTargetParamsName = "toNR" (must match above)
snmpTargetParamsMPModel = 3 (SNMPv3)
snmpTargetParamsSecurityModel = 4 (TransportSecurityModel)
snmpTargetParamsSecurityName = "Joe Cool"
snmpTargetParamsSecurityLevel = 3 (authPriv)
snmpTargetParamsStorageType = 3 (nonVolatile)
snmpTargetParamsRowStatus = 4 (createAndGo0A.2. Configuring TLSTM to Utilize a Simple Derivation of tmSecurityName 🧩
This row configures the snmpTlstmCertToTSNTable to map a validated client certificate, referenced by the client's public X.509 hash fingerprint, to a tmSecurityName. It uses the subjectAltName component of the certificate to do that 🍓
snmpTlstmCertToTSNID = 1
(chosen by ordering preference)
snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
snmpTlstmCertToTSNMapType = snmpTlstmCertSANAny
snmpTlstmCertToTSNData = "" (not used)
snmpTlstmCertToTSNStorageType = 3 (nonVolatile)
snmpTlstmCertToTSNRowStatus = 4 (createAndGo)⚠️ Okay, real talk: this type of configuration should only be used when the naming conventions of the (possibly multiple) Certification Authorities are well understood. That way, two different principals cannot inadvertently be identified by the same derived tmSecurityName. Don't skip this part, bestie 😭
A.3. Configuring TLSTM to Utilize Table-Driven Certificate Mapping 🗂️
This row configures the snmpTlstmCertToTSNTable to map a validated client certificate, referenced by the client's public X.509 hash fingerprint, to the directly specified tmSecurityName of "Joe Cool" 👑
snmpTlstmCertToTSNID = 2
(chosen by ordering preference)
snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
snmpTlstmCertToTSNMapType = snmpTlstmCertSpecified
snmpTlstmCertToTSNSecurityName = "Joe Cool"
snmpTlstmCertToTSNStorageType = 3 (nonVolatile)
snmpTlstmCertToTSNRowStatus = 4 (createAndGo)Author's Address 💌
Wes Hardaker
SPARTA, Inc.
P.O. Box 382
Davis, CA 95617
USA
Phone: +1 530 792 1913
EMail: ietf@hardakers.net📦 where this page comes from
- ietf: rfc5953 2010-08
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms