ISMS W. Hardaker
Internet-Draft Sparta, Inc.
Intended status: Standards Track February 2, 2010
Expires: August 6, 2010
Transport Layer Security (TLS) Transport Model for SNMP
draft-ietf-isms-dtls-tm-08.txt
Abstract
This document describes a Transport Model for the Simple Network
Management Protocol (SNMP), that uses either the Transport Layer
Security protocol or the Datagram Transport Layer Security (DTLS)
protocol. The TLS and DTLS protocols provide authentication and
privacy services for SNMP applications. This document describes how
the TLS Transport Model (TLSTM) implements the needed features of a
SNMP Transport Subsystem to make this protection possible in an
interoperable way.
This transport model is designed to meet the security and operational
needs of network administrators. It supports sending of SNMP
messages over TLS/TCP, DTLS/UDP and DTLS/SCTP. The TLS mode can make
use of TCP's improved support for larger packet sizes and the DTLS
mode provides potentially superior operation in environments where a
connectionless (e.g. UDP or SCTP) transport is preferred. Both TLS
and DTLS integrate well into existing public keying infrastructures.
This document also defines a portion of the Management Information
Base (MIB) for use with network management protocols. In particular
it defines objects for managing the TLS Transport Model for SNMP.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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The list of current Internet-Drafts can be accessed at
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http://www.ietf.org/ietf/1id-abstracts.txt.
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This Internet-Draft will expire on August 6, 2010.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . . . . 12
3.1.3. (D)TLS Sessions . . . . . . . . . . . . . . . . . . . 12
3.2. Security Parameter Passing . . . . . . . . . . . . . . . . 13
3.3. Notifications and Proxy . . . . . . . . . . . . . . . . . 14
4. Elements of the Model . . . . . . . . . . . . . . . . . . . . 14
4.1. X.509 Certificates . . . . . . . . . . . . . . . . . . . . 15
4.1.1. Provisioning for the Certificate . . . . . . . . . . . 15
4.2. Messages . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.3. SNMP Services . . . . . . . . . . . . . . . . . . . . . . 16
4.3.1. SNMP Services for an Outgoing Message . . . . . . . . 17
4.3.2. SNMP Services for an Incoming Message . . . . . . . . 17
4.4. Cached Information and References . . . . . . . . . . . . 18
4.4.1. TLS Transport Model Cached Information . . . . . . . . 18
4.4.1.1. tmSecurityName . . . . . . . . . . . . . . . . . . 19
4.4.1.2. tmSessionID . . . . . . . . . . . . . . . . . . . 19
4.4.1.3. Session State . . . . . . . . . . . . . . . . . . 19
5. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 19
5.1. Procedures for an Incoming Message . . . . . . . . . . . . 20
5.1.1. DTLS Processing for Incoming Messages . . . . . . . . 20
5.1.2. Transport Processing for Incoming SNMP Messages . . . 22
5.2. Procedures for an Outgoing SNMP Message . . . . . . . . . 23
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 . . . . . . . . . . . . . . . . . . . . . 28
6.1. Structure of the MIB Module . . . . . . . . . . . . . . . 28
6.2. Textual Conventions . . . . . . . . . . . . . . . . . . . 29
6.3. Statistical Counters . . . . . . . . . . . . . . . . . . . 29
6.4. Configuration Tables . . . . . . . . . . . . . . . . . . . 29
6.4.1. Notifications . . . . . . . . . . . . . . . . . . . . 29
6.5. Relationship to Other MIB Modules . . . . . . . . . . . . 29
6.5.1. MIB Modules Required for IMPORTS . . . . . . . . . . . 30
7. MIB Module Definition . . . . . . . . . . . . . . . . . . . . 30
8. Operational Considerations . . . . . . . . . . . . . . . . . . 51
8.1. Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 52
8.2. Notification Receiver Credential Selection . . . . . . . . 52
8.3. contextEngineID Discovery . . . . . . . . . . . . . . . . 53
8.4. Transport Considerations . . . . . . . . . . . . . . . . . 53
9. Security Considerations . . . . . . . . . . . . . . . . . . . 53
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9.1. Certificates, Authentication, and Authorization . . . . . 53
9.2. Use with SNMPv1/SNMPv2c Messages . . . . . . . . . . . . . 54
9.3. MIB Module Security . . . . . . . . . . . . . . . . . . . 55
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 56
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 57
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 58
12.1. Normative References . . . . . . . . . . . . . . . . . . . 58
12.2. Informative References . . . . . . . . . . . . . . . . . . 59
Appendix A. (D)TLS Overview . . . . . . . . . . . . . . . . . . . 60
A.1. The (D)TLS Record Protocol . . . . . . . . . . . . . . . . 60
A.2. The (D)TLS Handshake Protocol . . . . . . . . . . . . . . 61
Appendix B. PKIX Certificate Infrastructure . . . . . . . . . . . 62
Appendix C. Target and Notification Configuration Example . . . . 63
C.1. Configuring the Notification Originator . . . . . . . . . 64
C.2. Configuring the Command Responder . . . . . . . . . . . . 64
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 65
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1. Introduction
It is important to understand the modular SNMPv3 architecture as
defined by [RFC3411] and enhanced by the Transport Subsystem
[RFC5590]. It is also important to understand the terminology of the
SNMPv3 architecture in order to understand where the Transport Model
described in this document fits into the architecture and how it
interacts with the other architecture subsystems. For a detailed
overview of the documents that describe the current Internet-Standard
Management Framework, please refer to Section 7 of [RFC3410].
This document describes a Transport Model that makes use of the
Transport Layer Security (TLS) [RFC5246] and the Datagram Transport
Layer Security (DTLS) Protocol [RFC4347], within a transport
subsystem [RFC5590]. DTLS is the datagram variant of the Transport
Layer Security (TLS) protocol [RFC5246]. The Transport Model in this
document is referred to as the Transport Layer Security Transport
Model (TLSTM). TLS and DTLS take advantage of the X.509 public
keying infrastructure [RFC5280]. While (D)TLS supports multiple
authentication mechanisms, this document only discusses X.509
certificate based authentication. Although other forms of
authentication are possible they are outside the scope of this
specification. This transport model is designed to meet the security
and operational needs of network administrators, operating in both
environments where a connectionless (e.g. UDP or SCTP) transport is
preferred and in environments where large quantities of data need to
be sent (e.g. over a TCP based stream). Both TLS and DTLS integrate
well into existing public keying infrastructures. This document
supports sending of SNMP messages over TLS/TCP, DTLS/UDP and DTLS/
SCTP.
This document also defines a portion of the Management Information
Base (MIB) for use with network management protocols. In particular
it defines objects for managing the TLS Transport Model for SNMP.
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58:
[RFC2578], [RFC2579] and [RFC2580].
The diagram shown below gives a conceptual overview of two SNMP
entities communicating using the TLS Transport Model. One entity
contains a command responder and notification originator application,
and the other a command generator and notification responder
application. It should be understood that this particular mix of
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application types is an example only and other combinations are
equally valid. Note: this diagram shows the Transport Security Model
(TSM) being used as the security model which is defined in [RFC5591].
+---------------------------------------------------------------------+
| Network |
+---------------------------------------------------------------------+
^ | ^ |
|Notifications |Commands |Commands |Notifications
+---|---------------------|--------+ +--|---------------|-------------+
| | V | | | V |
| +------------+ +------------+ | | +-----------+ +----------+ |
| | (D)TLS | | (D)TLS | | | | (D)TLS | | (D)TLS | |
| | Service | | Service | | | | Service | | Service | |
| | (Client) | | (Server) | | | | (Client) | | (Server)| |
| +------------+ +------------+ | | +-----------+ +----------+ |
| ^ ^ | | ^ ^ |
| | | | | | | |
| +-------------+ | | +--------------+ |
| +-----|--------------+ | | +-----|-----------+ |
| | V | +-------+ | | | V | +--------+ |
| | +--------+ | | | | | | +--------+ | | | |
| | | TLS TM |---------->| Cache | | | | | TLS TM | <---->| Cache | |
| | | | | | | | | | | | | | | |
| | +--------+ | +-------+ | | | +--------+ | +--------+ |
| |Transport Subsystem | ^ | | |Transport Sub. | ^ |
| +--------------------+ | | | +-----------------+ | |
| ^ +----+ | | ^ | |
| | | | | | | |
| v | | | V | |
| +-------+ +----------+ +-----+ | | | +-----+ +------+ +-----+ | |
| | | |Message | |Sec. | | | | | | | MP | |Sec. | | |
| | Disp. | |Processing| |Sub- | | | | |Disp.| | Sub- | |Sub- | | |
| | | |Subsystem | |sys. | | | | | | |system| |sys. | | |
| | | | | | | | | | | | | | | | | |
| | | | | |+---+| | | | | | | | |+---+| | |
| | | | +-----+ | || || | | | | | |+----+| || || | |
| | <--->|v3MP |<--->|TSM|<-+ | | | <-->|v3MP|<->|TSM|<-+ |
| | | | +-----+ | || || | | | | |+----+| || || |
| +-------+ | | |+---+| | | +-----+ | | |+---+| |
| ^ | | | | | | ^ | | | | |
| | +----------+ +-----+ | | | +------+ +-----+ |
| +-+------------+ | | +-+----------+ |
| ^ ^ | | | ^ |
| | | | | | | |
| v v | | v V |
| +-------------+ +--------------+ | | +-----------+ +--------------+ |
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| | COMMAND | | NOTIFICATION | | | | COMMAND | | NOTIFICATION | |
| | RESPONDER | | ORIGINATOR | | | | GENERATOR | | RECEIVER | |
| | application | | application | | | |application| | application | |
| +-------------+ +--------------+ | | +-----------+ +--------------+ |
| SNMP entity | | SNMP entity |
+----------------------------------+ +--------------------------------+
1.1. Conventions
For consistency with SNMP-related specifications, this document
favors terminology as defined in STD 62, rather than favoring
terminology that is consistent with non-SNMP specifications. This is
consistent with the IESG decision to not require the SNMPv3
terminology be modified to match the usage of other non-SNMP
specifications when SNMPv3 was advanced to Full Standard.
"Authentication" in this document typically refers to the English
meaning of "serving to prove the authenticity of" the message, not
data source authentication or peer identity authentication.
The terms "manager" and "agent" are not used in this document
because, in the [RFC3411] architecture, all SNMP entities have the
capability of acting as manager, agent, or both depending on the SNMP
application types supported in the implementation. Where distinction
is required, the application names of command generator, command
responder, notification originator, notification receiver, and proxy
forwarder are used. See "SNMP Applications" [RFC3413] for further
information.
Large portions of this document simultaneously refer to both TLS and
DTLS when discussing TLSTM components that function equally with
either protocol. "(D)TLS" is used in these places to indicate that
the statement applies to either or both protocols as appropriate.
When a distinction between the protocols is needed they are referred
to independently through the use of "TLS" or "DTLS". The Transport
Model, however, is named "TLS Transport Model" and refers not to the
TLS or DTLS protocol but to the standard defined in this document,
which includes support for both TLS and DTLS.
Throughout this document, the terms "client" and "server" are used to
refer to the two ends of the (D)TLS transport connection. The client
actively opens the (D)TLS connection, and the server passively
listens for the incoming (D)TLS connection. An SNMP entity may act
as a (D)TLS client or server or both, depending on the SNMP
applications supported.
The User-Based Security Model (USM) [RFC3414] is a mandatory-to-
implement Security Model in STD 62. While (D)TLS and USM frequently
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refer to a user, the terminology preferred in RFC3411 and in this
memo is "principal". A principal is the "who" on whose behalf
services are provided or processing takes place. A principal can be,
among other things, an individual acting in a particular role; a set
of individuals, with each acting in a particular role; an application
or a set of applications, or a combination of these within an
administrative domain.
Throughout this document, the term "session" is used to refer to a
secure association between two TLS Transport Models that permits the
transmission of one or more SNMP messages within the lifetime of the
session. The (D)TLS protocols also have an internal notion of a
session and although these two concepts of a session are related,
this document (unless otherwise specified) is referring to TLSTM's
specific session and not directly to the (D)TLS protocol's session.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. The Transport Layer Security Protocol
(D)TLS provides authentication, data message integrity, and privacy
at the transport layer. (See [RFC4347])
The primary goals of the TLS Transport Model are to provide privacy,
peer identity authentication and data integrity between two
communicating SNMP entities. The TLS and DTLS protocols provide a
secure transport upon which the TLSTM is based. An overview of
(D)TLS can be found in section Appendix A. Please refer to [RFC5246]
and [RFC4347] for complete descriptions of the protocols.
3. How the TLSTM fits into the Transport Subsystem
A transport model is a component of the Transport Subsystem. The TLS
Transport Model thus fits between the underlying (D)TLS transport
layer and the Message Dispatcher [RFC3411] component of the SNMP
engine and the Transport Subsystem.
The TLS Transport Model will establish a session between itself and
the TLS Transport Model of another SNMP engine. The sending
transport model passes unencrypted and unauthenticated messages from
the Dispatcher to (D)TLS to be encrypted and authenticated, and the
receiving transport model accepts decrypted and authenticated/
integrity-checked incoming messages from (D)TLS and passes them to
the Dispatcher.
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After a TLS Transport Model session is established, SNMP messages can
conceptually be sent through the session from one SNMP message
Dispatcher to another SNMP Message Dispatcher. If multiple SNMP
messages are needed to be passed between two SNMP applications they
MAY be passed through the same session. A TLSTM implementation
engine MAY choose to close a (D)TLS session to conserve resources.
The TLS Transport Model of an SNMP engine will perform the
translation between (D)TLS-specific security parameters and SNMP-
specific, model-independent parameters.
The diagram below depicts where the TLS Transport Model fits into the
architecture described in RFC3411 and the Transport Subsystem:
+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Subsystem | +--------+ |
| | +-----+ +-----+ +-------+ +-------+ | | | |
| | | UDP | | SSH | |(D)TLS | . . . | other |<--->| Cache | |
| | | | | TM | | TM | | | | | | |
| | +-----+ +-----+ +-------+ +-------+ | +--------+ |
| +--------------------------------------------------+ ^ |
| ^ | |
| | | |
| Dispatcher v | |
| +--------------+ +---------------------+ +----------------+ | |
| | Transport | | Message Processing | | Security | | |
| | Dispatch | | Subsystem | | Subsystem | | |
| | | | +------------+ | | +------------+ | | |
| | | | +->| v1MP |<--->| | USM | | | |
| | | | | +------------+ | | +------------+ | | |
| | | | | +------------+ | | +------------+ | | |
| | | | +->| v2cMP |<--->| | Transport | | | |
| | Message | | | +------------+ | | | Security |<--+ |
| | Dispatch <---->| +------------+ | | | Model | | |
| | | | +->| v3MP |<--->| +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | PDU Dispatch | | | +------------+ | | | Other | | |
| +--------------+ | +->| otherMP |<--->| | Model(s) | | |
| ^ | +------------+ | | +------------+ | |
| | +---------------------+ +----------------+ |
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| 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 provides protection against the threats
identified by the RFC 3411 architecture [RFC3411]:
1. Modification of Information - The modification threat is the
danger that an unauthorized entity may alter in-transit SNMP
messages generated on behalf of an authorized principal in such a
way as to effect unauthorized management operations, including
falsifying the value of an object.
(D)TLS provides verification that the content of each received
message has not been modified during its transmission through the
network, data has not been altered or destroyed in an
unauthorized manner, and data sequences have not been altered to
an extent greater than can occur non-maliciously.
2. Masquerade - The masquerade threat is the danger that management
operations unauthorized for a given principal may be attempted by
assuming the identity of another principal that has the
appropriate authorizations.
The TLSTM verifies of the identity of the (D)TLS server through
the use of the (D)TLS protocol and X.509 certificates. The TLS
Transport Model MUST support authentication of both the server
and the client.
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3. Message stream modification - The re-ordering, delay or replay of
messages can and does occur through the natural operation of many
connectionless transport services. The message stream
modification threat is the danger that messages may be
maliciously re-ordered, delayed or replayed to an extent which is
greater than can occur through the natural operation of
connectionless transport services, in order to effect
unauthorized management operations.
(D)TLS provides replay protection with a MAC that includes a
sequence number. Since UDP provides no sequencing ability, DTLS
uses a sliding window protocol with the sequence number used for
replay protection (see [RFC4347]).
4. Disclosure - The disclosure threat is the danger of eavesdropping
on the exchanges between SNMP engines.
(D)TLS provides protection against the disclosure of information
to unauthorized recipients or eavesdroppers by allowing for
encryption of all traffic between SNMP engines. The TLS
Transport Model SHOULD support the message encryption to protect
sensitive data from eavesdropping attacks.
5. Denial of Service - the RFC 3411 architecture [RFC3411] states
that denial of service (DoS) attacks need not be addressed by an
SNMP security protocol. However, datagram-based security
protocols like DTLS are susceptible to a variety of denial of
service attacks because they are more vulnerable to spoofed
messages.
In order to counter these attacks, DTLS borrows the stateless
cookie technique used by Photuris [RFC2522] and IKEv2 [RFC4306]
and is described fully in section 4.2.1 of [RFC4347]. This
mechanism, though, does not provide any defense against denial of
service attacks mounted from valid IP addresses. DTLS Transport
Model server implementations MUST support DTLS cookies.
Implementations are not required to perform the stateless cookie
exchange for every DTLS handshake, but in environments where an
overload on server side resources is detectable by the
implementation it is RECOMMENDED that the cookie exchange is
utilized by the implementation.
See Section 9 for more detail on the security considerations
associated with the TLSTM and these security threats.
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3.1.2. Message Protection
The RFC 3411 architecture recognizes three levels of security:
o without authentication and without privacy (noAuthNoPriv)
o with authentication but without privacy (authNoPriv)
o with authentication and with privacy (authPriv)
The TLS Transport Model determines from (D)TLS the identity of the
authenticated principal, the transport type and the transport address
associated with an incoming message. The TLS Transport Model
provides the identity and destination type and address to (D)TLS for
outgoing messages.
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 session provides security at least as high as
the requested level of security. How the security level is
translated into the algorithms used to provide data integrity and
privacy is implementation-dependent. However, the NULL integrity and
encryption algorithms MUST NOT be used to fulfill security level
requests for authentication or privacy. Implementations MAY choose
to force (D)TLS to only allow cipher_suites that provide both
authentication and privacy to guarantee this assertion.
If a suitable interface between the TLS Transport Model and the
(D)TLS Handshake Protocol is implemented to allow the selection of
security level dependent algorithms (for example a security level to
cipher_suites mapping table) then different security levels may be
utilized by the application.
The authentication, integrity and privacy algorithms used by the
(D)TLS Protocols may vary over time as the science of cryptography
continues to evolve and the development of (D)TLS continues over
time. Implementers are encouraged to plan for changes in operator
trust of particular algorithms. Implementations should offer
configuration settings for mapping algorithms to SNMPv3 security
levels.
3.1.3. (D)TLS Sessions
(D)TLS sessions are opened by the TLS Transport Model during the
elements of procedure for an outgoing SNMP message. Since the sender
of a message initiates the creation of a (D)TLS session if needed,
the (D)TLS session will already exist for an incoming message.
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Implementations MAY choose to instantiate (D)TLS sessions in
anticipation of outgoing messages. This approach might be useful to
ensure that a (D)TLS session to a given target can be established
before it becomes important to send a message over the (D)TLS
session. Of course, there is no guarantee that a pre-established
session will still be valid when needed.
DTLS sessions, 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
and DTLS over SCTP sessions, on the other hand, do not require a
unique pairing of address and port attributes since their lower layer
protocols (TCP and SCTP) already provide adequate session framing.
But they must still provide a unique tlstmSessionID for referencing
the session.
As an implementation hint: although the tlstmSessionID may be the
same as the (D)TLS internal SessionID caution must be exercised since
the (D)TLS internal SessionID may change over the life of the
connection as seen by the TLSTM (for example during renegotiation).
The tlstmSessionID identifier MUST NOT change during the entire
duration of the session from the TLSTM's perspective even if the TLS
internal session identifier does change.
3.2. Security Parameter Passing
For the (D)TLS server-side, (D)TLS-specific security parameters
(i.e., cipher_suites, X.509 certificate fields, IP address and port)
are translated by the TLS Transport Model into security parameters
for the TLS Transport Model and security model (e.g.,
tmSecurityLevel, tmSecurityName, transportDomain, transportAddress).
The transport-related and (D)TLS-security-related information,
including the authenticated identity, are stored in a cache
referenced by tmStateReference.
For the (D)TLS client-side, the TLS Transport Model takes input
provided by the Dispatcher in the sendMessage() Abstract Service
Interface (ASI) and input from the tmStateReference cache. The
(D)TLS Transport Model converts that information into suitable
security parameters for (D)TLS and establishes sessions as needed.
The elements of procedure in Section 5 discuss these concepts in much
greater detail.
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3.3. Notifications and Proxy
(D)TLS sessions may be initiated by (D)TLS clients on behalf of SNMP
appplications that initiate communications, such as command
generators, notification originators, proxy forwarders. Command
generators are frequently operated by a human, but notification
originators and proxy forwarders are usually unmanned automated
processes. The targets to whom notifications and proxied requests
should be sent is typically determined and configured by a network
administrator.
The SNMP-TARGET-MIB module [RFC3413] contains objects for defining
management targets, including transportDomain, transportAddress,
securityName, securityModel, and securityLevel parameters, for
notification originator, proxy forwarder, and SNMP-controllable
command generator applications. Transport domains and transport
addresses are configured in the snmpTargetAddrTable, and the
securityModel, securityName, and securityLevel parameters are
configured in the snmpTargetParamsTable. This document defines a MIB
module that extends the SNMP-TARGET-MIB's snmpTargetParamsTable to
specify a (D)TLS client-side certificate to use for the connection.
When configuring a (D)TLS target, the snmpTargetAddrTDomain and
snmpTargetAddrTAddress parameters in snmpTargetAddrTable should be
set to the snmpTLSTCPDomain, snmpDTLSUDPDomain, or snmpDTLSSCTPDomain
object and an appropriate snmpTLSAddress value. When used with the
SNMPv3 message processing model, the snmpTargetParamsMPModel column
of the snmpTargetParamsTable should be set to a value of 3. The
snmpTargetParamsSecurityName should be set to an appropriate
securityName value and the tlstmParamsClientFingerprint parameter of
the tlstmParamsTable should be set a value that refers to a locally
held certificate to be used. Other parameters, for example
cryptographic configuration such as which cipher suites to use, must
come from configuration mechanisms not defined in this document.
The securityName defined in the snmpTargetParamsSecurityName column
will be used by the access control model to authorize any
notifications that need to be sent.
4. Elements of the Model
This section contains definitions required to realize the (D)TLS
Transport Model defined by this document.
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4.1. X.509 Certificates
(D)TLS can make use of X.509 certificates for authentication of both
sides of the transport. This section discusses the use of X.509
certificates in the TLSTM. A brief overview of X.509 certificate
infrastructure can be found in Appendix B.
While (D)TLS supports multiple authentication mechanisms, this
document only discusses X.509 certificate based authentication.
Although other forms of authentication are possible they are outside
the scope of this specification. TLSTM implementations are REQUIRED
to support X.509 certificates.
4.1.1. Provisioning for the Certificate
Authentication using (D)TLS will require that SNMP entities are
provisioned with certificates, which are signed by trusted
certificate authorities (possibly the certificate itself).
Furthermore, SNMP entities will most commonly need to be provisioned
with root certificates which represent the list of trusted
certificate authorities that an SNMP entity can use for certificate
verification. SNMP entities SHOULD also be provisioned with a X.509
certificate revocation mechanism which can be used to verify that a
certificate has not been revoked. Trusted public keys from either CA
certificates and/or self-signed certificates, MUST be installed into
the server through a trusted out of band mechanism and their
authenticity MUST be verified before access is granted.
Having received a certificate from a connecting TLSTM client, the
authenticated tmSecurityName of the principal is derived using the
tlstmCertToTSNTable. This table allows mapping of incoming
connections to tmSecurityNames through defined transformations. The
transformations defined in the TLSTM-MIB include:
o Mapping a certificate's subjectAltName or CommonName components to
a tmSecurityName, or
o Mapping a certificate's fingerprint value to a directly specified
tmSecurityName
As an implementation hint: implementations may choose to discard any
connections for which no potential tlstmCertToTSNTable mapping exists
before performing certificate verification to avoid expending
computational resources associated with certificate verification.
Enterprise configurations are encouraged to map a "subjectAltName"
component of the X.509 certificate to the TLSTM specific
tmSecurityName. The authenticated identity can be obtained by the
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TLS Transport Model by extracting the subjectAltName(s) from the
peer's certificate. The receiving application will then have an
appropriate tmSecurityName for use by other SNMPv3 components like an
access control model.
An example of this type of mapping setup can be found in Appendix C.
This tmSecurityName may be later translated from a TLSTM specific
tmSecurityName to a SNMP engine securityName by the security model.
A security model, like the TSM security model [RFC5591], may perform
an identity mapping or a more complex mapping to derive the
securityName from the tmSecurityName offered by the TLS Transport
Model.
A pictorial view of the complete transformation process (using the
TSM security model for the example) is shown below:
+-------------+ +-------+ +-----+
| Certificate | | | | |
| Path | | TLSTM | tmpSecurityName | TSM |
| Validation | --> | | ----------------->| |
+-------------+ +-------+ +-----+
|
| securityName
V
+-------------+
| application |
+-------------+
4.2. Messages
As stated in Section 4.1.1 of [RFC4347], each DTLS record must fit
within a single DTLS datagram. The TLSTM SHOULD prohibit SNMP
messages from being sent that exceeds the maximum DTLS message size.
The TLSTM implementation SHOULD return an error when the DTLS message
size would be exceeded and the message won't be sent.
4.3. SNMP Services
This section describes the services provided by the TLS Transport
Model with their inputs and outputs. The services are between the
Transport Model and the Dispatcher.
The services are described as primitives of an abstract service
interface (ASI) and the inputs and outputs are described as abstract
data elements as they are passed in these abstract service
primitives.
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4.3.1. SNMP Services for an Outgoing Message
The Dispatcher passes the information to the TLS Transport Model
using the ASI defined in the transport subsystem:
statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- reference to transport state
)
The abstract data elements returned from or passed as parameters into
the abstract service primitives are as follows:
statusInformation: An indication of whether the sending of the
message was successful. If not, it is an indication of the
problem.
destTransportDomain: The transport domain for the associated
destTransportAddress. The Transport Model uses this parameter to
determine the transport type of the associated
destTransportAddress. This document specifies the snmpTLSDomain,
the snmpDTLSUDPDomain and the snmpDTLSSCTPDomain transport
domains.
destTransportAddress: The transport address of the destination TLS
Transport Model in a format specified by the SnmpTLSAddress
TEXTUAL-CONVENTION.
outgoingMessage: The outgoing message to send to (D)TLS for
encapsulation and transmission.
outgoingMessageLength: The length of the outgoingMessage field.
tmStateReference: A reference to tmState to be used when securing
outgoing messages.
4.3.2. SNMP Services for an Incoming Message
The TLS Transport Model processes the received message from the
network using the (D)TLS service and then passes it to the Dispatcher
using the following ASI:
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statusInformation =
receiveMessage(
IN transportDomain -- origin transport domain
IN transportAddress -- origin transport address
IN incomingMessage -- the message received
IN incomingMessageLength -- its length
IN tmStateReference -- reference to transport state
)
The abstract data elements returned from or passed as parameters into
the abstract service primitives are as follows:
statusInformation: An indication of whether the passing of the
message was successful. If not, it is an indication of the
problem.
transportDomain: The transport domain for the associated
transportAddress. This document specifies the snmpTLSDomain, the
snmpDTLSUDPDomain and the snmpDTLSSCTPDomain transport domains.
transportAddress: The transport address of the source of the
received message in a format specified by the SnmpTLSAddress
TEXTUAL-CONVENTION.
incomingMessage: The whole SNMP message after being processed by
(D)TLS and the (D)TLS transport layer data has been removed.
incomingMessageLength: The length of the incomingMessage field.
tmStateReference: A reference to tmSecurityData to be used by the
security model.
4.4. Cached Information and References
When performing SNMP processing, there are two levels of state
information that may need to be retained: the immediate state linking
a request-response pair, and potentially longer-term state relating
to transport and security. "Transport Subsystem for the Simple
Network Management Protocol" [RFC5590] defines general requirements
for caches and references.
4.4.1. TLS Transport Model Cached Information
The TLS Transport Model has specific responsibilities regarding the
cached information. See the Elements of Procedure in Section 5 for
detailed processing instructions on the use of the tmStateReference
fields by the TLS Transport Model.
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4.4.1.1. tmSecurityName
The tmSecurityName MUST be a human-readable name (in snmpAdminString
format) representing the identity that has been set according to the
procedures in Section 5. The tmSecurityName MUST be constant for all
traffic passing through an TLSTM session. Messages MUST NOT be sent
through an existing (D)TLS session 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
TLSTM-MIB's tlstmCertToTSNTable DESCRIPTION clause.
On the (D)TLS client side of a connection the tmSecurityName is
presented to the TLS Transport Model by the application (possibly
because of configuration specified in the SNMP-TARGET-MIB).
The securityName MAY be derived from the tmSecurityName by a Security
Model and MAY be used to configure notifications and access controls
in MIB modules. Transport Models SHOULD generate a predictable
tmSecurityName so operators will know what to use when configuring
MIB modules that use securityNames derived from tmSecurityNames.
4.4.1.2. tmSessionID
The tmSessionID MUST be recorded per message at the time of receipt.
When tmSameSecurity is set, the recorded tmSessionID can be used to
determine whether the (D)TLS session available for sending a
corresponding outgoing message is the same (D)TLS session as was used
when receiving the incoming message (e.g., a response to a request).
4.4.1.3. Session State
The per-session state that is referenced by tmStateReference may be
saved across multiple messages in a Local Configuration Datastore.
Additional session/connection state information might also be stored
in a Local Configuration Datastore.
5. Elements of Procedure
Abstract service interfaces have been defined by [RFC3411] and
further augmented by [RFC5590] to describe the conceptual data flows
between the various subsystems within an SNMP entity. The TLSTM uses
some of these conceptual data flows when communicating between
subsystems.
To simplify the elements of procedure, the release of state
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information is not always explicitly specified. As a general rule,
if state information is available when a message gets discarded, the
message-state information should also be released. If state
information is available when a session is closed, the session state
information should also be released. Sensitive information, like
cryptographic keys, should be overwritten appropriately prior to
being released.
An error indication in statusInformation will typically include the
Object Identifier (OID) and value for an incremented error counter.
This may be accompanied by the requested securityLevel and the
tmStateReference. Per-message context information is not accessible
to Transport Models, so for the returned counter OID and value,
contextEngine would be set to the local value of snmpEngineID and
contextName to the default context for error counters.
5.1. Procedures for an Incoming Message
This section describes the procedures followed by the (D)TLS
Transport Model when it receives a (D)TLS protected packet. The
required functionality is broken into two different sections.
Section 5.1.1 describes the processing required for de-multiplexing
multiple DTLS sessions, which is specifically needed for DTLS over
UDP sessions. It is assumed that TLS and DTLS/SCP protocol
implementations already provide appropriate message demultiplexing.
Section 5.1.2describes the transport processing required once the
(D)TLS processing has been completed. This will be needed for all
(D)TLS-based sessions.
5.1.1. DTLS Processing for Incoming Messages
DTLS over UDP is significantly different in terms of session handling
than when TLS or DTLS is run over session based streaming protocols
like TCP or SCTP. Specifically, the DTLS protocol, when run over
UDP, does not have a session identifier that allows implementations
to determine through which session a packet arrived. It is critical,
however, that implementations are always able to derive a
tlstmSessionID from any session demultiplexing process. When
establishing a new session implementations MUST use a different UDP
source port number for each active connection to a remote destination
IP-address/port-number combination to ensure the remote entity can
easily disambiguate between multiple sessions from a host to the same
port on a server.
A process for demultiplexing multiple DTLS sessions arriving over UDP
must be incorporated into the procedures for processing an incoming
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message. The steps in this section describe one possible method to
accomplish this, although any implementation-dependent method should
be suitable as long as the results are deterministic. The important
output results from the steps in this process are the
transportDomain, the transportAddress, the wholeMessage, the
wholeMessageLength, and a unique implementation-dependent session
identifier (tlstmSessionID).
This demultiplexing procedure assumes that upon session establishment
an entry in a local transport mapping table is created in the
Transport Model's Local Configuration Datastore (LCD). The transport
mapping table's entry should map a unique combination of the remote
address, remote port number, local address and local port number to
an implementation-dependent tlstmSessionID.
1) The TLS Transport Model examines the raw UDP message, in an
implementation-dependent manner.
2) The TLS Transport Model queries the LCD using the transport
parameters (source and destination addresses and ports) to
determine if a session already exists.
If a matching entry in the LCD does not exist then the message is
passed to DTLS for processing without a corresponding
tlstmSessionID. The incoming packet may result in a new session
being established if the receiving entity is acting as a DTLS
server. If DTLS returns success then stop processing of this
message. If DTLS returns an error then increment the
snmpTlstmSessionNoSessions counter and stop processing the
message.
Note that an entry would already exist if the client and server's
session establishment procedures had been successfully completed
previously (as described both above and in Section 5.3) even if
no message had yet been sent through the newly established
session. An entry may not exist, however, if a message not
intended the SNMP entity was routed to it by mistake. An entry
might also be missing because of a "broken" session (see
operational considerations).
3) Retrieve the tlstmSessionID from the LCD.
4) The UDP packet and the tlstmSessionID are passed to DTLS for
integrity checking and decryption. If processing does not return
an incomingMessage and an incomingMessageLength then processing
stops.
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5) Retrieve the incomingMessage and an incomingMessageLength from
DTLS. These results and the tlstmSessionID are used below in
Section 5.1.2 to complete the processing of the incoming message.
5.1.2. Transport Processing for Incoming SNMP Messages
The procedures in this section describe how the TLS Transport Model
should process messages that have already been properly extracted
from the (D)TLS stream. Note that care must be taken when processing
messages originating from either TLS or DTLS to ensure they're
complete and single. For example, multiple SNMP messages can be
passed through a single DTLS message and partial SNMP messages may be
received from a TLS stream. These steps describe the processing of a
singular SNMP message after it has been delivered from the (D)TLS
stream.
1) Determine the tlstmSessionID for the incoming message. The
tlstmSessionID MUST be a unique session identifier for this
(D)TLS connection. The contents and format of this identifier
are implementation-dependent as long as it is unique to the
session. A session identifier MUST NOT be reused until all
references to it are no longer in use. The tmSessionID is equal
to the tlstmSessionID discussed in Section 5.1.1. tmSessionID
refers to the session identifier when stored in the
tmStateReference and tlstmSessionID refers to the session
identifier when stored in the LCD. They MUST always be equal
when processing a given session's traffic.
If this is the first message received through this session and
the session does not have an assigned tlstmSessionID yet then the
snmpTlstmSessionAccepts counter is incremented and a
tlstmSessionID for the session is created. This will only happen
on the server side of a connection because a client would have
already assigned a tlstmSessionID during the openSession()
invocation. Implementations may have performed the procedures
described in Section 5.3.2 prior to this point or they may
perform them now, but the procedures described in Section 5.3.2
MUST be performed before continuing beyond this point.
2) Create a tmStateReference cache for the subsequent reference and
assign the following values within it:
tmTransportDomain = snmpTLSTCPDomain, snmpDTLSUDPDomain or
snmpDTLSSCTPDomain as appropriate.
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tmTransportAddress = The address the message originated from.
tmSecurityLevel = The derived tmSecurityLevel for the session,
as discussed in Section 3.1.2 and Section 5.3.
tmSecurityName = The derived tmSecurityName for the session as
discussed in Section 5.3. This value MUST be constant during
the lifetime of the (D)TLS session.
tmSessionID = The tlstmSessionID described in step 1 above.
3) The incomingMessage and incomingMessageLength are assigned values
from the (D)TLS processing.
4) The TLS Transport Model passes the transportDomain,
transportAddress, incomingMessage, and incomingMessageLength to
the Dispatcher using the receiveMessage ASI:
statusInformation =
receiveMessage(
IN transportDomain -- snmpTLSTCPDomain, snmpDTLSUDPDomain,
-- or snmpDTLSSCTPDomain
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 the
following ASI:
statusInformation =
sendMessage(
IN destTransportDomain -- transport domain to be used
IN destTransportAddress -- transport address to be used
IN outgoingMessage -- the message to send
IN outgoingMessageLength -- its length
IN tmStateReference -- transport info
)
This section describes the procedure followed by the TLS Transport
Model whenever it is requested through this ASI to send a message.
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1) If tmStateReference does not refer to a cache containing values
for tmTransportDomain, tmTransportAddress, tmSecurityName,
tmRequestedSecurityLevel, and tmSameSecurity, then increment the
snmpTlstmSessionInvalidCaches counter, discard the message, and
return the error indication in the statusInformation. Processing
of this message stops.
2) Extract the tmSessionID, tmTransportDomain, tmTransportAddress,
tmSecurityName, tmRequestedSecurityLevel, and tmSameSecurity
values from the tmStateReference. Note: The tmSessionID value
may be undefined if no session exists yet over which the message
can be sent.
3) If tmSameSecurity is true and either tmSessionID is undefined or
refers to a session that is no longer open then increment the
snmpTlstmSessionNoSessions counter, discard the message and
return the error indication in the statusInformation. Processing
of this message stops.
4) If tmSameSecurity is false and tmSessionID refers to a session
that is no longer available then an implementation SHOULD open a
new session using the openSession() ASI (described in greater
detail in step 5b). Instead of opening a new session an
implementation MAY return a snmpTlstmSessionNoSessions error to
the calling module and stop processing of the message.
5) If tmSessionID is undefined, then use tmTransportDomain,
tmTransportAddress, tmSecurityName and tmRequestedSecurityLevel
to see if there is a corresponding entry in the LCD suitable to
send the message over.
5a) If there is a corresponding LCD entry, then this session
will be used to send the message.
5b) If there is not a corresponding LCD entry, then open a
session using the openSession() ASI (discussed further in
Section 5.3.1). Implementations MAY wish to offer message
buffering to prevent redundant openSession() calls for the
same cache entry. If an error is returned from
openSession(), then discard the message, discard the
tmStateReference, increment the snmpTlstmSessionOpenErrors,
return an error indication to the calling module and stop
processing of the message.
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6) Using either the session indicated by the tmSessionID if there
was one or the session resulting from a previous step (4 or 5),
pass the outgoingMessage to (D)TLS for encapsulation and
transmission.
5.3. Establishing or Accepting a Session
Establishing a (D)TLS session as either a client or a server requires
slightly different processing. The following two sections describe
the necessary processing steps.
5.3.1. Establishing a Session as a Client
The TLS Transport Model provides the following primitive for use by a
client to establish a new (D)TLS session:
statusInformation = -- errorIndication or success
openSession(
IN tmStateReference -- transport information to be used
OUT tmStateReference -- transport information to be used
IN maxMessageSize -- of the sending SNMP entity
)
The following describes the procedure to follow when establishing a
SNMP over (D)TLS session between SNMP engines for exchanging SNMP
messages. This process is followed by any SNMP client's engine when
establishing a session for subsequent use.
This MAY be done automatically for an SNMP application that initiates
a transaction, such as a command generator, a notification
originator, or a proxy forwarder.
1) The snmpTlstmSessionOpens counter is incremented.
2) The client selects the appropriate certificate and cipher_suites
for the key agreement based on the tmSecurityName and the
tmRequestedSecurityLevel for the session. For sessions being
established as a result of a SNMP-TARGET-MIB based operation, the
certificate will potentially have been identified via the
tlstmParamsTable mapping and the cipher_suites will have to be
taken from system-wide or implementation-specific configuration.
Otherwise, the certificate and appropriate cipher_suites will
need to be passed to the openSession() ASI as supplemental
information or configured through an implementation-dependent
mechanism. It is also implementation-dependent and possibly
policy-dependent how tmRequestedSecurityLevel will be used to
influence the security capabilities provided by the (D)TLS
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session. However this is done, the security capabilities
provided by (D)TLS MUST be at least as high as the level of
security indicated by the tmRequestedSecurityLevel parameter.
The actual security level of the session is reported in the
tmStateReference cache as tmSecurityLevel. For (D)TLS to provide
strong authentication, each principal acting as a command
generator SHOULD have its own certificate.
3) Using the destTransportDomain and destTransportAddress values,
the client will initiate the (D)TLS handshake protocol to
establish session keys for message integrity and encryption.
If the attempt to establish a session is unsuccessful, then
snmpTlstmSessionOpenErrors is incremented, an error indication is
returned, and processing stops. If the session failed to open
because the presented server certificate was unknown or invalid
then the snmpTlstmSessionUnknownServerCertificate or
snmpTlstmSessionInvalidServerCertificates MUST be incremented and
a tlstmServerCertificateUnknown or tlstmServerInvalidCertificate
notification SHOULD be sent as appropriate. Reasons for server
certificate invalidation includes, but is not limited to,
cryptographic validation failures and an unexpected presented
certificate identity.
4) The (D)TLS client MUST then verify that the (D)TLS server's
presented certificate is the expected certificate. The (D)TLS
client MUST NOT transmit SNMP messages until the server
certificate has been authenticated and the client certificate has
been transmitted.
If the connection is being established from configuration based
on SNMP-TARGET-MIB configuration then the procedures in the
tlstmAddrTable DESCRIPTION clause should be followed to determine
if the presented identity matches the expectations of the
configuration. Validation procedures (like the path validation
procedures defined in [RFC5280] or through the use of
fingerprints as defined by the tlstmAddrServerIdentity column)
MUST be followed. If a server identity name has been configured
in the tlstmAddrServerIdentity column then this reference
identity must be compared against the presented identity (for
example using procedures described in
[I-D.saintandre-tls-server-id-check]).
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.
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5) (D)TLS provides assurance that the authenticated identity has
been signed by a trusted configured certificate authority. If
verification of the server's certificate fails in any way (for
example because of failures in cryptographic verification or the
presented identity did not match the expected named entity) then
the session establishment MUST fail, the
snmpTlstmSessionInvalidServerCertificates object is incremented.
If the session can not be opened for any reason at all, including
cryptographic verification failures, then the
snmpTlstmSessionOpenErrors counter is incremented and processing
stops.
6) The TLSTM-specific session identifier (tlstmSessionID) is set in
the tmSessionID of the tmStateReference passed to the TLS
Transport Model to indicate that the session has been established
successfully and to point to a specific (D)TLS session for future
use. The tlstmSessionID is also stored in the LCD for later
lookup during processing of incoming messages (Section 5.1.2).
5.3.2. Accepting a Session as a Server
A (D)TLS server should accept new session connections from any client
that it is able to verify the client's credentials for. This is done
by authenticating the client's presented certificate through a
certificate path validation process (e.g. [RFC5280]) or through
certificate fingerprint verification using fingerprints configure in
the tlstmCertToTSNTable. Afterward the server will determine the
identity of the remote entity using the following procedures.
The (D)TLS server identifies the authenticated identity from the
(D)TLS client's principal certificate using configuration information
from the tlstmCertToTSNTable mapping table. The (D)TLS server MUST
request and expect a certificate from the client and MUST NOT accept
SNMP messages over the (D)TLS session 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 tlstmCertToTSNTable 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 tlstmCertToTSNTable) then the session
establishment MUST fail, the
snmpTlstmSessionInvalidClientCertificates object is incremented. If
the session can not be opened for any reason at all, including
cryptographic verification failures, then the
snmpTlstmSessionOpenErrors counter is incremented and processing
stops.
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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, UDP or SCTP port.
5.4. Closing a Session
The TLS Transport Model provides the following primitive to close a
session:
statusInformation =
closeSession(
IN tmSessionID -- session ID of the session to be closed
)
The following describes the procedure to follow to close a session
between a client and server. This process is followed by any SNMP
engine closing the corresponding SNMP session.
1) Increment either the snmpTlstmSessionClientCloses or the
snmpTlstmSessionServerCloses counter as appropriate.
2) Look up the session using the tmSessionID.
3) If there is no open session associated with the tmSessionID, then
closeSession processing is completed.
4) Have (D)TLS close the specified session. This SHOULD include
sending a close_notify TLS Alert to inform the other side that
session cleanup may be performed.
6. MIB Module Overview
This MIB module provides management of the TLS Transport Model. It
defines needed textual conventions, statistical counters,
notifications and configuration infrastructure necessary for session
establishment. Example usage of the configuration tables can be
found in Appendix C.
6.1. Structure of the MIB Module
Objects in this MIB module are arranged into subtrees. Each subtree
is organized as a set of related objects. The overall structure and
assignment of objects to their subtrees, and the intended purpose of
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each subtree, is shown below.
6.2. Textual Conventions
Generic and Common Textual Conventions used in this module can be
found summarized at http://www.ops.ietf.org/mib-common-tcs.html
This module defines the following new Textual Conventions:
o A new TransportAddress format for describing (D)TLS connection
addressing requirements.
o A certificate fingerprint allowing MIB module objects to
generically refer to a stored X.509 certificate using a
cryptographic hash as a reference pointer.
6.3. Statistical Counters
The TLSTM-MIB defines some counters that can provide network managers
with information about (D)TLS session usage and potential errors that
a MIB-instrumented device may be experiencing.
6.4. Configuration Tables
The TLSTM-MIB defines configuration tables that a manager can use for
configuring a MIB-instrumented device for sending and receiving SNMP
messages over (D)TLS. In particular, there are MIB tables that
extend the SNMP-TARGET-MIB for configuring (D)TLS certificate usage
and a MIB table for mapping incoming (D)TLS client certificates to
SNMPv3 securityNames.
6.4.1. Notifications
The TLSTM-MIB defines notifications to alert management stations when
a (D)TLS connection fails because a server's presented certificate
did not meet an expected value (tlstmServerCertificateUnknown) or
because cryptographic validation failed
(tlstmServerInvalidCertificate).
6.5. Relationship to Other MIB Modules
Some management objects defined in other MIB modules are applicable
to an entity implementing the TLS Transport Model. In particular, it
is assumed that an entity implementing the TLSTM-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].
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The TLSTM-MIB module contained in this document is for managing TLS
Transport Model information.
6.5.1. MIB Modules Required for IMPORTS
The TLSTM-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
TLSTM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY, snmpModules, snmpDomains,
Counter32, Unsigned32, NOTIFICATION-TYPE
FROM SNMPv2-SMI
TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType,
AutonomousType
FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
FROM SNMPv2-CONF
SnmpAdminString
FROM SNMP-FRAMEWORK-MIB
snmpTargetParamsName, snmpTargetAddrName
FROM SNMP-TARGET-MIB
;
tlstmMIB MODULE-IDENTITY
LAST-UPDATED "201002020000Z"
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.
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7110 Samuel Morse Drive
Columbia, MD 21046
USA
Co-editors:
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).
This version of this MIB module is part of RFC XXXX;
see the RFC itself for full legal notices."
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note
REVISION "201002020000Z"
DESCRIPTION "The initial version, published in RFC XXXX."
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and remove this note
::= { snmpModules xxxx }
-- RFC Ed.: replace xxxx with IANA-assigned number and
-- remove this note
-- ************************************************
-- subtrees of the TLSTM-MIB
-- ************************************************
tlstmNotifications OBJECT IDENTIFIER ::= { tlstmMIB 0 }
tlstmIdentities OBJECT IDENTIFIER ::= { tlstmMIB 1 }
tlstmObjects OBJECT IDENTIFIER ::= { tlstmMIB 2 }
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tlstmConformance OBJECT IDENTIFIER ::= { tlstmMIB 3 }
-- ************************************************
-- tlstmObjects - Objects
-- ************************************************
snmpTLSTCPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over TLS transport domain. The corresponding
transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpTLSTCPDomain is 'tls'. This prefix may be used by
security models or other components to identify which secure
transport infrastructure authenticated a securityName."
::= { snmpDomains xx }
-- RFC Ed.: replace xx with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'tls' with the actual IANA assigned prefix string
-- if 'tls' is not assigned to this document.
snmpDTLSUDPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over DTLS/UDP transport domain. The corresponding
transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpDTLSUDPDomain is 'dudp'. This prefix may be used by
security models or other components to identify which secure
transport infrastructure authenticated a securityName."
::= { snmpDomains yy }
-- RFC Ed.: replace yy with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'dudp' with the actual IANA assigned prefix string
-- if 'dudp' is not assigned to this document.
snmpDTLSSCTPDomain OBJECT-IDENTITY
STATUS current
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DESCRIPTION
"The SNMP over DTLS/SCTP transport domain. The corresponding
transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpDTLSSCTPDomain is 'dsct'. This prefix may be used by
security models or other components to identify which secure
transport infrastructure authenticated a securityName."
::= { snmpDomains zz }
-- RFC Ed.: replace zz with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'dsct' with the actual IANA assigned prefix string
-- if 'dsct' is not assigned to this document.
SnmpTLSAddress ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1a"
STATUS current
DESCRIPTION
"Represents a IPv4 address, an IPv6 address or an US-ASCII
encoded hostname and port number.
An IPv4 address must be in dotted decimal format followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number
in US-ASCII.
An IPv6 address must be a colon separated format, surrounded
by square brackets ('[', US-ASCII character 0x5B, and ']',
US-ASCII character 0x5D), followed by a colon ':' (US-ASCII
character 0x3A) and a decimal port number in US-ASCII.
A hostname is always in US-ASCII (as per RFC1033);
internationalized hostnames are encoded in US-ASCII as
specified in RFC 3490. The hostname is followed by a colon
':' (US-ASCII character 0x3A) and a decimal port number in
US-ASCII. The name SHOULD be fully qualified whenever
possible.
Values of this textual convention may not be directly usable
as transport-layer addressing information, and may require
run-time resolution. As such, applications that write them
must be prepared for handling errors if such values are not
supported, or cannot be resolved (if resolution occurs at the
time of the management operation).
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The DESCRIPTION clause of TransportAddress objects that may
have SnmpTLSAddress values must fully describe how (and
when) such names are to be resolved to IP addresses and vice
versa.
This textual convention SHOULD NOT be used directly in object
definitions since it restricts addresses to a specific
format. However, if it is used, it MAY be used either on its
own or in conjunction with TransportAddressType or
TransportDomain as a pair.
When this textual convention is used as a syntax of an index
object, there may be issues with the limit of 128
sub-identifiers specified in SMIv2 (STD 58). It is RECOMMENDED
that all MIB documents using this textual convention make
explicit any limitations on index component lengths that
management software must observe. This may be done either by
including SIZE constraints on the index components or by
specifying applicable constraints in the conceptual row
DESCRIPTION clause or in the surrounding documentation."
REFERENCE
"RFC 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE
RFC 3490: Internationalizing Domain Names in Applications
RFC 3986: Uniform Resource Identifier (URI): Generic Syntax
RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
"
SYNTAX OCTET STRING (SIZE (1..255))
Fingerprint ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1x:254x"
STATUS current
DESCRIPTION
"A Fingerprint value that can be used to uniquely reference
other data of potentially arbitrary length.
A Fingerprint value is composed of a 1-octet hashing algorithm
identifier followed by the fingerprint value. The octet value
encoded is taken from the IANA TLS HashAlgorithm Registry
(RFC5246). The remaining octets are filled using the results
of the hashing algorithm.
This TEXTUAL-CONVENTION allows for a zero-length (blank)
Fingerprint value for use in tables where the fingerprint value
may be optional. MIB definitions or implementations may refuse
to accept a zero-length value as appropriate."
REFERENCE
"RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2
http://www.iana.org/assignments/tls-parameters/
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"
SYNTAX OCTET STRING (SIZE (0..255))
-- Identities for use in the tlstmCertToTSNTable
tlstmCertToTSNMIdentities OBJECT IDENTIFIER ::= { tlstmIdentities 1 }
tlstmCertSpecified 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 tlstmCertToTSNData
column. The tlstmCertToTSNData column must contain
a non-zero length SnmpAdminString compliant value or
the mapping described in this row must be considered
a failure."
::= { tlstmCertToTSNMIdentities 1 }
tlstmCertSANRFC822Name OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a subjectAltName's rfc822Name to a
tmSecurityName. The local part of the rfc822Name is
passed unaltered but the host-part of the name must
be passed in lower case.
Example rfc822Name Field: FooBar@Example.COM
is mapped to tmSecurityName: FooBar@example.com"
::= { tlstmCertToTSNMIdentities 2 }
tlstmCertSANDNSName OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a subjectAltName's dNSName to a
tmSecurityName by directly passing the value without
any transformations."
::= { tlstmCertToTSNMIdentities 3 }
tlstmCertSANIpAddress 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 hexadecimal string without any colon
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separators.
Note that the resulting length is the maximum
length supported by the View-Based Access Control
Model (VACM). Note that using both the Transport
Security Model's support for transport prefixes
(see the SNMP-TSM-MIB's
snmpTsmConfigurationUsePrefix object for details)
will result in securityName lengths that exceed
what VACM can handle."
::= { tlstmCertToTSNMIdentities 4 }
tlstmCertSANAny OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps any of the following fields using the
corresponding mapping algorithms:
|------------+------------------------|
| Type | Algorithm |
|------------+------------------------|
| rfc822Name | tlstmCertSANRFC822Name |
| dNSName | tlstmCertSANDNSName |
| iPAddress | tlstmCertSANIpAddress |
|------------+------------------------|
The first matching subjectAltName value found in the
certificate of the above types MUST be used when
deriving the tmSecurityName."
::= { tlstmCertToTSNMIdentities 5 }
tlstmCertCommonName OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a certificate's CommonName to a
tmSecurityName by directly passing the value without
any transformations."
::= { tlstmCertToTSNMIdentities 6 }
-- The snmpTlstmSession Group
snmpTlstmSession OBJECT IDENTIFIER ::= { tlstmObjects 1 }
snmpTlstmSessionOpens OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request has been executed
as an (D)TLS client, regardless of whether it succeeded or
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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 server has accepted a (D)TLS session and
at least one SNMP message has been accepted 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
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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 tlstmCertToTSNTable."
::= { snmpTlstmSession 7 }
snmpTlstmSessionUnknownServerCertificate OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing session was not established
on an (D)TLS client because the server certificate presented
by a SNMP over (D)TLS server was invalid because no
configured fingerprint or CA was acceptable to validate it.
This may result because there was no entry in the
tlstmAddrTable or because no path could be found to a known
certificate authority."
::= { snmpTlstmSession 8 }
snmpTlstmSessionInvalidServerCertificates OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing session was not established
on an (D)TLS client because the server certificate presented
by an SNMP over (D)TLS server could not be validated even if
the fingerprint or expected validation path was known. I.E.,
a cryptographic validation error occurred during certificate
validation processing.
Reasons for invalidation include, but are not
limited to, cryptographic validation failures."
::= { snmpTlstmSession 9 }
snmpTlstmSessionInvalidCaches OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
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STATUS current
DESCRIPTION
"The number of outgoing messages dropped because the
tmStateReference referred to an invalid cache."
::= { snmpTlstmSession 10 }
-- Configuration Objects
tlstmConfig OBJECT IDENTIFIER ::= { tlstmObjects 2 }
-- Certificate mapping
tlstmCertificateMapping OBJECT IDENTIFIER ::= { tlstmConfig 1 }
tlstmCertToTSNCount OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the tlstmCertToTSNTable"
::= { tlstmCertificateMapping 1 }
tlstmCertToTSNTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the tlstmCertToTSNTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { tlstmCertificateMapping 2 }
tlstmCertToTSNTable OBJECT-TYPE
SYNTAX SEQUENCE OF TlstmCertToTSNEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A table listing the fingerprints of X.509 certificates known
to the entity and the associated method for determining the
SNMPv3 security name from a certificate.
On an incoming (D)TLS/SNMP connection the client's presented
certificate must be examined and validated based on an
established trusted path from a CA certificate or self-signed
public certificate (e.g. RFC5280). This table provides a
mapping from a validated certificate to a tmSecurityName.
This table does not provide any mechanisms for uploading
trusted certificates; the transfer of any needed trusted
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certificates for path validation is expected to occur through
an out-of-band transfer.
Once the authenticity of a certificate has been verified, 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 tlstmCertToTSNID value. Each row's
tlstmCertToTSNFingerprint value determines whether the row is a
match for the incoming connection:
1) If the row's tlstmCertToTSNFingerprint value identifies
the presented certificate then consider the row as a
successful match.
2) If the row's tlstmCertToTSNFingerprint 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 tlstmCertToTSNMapType
value can be used to determine how the tmSecurityName to
associate with the session should be determined. See the
tlstmCertToTSNMapType column's DESCRIPTION for details on
determining the tmSecurityName value. If it is impossible to
determine a tmSecurityName from the row's data combined with the
data presented in the certificate then additional rows MUST be
searched looking for another potential match. If a resulting
tmSecurityName mapped from a given row is not compatible with
the needed requirements of a tmSecurityName (e.g., VACM imposes
a 32-octet-maximum length and the certificate derived
securityName could be longer) then it must be considered an
invalid match and additional rows MUST be searched looking for
another potential match.
Missing values of tlstmCertToTSNID are acceptable and
implementations should continue to the next highest numbered
row. E.G., the table may legally contain only two rows with
tlstmCertToTSNID values of 10 and 20.
Users are encouraged to make use of certificates with
subjectAltName fields that can be used as tmSecurityNames so
that a single root CA certificate can allow all child
certificate's subjectAltName to map directly to a
tmSecurityName via a 1:1 transformation. However, this table
is flexible to allow for situations where existing deployed
certificate infrastructures do not provide adequate
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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."
::= { tlstmCertificateMapping 3 }
tlstmCertToTSNEntry OBJECT-TYPE
SYNTAX TlstmCertToTSNEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A row in the tlstmCertToTSNTable that specifies a mapping for
an incoming (D)TLS certificate to a tmSecurityName to use for a
connection."
INDEX { tlstmCertToTSNID }
::= { tlstmCertToTSNTable 1 }
TlstmCertToTSNEntry ::= SEQUENCE {
tlstmCertToTSNID Unsigned32,
tlstmCertToTSNFingerprint Fingerprint,
tlstmCertToTSNMapType AutonomousType,
tlstmCertToTSNData OCTET STRING,
tlstmCertToTSNStorageType StorageType,
tlstmCertToTSNRowStatus RowStatus
}
tlstmCertToTSNID 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."
::= { tlstmCertToTSNEntry 1 }
tlstmCertToTSNFingerprint OBJECT-TYPE
SYNTAX Fingerprint (SIZE(1..255))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a X.509 certificate. The results of
a successful matching fingerprint to either the trusted CA in
the certificate validation path or to the certificate itself
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is dictated by the tlstmCertToTSNMapType column."
::= { tlstmCertToTSNEntry 2 }
tlstmCertToTSNMapType 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 tlstmCertToTSNFingerprint matches to
look for a mapping that succeeds."
DEFVAL { tlstmCertSpecified }
::= { tlstmCertToTSNEntry 3 }
tlstmCertToTSNData 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 tlstmCertToTSNMapType 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 { "" }
::= { tlstmCertToTSNEntry 4 }
tlstmCertToTSNStorageType 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 }
::= { tlstmCertToTSNEntry 5 }
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tlstmCertToTSNRowStatus 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, a manager 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
tlstmParamsRowStatus column is 'notReady'.
In particular, a newly created row cannot be made active until
the corresponding tlstmCertToTSNFingerprint,
tlstmCertToTSNMapType, and tlstmCertToTSNData columns have been
set.
The following objects may not be modified while the
value of this object is active(1):
- tlstmCertToTSNFingerprint
- tlstmCertToTSNMapType
- tlstmCertToTSNData
An attempt to set these objects while the value of
tlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { tlstmCertToTSNEntry 6 }
-- Maps tmSecurityNames to certificates for use by the SNMP-TARGET-MIB
tlstmParamsCount OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the tlstmParamsTable"
::= { tlstmCertificateMapping 4 }
tlstmParamsTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the tlstmParamsTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
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::= { tlstmCertificateMapping 5 }
tlstmParamsTable OBJECT-TYPE
SYNTAX SEQUENCE OF TlstmParamsEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table is used by a (D)TLS client when a (D)TLS session 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."
::= { tlstmCertificateMapping 6 }
tlstmParamsEntry OBJECT-TYPE
SYNTAX TlstmParamsEntry
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 }
::= { tlstmParamsTable 1 }
TlstmParamsEntry ::= SEQUENCE {
tlstmParamsClientFingerprint Fingerprint,
tlstmParamsStorageType StorageType,
tlstmParamsRowStatus RowStatus
}
tlstmParamsClientFingerprint OBJECT-TYPE
SYNTAX Fingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a X.509 certificate. This object
should store the hash of a locally held X.509 certificate that
should be used when initiating a (D)TLS connection as a (D)TLS
client."
::= { tlstmParamsEntry 1 }
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tlstmParamsStorageType 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 }
::= { tlstmParamsEntry 2 }
tlstmParamsRowStatus 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, a manager 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
tlstmParamsRowStatus column is 'notReady'.
In particular, a newly created row cannot be made active until
the corresponding tlstmParamsClientFingerprint column has
been set.
The tlstmParamsClientFingerprint object may not be modified
while the value of this object is active(1).
An attempt to set these objects while the value of
tlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { tlstmParamsEntry 3 }
tlstmAddrCount OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the tlstmAddrTable"
::= { tlstmCertificateMapping 7 }
tlstmAddrTableLastChanged OBJECT-TYPE
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SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the tlstmAddrTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { tlstmCertificateMapping 8 }
tlstmAddrTable OBJECT-TYPE
SYNTAX SEQUENCE OF TlstmAddrEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table is used by a (D)TLS client when a (D)TLS session
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 validate the certificate that the server presents.
If there is a row in this table corresponding to the entry in
the SNMP-TARGET-MIB that was used to establish the session
(and that row is active), then the fingerprint of the server's
presented certificate is compared with the value of the
tlstmAddrServerFingerprint column. If fingerprint does not
match, then the connection MUST NOT be established.
If the row exists with a zero-length
tlstmAddrServerFingerprint value and the certificate can be
validated through another certificate validation path (such as
the path validation procedures defined in [RFC5280]) then the
server's presented identity should be checked against the
value of the tlstmAddrServerIdentity column. If the server's
identity does not match the reference identity found in the
tlstmAddrServerIdentity column then the connection MUST NOT be
established.
A tlstmAddrServerIdentity may contain a single ASCII '*'
character (ASCII code 0x2a) to match any server's identity if
the tlstmAddrServerFingerprint column is not blank. A row
MUST NOT contain both a blank tlstmAddrServerFingerprint
column and a '*' in the tlstmAddrServerIdentity column since
this would insecurely accept any presented certificate.
If there is no row in this table corresponding to an entry in
the SNMP-TARGET-MIB and another certificate validation path
algorithm (such as the path validation procedures defined in
[RFC5280]) can be used, then the connection SHOULD still
proceed."
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::= { tlstmCertificateMapping 9 }
tlstmAddrEntry OBJECT-TYPE
SYNTAX TlstmAddrEntry
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
tlstmAddrEntry exists for a given snmpTargetAddrEntry then the
presented server certificate MUST match or the connection MUST
NOT be established. If a row in this table does not exist to
match a snmpTargetAddrEntry row then the connection SHOULD
still proceed if some other certificate validation path
algorithm (e.g. RFC5280) can be used."
INDEX { IMPLIED snmpTargetAddrName }
::= { tlstmAddrTable 1 }
TlstmAddrEntry ::= SEQUENCE {
tlstmAddrServerFingerprint Fingerprint,
tlstmAddrServerIdentity SnmpAdminString,
tlstmAddrStorageType StorageType,
tlstmAddrRowStatus RowStatus
}
tlstmAddrServerFingerprint OBJECT-TYPE
SYNTAX Fingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a public X.509 certificate. This
object should store the hash of the public X.509 certificate
that the remote server should present during the (D)TLS
connection setup. The fingerprint of the presented
certificate and this hash value MUST match exactly or the
connection MUST NOT be established."
DEFVAL { "" }
::= { tlstmAddrEntry 1 }
tlstmAddrServerIdentity OBJECT-TYPE
SYNTAX SnmpAdminString
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The reference identity to check against the identity
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presented by the remote system. A single ASCII '*' character
(ASCII code 0x2a) may be used as a wildcard string and will
match any presented server identity."
REFERENCE "draft-saintandre-tls-server-id-check"
DEFVAL { "*" }
::= { tlstmAddrEntry 2 }
tlstmAddrStorageType 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 }
::= { tlstmAddrEntry 3 }
tlstmAddrRowStatus 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, a manager 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 tlstmAddrRowStatus
column is 'notReady'.
In particular, a newly created row cannot be made active until
the corresponding tlstmAddrServerFingerprint column has been
set.
Rows MUST NOT be active if the tlstmAddrServerFingerprint
column is blank and the tlstmAddrServerIdentity is set to '*'
since this would insecurely accept any presented certificate.
The tlstmAddrServerFingerprint object may not be modified
while the value of this object is active(1).
An attempt to set these objects while the value of
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tlstmAddrRowStatus is active(1) will result in
an inconsistentValue error."
::= { tlstmAddrEntry 4 }
-- ************************************************
-- tlstmNotifications - Notifications Information
-- ************************************************
tlstmServerCertificateUnknown NOTIFICATION-TYPE
OBJECTS { snmpTlstmSessionUnknownServerCertificate }
STATUS current
DESCRIPTION
"Notification that the server certificate presented by a SNMP
over (D)TLS server was invalid because no configured
fingerprint or CA was acceptable to validate it. This may
be because there was no entry in the tlstmAddrTable or
because no path could be found to known certificate
authority.
To avoid notification loops, this notification MUST NOT be
sent to servers that themselves have triggered the
notification."
::= { tlstmNotifications 1 }
tlstmServerInvalidCertificate NOTIFICATION-TYPE
OBJECTS { tlstmAddrServerFingerprint,
snmpTlstmSessionInvalidServerCertificates}
STATUS current
DESCRIPTION
"Notification that the server certificate presented by an SNMP
over (D)TLS server could not be validated even if the
fingerprint or expected validation path was known. I.E., a
cryptographic validation occurred during certificate
validation processing.
To avoid notification loops, this notification MUST NOT be
sent to servers that themselves have triggered the
notification."
::= { tlstmNotifications 2 }
-- ************************************************
-- tlstmCompliances - Conformance Information
-- ************************************************
tlstmCompliances OBJECT IDENTIFIER ::= { tlstmConformance 1 }
tlstmGroups OBJECT IDENTIFIER ::= { tlstmConformance 2 }
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-- ************************************************
-- Compliance statements
-- ************************************************
tlstmCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines that support the
TLSTM-MIB"
MODULE
MANDATORY-GROUPS { tlstmStatsGroup,
tlstmIncomingGroup,
tlstmOutgoingGroup,
tlstmNotificationGroup }
::= { tlstmCompliances 1 }
-- ************************************************
-- Units of conformance
-- ************************************************
tlstmStatsGroup OBJECT-GROUP
OBJECTS {
snmpTlstmSessionOpens,
snmpTlstmSessionClientCloses,
snmpTlstmSessionOpenErrors,
snmpTlstmSessionAccepts,
snmpTlstmSessionServerCloses,
snmpTlstmSessionNoSessions,
snmpTlstmSessionInvalidClientCertificates,
snmpTlstmSessionUnknownServerCertificate,
snmpTlstmSessionInvalidServerCertificates,
snmpTlstmSessionInvalidCaches
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
statistical information of an SNMP engine which
implements the SNMP TLS Transport Model."
::= { tlstmGroups 1 }
tlstmIncomingGroup OBJECT-GROUP
OBJECTS {
tlstmCertToTSNCount,
tlstmCertToTSNTableLastChanged,
tlstmCertToTSNFingerprint,
tlstmCertToTSNMapType,
tlstmCertToTSNData,
tlstmCertToTSNStorageType,
tlstmCertToTSNRowStatus
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}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
incoming connection certificate mappings to
tmSecurityNames of an SNMP engine which implements the
SNMP TLS Transport Model."
::= { tlstmGroups 2 }
tlstmOutgoingGroup OBJECT-GROUP
OBJECTS {
tlstmParamsCount,
tlstmParamsTableLastChanged,
tlstmParamsClientFingerprint,
tlstmParamsStorageType,
tlstmParamsRowStatus,
tlstmAddrCount,
tlstmAddrTableLastChanged,
tlstmAddrServerFingerprint,
tlstmAddrServerIdentity,
tlstmAddrStorageType,
tlstmAddrRowStatus
}
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."
::= { tlstmGroups 3 }
tlstmNotificationGroup NOTIFICATION-GROUP
NOTIFICATIONS {
tlstmServerCertificateUnknown,
tlstmServerInvalidCertificate
}
STATUS current
DESCRIPTION
"Notifications"
::= { tlstmGroups 4 }
END
8. Operational Considerations
This section discusses various operational aspects of deploying
TLSTM.
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8.1. Sessions
A session is discussed throughout this document as meaning a security
association between the (D)TLS client and the (D)TLS server. State
information for the sessions are maintained in each TLSTM
implementation and this information is created and destroyed as
sessions are opened and closed. A "broken" session (one side up and
one side down) can result if one side of a session is brought down
abruptly (i.e., reboot, power outage, etc.). Whenever possible,
implementations SHOULD provide graceful session termination through
the use of disconnect messages. Implementations SHOULD also have a
system in place for detecting "broken" sessions through the use of
heartbeats [I-D.seggelmann-tls-dtls-heartbeat] or other detection
mechanisms.
Implementations SHOULD limit the lifetime of established sessions
depending on the algorithms used for generation of the master session
secret, the privacy and integrity algorithms used to protect
messages, the environment of the session, the amount of data
transferred, and the sensitivity of the data.
8.2. Notification Receiver Credential Selection
When an SNMP engine needs to establish an outgoing session for
notifications, the snmpTargetParamsTable includes an entry for the
snmpTargetParamsSecurityName of the target. Servers that wish to
support multiple principals at a particular port SHOULD make use of
the Server Name Indication extension defined in Section 3.1 of
[RFC4366]. Without the Server Name Indication the receiving SNMP
engine (Server) will not know which (D)TLS certificate to offer to
the Client so that the tmSecurityName identity-authentication will be
successful.
Another solution is to maintain a one-to-one mapping between
certificates and incoming ports for notification receivers. This can
be handled at the notification originator by configuring the
snmpTargetAddrTable (snmpTargetAddrTDomain and
snmpTargetAddrTAddress) and requiring the receiving SNMP engine to
monitor multiple incoming static ports based on which principals are
capable of receiving notifications.
Implementations MAY also choose to designate a single Notification
Receiver Principal to receive all incoming notifications or select an
implementation specific method of selecting a server certificate to
present to clients.
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8.3. contextEngineID Discovery
Most command responders have contextEngineIDs that are identical to
the USM securityEngineID. USM provides a discovery service that
allows command generators to determine a securityEngineID and thus a
default contextEngineID to use. Because the TLS Transport Model does
not make use of a securityEngineID, it may be difficult for command
generators to discover a suitable default contextEngineID.
Implementations should consider offering another engineID discovery
mechanism to continue providing Command Generators with a suitable
contextEngineID mechanism. A recommended discovery solution is
documented in [RFC5343].
8.4. Transport Considerations
This document defines how SNMP messages can be transmitted over the
TLS and DTLS based protocols. Each of these protocols are
additionally based on other transports (TCP, UDP and SCTP). These
three protocols also have operational considerations that must be
taken into consideration when selecting a (D)TLS based protocol to
use such as its performance in degraded or limited networks. It is
beyond the scope of this document to summarize the characteristics of
these transport mechanisms. Please refer to the base protocol
documents for details on messaging considerations with respect to MTU
size, fragmentation, performance in lossy-networks, etc.
9. Security Considerations
This document describes a transport model that permits SNMP to
utilize (D)TLS security services. The security threats and how the
(D)TLS transport model mitigates these threats are covered in detail
throughout this document. Security considerations for DTLS are
covered in [RFC4347] and security considerations for TLS are
described in Section 11 and Appendices D, E, and F of TLS 1.2
[RFC5246]. DTLS adds to the security considerations of TLS only
because it is more vulnerable to denial of service attacks. A random
cookie exchange was added to the handshake to prevent anonymous
denial of service attacks. RFC 4347 recommends that the cookie
exchange is utilized for all handshakes. It is also RECOMMENDED by
this specification that users enable this cookie exchange.
9.1. Certificates, Authentication, and Authorization
Implementations are responsible for providing a security certificate
installation and configuration mechanism. Implementations SHOULD
support certificate revocation lists.
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(D)TLS provides for authentication of the identity of both the (D)TLS
server and the (D)TLS client. Access to MIB objects for the
authenticated principal MUST be enforced by an access control
subsystem (e.g. the VACM).
Authentication of the command generator principal's identity is
important for use with the SNMP access control subsystem to ensure
that only authorized principals have access to potentially sensitive
data. The authenticated identity of the command generator
principal's certificate is mapped to an SNMP model-independent
securityName for use with SNMP access control.
The (D)TLS handshake only provides assurance that the certificate of
the authenticated identity has been signed by an configured accepted
Certificate Authority. (D)TLS has no way to further authorize or
reject access based on the authenticated identity. An Access Control
Model (such as the VACM) provides access control and authorization of
a command generator's requests to a command responder and a
notification responder's authorization to receive Notifications from
a notification originator. However to avoid man-in-the-middle
attacks both ends of the (D)TLS based connection MUST check the
certificate presented by the other side against what was expected.
For example, command generators must check that the command responder
presented and authenticated itself with a X.509 certificate that was
expected. Not doing so would allow an impostor, at a minimum, to
present false data, receive sensitive information and/or provide a
false belief that configuration was actually received and acted upon.
Authenticating and verifying the identity of the (D)TLS server and
the (D)TLS client for all operations ensures the authenticity of the
SNMP engine that provides MIB data.
The instructions found in the DESCRIPTION clause of the
tlstmCertToTSNTable object must be followed exactly. It is also
important that the rows of the table be searched in prioritized order
starting with the row containing the lowest numbered tlstmCertToTSNID
value.
9.2. Use with SNMPv1/SNMPv2c Messages
The SNMPv1 and SNMPv2c message processing described in [RFC3584] (BCP
74) always selects the SNMPv1 or SNMPv2c Security Models,
respectively. Both of these and the User-based Security Model
typically used with SNMPv3 derive the securityName and securityLevel
from the SNMP message received, even when the message was received
over a secure transport. Access control decisions are therefore made
based on the contents of the SNMP message, rather than using the
authenticated identity and securityLevel provided by the TLS
Transport Model.
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9.3. MIB Module Security
There are a number of management objects defined in this MIB module
with a MAX-ACCESS clause of read-write and/or read-create. Such
objects may be considered sensitive or vulnerable in some network
environments. The support for SET operations in a non-secure
environment without proper protection can have a negative effect on
network operations. These are the tables and objects and their
sensitivity/vulnerability:
o The tlstmParamsTable can be used to change the outgoing X.509
certificate used to establish a (D)TLS connection. Modification
to objects in this table need to be adequately authenticated since
modification to values in this table will have profound impacts to
the security of outbound connections from the device. Since
knowledge of authorization rules and certificate usage mechanisms
may be considered sensitive, protection from disclosure of the
SNMP traffic via encryption is also highly recommended.
o The tlstmAddrTable can be used to change the expectations of the
certificates presented by a remote (D)TLS server. Modification to
objects in this table need to be adequately authenticated since
modification to values in this table will have profound impacts to
the security of outbound connections from the device. Since
knowledge of authorization rules and certificate usage mechanisms
may be considered sensitive, protection from disclosure of the
SNMP traffic via encryption is also highly recommended.
o The tlstmCertToTSNTable is used to specify the mapping of incoming
X.509 certificates to tmSecurityNames which eventually get mapped
to a SNMPv3 securityName. Modification to objects in this table
need to be adequately authenticated since modification to values
in this table will have profound impacts to the security of
incoming connections to the device. Since knowledge of
authorization rules and certificate usage mechanisms may be
considered sensitive, protection from disclosure of the SNMP
traffic via encryption is also highly recommended.
Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability:
o This MIB contains a collection of counters that monitor the (D)TLS
connections being established with a device. Since knowledge of
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connection and certificate usage mechanisms may be considered
sensitive, protection from disclosure of the SNMP traffic via
encryption is also highly recommended.
SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPsec),
even then, there is no control as to who on the secure network is
allowed to access and GET/SET (read/change/create/delete) the objects
in this MIB module.
It is RECOMMENDED that implementers consider the security features as
provided by the SNMPv3 framework (see [RFC3410], section 8),
including full support for the SNMPv3 cryptographic mechanisms (for
authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them.
10. IANA Considerations
IANA is requested to assign:
1. a TCP port number above 1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for receipt of SNMP command messages over a
TLS Transport Model as defined in this document,
2. a TCP port number above 1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for receipt of SNMP notification messages
over a TLS Transport Model as defined in this document,
3. a UDP port number above 1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for receipt of SNMP command messages over a
DTLS/UDP connection as defined in this document,
4. a UDP port number above 1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for receipt of SNMP notification messages
over a DTLS/UDP connection as defined in this document,
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5. a SCTP port number above 1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for receipt of SNMP command messages over a
DTLS/SCTP connection as defined in this document,
6. a SCTP port number above 1023 in the
http://www.iana.org/assignments/port-numbers registry which will
be the default port for receipt of SNMP notification messages
over a DTLS/SCTP connection as defined in this document,
7. an SMI number under snmpDomains for the snmpTLSTCPDomain object
identifier,
8. an SMI number under snmpDomains for the snmpDTLSUDPDomain object
identifier,
9. an SMI number under snmpDomains for the snmpDTLSSCTPDomain
object identifier,
10. a SMI number under snmpModules, for the MIB module in this
document,
11. "tls" as the corresponding prefix for the snmpTLSTCPDomain in
the SNMP Transport Model registry,
12. "dudp" as the corresponding prefix for the snmpDTLSUDPDomain in
the SNMP Transport Model registry,
13. "dsct" as the corresponding prefix for the snmpDTLSSCTPDomain in
the SNMP Transport Model registry;
If possible, IANA is requested to use matching port numbers for all
assignments for SNMP Commands being sent over TLS, DTLS/UDP, DTLS/
SCTP.
If possible, IANA is requested to use matching port numbers for all
assignments for SNMP Notifications being sent over TLS, DTLS/UDP,
DTLS/SCTP.
Editor's note: this section should be replaced with appropriate
descriptive assignment text after IANA assignments are made and prior
to publication.
11. Acknowledgements
This document closely follows and copies the Secure Shell Transport
Model for SNMP defined by David Harrington and Joseph Salowey in
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[RFC5292].
This document was reviewed by the following people who helped provide
useful comments (in alphabetical order): Andy Donati, Pasi Eronen,
David Harrington, Jeffrey Hutzelman, Alan Luchuk, Tom Petch, Randy
Presuhn, Ray Purvis, Joseph Salowey, Jurgen Schonwalder, Dave Shield,
Robert Story.
This work was supported in part by the United States Department of
Defense. Large portions of this document are based on work by
General Dynamics C4 Systems and the following individuals: Brian
Baril, Kim Bryant, Dana Deluca, Dan Hanson, Tim Huemiller, John
Holzhauer, Colin Hoogeboom, Dave Kornbau, Chris Knaian, Dan Knaul,
Charles Limoges, Steve Moccaldi, Gerardo Orlando, and Brandon Yip.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, April 1999.
[RFC2580] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580,
April 1999.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network 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.
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[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.
[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.
[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.
12.2. Informative References
[RFC2522] Karn, P. and W. Simpson, "Photuris: Session-Key Management
Protocol", RFC 2522, March 1999.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006.
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[RFC5292] Chen, E. and S. Sangli, "Address-Prefix-Based Outbound
Route Filter for BGP-4", RFC 5292, August 2008.
[RFC5343] Schoenwaelder, J., "Simple Network Management Protocol
(SNMP) Context EngineID Discovery", RFC 5343,
September 2008.
[I-D.saintandre-tls-server-id-check]
Saint-Andre, P., Zeilenga, K., Hodges, J., and B. Morgan,
"Best Practices for Checking of Server Identities in the
Context of Transport Layer Security (TLS)".
[I-D.seggelmann-tls-dtls-heartbeat]
Seggelmann, R., Tuexen, M., and M. Williams, "Transport
Layer Security and Datagram Transport Layer Security
Heartbeat Extension".
[AES] National Institute of Standards, "Specification for the
Advanced Encryption Standard (AES)".
[DES] National Institute of Standards, "American National
Standard for Information Systems-Data Link Encryption".
[DSS] National Institute of Standards, "Digital Signature
Standard".
[RSA] Rivest, R., Shamir, A., and L. Adleman, "A Method for
Obtaining Digital Signatures and Public-Key
Cryptosystems".
[X509] , ITU., "INFORMATION TECHNOLOGY OPEN SYSTEMS
INTERCONNECTION THE DIRECTORY: PUBLIC-KEY AND ATTRIBUTE
CERTIFICATE FRAMEWORKS".
Appendix A. (D)TLS Overview
The (D)TLS protocol is composed of two layers: the (D)TLS Record
Protocol and the (D)TLS Handshake Protocol. The following
subsections provide an overview of these two layers. Please refer to
[RFC4347] for a complete description of the protocol.
A.1. The (D)TLS Record Protocol
At the lowest layer, layered on top of the transport control protocol
or a datagram transport protocol (e.g. UDP or SCTP) is the (D)TLS
Record Protocol.
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The (D)TLS Record Protocol provides security that has three basic
properties:
o The session can be confidential. Symmetric cryptography is used
for data encryption (e.g., [AES], [DES] etc.). The keys for this
symmetric encryption are generated uniquely for each session and
are based on a secret negotiated by another protocol (such as the
(D)TLS Handshake Protocol). The Record Protocol can also be used
without encryption.
o Messages can have data integrity. Message transport includes a
message integrity check using a keyed MAC. Secure hash functions
(e.g., SHA, MD5, etc.) are used for MAC computations. The Record
Protocol can operate without a MAC, but is generally only used in
this mode while another protocol is using the Record Protocol as a
transport for negotiating security parameters.
o Messages are protected against replay. (D)TLS uses explicit
sequence numbers and integrity checks. DTLS uses a sliding window
to protect against replay of messages within a session.
(D)TLS also provides protection against replay of entire sessions.
In a properly-implemented keying material exchange, both sides will
generate new random numbers for each exchange. This results in
different encryption and integrity keys for every session.
A.2. The (D)TLS Handshake Protocol
The (D)TLS Record Protocol is used for encapsulation of various
higher-level protocols. One such encapsulated protocol, the (D)TLS
Handshake Protocol, allows the server and client to authenticate each
other and to negotiate an integrity algorithm, an encryption
algorithm and cryptographic keys before the application protocol
transmits or receives its first octet of data. Only the (D)TLS
client can initiate the handshake protocol. The (D)TLS Handshake
Protocol provides security that has four basic properties:
o The peer's identity can be authenticated using asymmetric (public
key) cryptography (e.g., RSA [RSA], DSS [DSS], etc.). This
authentication can be made optional, but is generally required by
at least one of the peers.
(D)TLS supports three authentication modes: authentication of both
the server and the client, server authentication with an
unauthenticated client, and total anonymity. For authentication
of both entities, each entity provides a valid certificate chain
leading to an acceptable certificate authority. Each entity is
responsible for verifying that the other's certificate is valid
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and has not expired or been revoked. See
[I-D.saintandre-tls-server-id-check] for further details on
standardized processing when checking server certificate
identities.
o The negotiation of a shared secret is secure: the negotiated
secret is unavailable to eavesdroppers, and for any authenticated
handshake the secret cannot be obtained, even by an attacker who
can place himself in the middle of the session.
o The negotiation is not vulnerable to malicious modification: it is
infeasible for an attacker to modify negotiation communication
without being detected by the parties to the communication.
o DTLS uses a stateless cookie exchange to protect against anonymous
denial of service attacks and has retransmission timers, sequence
numbers, and counters to handle message loss, reordering, and
fragmentation.
Appendix B. PKIX Certificate Infrastructure
Users of a public key from a PKIX / X.509 certificate can be be
confident that the associated private key is owned by the correct
remote subject (person or system) with which an encryption or digital
signature mechanism will be used. This confidence is obtained
through the use of public key certificates, which are data structures
that bind public key values to subjects. The binding is asserted by
having a trusted CA digitally sign each certificate. The CA may base
this assertion upon technical means (i.e., proof of possession
through a challenge-response protocol), presentation of the private
key, or on an assertion by the subject. A certificate has a limited
valid lifetime which is indicated in its signed contents. Because a
certificate's signature and timeliness can be independently checked
by a certificate-using client, certificates can be distributed via
untrusted communications and server systems, and can be cached in
unsecured storage in certificate-using systems.
ITU-T X.509 (formerly CCITT X.509) or ISO/IEC/ITU 9594-8 [X509],
which was first published in 1988 as part of the X.500 Directory
recommendations, defines a standard certificate format which is a
certificate which binds a subject (principal) to a public key value.
This was later further expanded and documented in [RFC5280].
A X.509 certificate is a sequence of three required fields:
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tbsCertificate: The tbsCertificate field contains the names of the
subject and issuer, a public key associated with the subject, a
validity period, and other associated information. This field may
also contain extension components.
signatureAlgorithm: The signatureAlgorithm field contains the
identifier for the cryptographic algorithm used by the certificate
authority (CA) to sign this certificate.
signatureValue: The signatureValue field contains a digital
signature computed by the CA upon the ASN.1 DER encoded
tbsCertificate field. The ASN.1 DER encoded tbsCertificate is
used as the input to the signature function. This signature value
is then ASN.1 DER encoded as a BIT STRING and included in the
Certificate's signature field. By generating this signature, the
CA certifies the validity of the information in the tbsCertificate
field. In particular, the CA certifies the binding between the
public key material and the subject of the certificate.
The basic X.509 authentication procedure is as follows: A system is
initialized with a number of root certificates that contain the
public keys of a number of trusted CAs. When a system receives a
X.509 certificate, signed by one of those CAs, the certificate has to
be verified. It first checks the signatureValue field by using the
public key of the corresponding trusted CA. Then it compares the
digest of the received certificate with a digest of the
tbsCertificate field. If they match, then the subject in the
tbsCertificate field is authenticated.
Appendix C. Target and Notification Configuration Example
Configuring the SNMP-TARGET-MIB and NOTIFICATION-MIB along with
access control settings for the SNMP-VIEW-BASED-ACM-MIB can be a
daunting task without an example to follow. The following section
describes an example of what pieces must be in place to accomplish
this configuration.
The isAccessAllowed() ASI requires configuration to exist in the
following SNMP-VIEW-BASED-ACM-MIB tables:
vacmSecurityToGroupTable
vacmAccessTable
vacmViewTreeFamilyTable
The only table that needs to be discussed as particularly different
here is the vacmSecurityToGroupTable. This table is indexed by both
the SNMPv3 security model and the security name. The security model,
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when TLSTM is in use, should be set to the value of 4, corresponding
to the TSM [RFC5591]. An example vacmSecurityToGroupTable row might
be filled out as follows (using a single SNMP SET request):
vacmSecurityModel = 4 (TSM)
vacmSecurityName = "blueberry"
vacmGroupName = "administrators"
vacmSecurityToGroupStorageType = 3 (nonVolatile)
vacmSecurityToGroupStatus = 4 (createAndGo)
This example will assume that the "administrators" group has been
given proper permissions via rows in the vacmAccessTable and
vacmViewTreeFamilyTable.
Depending on whether this VACM configuration is for a Command
Responder or a command generator the security name "blueberry" will
come from a few different locations.
C.1. Configuring the Notification Originator
For notification originators performing authorization checks, the
server's certificate must be verified against the expected
certificate before proceeding to send the notification. The expected
certificate from the server may be listed in the tlstmAddrTable or
may be determined through other X.509 path validation mechanisms.
The securityName to use for VACM authorization checks is set by the
SNMP-TARGET-MIB's snmpTargetParamsSecurityName column.
The certificate that the notification originator should present to
the server is taken from the tlstmParamsClientFingerprint column from
the appropriate entry in the tlstmParamsTable table.
C.2. Configuring the Command Responder
For command responder applications, the vacmSecurityName "blueberry"
value is a value that derived from an incoming (D)TLS session. The
mapping from a recevied (D)TLS client certificate to a tmSecurityName
is done with the tlstmCertToTSNTable. The certificates must be
loaded into the device so that a tlstmCertToTSNEntry may refer to it.
As an example, consider the following entry which will provide a
mapping from a client's public X.509's hash fingerprint directly to
the "blueberry" tmSecurityName:
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tlstmCertToTSNID = 1 (chosen by ordering preference)
tlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
tlstmCertToTSNMapType = 1 (specified)
tlstmCertToTSNSecurityName = "blueberry"
tlstmCertToTSNStorageType = 3 (nonVolatile)
tlstmCertToTSNRowStatus = 4 (createAndGo)
The above is an example of how to map a particular certificate to a
particular tmSecurityName. It is recommended, however, that users
make use of direct subjectAltName or CommonName mappings where
possible as it provides a more scalable approach to certificate
management. This entry provides an example of using a subjectAltName
mapping:
tlstmCertToTSNID = 1 (chosen by ordering preference)
tlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
tlstmCertToTSNMapType = 2 (bySubjectAltName)
tlstmCertToTSNSANType = 1 (any)
tlstmCertToTSNStorageType = 3 (nonVolatile)
tlstmCertToTSNRowStatus = 4 (createAndGo)
The above entry indicates the subjectAltName field for certificates
created by an issuing certificate with a corresponding fingerprint
will be trusted to always produce common names that are directly one-
to-one mappable into tmSecurityNames. This type of configuration
should only be used when the certificate authorities naming
conventions are carefully controlled.
In the example, if the incoming (D)TLS client provided certificate
contained a subjectAltName where the first listed subjectAltName in
the extension is the rfc822Name of "blueberry@example.com", the
certificate was signed by a certificate matching the
tlstmCertToTSNFingerprint value and the CA's certificate was properly
installed on the device then the string "blueberry@example.com" would
be used as the tmSecurityName for the session.
Author's Address
Wes Hardaker
Sparta, Inc.
P.O. Box 382
Davis, CA 95617
USA
Phone: +1 530 792 1913
Email: ietf@hardakers.net
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