One document matched: draft-ietf-isms-dtls-tm-13.xml
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<rfc category="std" ipr="pre5378Trust200902" docName="draft-ietf-isms-dtls-tm-13.txt">
<front>
<title abbrev="TLS Transport Model for SNMP">
Transport Layer Security (TLS) Transport Model for the Simple
Network Management Protocol (SNMP)
</title>
<author initials="W.H." surname="Hardaker" fullname="Wes Hardaker">
<organization>Sparta, Inc.</organization>
<address>
<postal>
<street>P.O. Box 382</street>
<city>Davis</city>
<region>CA</region>
<code>95617</code>
<country>USA</country>
</postal>
<phone>+1 530 792 1913</phone>
<email>ietf@hardakers.net</email>
</address>
</author>
<date month="May" year="2010"/>
<area>Security</area>
<workgroup>ISMS</workgroup>
<keyword>Network Management</keyword>
<keyword>Management Information Base</keyword>
<keyword>MIB</keyword>
<keyword>SMIv2</keyword>
<keyword>TLS</keyword>
<keyword>DTLS</keyword>
<keyword>SNMP</keyword>
<abstract>
<t>
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.
</t>
<t>
This transport model is designed to meet the security and
operational needs of network administrators. It supports
sending of SNMP messages over TLS/TCP and DTLS/UDP. The TLS
mode can make use of TCP's improved support for larger packet
sizes and the DTLS mode provides potentially superior
operation in environments where a connectionless (e.g. UDP)
transport is preferred. Both TLS and DTLS integrate well into
existing public keying infrastructures.
</t>
<t>
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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
<!-- Begin text copied from 5591 -->
It is important to understand the modular SNMPv3 architecture
as defined by <xref target="RFC3411" /> and enhanced by the
Transport Subsystem <xref target="RFC5590" />.
<!-- End text copied from 5591 -->
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.
<!-- Begin Network Management Boiler Text -->
For a detailed overview of the documents that describe the
current Internet-Standard Management Framework, please refer
to Section 7 of <xref target="RFC3410" />.
<!-- End Network Management Boiler Text -->
</t>
<t>
This document describes a Transport Model that makes use of
the Transport Layer Security (TLS) <xref target="RFC5246" />
and the Datagram Transport Layer Security (DTLS) Protocol
<xref target="RFC4347" />, within a transport subsystem <xref
target="RFC5590" />. DTLS is the datagram variant of the
Transport Layer Security (TLS) protocol <xref target="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
<xref target="RFC5280" />. While (D)TLS supports multiple
authentication mechanisms, this document only discusses X.509
certificate based authentication. Although other forms of
authentication are possible they are outside the scope of this
specification. This transport model is designed to meet the
security and operational needs of network administrators,
operating in both environments where a connectionless
(e.g. UDP) transport is preferred and in environments where
large quantities of data need to be sent (e.g. over a TCP
based stream). Both TLS and DTLS integrate well into existing
public keying infrastructures. This document supports sending
of SNMP messages over TLS/TCP and DTLS/UDP.
</t>
<t>
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.
</t>
<t>
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: <xref
target="RFC2578"/>, <xref target="RFC2579"/> and <xref
target="RFC2580"/>.
</t>
<t>
The diagram shown below gives a conceptual overview of two
SNMP entities communicating using the TLS Transport Model
(shown as "TLS TM"). One entity contains a command
responder and notification originator application, and the
other a command generator and notification receiver
application. It should be understood that this particular mix
of application types is an example only and other combinations
are equally valid. Note: this diagram shows the Transport
Security Model (TSM) being used as the security model which is
defined in <xref target="RFC5591" />.
</t>
<t>
<figure>
<artwork>
+---------------------------------------------------------------------+
| Network |
+---------------------------------------------------------------------+
^ | ^ |
|Notifications |Commands |Commands |Notifications
+---|---------------------|-------+ +--|---------------|--------------+
| | V | | | V |
| +------------+ +------------+ | | +-----------+ +----------+ |
| | (D)TLS | | (D)TLS | | | | (D)TLS | | (D)TLS | |
| | (Client) | | (Server) | | | | (Client) | | (Server) | |
| +------------+ +------------+ | | +-----------+ +----------+ |
| ^ ^ | | ^ ^ |
| | | | | | | |
| +-------------+ | | +--------------+ |
| +-----|------------+ | | +-----|------------+ |
| | V | | | | V | |
| | +--------+ | +-----+ | | | +--------+ | +-----+ |
| | | TLS TM |<--------->|Cache| | | | | TLS TM |<--------->|Cache| |
| | +--------+ | +-----+ | | | +--------+ | +-----+ |
| |Transport Subsys. | ^ | | |Transport Subsys. | ^ |
| +------------------+ | | | +------------------+ | |
| ^ | | | ^ | |
| | +--+ | | | +--+ |
| v | | | V | |
| +-----+ +--------+ +-------+ | | | +-----+ +--------+ +-------+ | |
| | | |Message | |Securi.| | | | | | |Message | |Securi.| | |
| |Disp.| |Proc. | |Subsys.| | | | |Disp.| |Proc. | |Subsys.| | |
| | | |Subsys. | | | | | | | | |Subsys. | | | | |
| | | | | | | | | | | | | | | | | |
| | | | +----+ | | +---+ | | | | | | | +----+ | | +---+ | | |
| | <--->|v3MP|<--> |TSM|<--+ | | | <--->|v3MP|<--->|TSM|<--+ |
| | | | +----+ | | +---+ | | | | | | +----+ | | +---+ | |
| | | | | | | | | | | | | | | |
| +-----+ +--------+ +-------+ | | +-----+ +--------+ +-------+ |
| ^ | | ^ |
| | | | | |
| +-+------------+ | | +-+----------+ |
| | | | | | | |
| v v | | v V |
| +-------------+ +-------------+ | | +-------------+ +-------------+ |
| | COMMAND | | NOTIFICAT. | | | | COMMAND | | NOTIFICAT. | |
| | RESPONDER | | ORIGINATOR | | | | GENERATOR | | RECEIVER | |
| | application | | application | | | | application | | application | |
| +-------------+ +-------------+ | | +-------------+ +-------------+ |
| SNMP entity | | SNMP entity |
+---------------------------------+ +---------------------------------+
</artwork>
</figure>
</t>
<section title="Conventions" anchor="conventions">
<!-- BEGIN Copied From RFC5592 -->
<t>
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.
</t>
<t>
"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.
</t>
<t>
The terms "manager" and "agent" are not used in this
document because, in the <xref target="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" <xref target="RFC3413"/> for further
information.
</t>
<!-- END Copied From RFC5592 -->
<t>
Large portions of this document simultaneously refer to both
TLS and DTLS when discussing TLSTM components that function
equally with either protocol. "(D)TLS" is used in these
places to indicate that the statement applies to either or
both protocols as appropriate. When a distinction between
the protocols is needed they are referred to independently
through the use of "TLS" or "DTLS". The Transport Model,
however, is named "TLS Transport Model" and refers not to
the TLS or DTLS protocol but to the specification in this
document, which includes support for both TLS and DTLS.
</t>
<t>
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.
</t>
<t>
The User-Based Security Model (USM) <xref
target="RFC3414"></xref> is a mandatory-to-implement
Security Model in STD 62. While (D)TLS and USM frequently
refer to a user, the terminology preferred in RFC3411 and in
this memo is "principal". A principal is the "who" on whose
behalf services are provided or processing takes place. A
principal can be, among other things, an individual acting
in a particular role; a set of individuals, with each acting
in a particular role; an application or a set of
applications, or a combination of these within an
administrative domain.
</t>
<t>
Throughout this document, the term "session" is used to
refer to a secure association between two TLS Transport
Models that permits the transmission of one or more SNMP
messages within the lifetime of the session. The (D)TLS
protocols also have an internal notion of a session and
although these two concepts of a session are related, when
the term "session" is used this document is referring to the
TLSTM's specific session and not directly to the (D)TLS
protocol's session.
</t>
<t>
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 <xref target="RFC2119" />.
</t>
</section>
</section>
<section title="The Transport Layer Security Protocol">
<t>
(D)TLS provides authentication, data message integrity, and
privacy at the transport layer. (See <xref target="RFC4347" />)
</t>
<t>
The primary goals of the TLS Transport Model are to provide
privacy, peer identity authentication and data integrity
between two communicating SNMP entities. The TLS and DTLS
protocols provide a secure transport upon which the TLSTM is
based. Please refer to <xref target="RFC5246" /> and <xref
target="RFC4347" /> for complete descriptions of the
protocols.
</t>
</section>
<section title="How the TLSTM fits into the Transport Subsystem">
<t>
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 <xref
target="RFC3411" /> component of the SNMP engine.
</t>
<t>
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.
</t>
<t>
After a TLS Transport Model session is established, SNMP
messages can conceptually be sent through the session from one
SNMP message Dispatcher to another SNMP Message Dispatcher.
If multiple SNMP messages are needed to be passed between two
SNMP applications they MAY be passed through the same session.
A TLSTM implementation engine MAY choose to close the session
to conserve resources.
</t>
<t>
The TLS Transport Model of an SNMP engine will perform the
translation between (D)TLS-specific security parameters and
SNMP- specific, model-independent parameters.
</t>
<t>
The diagram below depicts where the TLS Transport Model (shown
as "(D)TLS TM") fits into the architecture described in
RFC3411 and the Transport Subsystem:
</t>
<t>
<figure>
<artwork>
+------------------------------+
| Network |
+------------------------------+
^ ^ ^
| | |
v v v
+-------------------------------------------------------------------+
| +--------------------------------------------------+ |
| | Transport Subsystem | +--------+ |
| | +-----+ +-----+ +-------+ +-------+ | | | |
| | | UDP | | SSH | |(D)TLS | . . . | other |<--->| Cache | |
| | | | | TM | | TM | | | | | | |
| | +-----+ +-----+ +-------+ +-------+ | +--------+ |
| +--------------------------------------------------+ ^ |
| ^ | |
| | | |
| Dispatcher v | |
| +--------------+ +---------------------+ +----------------+ | |
| | Transport | | Message Processing | | Security | | |
| | Dispatch | | Subsystem | | Subsystem | | |
| | | | +------------+ | | +------------+ | | |
| | | | +->| v1MP |<--->| | USM | | | |
| | | | | +------------+ | | +------------+ | | |
| | | | | +------------+ | | +------------+ | | |
| | | | +->| v2cMP |<--->| | Transport | | | |
| | Message | | | +------------+ | | | Security |<--+ |
| | Dispatch <---->| +------------+ | | | Model | | |
| | | | +->| v3MP |<--->| +------------+ | |
| | | | | +------------+ | | +------------+ | |
| | PDU Dispatch | | | +------------+ | | | Other | | |
| +--------------+ | +->| otherMP |<--->| | Model(s) | | |
| ^ | +------------+ | | +------------+ | |
| | +---------------------+ +----------------+ |
| v |
| +-------+-------------------------+---------------+ |
| ^ ^ ^ |
| | | | |
| v v v |
| +-------------+ +---------+ +--------------+ +-------------+ |
| | COMMAND | | ACCESS | | NOTIFICATION | | PROXY | |
| | RESPONDER |<->| CONTROL |<->| ORIGINATOR | | FORWARDER | |
| | application | | | | applications | | application | |
| +-------------+ +---------+ +--------------+ +-------------+ |
| ^ ^ |
| | | |
| v v |
| +----------------------------------------------+ |
| | MIB instrumentation | SNMP entity |
+-------------------------------------------------------------------+
</artwork>
</figure>
</t>
<section title="Security Capabilities of this Model">
<section title="Threats">
<t>
The TLS Transport Model provides protection against the
threats identified by the RFC 3411 architecture <xref
target="RFC3411" />:
<list style="format %d." counter="threats">
<t>
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.
<vspace blankLines='1' />
(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.
</t>
<!-- Mostly verbatim copy from RFC3411 -->
<t>
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.
<vspace blankLines='1' />
The TLSTM verifies of the identity of the (D)TLS
server through the use of the (D)TLS protocol and
X.509 certificates. A TLS Transport Model
implementation MUST support authentication of both the
server and the client.
</t>
<t>
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.
<vspace blankLines='1' />
(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 <xref target="RFC4347" />).
</t>
<t>
Disclosure - The disclosure threat is the danger of
eavesdropping on the exchanges between SNMP engines.
<vspace blankLines='1' />
(D)TLS provides protection against the disclosure of
information to unauthorized recipients or
eavesdroppers by allowing for encryption of all
traffic between SNMP engines. A TLS Transport Model
implementation MUST support message encryption to
protect sensitive data from eavesdropping attacks.
</t>
<t>
Denial of Service - the RFC 3411 architecture <xref
target="RFC3411" /> states that denial of service
(DoS) attacks need not be addressed by an SNMP
security protocol. However, connectionless transports
(like DTLS over UDP) are susceptible to a variety of
denial of service attacks because they are more
vulnerable to spoofed IP addresses. See <xref
target="dtlsusage" /> for details how the cookie
mechanism is used. Note, however, that this mechanism
does not provide any defense against denial of service
attacks mounted from valid IP addresses.
</t>
</list>
</t>
<t>
See <xref target="securityconsiderations" /> for more
detail on the security considerations associated with the
TLSTM and these security threats.
</t>
</section>
<section title="Message Protection" anchor="seclevel">
<t>
The RFC 3411 architecture recognizes three levels of security:
<list style="symbols">
<t>without authentication and without privacy (noAuthNoPriv)</t>
<t>with authentication but without privacy (authNoPriv)</t>
<t>with authentication and with privacy (authPriv)</t>
</list>
</t>
<t>
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.
</t>
<t>
When an application requests a session for a message it
also requests a security level for that session. The TLS
Transport Model MUST ensure that the (D)TLS connection
provides security at least as high as the requested level
of security. How the security level is translated into
the algorithms used to provide data integrity and privacy
is implementation-dependent. However, the NULL integrity
and encryption algorithms MUST NOT be used to fulfill
security level requests for authentication or privacy.
Implementations MAY choose to force (D)TLS to only allow
cipher_suites that provide both authentication and privacy
to guarantee this assertion.
</t>
<t>
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.
</t>
<t>
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.
</t>
</section>
<section title="(D)TLS Connections" anchor="sessions">
<t>
(D)TLS connections are opened by the TLS Transport Model
during the elements of procedure for an outgoing SNMP
message. Since the sender of a message initiates the
creation of a (D)TLS connection if needed, the (D)TLS
connection will already exist for an incoming message.
</t>
<t>
Implementations MAY choose to instantiate (D)TLS
connections in anticipation of outgoing messages. This
approach might be useful to ensure that a (D)TLS
connection to a given target can be established before it
becomes important to send a message over the (D)TLS
connection. Of course, there is no guarantee that a
pre-established session will still be valid when needed.
</t>
<t>
DTLS connections, when used over UDP, are uniquely
identified within the TLS Transport Model by the
combination of transportDomain, transportAddress,
tmSecurityName, and requestedSecurityLevel associated with
each session. Each unique combination of these parameters
MUST have a locally-chosen unique tlstmSessionID for each
active session. For further information see <xref
target="eop" />. TLS over TCP sessions, on the other
hand, do not require a unique pairing of address and port
attributes since their lower layer protocols (TCP) already
provide adequate session framing. But they must still
provide a unique tlstmSessionID for referencing the
session.
</t>
<t>
The tlstmSessionID identifier MUST NOT change during the
entire duration of the session from the TLSTM's
perspective, and MUST uniquely identify a single session.
As an implementation hint: note that the (D)TLS internal
SessionID does not meet these requirements, since it can
change over the life of the connection as seen by the
TLSTM (for example, during renegotiation), and does not
necessarily uniquely identify a TLSTM session (there can
be multiple TLSTM sessions sharing the same D(TLS)
internal SessionID).
</t>
</section>
</section>
<section title="Security Parameter Passing">
<t>
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.
</t>
<t>
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.
</t>
<t>
The elements of procedure in <xref target="eop" /> discuss
these concepts in much greater detail.
</t>
</section>
<section title="Notifications and Proxy">
<t>
(D)TLS connections may be initiated by (D)TLS clients on
behalf of SNMP appplications that initiate communications,
such as command generators, notification originators, proxy
forwarders. Command generators are frequently operated by a
human, but notification originators and proxy forwarders are
usually unmanned automated processes. The targets to whom
notifications and proxied requests should be sent is
typically determined and configured by a network
administrator.
</t>
<t>
The SNMP-TARGET-MIB module <xref target="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.
</t>
<t>
When configuring a (D)TLS target, the snmpTargetAddrTDomain
and snmpTargetAddrTAddress parameters in snmpTargetAddrTable
SHOULD be set to the snmpTLSTCPDomain or snmpDTLSUDPDomain
object and an appropriate snmpTLSAddress value. When used
with the SNMPv3 message processing model, the
snmpTargetParamsMPModel column of the snmpTargetParamsTable
SHOULD be set to a value of 3. The
snmpTargetParamsSecurityName SHOULD be set to an appropriate
securityName value and the snmpTlstmParamsClientFingerprint
parameter of the snmpTlstmParamsTable SHOULD be set a value
that refers to a locally held certificate (and the
corresponding private key) to be used. Other parameters,
for example cryptographic configuration such as which cipher
suites to use, must come from configuration mechanisms not
defined in this document.
</t>
<t>
The securityName defined in the snmpTargetParamsSecurityName
column will be used by the access control model to authorize
any notifications that need to be sent.
</t>
</section>
</section>
<section title="Elements of the Model">
<t>
This section contains definitions required to realize the
(D)TLS Transport Model defined by this document.
</t>
<section title="X.509 Certificates">
<t>
(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.
</t>
<t>
While (D)TLS supports multiple authentication mechanisms,
this document only discusses X.509 certificate based
authentication; other forms of authentication are
outside the scope of this specification. TLSTM
implementations are REQUIRED to support X.509 certificates.
</t>
<section title="Provisioning for the Certificate" anchor="provisioning">
<t>
Authentication using (D)TLS will require that SNMP
entities have certificates, either signed by trusted
certification authorities, or self-signed. Furthermore,
SNMP entities will most commonly need to be provisioned
with root certificates which represent the list of trusted
certificate authorities that an SNMP entity can use for
certificate verification. SNMP entities SHOULD also be
provisioned with a X.509 certificate revocation mechanism
which can be used to verify that a certificate has not
been revoked. Trusted public keys from either CA
certificates and/or self-signed certificates MUST be
installed into the server through a trusted out of band
mechanism and their authenticity MUST be verified before
access is granted.
</t>
<t>
Having received a certificate from a connecting TLSTM
client, the authenticated tmSecurityName of the principal
is derived using the snmpTlstmCertToTSNTable. This table
allows mapping of incoming connections to tmSecurityNames
through defined transformations. The transformations
defined in the SNMP-TLS-TM-MIB include:
<list style="symbols">
<t>
Mapping a certificate's subjectAltName or CommonName
components to a tmSecurityName, or
</t>
<t>
Mapping a certificate's fingerprint value to a
directly specified tmSecurityName
</t>
</list>
</t>
<t>
As an implementation hint: implementations may choose to
discard any connections for which no potential
snmpTlstmCertToTSNTable mapping exists before performing
certificate verification to avoid expending computational
resources associated with certificate verification.
</t>
<t>
Deployments SHOULD map the "subjectAltName" component of
X.509 certificates to the TLSTM specific tmSecurityNames.
The authenticated identity can be obtained by the TLS
Transport Model by extracting the subjectAltName(s) from
the peer's certificate. The receiving application will
then have an appropriate tmSecurityName for use by other
SNMPv3 components like an access control model.
</t>
<t>
An example of this type of mapping setup can be found in
<xref target="examples" />.
</t>
<t>
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 <xref target="RFC5591" />, may perform an
identity mapping or a more complex mapping to derive the
securityName from the tmSecurityName offered by the TLS
Transport Model.
</t>
<t>
The standard VACM access control model constrains
securityNames to be 32 octets or less in length. A TLSTM
generated tmSecurityName, possibly in combination with a
messaging or security model that increases the length of
the securityName, might cause the securityName length to
exceed 32 octets. For example, a 32 octet tmSecurityName
derived from an IPv6 address, paired with a TSM prefix,
will generate a 36 octet securityName. Such a securityName
will not be able to be used with standard VACM or TARGET
MIB modules. Operators should be careful to select
algorithms and subjectAltNames to avoid this situation.
</t>
<t>
A pictorial view of the complete transformation process
(using the TSM security model for the example) is shown
below:
<figure>
<artwork>
+-------------+ +-------+ +-----+
| Certificate | | | | |
| Path | | TLSTM | tmSecurityName | TSM |
| Validation | --> | | ----------------->| |
+-------------+ +-------+ +-----+
|
| securityName
V
+-------------+
| application |
+-------------+
</artwork>
</figure>
</t>
</section>
</section>
<section title="(D)TLS Usage" anchor="dtlsusage">
<t>
(D)TLS MUST negotiate a cipher suite that uses X.509
certificates for authentication, and MUST authenticate both
the client and the server. The mandatory-to-implement
cipher suite is specified in the TLS specification <xref
target="RFC5246" />.
</t>
<t>
TLSTM verifies the certificates when the connection is
opened (see Section 5.3). For this reason, TLS
renegotiation with different certificates MUST NOT be done.
That is, implementations MUST either disable renegotiation
completely (RECOMMENDED), or MUST present the same
certificate during renegotiation (and MUST verify that the
other end presented the same certificate).
</t>
<t>
For DTLS over UDP, each SNMP message MUST be placed in a
single UDP datagram; it MAY be split to multiple DTLS
records. In other words, if a single datagram contains
multiple DTLS application_data records, they are
concatenated when received. The TLSTM implementation SHOULD
return an error if the SNMP message does not fit in the UDP
datagram, and thus cannot be sent.
</t>
<t>
For DTLS over UDP, the DTLS server implementation MUST
support DTLS cookies (<xref target="RFC4347" /> already
requires that clients support DTLS cookies).
Implementations are not required to perform the cookie
exchange for every DTLS handshake; however, enabling it by
default is RECOMMENDED.
</t>
<t>
For DTLS, replay protection MUST be used.
</t>
</section>
<section title="SNMP Services ">
<t>
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.
</t>
<t>
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.
</t>
<section title="SNMP Services for an Outgoing Message">
<t>
The Dispatcher passes the information to the TLS Transport
Model using the ASI defined in the transport subsystem:
<figure>
<artwork>
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
)
</artwork>
</figure>
</t>
<t>
The abstract data elements returned from or passed as
parameters into the abstract service primitives are as
follows:
<list style="hanging">
<t hangText="statusInformation:">
An indication of whether the sending of the message
was successful. If not, it is an indication of the
problem.
</t>
<t hangText="destTransportDomain:">
The transport domain for the associated
destTransportAddress. The Transport Model uses this
parameter to determine the transport type of the
associated destTransportAddress. This document
specifies the snmpTLSTCPDomain and the
snmpDTLSUDPDomain transport domains.
</t>
<t hangText="destTransportAddress:">
The transport address of the destination TLS Transport
Model in a format specified by the SnmpTLSAddress
TEXTUAL-CONVENTION.
</t>
<t hangText="outgoingMessage:">
The outgoing message to send to (D)TLS for
encapsulation and transmission.
</t>
<t hangText="outgoingMessageLength:">
The length of the outgoingMessage.
</t>
<t hangText="tmStateReference:">
A reference used to pass model-specific and
mechanism-specific parameters between the Transport
Subsystem and transport-aware Security Models.
</t>
</list>
</t>
</section>
<section title="SNMP Services for an Incoming Message">
<t>
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:
</t>
<t>
<figure>
<artwork>
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
)
</artwork>
</figure>
</t>
<t>
The abstract data elements returned from or passed as
parameters into the abstract service primitives are as
follows:
<list style="hanging">
<t hangText="statusInformation:">
An indication of whether the passing of the message
was successful. If not, it is an indication of the
problem.
</t>
<t hangText="transportDomain:">
The transport domain for the associated
transportAddress. This document specifies the
snmpTLSTCPDomain and the snmpDTLSUDPDomain transport
domains.
</t>
<t hangText="transportAddress:">
The transport address of the source of the received
message in a format specified by the SnmpTLSAddress
TEXTUAL-CONVENTION.
</t>
<t hangText="incomingMessage:">
The whole SNMP message after being processed by (D)TLS.
</t>
<t hangText="incomingMessageLength:">
The length of the incomingMessage.
</t>
<t hangText="tmStateReference:">
A reference used to pass model-specific and
mechanism-specific parameters between the Transport
Subsystem and transport-aware Security Models.
</t>
</list>
</t>
</section>
</section>
<!-- Begin boiler plate from RFC5592 -->
<section title="Cached Information and References">
<t>
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. <xref target="RFC5590">"Transport Subsystem for
the Simple Network Management Protocol" </xref> defines
general requirements for caches and references.
</t>
<!-- End boiler plate from RFC5592 -->
<section title="TLS Transport Model Cached Information">
<!-- BEGIN text matching RFC5592 -->
<t>
The TLS Transport Model has specific responsibilities
regarding the cached information. See the Elements of
Procedure in <xref target="eop" /> for detailed processing
instructions on the use of the tmStateReference fields by
the TLS Transport Model.
</t>
<section title="tmSecurityName">
<t>
The tmSecurityName MUST be a human-readable name (in
snmpAdminString format) representing the identity that
has been set according to the procedures in <xref
target="eop" />. The tmSecurityName MUST be constant
for all traffic passing through a single TLSTM session.
Messages MUST NOT be sent through an existing (D)TLS
connection that was established using a different
tmSecurityName.
</t>
<t>
On the (D)TLS server side of a connection the
tmSecurityName is derived using the procedures described
in <xref target="establishserver" /> and the SNMP-TLS-TM-MIB's
snmpTlstmCertToTSNTable DESCRIPTION clause.
</t>
<t>
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 Security Model
likely derived the tmSecurityName from the securityName
presented to the Security Model by the application
(possibly because of configuration specified in the
SNMP-TARGET-MIB).
</t>
<t>
Transport-model-aware security models derive
tmSecurityName from a securityName, possibly configured
in MIB modules for notifications and access controls.
Transport Models SHOULD use predictable tmSecurityNames
so operators will know what to use when configuring MIB
modules that use securityNames derived from
tmSecurityNames. The TLSTM generates predictable
tmSecurityNames based on the configuration found in the
SNMP-TLS-TM-MIB's snmpTlstmCertToTSNTable and relies on
the network operators to have configured this table
appropriately.
</t>
</section>
<section title="tmSessionID">
<t>
The tmSessionID MUST be recorded per message at the time
of receipt. When tmSameSecurity is set, the recorded
tmSessionID can be used to determine whether the (D)TLS
connection available for sending a corresponding
outgoing message is the same (D)TLS connection as was
used when receiving the incoming message (e.g., a
response to a request).
</t>
</section>
<section title="Session State">
<t>
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.
</t>
</section>
<!-- END text matching RFC5592 -->
</section>
</section>
</section>
<section title="Elements of Procedure" anchor="eop">
<t>
<!-- BEGIN text copied from RFC5592 -->
Abstract service interfaces have been defined by <xref
target="RFC3411" /> and further augmented by <xref
target="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.
</t>
<t>
To simplify the elements of procedure, the release of state
information is not always explicitly specified. As a general rule, if
state information is available when a message gets discarded, the
message-state information should also be released. If state
information is available when a session is closed, the session state
information should also be released.
<!-- BEGIN added beyond what RFC5592 had in it: -->
Sensitive information, like cryptographic keys, should be
overwritten appropriately prior to being released.
<!-- END added beyond what RFC5592 had in it: -->
</t>
<t>
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.
</t>
<!-- END text copied from RFC5592 -->
<section title="Procedures for an Incoming Message">
<t>
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.
</t>
<t>
<xref target="dtlsprocessing" /> describes the processing
required for de-multiplexing multiple DTLS connections,
which is specifically needed for DTLS over UDP sessions. It
is assumed that TLS protocol implementations already provide
appropriate message demultiplexing.
</t>
<t>
<xref target="snmpinprocessing" /> describes the transport
processing required once the (D)TLS processing has been
completed. This will be needed for all (D)TLS-based
connections.
</t>
<section title="DTLS over UDP Processing for Incoming Messages"
anchor="dtlsprocessing">
<t>
For connection-oriented transport protocols, such as TCP,
the transport protocol takes care of demultiplexing
incoming packets to the right connection. Depending on the
DTLS implementation, for DTLS over UDP, this
demultiplexing may need to be done by the TLSTM
implementation.
</t>
<t>
Like TCP, DTLS over UDP uses the four-tuple <source IP,
destination IP, source port, destination port> for
identifying the connection (and relevant DTLS connection
state). This means that when establishing a new session,
implementations MUST use a different UDP source port
number for each active connection to a remote destination
IP-address/port-number combination to ensure the remote
entity can disambiguate between multiple connections.
</t>
<t>
If demultiplexing received UDP datagrams to DTLS
connection state is done by the TLSTM implementation
(instead of the DTLS implementation), the steps below
describe one possible method to accomplish this.
</t>
<t>
The important output results from the steps in this
process are the remote transport address, incomingMessage,
incomingMessageLength, and the tlstmSessionID.
</t>
<t>
<list style="format %d)">
<t>
The TLS Transport Model examines the raw UDP message,
in an implementation-dependent manner.
</t>
<t>
The TLS Transport Model queries the Local
Configuration Datastore (LCD) (see <xref
target="RFC3411" /> Section 3.4.2) using the transport
parameters (source and destination IP addresses and
ports) to determine if a session already exists.
<list style="format 2%c)">
<t>
If a matching entry in the LCD does not exist,
then the UDP packet is passed to the DTLS
implementation for processing. If the DTLS
implementation decides to continue with the
connection and allocate state for it, it returns a
new DTLS connection handle (an implementation
dependent detail). In this case, TLSTM selects a
new tlstmSessionId, and caches this and the DTLS
connection handle as a new entry in the LCD
(indexed by the transport parameters). If the
DTLS implementation returns an error or does not
allocate connection state (which can happen with
the stateless cookie exchange), processing stops.
</t>
<t>
If a session does exist in the LCD then its DTLS
connection handle (an implementation dependent
detail) and its tlstmSessionId is extracted from
the LCD. The UDP packet and the connection handle
is passed to the DTLS implementation. If the DTLS
implementation returns success but does not return
an incomingMessage and an incomingMessageLength
then processing stops (this is the case when the
UDP datagram contained DTLS handshake messages,
for example). If the DTLS implementation returns
an error then processing stops.
</t>
</list>
</t>
<t>
Retrieve the incomingMessage and an
incomingMessageLength from DTLS. These results and
the tlstmSessionID are used below in <xref
target="snmpinprocessing" /> to complete the
processing of the incoming message.
</t>
</list>
</t>
</section>
<section title="Transport Processing for Incoming SNMP Messages"
anchor="snmpinprocessing">
<t>
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.
<list style="format %d)">
<t>
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 <xref
target="dtlsprocessing" />. 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.
<vspace blankLines='1' />
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 <xref
target="establishserver" /> prior to this point or
they may perform them now, but the procedures
described in <xref target="establishserver" /> MUST be
performed before continuing beyond this point.
</t>
<t>
Create a tmStateReference cache for the subsequent reference and
assign the following values within it:
<list style="hanging">
<t hangText="tmTransportDomain">
= snmpTLSTCPDomain or snmpDTLSUDPDomain as
appropriate.
</t>
<t hangText="tmTransportAddress">
= The address the message originated from.
</t>
<t hangText="tmSecurityLevel">
= The derived tmSecurityLevel for the session, as
discussed in <xref target="seclevel" /> and <xref
target="establishsession" />.
</t>
<t hangText="tmSecurityName">
= The derived tmSecurityName for the session as
discussed in <xref target="establishsession" />.
This value MUST be constant during the lifetime of
the session.
</t>
<t hangText="tmSessionID">
= The tlstmSessionID described in step 1 above.
</t>
</list>
</t>
<t>
The incomingMessage and incomingMessageLength are
assigned values from the (D)TLS processing.
</t>
<t>
The TLS Transport Model passes the transportDomain,
transportAddress, incomingMessage, and
incomingMessageLength to the Dispatcher using the
receiveMessage ASI:
<figure>
<artwork><![CDATA[
statusInformation =
receiveMessage(
IN transportDomain -- snmpTLSTCPDomain or snmpDTLSUDPDomain,
IN transportAddress -- address for the received message
IN incomingMessage -- the whole SNMP message from (D)TLS
IN incomingMessageLength -- the length of the SNMP message
IN tmStateReference -- transport info
)
]]>
</artwork>
</figure>
</t>
</list>
</t>
</section>
</section>
<section title="Procedures for an Outgoing SNMP Message">
<t>
The Dispatcher sends a message to the TLS Transport Model
using the following ASI:
<figure>
<artwork><![CDATA[
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
)
]]></artwork>
</figure>
</t>
<t>
This section describes the procedure followed by the TLS
Transport Model whenever it is requested through this ASI to
send a message.
<list style="format %d)">
<t>
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.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
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.
<list style="format 5%c)" counter="step4">
<t>
If there is a corresponding LCD entry, then this
session will be used to send the message.
</t>
<t>
If there is no corresponding LCD entry, then open a
session using the openSession() ASI (discussed
further in <xref target="establishclient" />).
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.
</t>
</list>
</t>
<t>
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.
</t>
</list>
</t>
</section>
<section title="Establishing or Accepting a Session"
anchor="establishsession">
<t>
Establishing a (D)TLS connection as either a client or a
server requires slightly different processing. The
following two sections describe the necessary processing
steps.
</t>
<section title="Establishing a Session as a Client"
anchor="establishclient">
<t>
The TLS Transport Model provides the following primitive
for use by a client to establish a new (D)TLS connection:
</t>
<t>
<figure>
<artwork>
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
)
</artwork>
</figure>
</t>
<t>
The following describes the procedure to follow when
establishing a SNMP over (D)TLS connection between SNMP
engines for exchanging SNMP messages. This process is
followed by any SNMP client's engine when establishing a
session for subsequent use.
</t>
<t>
This procedure MAY be done automatically for an SNMP
application that initiates a transaction, such as a
command generator, a notification originator, or a proxy
forwarder.
<list style="format %d)">
<t>
The snmpTlstmSessionOpens counter is incremented.
</t>
<t>
The client selects the appropriate certificate and
cipher_suites for the key agreement based on the
tmSecurityName and the tmRequestedSecurityLevel for
the session. For sessions being established as a
result of a SNMP-TARGET-MIB based operation, the
certificate will potentially have been identified via
the snmpTlstmParamsTable mapping and the cipher_suites
will have to be taken from system-wide or
implementation-specific configuration. If no row in
the snmpTlstmParamsTable exists then implementations MAY
choose to establish the connection using a default
client certificate available to the application.
Otherwise, the certificate and appropriate
cipher_suites will need to be passed to the
openSession() ASI as supplemental information or
configured through an implementation-dependent
mechanism. It is also implementation-dependent and
possibly policy-dependent how tmRequestedSecurityLevel
will be used to influence the security capabilities
provided by the (D)TLS connection. However this is
done, the security capabilities provided by (D)TLS
MUST be at least as high as the level of security
indicated by the tmRequestedSecurityLevel parameter.
The actual security level of the session is reported
in the tmStateReference cache as tmSecurityLevel. For
(D)TLS to provide strong authentication, each
principal acting as a command generator SHOULD have
its own certificate.
</t>
<t>
Using the destTransportDomain and destTransportAddress
values, the client will initiate the (D)TLS handshake
protocol to establish session keys for message
integrity and encryption.
<vspace blankLines='1' />
If the attempt to establish a session is unsuccessful,
then snmpTlstmSessionOpenErrors is incremented, an
error indication is returned, and processing stops.
If the session failed to open because the presented
server certificate was unknown or invalid then the
snmpTlstmSessionUnknownServerCertificate or
snmpTlstmSessionInvalidServerCertificates MUST be
incremented and a snmpTlstmServerCertificateUnknown or
snmpTlstmServerInvalidCertificate notification SHOULD be
sent as appropriate. Reasons for server certificate
invalidation includes, but is not limited to,
cryptographic validation failures and an unexpected
presented certificate identity.
</t>
<t>
The (D)TLS client MUST then verify that the (D)TLS
server's presented certificate is the expected
certificate. The (D)TLS client MUST NOT transmit SNMP
messages until the server certificate has been
authenticated, the client certificate has been
transmitted and the TLS connection has been fully
established.
<vspace blankLines='1' />
If the connection is being established from
configuration based on SNMP-TARGET-MIB configuration,
then the snmpTlstmAddrTable DESCRIPTION clause describes
how the verification is done (using either a
certificate fingerprint, or an identity authenticated
via certification path validation).
<vspace blankLines='1' />
If the connection is being established for reasons
other than configuration found in the SNMP-TARGET-MIB
then configuration and procedures outside the scope of
this document should be followed. Configuration
mechanisms SHOULD be similar in nature to those
defined in the snmpTlstmAddrTable to ensure consistency
across management configuration systems. For example,
a command-line tool for generating SNMP GETs might
support specifying either the server's certificate
fingerprint or the expected host name as a command
line argument.
</t>
<t>
(D)TLS provides assurance that the authenticated
identity has been signed by a trusted configured
certification authority. If verification of the
server's certificate fails in any way (for example
because of failures in cryptographic verification or
the presented identity did not match the expected
named entity) then the session establishment MUST
fail, the snmpTlstmSessionInvalidServerCertificates
object is incremented. If the session can not be
opened for any reason at all, including cryptographic
verification failures and snmpTlstmCertToTSNTable
lookup failures, then the snmpTlstmSessionOpenErrors
counter is incremented and processing stops.
</t>
<t>
The TLSTM-specific session identifier (tlstmSessionID)
is set in the tmSessionID of the tmStateReference
passed to the TLS Transport Model to indicate that the
session has been established successfully and to point
to a specific (D)TLS connection for future use. The
tlstmSessionID is also stored in the LCD for later
lookup during processing of incoming messages (<xref
target="snmpinprocessing" />).
</t>
</list>
</t>
</section>
<section title="Accepting a Session as a Server"
anchor="establishserver">
<t>
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. <xref target="RFC5280" />) or
through certificate fingerprint verification using
fingerprints configured in the snmpTlstmCertToTSNTable.
Afterward the server will determine the identity of the
remote entity using the following procedures.
</t>
<t>
The (D)TLS server identifies the authenticated identity
from the (D)TLS client's principal certificate using
configuration information from the snmpTlstmCertToTSNTable
mapping table. The (D)TLS server MUST request and expect
a certificate from the client and MUST NOT accept SNMP
messages over the (D)TLS connection until the client has
sent a certificate and it has been authenticated. The
resulting derived tmSecurityName is recorded in the
tmStateReference cache as tmSecurityName. The details of
the lookup process are fully described in the DESCRIPTION
clause of the snmpTlstmCertToTSNTable MIB object. If any
verification fails in any way (for example because of
failures in cryptographic verification or because of the
lack of an appropriate row in the snmpTlstmCertToTSNTable)
then the session establishment MUST fail, and the
snmpTlstmSessionInvalidClientCertificates object is
incremented. If the session can not be opened for any
reason at all, including cryptographic verification
failures, then the snmpTlstmSessionOpenErrors counter is
incremented and processing stops.
</t>
<t>
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 <xref
target="RFC4366" />. Supporting this will allow, for
example, sending notifications to a specific principal at
a given TCP or UDP port.
</t>
</section>
</section>
<section title="Closing a Session">
<t>
The TLS Transport Model provides the following primitive to
close a session:
</t>
<t>
<figure>
<artwork>
statusInformation =
closeSession(
IN tmSessionID -- session ID of the session to be closed
)
</artwork>
</figure>
</t>
<t>
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.
<list style="format %d)">
<t>
Increment either the snmpTlstmSessionClientCloses or the
snmpTlstmSessionServerCloses counter as appropriate.
</t>
<t>
Look up the session using the tmSessionID.
</t>
<t>
If there is no open session associated with the
tmSessionID, then closeSession processing is completed.
</t>
<t>
Have (D)TLS close the specified connection. This MUST
include sending a close_notify TLS Alert to inform the
other side that session cleanup may be performed.
</t>
</list>
</t>
</section>
</section>
<section title="MIB Module Overview">
<t>
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 <xref target="examples"
/>.
</t>
<section title="Structure of the MIB Module">
<t>
Objects in this MIB module are arranged into subtrees. Each
subtree is organized as a set of related objects. The
overall structure and assignment of objects to their
subtrees, and the intended purpose of each subtree, is shown
below.
</t>
</section>
<section title="Textual Conventions">
<t>
Generic and Common Textual Conventions used in this module
can be found summarized at
http://www.ops.ietf.org/mib-common-tcs.html
</t>
<t>
This module defines the following new Textual Conventions:
<list style="symbols">
<t>
A new TransportAddress format for describing (D)TLS
connection addressing requirements.
</t>
<t>
A certificate fingerprint allowing MIB module objects to
generically refer to a stored X.509 certificate using a
cryptographic hash as a reference pointer.
</t>
</list>
</t>
</section>
<section title="Statistical Counters">
<t>
The SNMP-TLS-TM-MIB defines counters that provide network
management stations with information about session usage and
potential errors that a device may be
experiencing.
</t>
</section>
<section title="Configuration Tables">
<t>
The SNMP-TLS-TM-MIB defines configuration tables that an
administrator can use for configuring a device for sending
and receiving SNMP messages over (D)TLS. In particular,
there are MIB tables that extend the SNMP-TARGET-MIB for
configuring (D)TLS certificate usage and a MIB table for
mapping incoming (D)TLS client certificates to SNMPv3
securityNames.
</t>
<section title="Notifications">
<t>
The SNMP-TLS-TM-MIB defines notifications to alert management
stations when a (D)TLS connection fails because a server's
presented certificate did not meet an expected value
(snmpTlstmServerCertificateUnknown) or because cryptographic
validation failed (snmpTlstmServerInvalidCertificate).
</t>
</section>
</section>
<section title="Relationship to Other MIB Modules">
<t>
Some management objects defined in other MIB modules are
applicable to an entity implementing the TLS Transport
Model. In particular, it is assumed that an entity
implementing the SNMP-TLS-TM-MIB will implement the SNMPv2-MIB
<xref target="RFC3418" />, the SNMP-FRAMEWORK-MIB <xref
target="RFC3411" />, the SNMP-TARGET-MIB <xref target="RFC3413" />,
the SNMP-NOTIFICATION-MIB <xref target="RFC3413" /> and the
SNMP-VIEW-BASED-ACM-MIB <xref target="RFC3415" />.
</t>
<t>
The SNMP-TLS-TM-MIB module contained in this document is for
managing TLS Transport Model information.
</t>
<section title="MIB Modules Required for IMPORTS">
<t>
The SNMP-TLS-TM-MIB module imports items from SNMPv2-SMI <xref
target="RFC2578" />, SNMPv2-TC <xref target="RFC2579" />,
SNMP-FRAMEWORK-MIB <xref target="RFC3411" />,
SNMP-TARGET-MIB <xref target="RFC3413" /> and SNMPv2-CONF
<xref target="RFC2580" />.
</t>
</section>
</section>
</section>
<section title="MIB Module Definition" anchor="mib">
<t>
<figure>
<artwork>
SNMP-TLS-TM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
OBJECT-IDENTITY, mib-2, snmpDomains,
Counter32, Unsigned32, Gauge32, NOTIFICATION-TYPE
FROM SNMPv2-SMI -- RFC2578 or any update thereof
TEXTUAL-CONVENTION, TimeStamp, RowStatus, StorageType,
AutonomousType
FROM SNMPv2-TC -- RFC2579 or any update thereof
MODULE-COMPLIANCE, OBJECT-GROUP, NOTIFICATION-GROUP
FROM SNMPv2-CONF -- RFC2580 or any update thereof
SnmpAdminString
FROM SNMP-FRAMEWORK-MIB -- RFC3411 or any update thereof
snmpTargetParamsName, snmpTargetAddrName
FROM SNMP-TARGET-MIB -- RFC3413 or any update thereof
;
snmpTlstmMIB MODULE-IDENTITY
LAST-UPDATED "201005070000Z"
ORGANIZATION "ISMS Working Group"
CONTACT-INFO "WG-EMail: isms@lists.ietf.org
Subscribe: isms-request@lists.ietf.org
Chairs:
Juergen Schoenwaelder
Jacobs University Bremen
Campus Ring 1
28725 Bremen
Germany
+49 421 200-3587
j.schoenwaelder@jacobs-university.de
Russ Mundy
SPARTA, Inc.
7110 Samuel Morse Drive
Columbia, MD 21046
USA
Editor:
Wes Hardaker
Sparta, Inc.
P.O. Box 382
Davis, CA 95617
USA
ietf@hardakers.net
"
DESCRIPTION "
The TLS Transport Model MIB
Copyright (c) 2010 IETF Trust and the persons identified as
the document authors. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info)."
REVISION "201005070000Z"
DESCRIPTION "This version of this MIB module is part of
RFC XXXX; see the RFC itself for full legal
notices."
-- NOTE to RFC editor: replace XXXX with actual RFC number
-- for this document and change the date to the
-- current date and remove this note
::= { mib-2 www }
-- RFC Ed.: replace www with IANA-assigned number under the mib-2
-- SNMP OID tree and remove this note
-- ************************************************
-- subtrees of the SNMP-TLS-TM-MIB
-- ************************************************
snmpTlstmNotifications OBJECT IDENTIFIER ::= { snmpTlstmMIB 0 }
snmpTlstmIdentities OBJECT IDENTIFIER ::= { snmpTlstmMIB 1 }
snmpTlstmObjects OBJECT IDENTIFIER ::= { snmpTlstmMIB 2 }
snmpTlstmConformance OBJECT IDENTIFIER ::= { snmpTlstmMIB 3 }
-- ************************************************
-- snmpTlstmObjects - Objects
-- ************************************************
snmpTLSTCPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over TLS transport domain. The corresponding
transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpTLSTCPDomain is 'tls'. This prefix may be used by
security models or other components to identify which secure
transport infrastructure authenticated a securityName."
REFERENCE
"RFC 2579: Textual Conventions for SMIv2"
::= { snmpDomains xx }
-- RFC Ed.: replace xx with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'tls' with the actual IANA assigned prefix string
-- if 'tls' is not assigned to this document.
snmpDTLSUDPDomain OBJECT-IDENTITY
STATUS current
DESCRIPTION
"The SNMP over DTLS/UDP transport domain. The corresponding
transport address is of type SnmpTLSAddress.
The securityName prefix to be associated with the
snmpDTLSUDPDomain is 'dtls'. This prefix may be used by
security models or other components to identify which secure
transport infrastructure authenticated a securityName."
REFERENCE
"RFC 2579: Textual Conventions for SMIv2"
::= { snmpDomains yy }
-- RFC Ed.: replace yy with IANA-assigned number and
-- remove this note
-- RFC Ed.: replace 'dtls' with the actual IANA assigned prefix string
-- if 'dtls' is not assigned to this document.
SnmpTLSAddress ::= TEXTUAL-CONVENTION
DISPLAY-HINT "1a"
STATUS current
DESCRIPTION
"Represents a IPv4 address, an IPv6 address or an US-ASCII
encoded hostname and port number.
An IPv4 address must be in dotted decimal format followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number
in US-ASCII.
An IPv6 address must be a colon separated format (as described
in I-D.ietf-6man-text-addr-representation), surrounded by
square brackets ('[', US-ASCII character 0x5B, and ']',
US-ASCII character 0x5D), followed by a colon ':' (US-ASCII
character 0x3A) and a decimal port number in US-ASCII.
A hostname is always in US-ASCII (as per RFC1033);
internationalized hostnames are encoded in US-ASCII as domain
names after transformation via the ToASCII operation specified
in RFC 3490. The ToASCII operation MUST be performed with the
UseSTD3ASCIIRules flag set. The hostname is followed by a
colon ':' (US-ASCII character 0x3A) and a decimal port number
in US-ASCII. The name SHOULD be fully qualified whenever
possible.
Values of this textual convention may not be directly usable
as transport-layer addressing information, and may require
run-time resolution. As such, applications that write them
must be prepared for handling errors if such values are not
supported, or cannot be resolved (if resolution occurs at the
time of the management operation).
The DESCRIPTION clause of TransportAddress objects that may
have SnmpTLSAddress values must fully describe how (and
when) such names are to be resolved to IP addresses and vice
versa.
This textual convention SHOULD NOT be used directly in object
definitions since it restricts addresses to a specific
format. However, if it is used, it MAY be used either on its
own or in conjunction with TransportAddressType or
TransportDomain as a pair.
When this textual convention is used as a syntax of an index
object, there may be issues with the limit of 128
sub-identifiers specified in SMIv2 (STD 58). It is RECOMMENDED
that all MIB documents using this textual convention make
explicit any limitations on index component lengths that
management software must observe. This may be done either by
including SIZE constraints on the index components or by
specifying applicable constraints in the conceptual row
DESCRIPTION clause or in the surrounding documentation."
REFERENCE
"RFC 1033: DOMAIN ADMINISTRATORS OPERATIONS GUIDE
RFC 3490: Internationalizing Domain Names in Applications
I-D.ietf-6man-text-addr-representation:
A Recommendation for IPv6 Address Text Representation
"
SYNTAX OCTET STRING (SIZE (1..255))
-- RFC Editor: if I-D.ietf-6man-text-addr-representation fails to get
-- published then replace the reference to
-- I-D.ietf-6man-text-addr-representation with a reference to
-- "RFC3513: Internet Protocol Version 6 (IPv6) Addressing Architecture"
-- instead.
SnmpTLSFingerprint ::= 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 SnmpTLSFingerprint value is composed of a 1-octet hashing
algorithm identifier followed by the fingerprint value. The
octet value encoded is taken from the IANA TLS HashAlgorithm
Registry (RFC5246). The remaining octets are filled using the
results of the hashing algorithm.
This TEXTUAL-CONVENTION allows for a zero-length (blank)
SnmpTLSFingerprint value for use in tables where the
fingerprint value may be optional. MIB definitions or
implementations may refuse to accept a zero-length value as
appropriate."
REFERENCE "RFC 5246: The Transport Layer
Security (TLS) Protocol Version 1.2
http://www.iana.org/assignments/tls-parameters/
"
SYNTAX OCTET STRING (SIZE (0..255))
-- Identities for use in the snmpTlstmCertToTSNTable
snmpTlstmCertToTSNMIdentities OBJECT IDENTIFIER
::= { snmpTlstmIdentities 1 }
snmpTlstmCertSpecified OBJECT-IDENTITY
STATUS current
DESCRIPTION "Directly specifies the tmSecurityName to be used for
this certificate. The value of the tmSecurityName
to use is specified in the snmpTlstmCertToTSNData
column. The snmpTlstmCertToTSNData column must
contain a non-zero length SnmpAdminString compliant
value or the mapping described in this row must be
considered a failure."
::= { snmpTlstmCertToTSNMIdentities 1 }
snmpTlstmCertSANRFC822Name OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a subjectAltName's rfc822Name to a
tmSecurityName. The local part of the rfc822Name is
passed unaltered but the host-part of the name must
be passed in lower case. This mapping results in a
1:1 correspondence between equivalent subjectAltName
rfc822Name values and tmSecurityName values except
that the host-part of the name MUST be passed in
lower case.
Example rfc822Name Field: FooBar@Example.COM
is mapped to tmSecurityName: FooBar@example.com"
::= { snmpTlstmCertToTSNMIdentities 2 }
snmpTlstmCertSANDNSName OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a subjectAltName's dNSName to a
tmSecurityName after first converting it to all
lower case (RFC5280 does not specify converting to
lower case so this involves an extra step). This
mapping results in a 1:1 correspondence between
subjectAltName dNSName values and the tmSecurityName
values."
REFERENCE "RFC5280 - Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation
List (CRL) Profile"
::= { snmpTlstmCertToTSNMIdentities 3 }
snmpTlstmCertSANIpAddress OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a subjectAltName's iPAddress to a
tmSecurityName by transforming the binary encoded
address as follows:
1) for IPv4 the value is converted into a decimal
dotted quad address (e.g. '192.0.2.1')
2) for IPv6 addresses the value is converted into a
32-character all lowercase hexadecimal string
without any colon separators.
This mapping results in a 1:1 correspondence between
subjectAltName iPAddress values and the
tmSecurityName values.
The resulting length is the maximum length supported
by the View-Based Access Control Model (VACM).
Using both the Transport Security Model's support
for transport prefixes (see the SNMP-TSM-MIB's
snmpTsmConfigurationUsePrefix object for details)
will result in securityName lengths that exceed what
VACM can handle."
::= { snmpTlstmCertToTSNMIdentities 4 }
snmpTlstmCertSANAny OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps any of the following fields using the
corresponding mapping algorithms:
|------------+----------------------------|
| Type | Algorithm |
|------------+----------------------------|
| rfc822Name | snmpTlstmCertSANRFC822Name |
| dNSName | snmpTlstmCertSANDNSName |
| iPAddress | snmpTlstmCertSANIpAddress |
|------------+----------------------------|
The first matching subjectAltName value found in the
certificate of the above types MUST be used when
deriving the tmSecurityName. The mapping algorithm
specified in the 'Algorithm' column MUST be used to
derive the tmSecurityName.
This mapping results in a 1:1 correspondence between
subjectAltName values and tmSecurityName values. The
three sub-mapping algorithms produced by this
combined algorithm cannot produce conflicting
results between themselves."
::= { snmpTlstmCertToTSNMIdentities 5 }
snmpTlstmCertCommonName OBJECT-IDENTITY
STATUS current
DESCRIPTION "Maps a certificate's CommonName to a tmSecurityName
after converting it to a UTF-8 encoding. The usage
of CommonNames is deprecated and users are
encouraged to use subjectAltName mapping methods
instead. This mapping results in a 1:1
correspondence between certificate CommonName values
and tmSecurityName values."
::= { snmpTlstmCertToTSNMIdentities 6 }
-- The snmpTlstmSession Group
snmpTlstmSession OBJECT IDENTIFIER ::= { snmpTlstmObjects 1 }
snmpTlstmSessionOpens OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request has been executed
as an (D)TLS client, regardless of whether it succeeded or
failed."
::= { snmpTlstmSession 1 }
snmpTlstmSessionClientCloses OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times a closeSession() request has been
executed as an (D)TLS client, regardless of whether it
succeeded or failed."
::= { snmpTlstmSession 2 }
snmpTlstmSessionOpenErrors OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an openSession() request failed to open a
session as a (D)TLS client, for any reason."
::= { snmpTlstmSession 3 }
snmpTlstmSessionAccepts OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times a (D)TLS server has accepted a new
connection from a client and has received at least one SNMP
message through it."
::= { snmpTlstmSession 4 }
snmpTlstmSessionServerCloses OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times a closeSession() request has been
executed as an (D)TLS server, regardless of whether it
succeeded or failed."
::= { snmpTlstmSession 5 }
snmpTlstmSessionNoSessions OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing message was dropped because
the session associated with the passed tmStateReference was no
longer (or was never) available."
::= { snmpTlstmSession 6 }
snmpTlstmSessionInvalidClientCertificates OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an incoming session was not established
on an (D)TLS server because the presented client certificate
was invalid. Reasons for invalidation include, but are not
limited to, cryptographic validation failures or lack of a
suitable mapping row in the snmpTlstmCertToTSNTable."
::= { snmpTlstmSession 7 }
snmpTlstmSessionUnknownServerCertificate OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing session was not established
on an (D)TLS client because the server certificate presented
by a SNMP over (D)TLS server was invalid because no
configured fingerprint or CA was acceptable to validate it.
This may result because there was no entry in the
snmpTlstmAddrTable or because no path could be found to a
known certification authority."
::= { snmpTlstmSession 8 }
snmpTlstmSessionInvalidServerCertificates OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of times an outgoing session was not established
on an (D)TLS client because the server certificate presented
by an SNMP over (D)TLS server could not be validated even if
the fingerprint or expected validation path was known. I.E.,
a cryptographic validation error occurred during certificate
validation processing.
Reasons for invalidation include, but are not
limited to, cryptographic validation failures."
::= { snmpTlstmSession 9 }
snmpTlstmSessionInvalidCaches OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of outgoing messages dropped because the
tmStateReference referred to an invalid cache."
::= { snmpTlstmSession 10 }
-- Configuration Objects
snmpTlstmConfig OBJECT IDENTIFIER ::= { snmpTlstmObjects 2 }
-- Certificate mapping
snmpTlstmCertificateMapping OBJECT IDENTIFIER ::= { snmpTlstmConfig 1 }
snmpTlstmCertToTSNCount OBJECT-TYPE
SYNTAX Gauge32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the
snmpTlstmCertToTSNTable"
::= { snmpTlstmCertificateMapping 1 }
snmpTlstmCertToTSNTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the snmpTlstmCertToTSNTable was
last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { snmpTlstmCertificateMapping 2 }
snmpTlstmCertToTSNTable OBJECT-TYPE
SYNTAX SEQUENCE OF SnmpTlstmCertToTSNEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table is used by a (D)TLS server to map the (D)TLS
client's presented X.509 certificate to a tmSecurityName.
On an incoming (D)TLS/SNMP connection the client's presented
certificate must either be validated based on an established
trust anchor, or it must directly match a fingerprint in this
table. This table does not provide any mechanisms for
configuring the trust anchors; the transfer of any needed
trusted certificates for path validation is expected to occur
through an out-of-band transfer.
Once the certificate has been found acceptable (either by path
validation or directly matching a fingerprint in this table),
this table is consulted to determine the appropriate
tmSecurityName to identify with the remote connection. This
is done by considering each active row from this table in
prioritized order according to its snmpTlstmCertToTSNID value.
Each row's snmpTlstmCertToTSNFingerprint value determines
whether the row is a match for the incoming connection:
1) If the row's snmpTlstmCertToTSNFingerprint value
identifies the presented certificate then consider the
row as a successful match.
2) If the row's snmpTlstmCertToTSNFingerprint value
identifies a locally held copy of a trusted CA
certificate and that CA certificate was used to
validate the path to the presented certificate then
consider the row as a successful match.
Once a matching row has been found, the
snmpTlstmCertToTSNMapType value can be used to determine how
the tmSecurityName to associate with the session should be
determined. See the snmpTlstmCertToTSNMapType column's
DESCRIPTION for details on determining the tmSecurityName
value. If it is impossible to determine a tmSecurityName from
the row's data combined with the data presented in the
certificate then additional rows MUST be searched looking for
another potential match. If a resulting tmSecurityName mapped
from a given row is not compatible with the needed
requirements of a tmSecurityName (e.g., VACM imposes a
32-octet-maximum length and the certificate derived
securityName could be longer) then it must be considered an
invalid match and additional rows MUST be searched looking for
another potential match.
If no matching and valid row can be found, the connection MUST
be closed and SNMP messages MUST NOT be accepted over it.
Missing values of snmpTlstmCertToTSNID are acceptable and
implementations should continue to the next highest numbered
row. It is recommended that administrators skip index values
to leave room for the insertion of future rows (E.G., use values
of 10 and 20 when creating initial rows).
Users are encouraged to make use of certificates with
subjectAltName fields that can be used as tmSecurityNames so
that a single root CA certificate can allow all child
certificate's subjectAltName to map directly to a
tmSecurityName via a 1:1 transformation. However, this table
is flexible to allow for situations where existing deployed
certificate infrastructures do not provide adequate
subjectAltName values for use as tmSecurityNames.
Certificates may also be mapped to tmSecurityNames using the
CommonName portion of the Subject field. However, the usage
of the CommonName field is deprecated and thus this usage is
NOT RECOMMENDED. Direct mapping from each individual
certificate fingerprint to a tmSecurityName is also possible
but requires one entry in the table per tmSecurityName and
requires more management operations to completely configure a
device."
::= { snmpTlstmCertificateMapping 3 }
snmpTlstmCertToTSNEntry OBJECT-TYPE
SYNTAX SnmpTlstmCertToTSNEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A row in the snmpTlstmCertToTSNTable that specifies a mapping
for an incoming (D)TLS certificate to a tmSecurityName to use
for a connection."
INDEX { snmpTlstmCertToTSNID }
::= { snmpTlstmCertToTSNTable 1 }
SnmpTlstmCertToTSNEntry ::= SEQUENCE {
snmpTlstmCertToTSNID Unsigned32,
snmpTlstmCertToTSNFingerprint SnmpTLSFingerprint,
snmpTlstmCertToTSNMapType AutonomousType,
snmpTlstmCertToTSNData OCTET STRING,
snmpTlstmCertToTSNStorageType StorageType,
snmpTlstmCertToTSNRowStatus RowStatus
}
snmpTlstmCertToTSNID OBJECT-TYPE
SYNTAX Unsigned32 (1..4294967295)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A unique, prioritized index for the given entry. Lower
numbers indicate a higher priority."
::= { snmpTlstmCertToTSNEntry 1 }
snmpTlstmCertToTSNFingerprint OBJECT-TYPE
SYNTAX SnmpTLSFingerprint (SIZE(1..255))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a X.509 certificate. The results of
a successful matching fingerprint to either the trusted CA in
the certificate validation path or to the certificate itself
is dictated by the snmpTlstmCertToTSNMapType column."
::= { snmpTlstmCertToTSNEntry 2 }
snmpTlstmCertToTSNMapType OBJECT-TYPE
SYNTAX AutonomousType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"Specifies the mapping type for deriving a tmSecurityName from
a certificate. Details for mapping of a particular type SHALL
be specified in the DESCRIPTION clause of the OBJECT-IDENTITY
that describes the mapping. If a mapping succeeds it will
return a tmSecurityName for use by the TLSTM model and
processing stops.
If the resulting mapped value is not compatible with the
needed requirements of a tmSecurityName (e.g., VACM imposes a
32-octet-maximum length and the certificate derived
securityName could be longer) then future rows MUST be
searched for additional snmpTlstmCertToTSNFingerprint matches
to look for a mapping that succeeds.
Suitable values for assigning to this object that are defined
within the SNMP-TLS-TM-MIB can be found in the
snmpTlstmCertToTSNMIdentities portion of the MIB tree."
DEFVAL { snmpTlstmCertSpecified }
::= { snmpTlstmCertToTSNEntry 3 }
snmpTlstmCertToTSNData OBJECT-TYPE
SYNTAX OCTET STRING (SIZE(0..1024))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"Auxiliary data used as optional configuration information for
a given mapping specified by the snmpTlstmCertToTSNMapType
column. Only some mapping systems will make use of this
column. The value in this column MUST be ignored for any
mapping type that does not require data present in this
column."
DEFVAL { "" }
::= { snmpTlstmCertToTSNEntry 4 }
snmpTlstmCertToTSNStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { snmpTlstmCertToTSNEntry 5 }
snmpTlstmCertToTSNRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, an administrator must set this
object to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are appropriately
configured, the value of the corresponding instance of the
snmpTlstmParamsRowStatus column is notReady(3).
In particular, a newly created row cannot be made active until
the corresponding snmpTlstmCertToTSNFingerprint,
snmpTlstmCertToTSNMapType, and snmpTlstmCertToTSNData columns
have been set.
The following objects may not be modified while the
value of this object is active(1):
- snmpTlstmCertToTSNFingerprint
- snmpTlstmCertToTSNMapType
- snmpTlstmCertToTSNData
An attempt to set these objects while the value of
snmpTlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { snmpTlstmCertToTSNEntry 6 }
-- Maps tmSecurityNames to certificates for use by the SNMP-TARGET-MIB
snmpTlstmParamsCount OBJECT-TYPE
SYNTAX Gauge32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the snmpTlstmParamsTable"
::= { snmpTlstmCertificateMapping 4 }
snmpTlstmParamsTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the snmpTlstmParamsTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { snmpTlstmCertificateMapping 5 }
snmpTlstmParamsTable OBJECT-TYPE
SYNTAX SEQUENCE OF SnmpTlstmParamsEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table is used by a (D)TLS client when a (D)TLS
connection is being set up using an entry in the
SNMP-TARGET-MIB. It extends the SNMP-TARGET-MIB's
snmpTargetParamsTable with a fingerprint of a certificate to
use when establishing such a (D)TLS connection."
::= { snmpTlstmCertificateMapping 6 }
snmpTlstmParamsEntry OBJECT-TYPE
SYNTAX SnmpTlstmParamsEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A conceptual row containing a fingerprint hash of a locally
held certificate for a given snmpTargetParamsEntry. The
values in this row should be ignored if the connection that
needs to be established, as indicated by the SNMP-TARGET-MIB
infrastructure, is not a certificate and (D)TLS based
connection. The connection SHOULD NOT be established if the
certificate fingerprint stored in this entry does not point to
a valid locally held certificate or if it points to an
unusable certificate (such as might happen when the
certificate's expiration date has been reached)."
INDEX { IMPLIED snmpTargetParamsName }
::= { snmpTlstmParamsTable 1 }
SnmpTlstmParamsEntry ::= SEQUENCE {
snmpTlstmParamsClientFingerprint SnmpTLSFingerprint,
snmpTlstmParamsStorageType StorageType,
snmpTlstmParamsRowStatus RowStatus
}
snmpTlstmParamsClientFingerprint OBJECT-TYPE
SYNTAX SnmpTLSFingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"This object stores the hash of the public portion of a
locally held X.509 certificate. The X.509 certificate, its
public key, and the corresponding private key will be used
when initiating a (D)TLS connection as a (D)TLS client."
::= { snmpTlstmParamsEntry 1 }
snmpTlstmParamsStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { snmpTlstmParamsEntry 2 }
snmpTlstmParamsRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, an administrator must set this
object to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are appropriately
configured, the value of the corresponding instance of the
snmpTlstmParamsRowStatus column is notReady(3).
In particular, a newly created row cannot be made active until
the corresponding snmpTlstmParamsClientFingerprint column has
been set.
The snmpTlstmParamsClientFingerprint object may not be modified
while the value of this object is active(1).
An attempt to set these objects while the value of
snmpTlstmParamsRowStatus is active(1) will result in
an inconsistentValue error."
::= { snmpTlstmParamsEntry 3 }
snmpTlstmAddrCount OBJECT-TYPE
SYNTAX Gauge32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"A count of the number of entries in the snmpTlstmAddrTable"
::= { snmpTlstmCertificateMapping 7 }
snmpTlstmAddrTableLastChanged OBJECT-TYPE
SYNTAX TimeStamp
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The value of sysUpTime.0 when the snmpTlstmAddrTable
was last modified through any means, or 0 if it has not been
modified since the command responder was started."
::= { snmpTlstmCertificateMapping 8 }
snmpTlstmAddrTable OBJECT-TYPE
SYNTAX SEQUENCE OF SnmpTlstmAddrEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table is used by a (D)TLS client when a (D)TLS
connection is being set up using an entry in the
SNMP-TARGET-MIB. It extends the SNMP-TARGET-MIB's
snmpTargetAddrTable so that the client can verify that the
correct server has been reached. This verification can use
either a certificate fingerprint, or an identity
authenticated via certification path validation.
If there is an active row in this table corresponding to the
entry in the SNMP-TARGET-MIB that was used to establish the
connection, and the row's snmpTlstmAddrServerFingerprint
column has non-empty value, then the server's presented
certificate is compared with the
snmpTlstmAddrServerFingerprint value (and the
snmpTlstmAddrServerIdentity column is ignored). If the
fingerprint matches, the verification has succeeded. If the
fingerprint does not match then the connection MUST be
closed.
If the server's presented certificate has passed
certification path validation [RFC5280] to a configured
trust anchor, and an active row exists with a zero-length
snmpTlstmAddrServerFingerprint value, then the
snmpTlstmAddrServerIdentity column contains the expected
host name. This expected host name is then compared against
the server's certificate as follows:
- Implementations MUST support matching the expected host
name against a dNSName in the subjectAltName extension
field and MAY support checking the name against the
CommonName portion of the subject distinguished name.
- The '*' (ASCII 0x2a) wildcard character is allowed in the
dNSName of the subjectAltName extension (and in common
name, if used to store the host name), but only as the
left-most (least significant) DNS label in that value.
This wildcard matches any left-most DNS label in the
server name. That is, the subject *.example.com matches
the server names a.example.com and b.example.com, but does
not match example.com or a.b.example.com. Implementations
MUST support wildcards in certificates as specified above,
but MAY provide a configuration option to disable them.
- If the locally configured name is an internationalized
domain name, conforming implementations MUST convert it to
the ASCII Compatible Encoding (ACE) format for performing
comparisons, as specified in Section 7 of [RFC5280].
If the expected host name fails these conditions then the
connection MUST be closed.
If there is no row in this table corresponding to the entry
in the SNMP-TARGET-MIB and the server can be authorized by
another, implementation dependent means, then the connection
MAY still proceed."
::= { snmpTlstmCertificateMapping 9 }
snmpTlstmAddrEntry OBJECT-TYPE
SYNTAX SnmpTlstmAddrEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"A conceptual row containing a copy of a certificate's
fingerprint for a given snmpTargetAddrEntry. The values in
this row should be ignored if the connection that needs to be
established, as indicated by the SNMP-TARGET-MIB
infrastructure, is not a (D)TLS based connection. If an
snmpTlstmAddrEntry exists for a given snmpTargetAddrEntry then
the presented server certificate MUST match or the connection
MUST NOT be established. If a row in this table does not
exist to match a snmpTargetAddrEntry row then the connection
SHOULD still proceed if some other certificate validation path
algorithm (e.g. RFC5280) can be used."
INDEX { IMPLIED snmpTargetAddrName }
::= { snmpTlstmAddrTable 1 }
SnmpTlstmAddrEntry ::= SEQUENCE {
snmpTlstmAddrServerFingerprint SnmpTLSFingerprint,
snmpTlstmAddrServerIdentity SnmpAdminString,
snmpTlstmAddrStorageType StorageType,
snmpTlstmAddrRowStatus RowStatus
}
snmpTlstmAddrServerFingerprint OBJECT-TYPE
SYNTAX SnmpTLSFingerprint
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A cryptographic hash of a public X.509 certificate. This
object should store the hash of the public X.509 certificate
that the remote server should present during the (D)TLS
connection setup. The fingerprint of the presented
certificate and this hash value MUST match exactly or the
connection MUST NOT be established."
DEFVAL { "" }
::= { snmpTlstmAddrEntry 1 }
snmpTlstmAddrServerIdentity OBJECT-TYPE
SYNTAX SnmpAdminString
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The reference identity to check against the identity
presented by the remote system."
DEFVAL { "" }
::= { snmpTlstmAddrEntry 2 }
snmpTlstmAddrStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row. Conceptual rows
having the value 'permanent' need not allow write-access to
any columnar objects in the row."
DEFVAL { nonVolatile }
::= { snmpTlstmAddrEntry 3 }
snmpTlstmAddrRowStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row. This object may be used
to create or remove rows from this table.
To create a row in this table, an administrator must set this
object to either createAndGo(4) or createAndWait(5).
Until instances of all corresponding columns are
appropriately configured, the value of the
corresponding instance of the snmpTlstmAddrRowStatus
column is notReady(3).
In particular, a newly created row cannot be made active until
the corresponding snmpTlstmAddrServerFingerprint column has been
set.
Rows MUST NOT be active if the snmpTlstmAddrServerFingerprint
column is blank and the snmpTlstmAddrServerIdentity is set to
'*' since this would insecurely accept any presented
certificate.
The snmpTlstmAddrServerFingerprint object may not be modified
while the value of this object is active(1).
An attempt to set these objects while the value of
snmpTlstmAddrRowStatus is active(1) will result in
an inconsistentValue error."
::= { snmpTlstmAddrEntry 4 }
-- ************************************************
-- snmpTlstmNotifications - Notifications Information
-- ************************************************
snmpTlstmServerCertificateUnknown NOTIFICATION-TYPE
OBJECTS { snmpTlstmSessionUnknownServerCertificate }
STATUS current
DESCRIPTION
"Notification that the server certificate presented by a SNMP
over (D)TLS server was invalid because no configured
fingerprint or CA was acceptable to validate it. This may be
because there was no entry in the snmpTlstmAddrTable or
because no path could be found to known certificate
authority.
To avoid notification loops, this notification MUST NOT be
sent to servers that themselves have triggered the
notification."
::= { snmpTlstmNotifications 1 }
snmpTlstmServerInvalidCertificate NOTIFICATION-TYPE
OBJECTS { snmpTlstmAddrServerFingerprint,
snmpTlstmSessionInvalidServerCertificates}
STATUS current
DESCRIPTION
"Notification that the server certificate presented by an SNMP
over (D)TLS server could not be validated even if the
fingerprint or expected validation path was known. I.E., a
cryptographic validation error occurred during certificate
validation processing.
To avoid notification loops, this notification MUST NOT be
sent to servers that themselves have triggered the
notification."
::= { snmpTlstmNotifications 2 }
-- ************************************************
-- snmpTlstmCompliances - Conformance Information
-- ************************************************
snmpTlstmCompliances OBJECT IDENTIFIER ::= { snmpTlstmConformance 1 }
snmpTlstmGroups OBJECT IDENTIFIER ::= { snmpTlstmConformance 2 }
-- ************************************************
-- Compliance statements
-- ************************************************
snmpTlstmCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines that support the
SNMP-TLS-TM-MIB"
MODULE
MANDATORY-GROUPS { snmpTlstmStatsGroup,
snmpTlstmIncomingGroup,
snmpTlstmOutgoingGroup,
snmpTlstmNotificationGroup }
::= { snmpTlstmCompliances 1 }
-- ************************************************
-- Units of conformance
-- ************************************************
snmpTlstmStatsGroup OBJECT-GROUP
OBJECTS {
snmpTlstmSessionOpens,
snmpTlstmSessionClientCloses,
snmpTlstmSessionOpenErrors,
snmpTlstmSessionAccepts,
snmpTlstmSessionServerCloses,
snmpTlstmSessionNoSessions,
snmpTlstmSessionInvalidClientCertificates,
snmpTlstmSessionUnknownServerCertificate,
snmpTlstmSessionInvalidServerCertificates,
snmpTlstmSessionInvalidCaches
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
statistical information of an SNMP engine which
implements the SNMP TLS Transport Model."
::= { snmpTlstmGroups 1 }
snmpTlstmIncomingGroup OBJECT-GROUP
OBJECTS {
snmpTlstmCertToTSNCount,
snmpTlstmCertToTSNTableLastChanged,
snmpTlstmCertToTSNFingerprint,
snmpTlstmCertToTSNMapType,
snmpTlstmCertToTSNData,
snmpTlstmCertToTSNStorageType,
snmpTlstmCertToTSNRowStatus
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
incoming connection certificate mappings to
tmSecurityNames of an SNMP engine which implements the
SNMP TLS Transport Model."
::= { snmpTlstmGroups 2 }
snmpTlstmOutgoingGroup OBJECT-GROUP
OBJECTS {
snmpTlstmParamsCount,
snmpTlstmParamsTableLastChanged,
snmpTlstmParamsClientFingerprint,
snmpTlstmParamsStorageType,
snmpTlstmParamsRowStatus,
snmpTlstmAddrCount,
snmpTlstmAddrTableLastChanged,
snmpTlstmAddrServerFingerprint,
snmpTlstmAddrServerIdentity,
snmpTlstmAddrStorageType,
snmpTlstmAddrRowStatus
}
STATUS current
DESCRIPTION
"A collection of objects for maintaining
outgoing connection certificates to use when opening
connections as a result of SNMP-TARGET-MIB settings."
::= { snmpTlstmGroups 3 }
snmpTlstmNotificationGroup NOTIFICATION-GROUP
NOTIFICATIONS {
snmpTlstmServerCertificateUnknown,
snmpTlstmServerInvalidCertificate
}
STATUS current
DESCRIPTION
"Notifications"
::= { snmpTlstmGroups 4 }
END
</artwork>
</figure>
</t>
</section>
<section title="Operational Considerations">
<t>
This section discusses various operational aspects of
deploying TLSTM.
</t>
<section title="Sessions">
<t>
A session is discussed throughout this document as meaning a
security association between two TLSTM instances. State
information for the sessions are maintained in each TLSTM
implementation and this information is created and destroyed
as sessions are opened and closed. A "broken" session (one
side up and one side down) can result if one side of a
session is brought down abruptly (i.e., reboot, power
outage, etc.). Whenever possible, implementations SHOULD
provide graceful session termination through the use of
TLS disconnect messages. Implementations SHOULD also have a
system in place for detecting "broken" sessions through the
use of heartbeats <xref
target="I-D.seggelmann-tls-dtls-heartbeat" /> or other
detection mechanisms.
</t>
<t>
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.
</t>
</section>
<section title="Notification Receiver Credential Selection">
<t>
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 <xref
target="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.
</t>
<t>
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.
</t>
<t>
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.
</t>
</section>
<section title="contextEngineID Discovery">
<t>
SNMPv3 requires that an application know the identifier
(snmpEngineID) of the remote SNMP protocol engine in order to
retrieve or manipulate objects maintained on the remote SNMP
entity.
</t>
<t>
<xref target="RFC5343" /> introduces a well-known
localEngineID and a discovery mechanism that can be used to
learn the snmpEngineID of a remote SNMP protocol engine.
Implementations are RECOMMENDED to support and use the
contextEngineID discovery mechanism defined in <xref
target="RFC5343" />.
</t>
</section>
<section title="Transport Considerations">
<t>
This document defines how SNMP messages can be transmitted
over the TLS and DTLS based protocols. Each of these
protocols are additionally based on other transports (TCP
and UDP). These two base protocols also have operational
considerations that must be taken into consideration when
selecting a (D)TLS based protocol to use such as its
performance in degraded or limited networks. It is beyond
the scope of this document to summarize the characteristics
of these transport mechanisms. Please refer to the base
protocol documents for details on messaging considerations
with respect to MTU size, fragmentation, performance in
lossy-networks, etc.
</t>
</section>
</section>
<section title="Security Considerations"
anchor="securityconsiderations">
<t>
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 <xref target="RFC4347"
/> and security considerations for TLS are described in
Section 11 and Appendices D, E, and F of TLS 1.2 <xref
target="RFC5246" />. When run over a connectionless transport
such as UDP, DTLS is more vulnerable to denial of service
attacks from spoofed IP addresses; see Section
4.2 for details how the cookie exchange is used to address this issue.
</t>
<section title="Certificates, Authentication, and Authorization">
<t>
Implementations are responsible for providing a security
certificate installation and configuration mechanism.
Implementations SHOULD support certificate revocation lists.
</t>
<t>
(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).
</t>
<t>
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.
</t>
<t>
The (D)TLS handshake only provides assurance that the
certificate of the authenticated identity has been signed by
an configured accepted certification authority. (D)TLS has
no way to further authorize or reject access based on the
authenticated identity. An Access Control Model (such as
the VACM) provides access control and authorization of a
command generator's requests to a command responder and a
notification receiver's authorization to receive
Notifications from a notification originator. However to
avoid man-in-the-middle attacks both ends of the (D)TLS
based connection MUST check the certificate presented by the
other side against what was expected. For example, command
generators must check that the command responder presented
and authenticated itself with a X.509 certificate that was
expected. Not doing so would allow an impostor, at a
minimum, to present false data, receive sensitive
information and/or provide a false belief that configuration
was actually received and acted upon. Authenticating and
verifying the identity of the (D)TLS server and the (D)TLS
client for all operations ensures the authenticity of the
SNMP engine that provides MIB data.
</t>
<t>
The instructions found in the DESCRIPTION clause of the
snmpTlstmCertToTSNTable object must be followed exactly. It is also
important that the rows of the table be searched in prioritized order
starting with the row containing the lowest numbered snmpTlstmCertToTSNID
value.
</t>
</section>
<section title="(D)TLS Security Considerations">
<t>This section discusses security considerations specific to
the usage of (D)TLS.</t>
<section title="TLS Version Requirements">
<t>
Implementations of TLS typically support multiple
versions of the Transport Layer Security protocol as well as
the older Secure Sockets Layer (SSL) protocol. Because of
known security vulnerabilities, TLSTM clients and servers
MUST NOT request, offer, or use SSL 2.0. See Appendix E.2
of <xref target="RFC5246" /> for further details.
</t>
</section>
<section title="Perfect Forward Secrecy">
<t>
The use of Perfect Forward Secrecy is RECOMMENDED and can
be provided by (D)TLS with appropriately selected cipher
suites, as discussed in Appendix F of <xref target="RFC5246" />.
</t>
</section>
</section>
<section title="Use with SNMPv1/SNMPv2c Messages">
<t>
<!-- BEGIN copied from RFC5592 -->
The SNMPv1 and SNMPv2c message
processing described in <xref target="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.
<!-- END copied from RFC5592 -->
<!-- Extra text added to provide clarification based on
comment from Dan Romascanu -->
It is RECOMMENDED that only SNMPv3 messages using the
Transport Security Model (TSM) or another
secure-transport aware security model be sent over the
TLSTM transport.
</t>
<t>
Using a non-transport-aware Security Model with a secure
Transport Model is NOT RECOMMENDED. See <xref
target="RFC5590" /> Section 7.1 for additional details on
the coexistence of security-aware transports and
non-transport-aware security models.
</t>
</section>
<section title="MIB Module Security">
<t>
<!-- BEGIN modifications of template from mib-doc-template-xml-04.xml -->
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:
<list style="symbols">
<t>
The snmpTlstmParamsTable can be used to change the outgoing
X.509 certificate used to establish a (D)TLS connection.
Modification to objects in this table need to be
adequately authenticated since modification to values in
this table will have profound impacts to the security of
outbound connections from the device. Since knowledge
of authorization rules and certificate usage mechanisms
may be considered sensitive, protection from disclosure
of the SNMP traffic via encryption is also highly
recommended.
</t>
<t>
The snmpTlstmAddrTable can be used to change the
expectations of the certificates presented by a remote
(D)TLS server. Modification to objects in this table
need to be adequately authenticated since modification
to values in this table will have profound impacts to
the security of outbound connections from the device.
Since knowledge of authorization rules and certificate
usage mechanisms may be considered sensitive, protection
from disclosure of the SNMP traffic via encryption is
also highly recommended.
</t>
<t>
The snmpTlstmCertToTSNTable is used to specify the
mapping of incoming X.509 certificates to
tmSecurityNames which eventually get mapped to a SNMPv3
securityName. Modification to objects in this table
need to be adequately authenticated since modification
to values in this table will have profound impacts to
the security of incoming connections to the device.
Since knowledge of authorization rules and certificate
usage mechanisms may be considered sensitive, protection
from disclosure of the SNMP traffic via encryption is
also highly recommended. When this table contains a
significant number of rows it may affect the system
performance when accepting new (D)TLS connections.
</t>
</list>
</t>
<t>
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:
<list style="symbols">
<t>
This MIB contains a collection of counters that monitor
the (D)TLS connections being established with a device.
Since knowledge of connection and certificate usage
mechanisms may be considered sensitive, protection from
disclosure of the SNMP traffic via encryption is also
highly recommended.
</t>
</list>
</t>
<!-- END modifications of template from mib-doc-template-xml-04.xml -->
<!-- BEGIN copied text from mib-doc-template-xml-04.xml -->
<t>
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.
</t>
<t>
It is RECOMMENDED that implementers consider the security
features as provided by the SNMPv3 framework (see <xref
target="RFC3410"/>, section 8), including full support for
the SNMPv3 cryptographic mechanisms (for authentication and
privacy).
</t>
<t>
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.
</t>
<!-- END copied text from mib-doc-template-xml-04.xml -->
</section>
</section>
<section title="IANA Considerations">
<t>
IANA is requested to assign:
<list style="numbers">
<t>
Two TCP/UDP port numbers from the "Registered Ports" range
of the Port Numbers registry, with the following keywords
(where TBD1 and TBD2 correspond to the assigned port numbers):
<figure>
<artwork>
Keyword Decimal Description References
------- ------- ----------- ----------
snmptls TBD1/tcp SNMP-TLS [RFC-isms-dtls-tm]
snmpdtls TBD1/udp SNMP-DTLS [RFC-isms-dtls-tm]
snmptls-trap TBD2/tcp SNMP-Trap-TLS [RFC-isms-dtls-tm]
snmpdtls-trap TBD2/udp SNMP-Trap-DTLS [RFC-isms-dtls-tm]
</artwork>
</figure>
These are the default ports for receipt of SNMP command
messages (snmptls and snmpdtls) and SNMP notification
messages (snmptls-trap and snmpdtls-trap) over a TLS
Transport Model as defined in this document.
</t>
<t>
An SMI number under snmpDomains for the snmpTLSTCPDomain
object identifier,
</t>
<t>
An SMI number under snmpDomains for the snmpDTLSUDPDomain
object identifier,
</t>
<t>
A SMI number under mib-2, for the MIB module in this
document,
</t>
<t>
"tls" as the corresponding prefix for the snmpTLSTCPDomain
in the SNMP Transport Model registry,
</t>
<t>
"dtls" as the corresponding prefix for the
snmpDTLSUDPDomain in the SNMP Transport Model registry,
</t>
</list>
</t>
<t>
RFC Editor's note: this section should be replaced with
appropriate descriptive assignment text after IANA assignments
are made and prior to publication.
</t>
</section>
<section title="Acknowledgements">
<t>
This document closely follows and copies the Secure Shell
Transport Model for SNMP documented by David Harrington and
Joseph Salowey in <xref target="RFC5592" />.
</t>
<t>
This document was reviewed by the following people who helped
provide useful comments (in alphabetical order): Andy Donati,
Pasi Eronen, David Harrington, Jeffrey Hutzelman, Alan Luchuk,
Michael Peck, Tom Petch, Randy Presuhn, Ray Purvis, Peter
Saint-Andre, Joseph Salowey, Jurgen Schonwalder, Dave Shield,
Robert Story.
</t>
<t>
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.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc1033;
&rfc2119;
&rfc2578;
&rfc2579;
&rfc2580;
&rfc3411;
&rfc3413;
&rfc3414;
&rfc3415;
&rfc3418;
&rfc3490;
&rfc3584;
&rfc4347;
<!-- RFC Editor: the reference below to RFC4366 is correct even
though it's obsolete. The section we're referencing doesn't
exist in the new version. -->
&rfc4366;
&rfc5246;
&rfc5280;
&rfc5590;
&rfc5591;
<reference anchor="I-D.draft-ietf-6man-text-addr-representation">
<front>
<title>A Recommendation for IPv6 Address Text Representation</title>
<author initials="S.K." surname="Kawamura" fullname="Seiichi Kawamura">
<organization>NEC BIGLOBE, Ltd.</organization>
</author>
<author initials="M.K." surname="Kawashima" fullname="Masanobu Kawashima">
<organization>NEC AccessTechnica, Ltd.</organization>
</author>
</front>
</reference>
</references>
<references title="Informative References">
&rfc3410;
&rfc5343;
&rfc5592;
<reference anchor="I-D.seggelmann-tls-dtls-heartbeat">
<front>
<title>Transport Layer Security and Datagram Transport Layer Security Heartbeat Extension</title>
<author initials="R.S." surname="Seggelmann"
fullname="Robin Seggelmann">
<organization>Muenster Univ. of Applied Sciences</organization>
</author>
<author initials="M.T." surname="Tuexen"
fullname="Michael Tuexen">
<organization>Muenster Univ. of Applied Sciences</organization>
</author>
<author initials="M.W." surname="Williams"
fullname="Michael Williams">
</author>
</front>
</reference>
</references>
<section title="Target and Notification Configuration Example" anchor="examples">
<t>
The following sections describe example configuration for the
SNMP-TLS-TM-MIB, the SNMP-TARGET-MIB, the NOTIFICATION-MIB and
the SNMP-VIEW-BASED-ACM-MIB.
</t>
<section title="Configuring a Notification Originator">
<t>The following row adds the "Joe Cool" user to
the "administrators" group:</t>
<t>
<figure>
<artwork>
vacmSecurityModel = 4 (TSM)
vacmSecurityName = "Joe Cool"
vacmGroupName = "administrators"
vacmSecurityToGroupStorageType = 3 (nonVolatile)
vacmSecurityToGroupStatus = 4 (createAndGo)
</artwork>
</figure>
</t>
<t>The following row configures the snmpTlstmAddrTable to use
certificate path validation and to require the remote
notification receiver to present a certificate for the
"server.example.org" identity.</t>
<t>
<figure>
<artwork>
snmpTargetAddrName = "toNRAddr"
snmpTlstmAddrServerFingerprint = ""
snmpTlstmAddrServerIdentity = "server.example.org"
snmpTlstmAddrStorageType = 3 (nonVolatile)
snmpTlstmAddrRowStatus = 4 (createAndGo)
</artwork>
</figure>
</t>
<t>The following row configures the snmpTargetAddrTable to
send notifications using TLS/TCP to the snmptls-trap port at
192.0.2.1:</t>
<t>
<figure>
<artwork>
snmpTargetAddrName = "toNRAddr"
snmpTargetAddrTDomain = snmpTLSTCPDomain
snmpTargetAddrTAddress = "192.0.2.1:XXXsnmptls-trap"
snmpTargetAddrTimeout = 1500
snmpTargetAddrRetryCount = 3
snmpTargetAddrTagList = "toNRTag"
snmpTargetAddrParams = "toNR" (MUST match above)
snmpTargetAddrStorageType = 3 (nonVolatile)
snmpTargetAddrColumnStatus = 4 (createAndGo)
</artwork>
</figure>
</t>
<t>RFC Editor's note: replace the string "XXXsnmptls-trap" above
with the appropriately assigned "snmptls-trap" port.</t>
<t>The following row configures the snmpTargetParamsTable to
send the notifications to "Joe Cool", using authPriv SNMPv3
notifications through the TransportSecurityModel [RFC5591]:</t>
<t>
<figure>
<artwork>
snmpTargetParamsName = toNR
snmpTargetParamsMPModel = SNMPv3
snmpTargetParamsSecurityModel = 4 (TransportSecurityModel)
snmpTargetParamsSecurityName = "Joe Cool"
snmpTargetParamsSecurityLevel = 3 (authPriv)
snmpTargetParamsStorageType = 3 (nonVolatile)
snmpTargetParamsRowStatus = 4 (createAndGo0
</artwork>
</figure>
</t>
</section>
<section title="Configuring TLSTM to Utilize a Simple Derivation of tmSecurityName">
<t>The following row configures the snmpTlstmCertToTSNTable to
map a validated client certificate, referenced by the client's
public X.509 hash fingerprint, to a tmSecurityName using the
subjectAltName component of the certificate.</t>
<t>
<figure>
<artwork>
snmpTlstmCertToTSNID = 1
(chosen by ordering preference)
snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
snmpTlstmCertToTSNMapType = snmpTlstmCertSANAny
snmpTlstmCertToTSNData = "" (not used)
snmpTlstmCertToTSNStorageType = 3 (nonVolatile)
snmpTlstmCertToTSNRowStatus = 4 (createAndGo)
</artwork>
</figure>
</t>
<t>This type of configuration should only be used when the naming
conventions of the (possibly multiple) certificate authorities are
well understood, so two different principals cannot inadvertently be
identified by the same derived tmSecurityName.</t>
</section>
<section title="Configuring TLSTM to Utilize Table-Driven Certificate Mapping">
<t>The following row configures the snmpTlstmCertToTSNTable to
map a validated client certificate, referenced by the client's
public X.509 hash fingerprint, to the directly specified
tmSecurityName of "Joe Cool".</t>
<t>
<figure>
<artwork>
snmpTlstmCertToTSNID = 1
(chosen by ordering preference)
snmpTlstmCertToTSNFingerprint = HASH (appropriate fingerprint)
snmpTlstmCertToTSNMapType = snmpTlstmCertSpecified
snmpTlstmCertToTSNSecurityName = "Joe Cool"
snmpTlstmCertToTSNStorageType = 3 (nonVolatile)
snmpTlstmCertToTSNRowStatus = 4 (createAndGo)
</artwork>
</figure>
</t>
</section>
</section>
</back>
</rfc>
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