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Network Working Group D. Black
Request for Comments: 4088 EMC Corporation
Category: Standards Track K. McCloghrie
Cisco Systems
J. Schoenwaelder
International University Bremen
June 2005
Uniform Resource Identifier (URI) Scheme for the
Simple Network Management Protocol (SNMP)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The Simple Network Management Protocol (SNMP) and the Internet
Standard Management Framework are widely used for the management of
communication devices, creating a need to specify SNMP access
(including access to SNMP MIB object instances) from non-SNMP
management environments. For example, when out-of-band IP management
is used via a separate management interface (e.g., for a device that
does not support in-band IP access), a uniform way to indicate how to
contact the device for management is needed. Uniform Resource
Identifiers (URIs) fit this need well, as they allow a single text
string to indicate a management access communication endpoint for a
wide variety of IP-based protocols.
This document defines a URI scheme so that SNMP can be designated as
the protocol used for management. The scheme also allows a URI to
designate one or more MIB object instances.
Black, et al. Standards Track [Page 1]
RFC 4088 URI Scheme for SNMP June 2005
Table of Contents
1. Introduction.................................................. 2
2. Usage......................................................... 3
3. Syntax of an SNMP URI......................................... 4
3.1. Relative Reference Considerations........................ 5
4. Semantics and Operations...................................... 6
4.1. SNMP Service URIs........................................ 6
4.2. SNMP Object URIs......................................... 7
4.2.1. SNMP Object URI Data Access....................... 8
4.3. OID Groups in SNMP URIs.................................. 10
4.4. Interoperability Considerations.......................... 10
5. Examples...................................................... 11
6. Security Considerations....................................... 12
6.1. SNMP URI to SNMP Gateway Security Considerations......... 13
7. IANA Considerations........................................... 14
8. Normative References.......................................... 14
9. Informative References........................................ 15
10. Acknowledgements............................................. 16
Appendix A. Registration Template................................ 17
1. Introduction
SNMP and the Internet-Standard Management Framework were originally
devised to manage IP devices via in-band means, in which management
access is primarily via the same interface(s) used to send and
receive IP traffic. SNMP's wide adoption has resulted in its use for
managing communication devices that do not support in-band IP access
(e.g., Fibre Channel devices); a separate out-of-band IP interface is
often used for management. URIs provide a convenient way to locate
that interface and specify the protocol to be used for management;
one possible scenario is for an in-band query to return a URI that
indicates how the device is managed. This document specifies a URI
scheme to permit SNMP (including a specific SNMP context) to be
designated as the management protocol by such a URI. This scheme
also allows a URI to refer to specific object instances within an
SNMP MIB.
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to Section 7 of
[RFC3410].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Black, et al. Standards Track [Page 2]
RFC 4088 URI Scheme for SNMP June 2005
2. Usage
There are two major classes of SNMP URI usage: configuration and
gateways between SNMP and other protocols that use SNMP URIs.
An SNMP URI used for configuration indicates the location of
management information as part of the configuration of an application
containing an SNMP manager. The URI can be obtained from a
configuration file or may be provided by a managed device (see
Section 1 for an example). Management information is exchanged
between the SNMP manager and agent, but it does not flow beyond the
manager, as shown in the following diagram:
*********** SNMP-Request *********
* *================>* *
URI ---------->* Manager * * Agent *
* *<================* *
*********** SNMP-Response *********
^
|
Other Config Info ------------+
Additional configuration information (e.g., a security secret or key)
may be provided via an interface other than that used for the URI.
For example, when a managed device provides an SNMP URI in an
unprotected fashion, that device should not provide a secret or key
required to use the URI. The secret or key should instead be pre-
configured in or pre-authorized to the manager; see Section 6.
For gateway usage, clients employ SNMP URIs to request management
information via an SNMP URI to SNMP gateway (also called an SNMP
gateway in this document). The SNMP manager within the SNMP gateway
accesses the management information and returns it to the requesting
client, as shown in the following diagram:
SNMP gateway
********** URI *********** SNMP-Request *********
* *===========>* *================>* *
* Client * * Manager * * Agent *
* *<===========* *<================* *
********** Info *********** SNMP-Response *********
^
|
Other Config Info ------------+
Additional configuration information (e.g., security secrets or keys)
may be provided via an interface other than that used for the URI.
For example, some types of security information, including secrets
Black, et al. Standards Track [Page 3]
RFC 4088 URI Scheme for SNMP June 2005
and keys, should be pre-configured in or pre-authorized to the
manager rather than be provided by the client; see Section 6.
3. Syntax of an SNMP URI
An SNMP URI has the following ABNF [RFC2234] syntax, based on the
ABNF syntax rules for userinfo, host, port, and (path) segment in
[RFC3986] and the ABNF syntax rule for HEXDIG in [RFC2234]:
snmp-uri = "snmp://" snmp-authority [ context [ oids ]]
snmp-authority = [ securityName "@" ] host [ ":" port ]
securityName = userinfo ; SNMP securityName
context = "/" contextName [ ";" contextEngineID ]
contextName = segment ; SNMP contextName
contextEngineID = 1*(HEXDIG HEXDIG) ; SNMP contextEngineID
oids = "/" ( oid / oid-group ) [ suffix ]
oid-group = "(" oid *( "," oid ) ")"
oid = < as specified by [RFC 3061] >
suffix = "+" / ".*"
The userinfo and (path) segment ABNF rules are reused for syntax
only. In contrast, host and port have both the syntax and semantics
specified in [RFC3986]. See [RFC3411] for the semantics of
securityName, contextEngineID, and contextName.
The snmp-authority syntax matches the URI authority syntax in Section
3.2 of [RFC3986], with the additional restriction that the userinfo
component of an authority (when present) MUST be an SNMP
securityName. If the securityName is empty or not given, the entity
making use of an SNMP URI is expected to know what SNMP securityName
to use if one is required. Inclusion of authentication information
(e.g., passwords) in URIs has been deprecated (see Section 3.2.1 of
[RFC3986]), so any secret or key required for SNMP access must be
provided via other means that may be out-of-band with respect to
communication of the URI. If the port is empty or not given, port
161 is assumed.
If the contextName is empty or not given, the zero-length string ("")
is assumed, as it is the default SNMP context. An SNMP
contextEngineID is a variable-format binary element that is usually
discovered by an SNMP manager. An SNMP URI encodes a contextEngineID
as hexadecimal digits corresponding to a sequence of bytes. If the
contextEngineID is empty or not given, the context engine is to be
discovered by querying the SNMP agent at the specified host and port;
see Section 4.1 below. The contextEngineID component of the URI
Black, et al. Standards Track [Page 4]
RFC 4088 URI Scheme for SNMP June 2005
SHOULD be present if more than one context engine at the designated
host and port supports the designated context.
An SNMP URI that designates the default SNMP context ("") MAY end
with the "/" character that introduces the contextName component. An
SNMP URI MUST NOT end with the "/" character that introduces an oid
or oid-group component, as the empty string is not a valid OID for
SNMP.
The encoding rules specified in [RFC3986] MUST be used for SNMP URIs,
including the use of percent encoding ("%" followed by two hex
digits) as needed to represent characters defined as reserved in
[RFC3986] and any characters not allowed in a URI. SNMP permits any
UTF-8 character to be used in a securityName or contextName; all
multi-byte UTF-8 characters in an SNMP URI MUST be percent encoded as
specified in Sections 2.1 and 2.5 of [RFC3986]. These requirements
are a consequence of reusing the ABNF syntax rules for userinfo and
segment from [RFC3986].
SNMP URIs will generally be short enough to avoid implementation
string-length limits (e.g., that may occur at 255 characters). Such
limits may be a concern for large OID groups; relative references to
URIs (see Section 4.2 of [RFC3986]) may provide an alternative in
some circumstances.
Use of IP addresses in SNMP URIs is acceptable in situations where
dependence on availability of DNS service is undesirable or must be
avoided; otherwise, IP addresses should not be used (see [RFC1900]
for further explanation).
3.1. Relative Reference Considerations
Use of the SNMP default context (zero-length string) within an SNMP
URI can result in a second instance of "//" in the URI, such as the
following:
snmp://<host>//<oid>
This is allowed by [RFC3986] syntax; if a URI parser does not handle
the second "//" correctly, the parser is broken and needs to be
fixed. This example is important because use of the SNMP default
context in SNMP URIs is expected to be common.
On the other hand, the second occurrence of "//" in an absolute SNMP
URI affects usage of relative references to that URI (see Section 4.2
of [RFC3986]) because a "//" at the start of a relative reference
always introduces a URI authority component (host plus optional
userinfo and/or port; see [RFC3986]). Specifically, a relative
Black, et al. Standards Track [Page 5]
RFC 4088 URI Scheme for SNMP June 2005
reference of the form //<oid2> will not work, because the "//" will
cause <oid2> to be parsed as a URI authority, resulting in a syntax
error when the parser fails to find a host in <oid2> . To avoid this
problem, relative references that start with "//" but do not contain
a URI authority component MUST NOT be used. Functionality equivalent
to any such forbidden relative reference can be obtained by prefixing
"." or ".." to the forbidden relative reference (e.g., ..//<oid2>).
The prefix to use depends on the base URI.
4. Semantics and Operations
An SNMP URI that does not include any OIDs is called an SNMP service
URI because it designates a communication endpoint for access to SNMP
management service. An SNMP URI that includes one or more OIDs is
called an SNMP object URI because it designates one or more object
instances in an SNMP MIB. The expected means of using an SNMP URI is
to employ an SNMP manager to access the SNMP context designated by
the URI via the SNMP agent at the host and port designated by the
URI.
4.1. SNMP Service URIs
An SNMP service URI does not designate a data object, but rather an
SNMP context to be accessed by a service; the telnet URI scheme
[RFC1738] is another example of URIs that designate service access.
If the contextName in the URI is empty or not given, "" (the zero-
length string) is assumed, as it is the default SNMP context.
If a contextEngineID is given in an SNMP service URI, the context
engine that it designates is to be used. If the contextEngineID is
empty or not given in the URI, the context engine is to be
discovered; the context engine to be used is the one that supports
the context designated by the URI. The contextEngineID component of
the URI SHOULD be present if more than one context engine at the
designated host and port supports the designated context.
Many common uses of SNMP URIs are expected to omit (i.e., default)
the contextEngineID because they do not involve SNMP proxy agents,
which are the most common reason for multiple SNMP context engines to
exist at a single host and port. Specifically, when an SNMP agent is
local to the network interface that it manages, the agent will
usually have only one context engine, in which case it is safe to
omit the contextEngineID component of an SNMP URI. In addition, many
SNMP agents that are local to a network interface support only the
default SNMP context (zero-length string).
Black, et al. Standards Track [Page 6]
RFC 4088 URI Scheme for SNMP June 2005
4.2. SNMP Object URIs
An SNMP object URI contains one or more OIDs. The URI is used by
first separating the OID or OID group (including its preceding slash
plus any parentheses and suffix) and then processing the resulting
SNMP service URI as specified in Section 4.1 (above) to determine the
SNMP context to be accessed. The OID or OID group is then used to
generate SNMP operations directed to that SNMP context.
The semantics of an SNMP object URI depend on whether the OID or OID
group has a suffix and what that suffix is. There are three possible
formats; in each case, the MIB object instances are designated within
the SNMP context specified by the service URI portion of the SNMP
object URI. The semantics of an SNMP object URI that contains a
single OID are as follows:
(1) An OID without a suffix designates the MIB object instance
named by the OID.
(2) An OID with a "+" suffix designates the lexically next MIB
object instance following the OID.
(3) An OID with a ".*" suffix designates the set of MIB object
instances for which the OID is a strict lexical prefix; this
does not include the MIB object instance named by the OID.
An OID group in an SNMP URI consists of a set of OIDs in parentheses.
In each case, the OID group semantics are the extension of the single
OID semantics to each OID in the group (e.g., a URI with a "+" suffix
designates the set of MIB object instances consisting of the
lexically next instance for each OID in the OID group).
When there is a choice among URI formats to designate the same MIB
object instance or instances, the above list is in order of
preference (no suffix is most preferable), as it runs from most
precise to least precise. This is because an OID without a suffix
precisely designates an object instance, whereas a "+" suffix
designates the next object instance, which may change, and the ".*"
suffix could designate multiple object instances. Multiple
syntactically distinct SNMP URIs SHOULD NOT be used to designate the
same MIB object instance or set of instances, as this may cause
unexpected results in URI-based systems that use string comparison to
test URIs for equality.
SNMP object URIs designate the data to be accessed, as opposed to the
specific SNMP operations to be used for access; Section 4.2.1
provides examples of how SNMP operations can be used to access data
for SNMP object URIs. Nonetheless, any applicable SNMP operation,
Black, et al. Standards Track [Page 7]
RFC 4088 URI Scheme for SNMP June 2005
including GetBulk, MAY be used to access data for all or part of one
or more SNMP object URIs (e.g., via use of multiple variable bindings
in a single operation); it is not necessary to use the specific
operations described in Section 4.2.1 as long as the results
(returned variable bindings or error) could have been obtained by
following Section 4.2.1's descriptions. The use of relative
references that do not change the contextName (i.e., ./<oid>) should
be viewed as a hint that optimization of SNMP access across multiple
SNMP URIs may be possible.
An SNMP object URI MAY also be used to specify a MIB object instance
or instances to be written; this causes generation of an SNMP Set
operation instead of a Get. The "+" and ".*" suffixes MUST NOT be
used in this case; any attempt to do so is an error that MUST NOT
generate any SNMP Set operations. Values to be written to the MIB
object instance or instances are not specified within an SNMP object
URI.
SNMP object URIs designate data in SNMP MIBs and hence do not provide
the means to generate all possible SNMP protocol operations. For
example, data access for an SNMP object URI cannot directly generate
either Snmpv2-Trap or InformRequest notifications, although side
effects of data access could cause such notifications (depending on
the MIB). In addition, whether and how GetBulk is used for an SNMP
object URI with a ".*" suffix is implementation specific.
4.2.1. SNMP Object URI Data Access
Data access based on an SNMP object URI returns an SNMP variable
binding for each MIB object instance designated by the URI, or an
SNMP error if the operation fails. An SNMP variable binding binds a
variable name (OID) to a value or an SNMP exception (see [RFC3416]).
The SNMP operation or operations needed to access data designated by
an SNMP object URI depend on the OID or OID group suffix or absence
thereof. The following descriptions are not the only method of
performing data access for an SNMP object URI; any suitable SNMP
operations may be used as long as the results (returned variable
bindings or error) are functionally equivalent.
(1) For an OID or OID group without a suffix, an SNMP Get
operation is generated using each OID as a variable binding
name. If an SNMP error occurs, that error is the result of
URI data access; otherwise, the returned variable binding or
bindings are the result of URI data access. Note that any
returned variable binding may contain an SNMP "noSuchObject"
or "noSuchInstance" exception.
Black, et al. Standards Track [Page 8]
RFC 4088 URI Scheme for SNMP June 2005
(2) For an OID or OID group with a "+" suffix, an SNMP GetNext
operation is generated using each OID as a variable binding
name. If an SNMP error occurs, that error is the result of
URI data access; otherwise, the returned variable binding or
bindings are the result of URI data access. Note that any
returned variable binding may contain an SNMP "endOfMibView"
exception.
(3) For an OID or OID group with a ".*" suffix, an SNMP GetNext
operation is initially generated using each OID as a variable
binding name. If the result is an SNMP error, that error is
the result of URI data access. If all returned variable
bindings contain either a) an OID for which the corresponding
URI OID is not a lexical prefix or b) an SNMP "endOfMibView"
exception, then the returned variable bindings are the result
of URI data access.
Otherwise, the results of the GetNext operation are saved, and
another SNMP GetNext operation is generated using the newly
returned OIDs as variable binding names. This is repeated
(save the results and generate a GetNext with newly returned
OIDs as variable binding names) until all the returned
variable bindings from a GetNext contain either a) an OID for
which the corresponding URI OID is not a lexical prefix or b)
an SNMP "endOfMibView" exception. The results from all of the
GetNext operations are combined to become the overall result
of URI data access; this may include variable bindings whose
OID is not a lexical extension of the corresponding URI OID.
If the OID subtrees (set of OIDs for which a specific URI OID
is a lexical prefix) are not the same size for all OIDs in the
OID group, the largest subtree determines when this iteration
ends. SNMP GetBulk operations MAY be used to optimize this
iterated access.
Whenever a returned variable binding contains an OID for which
the corresponding URI OID is not a lexical prefix or an SNMP
"endOfMibView" exception, iteration of that element of the OID
group MAY cease, reducing the number of variable bindings used
in subsequent GetNext operations. In this case, the results
of URI data access for the SNMP URI will not consist entirely
of OID-group-sized sets of variable bindings. Even if this
does not occur, the last variable binding returned for each
member of the OID group will generally contain an SNMP
"endOfMibView" exception or an OID for which the corresponding
URI OID is not a lexical prefix.
Black, et al. Standards Track [Page 9]
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4.3. OID Groups in SNMP URIs
Parenthesized OID groups in SNMP URIs are intended to support MIB
object instances for which access via a single SNMP operation is
required to ensure consistent results. Therefore, the OIDs within an
OID group in an SNMP URI SHOULD be accessed by a single SNMP
operation containing a variable binding corresponding to each OID in
the group. A specific example involves the InetAddress and
InetAddressType textual conventions defined in [RFC4001], for which
the format of an InetAddress instance is specified by an associated
InetAddressType instance. If two such associated instances are read
via separate SNMP operations, the resulting values could be
inconsistent (e.g., due to an intervening Set), causing the
InetAddress value to be interpreted incorrectly.
This single operation requirement ("SHOULD") also applies to each OID
group resulting from iterated access for an SNMP URI with a ".*"
suffix. When members of an SNMP URI OID group differ in the number
of OIDs for which each is a lexical prefix, this iteration may
overrun by returning numerous variable bindings for which the
corresponding OID in the OID group is not a lexical prefix. Such
overrun can be avoided by using relative references within the same
context (i.e., ./<oid>.* ) when it is not important to access
multiple MIB object instances in a single SNMP operation.
4.4. Interoperability Considerations
This document defines a transport-independent "snmp" scheme that is
intended to accommodate SNMP transports other than UDP. UDP is the
default transport for access to information specified by an SNMP URI
for backward compatibility with existing usage, but other transports
MAY be used. If more than one transport can be used (e.g., SNMP over
TCP [RFC3430] in addition to SNMP over UDP), the information or SNMP
service access designated by an SNMP URI SHOULD NOT depend on which
transport is used (for SNMP over TCP, this is implied by Section 2 of
[RFC3430]).
An SNMP URI designates use of SNMPv3 as specified by [RFC3416],
[RFC3417], and related documents, but older versions of SNMP MAY be
used in accordance with [RFC3584] when usage of such older versions
is unavoidable. For SNMPv1 and SNMPv2c, the securityName,
contextName, and contextEngineID elements of an SNMP URI are mapped
to/from the community name, as described in [RFC3584]. When the
community name is kept secret as a weak form of authentication, this
mapping should be configured so that these three elements do not
reveal information about the community name. If this is not done,
then any SNMP URI component that would disclose significant
information about a secret community name SHOULD be omitted. Note
Black, et al. Standards Track [Page 10]
RFC 4088 URI Scheme for SNMP June 2005
that some community names contain reserved characters (e.g., "@")
that require percent encoding when they are used in an SNMP URI.
SNMP versions (e.g., v3) have been omitted from the SNMP URI scheme
to permit use of older versions of SNMP, as well as any possible
future successor to SNMPv3.
5. Examples
snmp://example.com
This example designates the default SNMP context at the SNMP agent at
port 161 of host example.com .
snmp://tester5@example.com:8161
This example designates the default SNMP context at the SNMP agent at
port 8161 of host example.com and indicates that the SNMP
securityName "tester5" is to be used to access that agent. A
possible reason to use a non-standard port is for testing a new
version of SNMP agent code.
snmp://example.com/bridge1
This example designates the "bridge1" SNMP context at example.com.
Because the contextEngineID component of the URI is omitted, there
SHOULD be at most one SNMP context engine at example.com that
supports the "bridge1" context.
snmp://example.com/bridge1;800002b804616263
This example designates the "bridge1" context at snmp.example.com via
the SNMP context engine 800002b804616263 (string representation of a
hexadecimal value). This avoids ambiguity if any other context
engine supports a "bridge1" context. The above two examples are
based on the figure in Section 3.3 of [RFC3411].
snmp://example.com//1.3.6.1.2.1.1.3.0
snmp://example.com//1.3.6.1.2.1.1.3+
snmp://example.com//1.3.6.1.2.1.1.3.*
These three examples all designate the sysUpTime.0 object instance in
the SNMPv2-MIB or RFC1213-MIB for the default SNMP context ("") at
example.com as sysUpTime.0 is:
a) designated directly by OID 1.3.6.1.2.1.1.3.0,
b) the lexically next MIB object instance after the OID
1.3.6.1.2.1.1.3, and
Black, et al. Standards Track [Page 11]
RFC 4088 URI Scheme for SNMP June 2005
c) the only MIB object instance whose OID has 1.3.6.1.2.1.1.3 as a
lexical prefix.
These three examples are provided for illustrative purposes only, as
multiple syntactically distinct URIs SHOULD NOT be used to designate
the same MIB object instance, in order to avoid unexpected results in
URI-based systems that use string comparison to test URIs for
equality.
snmp://example.com/bridge1/1.3.6.1.2.1.2.2.1.8.*
This example designates the ifOperStatus column of the IF-MIB in the
bridge1 SNMP context at example.com.
snmp://example.com//(1.3.6.1.2.1.2.2.1.7,1.3.6.1.2.1.2.2.1.8).*
This example designates all (ifAdminStatus, ifOperStatus) pairs in
the IF-MIB in the default SNMP context at example.com.
6. Security Considerations
An intended use of this URI scheme is designation of the location of
management access to communication devices. Such location
information may be considered sensitive in some environments, making
it important to control access to this information and possibly even
to encrypt it when it is sent over the network. All uses of this URI
scheme should provide security mechanisms appropriate to the
environments in which such uses are likely to be deployed.
The SNMP architecture includes control of access to management
information (see Section 4.3 of [RFC3411]). An SNMP URI does not
contain sufficient security information to obtain access in all
situations, as the SNMP URI syntax is incapable of encoding SNMP
securityModels, SNMP securityLevels, and credential or keying
information for SNMP securityNames. Other means are necessary to
provide such information; one possibility is out-of-band pre-
configuration of the SNMP manager, as shown in the diagrams in
Section 2.
By itself, the presence of a securityName in an SNMP URI does not
authorize use of that securityName to access management information.
Instead, the SNMP manager SHOULD match the securityName in the URI to
an SNMP securityName and associated security information that have
been pre-configured for use by the manager. If an SNMP URI contains
a securityName that the SNMP manager is not provisioned to use, SNMP
operations for that URI SHOULD NOT be generated.
Black, et al. Standards Track [Page 12]
RFC 4088 URI Scheme for SNMP June 2005
SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example, via use of IPsec),
there is no control over who on the secure network is allowed to
access and GET/SET (read/change/create/delete) the objects in MIB
modules. It is RECOMMENDED that implementers consider the security
features provided by the SNMPv3 framework (see [RFC3410], Section 8,
for an overview), including full support for SNMPv3 cryptographic
mechanisms (for authentication and privacy). This is of additional
importance for MIB elements considered sensitive or vulnerable
because GETs have side effects.
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 a MIB
module instance is properly configured to give access to the objects
only to those principals (users) that have legitimate rights to
indeed GET or SET (read/change/create/delete) them.
6.1. SNMP URI to SNMP Gateway Security Considerations
Additional security considerations apply to SNMP gateways that
generate SNMP operations for SNMP URIs and return the results to
clients (see Section 2) because management information is
communicated beyond the SNMP framework. In general, an SNMP gateway
should have some knowledge of the structure and function of the
management information that it accesses via SNMP. Among other
benefits, this allows an SNMP gateway to avoid SNMP access control
failures because the gateway can reject an SNMP URI that will cause
such failures before generating any SNMP operations.
SNMP gateways SHOULD impose authorization or access-control checks on
all clients. If an SNMP gateway does not impose authorization or
access controls, the gateway MUST NOT automatically obtain or use
SNMP authentication material for arbitrary securityNames, as doing so
would defeat SNMP's access controls. Instead, all SNMP gateways
SHOULD authenticate each client and check the client's authorization
to use a securityName in an SNMP URI before using the securityName on
behalf of that client.
An SNMP gateway is also responsible for ensuring that all of its
communication is appropriately secured. Specifically, an SNMP
gateway SHOULD ensure that communication of management information
with any client is protected to at least the SNMP securityLevel used
for the corresponding SNMP access (see Section 3.4.3 of [RFC3411] for
more information on securityLevel). If the client provides SNMP
security information, the SNMP gateway SHOULD authenticate the client
and SHOULD ensure that an authenticated cryptographic integrity check
Black, et al. Standards Track [Page 13]
RFC 4088 URI Scheme for SNMP June 2005
is used for that communication to prevent modification of the
security information. In addition, if a client provides any key or
secret, the SNMP gateway SHOULD ensure that encryption is used in
addition to the integrity check for that communication to prevent
disclosure of keys or secrets.
There are management objects defined in SNMP MIBs whose MAX-ACCESS is
read-write and/or read-create. Such objects may be considered
sensitive or vulnerable in some network environments. SNMP gateway
support for SNMP SET operations in a non-secure environment without
proper protection can have a negative effect on network operations.
The individual MIB module specifications, and especially their
security considerations, should be consulted for further information.
Some readable objects in some MIB modules (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 access to these objects via an SNMP gateway and
possibly to even encrypt the values of these objects when they are
sent over the network. The individual MIB module specifications, and
especially their security considerations, should be consulted for
further information. This consideration also applies to objects for
which read operations have side effects.
7. IANA Considerations
The IANA has registered the URL registration template found in
Appendix A in accordance with [RFC2717].
8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC3061] Mealling, M., "A URN Namespace of Object Identifiers", RFC
3061, February 2001.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
December 2002.
[RFC3416] Presuhn, R., "Version 2 of the Protocol Operations for the
Simple Network Management Protocol (SNMP)", STD 62, RFC
3416, December 2002.
Black, et al. Standards Track [Page 14]
RFC 4088 URI Scheme for SNMP June 2005
[RFC3417] Presuhn, R., "Transport Mappings for the Simple Network
Management Protocol (SNMP)", STD 62, RFC 3417, December
2002.
[RFC3584] Frye, R., Levi, D., Routhier, S., and B. Wijnen,
"Coexistence between Version 1, Version 2, and Version 3 of
the Internet-standard Network Management Framework", BCP
74, RFC 3584, August 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC
3986, January 2005.
9. Informative References
[RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, December 1994.
[RFC1900] Carpenter, B. and Y. Rekhter, "Renumbering Needs Work", RFC
1900, February 1996.
[RFC2717] Petke, R. and I. King, "Registration Procedures for URL
Scheme Names", BCP 35, RFC 2717, November 1999.
[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410, December 2002.
[RFC3430] Schoenwaelder, J., "Simple Network Management Protocol Over
Transmission Control Protocol Transport Mapping", RFC 3430,
December 2002.
[RFC3617] Lear, E., "Uniform Resource Identifier (URI) Scheme and
Applicability Statement for the Trivial File Transfer
Protocol (TFTP)", RFC 3617, October 2003.
[RFC4001] Daniele, M., Haberman, B., Routhier, S., and J.
Schoenwaelder, "Textual Conventions for Internet Network
Addresses", RFC 4001, February 2005.
Black, et al. Standards Track [Page 15]
RFC 4088 URI Scheme for SNMP June 2005
10. Acknowledgements
Portions of this document were adapted from Eliot Lear's TFTP URI
scheme specification [RFC3617]. Portions of the security
considerations were adapted from the widely used security
considerations "boilerplate" for MIB modules. Comments from Ted
Hardie, Michael Mealing, Larry Masinter, Frank Strauss, Bert Wijnen,
Steve Bellovin, the mreview@ops.ietf.org mailing list and the
uri@w3c.org mailing list on earlier versions of this document have
resulted in significant improvements and are gratefully acknowledged.
Black, et al. Standards Track [Page 16]
RFC 4088 URI Scheme for SNMP June 2005
Appendix A. Registration Template
URL scheme name: snmp
URL scheme syntax: Section 3
Character encoding considerations: Section 3
Intended usage: Sections 1 and 2
Applications and/or protocols which use this scheme: SNMP, all
versions, see [RFC3410] and [RFC3584]. Also SNMP over TCP,
see [RFC3430].
Interoperability considerations: Section 4.4
Security considerations: Section 6
Relevant publications: See [RFC3410] for list. Also [RFC3430]
and [RFC3584].
Contact: David L. Black, see below
Author/Change Controller: IESG
Authors' Addresses
David L. Black
EMC Corporation
176 South Street
Hopkinton, MA 01748
Phone: +1 (508) 293-7953
EMail: black_david@emc.com
Keith McCloghrie
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA USA 95134
Phone: +1 (408) 526-5260
EMail: kzm@cisco.com
Juergen Schoenwaelder
International University Bremen
P.O. Box 750 561
28725 Bremen
Germany
Phone: +49 421 200 3587
EMail: j.schoenwaelder@iu-bremen.de
Black, et al. Standards Track [Page 17]
RFC 4088 URI Scheme for SNMP June 2005
Full Copyright Statement
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Black, et al. Standards Track [Page 18]
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