RFC 2575
Network Working Group B. Wijnen
Request for Comments: 2575 IBM T. J. Watson Research
Obsoletes: RFC 2275 R. Presuhn
Category: Standards Track BMC Software, Inc.
K. McCloghrie
Cisco Systems, Inc.
April 1999
View-based Access Control Model (VACM) 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 (1999). All Rights Reserved.
Abstract
This document describes the View-based Access Control Model for use
in the SNMP architecture [RFC2571]. It defines the Elements of
Procedure for controlling access to management information. This
document also includes a MIB for remotely managing the configuration
parameters for the View-based Access Control Model.
Table of Contents
1. Introduction 2
1.2. Access Control 3
1.3. Local Configuration Datastore 3
2. Elements of the Model 3
2.1. Groups 3
2.2. securityLevel 4
2.3. Contexts 4
2.4. MIB Views and View Families 4
2.4.1. View Subtree 5
2.4.2. ViewTreeFamily 5
2.5. Access Policy 6
3. Elements of Procedure 6
3.1. Overview of isAccessAllowed Process 8
3.2. Processing the isAccessAllowed Service Request 9
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4. Definitions 10
5. Intellectual Property 27
6. Acknowledgements 28
7. Security Considerations 29
7.1. Recommended Practices 29
7.2. Defining Groups 30
7.3. Conformance 30
7.4. Access to the SNMP-VIEW-BASED-ACM-MIB 30
8. References 31
9. Editors' Addresses 32
A.1. Installation Parameters 33
B. Change Log 37
C. Full Copyright Statement 38
1. Introduction
The Architecture for describing Internet Management Frameworks
[RFC2571] describes that an SNMP engine is composed of:
1) a Dispatcher
2) a Message Processing Subsystem,
3) a Security Subsystem, and
4) an Access Control Subsystem.
Applications make use of the services of these subsystems.
It is important to understand the SNMP architecture and its
terminology to understand where the View-based Access Control Model
described in this document fits into the architecture and interacts
with other subsystems within the architecture. The reader is
expected to have read and understood the description and terminology
of the SNMP architecture, as defined in [RFC2571].
The Access Control Subsystem of an SNMP engine has the responsibility
for checking whether a specific type of access (read, write, notify)
to a particular object (instance) is allowed.
It is the purpose of this document to define a specific model of the
Access Control Subsystem, designated the View-based Access Control
Model. Note that this is not necessarily the only Access Control
Model.
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].
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1.2. Access Control
Access Control occurs (either implicitly or explicitly) in an SNMP
entity when processing SNMP retrieval or modification request
messages from an SNMP entity. For example a Command Responder
application applies Access Control when processing requests that it
received from a Command Generator application. These requests
contain Read Class and Write Class PDUs as defined in [RFC2571].
Access Control also occurs in an SNMP entity when an SNMP
notification message is generated (by a Notification Originator
application). These notification messages contain Notification Class
PDUs as defined in [RFC2571].
The View-based Access Control Model defines a set of services that an
application (such as a Command Responder or a Notification Originator
application) can use for checking access rights. It is the
responsibility of the application to make the proper service calls
for access checking.
1.3. Local Configuration Datastore
To implement the model described in this document, an SNMP entity
needs to retain information about access rights and policies. This
information is part of the SNMP engine's Local Configuration
Datastore (LCD). See [RFC2571] for the definition of LCD.
In order to allow an SNMP entity's LCD to be remotely configured,
portions of the LCD need to be accessible as managed objects. A MIB
module, the View-based Access Control Model Configuration MIB, which
defines these managed object types is included in this document.
2. Elements of the Model
This section contains definitions to realize the access control
service provided by the View-based Access Control Model.
2.1. Groups
A group is a set of zero or more tuples
on whose behalf SNMP management objects can be accessed. A group
defines the access rights afforded to all securityNames which belong
to that group. The combination of a securityModel and a securityName
maps to at most one group. A group is identified by a groupName.
The Access Control module assumes that the securityName has already
been authenticated as needed and provides no further authentication
of its own.
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The View-based Access Control Model uses the securityModel and the
securityName as inputs to the Access Control module when called to
check for access rights. It determines the groupName as a function
of securityModel and securityName.
2.2. securityLevel
Different access rights for members of a group can be defined for
different levels of security, i.e., noAuthNoPriv, authNoPriv, and
authPriv. The securityLevel identifies the level of security that
will be assumed when checking for access rights. See the SNMP
Architecture document [RFC2571] for a definition of securityLevel.
The View-based Access Control Model requires that the securityLevel
is passed as input to the Access Control module when called to check
for access rights.
2.3. Contexts
An SNMP context is a collection of management information accessible
by an SNMP entity. An item of management information may exist in
more than one context. An SNMP entity potentially has access to many
contexts. Details about the naming of management information can be
found in the SNMP Architecture document [RFC2571].
The View-based Access Control Model defines a vacmContextTable that
lists the locally available contexts by contextName.
2.4. MIB Views and View Families
For security reasons, it is often valuable to be able to restrict the
access rights of some groups to only a subset of the management
information in the management domain. To provide this capability,
access to a context is via a "MIB view" which details a specific set
of managed object types (and optionally, the specific instances of
object types) within that context. For example, for a given context,
there will typically always be one MIB view which provides access to
all management information in that context, and often there will be
other MIB views each of which contains some subset of the
information. So, the access allowed for a group can be restricted in
the desired manner by specifying its rights in terms of the
particular (subset) MIB view it can access within each appropriate
context.
Since managed object types (and their instances) are identified via
the tree-like naming structure of ISO's OBJECT IDENTIFIERs [ISO-
ASN.1, RFC2578], it is convenient to define a MIB view as the
combination of a set of "view subtrees", where each view subtree is a
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subtree within the managed object naming tree. Thus, a simple MIB
view (e.g., all managed objects within the Internet Network
Management Framework) can be defined as a single view subtree, while
more complicated MIB views (e.g., all information relevant to a
particular network interface) can be represented by the union of
multiple view subtrees.
While any set of managed objects can be described by the union of
some number of view subtrees, situations can arise that would require
a very large number of view subtrees. This could happen, for
example, when specifying all columns in one conceptual row of a MIB
table because they would appear in separate subtrees, one per column,
each with a very similar format. Because the formats are similar,
the required set of subtrees can easily be aggregated into one
structure. This structure is named a family of view subtrees after
the set of subtrees that it conceptually represents. A family of
view subtrees can either be included or excluded from a MIB view.
2.4.1. View Subtree
A view subtree is the set of all MIB object instances which have a
common ASN.1 OBJECT IDENTIFIER prefix to their names. A view subtree
is identified by the OBJECT IDENTIFIER value which is the longest
OBJECT IDENTIFIER prefix common to all (potential) MIB object
instances in that subtree.
2.4.2. ViewTreeFamily
A family of view subtrees is a pairing of an OBJECT IDENTIFIER value
(called the family name) together with a bit string value (called the
family mask). The family mask indicates which sub-identifiers of the
associated family name are significant to the family's definition.
For each possible managed object instance, that instance belongs to a
particular ViewTreeFamily if both of the following conditions are
true:
- the OBJECT IDENTIFIER name of the managed object instance
contains at least as many sub-identifiers as does the family name,
and
- each sub-identifier in the OBJECT IDENTIFIER name of the managed
object instance matches the corresponding sub-identifier of the
family name whenever the corresponding bit of the associated family
mask is non-zero.
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When the configured value of the family mask is all ones, the view
subtree family is identical to the single view subtree identified by
the family name.
When the configured value of the family mask is shorter than required
to perform the above test, its value is implicitly extended with
ones. Consequently, a view subtree family having a family mask of
zero length always corresponds to a single view subtree.
2.5. Access Policy
The View-based Access Control Model determines the access rights of a
group, representing zero or more securityNames which have the same
access rights. For a particular context, identified by contextName,
to which a group, identified by groupName, has access using a
particular securityModel and securityLevel, that group's access
rights are given by a read-view, a write-view and a notify-view.
The read-view represents the set of object instances authorized for
the group when reading objects. Reading objects occurs when
processing a retrieval operation (when handling Read Class PDUs).
The write-view represents the set of object instances authorized for
the group when writing objects. Writing objects occurs when
processing a write operation (when handling Write Class PDUs).
The notify-view represents the set of object instances authorized for
the group when sending objects in a notification, such as when
sending a notification (when sending Notification Class PDUs).
3. Elements of Procedure
This section describes the procedures followed by an Access Control
module that implements the View-based Access Control Model when
checking access rights as requested by an application (for example a
Command Responder or a Notification Originator application). The
abstract service primitive is:
statusInformation = -- success or errorIndication
isAccessAllowed(
securityModel -- Security Model in use
securityName -- principal who wants access
securityLevel -- Level of Security
viewType -- read, write, or notify view
contextName -- context containing variableName
variableName -- OID for the managed object
)
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The abstract data elements are:
statusInformation - one of the following:
accessAllowed - a MIB view was found and access is granted.
notInView - a MIB view was found but access is denied.
The variableName is not in the configured
MIB view for the specified viewType (e.g., in
the relevant entry in the vacmAccessTable).
noSuchView - no MIB view found because no view has been
configured for specified viewType (e.g., in
the relevant entry in the vacmAccessTable).
noSuchContext - no MIB view found because of no entry in the
vacmContextTable for specified contextName.
noGroupName - no MIB view found because no entry has been
configured in the vacmSecurityToGroupTable
for the specified combination of
securityModel and securityName.
noAccessEntry - no MIB view found because no entry has been
configured in the vacmAccessTable for the
specified combination of contextName,
groupName (from vacmSecurityToGroupTable),
securityModel and securityLevel.
otherError - failure, an undefined error occurred.
securityModel - Security Model under which access is requested.
securityName - the principal on whose behalf access is requested.
securityLevel - Level of Security under which access is requested.
viewType - view to be checked (read, write or notify).
contextName - context in which access is requested.
variableName - object instance to which access is requested.
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3.1. Overview of isAccessAllowed Process
The following picture shows how the decision for access control is made
by the View-based Access Control Model.
+--------------------------------------------------------------------+
| |
| +-> securityModel -+ |
| | (a) | |
| who -+ +-> groupName ----+ |
| (1) | | (x) | |
| +-> securityName --+ | |
| (b) | |
| | |
| where -> contextName ---------------------+ |
| (2) (e) | |
| | |
| | |
| +-> securityModel -------------------+ |
| | (a) | |
| how -+ +-> viewName -+ |
| (3) | | (y) | |
| +-> securityLevel -------------------+ | |
| (c) | +-> yes/no |
| | | decision |
| why ---> viewType (read/write/notify) ----+ | (z) |
| (4) (d) | |
| | |
| what --> object-type ------+ | |
| (5) (m) | | |
| +-> variableName (OID) ------+ |
| | (f) |
| which -> object-instance --+ |
| (6) (n) |
| |
+--------------------------------------------------------------------+
How the decision for isAccessAllowed is made.
1) Inputs to the isAccessAllowed service are:
(a) securityModel -- Security Model in use
(b) securityName -- principal who wants to access
(c) securityLevel -- Level of Security
(d) viewType -- read, write, or notify view
(e) contextName -- context containing variableName
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(f) variableName -- OID for the managed object
-- this is made up of:
- object-type (m)
- object-instance (n)
2) The partial "who" (1), represented by the securityModel (a) and
the securityName (b), are used as the indices (a,b) into the
vacmSecurityToGroupTable to find a single entry that produces a
group, represented by groupName (x).
3) The "where" (2), represented by the contextName (e), the "who",
represented by the groupName (x) from the previous step, and the
"how" (3), represented by securityModel (a) and securityLevel (c),
are used as indices (e,x,a,c) into the vacmAccessTable to find a
single entry that contains three MIB views.
4) The "why" (4), represented by the viewType (d), is used to select
the proper MIB view, represented by a viewName (y), from the
vacmAccessEntry selected in the previous step. This viewName (y) is
an index into the vacmViewTreeFamilyTable and selects the set of
entries that define the variableNames which are included in or
excluded from the MIB view identified by the viewName (y).
5) The "what" (5) type of management data and "which" (6) particular
instance, represented by the variableName (f), is then checked to be
in the MIB view or not, e.g., the yes/no decision (z).
3.2. Processing the isAccessAllowed Service Request
This section describes the procedure followed by an Access Control
module that implements the View-based Access Control Model whenever
it receives an isAccessAllowed request.
1) The vacmContextTable is consulted for information about
the SNMP context identified by the contextName. If information
about this SNMP context is absent from the table, then an
errorIndication (noSuchContext) is returned to the calling module.
2) The vacmSecurityToGroupTable is consulted for mapping the
securityModel and securityName to a groupName. If the information
about this combination is absent from the table, then an
errorIndication (noGroupName) is returned to the calling module.
3) The vacmAccessTable is consulted for information about the
groupName, contextName, securityModel and securityLevel. If
information about this combination is absent from the table, then
an errorIndication (noAccessEntry) is returned to the calling
module.
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4) a) If the viewType is "read", then the read view is used for
checking access rights.
b) If the viewType is "write", then the write view is used for
checking access rights.
c) If the viewType is "notify", then the notify view is used
for checking access rights.
If the view to be used is the empty view (zero length viewName)
then an errorIndication (noSuchView) is returned to the calling
module.
5) a) If there is no view configured for the specified viewType,
then an errorIndication (noSuchView) is returned to the calling
module.
b) If the specified variableName (object instance) is not in the
MIB view (see DESCRIPTION clause for vacmViewTreeFamilyTable in
section 4), then an errorIndication (notInView) is returned to
the calling module.
Otherwise,
c) The specified variableName is in the MIB view.
A statusInformation of success (accessAllowed) is returned to
the calling module.
4. Definitions
SNMP-VIEW-BASED-ACM-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
MODULE-IDENTITY, OBJECT-TYPE,
snmpModules FROM SNMPv2-SMI
TestAndIncr,
RowStatus, StorageType FROM SNMPv2-TC
SnmpAdminString,
SnmpSecurityLevel,
SnmpSecurityModel FROM SNMP-FRAMEWORK-MIB;
snmpVacmMIB MODULE-IDENTITY
LAST-UPDATED "9901200000Z" -- 20 Jan 1999, midnight
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG-email: snmpv3@lists.tislabs.com
Subscribe: majordomo@lists.tislabs.com
In message body: subscribe snmpv3
Wijnen, et al. Standards Track [Page 10]
RFC 2575 VACM for SNMP April 1999
Chair: Russ Mundy
Trusted Information Systems
postal: 3060 Washington Rd
Glenwood MD 21738
USA
email: mundy@tislabs.com
phone: +1-301-854-6889
Co-editor: Bert Wijnen
IBM T.J. Watson Research
postal: Schagen 33
3461 GL Linschoten
Netherlands
email: wijnen@vnet.ibm.com
phone: +31-348-432-794
Co-editor: Randy Presuhn
BMC Software, Inc
postal: 965 Stewart Drive
Sunnyvale, CA 94086
USA
email: randy_presuhn@bmc.com
phone: +1-408-616-3100
Co-editor: Keith McCloghrie
Cisco Systems, Inc.
postal: 170 West Tasman Drive
San Jose, CA 95134-1706
USA
email: kzm@cisco.com
phone: +1-408-526-5260
"
DESCRIPTION "The management information definitions for the
View-based Access Control Model for SNMP.
"
-- Revision history
REVISION "9901200000Z" -- 20 Jan 1999, midnight
DESCRIPTION "Clarifications, published as RFC2575"
REVISION "9711200000Z" -- 20 Nov 1997, midnight
DESCRIPTION "Initial version, published as RFC2275"
::= { snmpModules 16 }
-- Administrative assignments ****************************************
vacmMIBObjects OBJECT IDENTIFIER ::= { snmpVacmMIB 1 }
vacmMIBConformance OBJECT IDENTIFIER ::= { snmpVacmMIB 2 }
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-- Information about Local Contexts **********************************
vacmContextTable OBJECT-TYPE
SYNTAX SEQUENCE OF VacmContextEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The table of locally available contexts.
This table provides information to SNMP Command
Generator applications so that they can properly
configure the vacmAccessTable to control access to
all contexts at the SNMP entity.
This table may change dynamically if the SNMP entity
allows that contexts are added/deleted dynamically
(for instance when its configuration changes). Such
changes would happen only if the management
instrumentation at that SNMP entity recognizes more
(or fewer) contexts.
The presence of entries in this table and of entries
in the vacmAccessTable are independent. That is, a
context identified by an entry in this table is not
necessarily referenced by any entries in the
vacmAccessTable; and the context(s) referenced by an
entry in the vacmAccessTable does not necessarily
currently exist and thus need not be identified by an
entry in this table.
This table must be made accessible via the default
context so that Command Responder applications have
a standard way of retrieving the information.
This table is read-only. It cannot be configured via
SNMP.
"
::= { vacmMIBObjects 1 }
vacmContextEntry OBJECT-TYPE
SYNTAX VacmContextEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "Information about a particular context."
INDEX {
vacmContextName
}
::= { vacmContextTable 1 }
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VacmContextEntry ::= SEQUENCE
{
vacmContextName SnmpAdminString
}
vacmContextName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-only
STATUS current
DESCRIPTION "A human readable name identifying a particular
context at a particular SNMP entity.
The empty contextName (zero length) represents the
default context.
"
::= { vacmContextEntry 1 }
-- Information about Groups ******************************************
vacmSecurityToGroupTable OBJECT-TYPE
SYNTAX SEQUENCE OF VacmSecurityToGroupEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "This table maps a combination of securityModel and
securityName into a groupName which is used to define
an access control policy for a group of principals.
"
::= { vacmMIBObjects 2 }
vacmSecurityToGroupEntry OBJECT-TYPE
SYNTAX VacmSecurityToGroupEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "An entry in this table maps the combination of a
securityModel and securityName into a groupName.
"
INDEX {
vacmSecurityModel,
vacmSecurityName
}
::= { vacmSecurityToGroupTable 1 }
VacmSecurityToGroupEntry ::= SEQUENCE
{
vacmSecurityModel SnmpSecurityModel,
vacmSecurityName SnmpAdminString,
vacmGroupName SnmpAdminString,
vacmSecurityToGroupStorageType StorageType,
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vacmSecurityToGroupStatus RowStatus
}
vacmSecurityModel OBJECT-TYPE
SYNTAX SnmpSecurityModel(1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The Security Model, by which the vacmSecurityName
referenced by this entry is provided.
Note, this object may not take the 'any' (0) value.
"
::= { vacmSecurityToGroupEntry 1 }
vacmSecurityName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The securityName for the principal, represented in a
Security Model independent format, which is mapped by
this entry to a groupName.
"
::= { vacmSecurityToGroupEntry 2 }
vacmGroupName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The name of the group to which this entry (e.g., the
combination of securityModel and securityName)
belongs.
This groupName is used as index into the
vacmAccessTable to select an access control policy.
However, a value in this table does not imply that an
instance with the value exists in table vacmAccesTable.
"
::= { vacmSecurityToGroupEntry 3 }
vacmSecurityToGroupStorageType 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 }
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::= { vacmSecurityToGroupEntry 4 }
vacmSecurityToGroupStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The status of this conceptual row.
Until instances of all corresponding columns are
appropriately configured, the value of the
corresponding instance of the vacmSecurityToGroupStatus
column is 'notReady'.
In particular, a newly created row cannot be made
active until a value has been set for vacmGroupName.
The RowStatus TC [RFC2579] requires that this
DESCRIPTION clause states under which circumstances
other objects in this row can be modified:
The value of this object has no effect on whether
other objects in this conceptual row can be modified.
"
::= { vacmSecurityToGroupEntry 5 }
-- Information about Access Rights ***********************************
vacmAccessTable OBJECT-TYPE
SYNTAX SEQUENCE OF VacmAccessEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The table of access rights for groups.
Each entry is indexed by a groupName, a contextPrefix,
a securityModel and a securityLevel. To determine
whether access is allowed, one entry from this table
needs to be selected and the proper viewName from that
entry must be used for access control checking.
To select the proper entry, follow these steps:
1) the set of possible matches is formed by the
intersection of the following sets of entries:
the set of entries with identical vacmGroupName
the union of these two sets:
- the set with identical vacmAccessContextPrefix
- the set of entries with vacmAccessContextMatch
value of 'prefix' and matching
Wijnen, et al. Standards Track [Page 15]
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vacmAccessContextPrefix
intersected with the union of these two sets:
- the set of entries with identical
vacmSecurityModel
- the set of entries with vacmSecurityModel
value of 'any'
intersected with the set of entries with
vacmAccessSecurityLevel value less than or equal
to the requested securityLevel
2) if this set has only one member, we're done
otherwise, it comes down to deciding how to weight
the preferences between ContextPrefixes,
SecurityModels, and SecurityLevels as follows:
a) if the subset of entries with securityModel
matching the securityModel in the message is
not empty, then discard the rest.
b) if the subset of entries with
vacmAccessContextPrefix matching the contextName
in the message is not empty,
then discard the rest
c) discard all entries with ContextPrefixes shorter
than the longest one remaining in the set
d) select the entry with the highest securityLevel
Please note that for securityLevel noAuthNoPriv, all
groups are really equivalent since the assumption that
the securityName has been authenticated does not hold.
"
::= { vacmMIBObjects 4 }
vacmAccessEntry OBJECT-TYPE
SYNTAX VacmAccessEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "An access right configured in the Local Configuration
Datastore (LCD) authorizing access to an SNMP context.
Entries in this table can use an instance value for
object vacmGroupName even if no entry in table
vacmAccessSecurityToGroupTable has a corresponding
value for object vacmGroupName.
"
INDEX { vacmGroupName,
vacmAccessContextPrefix,
vacmAccessSecurityModel,
vacmAccessSecurityLevel
}
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RFC 2575 VACM for SNMP April 1999
::= { vacmAccessTable 1 }
VacmAccessEntry ::= SEQUENCE
{
vacmAccessContextPrefix SnmpAdminString,
vacmAccessSecurityModel SnmpSecurityModel,
vacmAccessSecurityLevel SnmpSecurityLevel,
vacmAccessContextMatch INTEGER,
vacmAccessReadViewName SnmpAdminString,
vacmAccessWriteViewName SnmpAdminString,
vacmAccessNotifyViewName SnmpAdminString,
vacmAccessStorageType StorageType,
vacmAccessStatus RowStatus
}
vacmAccessContextPrefix OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "In order to gain the access rights allowed by this
conceptual row, a contextName must match exactly
(if the value of vacmAccessContextMatch is 'exact')
or partially (if the value of vacmAccessContextMatch
is 'prefix') to the value of the instance of this
object.
"
::= { vacmAccessEntry 1 }
vacmAccessSecurityModel OBJECT-TYPE
SYNTAX SnmpSecurityModel
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "In order to gain the access rights allowed by this
conceptual row, this securityModel must be in use.
"
::= { vacmAccessEntry 2 }
vacmAccessSecurityLevel OBJECT-TYPE
SYNTAX SnmpSecurityLevel
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The minimum level of security required in order to
gain the access rights allowed by this conceptual
row. A securityLevel of noAuthNoPriv is less than
authNoPriv which in turn is less than authPriv.
If multiple entries are equally indexed except for
this vacmAccessSecurityLevel index, then the entry
Wijnen, et al. Standards Track [Page 17]
RFC 2575 VACM for SNMP April 1999
which has the highest value for
vacmAccessSecurityLevel is selected.
"
::= { vacmAccessEntry 3 }
vacmAccessContextMatch OBJECT-TYPE
SYNTAX INTEGER
{ exact (1), -- exact match of prefix and contextName
prefix (2) -- Only match to the prefix
}
MAX-ACCESS read-create
STATUS current
DESCRIPTION "If the value of this object is exact(1), then all
rows where the contextName exactly matches
vacmAccessContextPrefix are selected.
If the value of this object is prefix(2), then all
rows where the contextName whose starting octets
exactly match vacmAccessContextPrefix are selected.
This allows for a simple form of wildcarding.
"
DEFVAL { exact }
::= { vacmAccessEntry 4 }
vacmAccessReadViewName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The value of an instance of this object identifies
the MIB view of the SNMP context to which this
conceptual row authorizes read access.
The identified MIB view is that one for which the
vacmViewTreeFamilyViewName has the same value as the
instance of this object; if the value is the empty
string or if there is no active MIB view having this
value of vacmViewTreeFamilyViewName, then no access
is granted.
"
DEFVAL { ''H } -- the empty string
::= { vacmAccessEntry 5 }
vacmAccessWriteViewName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The value of an instance of this object identifies
the MIB view of the SNMP context to which this
Wijnen, et al. Standards Track [Page 18]
RFC 2575 VACM for SNMP April 1999
conceptual row authorizes write access.
The identified MIB view is that one for which the
vacmViewTreeFamilyViewName has the same value as the
instance of this object; if the value is the empty
string or if there is no active MIB view having this
value of vacmViewTreeFamilyViewName, then no access
is granted.
"
DEFVAL { ''H } -- the empty string
::= { vacmAccessEntry 6 }
vacmAccessNotifyViewName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The value of an instance of this object identifies
the MIB view of the SNMP context to which this
conceptual row authorizes access for notifications.
The identified MIB view is that one for which the
vacmViewTreeFamilyViewName has the same value as the
instance of this object; if the value is the empty
string or if there is no active MIB view having this
value of vacmViewTreeFamilyViewName, then no access
is granted.
"
DEFVAL { ''H } -- the empty string
::= { vacmAccessEntry 7 }
vacmAccessStorageType 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 }
::= { vacmAccessEntry 8 }
vacmAccessStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The status of this conceptual row.
Wijnen, et al. Standards Track [Page 19]
RFC 2575 VACM for SNMP April 1999
The RowStatus TC [RFC2579] requires that this
DESCRIPTION clause states under which circumstances
other objects in this row can be modified:
The value of this object has no effect on whether
other objects in this conceptual row can be modified.
"
::= { vacmAccessEntry 9 }
-- Information about MIB views ***************************************
-- Support for instance-level granularity is optional.
--
-- In some implementations, instance-level access control
-- granularity may come at a high performance cost. Managers
-- should avoid requesting such configurations unnecessarily.
vacmMIBViews OBJECT IDENTIFIER ::= { vacmMIBObjects 5 }
vacmViewSpinLock OBJECT-TYPE
SYNTAX TestAndIncr
MAX-ACCESS read-write
STATUS current
DESCRIPTION "An advisory lock used to allow cooperating SNMP
Command Generator applications to coordinate their
use of the Set operation in creating or modifying
views.
When creating a new view or altering an existing
view, it is important to understand the potential
interactions with other uses of the view. The
vacmViewSpinLock should be retrieved. The name of
the view to be created should be determined to be
unique by the SNMP Command Generator application by
consulting the vacmViewTreeFamilyTable. Finally,
the named view may be created (Set), including the
advisory lock.
If another SNMP Command Generator application has
altered the views in the meantime, then the spin
lock's value will have changed, and so this creation
will fail because it will specify the wrong value for
the spin lock.
Since this is an advisory lock, the use of this lock
is not enforced.
"
::= { vacmMIBViews 1 }
Wijnen, et al. Standards Track [Page 20]
RFC 2575 VACM for SNMP April 1999
vacmViewTreeFamilyTable OBJECT-TYPE
SYNTAX SEQUENCE OF VacmViewTreeFamilyEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "Locally held information about families of subtrees
within MIB views.
Each MIB view is defined by two sets of view subtrees:
- the included view subtrees, and
- the excluded view subtrees.
Every such view subtree, both the included and the
excluded ones, is defined in this table.
To determine if a particular object instance is in
a particular MIB view, compare the object instance's
OBJECT IDENTIFIER with each of the MIB view's active
entries in this table. If none match, then the
object instance is not in the MIB view. If one or
more match, then the object instance is included in,
or excluded from, the MIB view according to the
value of vacmViewTreeFamilyType in the entry whose
value of vacmViewTreeFamilySubtree has the most
sub-identifiers. If multiple entries match and have
the same number of sub-identifiers (when wildcarding
is specified with the value of vacmViewTreeFamilyMask),
then the lexicographically greatest instance of
vacmViewTreeFamilyType determines the inclusion or
exclusion.
An object instance's OBJECT IDENTIFIER X matches an
active entry in this table when the number of
sub-identifiers in X is at least as many as in the
value of vacmViewTreeFamilySubtree for the entry,
and each sub-identifier in the value of
vacmViewTreeFamilySubtree matches its corresponding
sub-identifier in X. Two sub-identifiers match
either if the corresponding bit of the value of
vacmViewTreeFamilyMask for the entry is zero (the
'wild card' value), or if they are equal.
A 'family' of subtrees is the set of subtrees defined
by a particular combination of values of
vacmViewTreeFamilySubtree and vacmViewTreeFamilyMask.
In the case where no 'wild card' is defined in the
vacmViewTreeFamilyMask, the family of subtrees reduces
to a single subtree.
When creating or changing MIB views, an SNMP Command
Wijnen, et al. Standards Track [Page 21]
RFC 2575 VACM for SNMP April 1999
Generator application should utilize the
vacmViewSpinLock to try to avoid collisions. See
DESCRIPTION clause of vacmViewSpinLock.
When creating MIB views, it is strongly advised that
first the 'excluded' vacmViewTreeFamilyEntries are
created and then the 'included' entries.
When deleting MIB views, it is strongly advised that
first the 'included' vacmViewTreeFamilyEntries are
deleted and then the 'excluded' entries.
If a create for an entry for instance-level access
control is received and the implementation does not
support instance-level granularity, then an
inconsistentName error must be returned.
"
::= { vacmMIBViews 2 }
vacmViewTreeFamilyEntry OBJECT-TYPE
SYNTAX VacmViewTreeFamilyEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "Information on a particular family of view subtrees
included in or excluded from a particular SNMP
context's MIB view.
Implementations must not restrict the number of
families of view subtrees for a given MIB view,
except as dictated by resource constraints on the
overall number of entries in the
vacmViewTreeFamilyTable.
If no conceptual rows exist in this table for a given
MIB view (viewName), that view may be thought of as
consisting of the empty set of view subtrees.
"
INDEX { vacmViewTreeFamilyViewName,
vacmViewTreeFamilySubtree
}
::= { vacmViewTreeFamilyTable 1 }
VacmViewTreeFamilyEntry ::= SEQUENCE
{
vacmViewTreeFamilyViewName SnmpAdminString,
vacmViewTreeFamilySubtree OBJECT IDENTIFIER,
vacmViewTreeFamilyMask OCTET STRING,
vacmViewTreeFamilyType INTEGER,
Wijnen, et al. Standards Track [Page 22]
RFC 2575 VACM for SNMP April 1999
vacmViewTreeFamilyStorageType StorageType,
vacmViewTreeFamilyStatus RowStatus
}
vacmViewTreeFamilyViewName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The human readable name for a family of view subtrees.
"
::= { vacmViewTreeFamilyEntry 1 }
vacmViewTreeFamilySubtree OBJECT-TYPE
SYNTAX OBJECT IDENTIFIER
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The MIB subtree which when combined with the
corresponding instance of vacmViewTreeFamilyMask
defines a family of view subtrees.
"
::= { vacmViewTreeFamilyEntry 2 }
vacmViewTreeFamilyMask OBJECT-TYPE
SYNTAX OCTET STRING (SIZE (0..16))
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The bit mask which, in combination with the
corresponding instance of vacmViewTreeFamilySubtree,
defines a family of view subtrees.
Each bit of this bit mask corresponds to a
sub-identifier of vacmViewTreeFamilySubtree, with the
most significant bit of the i-th octet of this octet
string value (extended if necessary, see below)
corresponding to the (8*i - 7)-th sub-identifier, and
the least significant bit of the i-th octet of this
octet string corresponding to the (8*i)-th
sub-identifier, where i is in the range 1 through 16.
Each bit of this bit mask specifies whether or not
the corresponding sub-identifiers must match when
determining if an OBJECT IDENTIFIER is in this
family of view subtrees; a '1' indicates that an
exact match must occur; a '0' indicates 'wild card',
i.e., any sub-identifier value matches.
Thus, the OBJECT IDENTIFIER X of an object instance
is contained in a family of view subtrees if, for
Wijnen, et al. Standards Track [Page 23]
RFC 2575 VACM for SNMP April 1999
each sub-identifier of the value of
vacmViewTreeFamilySubtree, either:
the i-th bit of vacmViewTreeFamilyMask is 0, or
the i-th sub-identifier of X is equal to the i-th
sub-identifier of the value of
vacmViewTreeFamilySubtree.
If the value of this bit mask is M bits long and
there are more than M sub-identifiers in the
corresponding instance of vacmViewTreeFamilySubtree,
then the bit mask is extended with 1's to be the
required length.
Note that when the value of this object is the
zero-length string, this extension rule results in
a mask of all-1's being used (i.e., no 'wild card'),
and the family of view subtrees is the one view
subtree uniquely identified by the corresponding
instance of vacmViewTreeFamilySubtree.
Note that masks of length greater than zero length
do not need to be supported. In this case this
object is made read-only.
"
DEFVAL { ''H }
::= { vacmViewTreeFamilyEntry 3 }
vacmViewTreeFamilyType OBJECT-TYPE
SYNTAX INTEGER { included(1), excluded(2) }
MAX-ACCESS read-create
STATUS current
DESCRIPTION "Indicates whether the corresponding instances of
vacmViewTreeFamilySubtree and vacmViewTreeFamilyMask
define a family of view subtrees which is included in
or excluded from the MIB view.
"
DEFVAL { included }
::= { vacmViewTreeFamilyEntry 4 }
vacmViewTreeFamilyStorageType 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
Wijnen, et al. Standards Track [Page 24]
RFC 2575 VACM for SNMP April 1999
allow write-access to any columnar objects in the row.
"
DEFVAL { nonVolatile }
::= { vacmViewTreeFamilyEntry 5 }
vacmViewTreeFamilyStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION "The status of this conceptual row.
The RowStatus TC [RFC2579] requires that this
DESCRIPTION clause states under which circumstances
other objects in this row can be modified:
The value of this object has no effect on whether
other objects in this conceptual row can be modified.
"
::= { vacmViewTreeFamilyEntry 6 }
-- Conformance information *******************************************
vacmMIBCompliances OBJECT IDENTIFIER ::= { vacmMIBConformance 1 }
vacmMIBGroups OBJECT IDENTIFIER ::= { vacmMIBConformance 2 }
-- Compliance statements *********************************************
vacmMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION "The compliance statement for SNMP engines which
implement the SNMP View-based Access Control Model
configuration MIB.
"
MODULE -- this module
MANDATORY-GROUPS { vacmBasicGroup }
OBJECT vacmAccessContextMatch
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT vacmAccessReadViewName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT vacmAccessWriteViewName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
Wijnen, et al. Standards Track [Page 25]
RFC 2575 VACM for SNMP April 1999
OBJECT vacmAccessNotifyViewName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT vacmAccessStorageType
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT vacmAccessStatus
MIN-ACCESS read-only
DESCRIPTION "Create/delete/modify access to the
vacmAccessTable is not required.
"
OBJECT vacmViewTreeFamilyMask
WRITE-SYNTAX OCTET STRING (SIZE (0))
MIN-ACCESS read-only
DESCRIPTION "Support for configuration via SNMP of subtree
families using wild-cards is not required.
"
OBJECT vacmViewTreeFamilyType
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT vacmViewTreeFamilyStorageType
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT vacmViewTreeFamilyStatus
MIN-ACCESS read-only
DESCRIPTION "Create/delete/modify access to the
vacmViewTreeFamilyTable is not required.
"
::= { vacmMIBCompliances 1 }
-- Units of conformance **********************************************
vacmBasicGroup OBJECT-GROUP
OBJECTS {
vacmContextName,
vacmGroupName,
vacmSecurityToGroupStorageType,
vacmSecurityToGroupStatus,
vacmAccessContextMatch,
vacmAccessReadViewName,
vacmAccessWriteViewName,
vacmAccessNotifyViewName,
Wijnen, et al. Standards Track [Page 26]
RFC 2575 VACM for SNMP April 1999
vacmAccessStorageType,
vacmAccessStatus,
vacmViewSpinLock,
vacmViewTreeFamilyMask,
vacmViewTreeFamilyType,
vacmViewTreeFamilyStorageType,
vacmViewTreeFamilyStatus
}
STATUS current
DESCRIPTION "A collection of objects providing for remote
configuration of an SNMP engine which implements
the SNMP View-based Access Control Model.
"
::= { vacmMIBGroups 1 }
END
5. Intellectual Property
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
Wijnen, et al. Standards Track [Page 27]
RFC 2575 VACM for SNMP April 1999
6. Acknowledgements
This document is the result of the efforts of the SNMPv3 Working
Group. Some special thanks are in order to the following SNMPv3 WG
members:
Harald Tveit Alvestrand (Maxware)
Dave Battle (SNMP Research, Inc.)
Alan Beard (Disney Worldwide Services)
Paul Berrevoets (SWI Systemware/Halcyon Inc.)
Martin Bjorklund (Ericsson)
Uri Blumenthal (IBM T.J. Watson Research Center)
Jeff Case (SNMP Research, Inc.)
John Curran (BBN)
Mike Daniele (Compaq Computer Corporation)
T. Max Devlin (Eltrax Systems)
John Flick (Hewlett Packard)
Rob Frye (MCI)
Wes Hardaker (U.C.Davis, Information Technology - D.C.A.S.)
David Harrington (Cabletron Systems Inc.)
Lauren Heintz (BMC Software, Inc.)
N.C. Hien (IBM T.J. Watson Research Center)
Michael Kirkham (InterWorking Labs, Inc.)
Dave Levi (SNMP Research, Inc.)
Louis A Mamakos (UUNET Technologies Inc.)
Joe Marzot (Nortel Networks)
Paul Meyer (Secure Computing Corporation)
Keith McCloghrie (Cisco Systems)
Bob Moore (IBM)
Russ Mundy (TIS Labs at Network Associates)
Bob Natale (ACE*COMM Corporation)
Mike O'Dell (UUNET Technologies Inc.)
Dave Perkins (DeskTalk)
Peter Polkinghorne (Brunel University)
Randy Presuhn (BMC Software, Inc.)
David Reeder (TIS Labs at Network Associates)
David Reid (SNMP Research, Inc.)
Aleksey Romanov (Quality Quorum)
Shawn Routhier (Epilogue)
Juergen Schoenwaelder (TU Braunschweig)
Bob Stewart (Cisco Systems)
Mike Thatcher (Independent Consultant)
Bert Wijnen (IBM T.J. Watson Research Center)
Wijnen, et al. Standards Track [Page 28]
RFC 2575 VACM for SNMP April 1999
The document is based on recommendations of the IETF Security and
Administrative Framework Evolution for SNMP Advisory Team. Members
of that Advisory Team were:
David Harrington (Cabletron Systems Inc.)
Jeff Johnson (Cisco Systems)
David Levi (SNMP Research Inc.)
John Linn (Openvision)
Russ Mundy (Trusted Information Systems) chair
Shawn Routhier (Epilogue)
Glenn Waters (Nortel)
Bert Wijnen (IBM T. J. Watson Research Center)
As recommended by the Advisory Team and the SNMPv3 Working Group
Charter, the design incorporates as much as practical from previous
RFCs and drafts. As a result, special thanks are due to the authors
of previous designs known as SNMPv2u and SNMPv2*:
Jeff Case (SNMP Research, Inc.)
David Harrington (Cabletron Systems Inc.)
David Levi (SNMP Research, Inc.)
Keith McCloghrie (Cisco Systems)
Brian O'Keefe (Hewlett Packard)
Marshall T. Rose (Dover Beach Consulting)
Jon Saperia (BGS Systems Inc.)
Steve Waldbusser (International Network Services)
Glenn W. Waters (Bell-Northern Research Ltd.)
7. Security Considerations
7.1. Recommended Practices
This document is meant for use in the SNMP architecture. The View-
based Access Control Model described in this document checks access
rights to management information based on:
- contextName, representing a set of management information at the
managed system where the Access Control module is running.
- groupName, representing a set of zero or more securityNames.
The combination of a securityModel and a securityName is mapped
into a group in the View-based Access Control Model.
- securityModel under which access is requested.
- securityLevel under which access is requested.
- operation performed on the management information.
- MIB views for read, write or notify access.
Wijnen, et al. Standards Track [Page 29]
RFC 2575 VACM for SNMP April 1999
When the User-based Access Control module is called for checking
access rights, it is assumed that the calling module has ensured the
authentication and privacy aspects as specified by the securityLevel
that is being passed.
When creating entries in or deleting entries from the
vacmViewTreeFamilyTable it is important to do such in the sequence as
recommended in the DESCRIPTION clause of the vacmViewTreeFamilyTable
definition. Otherwise unwanted access may be granted while changing
the entries in the table.
7.2. Defining Groups
The groupNames are used to give access to a group of zero or more
securityNames. Within the View-Based Access Control Model, a
groupName is considered to exist if that groupName is listed in the
vacmSecurityToGroupTable.
By mapping the combination of a securityModel and securityName into a
groupName, an SNMP Command Generator application can add/delete
securityNames to/from a group, if proper access is allowed.
Further it is important to realize that the grouping of
tuples in the vacmSecurityToGroupTable
does not take securityLevel into account. It is therefore important
that the security administrator uses the securityLevel index in the
vacmAccessTable to separate noAuthNoPriv from authPriv and/or
authNoPriv access.
7.3. Conformance
For an implementation of the View-based Access Control Model to be
conformant, it MUST implement the SNMP-VIEW-BASED-ACM-MIB according
to the vacmMIBCompliance. It also SHOULD implement the initial
configuration, described in appendix A.
7.4. Access to the SNMP-VIEW-BASED-ACM-MIB
The objects in this MIB control the access to all MIB data that is
accessible via the SNMP engine and they may be considered sensitive
in many environments. It is important to closely control (both read
and write) access to these to these MIB objects by using
appropriately configured Access Control models (for example the
View-based Access Control Model as specified in this document).
Wijnen, et al. Standards Track [Page 30]
RFC 2575 VACM for SNMP April 1999
8. References
[RFC2578] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Structure of Management Information Version 2 (SMIv2)",
STD 58, RFC 2578, April 1999.
[RFC2579] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Textual Conventions for SMIv2", STD 58, RFC 2579, April
1999.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2571] Harrington, D., Presuhn, R. and B. Wijnen, "An
Architecture for describing SNMP Management Frameworks",
RFC 2571, April 1999.
[RFC2572] Case, J., Harrington, D., Presuhn, R. and B. Wijnen,
"Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)", RFC 2572, April
1999.
[RFC2574] Blumenthal, U. and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management
Protocol (SNMPv3)", RFC 2574, April 1999.
[ISO-ASN.1] Information processing systems - Open Systems
Interconnection - Specification of Abstract Syntax
Notation One (ASN.1), International Organization for
Standardization. International Standard 8824, (December,
1987).
Wijnen, et al. Standards Track [Page 31]
RFC 2575 VACM for SNMP April 1999
9. Editors' Addresses
Bert Wijnen
IBM T. J. Watson Research
Schagen 33
3461 GL Linschoten
Netherlands
Phone: +31-348-432-794
EMail: wijnen@vnet.ibm.com
Randy Presuhn
BMC Software, Inc
965 Stewart Drive
Sunnyvale, CA 94086
USA
Phone: +1-408-616-3100
EMail: randy_presuhn@bmc.com
Keith McCloghrie
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
USA
Phone: +1-408-526-5260
EMail: kzm@cisco.com
Wijnen, et al. Standards Track [Page 32]
RFC 2575 VACM for SNMP April 1999
APPENDIX A - Installation
A.1. Installation Parameters
During installation, an authoritative SNMP engine which supports this
View-based Access Control Model SHOULD be configured with several
initial parameters. These include for the View-based Access Control
Model:
1) A security configuration
The choice of security configuration determines if initial
configuration is implemented and if so how. One of three possible
choices is selected:
- initial-minimum-security-configuration
- initial-semi-security-configuration
- initial-no-access-configuration
In the case of a initial-no-access-configuration, there is no initial
configuration, and so the following steps are irrelevant.
2) A default context
One entry in the vacmContextTable with a contextName of "" (the empty
string), representing the default context. Note that this table gets
created automatically if a default context exists.
vacmContextName ""
3) An initial group
One entry in the vacmSecurityToGroupTable to allow access to group
"initial".
vacmSecurityModel 3 (USM)
vacmSecurityName "initial"
vacmGroupName "initial"
vacmSecurityToGroupStorageType anyValidStorageType
vacmSecurityToGroupStatus active
Wijnen, et al. Standards Track [Page 33]
RFC 2575 VACM for SNMP April 1999
4) Initial access rights
Three entries in the vacmAccessTable as follows:
- read-notify access for securityModel USM, securityLevel
"noAuthNoPriv" on behalf of securityNames that belong to the group
"initial" to the MIB view in the default context with
contextName "".
- read-write-notify access for securityModel USM, securityLevel
"authNoPriv" on behalf of securityNames that belong to the group
"initial" to the MIB view in the default context with
contextName "".
- if privacy is supported,
read-write-notify access for securityModel USM, securityLevel
"authPriv" on behalf of securityNames that belong to the group
"initial" to the MIB view in the default context with
contextName "".
That translates into the following entries in the vacmAccessTable.
- One entry to be used for unauthenticated access (noAuthNoPriv):
vacmGroupName "initial"
vacmAccessContextPrefix ""
vacmAccessSecurityModel 3 (USM)
vacmAccessSecurityLevel noAuthNoPriv
vacmAccessContextMatch exact
vacmAccessReadViewName "restricted"
vacmAccessWriteViewName ""
vacmAccessNotifyViewName "restricted"
vacmAccessStorageType anyValidStorageType
vacmAccessStatus active
- One entry to be used for authenticated access (authNoPriv)
with optional privacy (authPriv):
vacmGroupName "initial"
vacmAccessContextPrefix ""
vacmAccessSecurityModel 3 (USM)
vacmAccessSecurityLevel authNoPriv
vacmAccessContextMatch exact
vacmAccessReadViewName "internet"
vacmAccessWriteViewName "internet"
vacmAccessNotifyViewName "internet"
vacmAccessStorageType anyValidStorageType
vacmAccessStatus active
Wijnen, et al. Standards Track [Page 34]
RFC 2575 VACM for SNMP April 1999
5) Two MIB views, of which the second one depends on the security
configuration.
- One view, the view, for authenticated access:
- the MIB view is the following subtree:
"internet" (subtree 1.3.6.1)
- A second view, the view, for unauthenticated
access. This view is configured according to the selected
security configuration:
- For the initial-no-access-configuration there is no default
initial configuration, so no MIB views are pre-scribed.
- For the initial-semi-secure-configuration:
the MIB view is the union of these subtrees:
(a) "system" (subtree 1.3.6.1.2.1.1) [RFC1907]
(b) "snmp" (subtree 1.3.6.1.2.1.11) [RFC1907]
(c) "snmpEngine" (subtree 1.3.6.1.6.3.10.2.1) [RFC2571]
(d) "snmpMPDStats" (subtree 1.3.6.1.6.3.11.2.1) [RFC2572]
(e) "usmStats" (subtree 1.3.6.1.6.3.15.1.1) [RFC2574]
- For the initial-minimum-secure-configuration:
the MIB view is the following subtree.
"internet" (subtree 1.3.6.1)
This translates into the following "internet" entry in the
vacmViewTreeFamilyTable:
minimum-secure semi-secure
---------------- ---------------
vacmViewTreeFamilyViewName "internet" "internet"
vacmViewTreeFamilySubtree 1.3.6.1 1.3.6.1
vacmViewTreeFamilyMask "" ""
vacmViewTreeFamilyType 1 (included) 1 (included)
vacmViewTreeFamilyStorageType anyValidStorageType anyValidStorageType
vacmViewTreeFamilyStatus active active
Wijnen, et al. Standards Track [Page 35]
RFC 2575 VACM for SNMP April 1999
In addition it translates into the following "restricted" entries
in the vacmViewTreeFamilyTable:
minimum-secure semi-secure
---------------- ---------------
vacmViewTreeFamilyViewName "restricted" "restricted"
vacmViewTreeFamilySubtree 1.3.6.1 1.3.6.1.2.1.1
vacmViewTreeFamilyMask "" ""
vacmViewTreeFamilyType 1 (included) 1 (included)
vacmViewTreeFamilyStorageType anyValidStorageType anyValidStorageType
vacmViewTreeFamilyStatus active active
vacmViewTreeFamilyViewName "restricted"
vacmViewTreeFamilySubtree 1.3.6.1.2.1.11
vacmViewTreeFamilyMask ""
vacmViewTreeFamilyType 1 (included)
vacmViewTreeFamilyStorageType anyValidStorageType
vacmViewTreeFamilyStatus active
vacmViewTreeFamilyViewName "restricted"
vacmViewTreeFamilySubtree 1.3.6.1.6.3.10.2.1
vacmViewTreeFamilyMask ""
vacmViewTreeFamilyType 1 (included)
vacmViewTreeFamilyStorageType anyValidStorageType
vacmViewTreeFamilyStatus active
vacmViewTreeFamilyViewName "restricted"
vacmViewTreeFamilySubtree 1.3.6.1.6.3.11.2.1
vacmViewTreeFamilyMask ""
vacmViewTreeFamilyType 1 (included)
vacmViewTreeFamilyStorageType anyValidStorageType
vacmViewTreeFamilyStatus active
vacmViewTreeFamilyViewName "restricted"
vacmViewTreeFamilySubtree 1.3.6.1.6.3.15.1.1
vacmViewTreeFamilyMask ""
vacmViewTreeFamilyType 1 (included)
vacmViewTreeFamilyStorageType anyValidStorageType
vacmViewTreeFamilyStatus active
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RFC 2575 VACM for SNMP April 1999
B. Change Log
Changes made since RFC2275:
- Added text to vacmSecurityToGroupStatus DESCRIPTION clause to
clarify under which conditions an entry in the
vacmSecurityToGroupTable can be made active.
- Added REVISION clauses to MODULE-IDENTITY
- Clarified text in vacmAccessTable DESCRIPTION clause.
- Added a DEFVAL clause to vacmAccessContextMatch object.
- Added missing columns in Appendix A and re-arranged for clarity.
- Fixed oids in appendix A.
- Use the PDU Class terminology instead of RFC1905 PDU types.
- Added section 7.4 about access control to the MIB.
- Fixed references to new/revised documents
- Fix Editor contact information.
- fixed spelling errors
- removed one vacmAccesEntry from sample in appendix A.
- made some more clarifications.
- updated acknowledgement section.
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RFC 2575 VACM for SNMP April 1999
C. Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by
the Internet Society.
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