9901200000Z

SNMPv3 Working Group

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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

The management information definitions for the
View-based Access Control Model for SNMP.

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.

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.

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

        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.

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

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.

Information about a particular context.

An entry in this table maps the combination of a
securityModel and securityName into a groupName.

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.

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.

A human readable name identifying a particular
context at a particular SNMP entity.

The empty contextName (zero length) represents the
default context.

The Security Model, by which the vacmSecurityName
referenced by this entry is provided.

Note, this object may not take the 'any' (0) value.

The securityName for the principal, represented in a
Security Model independent format, which is mapped by
this entry to a groupName.

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.

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.

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.

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.

In order to gain the access rights allowed by this
conceptual row, this securityModel must be in use.

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

which has the highest value for
vacmAccessSecurityLevel is selected.

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.

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.

The value of an instance of this object identifies
the MIB view of the SNMP context to which this

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.

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.

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.

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.

The human readable name for a family of view subtrees.

The MIB subtree which when combined with the
corresponding instance of vacmViewTreeFamilyMask
defines a family of view subtrees.

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

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.

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.

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.

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.

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.

A collection of objects providing for remote
configuration of an SNMP engine which implements
the SNMP View-based Access Control Model.