Network Working Group J. Galvin
Request for Comments: 1445 Trusted Information Systems
K. McCloghrie
Hughes LAN Systems
April 1993
Administrative Model
for version 2 of the
Simple Network Management Protocol (SNMPv2)
Status of this Memo
This RFC specifes an IAB standards track protocol for the
Internet community, and requests discussion and suggestions
for improvements. Please refer to the current edition of the
"IAB Official Protocol Standards" for the standardization
state and status of this protocol. Distribution of this memo
is unlimited.
Table of Contents
1 Introduction .......................................... 2
1.1 A Note on Terminology ............................... 2
2 Elements of the Model ................................. 3
2.1 SNMPv2 Party ........................................ 3
2.2 SNMPv2 Entity ....................................... 6
2.3 SNMPv2 Management Station ........................... 7
2.4 SNMPv2 Agent ........................................ 7
2.5 View Subtree ........................................ 7
2.6 MIB View ............................................ 8
2.7 Proxy Relationship .................................. 8
2.8 SNMPv2 Context ...................................... 10
2.9 SNMPv2 Management Communication ..................... 10
2.10 SNMPv2 Authenticated Management Communication ...... 12
2.11 SNMPv2 Private Management Communication ............ 13
2.12 SNMPv2 Management Communication Class .............. 14
2.13 SNMPv2 Access Control Policy ....................... 14
3 Elements of Procedure ................................. 17
3.1 Generating a Request ................................ 17
3.2 Processing a Received Communication ................. 18
3.3 Generating a Response ............................... 21
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4 Application of the Model .............................. 23
4.1 Non-Secure Minimal Agent Configuration .............. 23
4.2 Secure Minimal Agent Configuration .................. 26
4.3 MIB View Configurations ............................. 28
4.4 Proxy Configuration ................................. 32
4.4.1 Foreign Proxy Configuration ....................... 33
4.4.2 Native Proxy Configuration ........................ 37
4.5 Public Key Configuration ............................ 41
5 Security Considerations ............................... 44
6 Acknowledgements ...................................... 45
7 References ............................................ 46
8 Authors' Addresses .................................... 47
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1. Introduction
A network management system contains: several (potentially
many) nodes, each with a processing entity, termed an agent,
which has access to management instrumentation; at least one
management station; and, a management protocol, used to convey
management information between the agents and management
stations. Operations of the protocol are carried out under an
administrative framework which defines both authentication and
authorization policies.
Network management stations execute management applications
which monitor and control network elements. Network elements
are devices such as hosts, routers, terminal servers, etc.,
which are monitored and controlled through access to their
management information.
It is the purpose of this document, the Administrative Model
for SNMPv2, to define how the administrative framework is
applied to realize effective network management in a variety
of configurations and environments.
The model described here entails the use of distinct
identities for peers that exchange SNMPv2 messages. Thus, it
represents a departure from the community-based administrative
model of the original SNMP [1]. By unambiguously identifying
the source and intended recipient of each SNMPv2 message, this
new strategy improves upon the historical community scheme
both by supporting a more convenient access control model and
allowing for effective use of asymmetric (public key) security
protocols in the future.
1.1. A Note on Terminology
For the purpose of exposition, the original Internet-standard
Network Management Framework, as described in RFCs 1155, 1157,
and 1212, is termed the SNMP version 1 framework (SNMPv1).
The current framework is termed the SNMP version 2 framework
(SNMPv2).
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2. Elements of the Model
2.1. SNMPv2 Party
A SNMPv2 party is a conceptual, virtual execution environment
whose operation is restricted (for security or other purposes)
to an administratively defined subset of all possible
operations of a particular SNMPv2 entity (see Section 2.2).
Whenever a SNMPv2 entity processes a SNMPv2 message, it does
so by acting as a SNMPv2 party and is thereby restricted to
the set of operations defined for that party. The set of
possible operations specified for a SNMPv2 party may be
overlapping or disjoint with respect to the sets of other
SNMPv2 parties; it may also be a proper or improper subset of
all possible operations of the SNMPv2 entity.
Architecturally, each SNMPv2 party comprises
o a single, unique party identity,
o a logical network location at which the party executes,
characterized by a transport protocol domain and
transport addressing information,
o a single authentication protocol and associated
parameters by which all protocol messages originated by
the party are authenticated as to origin and integrity,
and
o a single privacy protocol and associated parameters by
which all protocol messages received by the party are
protected from disclosure.
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Conceptually, each SNMPv2 party may be represented by an ASN.1
value with the following syntax:
SnmpParty ::= SEQUENCE {
partyIdentity
OBJECT IDENTIFIER,
partyTDomain
OBJECT IDENTIFIER,
partyTAddress
OCTET STRING,
partyMaxMessageSize
INTEGER,
partyAuthProtocol
OBJECT IDENTIFIER,
partyAuthClock
INTEGER,
partyAuthPrivate
OCTET STRING,
partyAuthPublic
OCTET STRING,
partyAuthLifetime
INTEGER,
partyPrivProtocol
OBJECT IDENTIFIER,
partyPrivPrivate
OCTET STRING,
partyPrivPublic
OCTET STRING
}
For each SnmpParty value that represents a SNMPv2 party, the
following statements are true:
o Its partyIdentity component is the party identity.
o Its partyTDomain component is called the transport domain
and indicates the kind of transport service by which the
party receives network management traffic. An example of
a transport domain is snmpUDPDomain (SNMPv2 over UDP,
using SNMPv2 parties).
o Its partyTAddress component is called the transport
addressing information and represents a transport service
address by which the party receives network management
traffic.
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o Its partyMaxMessageSize component is called the maximum
message size and represents the length in octets of the
largest SNMPv2 message this party is prepared to accept.
o Its partyAuthProtocol component is called the
authentication protocol and identifies a protocol and a
mechanism by which all messages generated by the party
are authenticated as to integrity and origin. In this
context, the value noAuth signifies that messages
generated by the party are not authenticated as to
integrity and origin.
o Its partyAuthClock component is called the authentication
clock and represents a notion of the current time that is
specific to the party. The significance of this
component is specific to the authentication protocol.
o Its partyAuthPrivate component is called the private
authentication key and represents any secret value needed
to support the authentication protocol. The significance
of this component is specific to the authentication
protocol.
o Its partyAuthPublic component is called the public
authentication key and represents any public value that
may be needed to support the authentication protocol.
The significance of this component is specific to the
authentication protocol.
o Its partyAuthLifetime component is called the lifetime
and represents an administrative upper bound on
acceptable delivery delay for protocol messages generated
by the party. The significance of this component is
specific to the authentication protocol.
o Its partyPrivProtocol component is called the privacy
protocol and identifies a protocol and a mechanism by
which all protocol messages received by the party are
protected from disclosure. In this context, the value
noPriv signifies that messages received by the party are
not protected from disclosure.
o Its partyPrivPrivate component is called the private
privacy key and represents any secret value needed to
support the privacy protocol. The significance of this
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component is specific to the privacy protocol.
o Its partyPrivPublic component is called the public
privacy key and represents any public value that may be
needed to support the privacy protocol. The significance
of this component is specific to the privacy protocol.
If, for all SNMPv2 parties realized by a SNMPv2 entity, the
authentication protocol is noAuth and the privacy protocol is
noPriv, then that entity is called non-secure.
2.2. SNMPv2 Entity
A SNMPv2 entity is an actual process which performs network
management operations by generating and/or responding to
SNMPv2 protocol messages in the manner specified in [2]. When
a SNMPv2 entity is acting as a particular SNMPv2 party (see
Section 2.1), the operation of that entity must be restricted
to the subset of all possible operations that is
administratively defined for that party.
By definition, the operation of a SNMPv2 entity requires no
concurrency between processing of any single protocol message
(by a particular SNMPv2 party) and processing of any other
protocol message (by a potentially different SNMPv2 party).
Accordingly, implementation of a SNMPv2 entity to support more
than one party need not be multi-threaded. However, there may
be situations where implementors may choose to use multi-
threading.
Architecturally, every SNMPv2 entity maintains a local
database that represents all SNMPv2 parties known to it -
those whose operation is realized locally, those whose
operation is realized by proxy interactions with remote
parties or devices, and those whose operation is realized by
remote entities. In addition, every SNMPv2 entity maintains a
local database that represents all managed object resources
(see Section 2.8) which are known to the SNMPv2 entity.
Finally, every SNMPv2 entity maintains a local database that
represents an access control policy (see Section 2.11) that
defines the access privileges accorded to known SNMPv2
parties.
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2.3. SNMPv2 Management Station
A SNMPv2 management station is the operational role assumed by
a SNMPv2 party when it initiates SNMPv2 management operations
by the generation of appropriate SNMPv2 protocol messages or
when it receives and processes trap notifications.
Sometimes, the term SNMPv2 management station is applied to
partial implementations of the SNMPv2 (in graphics
workstations, for example) that focus upon this operational
role. Such partial implementations may provide for
convenient, local invocation of management services, but they
may provide little or no support for performing SNMPv2
management operations on behalf of remote protocol users.
2.4. SNMPv2 Agent
A SNMPv2 agent is the operational role assumed by a SNMPv2
party when it performs SNMPv2 management operations in
response to received SNMPv2 protocol messages such as those
generated by a SNMPv2 management station (see Section 2.3).
Sometimes, the term SNMPv2 agent is applied to partial
implementations of the SNMPv2 (in embedded systems, for
example) that focus upon this operational role. Such partial
implementations provide for realization of SNMPv2 management
operations on behalf of remote users of management services,
but they may provide little or no support for local invocation
of such services.
2.5. 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.
When the OBJECT IDENTIFIER prefix identifying a view subtree
is longer than the OBJECT IDENTIFIER of an object type defined
according to the SMI [3], then the use of such a view subtree
for access control has granularity at the object instance
level. Such granularity is considered beyond the scope of a
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SNMPv2 entity acting in an agent role. As such, no
implementation of a SNMPv2 entity acting in an agent role is
required to support values of viewSubtree [6] which have more
sub-identifiers than is necessary to identify a particular
leaf object type. However, access control information is also
used in determining which SNMPv2 entities acting in a manager
role should receive trap notifications (Section 4.2.6 of [2]).
As such, agent implementors might wish to provide instance-
level granularity in order to allow a management station to
use fine-grain configuration of trap notifications.
2.6. MIB View
A MIB view is a subset of the set of all instances of all
object types defined according to the SMI [3] (i.e., of the
universal set of all instances of all MIB objects), subject to
the following constraints:
o Each element of a MIB view is uniquely named by an ASN.1
OBJECT IDENTIFIER value. As such, identically named
instances of a particular object type (e.g., in different
agents) must be contained within different MIB views.
That is, a particular object instance name resolves
within a particular MIB view to at most one object
instance.
o Every MIB view is defined as a collection of view
subtrees.
2.7. Proxy Relationship
A proxy relationship exists when, in order to process a
received management request, a SNMPv2 entity must communicate
with another, logically remote, entity. A SNMPv2 entity which
processes management requests using a proxy relationship is
termed a SNMPv2 proxy agent.
When communication between a logically remote party and a
SNMPv2 entity is via the SNMPv2 (over any transport protocol),
then the proxy party is called a SNMPv2 native proxy
relationship. Deployment of SNMPv2 native proxy relationships
is a means whereby the processing or bandwidth costs of
management may be amortized or shifted - thereby facilitating
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the construction of large management systems.
When communication between a logically remote party and a
SNMPv2 entity party is not via the SNMPv2, then the proxy
party is called a SNMPv2 foreign proxy relationship.
Deployment of foreign proxy relationships is a means whereby
otherwise unmanageable devices or portions of an internet may
be managed via the SNMPv2.
The transparency principle that defines the behavior of a
SNMPv2 entity in general applies in particular to a SNMPv2
proxy relationship:
The manner in which one SNMPv2 entity processes SNMPv2
protocol messages received from another SNMPv2 entity is
entirely transparent to the latter.
The transparency principle derives directly from the
historical SNMP philosophy of divorcing architecture from
implementation. To this dichotomy are attributable many of
the most valuable benefits in both the information and
distribution models of the Internet-standard Network
Management Framework, and it is the architectural cornerstone
upon which large management systems may be built. Consistent
with this philosophy, although the implementation of SNMPv2
proxy agents in certain environments may resemble that of a
transport-layer bridge, this particular implementation
strategy (or any other!) does not merit special recognition
either in the SNMPv2 management architecture or in standard
mechanisms for proxy administration.
Implicit in the transparency principle is the requirement that
the semantics of SNMPv2 management operations are preserved
between any two SNMPv2 peers. In particular, the "as if
simultaneous" semantics of a Set operation are extremely
difficult to guarantee if its scope extends to management
information resident at multiple network locations. For this
reason, proxy configurations that admit Set operations that
apply to information at multiple locations are discouraged,
although such operations are not explicitly precluded by the
architecture in those rare cases where they might be supported
in a conformant way.
Also implicit in the transparency principle is the requirement
that, throughout its interaction with a proxy agent, a
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management station is supplied with no information about the
nature or progress of the proxy mechanisms by which its
requests are realized. That is, it should seem to the
management station - except for any distinction in underlying
transport address - as if it were interacting via SNMPv2
directly with the proxied device. Thus, a timeout in the
communication between a proxy agent and its proxied device
should be represented as a timeout in the communication
between the management station and the proxy agent.
Similarly, an error response from a proxied device should - as
much as possible - be represented by the corresponding error
response in the interaction between the proxy agent and
management station.
2.8. SNMPv2 Context
A SNMPv2 context is a collection of managed object resources
accessible by a SNMPv2 entity. The object resources
identified by a context are either local or remote.
A SNMPv2 context referring to local object resources is
identified as a MIB view. In this case, a SNMPv2 entity uses
local mechanisms to access the management information
identified by the SNMPv2 context.
A remote SNMPv2 context referring to remote object resources
is identified as a proxy relationship. In this case, a SNMPv2
entity acts as a proxy agent to access the management
information identified by the SNMPv2 context.
2.9. SNMPv2 Management Communication
A SNMPv2 management communication is a communication from one
specified SNMPv2 party to a second specified SNMPv2 party
about management information that is contained in a SNMPv2
context accessible by the appropriate SNMPv2 entity. In
particular, a SNMPv2 management communication may be
o a query by the originating party about information
accessible to the addressed party (e.g., getRequest,
getNextRequest, or getBulkRequest),
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o an indicative assertion to the addressed party about
information accessible to the originating party (e.g.,
Response, InformRequest, or SNMPv2-Trap),
o an imperative assertion by the originating party about
information accessible to the addressed party (e.g.,
setRequest), or
o a confirmation to the addressed party about information
received by the originating party (e.g., a Response
confirming an InformRequest).
A management communication is represented by an ASN.1 value
with the following syntax:
SnmpMgmtCom ::= [2] IMPLICIT SEQUENCE {
dstParty
OBJECT IDENTIFIER,
srcParty
OBJECT IDENTIFIER,
context
OBJECT IDENTIFIER,
pdu
PDUs
}
For each SnmpMgmtCom value that represents a SNMPv2 management
communication, the following statements are true:
o Its dstParty component is called the destination and
identifies the SNMPv2 party to which the communication is
directed.
o Its srcParty component is called the source and
identifies the SNMPv2 party from which the communication
is originated.
o Its context component identifies the SNMPv2 context
containing the management information referenced by the
communication.
o Its pdu component has the form and significance
attributed to it in [2].
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2.10. SNMPv2 Authenticated Management Communication
A SNMPv2 authenticated management communication is a SNMPv2
management communication (see Section 2.9) for which the
originating SNMPv2 party is (possibly) reliably identified and
for which the integrity of the transmission of the
communication is (possibly) protected. An authenticated
management communication is represented by an ASN.1 value with
the following syntax:
SnmpAuthMsg ::= [1] IMPLICIT SEQUENCE {
authInfo
ANY, -- defined by authentication protocol
authData
SnmpMgmtCom
}
For each SnmpAuthMsg value that represents a SNMPv2
authenticated management communication, the following
statements are true:
o Its authInfo component is called the authentication
information and represents information required in
support of the authentication protocol used by the SNMPv2
party originating the message. The detailed significance
of the authentication information is specific to the
authentication protocol in use; it has no effect on the
application semantics of the communication other than its
use by the authentication protocol in determining whether
the communication is authentic or not.
o Its authData component is called the authentication data
and represents a SNMPv2 management communication.
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2.11. SNMPv2 Private Management Communication
A SNMPv2 private management communication is a SNMPv2
authenticated management communication (see Section 2.10) that
is (possibly) protected from disclosure. A private management
communication is represented by an ASN.1 value with the
following syntax:
SnmpPrivMsg ::= [1] IMPLICIT SEQUENCE {
privDst
OBJECT IDENTIFIER,
privData
[1] IMPLICIT OCTET STRING
}
For each SnmpPrivMsg value that represents a SNMPv2 private
management communication, the following statements are true:
o Its privDst component is called the privacy destination
and identifies the SNMPv2 party to which the
communication is directed.
o Its privData component is called the privacy data and
represents the (possibly encrypted) serialization
(according to the conventions of [5]) of a SNMPv2
authenticated management communication (see Section
2.10).
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2.12. SNMPv2 Management Communication Class
A SNMPv2 management communication class corresponds to a
specific SNMPv2 PDU type defined in [2]. A management
communication class is represented by an ASN.1 INTEGER value
according to the type of the identifying PDU (see Table 1).
Get 1
GetNext 2
Response 4
Set 8
-- unused 16
GetBulk 32
Inform 64
SNMPv2-Trap 128
Table 1: Management Communication Classes
The value by which a communication class is represented is
computed as 2 raised to the value of the ASN.1 context-
specific tag for the appropriate SNMPv2 PDU.
A set of management communication classes is represented by
the ASN.1 INTEGER value that is the sum of the representations
of the communication classes in that set. The null set is
represented by the value zero.
2.13. SNMPv2 Access Control Policy
A SNMPv2 access control policy is a specification of a local
access policy in terms of a SNMPv2 context and the management
communication classes which are authorized between a pair of
SNMPv2 parties. Architecturally, such a specification
comprises four parts:
o the targets of SNMPv2 access control - the SNMPv2 parties
that may perform management operations as requested by
management communications received from other parties,
o the subjects of SNMPv2 access control - the SNMPv2
parties that may request, by sending management
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communications to other parties, that management
operations be performed,
o the managed object resources of SNMPv2 access control -
the SNMPv2 contexts which identify the management
information on which requested management operations are
to be performed, and
o the policy that specifies the classes of SNMPv2
management communications pertaining to a particular
SNMPv2 context that a particular target is authorized to
accept from a particular subject.
Conceptually, a SNMPv2 access policy is represented by a
collection of ASN.1 values with the following syntax:
AclEntry ::= SEQUENCE {
aclTarget
OBJECT IDENTIFIER,
aclSubject
OBJECT IDENTIFIER,
aclResources
OBJECT IDENTIFIER,
aclPrivileges
INTEGER
}
For each such value that represents one part of a SNMPv2
access policy, the following statements are true:
o Its aclTarget component is called the target and
identifies the SNMPv2 party to which the partial policy
permits access.
o Its aclSubject component is called the subject and
identifies the SNMPv2 party to which the partial policy
grants privileges.
o Its aclResources component is called the managed object
resources and identifies the SNMPv2 context referenced by
the partial policy.
o Its aclPrivileges component is called the privileges and
represents a set of SNMPv2 management communication
classes which, when they reference the specified SNMPv2
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context, are authorized to be processed by the specified
target party when received from the specified subject
party.
The application of SNMPv2 access control policy only occurs on
receipt of management communications; it is not applied on
transmission of management communications. Note, however,
that ASN.1 values, having the syntax AclEntry, are also used
in determining the destinations of a SNMPv2-Trap [2].
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3. Elements of Procedure
This section describes the procedures followed by a SNMPv2
entity in processing SNMPv2 messages. These procedures are
independent of the particular authentication and privacy
protocols that may be in use.
3.1. Generating a Request
This section describes the procedure followed by a SNMPv2
entity whenever either a management request or a trap
notification is to be transmitted by a SNMPv2 party.
(1) A SnmpMgmtCom value is constructed for which the srcParty
component identifies the originating party, for which the
dstParty component identifies the receiving party, for
which the context component identifies the desired SNMPv2
context, and for which the pdu component represents the
desired management operation.
(2) The local database of party information is consulted to
determine the authentication protocol and other relevant
information for the originating and receiving SNMPv2
parties.
(3) A SnmpAuthMsg value is constructed with the following
properties:
Its authInfo component is constructed according to
the authentication protocol specified for the
originating party.
In particular, if the authentication protocol for
the originating SNMPv2 party is identified as
noAuth, then this component corresponds to the
OCTET STRING value of zero length.
Its authData component is the constructed SnmpMgmtCom
value.
(4) The local database of party information is consulted to
determine the privacy protocol and other relevant
information for the receiving SNMPv2 party.
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(5) A SnmpPrivMsg value is constructed with the following
properties:
Its privDst component identifies the receiving
SNMPv2 party.
Its privData component is the (possibly encrypted)
serialization of the SnmpAuthMsg value according to
the conventions of [5].
In particular, if the privacy protocol for the
receiving SNMPv2 party is identified as noPriv,
then the privData component is unencrypted.
Otherwise, the privData component is processed
according to the privacy protocol.
(6) The constructed SnmpPrivMsg value is serialized according
to the conventions of [5].
(7) The serialized SnmpPrivMsg value is transmitted using the
transport address and transport domain for the receiving
SNMPv2 party.
Note that the above procedure does not include any application
of any SNMPv2 access control policy (see section 2.13).
3.2. Processing a Received Communication
This section describes the procedure followed by a SNMPv2
entity whenever a management communication is received.
(1) The snmpStatsPackets counter [7] is incremented. If the
received message is not the serialization (according to
the conventions of [5]) of an SnmpPrivMsg value, then
that message is discarded without further processing.
(If the first octet of the packet has the value
hexadecimal 30, then the snmpStats30Something counter [7]
is incremented prior to discarding the message; otherwise
the snmpStatsEncodingErrors counter [7] is incremented.)
(2) The local database of party information is consulted for
information about the receiving SNMPv2 party identified
by the privDst component of the SnmpPrivMsg value.
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(3) If information about the receiving SNMPv2 party is absent
from the local database of party information, or
indicates that the receiving party's operation is not
realized by the local SNMPv2 entity, then the received
message is discarded without further processing, after
the snmpStatsUnknownDstParties counter [7] is
incremented.
(4) An ASN.1 OCTET STRING value is constructed (possibly by
decryption, according to the privacy protocol in use)
from the privData component of said SnmpPrivMsg value.
In particular, if the privacy protocol recorded for the
party is noPriv, then the OCTET STRING value corresponds
exactly to the privData component of the SnmpPrivMsg
value.
(5) If the OCTET STRING value is not the serialization
(according to the conventions of [5]) of an SnmpAuthMsg
value, then the received message is discarded without
further processing, after the snmpStatsEncodingErrors
counter [7] is incremented.
(6) If the dstParty component of the authData component of
the obtained SnmpAuthMsg value is not the same as the
privDst component of the SnmpPrivMsg value, then the
received message is discarded without further processing,
after the snmpStatsDstPartyMismatches counter [7] is
incremented.
(7) The local database of party information is consulted for
information about the originating SNMPv2 party identified
by the srcParty component of the authData component of
the SnmpAuthMsg value.
(8) If information about the originating SNMPv2 party is
absent from the local database of party information, then
the received message is discarded without further
processing, after the snmpStatsUnknownSrcParties counter
[7] is incremented.
(9) The obtained SnmpAuthMsg value is evaluated according to
the authentication protocol and other relevant
information associated with the originating and receiving
SNMPv2 parties in the local database of party
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information.
In particular, if the authentication protocol is
identified as noAuth, then the SnmpAuthMsg value is
always evaluated as authentic.
(10) If the SnmpAuthMsg value is evaluated as unauthentic,
then the received message is discarded without further
processing, and if the snmpV2EnableAuthenTraps object [7]
is enabled, then the SNMPv2 entity sends
authorizationFailure traps [7] according to its
configuration (Section 4.2.6 of[2]).
(11) The SnmpMgmtCom value is extracted from the authData
component of the SnmpAuthMsg value.
(12) The local database of context information is consulted
for information about the SNMPv2 context identified by
the context component of the SnmpMgmtCom value.
(13) If information about the SNMPv2 context is absent from
the local database of context information, then the
received message is discarded without further processing,
after the snmpStatsUnknownContexts counter [7] is
incremented.
(14) The local database of access policy information is
consulted for access privileges permitted by the local
access policy to the originating SNMPv2 party with
respect to the receiving SNMPv2 party and the indicated
SNMPv2 context.
(15) The management communication class is determined from the
ASN.1 tag value associated with the PDUs component of the
SnmpMgmtCom value. If the management information class
of the received message is either 32, 8, 2, or 1 (i.e.,
GetBulk, Set, GetNext or Get) and the SNMPv2 context is
not realized by the local SNMPv2 entity, then the
received message is discarded without further processing,
after the snmpStatsUnknownContexts counter [7] is
incremented.
(16) If the management communication class of the received
message is either 128, 64 or 4 (i.e., SNMPv2-Trap,
Inform, or Response) and this class is not among the
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access privileges, then the received message is discarded
without further processing, after the
snmpStatsBadOperations counter [7] is incremented.
(17) If the management communication class of the received
message is not among the access privileges, then the
received message is discarded without further processing
after generation and transmission of a response message.
This response message is directed to the originating
SNMPv2 party on behalf of the receiving SNMPv2 party.
Its context, var-bind-list and request-id components are
identical to those of the received request. Its error-
index component is zero and its error-status component is
authorizationError [2].
(18) If the SNMPv2 context refers to local object resources,
then the management operation represented by the
SnmpMgmtCom value is performed by the receiving SNMPv2
entity with respect to the MIB view identified by the
SNMPv2 context according to the procedures set forth in
[2].
(19) If the SNMPv2 context refers to remote object resources,
then the management operation represented by the
SnmpMgmtCom value is performed through the appropriate
proxy relationship.
3.3. Generating a Response
The procedure for generating a response to a SNMPv2 management
request is identical to the procedure for transmitting a
request (see Section 3.1), with these exceptions:
(1) In Step 1, the dstParty component of the responding
SnmpMgmtCom value is taken from the srcParty component of
the original SnmpMgmtCom value; the srcParty component of
the responding SnmpMgmtCom value is taken from the
dstParty component of the original SnmpMgmtCom value; the
context component of the responding SnmpMgmtCom value is
taken from the context component of the original
SnmpMgmtCom value; and, the pdu component of the
responding SnmpMgmtCom value is the response which
results from applying the operation specified in the
original SnmpMgmtCom value.
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(2) In Step 7, the serialized SnmpPrivMsg value is
transmitted using the transport address and transport
domain from which its corresponding request originated -
even if that is different from the transport information
recorded in the local database of party information.
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4. Application of the Model
This section describes how the administrative model set forth
above is applied to realize effective network management in a
variety of configurations and environments. Several types of
administrative configurations are identified, and an example
of each is presented.
4.1. Non-Secure Minimal Agent Configuration
This section presents an example configuration for a minimal,
non-secure SNMPv2 agent that interacts with one or more SNMPv2
management stations. Table 2 presents information about
SNMPv2 parties that is known both to the minimal agent and to
the manager, while Table 3 presents similarly common
information about the local access policy.
As represented in Table 2, the example agent party operates at
UDP port 161 at IP address 1.2.3.4 using the party identity
gracie; the example manager operates at UDP port 2001 at IP
address 1.2.3.5 using the identity george. At minimum, a
non-secure SNMPv2 agent implementation must provide for
administrative configuration (and non-volatile storage) of the
identities and transport addresses of two SNMPv2 parties:
itself and a remote peer. Strictly speaking, other
information about these two parties (including access policy
information) need not be configurable.
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Identity gracie george
(agent) (manager)
Domain snmpUDPDomain snmpUDPDomain
Address 1.2.3.4, 161 1.2.3.5, 2001
Auth Prot noAuth noAuth
Auth Priv Key "" ""
Auth Pub Key "" ""
Auth Clock 0 0
Auth Lifetime 0 0
Priv Prot noPriv noPriv
Priv Priv Key "" ""
Priv Pub Key "" ""
Table 2: Party Information for Minimal Agent
Target Subject Context Privileges
gracie george local 35 (Get, GetNext & GetBulk)
george gracie local 132 (Response & SNMPv2-Trap)
Table 3: Access Information for Minimal Agent
Suppose that the managing party george wishes to interrogate
management information about the SNMPv2 context named "local"
held by the agent named gracie by issuing a SNMPv2 GetNext
request message. The manager consults its local database of
party information. Because the authentication protocol for
the party george is recorded as noAuth, the GetNext request
message generated by the manager is not authenticated as to
origin and integrity. Because, according to the manager's
local database of party information, the privacy protocol for
the party gracie is noPriv, the GetNext request message is not
protected from disclosure. Rather, it is simply assembled,
serialized, and transmitted to the transport address (IP
address 1.2.3.4, UDP port 161) associated in the manager's
local database of party information with the party gracie.
When the GetNext request message is received at the agent, the
identity of the party to which it is directed (gracie) is
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extracted from the message, and the receiving entity consults
its local database of party information. Because the privacy
protocol for the party gracie is recorded as noPriv, the
received message is assumed not to be protected from
disclosure. Similarly, the identity of the originating party
(george) is extracted, and the local database of party
information is consulted. Because the authentication protocol
for the party george is recorded as noAuth, the received
message is immediately accepted as authentic.
The received message is fully processed only if the agent's
local database of access policy information authorizes GetNext
request communications by the party george to the agent party
gracie with respect to the SNMPv2 context "local". The
database of access policy information presented as Table 3
authorizes such communications (as well as Get and GetBulk
operations).
When the received request is processed, a Response message is
generated which references the SNMPv2 context "local" and
identifies gracie as the source party and george, the party
from which the request originated, as the destination party.
Because the authentication protocol for gracie is recorded in
the local database of party information as noAuth, the
generated Response message is not authenticated as to origin
or integrity. Because, according to the local database of
party information, the privacy protocol for the party george
is noPriv, the response message is not protected from
disclosure. The response message is transmitted to the
transport address from which the corresponding request
originated - without regard for the transport address
associated with george in the local database of party
information.
When the generated response is received by the manager, the
identity of the party to which it is directed (george) is
extracted from the message, and the manager consults its local
database of party information. Because the privacy protocol
for the party george is recorded as noPriv, the received
response is assumed not to be protected from disclosure.
Similarly, the identity of the originating party (gracie) is
extracted, and the local database of party information is
consulted. Because the authentication protocol for the party
gracie is recorded as noAuth, the received response is
immediately accepted as authentic.
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The received message is fully processed only if the manager's
local database of access policy information authorizes
Response communications from the party gracie to the manager
party george which reference the SNMPv2 context "local". The
database of access policy information presented as Table 3
authorizes such Response messages (as well as SNMPv2-Trap
messages).
4.2. Secure Minimal Agent Configuration
This section presents an example configuration for a secure,
minimal SNMPv2 agent that interacts with a single SNMPv2
management station. Table 4 presents information about SNMPv2
parties that is known both to the minimal agent and to the
manager, while Table 5 presents similarly common information
about the local access policy.
The interaction of manager and agent in this configuration is
very similar to that sketched above for the non-secure minimal
agent - except that all protocol messages are authenticated as
to origin and integrity and protected from disclosure. This
example requires encryption in order to support distribution
of secret keys via the SNMPv2 itself. A more elaborate
example comprising an additional pair of SNMPv2 parties could
support the exchange of non-secret information in
authenticated messages without incurring the cost of
encryption.
An actual secure agent configuration may require SNMPv2
parties for which the authentication and privacy protocols are
noAuth and noPriv, respectively, in order to support clock
synchronization (see [6]). For clarity, these additional
parties are not represented in this example.
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Identity ollie stan
(agent) (manager)
Domain snmpUDPDomain snmpUDPDomain
Address 1.2.3.4, 161 1.2.3.5, 2001
Auth Prot v2md5AuthProtocol v2md5AuthProtocol
Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789"
Auth Pub Key "" ""
Auth Clock 0 0
Auth Lifetime 300 300
Priv Prot desPrivProtocol desPrivProtocol
Priv Priv Key "MNOPQR0123456789" "STUVWX0123456789"
Priv Pub Key "" ""
Table 4: Party Information for Secure Minimal Agent
Target Subject Context Privileges
ollie stan local 35 (Get, GetNext & GetBulk)
stan ollie local 132 (Response & SNMPv2-Trap)
Table 5: Access Information for Secure Minimal Agent
As represented in Table 4, the example agent party operates at
UDP port 161 at IP address 1.2.3.4 using the party identity
ollie; the example manager operates at UDP port 2001 at IP
address 1.2.3.5 using the identity stan. At minimum, a secure
SNMPv2 agent implementation must provide for administrative
configuration (and non-volatile storage) of relevant
information about two SNMPv2 parties: itself and a remote
peer. Both ollie and stan authenticate all messages that they
generate by using the SNMPv2 authentication protocol
v2md5AuthProtocol and their distinct, private authentication
keys. Although these private authentication key values
("0123456789ABCDEF" and "GHIJKL0123456789") are presented here
for expository purposes, knowledge of private authentication
keys is not normally afforded to human beings and is confined
to those portions of the protocol implementation that require
it.
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When using the v2md5AuthProtocol, the public authentication
key for each SNMPv2 party is never used in authentication and
verification of SNMPv2 exchanges. Also, because the
v2md5AuthProtocol is symmetric in character, the private
authentication key for each party must be known to another
SNMPv2 party with which authenticated communication is
desired. In contrast, asymmetric (public key) authentication
protocols would not depend upon sharing of a private key for
their operation.
All protocol messages generated for transmission to the party
stan are encrypted using the desPrivProtocol privacy protocol
and the private key "STUVWX0123456789"; they are decrypted
upon reception according to the same protocol and key.
Similarly, all messages generated for transmission to the
party ollie are encrypted using the desPrivProtocol protocol
and private privacy key "MNOPQR0123456789"; they are
correspondingly decrypted on reception. As with
authentication keys, knowledge of private privacy keys is not
normally afforded to human beings and is confined to those
portions of the protocol implementation that require it.
4.3. MIB View Configurations
This section describes a convention for the definition of MIB
views and, using that convention, presents example
configurations of MIB views for SNMPv2 contexts that refer to
local object resources.
A MIB view is defined by a collection of view subtrees (see
Section 2.6), and any MIB view may be represented in this way.
Because MIB view definitions may, in certain cases, comprise a
very large number of view subtrees, a convention for
abbreviating MIB view definitions is desirable.
The convention adopted in [4] supports abbreviation of MIB
view definitions in terms of families of view subtrees that
are either included in or excluded from the definition of the
relevant MIB view. By this convention, a table locally
maintained by each SNMPv2 entity defines the MIB view
associated with each SNMPv2 context that refers to local
object resources. Each entry in the table represents a family
of view subtrees that (according to the type of that entry) is
either included in or excluded from the MIB view of some
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SNMPv2 context. Each table entry represents a subtree family
as a pairing of an OBJECT IDENTIFIER value (called the family
name) together with a bitstring value (called the family
mask). The family mask indicates which sub-identifiers of the
associated family name are significant to the definition of
the represented subtree family. For each possible MIB object
instance, that instance belongs to the view subtree family
represented by a particular table entry if
o the OBJECT IDENTIFIER name of that MIB object instance
comprises at least as many sub-identifiers as does the
family name for said table entry, and
o each sub-identifier in the name of said MIB object
instance matches the corresponding sub-identifier of the
relevant family name whenever the corresponding bit of
the associated family mask is non-zero.
The appearance of a MIB object instance in the MIB view for a
particular SNMPv2 context is related to the membership of that
instance in the subtree families associated with that SNMPv2
context in local table entries:
o If a MIB object instance belongs to none of the relevant
subtree families, then that instance is not in the MIB
view for the relevant SNMPv2 context.
o If a MIB object instance belongs to the subtree family
represented by exactly one of the relevant table entries,
then that instance is included in, or excluded from, the
relevant MIB view according to the type of that entry.
o If a MIB object instance belongs to the subtree families
represented by more than one of the relevant table
entries, then that instance is included in, or excluded
from, the relevant MIB view according to the type of the
single such table entry for which, first, the associated
family name comprises the greatest number of sub-
identifiers, and, second, the associated family name is
lexicographically greatest.
The subtree family represented by a table entry for which the
associated family mask is all ones corresponds to the single
view subtree identified by the family name for that entry.
Because the convention of [4] provides for implicit extension
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of family mask values with ones, the subtree family
represented by a table entry with a family mask of zero length
always corresponds to a single view subtree.
Context Type Family Name Family Mask
lucy included internet ''H
Table 6: View Definition for Minimal Agent
Using this convention for abbreviating MIB view definitions,
some of the most common definitions of MIB views may be
conveniently expressed. For example, Table 6 illustrates the
MIB view definitions required for a minimal SNMPv2 entity that
having a single SNMPv2 context for which the associated MIB
view embraces all instances of all MIB objects defined within
the SNMPv2 Network Management Framework. The represented
table has a single entry. The SNMPv2 context (lucy) for which
that entry defines the MIB view is identified in the first
column. The type of that entry (included) signifies that any
MIB object instance belonging to the subtree family
represented by that entry may appear in the MIB view for the
SNMPv2 context lucy. The family name for that entry is
internet, and the zero-length family mask value signifies that
the relevant subtree family corresponds to the single view
subtree rooted at that node.
Another example of MIB view definition (see Table 7) is that
of a SNMPv2 entity having multiple SNMPv2 contexts with
distinct MIB views. The MIB view associated with the SNMPv2
context lucy comprises all instances of all MIB objects
defined within the SNMPv2 Network Management Framework, except
those pertaining to the administration of SNMPv2 parties. In
contrast, the MIB view attributed to the SNMPv2 context ricky
contains only MIB object instances defined in the system group
of the Internet-standard MIB together with those object
instances by which SNMPv2 parties are administered.
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Context Type Family Name Family Mask
lucy included internet ''H
lucy excluded snmpParties ''H
ricky included system ''H
ricky included snmpParties ''H
Table 7: View Definition for Multiple Contexts
A more complicated example of MIB view configuration
illustrates the abbreviation of related collections of view
subtrees by view subtree families (see Table 8). In this
example, the MIB view associated with the SNMPv2 context lucy
includes all object instances in the system group of the
Internet-standard MIB together with some information related
to the second network interface attached to the managed
device. However, this interface-related information does not
include the speed of the interface. The family mask value
'FFA0'H in the second table entry signifies that a MIB object
instance belongs to the relevant subtree family if the initial
prefix of its name places it within the ifEntry portion of the
registration hierarchy and if the eleventh sub-identifier of
its name is 2. The MIB object instance representing the speed
of the second network interface belongs to the subtree
families represented by both the second and third entries of
the table, but that particular instance is excluded from the
MIB view for the SNMPv2 context lucy because the
lexicographically greater of the relevant family names appears
in the table entry with type excluded.
The MIB view for the SNMPv2 context ricky is also defined in
this example. The MIB view attributed to the SNMPv2 context
ricky includes all object instances in the icmp group of the
Internet-standard MIB, together with all information relevant
to the fifth network interface attached to the managed device.
In addition, the MIB view attributed to the SNMPv2 context
ricky includes the number of octets received on the fourth
attached network interface.
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Context Type Family Name Family Mask
lucy included system ''H
lucy included { ifEntry 0 2 } 'FFA0'H
lucy excluded { ifSpeed 2 } ''H
ricky included icmp ''H
ricky included { ifEntry 0 5 } 'FFA0'H
ricky included { ifInOctets 4 } ''H
Table 8: More Elaborate View Definitions
While, as suggested by the examples above, a wide range of MIB
view configurations are efficiently supported by the
abbreviated representation of [4], prudent MIB design can
sometimes further reduce the size and complexity of the most
likely MIB view definitions. On one hand, it is critical that
mechanisms for MIB view configuration impose no absolute
constraints either upon the access policies of local
administrations or upon the structure of MIB namespaces; on
the other hand, where the most common access policies are
known, the configuration costs of realizing those policies may
be slightly reduced by assigning to distinct portions of the
registration hierarchy those MIB objects for which local
policies most frequently require distinct treatment.
4.4. Proxy Configuration
This section presents examples of SNMPv2 proxy configurations.
On one hand, foreign proxy configurations provide the
capability to manage non-SNMP devices. On the other hand,
native proxy configurations allow an administrator to shift
the computational burden of rich management functionality away
from network devices whose primary task is not management. To
the extent that SNMPv2 proxy agents function as points of
aggregation for management information, proxy configurations
may also reduce the bandwidth requirements of large-scale
management activities.
The example configurations in this section are simplified for
clarity: actual configurations may require additional parties
in order to support clock synchronization and distribution of
secrets.
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4.4.1. Foreign Proxy Configuration
This section presents an example configuration by which a
SNMPv2 management station may manage network elements that do
not themselves support the SNMPv2. This configuration centers
on a SNMPv2 proxy agent that realizes SNMPv2 management
operations by interacting with a non-SNMPv2 device using a
proprietary protocol.
Table 9 presents information about SNMPv2 parties that is
recorded in the SNMPv2 proxy agent's local database of party
information. Table 10 presents information about proxy
relationships that is recorded in the SNMPv2 proxy agent's
local database of context information. Table 11 presents
information about SNMPv2 parties that is recorded in the
SNMPv2 management station's local database of party
information. Table 12 presents information about the database
of access policy information specified by the local
administration.
Identity groucho chico harpo
(manager) (proxy agent) (proxy dst)
Domain snmpUDPDomain snmpUDPDomain acmeMgmtPrtcl
Address 1.2.3.4, 2002 1.2.3.5, 161 0x98765432
Auth Prot v2md5AuthProtocol v2md5AuthProtocol noAuth
Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789" ""
Auth Pub Key "" "" ""
Auth Clock 0 0 0
Auth Lifetime 300 300 0
Priv Prot noPriv noPriv noPriv
Priv Priv Key "" "" ""
Priv Pub Key "" "" ""
Table 9: Party Information for Proxy Agent
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Context Proxy Destination Proxy Source Proxy Context
ducksoup harpo n/a n/a
Table 10: Proxy Relationships for Proxy Agent
Identity groucho chico
(manager) (proxy agent)
Domain snmpUDPDomain snmpUDPDomain
Address 1.2.3.4, 2002 1.2.3.5, 161
Auth Prot v2md5AuthProtocol v2md5AuthProtocol
Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789"
Auth Pub Key "" ""
Auth Clock 0 0
Auth Lifetime 300 300
Priv Prot noPriv noPriv
Priv Priv Key "" ""
Priv Pub Key "" ""
Table 11: Party Information for Management Station
Target Subject Context Privileges
chico groucho ducksoup 35 (Get, GetNext & GetBulk)
groucho chico ducksoup 132 (Response & SNMPv2-Trap)
Table 12: Access Information for Foreign Proxy
As represented in Table 9, the proxy agent party operates at
UDP port 161 at IP address 1.2.3.5 using the party identity
chico; and, the example manager operates at UDP port 2002 at
IP address 1.2.3.4 using the identity groucho. Both groucho
and chico authenticate all messages that they generate by
using the protocol v2md5AuthProtocol and their distinct,
private authentication keys. Although these private
authentication key values ("0123456789ABCDEF" and
"GHIJKL0123456789") are presented here for expository
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purposes, knowledge of private keys is not normally afforded
to human beings and is confined to those portions of the
protocol implementation that require it.
The party harpo does not send or receive SNMPv2 protocol
messages; rather, all communication with that party proceeds
via a hypothetical proprietary protocol identified by the
value acmeMgmtPrtcl. Because the party harpo does not
participate in the SNMPv2, many of the attributes recorded for
that party in the local database of party information are
ignored.
Table 10 shows the proxy relationships known to the proxy
agent. In particular, the SNMPv2 context ducksoup refers to a
relationship that is satisfied by the party harpo. (The
transport domain of the proxy destination party determines the
interpretation of the proxy source and proxy context
identities - in this case, use of the acmeMgmtPrtcl indicates
that the proxy source and context identities are ignored.)
In order to interrogate the proprietary device associated with
the party harpo, the management station groucho constructs a
SNMPv2 GetNext request contained within a SnmpMgmtCom value
which references the SNMPv2 context ducksoup, and transmits it
to the party chico operating (see Table 11) at UDP port 161,
and IP address 1.2.3.5. This request is authenticated using
the private authentication key "0123456789ABCDEF".
When that request is received by the party chico, the
originator of the message is verified as being the party
groucho by using local knowledge (see Table 9) of the private
authentication key "0123456789ABCDEF". Because party groucho
is authorized to issue GetNext (as well as Get and GetBulk)
requests with respect to party chico and the SNMPv2 context
ducksoup by the relevant access control policy (Table 12), the
request is accepted. Because the local database of context
information indicates that the SNMPv2 context ducksoup refers
to a proxy relationship, the request is satisfied by its
translation into appropriate operations of the acmeMgmtPrtcl
directed at party harpo. These new operations are transmitted
to the party harpo at the address 0x98765432 in the
acmeMgmtPrtcl domain.
When and if the proprietary protocol exchange between the
proxy agent and the proprietary device concludes, a SNMPv2
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Response management operation is constructed by the SNMPv2
party chico to relay the results to party groucho again
referring to the SNMPv2 context ducksoup. This response
communication is authenticated as to origin and integrity
using the authentication protocol v2md5AuthProtocol and
private authentication key "GHIJKL0123456789" specified for
transmissions from party chico. It is then transmitted to the
SNMPv2 party groucho operating at the management station at IP
address 1.2.3.4 and UDP port 2002 (the source address for the
corresponding request).
When this response is received by the party groucho, the
originator of the message is verified as being the party chico
by using local knowledge (see Table 11) of the private
authentication key "GHIJKL0123456789". Because party chico is
authorized to issue Response communications with respect to
party groucho and SNMPv2 context ducksoup by the relevant
access control policy (Table 12), the response is accepted,
and the interrogation of the proprietary device is complete.
It is especially useful to observe that the local database of
party information recorded at the proxy agent (Table 9) need
be neither static nor configured exclusively by the management
station. For instance, suppose that, in this example, the
acmeMgmtPrtcl was a proprietary, MAC-layer mechanism for
managing stations attached to a local area network. In such
an environment, the SNMPv2 party chico would reside at a
SNMPv2 proxy agent attached to such a LAN and could, by
participating in the LAN protocols, detect the attachment and
disconnection of various stations on the LAN. In this
scenario, the SNMPv2 proxy agent could easily adjust its local
database of party information to support indirect management
of the LAN stations by the SNMPv2 management station. For
each new LAN station detected, the SNMPv2 proxy agent would
add to its local database of party information an entry
analogous to that for party harpo (representing the new LAN
station itself), and also add to its local database of context
information an entry analogous to that for SNMPv2 context
ducksoup (representing a proxy relationship for that new
station in the SNMPv2 domain).
By using the SNMPv2 to interrogate the local database of party
information held by the SNMPv2 proxy agent, a SNMPv2
management station can discover and interact with new stations
as they are attached to the LAN.
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4.4.2. Native Proxy Configuration
This section presents an example configuration that supports
SNMPv2 native proxy operations - indirect interaction between
a SNMPv2 agent and a management station that is mediated by a
second SNMPv2 (proxy) agent.
This example configuration is similar to that presented in the
discussion of SNMPv2 foreign proxy above. In this example,
however, the party associated with the identity harpo receives
messages via the SNMPv2, and, accordingly interacts with the
SNMPv2 proxy agent chico using authenticated SNMPv2
communications.
Table 13 presents information about SNMPv2 parties that is
recorded in the SNMPv2 proxy agent's local database of party
information. Table 14 presents information about proxy
relationships that is recorded in the SNMPv2 proxy agent's
local database of context information. Table 11 presents
information about SNMPv2 parties that is recorded in the
SNMPv2 management station's local database of party
information. Table 15 presents information about the database
of access policy information specified by the local
administration.
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Identity groucho chico
(manager) (proxy agent)
Domain snmpUDPDomain snmpUDPDomain
Address 1.2.3.4, 2002 1.2.3.5, 161
Auth Prot v2md5AuthProtocol v2md5AuthProtocol
Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789"
Auth Pub Key "" ""
Auth Clock 0 0
Auth Lifetime 300 300
Priv Prot noPriv noPriv
Priv Priv Key "" ""
Priv Pub Key "" ""
Identity harpo zeppo
(proxy dst) (proxy src)
Domain snmpUDPDomain snmpUDPDomain
Address 1.2.3.6, 161 1.2.3.5, 161
Auth Prot v2md5AuthProtocol v2md5AuthProtocol
Auth Priv Key "MNOPQR0123456789" "STUVWX0123456789"
Auth Pub Key "" ""
Auth Clock 0 0
Auth Lifetime 300 300
Priv Prot noPriv noPriv
Priv Priv Key "" ""
Priv Pub Key "" ""
Table 13: Party Information for Proxy Agent
Context Proxy Destination Proxy Source Proxy Context
ducksoup harpo zeppo bigstore
bigstore groucho chico ducksoup
Table 14: Proxy Relationships for Proxy Agent
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Target Subject Context Privileges
chico groucho ducksoup 35 (Get, GetNext & GetBulk)
groucho chico ducksoup 132 (Response & SNMPv2-Trap)
harpo zeppo bigstore 35 (Get, GetNext & GetBulk)
zeppo harpo bigstore 132 (Response & SNMPv2-Trap)
Table 15: Access Information for Native Proxy
As represented in Table 13, the proxy agent party operates at
UDP port 161 at IP address 1.2.3.5 using the party identity
chico; the example manager operates at UDP port 2002 at IP
address 1.2.3.4 using the identity groucho; the proxy source
party operates at UDP port 161 at IP address 1.2.3.5 using the
party identity zeppo; and, the proxy destination party
operates at UDP port 161 at IP address 1.2.3.6 using the party
identity harpo. Messages generated by all four SNMPv2 parties
are authenticated as to origin and integrity by using the
authentication protocol v2md5AuthProtocol and distinct,
private authentication keys. Although these private
authentication key values ("0123456789ABCDEF",
"GHIJKL0123456789", "MNOPQR0123456789", and
"STUVWX0123456789") are presented here for expository
purposes, knowledge of private keys is not normally afforded
to human beings and is confined to those portions of the
protocol implementation that require it.
Table 14 shows the proxy relationships known to the proxy
agent. In particular, the SNMPv2 context ducksoup refers to a
relationship that is satisfied when the SNMPv2 party zeppo
communicates with the SNMPv2 party harpo and references the
SNMPv2 context bigstore.
In order to interrogate the proxied device associated with the
party harpo, the management station groucho constructs a
SNMPv2 GetNext request contained with a SnmpMgmtCom value
which references the SNMPv2 context ducksoup, and transmits it
to the party chico operating (see Table 11) at UDP port 161
and IP address 1.2.3.5. This request is authenticated using
the private authentication key "0123456789ABCDEF".
When that request is received by the party chico, the
originator of the message is verified as being the party
groucho by using local knowledge (see Table 13) of the private
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authentication key "0123456789ABCDEF". Because party groucho
is authorized to issue GetNext (as well as Get and GetBulk)
requests with respect to party chico and the SNMPv2 context
ducksoup by the relevant access control policy (Table 15), the
request is accepted. Because the local database of context
information indicates that the SNMPv2 context ducksoup refers
to a proxy relationship, the request is satisfied by its
translation into a corresponding SNMPv2 GetNext request
directed from party zeppo to party harpo referencing SNMPv2
context bigstore. This new communication is authenticated
using the private authentication key "STUVWX0123456789" and
transmitted to party harpo at the IP address 1.2.3.6.
When this new request is received by the party harpo, the
originator of the message is verified as being the party zeppo
by using local knowledge of the private authentication key
"STUVWX0123456789". Because party zeppo is authorized to
issue GetNext (as well as Get and GetBulk) requests with
respect to party harpo and the SNMPv2 context bigstore by the
relevant access control policy (Table 15), the request is
accepted. A SNMPv2 Response message representing the results
of the query is then generated by party harpo to party zeppo
referencing SNMPv2 context bigstore. This response
communication is authenticated as to origin and integrity
using the private authentication key "MNOPQR0123456789" and
transmitted to party zeppo at IP address 1.2.3.5 (the source
address for the corresponding request).
When this response is received by party zeppo, the originator
of the message is verified as being the party harpo by using
local knowledge (see Table 13) of the private authentication
key "MNOPQR0123456789". Because party harpo is authorized to
issue Response communications with respect to party zeppo and
SNMPv2 context bigstore by the relevant access control policy
(Table 15), the response is accepted, and is used to construct
a response to the original GetNext request, indicating a
SNMPv2 context of ducksoup. This response, from party chico
to party groucho, is authenticated as to origin and integrity
using the private authentication key "GHIJKL0123456789" and is
transmitted to the party groucho at IP address 1.2.3.4 (the
source address for the original request).
When this response is received by the party groucho, the
originator of the message is verified as being the party chico
by using local knowledge (see Table 13) of the private
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authentication key "GHIJKL0123456789". Because party chico is
authorized to issue Response communications with respect to
party groucho and SNMPv2 context ducksoup by the relevant
access control policy (Table 15), the response is accepted,
and the interrogation is complete.
4.5. Public Key Configuration
This section presents an example configuration predicated upon
a hypothetical security protocol. This hypothetical protocol
would be based on asymmetric (public key) cryptography as a
means for providing data origin authentication (but not
protection against disclosure). This example illustrates the
consistency of the administrative model with public key
technology, and the extension of the example to support
protection against disclosure should be apparent.
Identity ollie stan
(agent) (manager)
Domain snmpUDPDomain snmpUDPDomain
Address 1.2.3.4, 161 1.2.3.5, 2004
Auth Prot pkAuthProtocol pkAuthProtocol
Auth Priv Key "0123456789ABCDEF" ""
Auth Pub Key "0123456789abcdef" "ghijkl0123456789"
Auth Clock 0 0
Auth Lifetime 300 300
Priv Prot noPriv noPriv
Priv Priv Key "" ""
Priv Pub Key "" ""
Table 16: Party Information for Public Key Agent
The example configuration comprises a single SNMPv2 agent that
interacts with a single SNMPv2 management station. Tables 16
and 17 present information about SNMPv2 parties that is by the
agent and manager, respectively, while Table 5 presents
information about the local access policy that is known to
both manager and agent.
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Identity ollie stan
(agent) (manager)
Domain snmpUDPDomain snmpUDPDomain
Address 1.2.3.4, 161 1.2.3.5, 2004
Auth Prot pkAuthProtocol pkAuthProtocol
Auth Priv Key "" "GHIJKL0123456789"
Auth Pub Key "0123456789abcdef" "ghijkl0123456789"
Auth Clock 0 0
Auth Lifetime 300 300
Priv Prot noPriv noPriv
Priv Priv Key "" ""
Priv Pub Key "" ""
Table 17: Party Information for Public Key Management Station
As represented in Table 16, the example agent party operates
at UDP port 161 at IP address 1.2.3.4 using the party identity
ollie; the example manager operates at UDP port 2004 at IP
address 1.2.3.5 using the identity stan. Both ollie and stan
authenticate all messages that they generate as to origin and
integrity by using the hypothetical SNMPv2 authentication
protocol pkAuthProtocol and their distinct, private
authentication keys. Although these private authentication
key values ("0123456789ABCDEF" and "GHIJKL0123456789") are
presented here for expository purposes, knowledge of private
keys is not normally afforded to human beings and is confined
to those portions of the protocol implementation that require
it.
In most respects, the interaction between manager and agent in
this configuration is almost identical to that in the example
of the minimal, secure SNMPv2 agent described above. The most
significant difference is that neither SNMPv2 party in the
public key configuration has knowledge of the private key by
which the other party authenticates its transmissions.
Instead, for each received authenticated SNMPv2 communication,
the identity of the originator is verified by applying an
asymmetric cryptographic algorithm to the received message
together with the public authentication key for the
originating party. Thus, in this configuration, the agent
knows the manager's public key ("ghijkl0123456789") but not
its private key ("GHIJKL0123456789"); similarly, the manager
knows the agent's public key ("0123456789abcdef") but not its
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private key ("0123456789ABCDEF").
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5. Security Considerations
In order to participate in the administrative model set forth
in this memo, SNMPv2 implementations must support local, non-
volatile storage of the local database of party information.
Accordingly, every attempt has been made to minimize the
amount of non-volatile storage required.
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6. Acknowledgements
This document is based, almost entirely, on RFC 1351.
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7. References
[1] Case, J., Fedor, M., Schoffstall, M., Davin, J., "Simple
Network Management Protocol", STD 15, RFC 1157, SNMP
Research, Performance Systems International, MIT
Laboratory for Computer Science, May 1990.
[2] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Protocol Operations for version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1448, SNMP Research,
Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
Carnegie Mellon University, April 1993.
[3] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Structure of Management Information for version 2 of the
Simple Network Management Protocol (SNMPv2)", RFC 1442,
SNMP Research, Inc., Hughes LAN Systems, Dover Beach
Consulting, Inc., Carnegie Mellon University, April 1993.
[4] McCloghrie, K., and Galvin, J., "Party MIB for version 2
of the Simple Network Management Protocol (SNMPv2)", RFC
1447, Hughes LAN Systems, Trusted Information Systems,
April 1993.
[5] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Transport Mappings for version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1449, SNMP Research,
Inc., Hughes LAN Systems, Dover Beach Consulting, Inc.,
Carnegie Mellon University, April 1993.
[6] Galvin, J., and McCloghrie, K., "Security Protocols for
version 2 of the Simple Network Management Protocol
(SNMPv2)", RFC 1446, Trusted Information Systems, Hughes
LAN Systems, April 1993.
[7] Case, J., McCloghrie, K., Rose, M., and Waldbusser, S.,
"Management Information Base for version 2 of the Simple
Network Management Protocol (SNMPv2)", RFC 1450, SNMP
Research, Inc., Hughes LAN Systems, Dover Beach
Consulting, Inc., Carnegie Mellon University, April 1993.
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8. Authors' Addresses
James M. Galvin
Trusted Information Systems, Inc.
3060 Washington Road, Route 97
Glenwood, MD 21738
Phone: +1 301 854-6889
EMail: galvin@tis.com
Keith McCloghrie
Hughes LAN Systems
1225 Charleston Road
Mountain View, CA 94043
US
Phone: +1 415 966 7934
Email: kzm@hls.com
Galvin & McCloghrie [Page 47]
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