notification using the desired set of parameters.
4.3. Proxy Implementations
A proxy implementation may be used to enable communication between
entities which support different SNMP message versions. This is
accomplished in a proxy forwarder application by performing
translations on PDUs. These translations depend on the PDU type, the
SNMP version of the packet containing a received PDU, and the SNMP
version to be used to forward a received PDU. The following sections
describe these translations. In all cases other than those described
below, the proxy SHALL forward a received PDU without change, subject
to size constraints as defined in section 5.3 (Community MIB) of this
document. Note that in the following sections, the 'Upstream
Version' refers to the version used between the command generator or
notification receiver and the proxy, and the 'Downstream Version'
refers to the version used between the proxy and the command
responder or notification originator, regardless of the PDU type or
direction.
4.3.1. Upstream Version Greater Than Downstream Version
- If a GetBulkRequest-PDU is received and must be forwarded using
the SNMPv1 message version, the proxy forwarder SHALL act as if
the non-repeaters and max-repetitions fields were both set to 0,
and SHALL set the tag of the PDU to GetNextRequest-PDU.
- If a GetResponse-PDU is received whose error-status field has a
value of 'tooBig', and the message will be forwarded using the
SNMPv2c or SNMPv3 message version, and the original request
received by the proxy was not a GetBulkRequest-PDU, the proxy
forwarder SHALL remove the contents of the variable-bindings field
and ensure that the error-index field is set to 0 before
forwarding the response.
- If a GetResponse-PDU is received whose error-status field has a
value of 'tooBig', and the message will be forwarded using the
SNMPv2c or SNMPv3 message version, and the original request
received by the proxy was a GetBulkRequest-PDU, the proxy
forwarder SHALL re-send the forwarded request (which would have
been altered to be a GetNextRequest-PDU) with all but the first
variable-binding removed. The proxy forwarder SHALL only re-send
such a request a single time. If the resulting GetResponse-PDU
also contains an error-status field with a value of 'tooBig', then
the proxy forwarder SHALL remove the contents of the variable-
bindings field, and change the error-status field to 'noError',
and ensure that the error-index field is set to 0 before
forwarding the response. Note that if the original request only
contained a single variable-binding, the proxy may skip re-sending
the request and simply remove the variable-bindings and change the
error-status to 'noError'. Further note that, while it might have
been possible to fit more variable bindings if the proxy only re-
sent the request multiple times, and stripped only a single
variable binding from the request at a time, this is deemed too
expensive. The approach described here preserves the behaviour of
a GetBulkRequest as closely as possible, without incurring the
cost of re-sending the request multiple times.
- If a Trap-PDU is received, and will be forwarded using the SNMPv2c
or SNMPv3 message version, the proxy SHALL apply the translation
rules described in section 3, and SHALL forward the notification
as an SNMPv2-Trap-PDU.
Note that when an SNMPv1 agent generates a message containing a
Trap-PDU which is subsequently forwarded by one or more proxy
forwarders using SNMP versions other than SNMPv1, the community
string and agent-addr fields from the original message generated
by the SNMPv1 agent will be preserved through the use of the
snmpTrapAddress and snmpTrapCommunity objects.
4.3.2. Upstream Version Less Than Downstream Version
- If a GetResponse-PDU is received in response to a GetRequest-PDU
(previously generated by the proxy) which contains variable-
bindings of type Counter64 or which contain an SNMPv2 exception
code, and the message would be forwarded using the SNMPv1 message
version, the proxy MUST generate an alternate response PDU
consisting of the request-id and variable bindings from the
original SNMPv1 request, containing a noSuchName error-status
value, and containing an error-index value indicating the position
of the variable-binding containing the Counter64 type or exception
code.
- If a GetResponse-PDU is received in response to a GetNextRequest-
PDU (previously generated by the proxy) which contains variable-
bindings that contain an SNMPv2 exception code, and the message
would be forwarded using the SNMPv1 message version, the proxy
MUST generate an alternate response PDU consisting of the
request-id and variable bindings from the original SNMPv1 request,
containing a noSuchName error-status value, and containing an
error-index value indicating the position of the variable-binding
containing the exception code.
- If a GetResponse-PDU is received in response to a GetNextRequest-
PDU (previously generated by the proxy) which contains variable-
bindings of type Counter64, the proxy MUST re-send the entire
GetNextRequest-PDU, with the following modifications. For any
variable bindings in the received GetResponse which contained
Counter64 types, the proxy substitutes the object names of these
variable bindings for the corresponding object names in the
previously-sent GetNextRequest. The proxy MUST repeat this
process until no Counter64 objects are returned. Note that an
implementation may attempt to optimize this process of skipping
Counter64 objects. One approach to such an optimization would be
to replace the last sub-identifier of the object names of varbinds
containing a Counter64 type with 65535 if that sub-identifier is
less than 65535, or with 4294967295 if that sub-identifier is
greater than 65535. This approach should skip multiple instances
of the same Counter64 object, while maintaining compatibility with
some broken agent implementations (which only use 16-bit integers
for sub-identifiers).
Deployment Hint: The process of repeated GetNext requests used by
a proxy when Counter64 types are returned can be expensive. When
deploying a proxy, this can be avoided by configuring the target
agents to which the proxy forwards requests in a manner such that
any objects of type Counter64 are in fact not-in-view for the
principal that the proxy is using when communicating with these
agents. However, when using such a configuration, one should be
careful to use a different principal for communicating with the
target agent when an incoming SNMPv2c or SNMPv3 request is
received, to ensure that objects of type Counter64 are properly
returned.
- If a GetResponse-PDU is received which contains an SNMPv2 error-
status value of wrongValue, wrongEncoding, wrongType, wrongLength,
inconsistentValue, noAccess, notWritable, noCreation,
inconsistentName, resourceUnavailable, commitFailed, undoFailed,
or authorizationError, and the message would be forwarded using
the SNMPv1 message version, the error-status value is modified
using the mappings in section 4.4.
- If an SNMPv2-Trap-PDU is received, and will be forwarded using the
SNMPv1 message version, the proxy SHALL apply the translation
rules described in section 3, and SHALL forward the notification
as a Trap-PDU. Note that if the translation fails due to the
existence of a Counter64 data-type in the received SNMPv2-Trap-
PDU, the trap cannot be forwarded using SNMPv1.
- If an InformRequest-PDU is received, any configuration information
indicating that it would be forwarded using the SNMPv1 message
version SHALL be ignored. An InformRequest-PDU can only be
forwarded using the SNMPv2c or SNMPv3 message version. The
InformRequest-PDU may still be forwarded if there is other
configuration information indicating that it should be forwarded
using SNMPv2c or SNMPv3.
4.4. Error Status Mappings
The following tables shows the mappings of SNMPv1 error-status values
into SNMPv2 error-status values, and the mappings of SNMPv2 error-
status values into SNMPv1 error-status values.
SNMPv1 error-status SNMPv2 error-status
=================== ===================
noError noError
tooBig tooBig
noSuchName noSuchName
badValue badValue
genErr genErr
SNMPv2 error-status SNMPv1 error-status
=================== ===================
noError noError
tooBig tooBig
genErr genErr
wrongValue badValue
wrongEncoding badValue
wrongType badValue
wrongLength badValue
inconsistentValue badValue
noAccess noSuchName
notWritable noSuchName
noCreation noSuchName
inconsistentName noSuchName
resourceUnavailable genErr
commitFailed genErr
undoFailed genErr
authorizationError noSuchName
Whenever the SNMPv2 error-status value of authorizationError is
translated to an SNMPv1 error-status value of noSuchName, the value
of snmpInBadCommunityUses MUST be incremented.
5. Message Processing Models and Security Models
In order to adapt SNMPv1 (and SNMPv2c) into the SNMP architecture,
the following Message Processing (MP) models are defined in this
document:
- The SNMPv1 Message Processing Model
- The SNMPv1 Community-Based Security Model
- The SNMPv2c Message Processing Model
- The SNMPv2c Community-Based Security Model
In most respects, the SNMPv1 Message Processing Model and the SNMPv2c
Message Processing Model are identical, and so these are not
discussed independently in this document. Differences between the
two models are described as required.
Similarly, the SNMPv1 Community-Based Security Model and the SNMPv2c
Community-Based Security Model are nearly identical, and so are not
discussed independently. Differences between these two models are
also described as required.
5.1. Mappings
The SNMPv1 (and SNMPv2c) Message Processing Model and Security Model
require mappings between parameters used in SNMPv1 (and SNMPv2c)
messages, and the version independent parameters used in the SNMP
architecture [RFC3411]. The parameters which MUST be mapped consist
of the SNMPv1 (and SNMPv2c) community name, and the SNMP securityName
and contextEngineID/contextName pair. A MIB module (the SNMP-
COMMUNITY-MIB) is provided in this document in order to perform these
mappings. This MIB provides mappings in both directions, that is, a
community name may be mapped to a securityName, contextEngineID, and
contextName, or the combination of securityName, contextEngineID, and
contextName may be mapped to a community name.
5.2. The SNMPv1 MP Model and SNMPv1 Community-based Security Model
The SNMPv1 Message Processing Model handles processing of SNMPv1
messages. The processing of messages is handled generally in the
same manner as described in RFC1157 [RFC1157], with differences and
clarifications as described in the following sections. The
SnmpMessageProcessingModel value for SNMPv1 is 0 (the value for
SNMPv2c is 1).
5.2.1. Processing An Incoming Request
In RFC1157 [RFC1157], section 4.1, item (3) for an entity which
receives a message, states that various parameters are passed to the
"desired authentication scheme". The desired authentication scheme
in this case is the SNMPv1 Community-Based Security Model, which will
be called using the processIncomingMsg ASI. The parameters passed to
this ASI are:
- The messageProcessingModel, which will be 0 (or 1 for SNMPv2c).
- The maxMessageSize, which should be the maximum size of a message
that the receiving entity can generate (since there is no such
value in the received message).
- The securityParameters, which consist of the community string and
the message's source and destination transport domains and
addresses.
- The securityModel, which will be 1 (or 2 for SNMPv2c).
- The securityLevel, which will be noAuthNoPriv.
- The wholeMsg and wholeMsgLength.
The Community-Based Security Model will attempt to select a row in
the snmpCommunityTable. This is done by performing a search through
the snmpCommunityTable in lexicographic order. The first entry for
which the following matching criteria are satisfied will be selected:
- The community string is equal to the snmpCommunityName value.
- If the snmpCommunityTransportTag is an empty string, it is ignored
for the purpose of matching. If the snmpCommunityTransportTag is
not an empty string, the transportDomain and transportAddress from
which the message was received must match one of the entries in
the snmpTargetAddrTable selected by the snmpCommunityTransportTag
value. The snmpTargetAddrTMask object is used as described in
section 5.3 when checking whether the transportDomain and
transportAddress matches a entry in the snmpTargetAddrTable.
If no such entry can be found, an authentication failure occurs as
described in RFC1157 [RFC1157], and the snmpInBadCommunityNames
counter is incremented.
The parameters returned from the Community-Based Security Model are:
- The securityEngineID, which will always be the local value of
snmpEngineID.0.
- The securityName, which will be the value of
snmpCommunitySecurityName from the selected row in the
snmpCommunityTable.
- The scopedPDU. Note that this parameter will actually consist of
three values, the contextSnmpEngineID (which will be the value of
snmpCommunityContextEngineID from the selected entry in the
snmpCommunityTable), the contextName (which will be the value of
snmpCommunityContextName from the selected entry in the
snmpCommunityTable), and the PDU. These must be separate values,
since the first two do not actually appear in the message.
- The maxSizeResponseScopedPDU, which will be derived using the
minimum of the maxMessageSize above, and the value of
snmpTargetAddrMMS of the selected row in the snmpTargetAddrTable.
If no such entry was selected, then this value will be derived
from the maxMessageSize only.
- The securityStateReference, which MUST contain the community
string from the original request.
The appropriate SNMP application will then be called (depending on
the value of the contextEngineID and the request type in the PDU)
using the processPdu ASI. The parameters passed to this ASI are:
- The messageProcessingModel, which will be 0 (or 1 for SNMPv2c).
- The securityModel, which will be 1 (or 2 for SNMPv2c).
- The securityName, which was returned from the call to
processIncomingMsg.
- The securityLevel, which is noAuthNoPriv.
- The contextEngineID, which was returned as part of the ScopedPDU
from the call to processIncomingMsg.
- The contextName, which was returned as part of the ScopedPDU from
the call to processIncomingMsg.
- The pduVersion, which should indicate an SNMPv1 version PDU (if
the message version was SNMPv2c, this would be an SNMPv2 version
PDU).
- The PDU, which was returned as part of the ScopedPDU from the call
to processIncomingMsg.
- The maxSizeResponseScopedPDU which was returned from the call to
processIncomingMsg.
- The stateReference which was returned from the call to
processIncomingMsg.
The SNMP application should process the request as described
previously in this document. Note that access control is applied by
an SNMPv3 command responder application as usual. The parameters as
passed to the processPdu ASI will be used in calls to the
isAccessAllowed ASI.
5.2.2. Generating An Outgoing Response
There is no special processing required for generating an outgoing
response. However, the community string used in an outgoing response
must be the same as the community string from the original request.
The original community string MUST be present in the
securityStateReference information of the original request.
5.2.3. Generating An Outgoing Notification
In a multi-lingual SNMP entity, the parameters used for generating
notifications will be obtained by examining the SNMP-TARGET-MIB and
SNMP-NOTIFICATION-MIB. These parameters will be passed to the SNMPv1
Message Processing Model using the sendPdu ASI. The SNMPv1 Message
Processing Model will attempt to locate an appropriate community
string in the snmpCommunityTable based on the parameters passed to
the sendPdu ASI. This is done by performing a search through the
snmpCommunityTable in lexicographic order. The first entry for which
the following matching criteria are satisfied will be selected:
- The securityName must be equal to the snmpCommunitySecurityName
value.
- The contextEngineID must be equal to the
snmpCommunityContextEngineID value.
- The contextName must be equal to the snmpCommunityContextName
value.
- If the snmpCommunityTransportTag is an empty string, it is ignored
for the purpose of matching. If the snmpCommunityTransportTag is
not an empty string, the transportDomain and transportAddress must
match one of the entries in the snmpTargetAddrTable selected by
the snmpCommunityTransportTag value.
If no such entry can be found, the notification is not sent.
Otherwise, the community string used in the outgoing notification
will be the value of the snmpCommunityName column of the selected
row.
5.2.4. Proxy Forwarding Of Requests
In a proxy forwarding application, when a received request is to be
forwarded using the SNMPv1 Message Processing Model, the parameters
used for forwarding will be obtained by examining the SNMP-PROXY-MIB
and the SNMP-TARGET-MIB. These parameters will be passed to the
SNMPv1 Message Processing Model using the sendPdu ASI. The SNMPv1
Message Processing Model will attempt to locate an appropriate
community string in the snmpCommunityTable based on the parameters
passed to the sendPdu ASI. This is done by performing a search
through the snmpCommunityTable in lexicographic order. The first
entry for which the following matching criteria are satisfied will be
selected:
- The securityName must be equal to the snmpCommunitySecurityName
value.
- The contextEngineID must be equal to the
snmpCommunityContextEngineID value.
- The contextName must be equal to the snmpCommunityContextName
value.
If no such entry can be found, the proxy forwarding application
should follow the procedure described in RFC3413 [RFC3413], section
3.5.1.1, item (2). This procedure states that the snmpProxyDrops
counter [RFC3418] is incremented, and that a Response-PDU is
generated by calling the Dispatcher using the returnResponsePdu
abstract service interface.
5.3. The SNMP Community MIB Module
The SNMP-COMMUNITY-MIB contains objects for mapping between community
strings and version-independent SNMP message parameters. In
addition, this MIB provides a mechanism for performing source address
validation on incoming requests, and for selecting community strings
based on target addresses for outgoing notifications. These two
features are accomplished by providing a tag in the
snmpCommunityTable which selects sets of entries in the
snmpTargetAddrTable [RFC3413]. In addition, the SNMP-COMMUNITY-MIB
augments the snmpTargetAddrTable with a transport address mask value
and a maximum message size value. These values are used only where
explicitly stated. In cases where the snmpTargetAddrTable is used
without mention of these augmenting values, the augmenting values
should be ignored.
The mask value, snmpTargetAddrTMask, allows selected entries in the
snmpTargetAddrTable to specify multiple addresses (rather than just a
single address per entry). This would typically be used to specify a
subnet in an snmpTargetAddrTable rather than just a single address.
The mask value is used to select which bits of a transport address
must match bits of the corresponding instance of
snmpTargetAddrTAddress, in order for the transport address to match a
particular entry in the snmpTargetAddrTable. The value of an
instance of snmpTargetAddrTMask must always be an OCTET STRING whose
length is either zero or the same as that of the corresponding
instance of snmpTargetAddrTAddress.
Note that the snmpTargetAddrTMask object is only used where
explicitly stated. In particular, it is not used when generating
notifications (i.e., when generating notifications, entries in the
snmpTargetAddrTable only specify individual addresses). If use of
the snmpTargetAddrTMask object is not mentioned in text describing
matching addresses in the snmpTargetAddrTable, then its value MUST be
ignored.
When checking whether a transport address matches an entry in the
snmpTargetAddrTable, if the value of snmpTargetAddrTMask is a zero-
length OCTET STRING, the mask value is ignored, and the value of
snmpTargetAddrTAddress must exactly match a transport address.
Otherwise, each bit of each octet in the snmpTargetAddrTMask value
corresponds to the same bit of the same octet in the
snmpTargetAddrTAddress value. For bits that are set in the
snmpTargetAddrTMask value (i.e., bits equal to 1), the corresponding
bits in the snmpTargetAddrTAddress value must match the bits in a
transport address. If all such bits match, the transport address is
matched by that snmpTargetAddrTable entry. Otherwise, the transport
address is not matched.
The maximum message size value, snmpTargetAddrMMS, is used to
determine the maximum message size acceptable to another SNMP entity
when the value cannot be determined from the protocol.
SNMP-COMMUNITY-MIB DEFINITIONS ::= BEGIN
IMPORTS
IpAddress,
MODULE-IDENTITY,
OBJECT-TYPE,
Integer32,
snmpModules
FROM SNMPv2-SMI
RowStatus,
StorageType
FROM SNMPv2-TC
SnmpAdminString,
SnmpEngineID
FROM SNMP-FRAMEWORK-MIB
SnmpTagValue,
snmpTargetAddrEntry
FROM SNMP-TARGET-MIB
MODULE-COMPLIANCE,
OBJECT-GROUP
FROM SNMPv2-CONF;
snmpCommunityMIB MODULE-IDENTITY
LAST-UPDATED "200308060000Z" -- 06 Aug 2003, midnight
ORGANIZATION "SNMPv3 Working Group"
CONTACT-INFO "WG-email: snmpv3@lists.tislabs.com
Subscribe: majordomo@lists.tislabs.com
In msg body: subscribe snmpv3
Co-Chair: Russ Mundy
SPARTA, Inc
Postal: 7075 Samuel Morse Drive
Columbia, MD 21045
USA
EMail: mundy@tislabs.com
Phone: +1 410-872-1515
Co-Chair: David Harrington
Enterasys Networks
Postal: 35 Industrial Way
P. O. Box 5005
Rochester, New Hampshire 03866-5005
USA
EMail: dbh@enterasys.com
Phone: +1 603-337-2614
Co-editor: Rob Frye
Vibrant Solutions
Postal: 2711 Prosperity Ave
Fairfax, Virginia 22031
USA
E-mail: rfrye@vibrant-1.com
Phone: +1-703-270-2000
Co-editor: David B. Levi
Nortel Networks
Postal: 3505 Kesterwood Drive
Knoxville, Tennessee 37918
E-mail: dlevi@nortelnetworks.com
Phone: +1 865 686 0432
Co-editor: Shawn A. Routhier
Wind River Systems, Inc.
Postal: 500 Wind River Way
Alameda, CA 94501
E-mail: sar@epilogue.com
Phone: +1 510 749 2095
Co-editor: Bert Wijnen
Lucent Technologies
Postal: Schagen 33
3461 GL Linschoten
Netherlands
Email: bwijnen@lucent.com
Phone: +31-348-407-775
"
DESCRIPTION
"This MIB module defines objects to help support
coexistence between SNMPv1, SNMPv2c, and SNMPv3.
Copyright (C) The Internet Society (2003) This
version of this MIB module is part of RFC3584;
see the RFCitself for full legal notices."
REVISION "200308060000Z" -- 06 Aug 2003
DESCRIPTION
"Updated the LAST-UPDATED, CONTACT-INFO, and REVISION
clauses and added a copyright notice to the
DESCRIPTION clause of the MIB module's
MODULE-IDENTITY invocation.
Updated the description of snmpCommunityTransportTag
to make it consistent with the rest of the document.
Updated the description of `snmpTargetAddrMMS' to
clarify that a value of 0 means that the maximum
message size is unknown.
Changed the name of 'snmpCommunityGroup' to
snmpCommunityTableGroup to avoid a name conflict
with the SNMPv2-MIB.
Updated DESCRIPTION of snmpCommunityName.
Updated DESCRIPTION of snmpTrapCommunity.
Added snmpCommunityMIBFullCompliance.
This version published as RFC3584."
REVISION "200003060000Z" -- 6 Mar 2000
DESCRIPTION "This version published as RFC2576."
::= { snmpModules 18 }
-- Administrative assignments ************************************
snmpCommunityMIBObjects
OBJECT IDENTIFIER ::= { snmpCommunityMIB 1 }
snmpCommunityMIBConformance
OBJECT IDENTIFIER ::= { snmpCommunityMIB 2 }
--
-- The snmpCommunityTable contains a database of community
-- strings. This table provides mappings between community
-- strings, and the parameters required for View-based Access
-- Control.
--
snmpCommunityTable OBJECT-TYPE
SYNTAX SEQUENCE OF SnmpCommunityEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The table of community strings configured in the SNMP
engine's Local Configuration Datastore (LCD)."
::= { snmpCommunityMIBObjects 1 }
snmpCommunityEntry OBJECT-TYPE
SYNTAX SnmpCommunityEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Information about a particular community string."
INDEX { IMPLIED snmpCommunityIndex }
::= { snmpCommunityTable 1 }
SnmpCommunityEntry ::= SEQUENCE {
snmpCommunityIndex SnmpAdminString,
snmpCommunityName OCTET STRING,
snmpCommunitySecurityName SnmpAdminString,
snmpCommunityContextEngineID SnmpEngineID,
snmpCommunityContextName SnmpAdminString,
snmpCommunityTransportTag SnmpTagValue,
snmpCommunityStorageType StorageType,
snmpCommunityStatus RowStatus
}
snmpCommunityIndex OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The unique index value of a row in this table."
::= { snmpCommunityEntry 1 }
snmpCommunityName OBJECT-TYPE
SYNTAX OCTET STRING
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The community string for which a row in this table
represents a configuration. There is no SIZE constraint
specified for this object because RFC1157 does not
impose any explicit limitation on the length of community
strings (their size is constrained indirectly by the
SNMP message size)."
::= { snmpCommunityEntry 2 }
snmpCommunitySecurityName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(1..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"A human readable string representing the corresponding
value of snmpCommunityName in a Security Model
independent format."
::= { snmpCommunityEntry 3 }
snmpCommunityContextEngineID OBJECT-TYPE
SYNTAX SnmpEngineID
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The contextEngineID indicating the location of the
context in which management information is accessed
when using the community string specified by the
corresponding instance of snmpCommunityName.
The default value is the snmpEngineID of the entity in
which this object is instantiated."
::= { snmpCommunityEntry 4 }
snmpCommunityContextName OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The context in which management information is accessed
when using the community string specified by the
corresponding instance of snmpCommunityName."
DEFVAL { ''H } -- the empty string
::= { snmpCommunityEntry 5 }
snmpCommunityTransportTag OBJECT-TYPE
SYNTAX SnmpTagValue
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"This object specifies a set of transport endpoints
which are used in two ways:
- to specify the transport endpoints from which an
SNMP entity will accept management requests, and
- to specify the transport endpoints to which a
notification may be sent using the community
string matching the corresponding instance of
snmpCommunityName.
In either case, if the value of this object has
zero-length, transport endpoints are not checked when
either authenticating messages containing this community
string, nor when generating notifications.
The transports identified by this object are specified
in the snmpTargetAddrTable. Entries in that table
whose snmpTargetAddrTagList contains this tag value
are identified.
If a management request containing a community string
that matches the corresponding instance of
snmpCommunityName is received on a transport endpoint
other than the transport endpoints identified by this
object the request is deemed unauthentic.
When a notification is to be sent using an entry in
this table, if the destination transport endpoint of
the notification does not match one of the transport
endpoints selected by this object, the notification
is not sent."
DEFVAL { ''H } -- the empty string
::= { snmpCommunityEntry 6 }
snmpCommunityStorageType OBJECT-TYPE
SYNTAX StorageType
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The storage type for this conceptual row in the
snmpCommunityTable. Conceptual rows having the value
'permanent' need not allow write-access to any
columnar object in the row."
::= { snmpCommunityEntry 7 }
snmpCommunityStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this conceptual row in the
snmpCommunityTable.
An entry in this table is not qualified for activation
until instances of all corresponding columns have been
initialized, either through default values, or through
Set operations. The snmpCommunityName and
snmpCommunitySecurityName objects must be explicitly set.
There is no restriction on setting columns in this table
when the value of snmpCommunityStatus is active(1)."
::= { snmpCommunityEntry 8 }
--
-- The snmpTargetAddrExtTable
--
snmpTargetAddrExtTable OBJECT-TYPE
SYNTAX SEQUENCE OF SnmpTargetAddrExtEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The table of mask and maximum message size (mms) values
associated with the snmpTargetAddrTable.
The snmpTargetAddrExtTable augments the
snmpTargetAddrTable with a transport address mask value
and a maximum message size value. The transport address
mask allows entries in the snmpTargetAddrTable to define
a set of addresses instead of just a single address.
The maximum message size value allows the maximum
message size of another SNMP entity to be configured for
use in SNMPv1 (and SNMPv2c) transactions, where the
message format does not specify a maximum message size."
::= { snmpCommunityMIBObjects 2 }
snmpTargetAddrExtEntry OBJECT-TYPE
SYNTAX SnmpTargetAddrExtEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Information about a particular mask and mms value."
AUGMENTS { snmpTargetAddrEntry }
::= { snmpTargetAddrExtTable 1 }
SnmpTargetAddrExtEntry ::= SEQUENCE {
snmpTargetAddrTMask OCTET STRING,
snmpTargetAddrMMS Integer32
}
snmpTargetAddrTMask OBJECT-TYPE
SYNTAX OCTET STRING (SIZE (0..255))
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The mask value associated with an entry in the
snmpTargetAddrTable. The value of this object must
have the same length as the corresponding instance of
snmpTargetAddrTAddress, or must have length 0. An
attempt to set it to any other value will result in
an inconsistentValue error.
The value of this object allows an entry in the
snmpTargetAddrTable to specify multiple addresses.
The mask value is used to select which bits of
a transport address must match bits of the corresponding
instance of snmpTargetAddrTAddress, in order for the
transport address to match a particular entry in the
snmpTargetAddrTable. Bits which are 1 in the mask
value indicate bits in the transport address which
must match bits in the snmpTargetAddrTAddress value.
Bits which are 0 in the mask indicate bits in the
transport address which need not match. If the
length of the mask is 0, the mask should be treated
as if all its bits were 1 and its length were equal
to the length of the corresponding value of
snmpTargetAddrTable.
This object may not be modified while the value of the
corresponding instance of snmpTargetAddrRowStatus is
active(1). An attempt to set this object in this case
will result in an inconsistentValue error."
DEFVAL { ''H }
::= { snmpTargetAddrExtEntry 1 }
snmpTargetAddrMMS OBJECT-TYPE
SYNTAX Integer32 (0|484..2147483647)
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The maximum message size value associated with an entry
in the snmpTargetAddrTable. Note that a value of 0 means
that the maximum message size is unknown."
DEFVAL { 484 }
::= { snmpTargetAddrExtEntry 2 }
--
-- The snmpTrapAddress and snmpTrapCommunity objects are included
-- in notifications that are forwarded by a proxy, which were
-- originally received as SNMPv1 Trap messages.
--
snmpTrapAddress OBJECT-TYPE
SYNTAX IpAddress
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"The value of the agent-addr field of a Trap PDU which
is forwarded by a proxy forwarder application using
an SNMP version other than SNMPv1. The value of this
object SHOULD contain the value of the agent-addr field
from the original Trap PDU as generated by an SNMPv1
agent."
::= { snmpCommunityMIBObjects 3 }
snmpTrapCommunity OBJECT-TYPE
SYNTAX OCTET STRING
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"The value of the community string field of an SNMPv1
message containing a Trap PDU which is forwarded by a
a proxy forwarder application using an SNMP version
other than SNMPv1. The value of this object SHOULD
contain the value of the community string field from
the original SNMPv1 message containing a Trap PDU as
generated by an SNMPv1 agent. There is no SIZE
constraint specified for this object because RFC1157
does not impose any explicit limitation on the length
of community strings (their size is constrained
indirectly by the SNMP message size)."
::= { snmpCommunityMIBObjects 4 }
-- Conformance Information **************************************
snmpCommunityMIBCompliances OBJECT IDENTIFIER
::= { snmpCommunityMIBConformance 1 }
snmpCommunityMIBGroups OBJECT IDENTIFIER
::= { snmpCommunityMIBConformance 2 }
-- Compliance statements
snmpCommunityMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines which
implement the SNMP-COMMUNITY-MIB."
MODULE -- this module
MANDATORY-GROUPS { snmpCommunityTableGroup }
OBJECT snmpCommunityName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunitySecurityName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityContextEngineID
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityContextName
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityTransportTag
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityStorageType
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
OBJECT snmpCommunityStatus
MIN-ACCESS read-only
DESCRIPTION "Write access is not required."
::= { snmpCommunityMIBCompliances 1 }
snmpProxyTrapForwardCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines which
contain a proxy forwarding application which is
capable of forwarding SNMPv1 traps using SNMPv2c
or SNMPv3."
MODULE -- this module
MANDATORY-GROUPS { snmpProxyTrapForwardGroup }
::= { snmpCommunityMIBCompliances 2 }
snmpCommunityMIBFullCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for SNMP engines which
implement the SNMP-COMMUNITY-MIB with full read-create
access."
MODULE -- this module
MANDATORY-GROUPS { snmpCommunityTableGroup }
::= { snmpCommunityMIBCompliances 3 }
snmpCommunityTableGroup OBJECT-GROUP
OBJECTS {
snmpCommunityName,
snmpCommunitySecurityName,
snmpCommunityContextEngineID,
snmpCommunityContextName,
snmpCommunityTransportTag,
snmpCommunityStorageType,
snmpCommunityStatus,
snmpTargetAddrTMask,
snmpTargetAddrMMS
}
STATUS current
DESCRIPTION
"A collection of objects providing for configuration
of community strings for SNMPv1 (and SNMPv2c) usage."
::= { snmpCommunityMIBGroups 1 }
snmpProxyTrapForwardGroup OBJECT-GROUP
OBJECTS {
snmpTrapAddress,
snmpTrapCommunity
}
STATUS current
DESCRIPTION
"Objects which are used by proxy forwarding applications
when translating traps between SNMP versions. These are
used to preserve SNMPv1-specific information when
translating to SNMPv2c or SNMPv3."
::= { snmpCommunityMIBGroups 3 }
END
6. Intellectual Property Statement
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.
7. Acknowledgments
This document is the result of the efforts of the SNMPv3 Working
Group. The design of the SNMP-COMMUNITY-MIB incorporates work done
by the authors of SNMPv2*:
Jeff Case (SNMP Research, Inc.)
David Harrington (Enterasys Networks)
David Levi (Nortel Networks)
Brian O'Keefe (Hewlett Packard)
Jon Saperia (IronBridge Networks, Inc.)
Steve Waldbusser (International Network Services)
8. Security Considerations
Although SNMPv1 and SNMPv2 do not provide any security, allowing
community names to be mapped into securityName/contextName provides
the ability to use view-based access control to limit the access of
unsecured SNMPv1 and SNMPv2 operations. In fact, it is important for
network administrators to make use of this capability in order to
avoid unauthorized access to MIB data that would otherwise be secure.
When a proxy implementation translates messages between SNMPv1 (or
SNMPv2c) and SNMPv3, there may be a loss of security. For example,
an SNMPv3 message received using authentication and privacy which is
subsequently forwarded using SNMPv1 will lose the security benefits
of using authentication and privacy (also known as confidentiality).
Careful configuration of proxies is required to address such
situations. One approach to deal with such situations might be to
use an encrypted tunnel.
There are a number of management objects defined in this MIB module
with a MAX-ACCESS clause of read-write and/or read-create. Such
objects may be considered sensitive or vulnerable in some network
environments. The support for SET operations in a non-secure
environment without proper protection can have a negative effect on
network operations. These are the tables and objects and their
sensitivity/vulnerability:
- The snmpCommunityTable allows creation and deletion of community
strings, which is potentially a serious security hole. Access to
this table should be greatly restricted, preferably by only
allowing write access using SNMPv3 VACM and USM, with
authentication and privacy.
- The snmpTargetAddrExtTable contains write-able objects which may
also be considered sensitive, and so access to it should be
restricted as well.
Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability:
- The snmpCommunityTable has the potential to expose community
strings which provide access to more information than that which
is available using the usual 'public' community string. For this
reason, a security administrator may wish to limit accessibility
to objects in the snmpCommunityTable, and in particular, to make
it inaccessible when using the 'public' community string.
SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPSec),
even then, there is no control as to who on the secure network is
allowed to access and GET/SET (read/change/create/delete) the objects
in this MIB module.
It is RECOMMENDED that implementers consider the security features as
provided by the SNMPv3 framework (see [RFC3410], section 8),
including full support for the SNMPv3 cryptographic mechanisms (for
authentication and privacy).
Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them.
9. References
9.1. Normative References
[RFC1155] Rose, M. and K. McCloghrie, "Structure and Identification
of Management Information for TCP/IP-based internets",
STD 16, RFC1155, May 1990.
[RFC1157] Case, J., Fedor, M., Schoffstall, M. and C. Davin,
"Simple Network Management Protocol (SNMP)", STD 15, RFC
1157, May 1990.
[RFC1212] Rose, M. and K. McCloghrie, Eds., "Concise MIB
Definitions", STD 16, RFC1212, March 1991.
[RFC1215] Rose, M., "A Convention for Defining Traps for use with
the SNMP", RFC1215, March 1991.
[RFC1303] McCloghrie, K. and M. Rose, "A Convention for Describing
SNMP-based Agents", RFC1303, February 1992.
[RFC1901] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC1901,
January 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[RFC2578] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Structure of Management Information Version 2 (SMIv2)",
RFC2578, STD 58, April 1999.
[RFC2579] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Textual Conventions for SMIv2", STD 58, RFC2579, April
1999.
[RFC2580] McCloghrie, K., Perkins, D. and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC2580,
April 1999.
[RFC3411] Harrington, D., Presuhn, R. and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC3411,
December 2002.
[RFC3412] Case, J., Harrington, D., Presuhn, R. and B. Wijnen,
"Message Processing and Dispatching for the Simple
Network Management Protocol (SNMP)", STD 62, RFC3412,
December 2002.
[RFC3413] Levi, D., Meyer, P. and B. Stewart, "Simple Network
Management Protocol (SNMP) Applications", STD 62, RFC
3413, December 2002.
[RFC3414] Blumenthal, U. and B. Wijnen, "The User-Based Security
Model (USM) for Version 3 of the Simple Network
Management Protocol (SNMP)", STD 62, RFC3414, December
2002.
[RFC3415] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network
Management Protocol (SNMP)", STD 62, RFC3415, December
2002.
[