Network Working Group Dave Thaler
Internet-Draft Microsoft Corporation
Expires: May 2001 Satyen Chandragiri
Lucent Technologies
November 2000
Subtree Retrieval MIB
<draft-irtf-nmrg-get-subtree-mib-01.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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Internet-Drafts are draft documents valid for a maximum of six
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progress."
The list of current Internet-Drafts can be accessed at
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Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
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1. Introduction
This memo defines a portion of the Management Information Base
(MIB) for use with network management protocols in the Internet
community. In particular, it describes managed objects used for
retrieving subtrees of MIB objects without the overshoot problems
of the SNMP GetBulkRequest operation.
2. The SNMP Network Management Framework
The SNMP Management Framework presently consists of five major
components:
o An overall architecture, described in RFC 2571 [1].
o Mechanisms for describing and naming objects and events for
the purpose of management. The first version of this
Structure of Management Information (SMI) is called SMIv1 and
described in RFC 1155 [2], RFC 1212 [3] and RFC 1215 [4]. The
second version, called SMIv2, is described in RFC 2578 [5],
RFC 2579 [6] and RFC 2580 [7].
o Message protocols for transferring management information.
The first version of the SNMP message protocol is called
SNMPv1 and described in RFC 1157 [8]. A second version of the
SNMP message protocol, which is not an Internet standards
track protocol, is called SNMPv2c and described in RFC 1901
[9] and RFC 1906 [10]. The third version of the message
protocol is called SNMPv3 and described in RFC 1906 [10], RFC
2572 [11] and RFC 2574 [12].
o Protocol operations for accessing management information. The
first set of protocol operations and associated PDU formats
is described in RFC 1157 [8]. A second set of protocol
operations and associated PDU formats is described in RFC
1905 [13].
o A set of fundamental applications described in RFC 2573 [14]
and the view-based access control mechanism described in RFC
2575 [15].
Managed objects are accessed via a virtual information store,
termed the Management Information Base or MIB. Objects in the MIB
are defined using the mechanisms defined in the SMI.
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This memo specifies a MIB module that is compliant with the SMIv2.
A MIB conforming to the SMIv1 can be produced through the
appropriate translations. The resulting translated MIB must be
semantically equivalent, except where objects or events are
omitted because no translation is possible (use of Counter64).
Some machine readable information in SMIv2 will be converted into
textual descriptions in SMIv1 during the translation process.
However, this loss of machine readable information is not
considered to change the semantics of the MIB.
3. Overview
A major shortcoming of SNMP is the lack of a mechanism to
efficiently retrieve large amounts of MIB data from a device.
SNMPv1, though widely deployed, contains no provision for bulk
retrieval and the manager must use GetNextRequests to traverse the
MIB. This requires a large number of request-response exchanges
leading to high latency. To address this problem, the
GetBulkRequest operation [13] was introduced in SNMPv2.
The GetBulkRequest operation aims to minimize the number of
protocol exchanges required to retrieve a large amount of
management information by returning a series of variable bindings
in a single response. The requester is required to specify a "max-
repetitions" count, and the agent then fills in as many variable
bindings as it can without exceeding either this count, or the
maximum message size.
The main problem with retrieving tables using GetBulkRequest is
that the manager typically does not know the number of rows in the
table, and hence cannot set max-repetitions to the optimal value.
As a result, the manager must either set max-repetitions to some
huge value, resulting in a potentially large waste of bandwidth
when many more variable bindings are returned than are needed
(sometimes called "overshoot"), or else must issue multiple
GetBulkRequests sequentially to traverse a large table such as the
routing table in a backbone router.
This document describes a MIB that can be used by an application
to retrieve MIB information in a more efficient way without any
change to the SNMP protocol or SNMP protocol engines. This
operation, referred to as a "GetSubtree" request, allows a manager
to request the agent to retrieve a subtree of MIB data starting at
the root OID (specified by the manager) and including all object
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instances whose OID is prefixed by the root OID. The manager is
also provided the facility to specify several subtrees of data to
be retrieved in parallel by the agent.
This approach eliminates the guesswork involved in using the
GetBulkRequest operation and makes good use of bandwidth as only
those MIB objects of interest to the manager are retrieved (albeit
with some overhead).
3.1. Structure of the MIB
This MIB consists of two tables:
o getSubtreeRootTable - this table stores the root OID(s) of
the subtree(s) to be retrieved. Rows in this table are
indexed by getSubtreeRootOperationID which uniquely
identifies the retrieval operation in progress, and a
secondary index (getSubtreeRootOIDIndex) which identifies the
root OIDs associated with the request.
o getSubtreeControlTable - this table stores the main
getSubtree request information. The manager must create a row
which identifies the application (represented by an entry in
the snmpTargetAddrTable) as the response destination. Rows in
this table are indexed by getSubtreeRootOperationID from the
getSubtreeRootTable.
Note: The application must have been pre-configured as a
legal notification target in the SNMP-TARGET-MIB [14].
3.2. Operation
To set up a retrieval, an application issues a SetRequest to
perform a row creation in the getSubtreeRootTable using an
arbitrarily selected value for the primary index
(getSubtreeRootOperationID), a value of "1" for the secondary
index (getSubtreeRootOIDIndex), and the root OID of the subtree to
be retrieved. If the application wishes to retrieve multiple
subtrees simultaneously, it may do so by creating additional rows
for each subtree's root OID using the same primary index value and
sequentially increasing values for getSubtreeRootOIDIndex. The
purpose of starting the secondary index values at "1" for each new
GetSubtree operation is to avoid concurrency problems if another
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management application happens to select the same value of the
primary index for creating its rows in this table. Note that
creating rows in the getSubtreeRootTable in itself does not start
the retrieval process.
The manager must then create a row in the getSubtreeControlTable
using the same value of getSubtreeRootOperationID as the index and
identifying itself via the getSubtreeControlTarget object.
Creating a row in this table triggers the agent to begin sending
traps containing the requested information to the application, so
long as there are one or more entries in the getSubtreeRootTable
indexed by the same value of getSubtreeRootOperationID. If there
are no such entries, then this newly created row in the
getSubtreeControlTable will be deleted automatically by the agent.
It may also be that a manager may make one or more rows in the
getSubtreeRootTable and fail to make any entries in the
getSubtreeControlTable to drive the operation. In this case, the
agent may choose what to do with these "orphaned" entries. Options
include, but are not limited to: letting them exist indefinitely;
deleting them after some timeout period has elapsed; or deleting
them if there is a resource shortage. The choice is implementation
dependent.
Each trap generated by the agent contains a sequence number object
(which can be used to detect losses), a counter object, a flag
object signalling whether the trap is the final one in the
sequence, and a series of varbinds containing the next chunk from
the requested subtree. The agent will send as many varbinds in the
trap as possible without exceeding the maximum message size and
without going beyond the subtree. Multiple traps will be sent
until the entire subtree has been retrieved. If more than one
subtree has been requested, the agent will send repetitions
containing varbinds from each subtree until all subtrees have been
retrieved. The agent must ensure that each trap contains only an
integral number of repetitions.
If a manager detects a lost trap (or a sequence of lost traps), it
can request that portion of the subtree to be retransmitted using
a GetBulkRequest. The counter in each trap indicates the number of
repetitions transmitted thus far (including those sent in the
current trap). A management application can use this counter as a
hint when selecting a value for the max-repetitions field in the
GetBulkRequest when sending the retransmission request.
Once the entire retrieval operation is complete, the request will
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be deleted from getSubtreeControlTable along with all its
corresponding rows in getSubtreeRootTable.
Furthermore, if the request was in error (e.g., a human entered a
different OID from what was intended, causing the application to
receive large amounts of unwanted data), the MIB also provides a
way to halt an operation in progress, if the agent is able to
support this. Halting an operation in progress is accomplished
simply by allowing the application to delete the conceptual row in
getSubtreeControlTable corresponding to the outstanding operation.
If the retrieval operation is successfully aborted, the agent will
also automatically delete the rows from getSubtreeRootTable
corresponding to that operation.
3.3. Limitations
The limitations of this approach that come with not changing SNMP
include:
o To use this MIB to retrieve subtrees of information, the
application must be able to issue SETs (at least to this
MIB), not just GETs.
o The command responder and notification originator need to be
tightly coupled, as well as the command generator and
notification responder.
o The subagent implementing this MIB must be able to call back
into the SNMP engine to walk other MIBs, without causing a
deadlock.
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4. Definitions
GET-SUBTREE-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY, OBJECT-TYPE,
NOTIFICATION-TYPE, Unsigned32,
Counter32 FROM SNMPv2-SMI
RowStatus, TruthValue FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP,
NOTIFICATION-GROUP FROM SNMPv2-CONF
SnmpAdminString FROM SNMP-FRAMEWORK-MIB;
getSubtreeMIB MODULE-IDENTITY
LAST-UPDATED "0010201200Z"
ORGANIZATION "IRTF Network Management Research Group"
CONTACT-INFO
"Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
EMail: dthaler@microsoft.com
Satyen Chandragiri
Lucent Technologies, Inc.
101 Crawfords Corner Road
Holmdel, NJ 07733-3030
EMail: satyen@lucent.com"
DESCRIPTION
"This MIB module provides the ability to retrieve
arbitrary subtrees of OIDs (in parallel) by receiving
traps."
::= { XXX }
getSubtreeMIBObjects OBJECT IDENTIFIER ::= { getSubtreeMIB 1 }
getSubtree OBJECT IDENTIFIER ::= { getSubtreeMIBObjects 1 }
getSubtreeTraps OBJECT IDENTIFIER ::= { getSubtreeMIBObjects 2 }
--
-- GetSubtree Root Table
--
getSubtreeRootTable OBJECT-TYPE
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SYNTAX SEQUENCE OF GetSubtreeRootEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The (conceptual) table containing the root OID(s) of
the MIB subtree(s) to be retrieved. Multiple rows with
different values for getSubtreeRootOID may be created
if the manager wishes to retrieve several subtrees
simultaneously"
::= { getSubtree 1 }
getSubtreeRootEntry OBJECT-TYPE
SYNTAX GetSubtreeRootEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry (conceptual row) specifying the root OID of
the MIB subtree to be retrieved"
INDEX { getSubtreeRootOperationID, getSubtreeRootOIDIndex }
::= { getSubtreeRootTable 1 }
GetSubtreeRootEntry ::= SEQUENCE {
getSubtreeRootOperationID Unsigned32,
getSubtreeRootOIDIndex Unsigned32,
getSubtreeRootOID OBJECT IDENTIFIER,
getSubtreeRootStatus RowStatus
}
getSubtreeRootOperationID OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An integer uniquely identifying the GetSubtree
operation in progress. This value should be randomly
generated by a manager before attempting to create the
row."
::= { getSubtreeRootEntry 1 }
getSubtreeRootOIDIndex OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An index value used to associate various root OIDs
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with the same GetSubtree operation. This value should
be one for the first entry associated with a
particular retrieval operation and should be
sequentially incremented for each additional entry."
::= { getSubtreeRootEntry 2 }
getSubtreeRootOID OBJECT-TYPE
SYNTAX OBJECT IDENTIFIER
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The root OID of the subtree to be retrieved."
::= { getSubtreeRootEntry 3 }
getSubtreeRootStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this row. The manager should create one
row for each subtree to be retrieved. After the entire
subtree retrieval operation is completed (or if the
operation is aborted by the user) all rows in this
table corresponding to that operation are
automatically deleted by the agent.
Objects in this table cannot be modified while a
GetSubtree retrieval operation is in progress."
::= { getSubtreeRootEntry 4 }
--
-- GetSubtree Control Table
--
getSubtreeControlTable OBJECT-TYPE
SYNTAX SEQUENCE OF GetSubtreeControlEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The (conceptual) table used to control GetSubtree
operations in progress. This table is used in
conjunction with getSubtreeRootTable.
A manager interested in retrieving a subtree of MIB
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objects must first create an entry in the
getSubtreeRootTable specifying the root OID (s) of the
subtree(s) to be retrieved. It must then make a
corresponding entry in this table using the same
getSubtreeRootOperationID value and identifying itself
(via getSubtreeControlTarget) as the recipient of the
traps.
When the agent completes retrieval of all MIB
instances within the specified subtree(s) this
conceptual row will be automatically deleted."
::= { getSubtree 2 }
getSubtreeControlEntry OBJECT-TYPE
SYNTAX GetSubtreeControlEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry (conceptual row) containing the information
on a particular GetSubtree operation in progress."
INDEX { getSubtreeRootOperationID }
::= { getSubtreeControlTable 1 }
GetSubtreeControlEntry ::= SEQUENCE {
getSubtreeControlTarget SnmpAdminString,
getSubtreeControlSeqNumber Counter32,
getSubtreeControlCount Counter32,
getSubtreeControlDone TruthValue,
getSubtreeControlStatus RowStatus
}
getSubtreeControlTarget OBJECT-TYPE
SYNTAX SnmpAdminString
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"This object selects a management target defined in
the snmpTargetAddrTable (in the SNMP-TARGET-MIB). The
selected target is defined by an entry in the
snmpTargetAddrTable whose index value
(snmpTargetAddrName) is equal to this object."
::= { getSubtreeControlEntry 2 }
getSubtreeControlSeqNumber OBJECT-TYPE
SYNTAX Counter32
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MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of trap responses previously sent for this
GetSubtree request."
::= { getSubtreeControlEntry 3 }
getSubtreeControlCount OBJECT-TYPE
SYNTAX Counter32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number of repetitions transmitted thus far (up to
and including those sent in the current trap)"
::= { getSubtreeControlEntry 4 }
getSubtreeControlDone OBJECT-TYPE
SYNTAX TruthValue
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This is set to true in the last trap sent, and is set
to false otherwise."
::= { getSubtreeControlEntry 5 }
getSubtreeControlStatus OBJECT-TYPE
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this row, by which new entries may be
created, or old entries deleted from this table. Once
created, the row may be deleted, but other objects in
the row may not be modified. A row (and corresponding
rows in the getSubtreeRootTable) will be deleted
automatically by the agent once the operation has
completed. A row may be created using an instance
value for getSubtreeRootOperationID even if no entries
exist in getSubtreeRootTable indexed by that value.
Creating a row will cause the subtree retrieval
operation to commence if there are entries in the
getSubtreeRootTable indexed by the same value of
getSubtreeRootOperationID as this row. If the agent
allows aborting operations in progress, deleting a row
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will cause the operation to halt. If the operation is
successfully aborted, the rows in the
getSubtreeRootTable corresponding to this request will
also be automatically deleted by the agent."
::= { getSubtreeControlEntry 6 }
-- traps
getSubtreeTrapPrefix OBJECT IDENTIFIER ::= { getSubtreeTraps 0 }
getSubtreeResponse NOTIFICATION-TYPE
OBJECTS {
getSubtreeControlSeqNumber,
getSubtreeControlCount,
getSubtreeControlDone
}
STATUS current
DESCRIPTION
"In addition to the three objects above, this trap
also contains a series of varbinds containing the next
chunk of the subtree. The generating entity will
append, in order, as many variables to the variable-
bindings field as it can without exceeding the maximum
message size, and without going beyond the subtree of
OIDs requested. A series of such traps will be
generated until the end of the subtree is reached."
::= { getSubtreeTrapPrefix 1 }
-- conformance information
getSubtreeMIBConformance
OBJECT IDENTIFIER ::= { getSubtreeMIB 2 }
getSubtreeMIBCompliances
OBJECT IDENTIFIER ::= { getSubtreeMIBConformance 1 }
getSubtreeMIBGroups OBJECT IDENTIFIER ::= { getSubtreeMIBConformance 2 }
-- compliance statements
getSubtreeMIBCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"The compliance statement for the GetSubtree MIB."
MODULE -- this module
MANDATORY-GROUPS {
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getSubtreeObjectGroup,
getSubtreeNotificationGroup
}
::= { getSubtreeMIBCompliances 1 }
-- units of conformance
getSubtreeObjectGroup OBJECT-GROUP
OBJECTS {
getSubtreeRootOID,
getSubtreeRootStatus,
getSubtreeControlTarget,
getSubtreeControlSeqNumber,
getSubtreeControlCount,
getSubtreeControlDone,
getSubtreeControlStatus
}
STATUS current
DESCRIPTION
"A collection of objects to support requests for
subtree retrieval operations."
::= { getSubtreeMIBGroups 1 }
getSubtreeNotificationGroup NOTIFICATION-GROUP
NOTIFICATIONS { getSubtreeResponse }
STATUS current
DESCRIPTION
"The notification which an entity is required to
implement."
::= { getSubtreeMIBGroups 2 }
END
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5. Security Considerations
While unauthorized read access to the objects in this MIB is
relatively innocuous, unauthorized write access could trigger
sending of a potentially large amount of data to an authorized
notification receiver, which could be viewed as a denial-of-
service attack.
Hence, the support for SNMP operations in a non-secure environment
without proper protection can have a negative effect on network
operations.
SNMPv1 by itself is such an insecure environment. Even if the
network itself is secure (for example by using IPSec [16]), even
then, there is no control as to who on the secure network is
allowed to access and SET (change/create/delete) the objects in
this MIB.
It is recommended that the implementers consider the security
features as provided by the SNMPv3 framework. Specifically, the
use of the User-based Security Model RFC 2274 [12] and the View-
based Access Control Model RFC 2275 [15] is recommended.
It is then a customer/user responsibility to ensure that the SNMP
entity giving access to this MIB, is properly configured to give
access to those objects only to those principals (users) that have
legitimate rights to access them.
6. Authors' Addresses
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com
Satyen Chandragiri
Lucent Technologies, Inc.
101 Crawfords Corner Road
Holmdel, NJ 07733-3030
Phone: +1 732 949 2080
EMail: satyen@lucent.com
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7. References
[1] Wijnen, B., Harrington, D., and R. Presuhn, "An Architecture
for Describing SNMP Management Frameworks", RFC 2571,
Cabletron Systems, Inc., BMC Software, Inc., IBM T. J. Watson
Research, April 1999.
[2] Rose, M., and K. McCloghrie, "Structure and Identification of
Management Information for TCP/IP-based Internets", STD 16,
RFC 1155, Performance Systems International, Hughes LAN
Systems, May 1990.
[3] Rose, M., and K. McCloghrie, "Concise MIB Definitions", STD
16, RFC 1212, Performance Systems International, Hughes LAN
Systems, March 1991.
[4] M. Rose, "A Convention for Defining Traps for use with the
SNMP", RFC 1215, Performance Systems International, March
1991.
[5] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Structure
of Management Information Version 2 (SMIv2)", STD 58, RFC
2578, April 1999.
[6] McCloghrie, K., Perkins, D., and J. Schoenwaelder, "Textual
Conventions for SMIv2", STD 58, RFC 2579, April 1999.
[7] McCloghrie, K., Perkins, D., and J. Schoenwaelder,
"Conformance Statements for SMIv2", STD 58, RFC 2580, April
1999.
[8] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple
Network Management Protocol", STD 15, RFC 1157, SNMP
Research, Performance Systems International, Performance
Systems International, MIT Laboratory for Computer Science,
May 1990.
[9] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Introduction to Community-based SNMPv2", RFC 1901, SNMP
Research, Inc., Cisco Systems, Inc., Dover Beach Consulting,
Inc., International Network Services, January 1996.
[10] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Transport Mappings for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1906, SNMP Research, Inc.,
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Cisco Systems, Inc., Dover Beach Consulting, Inc.,
International Network Services, January 1996.
[11] Case, J., Harrington D., Presuhn R., and B. Wijnen, "Message
Processing and Dispatching for the Simple Network Management
Protocol (SNMP)", RFC 2572, SNMP Research, Inc., Cabletron
Systems, Inc., BMC Software, Inc., IBM T. J. Watson Research,
April 1999.
[12] Blumenthal, U., and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management Protocol
(SNMPv3)", RFC 2574, IBM T. J. Watson Research, April 1999.
[13] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser,
"Protocol Operations for Version 2 of the Simple Network
Management Protocol (SNMPv2)", RFC 1905, SNMP Research, Inc.,
Cisco Systems, Inc., Dover Beach Consulting, Inc.,
International Network Services, January 1996.
[14] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications",
RFC 2573, SNMP Research, Inc., Secure Computing Corporation,
Cisco Systems, April 1999.
[15] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based
Access Control Model (VACM) for the Simple Network Management
Protocol (SNMP)", RFC 2575, IBM T. J. Watson Research, BMC
Software, Inc., Cisco Systems, Inc., April 1999.
8. Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished
to others, and derivative works that comment on or otherwise
explain it or assist in its implmentation may be prepared, copied,
published and distributed, in whole or in part, without
restriction of any kind, provided that the above copyright notice
and this paragraph are included on all such copies and derivative
works. However, this document itself may not be modified in any
way, such as by removing the copyright notice or references to the
Internet Society or other Internet organizations, except as needed
for the purpose of developing Internet standards in which case the
procedures for copyrights defined in the Internet Standards
process must be followed, or as required to translate it into
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languages other than English.
The limited permissions granted above are perpetual and will not
be revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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