SNMP Version 2 (SNMPv2)

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SNMP Version 2(SNMPv2)

• J. Won-Ki Hong
• Dept. of Computer Science and Engineering
• POSTECH
• Tel [phone]
• Email jwkhong_at_postech.ac.kr

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Table of Contents

• The Birth of SNMPv2
• SNMPv2 RFCs
• SNMPv2 Enhancements
• SNMPv2 Protocol Operations
• SNMPv2 Coexistence with SNMPv1

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The Birth of SNMPv2

• a major problem with SNMP is the lack of security
• secure SNMP was proposed (July 1992) to solve
  this problem in SNMP
• Simple Management Protocol (SMP) was also
  proposed (July 1992) to extend the SNMP
  functionality
• secure SNMP SMP SNMPv2 (March 1993)
• a major security flaw was detected in this
  proposal and the security aspects were dropped
  and the result is community-based SNMPv2 (Jan.
  1996)

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SNMPv2 RFCs

• RFC 1901 (experimental)
• Introduction to Community-based SNMPv2
• RFC 1902 (draft) -gt RFC 2578 (standard)
• Structure of Management Information for SNMPv2
  (SMIv2)
• RFC 1903 (draft) -gt RFC 2579 (standard)
• Textual Conventions for SMIv2
• RFC 1904 (draft) -gt RFC 2580 (standard)
• Conformance Statements for SMIv2

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SNMPv2 RFCs (contd)

• RFC 1905 (draft)
• Protocol Operations for SNMPv2
• RFC 1906 (draft)
• Transport Mappings for SNMPv2
• RFC 1907 (draft)
• Management Information Base for SNMPv2
• RFC 1908 (draft)
• Coexistence between Version 1 and Version 2 of
  the Internet-standard Network Management Framework

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SNMPv2 Key Enhancements

• SMIv2 (a superset of SMIv1)
• provides more elaborate specification and
  documentation of managed objects and MIB modules
• object type macros expanded (see Fig. 11.1, 11.2
  Table 11.2)
• creating and deleting conceptual rows in a table
  (as used in RMON)
• notification definitions
• information modules
• new SNMP MIB definitions are defined using SMIv2
• Manager-to-Manager Capability
• for managing large, distributed networks
• Protocol Operations
• bulk management information retrieval
• manager-to-manager communication

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Comparison of Data Types
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Notification Type MACRO
NOTIFICATION-TYPE MACRO BEGIN TYPE NOTATION
ObjectsPart
STATUS Status
DESCRIPTION Text
ReferPart VALUE NOTATION value
(VALUE NotificationName) ObjectsPart
OBJECTS Objects empty Objects
Object Objects , Object Object value
(Name ObjectName) Status current
deprecated obsolete ReferPart
REFERENCE Text empty Text string
END
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Notification Type Example
coldStart NOTIFICATION-TYPE STATUS
current DESCRIPTION "A coldStart trap
signifies that the SNMPv2 entity, acting in
an agent role, is reinitializing itself and
that its configuration may have been
altered." snmpTraps 1 -- From RFC
1907
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Module Identity MACRO
MODULE-IDENTITY MACRO BEGIN TYPE NOTATION
LAST-UPDATED value (Update UTCTime)
ORGANIZATION Text
CONTACT-INFO
Text
DESCRIPTION Text
RevisionPart VALUE NOTATION value
(VALUE OBJECT IDENTIFIER) RevisionPart
Revisions empty Revisions Revision
Revisions Revision Revision REVISION value
(Update UTCTime)
DESCRIPTION Text Text string END
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Module Identity Example
rmon MODULE-IDENTITY LAST-UPDATED
"9605270000Z" ORGANIZATION "IETF RMON MIB
Working Group" CONTACT-INFO "Steve
Waldbusser (WG Editor) Postal
International Network Services 650
Castro Street, Suite 260 Mountain
View, CA 94041 Phone [phone]
Email waldbusser_at_ins.com
DESCRIPTION "The MIB module for managing
remote monitoring device implementations.
This MIB module augments the original RMON
MIB as specified in RFC 1757." mib-2
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Object Identity MACRO
OBJECT-IDENTITY MACRO BEGIN TYPE NOTATION
STATUS Status
DESCRIPTION Text
ReferPart VALUE NOTATION value
(VALUE OBJECT IDENTIFIER) Status current
deprecated obsolete ReferPart
REFERENCE Text empty Text string
END
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Object Identity Example
snmpUDPDomain OBJECT-IDENTITY STATUS
current DESCRIPTION "The SNMPv2 over
UDP transport domain. The corresponding
transport address is of type SnmpUDPAddress."
snmpDomains 1 -- from RFC 1906
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SNMPv2 MIB Access
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SNMPv2 Operations

• GetRequest - get the value for each listed object
• GetNextRequest - get next value for each listed
  object
• GetBulkRequest - get multiple values
• Response - respond to manager request
• SetRequest - set value for each listed object
• InformRequest - send unsolicited information from
  a manager to another
• SNMPv2-Trap - send unsolicited information from
  an agent to a manager

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SNMPv2 PDU Formats
PDU
community
version (1)
SNMPv2 Message
(a) GetRequest-PDU, GetNextRequest-PDU,
SetRequest-PDU, SNMPv2-Trap-PDU,
InformRequest-PDU
variable-bindings
error index
error status
request id
PDU type
(b) Response-PDU
variable-bindings
max- repetitions
non- repeaters
request id
PDU type
(c) GetBulkRequest-PDU
valueN
nameN
. . .
value2
name2
value1
name1
(d) variable-bindings
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GetBulkRequest

• used to minimize the exchanges required to
  retrieve a large amount of information
• selection principle is the same as GetNextRequest
• the next object instance in lexicographic order
• includes a list of (N R) variable names in the
  variable-bindings list
• the first N variables for retrieving single
  values
• the next R variables for retrieving multiple
  values
• non-repeaters and max-repetition fields are used
  to indicate the number of N and R variables

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Interpretation of GetBulkRequest Fields
name1 name2 .... nameN
nameN1 .... nameNR
For first N variables provide one value
each (first lexicographic successor)
For last R variables provide M values
each (first M lexicographic successors)
L number of names in variable-bindings field N
MAX MIN (non-repeaters, L), 0 M MAX
max-repetitions, 0 R L - N
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GetBulkRequest Example
GetBulkRequest (non-repeaters 2,
max-repeaters 6, X, Y, TA, TB, TC)
Manager issues request with six variable names
for the first two variable (non-repeaters2), a
single value is requested for the remaining
variables six successive values (max-repeaters6)
are requested.
Agent (e.g, router)
x
Y
Table a
TA
TB
TC
NMS
Agent returns single value for X, Y, and six
rows of table a
Response X, Y, TA(1), TB(1), TC(1),
TA(2), TB(2), TC(2),
TA(3), TB(3), TC(3),
TA(4), TB(4), TC(4),
TA(5), TB(5), TC(5),
TA(6), TB(6), TC(6)
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SNMPv2-Trap and InformRequest

• SNMPv2-Trap
• is sent from an agent to a manager when an
  unusual event occurs
• no response is required
• InformRequest
• is sent from a manager for passing information to
  an application running in another manager
• Response PDU is used to acknowledge the request
• for hierarchical or distributed management where
  multiple managers are involved

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SNMPv2 PDU Sequences
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PDU Comparisons
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Transport Mappings

• RFC 1906 specifies the mapping of SNMPv2 onto the
  following transport protocols
• User Datagram Protocol (UDP)
• OSI Connectionless-Mode Network Service (CLNS)
• OSI Connection-Oriented Network Service (CONS)
• Novell Internetwork Packet Exchange (IPX)
• Appletalk
• The SNMPv2 document states that UDP is the
  preferred mapping

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Coexistence by Means of Proxy Agent
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Coexistence by Means of Bilingual Manager
SNMPv2 manager
InformRequest, Response
GetRequest, GetNextRequest, SetRequest
Bilingual manager (v1, v2)
SNMPv1 agent
InformRequest, Response
SNMPv2-Trap, Response
GetResponse, Trap
SNMPv2 agent
getRequest, getNextRequest getBulkRequest,
setRequest
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Summary

• SNMPv2 is a natural extension of SNMPv1
• Key enhancements in SNMPv2 are
• more elaborate MIB specification capability
  (SMIv2)
• Manager-to-Manager communication
• Bulk information transfer
• SNMPv2 failed to improve on security
• More powerful but more complex than SNMPv1
• SNMPv3 focuses on improving the security aspect