Internet DRAFT - draft-haresh-sushrut-mib-classification
draft-haresh-sushrut-mib-classification
INTERNET-DRAFT Haresh Khandelwal & Sushrut Deshpande
Intended Status: Experimental Cisco Systems
Expires: March 2012
SNMPD to use cache and shared database based on MIB Classification
draft-haresh-sushrut-mib-classification-01
Abstract
This memo defines classification of SNMP MIBs to either use SNMP
cache database and shared database (SDB) mechanism to reduce high CPU
usage while SNMP GET REQUEST, GETNEXT REQUEST, GETBULK REQUEST are
continuously performed from network management system (NMS)/SNMP
manager/SNMP MIB browser to managed device.
Status of this Memo
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. MIB classification . . . . . . . . . . . . . . . . . . . . . . 3
2.1 How CPU usage goes high . . . . . . . . . . . . . . . . . . 3
2.2 MIB Classification . . . . . . . . . . . . . . . . . . . . . 4
2.3 How SNMP CACHE and SHARED DATABASE works . . . . . . . . . . 4
2.4 How CPU usage reduced . . . . . . . . . . . . . . . . . . . 4
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5 References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1 Normative References . . . . . . . . . . . . . . . . . . . 6
5.2 Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1 Introduction
Continuous GET REQUEST, GETNEXT REQUEST, GETBULK REQUEST on managed
device results into high CPU usage. High CPU usage is result of high
process interactions between SNMP process and requested OID's process
when OID came from GET REQUEST, GETNEXT REQUEST, GETBULK REQUEST.
This draft suggests the way to reduce these process interactions in
order to reduce CPU usage. This approach also suggests way to reduce
high CPU usage with accurate OID values.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. MIB classification
2.1 How CPU usage goes high
When SNMP protocol data units (SNMP PDU) are received by SNMPD
running on managed device (router, switch etc...), SNMPD de capsulate
PDU and retrieves requested ODI from PDU. After getting OIDs, SNMPD
interacts with process under whom requested OIDs and its value
reside.
For example, NMS sends SNMP GET REQUEST with seeking of interface
operational status whose OID is .1.3.6.1.2.1.2.2.1.8. This GET
REQUEST PDU is received at managed device's SNMPD which in turn de
capsulated PDU and find out that "ifOperStatus" is requested from
NMS. SNMPD then interacts with process who handles interface process
and gets OID value and builds RESPONSE PDU which sent to NMS.
Like as when NMS keeps polling managed device, it leads very high
process interactions between SNMPD and requested OID's. generally,
process interactions happen through common mechanism like MTS
(message transaction service) in NX-OS. processes talk with each
other using such messages. so, when processes have to talk with each
other frequently, transactions of interaction messages also go very
high. such high amount of transactions increase a CPU usage of the
system which in turns result into very high CPU usage. SNMP polling
is such a method which also leads to high CPU usage of managed
device. generally service providers keep monitoring network devices
using SNMP for all time and running other application parallel to
monitoring it. so if SNMP polling consume higher CPU, it may lead
other processes to CPU starvation which may lead device to strange
unknown behavior. To avoid this, we are proposing this solution where
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we reduce process interactions, so we can achieve less message
transactions and less CPU consumption.
2.2 MIB Classification
MIB Classification provides a solution to avoid high CPU usage. MIB
are classified into two categories.
i) Dynamic MIBs - Whose values change frequently (for example
ifMIB counters).
ii) Relatively Static MIBs - Whose values change occasionally
(for example VLAN MIB).
2.3 How SNMP CACHE and SHARED DATABASE works
SHARED DATABASE (SDB) is a database where component or process who
falls under "Dynamic MIBs" has to populate their supported ODIs
values. SNMPD will fetch ODI's value from this SHARED DATABASE when
ODI belongs to "Dynamic MIBs" category requested from NMS. Processes
taking part in SDB are completely responsible for OIDs values. So, if
it is ifMIB counter process for interface then it will be responsible
for interfaces counter values in SDB. SNMPD will pickup relevant
values for asked OIDs from SDB and will response back to MIB
browser/NMS.
SNMP CACHING is a database which is maintained by SNMPD of managed
device. This database contains ODIs values of "Relatively Static
MIBs". These ODI values filled to SNMP CACHE when SNMPD receives
ODI's value first time from requested OID's process.SNMPD will form
its own cache table which in turn, stores values of all processed
ODIs. So when next time same OID will be requested, SNMPD can
response from its own Cache table. Now, if value of OID from
"Relatively Static MIBs" changes, that process or component has to
inform SNMPD regarding its event with new values. SNMPD will update
its cache table with new ODI value.
SNMP cache table can be flushed in event of SNMP process
restart/crash/enable-disable. New cache table will be formed again
after recovery with 1st poll cycle.
SHARED DATABASE will be handled by individual process and should be
populated again in event of process crash/restart.
2.4 How CPU usage reduced
For NMS queries with MIB classification approach, SNMPD does not need
to talk with individual processes. According to MIB category, SNMP
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process will fetch ODIs value from either of these two databases.so,
by this way, we can reduce the interaction messages between SNMPD and
other processes and still having accurate OID values from accurately
maintained database. As high process interactions are reduced, it
will reduce CPU usage also.
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3 Security Considerations
This design is not changing SNMP packets. It does not apply on SNMP
SET operation. Communication between NMS and managed device is also
un changed, only internal process interaction changes are proposed
based on MIB classification.so, this design does not exhibit any
security threat.
4 IANA Considerations
5 References
5.1 Normative References
5.2 Informative References
[RFC2578] McCloghrie, et al., "Structure of Management Information
Version 2 (SMIv2)", RFC2578, April 1999.
[RFC3418] Presuhn, et al., "Management Information Base (MIB) for
the Simple Network Management Protocol (SNMP)", RFC3418, December
2002.
[RFC3411] Harrington, et al., "An Architecture for Describing Simple
Network Management Protocol (SNMP) Management Frameworks", RFC3411,
December 2002.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,May 2008
[RFC2119] Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119, March 1997
Authors' Addresses
Name
Haresh Khandelwal
Sushrut Deshpande
EMail: hkhandel@cisco.com, susdeshp@cisco.com
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