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SNMP (Simple Network Management Protocol)

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SNMP (Simple Network Management Protocol) Jon Sevy Geometric and Intelligent Computing Laboratory Department of Mathematics and Computer Science Drexel University – PowerPoint PPT presentation

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Title: SNMP (Simple Network Management Protocol)


1
SNMP(Simple Network Management Protocol)
  • Jon Sevy
  • Geometric and Intelligent Computing Laboratory
  • Department of Mathematics and Computer Science
  • Drexel University
  • http//gicl.mcs.drexel.edu

2
SNMP Overview
  • Define mechanism for remote management of network
    devices (routers, bridges, etc.)
  • Fundamental principle all device management done
    by simple variable value manipulation
  • Approach
  • standard means for specifying quantities
    recognized by devices
  • protocol for requesting, returning, notifying of
    changes of values

3
SNMP Message Protocol
  • Messages use UDP, ports 161 (requests/responses)
    and 162 (notifications)
  • Message types
  • GetRequest request values of variables from
    device
  • GetNextRequest request value of variable
    following the one supplied
  • GetResponse return values
  • SetRequest instruct device to set values of
    variables
  • Trap from device - notify monitor / manager of
    value change

4
SNMP Communities
  • Define communities specifying access to
    specific variable sets (read-write, read only,
    none)
  • Supply community name as password in each
    message
  • unencrypted in version of SNMP still widely used!!

5
SNMP Message Encoding
  • Encode message as byte stream using ASN.1 BER
    (Abstract Syntax Notation 1 Basic Encoding Rules)
  • Quantites encoded as Type,Length,Value triples
  • Types
  • Subset of basic ASN.1 types used in SNMP
    integer, octet string, object identifier
    (variable name), sequence
  • SNMP-defined types gauge, counter, IP address,
    etc.
  • Values
  • weirdly encoded!! (see ASN.1 specs)

6
SNMP SMI(Structure of Management Information)
  • Variables recognized by device supplied in MIB
    (Management Information Base)
  • text file giving variables and data structures
    defined using ASN.1
  • standard variable sets often provided as RFCs
  • device-specific sets provided by vendors
  • Management stations parse MIBs to determine
    variables available for management
  • obtain both data structure and management
    information

7
Example portion of MIB (from RFC 1213)
-- the Interfaces group --
Implementation of the Interfaces group is
mandatory for -- all systems.
ifNumber OBJECT-TYPE SYNTAX
INTEGER ACCESS read-only
STATUS mandatory DESCRIPTION
"The number of network
interfaces (regardless of
their current state) present on this system."
interfaces 1
8
ASN.1 Object Identifiers
  • Variables identified by globally unique strings
    of digits
  • ex 1.3.6.1.4.1.3.5.1.1
  • name space is hierarchical tree on next slide
  • in above, 1 stands for iso, 3 stands for org,
    6 stands for dod, 1 stands for internet, 4
    stands for private, etc.
  • Variable names are aliases for digit strings
    (within MIB)
  • From previous page ifNumber interfaces
    1
  • interfaces was previously defined in MIB as
    1.3.6.1.2.1.2, so ifNumber 1.3.6.1.2.1.2.1

9
Partial ASN.1 Object Identifier Tree(from ASN.1
Complete, J. Larmouth, Open Systems Solutions,
1999)
10
Application GICL SNMP Monitor
  • Java-based SNMP application
  • Query devices for available MIB variables
  • Set desired variable values
  • Current status
  • retrieve and display all values from device
  • automatically build data structures to hold
    retrieved values
  • Future work
  • incorporate MIB information via MIB parser
  • auto-generate GUI display
  • implement device discovery

11
References
  • Internet Standards 15, 16 and 17
  • ASN.1 Complete, J. Larmouth, Open Systems
    Solutions, 1999 (available online)
  • SNMP a guide to network management, S. Feit,
    McGraw-Hill, 1995
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