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Understanding SNMP: Simple Network Management Protocol Overview

SNMP, or Simple Network Management Protocol, is vital for managing network elements like routers, switches, and printers. It utilizes a manager-agent model and a Management Information Base (MIB) for data retrieval. SNMP allows querying devices for data, setting alarms, and aiding in growth planning. Object Identifiers (OIDs) uniquely identify objects in the MIB hierarchy, while community strings act as passwords for device access. SNMP operates over UDP and supports various versions, with SNMPv3 offering enhanced security features.

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Understanding SNMP: Simple Network Management Protocol Overview

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  1. SNMP M Clements 1 ENS

  2. Simple Network Management Protocol  Manages elements in networks – E.g. routers, switches, IP phones, printers etc.  Uses manager agent model – client server model  Consists of – Manager running network management system, agent, database of management information (Management Information Base MIB), managed devices (slaves), network protocol 2 ENS

  3. Uses of SNMP  Querying networked devices regularly to gain data to draw graphs  Warning administrator when managed device reached some predefined threshold – E.g. sys admin could monitor the temperature of a server chassis  Provides data for future growth planning 3 ENS

  4. Management Information Base (MIB)  Used to pull information from network devices that enable SNMP.  Tree structure – Variables represented as leaves on branches – E.g. "free memory", "system name", "number of running processes", "default route" – hierarchical namespace containing object identifiers (OID)  Used by manager and agent  Describes the structure of the management data of a device subsystem 4 ENS

  5. 5 ENS

  6. What is Object Identifier (OID)?  uniquely identify managed objects in a MIB hierarchy. 6 ENS

  7. Variable Descriptors  Variables described numerically  Selected from MIB tree  Uses numerical system  Abstract Syntax notation One (ASN.1) 7 ENS

  8. MIB group structure •ASN.1 standard describes data structures for representing, encoding, transmitting, and decoding data •Removes ambiguities by providing machine- independent method of addressing variables 8 ENS

  9. SNMP Operation  Manager can request information from managed device using GET, GETNEXT and GETBULK  Manager can update variables using SET  Agent can send data automatically using TRAP or INFORM to report alarms  Manager receives on UDP port 162  Agent receives on UDP port 161 9 ENS

  10. SNMP Communities  SNMP Communities: groups that devices and management stations running SNMP belong to.  Defines device groups where information is sent  Community name is used to identify the group  A SNMP device or agent may belong to more than one SNMP community and will not respond to requests from management stations that do not belong to one of its communities  SNMP default communities are: – Write = private – Read = public 10 ENS

  11. SNMP Community Strings  Like passwords for Community devices  Management device will need the strings to read and write to devices  Read-only community string often set to ‘public’  Read-write community string often set to ‘private’ 11 ENS

  12. Enable SNMP on Cisco Routers  Example here uses default strings  Enter configuration mode (Community strings are highlighted by red) Router(config)#snmp-server community public RO Router(config)#snmp-server community private RW  RO specifies read only access  RW specifies read write access  Management stations need to supply the correct community strings to access the MIB data on the managed device 12 ENS

  13. SNMP Versions  Currently up to SNMPv3  Many network elements support only SNMPv1 and SNMPv2c. Support for SNMPv3 is minimal SNMPv1 SNMPv2c SNMPv2u SNMPv2 SNMPv3 SNMPv1, implements community-based security SNMPv2 with community-based security SNMPv2 with user-based security SNMPv2 with party-based security SNMPv3, which implements user-based security 13 ENS

  14. Summary  SNMP manages networked devices  Uses GET, SET, GETNEXT, TRAP  Communities define groups for management  Community string like password  Public or private (default)  Uses UDP  Data held in MIB 14 ENS

  15. References http://www.geekball.net/linksys/picture4.png http://img.brothersoft.com/screenshots/softimag e/h/hilisoft_snmp_mib_browser-63133-1.jpeg http://publib.boulder.ibm.com/infocenter/tivihelp /v24r1/topic/com.ibm.netcool_ssm.doc/rg/ima ges/rmon1Grp.gif 15 ENS

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