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SNMP

An Introduction to Simple Network Management Protocol

Slides adapted from www.jasonslater.co.uk

Introduction

• Simple Network Management Protocol
• What it is
• Definition
• Why it is needed
• How it works
• Alternatives
• The Future

What is SNMP ?

• Simple Network Management Protocol
• It’s designed to be Simple
  • Only five commands in version 1
• It’s concerned with Network Management
  • Manage network performance
  • Identify and diagnose issues
  • Baseline/Plan for network growth
• It’s a Protocol
  • defined by the IETF (Internet Engineering Task Force)

Definition

“

SNMP (Simple Network Management Protocol) is an industry standard communication protocol for managing and monitoring network devices. Its purpose is to provide a small, common and simple set of commands that allow network devices to be managed.

”

Why is SNMP needed?

• Distributed ad-hoc devices across the network including repeaters, routers, bridges, switches, hub, ups devices all need management
• They all basically receive data in from the network, process it and put data back out onto the network
• They can sometimes be cumbersome to manage
• Inconsistent and differing interfaces require different resources

What is SNMP technically?

• Part of the TCP/IP model
  • TCP or UDP packets
• Defined through IETF RFC’s
• Uses Protocol Data Units (PDU’s) which are special forms of packet
• Uses a community string as password
  • Read-only and read/write
• Made up of 3 primary elements:
  • SNMP Managers (NMS receive messages from Agents, reporting, execute programs).
  • SNMP Agents — (software module in a managed device and talks to Managers)
    • Translates local info to MIB info
  • MIBs (Collection of definitions of device management information) organised by OID (Object ID)
• Rootless MIB hierarchy

Manager/Agent relationship

     NMS
     (Network Managemt Station)				 Managed System
    ┌─────────────┐                                     ┌─────────────┐
    │ Management  │-----------Commands-----------------▷│ Agent       │
    │ Process     │					│ Process     │
    ├ ─ ─ ─ ─ ─ ─ ┤◁----------Responses-----------------├ ─ ─ ─ ─ ─ ─ ┤
    │ Management  │					│ Management  │
    │ Information │					│ Information │
    │ Database    │◁----------Notifications-------------│ Database    │
    └─────────────┘                                     └─────────────┘

The MIB Namespace

                    root
           ┌──────────┼──────────────┐
           │          │              │
        itu-1 (0)   iso (1)       iso/itu-t (2)
                      │
           ┌──────────┼──────────────┬────────────┐
           │          │              │            │
    standard (0)   registration     member    Identified organization
                   authority (1)    body (2)   e.g. .com .org (3)
                                                  │
                                      dod (Department of Defense) (6)
                                                  │
                                              internet (1)
           ┌──────────┬────────┬────────┬─────────┴────┬────────────┐
           │          │        │        │              │            │
    directory (1)   mgmt (2) exp (3) private (4)  security (5)   snmpv2 (6)
                      │                 │
                   mib-2 (1)      enterprises (1)
                                        │
                 ┌───────────┬──────────┼──────────────┐
             cisco (9)    hp (11)   nec (119)     compaq (232)

Management Information Base

ftp://ftp.cisco.com/pub/mibs/v1/

nec              OBJECT IDENTIFIER ::= { enterprises 119 }
nec-mib          OBJECT IDENTIFIER ::= { nec 2 }
necProductDepend OBJECT IDENTIFIER ::= { nec-mib 3 }
atomis-mib       OBJECT IDENTIFIER ::= { necProductDepend 14 }
m5core-mib       OBJECT IDENTIFIER ::= { atomis-mib 3 }

node OBJECT IDENTIFIER ::= { m5core-mib 1 }
linf OBJECT IDENTIFIER ::= { m5core-mib 2 }
conn OBJECT IDENTIFIER ::= { m5core-mib 3 }
perf OBJECT IDENTIFIER ::= { m5core-mib 4 }

nodeFanStatus OBJECT-TYPE
SYNTAX INTEGER { up(1), down(2) }
ACCESS read-only
STATUS mandatory
DESCRIPTION "Operational FAN status"
::= { node 3 }

Example SNMP “GET” operation

1. User makes request to NMS
2. NMS initiates formal request
3. Request traverses network
4. Agent processes request
5. Agent formulates reply
6. NMS receives reply
7. User informed of result

How is SNMP defined?

• Uses ASN.1
  • Abstract Syntax Notation One (ASN.1)
  • Standards based “descriptive” language used to abstractly describe messages
    • Standardized in 1984 by CCITT and ISO in 1985
  • Uses predefined types
  • eg. Integer, Boolean, String
  • Uses OID — Object IDentifier
  • Uses MIB hierarchy with a rootless tree

ASN.1

Abstract Syntax Notation One (ASN.1) is a formal language for abstractly describing messages to be exchanged among an extensive range of applications involving the Internet, intelligent network, cellular phones, ground-to-air communications, electronic commerce, secure electronic services, interactive television, intelligent transportation systems, Voice Over IP and others.

Due to its streamlined encoding rules, ASN.1 is also reliable and ideal for wireless broadband and other resource-constrained environments. Its extensibility facilitates communications between newer and older versions of applications. In a world of change, ASN.1 is core technology, constantly adapting to new technologies.

SNMP v1

• Supports 5 operations (PDUs)
  • GetRequest
    • polls agents for information
  • GetNextRequest
    • requests the next item in a dataset
  • Set
    • requests a change to a value
  • GetResponse
    • sends a response to a Manager request
  • Trap
    • informs a Manager of an event

SNMP v2

• Never took off due to security concerns and disagreements
• v2 has several advantages over SNMPv1, including:
  • Expanded data types (e.g., 64 bit)
  • Added GetBulk Command
  • Added Inform Command (forwarding of TRAP info)
  • Better error handling (errors and exceptions)
• v2 addresses security issues missing from v1 including:
  • Authentication
  • Message integrity
  • Privacy
  • Authorization and access control
• Development of SNMP fragmented into different standards groups:
  • SNMPv2c
  • SNMPv2u
  • SNMPv2*

SNMP v3

• Security centric design
• v3 protocol was an attempt to consolidate the best features of the different versions of SNMP v2.
• v3 is gaining acceptance from big names in the industry (e.g. Cisco and HP)

Alternatives to SNMP

Summary

• SNMP is a network management protocol
  • Became popular because of its ‘simple’ nature
• Three versions of SNMP exist
  • though v2 never really took off
  • V3 only recently started to gain favour
• Uses ASN.1 syntax with a rootless MIB tree hierarchy
• A number of alternatives are available

References

• ftp://ftp.cisco.com/pub/mibs/v1/ (CISCO MIBs)
• ftp://ftp-sj.cisco.com/pub/mibs/oid/ (CISCO OIDs)
• http://www.ietf.org/rfc.html (IETF RFCs)
• http://www.opte.org (Internet Map)
• http://asn1.elibel.tm.fr/en/ (ASN.1)
• http://www.ietf.org/rfc/rfc2578.txt (MIB forming)

RFCs