SNMP Management Information
Dr.Moneeb Gohar
SNMP Management Information
 Database contains information about the elements to be managed : MIB
 Each resource to be managed is represented by object
 MIB : structured collection of such object having the form of tree
 Structure of Management Information (SMI)
Specified in RFC 1155
Providing a standardized technique for defining the structure of a particular
MIB
Providing a standardized technique for defining individual objects, including
the syntax and the value of each object
Defining objects
 MIB (Management Information Base)
a precise definition of the information accessible through a network
management protocol
each device must use the format for displaying information that is
defined by the MIB
RFC 1052


define an extended MIB for use with SNMP and CMIS/CMIP
is no longer realistic
RFC 1065: “Structure and Identification of Management Information
for TCP/IP based Internets (SMI)”

describe the syntax and type of information available in the MIB for TCP/IP
networks
RFC 1066



use the rules of the SMI
present the first version of the MIB for TCP/IP
known as MIB-I
MIB Structure
 Leaf objects of the tree to be actual managed objects to represent
some resource, activity, or related information
 Object identifier : a unique identifier for particular object type
Serving as name the object
internet OBJECT IDENTIFIER :: = { iso (1) org(3) dod (6) 1}
therefore, internet node’s object ID : 1.3.6.1
Object Syntax
 Universal types
UNIVERSAL class of ASN.1 consisting of application-independent data
types for defining MIB objects

integer (UNIVERSAL 2)

octetstring (UNIVERSAL 4)

null (UNIVERSAL 5)

object identifier (UNIVERSAL 6)

sequence, sequence-of (UNIVERSAL 16)
Object ID consisting of sequence of integers

for example : object ID for tcpConnTable : 1.3.6.1.2.1.6.13
iso org dod internet mgmt mib-2
tcp
1
6
3
6
1
2
1
tcpConnTable
13
Defining Tables
 The entire table represents a single instance of the object type
tcpConnTable.
 Each row is an instance of the object type tcpConnEntry.
SNMP Overview
RFC 1156

allow for expansion of the MIB for vendor specific enhancement
RFC 1158

propose a second MIB (MIB-II)

extend the information base defined in MIB-I

Note: most network devices have software agent that support MIB-II and their own
private extensions
Each MIB would focus on a specific technology

RFC 1743: IEEE 802.5 Token Ring Interface type MIB

RFC 1757: Remote Network Monitoring MIB (RMON)

RFC 1513: FDDI Interface type MIB

RFC 1493: Bridge MIB
SNMP Overview
 Object Identifier
ISO ASN.1 (Abstract Syntax Notation One) Syntax

a subset of ASN.1 defines the syntax for the MIB

use the tree architecture to organize all available information
–
labeled node
–
object identifier (OID) and sort text description
Root
Node (1)
Node (2)
Subtree
Node (1)
Node (2)
Node A (1)
Object (2)
Object (1)
Object A (1)
OID: 1.2.1.1 or
{node A 1}
SNMP Overview
Traversal of the MIB tree

root node
–
itu-t (0), administered by the ITU-T
–
iso (1), administered by the ISO
–
joint-iso-itu-t (2), jointly administered by ISO and ITU-T
•
internet: OID= 1.3.6.1 or {iso org(3) dod(6), 1}
ITU-T(0)
ISO(1)
joint-ISO-ITU-T (2)
…. org(3) …..
….. dod(6) …..
….. internet (1) …..
directory(1)
……
mgmt(2) ….
mib(1)
Experimental(3)
private(4)
enterprises(1)
SNMP Overview

directory (1)
–

reserved for future use
mgmt(2)
–
MIB-I originally assigned OID 1.3.6.1.2.1 or {mib 1}
–
MIB-I has been superseded by MIB-II
–
system(1): network device operating system
–
interfaces(2): network interface specific
–
address translation(3): address mappings
–
ip(4): Internet protocol specific
–
icmp(5): ICMP specific
–
tcp(6): transmission protocol specific
–
udp(7): user datagram protocol specific
–
egp(8): exterior gateway protocol specific
–
cmot(9): CMIP on TCP specific
–
transmission(10): transmission media specific
–
snmp(11): SNMP specific
SNMP Overview

experimental (3)
–

experimental protocols and MIB development intended to enter the standards
track
private(4)
–
used to specify objects defined unilaterally
–
enterprises(1) or {private 1}
•
•
•
an organization that has registered its own specific extensions to the MIB
vendor-specific MIBs are found
OID (1.3.6.1.4.1)
OIDs represent each manageable object with a unique sequence of numbers
and names

SNMP uses the number as an abbreviated form of the name
–
to make requests for data values
–
to identify each response that carries the values
SNMP Overview
The five SNMPv1message types (RFC1157)

Get-Request: retrieve information from device

Get-Response: agent responds to the Get-Request

Get-Next-Request: ask for the next specific object

Set-Request: for remote configuration parameter

Trap: an unsolicited message
Data Network
Managing host
station
MS-DOS
agent
agent
Host
agent
Terminal server
Router
agent
agent
Device
SNMP Overview
Format of SNMP
Version
Version
Version
Community
Community
Community
PDU
Request
0
Name X
0
type
ID
Get-Request, Get-Next-Request, Set-Request
PDU
type
PDU
type
Request Error
ID
status
Get-Response
Enterprise
Error
index
Agent Generic
addr
trap
Trap
Layer 7
SNMP
Layer 6
ISO presentation
Layer 5
ISO session
Layer 4
UDP
Layer 3
IP
Layer 2
ISO data link
Layer 1
Physical
Name X
Value X
……..
Value X
……...
Specific Time Name X Value X
trap
SNMP Overview
SNMP trap

an unsolicited message an agent sends to a station

inform the server about the occurrence of specific event

seven types of SNMP traps (MIB-II)
Managing host
–
coldstart of a system: reinitialing itself such that its configuration or protocol
has changed
–
warmstart of a system: reinitialing itself such that its configuration or protocol
has not changed
–
link down: a specific link has failed
Data Network
station
Device
agent
Link failure
Trap: interface #2, link down
SNMP Overview
–
link up: a specific link has come up
–
failure of authentication: a request does not provide proper authentication
–
EGP (Exterior Gateway Protocol) neighbor loss
• EGP is a reachability protocol used between data networks
–
enterprise specific
• a vendor to provide additional functionality that complements the generic traps
security

community string
–
station sends a particular password with each message
–
the password is referred to as the SNMP community string
SNMP Overview

Examples of an SNMP query
Managing host
station
Device
agent
Community
string: blee
SNMP Get, community string = blee
Communication string validated, SNMP Get-Response
Community string: blee
Managing host
Data Network
station
Device
agent
SNMP Set, community string= public
SNMP Trap, authentication failure