How to Write an MIB

1
How to Write an MIB

• The Monitoring Support for CUWiN Project
• Ray K. Lam
• May 21, 2007

2
Why Learning to Write an MIB?

• We want to monitor CUWiN nodes
• TX power, CS threshold, RSSI,
• SNMP is the tool
• SNMP agents at the nodes
• SNMP manager at our central authority
• SNMP organizes data as MIB
• MIB management information base

3
Outline

• Object Tree
• Structuring our data
• Defining Objects
• A simple example code
• More variations in the language

D. Mauro, K. Schmidt, Essential SNMP, Ch.
2.3-2.4 http//safari5.bvdep.com/0596000200/enettd
g-CHP-2-SECT-3
4
The Object Tree

• Managed objects
• Data to be monitored
• Organized into a tree
• Root
• Root-Node
• Subtree
• Group of related data
• Data in both leaf and non-leaf nodes

5
Object Identifier

• OID
• Object IDentifier
• Textual name
• iso.org.dod.internet
• Numerical string
• 1.3.6.1

6
The 1.3.6.1 Subtree

• The internet subtree is our focus
• Directory branch
• Unused
• Mgmt branch
• Standard objects
• Experimental branch
• Testing and research
• We may use it
• Private branch
• For enterprises, e.g. Cisco

7
Defining the Internet Subtree

• Internet OBJECT IDENTIFIER iso org(3)
  dod(6) 1
• Directory OBJECT IDENTIFIER internet 1
• Mgmt OBJECT IDENTIFIER internet 2
• Experimental OBJECT IDENTIFIER internet 3
• Private OBJECT IDENTIFIER internet 4

8
A Simple Example

• A stripped-down version of MIB-2
• See handout
• Usual structure
• Name of MIB
• Import other files
• Define OIDs
• Define actual objects

9
Name and Imports

• Name of the MIB RFC1213-MIB
• Imports (like include)
• Datatypes and OIDs from other files

RFC1213-MIB DEFINITIONS BEGIN
IMPORTS mgmt, NetworkAddress, IpAddress,
Counter, Gauge, TimeTicks FROM
RFC1155-SMI OBJECT-TYPE FROM RFC 1212
10
Defining OIDs

• mgmt uniquely defined by imports
• -- starts a comment

mib-2 OBJECT IDENTIFIER mgmt 1 --
groups in MIB-II system OBJECT IDENTIFIER
mib-2 1 interfaces OBJECT IDENTIFIER
mib-2 2 at OBJECT IDENTIFIER mib-2 3
ip OBJECT IDENTIFIER mib-2 4 icmp
OBJECT IDENTIFIER mib-2 5 tcp OBJECT
IDENTIFIER mib-2 6 udp OBJECT
IDENTIFIER mib-2 7 egp OBJECT
IDENTIFIER mib-2 8 transmission OBJECT
IDENTIFIER mib-2 10 snmp OBJECT
IDENTIFIER mib-2 11
11
Defining Objects

• The template

ltnamegt OBJECT-TYPE SYNTAX ltdatatypegt ACCESS
lteither read-only, read-write, write-only, or
not-accessiblegt STATUS lteither mandatory,
optional, or obsoletegt DESCRIPTION "Textual
description describing this particular managed
object." ltUnique OID that defines this
objectgt
12
Example Defining ifTable

• A table of network interfaces
• Object name ifTable (case sensitive)
• Datatype SEQUENCE OF IfEntry
• SEQUENCE OF is like array
• IfEntry to be defined

ifTable OBJECT-TYPE SYNTAX SEQUENCE OF
IfEntry ACCESS not-accessible STATUS
mandatory DESCRIPTION "A list of interface
entries. The number of entries is given by the
value of ifNumber." interfaces 2
13
Example Defining ifTable

• Access type not-accessible
• Cannot query an agent for this objects value
• Status mandatory
• An agent must implement this object
• OID
• 1.3.6.1.2.1.2.2 / iso.org.dod.internet.mgmt.interf
  aces.2

ifTable OBJECT-TYPE SYNTAX SEQUENCE OF
IfEntry ACCESS not-accessible STATUS
mandatory DESCRIPTION "A list of interface
entries. The number of entries is given by the
value of ifNumber." interfaces 2
14
Defining the IfEntry Sequence

• Need to define IfEntry for ifTable
• ifTable is an object
• IfEntry is a SEQUENCE a special datatype
• SEQUENCE is a list of other datatypes
• Represents columnar fields in a table

IfEntry SEQUENCE ifIndex INTEGER, ..
. ifSpecific OBJECT IDENTIFIER
15
Defining ifEntry

• ifEntry different from IfEntry
• ifEntry is an object
• IfEntry is a (user defined) datatype
• ifEntry defines a particular row in ifTable
• INDEX a unique key to identify a row

ifEntry OBJECT-TYPE SYNTAX IfEntry ACCESS
not-accessible STATUS mandatory DESCRIPTION
"An interface entry containing objects at the
subnetwork layer and below for a particular
interface." INDEX ifIndex ifTable 1
16
Defining ifIndex

• ifIndex is read-only

ifIndex OBJECT-TYPE SYNTAX INTEGER ACCESS
read-only STATUS mandatory DESCRIPTION "A
unique value for each interface. Its value
ranges between 1 and the value of ifNumber.
The value for each interface must remain
constant at least from one reinitialization of
the entity's network- management system to the
next reinitialization." ifEntry 1
17
The Remaining Things

• Definition for each object in the IfEntry
  sequence
• Omitted in the handout
• The END clause

18
More SMIv1 Datatypes

• INTEGER
• 32-bit number
• Often used to specify enumerated types
• 0 should NOT be used for enumeration
• Counter
• 32-bit number from 0 to 232 1
• Should only increase
• Wrap back to 0 when max is reached

19
More SMIv1 Datatypes

• IpAddress
• Gauge
• 32-bit number from 0 to 232 1
• Can increase or decrease
• TimeTicks
• 32-bit number from 0 to 232 1
• Measures time in hundredths of a second

20
SMIv2 Extensions

• New datatypes and changes
• OID of new branch
• iso.org.dod.internet.snmpV2.snmpModules.snmpMIB
  .snmpMIBObjects

21
Some New Datatypes

• Aliases (same as old datatypes)
• Integer32, Counter32, Gauge32
• Unsigned32
• 32-bit number from 0 to 232 1
• Counter64
• 64-bit version of Counter

22
New Object Definition Fields

• UnitsParts
• Describe the unit, e.g. seconds, milliseconds
• MAX-ACCESS
• read-only, read-write, read-create,
  not-accessible, accessible-for-notify
• Either ACCESS or MAX-ACCESS should appear

ltnamegt OBJECT-TYPE SYNTAX ltdatatypegt
UnitsParts ltOptional, see abovegt MAX-ACCESS
ltSee abovegt STATUS ltSee abovegt DESCRIPTION
"Textual description describing this
particular managed object." AUGMENTS ltname
of tablegt ltUnique OID that defines this
objectgt
23
New Object Definition Fields

• New keywords for STATUS
• Current, obsolete, and deprecated
• Current mandatory
• AUGMENTS
• Add a column to a table

ltnamegt OBJECT-TYPE SYNTAX ltdatatypegt
UnitsParts ltOptional, see abovegt MAX-ACCESS
ltSee abovegt STATUS ltSee abovegt DESCRIPTION
"Textual description describing this
particular managed object." AUGMENTS ltname
of tablegt ltUnique OID that defines this
objectgt
24
Other New Features

• New textual conventions
• Not sure about this
• Refer to the reference

D. Mauro, K. Schmidt, Essential SNMP, Ch.
2.3-2.4 http//safari5.bvdep.com/0596000200/enettd
g-CHP-2-SECT-3
Writing the MIB is not the hard part designing
is.