Discussion

such as GetNext and GetBulk), or as being read-write, meaning that the manager can
change the object’s information with an SNMP Set command.
MIBs are defined using a language called Abstract Syntax Notation 1 (ASN.1). The
IETF has defined a number of MIBs in various RFCs that contain objects common
across all network devices. Some of these MIBs are mandatory, while others are
optional. On NMS systems, most of the mandatory MIBs are typically compiled into
the SNMP manager software. If you need standard MIBs that are not provided with
your NMS, you can find them in the IETF RFCs and at other web sites, including
http://www.net-snmp.org, http://www.rfc-editor.org, and http://net-snmp.sourceforge.
net. There is a list of SMI numbers on the IANA web site (http://www.iana.org).
For objects specific to a device, the manufacturer of the device provides enterprisespecific
MIBs. They must have the same structure as standard MIBs. The following
example of the beginning Juniper chassis MIB illustrates the ASN.1 language:
-- Juniper Enterprise Specific MIB: Chassis MIB
JUNIPER-MIB DEFINITIONS ::= BEGIN
...
-- Juniper Box Anatomy MIB
-- Top level objects
jnxBoxClass OBJECT-TYPE
SYNTAX OBJECT IDENTIFIER
MAX-ACCESSread-only
STATUS current
DESCRIPTION
"The class of the box, indicating which product line
the box is about, for example, 'Internet Router'."
::= { jnxBoxAnatomy 1 }
jnxBoxDescr OBJECT-TYPE
SYNTAX DisplayString (SIZE (0..255))
MAX-ACCESSread-only
STATUS current
DESCRIPTION
"The name, model, or detailed description of the box,
indicating which product the box is about, for example
'M40'."
::= { jnxBoxAnatomy 2 }
jnxBoxSerialNo OBJECT-TYPE
SYNTAX DisplayString (SIZE (0..255))
MAX-ACCESSread-only
STATUS current
DESCRIPTION
"The serial number of this subject, blank if unknown
or unavailable."
::= { jnxBoxAnatomy 3 }
These three objects provide information about the physical Juniper Networks router,
specifically the family, model name, and serial number.
132 | Chapter 4: SNMP
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