User`s manual

MP-1xx/H.323
MP-1xx/H.323 User’s Manual 82 Document #: LTRT-00651
determined via SNMP without the overhead associated with logging into the device, or
establishing a TCP connection with the device.
" Get Next Request: Enables the SNMP standard network managers to "walk" through all
SNMP values of a device (via the "get-next" request) to determine all names and values that
the device supports. This is accomplished by beginning with the first SNMP object to be
fetched, fetching the next name with a "get-next", and repeating this operation until an error
is encountered (indicating that all MIB object names have been "walked").
" Set Request: The SNMP standard provides a method of effecting an action associated with
a device (via the "set" request) to accomplish activities such as disabling interfaces,
disconnecting Users, clearing registers, etc. This provides a way of configuring and
controlling network devices via SNMP.
" Trap Message: The SNMP standard furnishes a mechanism by which devices can "reach
out" to a network manager on their own (via the “trap" message) to notify the manager of a
problem with the device. This typically requires each device on the network to be configured
to issue SNMP traps to one or more network devices that are awaiting these traps. The Trap
messages are send to SNMP Manager. The IP address of SNMP Manager is defined in the
ini file or via Web browser (in Network Settings)
7.1.3 SNMP MIB Objects
The SNMP MIB is arranged in a tree-structured fashion, similar in many ways to a disk directory
structure of files. The top level SNMP branch begins with the ISO "internet" directory, which
contains four main branches:
" The "mgmt" SNMP branch contains the standard SNMP objects usually supported (at least
in part) by all network devices.
" The “private" SNMP branch contains those "extended" SNMP objects defined by network
equipment vendors.
" The "experimental" and "directory" SNMP branches, also defined within the "internet" root
directory, are usually devoid of any meaningful data or objects.
The "tree" structure described above is an integral part of the SNMP standard, however the most
pertinent parts of the tree are the "leaf" objects of the tree that provide actual management data
regarding the device. Generally, SNMP leaf objects can be partitioned into two similar but slightly
different types that reflect the organization of the tree structure:
" Discrete MIB Objects: Contain one precise piece of management data. These objects are
often distinguished from "Table" items (below) by adding a ".0" (dot-zero) extension to their
names. The operator must merely know the name of the object and no other information.
" Table MIB Objects: Contain multiple pieces of management data. These objects are
distinguished from "Discrete" items (above) by requiring a "." (dot) extension to their names
that uniquely distinguishes the particular value being referenced. The "." (dot) extension is
the "instance" number of an SNMP object. In the case of "Discrete" objects, this instance
number is zero. In the case of "Table" objects, this instance number is the index into the
SNMP table. SNMP tables are special types of SNMP objects, which allow parallel arrays of
information to be supported. Tables are distinguished from scalar objects, in that tables can
grow without bounds. For example, SNMP defines the "ifDescr" object (as a standard SNMP
object) that indicates the text description of each interface supported by a particular device.
Since network devices can be configured with more than one interface, this object could only
be represented as an array.
By convention, SNMP objects are always grouped in an "Entry" directory, within an object with a
"Table" suffix. (The "ifDescr" object described above resides in the "ifEntry" directory contained in
the "ifTable" directory).
7.1.4 SNMP Extensibility Feature
One of the principal components of any respectable SNMP manager is a “MIB Compiler" which
allows new MIB objects to be added to the management system. When a MIB is compiled into an
SNMP manager, the manager is made "aware" of new objects that are supported by agents on