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About SNMP
About SNMP
SNMP is a protocol used to exchange data about network activity. With SNMP,
data travels between a managed device and a network management station (NMS)
where users remotely manage the network. A managed device is anything that
runs SNMP, such as hosts, routers, and your Directory Server. An NMS is usually a
powerful workstation with one or more network management applications
installed. A network management application graphically shows information
about managed devices (which device is up or down, which and how many error
messages were received, and so on).
Information is transferred between the NMS and the managed device through the
use of two types of agents: the subagent and the master agent. The subagent
gathers information about the managed device and passes the information to the
master agent. Directory Server has a subagent. The master agent exchanges
information between the various subagents and the NMS. The master agent runs
on the same host machine as the subagents it talks to.
You can have multiple subagents installed on a host machine. For example, if you
have Directory Server, Netscape Enterprise Server, and Netscape Messaging Server
all installed on the same host, the subagents for each of these servers communicates
with the same master agent. In the Windows NT environment, the master agent is
the SNMP service provided by the Windows NT operating system. In the UNIX
environment, the master agent is installed with the Netscape Administration
Server.
Values for SNMP attributes, otherwise known as variables, that can be queried are
kept on the managed device and reported to the NMS as necessary. Each variable is
known as a managed object, which is anything the agent can access and send to the
NMS. All managed objects are defined in a management information base (MIB ),
which is a database with a tree-like hierarchy. The top level of the hierarchy
contains the most general information about the network. Each branch underneath
is more specific and deals with separate network areas.
SNMP Overview
SNMP exchanges network information in the form of protocol data unit (PDUs).
PDUs contain information about variables stored on the managed device. These
variables, also known as managed objects, have values and titles that are reported
to the NMS as necessary. Communication between an NMS and a managed device
takes place in one of two ways:
•
NMS-Initiated Communication
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Netscape Directory Server Administrator's Guide • January 2002
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