SNMP:
Ø
SNMP stands for Simple
Network Management Protocol.
Ø It is a standard way
of monitoring hardware and software from nearly any manufacturer, from Juniper, to
Cisco, to Microsoft, Unix, and everything in between.
Ø
It enables a central
management of network.
Ø
Using SNMP an administrator
can watch the entire network.
Ø
It works with TCP/IP
suite.
Ø
It uses UDP for transportation of data.
Ø
SNMP requires only
a couple of basic components to work: a management
station(called manager), and an agent.
Ø
SNMP is an application-level
protocol in which a few manager stations control a set of
agents.
Ø
The protocol is designed at the application
level so that it can monitor devices made by different
manufacturers and installed on different physical networks.
Ø
In other words, SNMP frees management
tasks from both the physical characteristics of the managed devices and the
underlying networking technology.
Ø
It can be used in a
heterogeneous internet made of different LANs and WANs
connected by routers made by different manufacturers.
Ø
A management station, called a
manager, is a host that runs the SNMP client program.
Ø
A managed station, called an agent, is a
router (or a host) that runs the SNMP server program.
Ø
Management is achieved through simple
interaction between a manager and an agent.
Ø
The management station is simply
software that collects information from your network. Most
management stations will poll (ask) your network for
information regularly.
Ø
The agent collects information, and
then sends it to the monitoring station whenever polled(asked). Agents
can also send notification to the management station without
being polled, for example if an error is detected.
Ø
The agent keeps
performance information in a database. The manager has access to
the values in the database.
Ø
For example, a router can store in appropriate variables, the number of packets
received and forwarded. The manager
can fetch and compare the values of these two
variables to see if the router is congested or not.
Ø
Agents
are usually built-in to your network hardware and software – they simply need
to be enabled and configured.
Ø
SNMP is very simple, yet
powerful. It has the ability to help you manage your
network by:
§ Provide Read/Write
abilities – for example you could
use it to reset passwords remotely, or re-configure
IP addresses.
§ Collect
information on how much bandwidth is being used.
§ Collect
error reports into a log, useful for troubleshooting and
identifying trends.
§ Email an
alert when your server is low on disk space.
§ Monitor
your servers’ CPU and Memory use, alert when thresholds are
exceeded.
§ Page or
send an SMS text-message when a device fails.
§ Can perform
active polling, i.e. Monitoring station asks devices for
status every few minutes.
§ Passive SNMP
– devices can send alerts to a monitoring station on error conditions.
Ø
Components Management in the Internet is achieved not only through the SNMP
protocol but also by using other protocols that cooperate with SNMP. At the top level, management is accomplished with two protocols.
1.
Structure of management information
(SMI)
2.
Management information base (MIB)
Ø
SMI - The SMI
is a component used in network management. Its functions are to name objects, to define the type of data that can be stored in an object, and to show how
to encode data for transmission over the network.
Ø
MIB - The
management information base (MIB) is the second
component used in network management. Each agent has its own MIB, which is a collection of all the objects
that the manager can manage. The objects in the MIB are categorized under eight
different groups. They are, system, interface,
address translation, ip, icmp, tcp, udp, and egp. Each group has defined
variables and/ or tables.
Ø SNMP defines
five messages: GetRequest, GetNextRequest, SetRequest, GetResponse, and Trap.
·
GetRequest: This message is sent from the manager
(client) to the agent (server) to retrieve the value of a variable.
·
GetNextRequest: This message is
sent from the manager to the agent to retrieve
the value of a variable.
·
The retrieved
value is the value of the object, following the defined object in
the message. It is mostly used to retrieve the values of the
entries in a table. If the manager does
not know the indexes of the entries, it cannot retrieve the values. However, it
can use GetNextRequest and define the object.
·
GetResponse: This message is
sent from an agent to a manager in
response to GetRequest and GetNextRequest. It contains the value of the variable(s) requested by the manager.
·
SetRequest: This message is
sent from the manager to the agent to set (store) a value in a variable.
·
Trap This
message is sent from the agent to the manager to report an event. For example, if the
agent is rebooted, it informs the manager and reports the time of rebooting.