2. SNMP
Estimated time to complete: 2-hr(s)
Unit Objective:
B
Identify the principles of network monitoring and management. Task(s): 3.10.1, 3.10.2, 3.10.3 MEAS: PC
Upon completion of this knowledge unit, you will be required to identify basic facts, terms, and relationships regarding but not limited to how
SNMP works in relation to a computer network, different types of SNMP PDUs and types of SNMP community strings associated with them.
There will be a eighteen-question quiz at the end of units 1-3 where you must score 70% or better.
NOTE: Ensure that you download the PDF unit locally and load it in Adobe Acrobat for full functionality.
Simple Network Management Protocol
As a Cyber Transport Systems Apprentice in the United States Air Force, you will not just be required to be familiar with NMS based solutions.
You will also need to be familiar with specific protocols that aid both computer network management and computer network monitoring. Simple
Network Management Protocol (SNMP) is a common protocol that allows for collection and organization of information about managed nodes
and pieces of network equipment on a computer network. The most current version of SNMP is Simple Network Management Protocol version
3 (SNMPv3), which provides both increased performance and security.
A basic SNMP architecture would have what is known as an Agent installed on endpoint nodes known as Managed Devices. Agents are software
modules configured to run on the managed device nodes and/or network equipment for the purpose of providing information to what is known as
the Network Management Station. The Network Management station is essentially what controls all SNMP managed devices and pieces of
network equipment and is commonly referred to as the manager.
Agents for managed devices in SNMP create what is known as a Management Information Base (MIB) which contains the relevant node related
information for SNMP. A MIB is a hierarchy or organized data structure of what is known as SNMP variables. SNMP variables are mostly
referred to as Object Identifiers (OIDs). OIDs are identifiers that help differentiate between managed devices. When changes are made or
viewed, you modify or read the individual relevant OID which is contained within the MIB. For example, if I wanted to change the hostname of a
specific SNMP managed device, I would use the network management station to modify the OID contained within the MIB provided by the agent
of the managed device.
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Simple Network Management Protocol PDUs
In relation to SNMP, there a variety of Manager-to-Agent requests associated with the protocol in relation to the network management station
and the managed device running an agent. Each request is represented by a different type of SNMP PDU. There are four in total that we need to be
concerned with:
GetRequest – Is a manager-to-agent request to retrieve the value of a node related SNMP variable.
SetRequest –Is a manager-to-agent request to change the value of a node related SNMP variable.
Response – is the return communication from the agent for GetRequest and SetRequest.
Trap – Is a notification from the agent to the manager. By rule of thumb, most of the communication involving SNMP PDUs are requests by the
network management station to the SNMP managed devices. However, criteria can be explicitly specified for managed devices which will trigger
these types of messages to be sent to notify the network management station when necessary. An example of this would include a network
administrator specifying a need to have a notification sent when the temperature of a switch or router reaches a certain threshold.
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Simple Network Management Protocol Authentication
SNMP uses what is known as Community Strings to establish trust between a network management station and agent on a managed device. For
SNMPv1 and SNMPv2 strings were individually password protected and required entering a password when attempting the related SNMP
function. SNMPv3 now supports more secure authentication via username and password associated with the network administrator. Each
community string is associated with a type of request listed above and are as follows:
Read-Only – this is the string associated with GetRequest PDUs. This allows read-only access of the managed device running a SNMP agent.
This is also referred to as the Public Community String.
Read-Write –this is the string associated with SetRequest PDUs. This allows read-write access of the managed device running a SNMP agent.
This is also referred to as the Private Community String.
Trap – this is the string associated with trap PDUs. This is sent with the trap PDUs.
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