SNMP Monitoring by doing SNMP GETs

Having established a firm reasoning as to why networks and network related applications should be monitored, it is important to now move onto discussing methods by which this monitoring process can take place.

In fact, there are a variety of methods utilized to monitor networks. SNMP monitoring is indeed one of the most effective and efficient network monitoring technologies used nowadays. In order to understand the technology behind network monitoring, we will briefly proceed to explain the underlying structures and their corresponding functions.

Network servers, routers, firewalls and other equipment usually have their statistics maintained in so called OIDs - Object Identifiers. These OIDs may be retrieved remotely on the network by means of utilizing the SNMP protocol - Simple Network Management Protocol.

Since every vendor has his own set of differently described OIDs, they usually (we know we do) offer their textual description of their set of SNMP variables and their possible values, as well as the OID functions they encompass. These textual description files are called Management Information Base or MIB for short.

Of course OIDs have to be collected in one entity in order to facilitate their finding. This one entity is actually called the Structure of Management Information (SMI) tree. And since the standard followed here is the Simple Network Management Protocol (SNMP), the SMIs are defined by the same respective standard.

Just like other tree-like structures, the Structure of Management Information (SMI) has a root node that branches into other branches and finally to leaves. Each branch adds its own reference value to the overall path. The path itself is made up of references separated with periods ".".

Through SNMP GETS and SETS, a simple request/ response protocol communicates management information between two entities; namely SNMP applications (also known as SNMP managers) and SNMP agents.

We will now move onto addressing how SNMP GETS may be useful in the process of SNMP monitoring. Habitually, you will have to first configure the SNMP port; i.e. set the number to usually a 161. You may also wish to assign it a different number for security reasons. Having done that, your software will usually allow you to then select the option of whether you wish to convert the SNMP check output result to textual representations.

From its name, SNMP GETS are used for read operations from the devices, while SNMP SETS are used for write operations. You will usually need to configure SNMP SETS before GETS. In order to allow for the host communities of these checks to have proper authentication, the network administrator will need to enter the community string. This SNMPv1 community string acts as the password key, and is usually "public" by default.

When using SNMP, the SNMP managers (SNMP applications) run in a network management station (NMS). From there, the SNMP applications issue queries to gather information about the external network devices. 'Information' here indicates some or all of the following: status, configuration, and performance of those external network devices (also known as network elements).

At this point, we will have to address the fact that there are several versions of SNMP; namely SNMP version 1, SNMP version 2 and SNMP version 3. Before you'll be able to perform the SETS then GETS, you will have to specify the required protocol version. In Servers Alive, you can do the SNMP SETS before the GETS only in SNMP versions 1 and 2; while in version 3 the GETS can still be done.

Once you select the required protocol version, some software applications require you to enter the specific SNMP device credentials (username and password).

There are other settings that you may adjust from the software's user interface. Some software allow such settings to include modifications to the SNMP checks return device status keywords that describe the device's activity and/ or accessibility levels.

After properly installing and configuring the IP address and SNMP settings, the network administrator will now be able to employ SNMP GETS and SETS to communicate with the network's different devices. The devices should - in turn - respond back with SNMP Traps.


Polling Individual OIDs: SNMP GETs

Harrison, Peter. Monitoring Server Performance. Ch. 22

Sellens, John. System and Network Monitoring and Management with SNMP.

Test 882: IBM Tivoli Enterprise Console V3.8 Network Management Implementation. IBM website.
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