SNMP interfaces monitoring
Using the SNMP Interfaces wizard of the module we can perform the SNMP walk to discover the interfaces of the monitoring device. We will have to fill in the data of target IP, port (default 161), execution server (default localconsole), community (default preconfigured), SNMP version (1,2c,3) and run the SNMP Walk.
We take as an example the object ifHCOutOctets with OID 188.8.131.52.184.108.40.206.220.127.116.11.10. This OID represents the number of octets (8bits) that have been sent by the interface 1 from the monitored device which returns the value in bytes/s. The type of module created will be (in this case set automatically by the wizard): Remote SNMP network agent, incremental data (remote_snmp_inc).
A module of incremental data type is used, as it is a counter, it cannot be treated as an absolute numerical data. It performs the calculation on the number of octets sent between the execution time interval.
octets transferred = 629145600
transfer time = 5 minutes(interval) = 5 x 60 = 300 seconds
transfer rate (B/s) = 629145600 / 300
transfer rate (B/s) = 20971520 B/s
Unit: where in this case we can select bytes/s within the dropdown of the units.
Post process: where we can select in the drop-down menu to pass us the data obtained from “Bytes to Kilobytes”, “Bytes to Megabytes”, “Bytes to Gigabytes”. Performs the calculation to make the conversion, it also allows us to enter a custom value by which to multiply or divide the data obtained. In this case the most usual would be to select, Bytes to Megabytes, which would be the same as doing:
transfer rate (MB/s) = 20971520 / 1024 / 1024
transfer rate (MB/s) = 20 MB/s
OIDs are a sequence of numbers that identify objects in a hierarchical structure within the network management information database (NMS). The structure of OIDs is similar to that of IP addresses in the network, where each level of the hierarchy is represented by a number. The OID structure is as follows:
The structure of the OID = 18.104.22.168.22.214.171.124.126.96.36.199.6.10, is as follows:
1: identifies the organization or entity that registered the object.
3: identifies the object within the organization.
6: identifies a specific value of the object within the organization.
188.8.131.52.184.108.40.206.6.10: identifies the interface.
Network bandwidth SNMP
To monitor the network bandwidth we have the Network bandwidth SNMP plugin that obtains the amount of information transmitted and received from the device, or the filtered interface, during the module interval.
We must select the plugin server type module and in the Plugin the Network bandwidth SNMP. We will have to configure the data: SNMP version (1,2c,3) Community, Host (by default that of the agent) Port (161 by default).
The plugin performs a calculation on the data obtained from the OID ifspeed with the bandwidth inUsage and outUsage, giving as a result the percentage of use as opposed to the previous measurements.