Simple Network Management Protocol or SNMP was created to provide a common protocol foundation that device manufacturers would use to expose the various aspects of the product so that network administrators know what to expect.
Information like routing network traffic stats, and CPU load, etc, can all be remotely accessed using SNMP. On devices supporting SNMP, it can be used to create configurations, but that’s beyond the scope of a single article.
Once connected to the device, you will have to ‘pull it’ for information through the use of OIDs. The various OIDs give various pieces of information. In this article, we will focus on network traffic.
SNMP information reading and graphing (OIDs)
For the sake of immediate gratification, the how-to-read-SNMP information is where we will begin since most people will not need the configuration part.
So you have configured the device for SNMP, but will you know which OIDs to read, and how do you actually do it? There are many commercial and free programs that can help you. We are going to look at a few free ones you will be able to utilize hassle-free for browsing and/or graphing the entire OIDs name space.
SolarWinds Bandwidth Monitor
A conversation about ‘network monitoring’ can’t really happen without SolarWinds coming up, since it is a major player in the SNMP field. We will not go into the endless networking products that SolarWinds has to offer, but instead, we are going to focus on a free utility called ‘Free Real Time Bandwidth Monitor.’
There are 2 disadvantages to this utility:
- It does not give the option to save or open configuration files.
- Its goal is to show network bandwidth, so it is not a good choice if you wish to retrieve other SNMP information.
If these limitations will be a problem, continue on to one of the other options available.
The real advantage of this program is that it is the only one that will tell you if your refresh interval is too short. It would appear that not all devices can or will update their statistics more than x times/sec. For example, Jupiter devices update every 7 seconds.
Flowalyzer & Plixer
Flowalyzer is a free utility that’s extremely simple to use. This utility’s advantage over Solarwinds is that you can extract the OIDs numerically in Flowalyzer. However, this program isn’t suitable for extended periods of monitoring as it randomly and oddly crashes.
It does have the advantage of allowing you to save its configuration into the files and then call upon them through associating the program to the file extension, but the program is very finicky about where you save the files.
Getif is old. Yes, there are options that are much newer, but this program is free, works well to get the job done, and since it’s the first program we used, we felt we should give it a homage.
Use this program or one that is similar so that you are able to extract more information than just the interface information of the device.
Enabling SNMP on the target device
Just about every good device that can be networked will support the exposure of its information in this manner. However, that being said, not every device will, and you may want to have a look at the documentation for your device to learn how to do this. We are going to look at some examples available, however, this isn’t a complete list.
- In the WebGUI, go to Services, then scroll down the page until you see SNMP.
- Select Enabled and then save the configuration.
- Once you’ve enabled it, you will be given the details that you can change. It is significant that you note what RO community you use. “Public” is the default; however, you can change this to any other value that you want. Save and apply the changes.
On Fortigate (FortiOS)
- Presuming that you are using a relatively current version of FortiOS that is V4 or higher, in the main window expand the Config panel and select SNMP.
- To create a new “SNMP v1/v2c” community, click on Create New.
- Fill in the community name and the range of IPs that are allowed to access.
- Save your settings.
You need to enable the interface that you wish to read from as well.
- Go to Config and then Network.
- Check the SNMP checkbox and then click OK at the bottom of the page.
On Juniper (JunOS)
- In the WebGUI, go to Configure -> Services -> SNMP.
- Click on Add.
- Enter the community name of your choice.
- Choose the authorization type.
- Save and commit your changes.
You can activate SNMP on Windows, however, it is seldom used or even discussed. You will have to install the service first.
- Install the service by going to Programs and Features.
- Go into Turning Windows features on or off.
- Scroll to find the Simple Network Management Protocol (SNMP). Check its checkbox and click OK for it to be installed.
- Once installed, you will configure the community string by opening Services.
- Scroll to find the service and go into its properties.
- Go to the Security
- To add a community, click on Add.
- Fill the desired community name and click Add and then OK for the settings to take effect.
There you have it. You should be ready to graph the network information, and we encourage you to explore what the SNMP protocol has to offer you beyond what we have talked about, like using traps and MIBs.