Find out what’s really happening in your network with LogRhythm NetMon Freemium

I recently discovered that LogRhythm, as well as very a full-featured Security Intelligence Platform and SIEM, also provide a “freemium” Network Monitor. The “freemium” refers to that fact that the software is 100% free, full-featured and not time-limited, but is capacity-limited. Those limits are 1Gbps of network bandwith and three days of history.

Those limits are fine for if you don’t already have anything like this currently running in your network, and depending on what kind of stuff you pump over your network, for the average small office they’ll be fine and give you some great insights into what’s going on.


The hardware requirements state that the system should have a minimum of 8GB RAM (12GB recommended), 4 CPU cores (minimum of 2), and unless you just want to monitor traffic from the NetMon box itself you’ll need two NICs.

NetMon freemium is available to download either as a VirtualBox VM, or as an ISO image. I chose the ISO option as I had an old Dell PowerEdge 2950 lying around so decided to run the software on that. I tried using Rufus but could not get it to boot properly, so I gave up and burnt the ISO onto a DVD.

I’d recommend plugging one of your two NICs into a network with DHCP enabled, and leave the other one disconnected initially. NetMon is based upon CentOS 7, and installation is really straightforward.

Once installed, you’ll be given a logon prompt. Log in as logrhythm with a password of changeme. Use the command:
ip address
to see what IP address has been obtained from DHCP – look for the line beginning inet in a section with eth near the beginning, e.g. 2: eth0. If DHCP didn’t work, reboot to get it to try again. Then from a web browser, open https://<ip address> and you’ll get a LogRhythm sign in page. (If you get a pop-up authentication box, just click Cancel on it, I’m not sure why this sometimes appears). The web-based credentials default to a username of admin and a password of changeme. Change the password.

Now connect the second NIC to your switch. From the NetMon GUI, go to Configuration – Engine, and set the Input Interface. This should be set to one of the options starting netmap, I only had one: netmap:eno2 so I picked this. Click Apply Changes then go to Diagnostics – Interface and start to watch the Packet Rate graph, this updates every few seconds so you can see the data start to arrive once you’ve done the network configuration on your switch.

I’ve configured the switch port to be in Switched Port ANalyser mode (SPAN), which is a way of sending all the traffic from one port or more ports or VLANs to another port. My office PCs are all on a particular VLAN so I’ve chosen to send all this traffic to my SPAN port. On a Cisco switch you do this by creating a monitor session. You can have multiple ones of these, and you may already have some set up, so first check what you have:

sh run | inc monitor

and you may be shown some lines such as:

monitor session 1 source interface Gi1/0/2 , Gi1/0/4
monitor session 1 destination interface Gi1/0/46

This means that in order to create a new monitor session, I have to use session 2, as session 1 is already in use. NIC2 of my server is plugged into port Gi1/0/47, and aside from a description, there is no other configuration on this switch port. To send all VLAN10 traffic to this port I used the commands:

conf t
monitor session 2 source vlan 10 both
monitor session 2 destination interface g1/0/47

At this point I saw the Received line jump up from zero in the Packet Rate graph, so I knew the command had worked and NetMon was receiving data.

Analyse your data

So now you’re getting data, and by clicking on the LogRhythm logo you’ll be taken to the dashboard, by default showing you:

  • Top Applications by Bandwidth (histogram)
  • Top Applications by Bandwidth (pie)
  • Top Applications by Packet Count (pie)
  • Analyze table

This gives a good overview of what’s happening right now on your network. You can click into the pie chart sections to filter data immediately, or click onto a section of the histogram to build a filter that sets the protocol and time range to give you more detail. For example, what’s all that smb traffic at 11:43? Click the pale blue section of the bar, click Apply Now and I get the timeline broken down into five second slots, and the Analyze Table lets me go through the sessions and see what was talking to what. I can see more information by clicking the “up” arrow just underneath the histogram, this gives me a table which shows the amount of data sent by the selected protocol per second:

Click on the date on one of these rows, e.g. the one where 72.326MB was transferred, and it’ll filter again to that time but at 100ms granularity. I now only have one entry in the Analyze Table at the bottom, and can not only see the source and destination IP addresses (sadly it doesn’t convert these into DNS names). By expanding the line in the Analyze Table, I can see lots of info, most interestingly (because this is the SMB protocol) a list of all the filenames accessed. In my case, I can now see that this traffic was caused by a machine doing a full Active Directory Group Policy refresh, which is perfectly normal.

Over to you

I’ve found this product to be pretty good, it’s giving me insight into something that I had no visibility of until now, and I suspect most people would find the same. There are a lot more features that I’ve not looked at yet, such as alarms, customising dashboards, charts and tables.

There are some videos showing how to use NetMon on LogRhythm’s YouTube channel, and there’s also a community site you can sign up to for free for more resources and to ask for help. All in all, NetMon Freemium is going to be a nice additional tool for keeping an eye on my systems and data.

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