When we visit our local doctor, sometimes we don’t always agree with what they have to say. Sure, we didn’t go to medical school and we don’t have a fancy degree on our wall. But heck, it’s our body and once in a while we know something just isn’t right. So what do we do? We get a second opinion. The same concept is important in almost any part of life – even network management. Sometimes something just doesn’t seem right, and we need to get a second opinion before we blindly trust what our hardware and software is telling us.
For years, Plixer (yes, even in our Somix days) has been using an excellent free tool called GetIf for walking MIBs and verifying SNMP information. It allows support technicians and users to verify device settings and configurations. It’s important to have these small, but incredibly useful, tools on hand. Whenever something doesn’t go as planned during setup, the first question to ask is always, “Is it the software or is it the hardware?” When helping customers and evaluators setup Denika Performance Trender to monitor their SNMP enabled devices, GetIf has always been invaluable in helping answer that question.
Recently, Plixer released a completely free tool that offers similar benefits for those of us working with NetFlow hardware. It’s called Flowalyzer. While Flowalyzer is capable of performing a few different operations in the configuration and testing of your NetFlow devices, the one I want to focus on here is The Listener.
Flowalyzer’s Listener tab fills a very similar need to the one GetIf does. It allows users to answer the question, “Is it the software or is it the hardware?” Just open Flowalyzer and click the Listener tab and you will automatically see any flows being sent to the PC on which you are running it. This allows you to verify that NetFlow is being sent from the hardware correctly. If Flowalyzer can see NetFlow coming in, but your NetFlow collector (Scrutinizer or otherwise) doesn’t see the flows, then most likely it’s a software configuration issue. However, on the flip-side, the absence of NetFlow coming into Flowalyzer makes it easy to confirm a hardware configuration problem.
Another way of testing your NetFlow collector is by using Flowalyzer’s NetFlow Generator. The NetFlow Generator simulates NetFlow and sFlow data streams and can be used to verify that the NetFlow collection software is correctly configured. All of this can be done before making any changes to the router. Is the NetFlow being sent from Flowalyzer showing up in your NetFlow tool? If so, great! If not, “Houston we have a problem!”
In addition to just confirming the presence of NetFlow, Flowalyzer, which is able to listen on multiple ports, can display packet count, version of NetFlow and the UDP port flows are coming in on. Just like Scrutinizer, Flowalyzer can show users which devices are sending the highest volume of traffic.
So the lesson here is, “Don’t struggle!” Make sure to use tools like Flowalyzer and GetIf for getting your second opinions. Never trust that your hardware is configured correctly or that your NetFlow reporting software is setup right… verify it with Flowalyzer NetFlow and sFlow Tester.