Network Monitoring - It's Your Livelihood

What are your daily duties as the VoIP network operations director? You have to keep your network up and running. You have to answer calls which may relate to situations like “X location is down” or “Y location is slow”.  My we suggest that you proactively monitor your network as described below and perform tasks like:

1. Monitor your network and take actions with respect to situations like device and line failures.
2. Analyze line/physical facility utilization, errors on the facility and be sure about network performance and conformance to SLAs.
3. Be aware of what "talks to what" and when?  Be sure how much bandwidth is needed for every single application riding your network (and the networks you traverse.)
4. Know your exact data flows over your networks.

If you have all this information at your disposal, people will think twice before they point finger at you. 

But how can you achieve this?

You need a phased approach to understand network monitoring. I am not talking about network layers, but network monitoring layers. We have to involve deeply to monitoring layers before deciding about network monitoring software needs. A simple summary could include these:

• Preconditions of network monitoring.
• Up/Down monitoring
• Performance Monitoring / SNMP monitoring
• Who talks with whom? / Netflow monitoring
• Data capture / Data sniffing

Preconditions of Network Monitoring
Network documentation is essential to monitor a network. Trying to set up network monitoring tools before going through the documentation is a complete waste of time. You will see everything green on the screen, but this maybe due to one of the redundant lines that are down. You will sit staring without knowing what is happening. Always remember, documentation comes first and everything follows.Suggested Network documentation tools: Powerpoint/Visio, NetViz


Up/Down monitoring
Design a map in which you can see some red and green lights glowing. Green means up and red means down. It is simple yet powerful. You will immediately come to know that there is some problem if the red light glows.This is based on ping. Almost every IP devices support echo/echo reply. So, you can monitor all IP devices in your network by using ping.  Go one step further by monitoring one application at a time present on a device instead of whole device. All network applications utilize TCP/UDP ports. You can monitor the applications by trying to access with telnet to its TCP/UDP ports. The port being open suggests that the application is running
Suggested monitoring tools: WhatsupGold, nmap


Performance monitoring / SNMP monitoring
The lines are up, the devices are up, but life is not perfect. People may complain about the performance of data lines, but are they saturated or do they have plenty of spare bandwidth?  Is there packet loss on the lines? Are routers running out of memory? We need SNMP to monitor the heart beat of the network.
Suggested monitoring tools: MRTG, Solarwinds Orion, PRTG


What is "talking" with what? / Netflow monitoring
You may realize that the line is full, but is someone or some applications increasing traffic load enormously. Who are they? Is it necessary traffic? In some devices, by using “ip accounting” command you can get an idea of current traffic sources and destinations. Nevertheless, to analyze and to optimize the traffic we need flow monitoring. We need to know source and destination IP addresses and TCP/UDP ports and number of packages/bytes.


Everyone blames the network speed until you publish an network usage report that clearly shows only 15% of the traffic is ERP traffic and rest comes from Internet access.You should know that flow monitoring tools requires more server resources, since they collect enormous amount of data.
Suggested monitoring tools: Fluke Netflow monitor, Paasler


Data capture / RMON – Sniffer tools
Sometimes you need to observe the exact data flow on the line and not just information about it. Just have a look at this sample scenario. After you find out that the web service causes inappropriately high network traffic, the owner of the application just can say “No, we are not pushing this much of data to network. We just respond Yes or No in this web service and it is just 100 bytes”. Therefore, you should sniff the data flow on the line. Maybe, you will find that web service responds yes or no (100 bytes) and with the definition of web service (6 kilobytes).
Suggested monitoring tools: Wireshark, Palladion


You can have a look at Network Monitoring Tools in Stanford University web site for a superb list of network monitoring tools. You can find another tidy list at Network Traffic Monitoring in Alan Kennington’s topology.org.