This is a guest blogpost by Erik Hjelmvik, an expert in network forensics and network security monitoring at NETRESEC.
Wireshark is the default goto tool for analyzing captured network traffic for most network engineers. But there are a few other free and open source alternatives that are sometimes overlooked, one of which is NetworkMiner (disclaimer: I’m the creator of NetworkMiner).
This post is not about software but hardware tools for network admins. Which network gadgets am I using during my daily business? At least three, namely the Airconsole, the Pockethernet and the ProfiShark, which help me in connecting to serial ports, testing basic network connectivity, and capturing packets in a high professional way. Come in and have a look at how I’m working.
This blog post is about using NetFlow for sending network traffic statistics to an nProbe collector which forwards the flows to the network analyzer ntopng. It refers to my blog post about installing ntopng on a Linux machine. I am sending the NetFlow packets from a Palo Alto Networks firewall.
My current ntopng installation uses a dedicated monitoring ethernet port (mirror port) in order to “see” everything that happens in that net. This has the major disadvantage that it only gets packets from directly connected layer 2 networks and vlans. NetFlow on the other hand can be used to send traffic statistics from different locations to a NetFlow flow collector, in this case to the tool nProbe. This single flow collector can receive flows from different subnets and routers/firewalls and even VPN tunnel interfaces, etc. However, it turned out that the “real-time” functionalities of NetFlow are limited since it only refreshes flows every few seconds/bytes, but does not give a real-time look at the network. It should be used only for statistics but not for real-time troubleshooting.
Some time ago I published a post introducing ntopng as an out-of-the-box network monitoring tool. I am running it on a Knoppix live Linux notebook with two network cards. However, I have a few customers that wanted a persistent installation of ntopng in their environment. So this is a step-by-step tutorial on how to install ntopng on a Ubuntu server with at least two NICs.
Some time ago I installed a new firewall at the customer’s site. Meanwhile the customer was interested in the flows that are traversing through the firewall right now. Oh. Good question. Of course it is easy to filter through log messages of firewalls, but theses logs are only for finished sessions. Yes, there are “session browsers” or the like on all firewalls, but they are not nice and handy to analyze the sessions in real-time.
The solution was to bring a network analyzer on a mirror port near to the firewall. I decided to use ntopng running on the live Linux distribution Knoppix. Great choice! An old notebook with two network adapters fits perfectly. A handful commands and you’re done: