Flow Views

[Ref: flow-tools, Network Flow Analysis.]

Table of Contents
  1. Sample Analysis
  2. Summary View

The most flexible, and difficult way to view your netflow data is to use the console tools from flow-tools. These console tools can be linked together (using the output of one utility as input to the next) to make detailed analysis/extraction of traffic data.

1. Sample Analysis

When you are initially capturing files, the directory may contain only a "tmp-v05" file. The files we will be analysing generally start with "ft-v05". Grab a cup of coffee and by the time you get back, the "ft-v05*" files should start appearing.

A simplified view, or "raw" dump of the netflow, is to take a point-in-time view through one of the 5-minute incremented log files. We'll use flow-cat and flow-print to take a look at one of the files.

# flow-cat ft-v05.2011-02-14.175500+1100 | flow-print | head -10
srcIP            dstIP            prot  srcPort  dstPort  octets      packets
192.168.20.61    10.1.0.7         6     1117     1116     48          1
10.1.0.7         192.168.20.61    6     1116     1117     40          1
192.168.20.61    10.1.0.7         6     1117     1116     48          1
10.1.0.7         192.168.20.61    6     1116     1117     40          1
192.168.110.33   10.0.0..38      17    10830       53     432         6
10.0.0..38       192.168.110.33  17       53    10830     168         3
192.168.110.33   10.0.0..38      17    10830       53     432         6
192.168.144.104  192.168.18.65    6     2680     1116     393         5
192.168.18.65    192.168.144.104  6     1116     2680     128         3

The above is displaying traffic between hosts on either side of the sensor. In the above screen-output:

  • 2 packets were sent from 192.168.20.61 to 10.1.0.7.
  • 2 packets seem to be alternated response
  • 6 packets were sent from 192.168.110.33 to 10.0.0..38
  • 3 packet response?
  • 6 packets were sent from 192.168.110.33 to 10.0.0..38
  • 5 packets were sent from 192.168.144.104 to 192.168.18.65
  • 3 packet response?

Some interesting facts are already visible, with the use of different protocols in the communications.

  • Protocol 6 - "TCP Protocol"
  • Protocol 17 - "UDP Protocol"

[Ref: Iana IPv4 Protocol Numbers]

192.168.110.33 and 10.0.0..38 seem to be:

  • exchanging Domain Name Services(DNS) (port 53) queries.
  • 432 octets (bytes) to make the request, and
  • 168 octets (bytes) for the response.

2. Summary View

Summary information on the packets in the log file can be viewed using flow-print

# flow-print -p < ft-v05.2011-02-14.175500+1100 | head -20
#
# mode:                 normal
# capture hostname:     hostname.example.com
# capture start:        Mon, 14 Feb 2011 17:55:00 +1100
# capture end:          Mon, 14 Feb 2011 18:00:00 +1100
# capture period:       300 seconds
# compress:             on
# byte order:           little
# stream version:       3
# export version:       5
# lost flows:           0
# corrupt packets:      0
# sequencer resets:     0
# capture flows:        4680
#
srcIP            dstIP            prot  srcPort  dstPort  octets      packets
192.168.20.61    10.1.0.7         6     1117     1116     48          1
10.1.0.7         192.168.20.61    6     1116     1117     40          1
192.168.20.61    10.1.0.7         6     1117     1116     48          1
10.1.0.7         192.168.20.61    6     1116     1117     40          1

The log file is a 5 minute segment of the traffic through hostname.example.com

Although the range of console tools allows very detailed analysis of the network data flow, it also requires a deeper knowledge of network flow, and the flow-tools kit itself. Pretty charts seems to impress and impart information(?), which is why such tools have evolved around flow-tools.

Get the book Network Flow Analysis The book shows you how to use the flow-tools commands, how they can be applied (why?) where and a good start to envisioning your prowess bringing world-peace (or at least do so in your own network.)