A Network Traffic Generator tool using Linux Utilities

    Most of the time in the development and testing of Networking products, we may need to test the product by injecting the traffic to it. We can use any traffic generator tools like Spirent or IXIA to construct and inject the traffic to our DUT (Device Under Test). These traffic generators are separate hardware devices that we need to purchase and for each type of feature on the device we need to get license too which is costlier.
   For simple testing, we can use the Linux utilities to construct and send the packet out of ethernet ports. We can connect our DUT to this ethernet port and test it.

   In this post we can see how to construct and send the packets on ethernet ports using Linux utilities. A prerequisite to use this script is that we need to have the ASCII hexdump of packet that we need to inject.

   The Linux utility "text2pcap" and open source tool "packEth" is used to generate and send out the traffic via particular ethernet port. The utility "text2pcap" is available by default in most Linux distributions. The "packEth" tool can be downloaded from here . Download the packEth tool for linux version.

    The "packEth" tool sends the packet given as input via an Ethernet interface that we specify. But the input file needs to be in "pcap" format. So, when we know the ASCII hexdump of packet that we need to send, we can use the utility "text2pcap" which will convert the text file which contains the packet content in ASCII hexdump format, into a "pcap" file. Then we can send that "pcap" file using the "packEth" tool.

text2pcap:
    This utility reads in an ASCII hex dump and writes the data described into pcap file.
 
    text2pcap -d <infile> <outfile>

    This command will read packet content from "infile" and  will generate the "outfile" in .pcap format. If there is any parse error while processing input file, it will be displayed on the screen. To know about the way of formatting the input file of "text2pcap" tool, click here.

How to install "packEth":

• Download the "packEth" tool for Linux version here.
• Extract the package using the command "tar xvjf packETH-1.9.tar.bz2"
• Go to "packETH-1.9/cli" and give "make". This will generate the "packETHCli" utility inside that path. This utility will send the packet out of the specified eth port.

How to use "packETHCli":
      packETHcli -i <Interface> -m 1 -f  <pcap_file> 

      This command will send out one instance of the given packet "pcap_file" out of the given "Interface".

     Use the command "packETHcli -h" to know more about the usage of utility.

Illustration:

    Consider the scenario where we have a file "garp_ascii_hex" which contains a GARP packet in ASCII HEX format.

[root@centos-5-vm cli]# cat garp_ascii_hex
0000  ff ff ff ff ff ff 02 02 02 02 02 02 08 06 00 01   ................
0010  08 00 06 04 00 01 02 02 02 02 02 02 c0 a8 01 01   ................
0020  ff ff ff ff ff ff c0 a8 01 01 00 00 00 00 00 00   ................
0030  00 00 00 00 00 00 00 00 00 00 00 00               ............
[root@centos-5-vm cli]#

   Now, we want to send this packet out of ethernet port using "packETHcli" utility. As "packETHcli" accepts only the files in .pcap format, we use the "text2pcap" utility to convert the above packet from ASCII HEX format into .pcap format.

    ./text2pcap  -d garp_ascii_hex  garp_pkt.pcap

[root@centos-5-vm cli]# text2pcap garp_ascii_hex garp_pkt.pcap
Input from: garp_ascii_hex
Output to: garp_pkt.pcap
Wrote packet of 60 bytes at 0
Read 1 potential packet, wrote 1 packet
[root@centos-5-vm cli]#


Note: The "text2pcap" utility will process the input file only when its content are in particular format. The man page says,
      "Text2pcap understands a hexdump of the form where each byte is individually displayed and surrounded with a space. Each line begins with an offset describing the position in the file. The offset is a hex number of more than two hex digits."

     Now, we want to send the packet "garp_pkt.pcap" out of "eth0" interface. We use the packETHcli utility to achieve the same.

    packETHcli -i eth0 -m 1 -f  garp_pkt.pcap

   This will send out the packet "garp_pkt.pcap" from eth0 interface.