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Wireshark - capture data

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Revision as of 14:24, 26 November 2008 by Asle (talk) (How to capture data)
Capturing ethernet data from AlphaCom

Sometimes it is useful for debugging purposes to analyse the data on the AlphaCom ethernet port. This article describes how to use the PC program Wireshark to capture data from the ethernet port of the AlphaCom.

In order to capture data you need the following equippment:

  • A PC with Wireshark installed
  • A netwok hub

Wireshark

Wireshark (formerly known as Ethereal) is a packet analyzer (also known as Ethernet sniffer) that can intercept and log traffic passing over the ethernet port. As data streams flow across the network, the sniffer captures each packet and eventually decodes and analyzes its content according.

Wireshark is freeware and can be downloaded from http://www.wireshark.org/.

The network hub

A protocol analyzer connected to a switch does not always receive all the desired packets since the switch separates the ports into different segments. Connecting the protocol analyzer to a hub allows it to see all the traffic on the segment. (Expensive switches can be configured to allow one port to listen in on traffic from another port. This is called port mirroring. However, these cost much more than a hub.)

So to capture the data a HUB must be used, not a switch.

How to capture data

Wireshark screenshot
  • Download and install Wireshark on a PC
  • Connect the hub between the AlphaCom and the IP network
  • Connect the PC to the hub
  • Start the Wireshark program
  • From the menu in Wireshark select 'Capture -> Options..', and in the field 'Interface' select your network card
  • Press 'Start' to start the capture. Now a smaller window opens showing the number of packets received.
  • When the capture is finnished, press 'Stop'
  • Save the captured data by selecting 'File -> Save As..'. Save the file with extension .cap. The file can be opened on any PC having the Wireshark program installed