Wireshark-users: Re: [Wireshark-users] EtherCAT can't be captured though Ethernet works

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From: N Nguyen <catsmemory2009@xxxxxxxxx>
Date: Fri, 10 Jun 2011 13:36:26 -0700 (PDT)
Hello,
Let say, when I type:  ethercat start; the ifconfig -a results in only lo. Therefore, only lo is available in the capture list, and hence, I cannot capture the frames.

When I type: ethercat stop. The ifconfig -a results in eth0, lo. This enables wireshark to capture the frames. But I can't use wireshark to capture EtherCAT frames at the moment.

The problem is that why my EtherCAT preempts the eth0 and wireshark could detect the NIC card?

Message: 7
Date: Fri, 10 Jun 2011 10:32:07 -0700
From: Guy Harris <guy@xxxxxxxxxxxx>
To: Community support list for Wireshark
    <wireshark-users@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-users] EtherCAT can't be captured though
    Ethernet    works
Message-ID: <E6D59BE9-EE4F-4662-B996-E6900DDE187E@xxxxxxxxxxxx>
Content-Type: text/plain; charset=us-ascii


On Jun 10, 2011, at 6:27 AM, N Nguyen wrote:

> I am using EtherCAT, and I'd like to use wireshark to capture the frames.
> If I stop the EtherCAT, the eth0 is listed in the capture list, and everything is OK.
> But if I start EtherCAT, the ifconfig tells that there's only local loopback lo 127.0.0.1. And apparently wireshark cannot capture the EtherCAT, although I am transferring frames via my NIC card (RTL 8139).

What do you mean by "stop the EtherCAT" and "start the EtherCAT"?  Is this something you do on the machine running Wireshark, or just on the network?  If it's something you do on the machine running Wireshark, perhaps the EtherCAT implementation somehow turns the Ethernet adapter into something that the rest of the networking stack doesn't recognize as a network interface, so that the rest of the networking stack - including the packet capture mechanism - can't use it.

(I'm guessing, from "local loopback lo 127.0.0.1", that you're running on Linux, where the loopback interface is generally called just "lo", rather than "lo0".  What does "ifconfig -a" report when EtherCAT has been started and when EtherCAT has been stopped?)