Re: CAN over Ethernet

[Kumquat KromKiller <kromkillerkumquat () gmail com>]

When I say plain, maybe I should have said that I'm working at FPGA-level.
Basically, when I receive a CAN message, I put everything between
start-of-frame and end-of-frame in the Ethernet payload and since the
length of the payload is less than 0x0600, I use the EtherType to store the
length.

If I hear you right, the best option for now is to comply with the
SocketCAN format, choose an unused EtherType and write a dissector that
basically just tell Wireshark that this particular EtherType is in fact
SocketCAN ?
That is great because the code for this dissector should be pretty small.

Still, it isn't out-of-the-box. Can you confirm me that this is not
possible ? (Again, I'm the one making the CAN over Ethernet bridging
device, I can do whatever I want with the payload.)


On Sat, Nov 7, 2015 at 4:19 PM, Michael Mann <mmann78 () netscape net> wrote:

> What is "plain encapsulation of CAN"?  SocketCAN has the format of 4 byte
> CAN ID. 4 byte length field followed by the CAN data.  This is currently
> only used in "file formats", not anything on the wire.  Doesn't mean you
> can't hook up to it, but your wire data will have to match.
>
> My suggestion would be to write your own dissector, but it should borrow
> HEAVILY from SocketCAN, including its dissector table.  I presume your
> "plain encapsulation of CAN" is slightly different from the 4 byte CAN ID +
> 4 byte length, so those are the discrepancies you need to address in your
> own dissector.  Once you have the data length and CAN ID, you can pass that
> data through the SocketCAN dissector table so it can dissect the next layer
> (CANopen, DeviceNet, etc)
>
> If you make your own dissector (or even modify SocketCAN), because there
> is no standard ethertype for this, you'll need to use Decode As to
> dissector and just register your dissector (handle) with the ethertype
> dissector table. (dissector_add_for_decode_as).
>
>
> -----Original Message-----
> From: Kumquat KromKiller <kromkillerkumquat () gmail com>
> To: Developer support list for Wireshark <wireshark-dev () wireshark org>
> Sent: Sat, Nov 7, 2015 9:12 am
> Subject: Re: [Wireshark-dev] CAN over Ethernet
>
> I choose how CAN messages will be transported, that is why I said I can
> add whatever layers I want between Ethernet and CAN.
>
> Right now, it's just plain encapsulation of CAN over Ethernet with a
> custom EtherType greater than 0x0600.
>
> Ideally, I would like to avoid making my own dissector. It would be great
> if captured traffic could be dissected with Wireshark out-of-the-box, even
> if I have to add several unnecessary layers between Ethernet and CAN.
>
> For example, SLL has a non-standard EtherType value for CAN messages but
> it cannot be encapsulated with Ethernet (there's no standard EtherType
> value for SLL)
>
> Maybe there's a combination of CANopen, SLL, EtherCAT, SocketCAN or
> whatever that can achieve this ?
>
>
> On Sat, Nov 7, 2015 at 1:57 PM, Roland Knall <rknall () gmail com> wrote:
>
> > Hi
> >
> > It depends how the CAN messages are being transported within Ethernet.
> > Then you could write a dissector for the method, which in turn calls the
> > CAN dissector.
> >
> > The same thing happens with a lot of other dissectors,the openSAFETY
> > disssector for instance.
> >
> > regards,
> > Roland
> >
> > On Sat, Nov 7, 2015 at 1:33 PM, Kumquat KromKiller <
> > kromkillerkumquat () gmail com> wrote:
> >
> > > Hi everyone,
> > >
> > > I need to transport CAN messages over Ethernet and I would like to be
> > > able to dissect them in Wireshark for debugging purposes.
> > >
> > > Considering the fact that I can add whatever layers I want between
> > > Ethernet and CAN, what would be the most efficient way to achieve this ?
> > >
> > > Thanks.
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