Wireshark · Wireshark-dev: [Wireshark-dev] Using find_conversation with multiple conversations conducted over the same UDP addr

[kelvin.proctor@xxxxxxxxxxxxxxxxxxxxxxxxx]

Hi Wireshark Dev List,

We have a network with DNP3.0 that is
using UDP.  We have a gateway device that communicates to a collections
of RTUs (RTU = Remote Terminal Unit, a device on the DNP3.0 network) over
a serial radio-modem network and we talk to the gateway using UDP / IP.

The DNP3.0 dissector uses the standard
calls to find_conversation etc... and fragment_add_seq_next etc... to do
application layer frame re-assembly as follows:

      if (! (tr_fir && tr_fin))
      {
        /* A fragmented packet
*/
        pinfo->fragmented =
TRUE;

        /* Look up the conversation
to get the fragment reassembly id */
        conversation = find_conversation(pinfo->fd->num,
&pinfo->src, &pinfo->dst,
          pinfo->ptype,
pinfo->srcport, pinfo->destport, 0);

        if (conversation == NULL)
{
          /* No conversation
yet, so make one */
          conversation =
conversation_new(pinfo->fd->num,  &pinfo->src, &pinfo->dst,
pinfo->ptype,
            pinfo->srcport,
pinfo->destport, 0);
        }

        conv_data_ptr = (dnp3_conv_t*)conversation_get_proto_data(conversation,
proto_dnp3);

        if (conv_data_ptr == NULL)
{
          /* New data structure
required */
          conv_data_ptr =
se_alloc(sizeof(dnp3_conv_t));

          /*** Increment
static global fragment reassembly id ***/
          conv_data_ptr->conv_seq_number
= seq_number++;

          conversation_add_proto_data(conversation,
proto_dnp3, (void *)conv_data_ptr);
        }
        conv_seq_number = conv_data_ptr->conv_seq_number;

        /*
        * Add the frame to
        * whatever reassembly
is in progress, if any, and see
        * if it's done.
        */

        frag_msg = fragment_add_seq_next(al_tvb,
0, pinfo, conv_seq_number,
            al_fragment_table,
            al_reassembled_table,
            tvb_reported_length(al_tvb),
/* As this is a constructed tvb, all of it is ok */
            !tr_fin);

        next_tvb = process_reassembled_data(al_tvb,
0, pinfo,
            "Reassembled
DNP 3.0 Application Layer message", frag_msg, &dnp3_frag_items,
            &update_col_info,
tr_tree);

Unfortunately this does not take into
account the fact that over the same IP address / port number pairs we may
receive messages from many different source RTUs that should be treated
as separate conversations.  The problem we have at the moment is that
we are getting fragment re-assembly occurring for fragments from difference
RTUs.

Is there a standard way to handle situations
like this?  If so can someone point me to the correct dissector to
look at?

We can provide packet captures that
demonstrate the issue if desired.   It is considered acceptable to
attach a .pcap file to a posting to this mailing list?

Thanks in advance,

Kelvin Proctor