Message datas are not shown in Wireshark?

[mirusu400]

Hello.

I'm trying to running a simple C++ example by this document, and trying to capture packets between publisher and subscriber

_2024_01_16_17_20_20_292.mp4

question_packet.zip
^ Here are some packets I've captured.

I can capture INFO_TS, DATA(p), INFO_DST, HEARTBEST, ACKNACK packets, but I can't find any packets about serving real messages (Such as CustomHello - In this case).

I've searching some documents about how the messages are served, but I can't find any informations about how publisher/subscriber managing their message data packets.

Is message datas are really serving via rtps? if not, How they serve their datas? Also, How can I capture these packets using wireshark?

[JesusPoderoso]

Hi @mirusu400, thanks for using Fast DDS.

User data transmissions are represented in Wireshark as DATA(w) and DATA(r).

Fast DDS uses by default shared memory prior than UDPv4 as builtin transport.
It may happen that the data transmission is performed through shared memory, and Wireshark is not able to track it in real-time.
You can configure the transport descriptor's attribute rtps_dump_file_ and follow this section indications to dump the traffic to a file, where you will be able to analyze the user traffic.
On the other hand, you can configure the participant transport to force the communication to be through UDP, so you can capture those packages in-real-time in Wireshark.

Following your suggested guidelines:

I'm trying to running a simple C++ example by this document, and trying to capture packets between publisher and subscriber

You should include the following code lines in the init() method, between lines 123-124 (before creating the participant). They disable default builtin transports, and set the user transport to use UDPv4

participantQos.transport().use_builtin_transports = false;
auto udp_transport = std::make_shared<UDPv4TransportDescriptor>();
participantQos.transport().user_transports.push_back(udp_transport);

TIP: You can try to apply the following filter in Wireshark to display only HelloWorld user data: rtps.param.topicName == HelloWorldTopic.