How capture traffic from docker container?

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I'm trying to follow the instructions in this answer over on stackexchange: https://stackoverflow.com/a/48386901/...

However, after creating and starting a docker container (step 2), I still don't see any interface that I could assume would correspond to that docker container.

As a test, I pinged a random website from the docker container, and went through all my interfaces in wireshark to see if I could find it. I couldn't. For details on that, please see this post I made on stack exchange https://superuser.com/questions/16856...

Why can't I see any interface corresponding to my docker container on wireshark?

Some background: The whole reason for this is that I want to set up a super secure way of using voip calling. Based on my limited understanding, I believe the best way to do this is to run the program inside a docker container so that it's isolated from my main system. Before I use it to actually communicate with others, I want to get a better understanding of all the data that's going in and out of the program (i.e. if there is any personally identifying data) by using wireshark to analyze packets. Please let me know if there's an easier way, or if I'm going about this the wrong way.