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Tcpdump allows you to record all traffic including the local REST HTTP that by default heads to http://localhost:90918081/EchoApp. To change this address, use application management settings from the command line interface.
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sip
websocket
ip.src==127.0.0.1 && tcp.dstport==90918081
The last filter is used for REST / HTTP traffic that locally flows through the port 9091 8081 if the local app EchoApp is queried.