I'd like to know what are the contents of a packet one application "APM Planner" send to another "MAVProxy". I know they are communicating over UDP port 14550. I tried using tcpdump by running the following commands

tcpdump -u port 14550 

and

tcpdump udp 

and

netstat -uanpc | grep 14550 

but none of them displayed me what these two applications are really exchange. I need something like cutecom for monitoring the UDP connection. Is there anything like this? When I run the command

netstat -lnpuc 

, it shows the following among its output

udp 5376 0 0.0.0.0:14550 0.0.0.0:* 23598/apmplanner2 

2 Answers

tcpdump supports UDP capturing. example usage:

tcpdump -n udp port 14550 

Edit

Because your applications are communicating with lo interface you must specify interface like this:

tcpdump -i lo -n udp port 14550 

this command print headers only. if you want to print data part of packet in hex and ASCII use this:

tcpdump -i lo -n udp port 14550 -X 

or if you want to save packets to a file and see it's content in Wireshark use this:

tcpdump -i lo -n udp port 14550 -w packets.pcap 

You can use ngrep. Example:

# Any UDP from any local interfaces to 91.22.38.4:12201 ngrep -W byline -d any udp and host 91.22.38.4 and dst port 12201