Why port listening with Netcat does not work

Question

I run the following command in Ubuntu:

nc -l -p 5004 -v >> /home/anders/Dropbox/netcatFiles/test 

which includes a command to make him listen to 5004.

I am sending an RTP stream to port 5004 using VLC. When I observe the loopback interface in Wireshark, I notice ICMP packets with the message "Destination unreachable".

Opening another VLC and telling him to play incoming data on port 5004, everything works and the stream plays.

What should I do to get Netcat to listen on port 5004?

Answer 1

I think you need to add the "-u" parameter so that it listens for UDP.

By default, netcat operates in TCP mode, but the RTP protocol is based on UDP.

“Transmission Control Protocol (TCP), although standardized for Using RTP, [5] is not commonly used in an RTP application because TCP maintains reliability over timeliness. Instead, most RTP implementations are built on user datagram protocol (UDP).”

http://en.wikipedia.org/wiki/Real-time_Transport_Protocol

Answer 2

do not use -p ( man nc (1) )

-p source_port Specifies what source port nc should use, subject to privilege and availability restrictions. Error using this option in connection with the -l option.

so just specify

 nc -l 5004 -v >> /home/anders/Dropbox/netcatFiles/test