Iperf3 uses TCP and UDP to work. I can only use UDP. How to tunnel the TCP connection alongside UDP so it works without setting a real TCP connection?

Question

Iperf3 uses two channels to communicate, one via TCP and the other via UDP. When its going to communicate to another host, it uses the same port for both channels.

For example: If I tell it to connect to port 3000 on the host, the TCP channel will connect on the host's port 3000 and the UDP channel too.

I need to encapsulate the TCP communication into UDP datagrams, send over UDP to the host on port 3000 and then de-encapsulate the TCP and demultiplex it so it gets delivered correctly at port 3000.

To achieve this, Im using socat to create a TCP-UDP tunnel like this (this tunnel is working!):

On the sender end:

socat -d tcp-listen:2000,reuseaddr,fork udp:54.226.25.18:3000

On the receiving end:

socat -d udp-listen:3000,reuseaddr,fork tcp:localhost:1080.

OK, now why I'm converting TCP to UDP and then from UDP to TCP again? I'm doing that because I was trying to use socks4, and it works only with TCP. I was using it to encapsulate the TCP and UDP traffic into TCP, then I convert this TCP stream into UDP and send over to the host with socat, like this:

On the sender end (tunnel+socks):

socat tcp-listen:2000 socks4a:localhost:54.226.25.18:3000 & socat tcp-listen:1080,reuseaddr,fork udp:54.226.25.18:3000 & nc localhost 2000

On the receiving end (tunnel):

socat udp-listen:3000,reuseaddr,fork tcp:localhost:1080 & nc -l 1080

This solution kinda works, this is what the receiving end receives:

�senderPcName54.226.25.18

But it only receives something the first time, when I send more data with netcat, nothing shows up on the receiving end.

Maybe this is happening because the way Im doing it theres nothing on the other side to open what is encapsulated into TCP and demultiplex it. This is my hunch, I might be wrong.

I tried to think on a solution using socks5 but I dont know how to send things through it (didn't find materials on how to do it) like I do with socks4 in this line:

socat tcp-listen:2000 socks4a:localhost:54.226.25.18:3000

I tried without success to install socat with socks5 support because it lacks files.

You can read about Iperf3's relevant behavior here: https://github.com/esnet/iperf/issues/1019

Obs: I NEED to tunnel over UDP. And I can only use ONE UDP port.

Any pointers on how to solve this with socks or with something new altogether is greatly appreciated.

Summary of my problem: Iperf3 uses TCP and UDP to work. I can only use UDP. How to tunnel the TCP connection alongside UDP so it works without setting a real TCP connection?

Your socks4 scenario does not work because the socks4 client is waiting for an answer from socks4 server, but there is none. — dest-unreach, Jul 13 '22 at 11:04
You mean no response from a socks4 server on the receiving end, right? Do you have any pointers on how to set up a socks4 server on the receiving end? — Thomas Vale, Jul 13 '22 at 14:48
In some distros there is the Dante socks server, I did not try it — dest-unreach, Jul 13 '22 at 19:20

score 0 · Answer 1 · answered Jul 13 '22 at 11:26

You will need some kind of multiplexer solution to drive both UDP and TCP through the UDP channel.

When you have root privilege on both computers, you can establish a Socat tunnel:

On sending side:

sudo socat -d -d -d -d TUN:192.168.255.1/24,up UDP:54.226.25.18:2000,bind=:2000

On receiving side:

sudo socat -d -d -d -d TUN:192.168.255.2/24,up UDP-LISTEN:2000

You should now be able to ping 192.168.255.2 from sender and 192.168.255.1 from receiver.

For testing UDP, enter on receiver:

socat UDP-LISTEN:3000 -

On sender:

socat - UDP:192.168.255.2:3000

Iperf3 uses TCP and UDP to work. I can only use UDP. How to tunnel the TCP connection alongside UDP so it works without setting a real TCP connection?

1 Answers1