Socat: Tunnel Ip Through Tty

socat: tunnel IP through TTY

Ha-ha, I works but there needs to be some magic :)

So, configure the 1st peer with:

PC1:
1) slattach -L -s 57600 -p slip /dev/ttyUSB0 &
2) ifconfig sl0 up
3) socat TUN:192.168.1.1/24,up INTERFACE:sl0 &

... and something like that on the 2nd peer:

PC2:
1) slattach -L -s 57600 -p slip /dev/ttyUSB0 &
2) ifconfig sl0 up
3) socat TUN:192.168.1.2/24,up INTERFACE:sl0 &

And now, you can successfully ping one PC from another:

PC1:
1) ping -c 5 192.168.1.2

PING 192.168.1.2 (192.168.1.2) 56(84) bytes of data.
64 bytes from 192.168.1.2: icmp_req=1 ttl=64 time=348 ms
64 bytes from 192.168.1.2: icmp_req=2 ttl=64 time=551 ms
64 bytes from 192.168.1.2: icmp_req=3 ttl=64 time=557 ms
64 bytes from 192.168.1.2: icmp_req=4 ttl=64 time=549 ms
64 bytes from 192.168.1.2: icmp_req=5 ttl=64 time=348 ms

--- 192.168.1.2 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4003ms
rtt min/avg/max/mdev = 348.116/471.143/557.128/100.177 ms

It's a little bit tricky because of slattach use but in fact any other solution must use something like slip to organize framing over the serial line. For example, PPP use HDLC-like frames.

socat with a virtual tty link and fork removes my pty link

Okay, I seem to have found a solution for myself. You have to create a virtual null modem pair first, then open one end of the virtual null modem pair and link it with the TCP listener.

socat -d -d PTY,raw,echo=0,link=/dev/ttyVA00 PTY,raw,echo=0,link=/dev/ttyVB00

Then

socat -d -d open:/dev/ttyVA00,nonblock,echo=0,raw TCP-LISTEN:11313,reuseaddr,fork 

I can connect as many clients as I want, and everything seems to be working.

IP tunnel over Linux serial default shell

On a normal linux, you could use socat.

This program allows you to connect several stream types (file, socket, tcp, udp, ...). In your case it would be tcp to file or more precisely a tcp socket at port xx to /dev/ttyUSB1. You should launch socat on both sides to build a tunnel.

Edit 1:
Sorry I got also disappointed by socat. I can't find a solution that keeps my TCP listener active for multiple successive connections, but handles only one connection at a time.

My solution is a simple C# program that uses 4 threads:
1. wait for input on stdin e.g. exit command
2. the TCP listener
3. the TCP worker thread for a active connection
4. if TCP is open, it opens another thread for COM

Thread 3 reads from TCP and writes to COM and Tread 4 reads from COM and writes to TCP. If thread gets a TCP close event, it stops thread 4, which closes COMx, and exits it self. Now thread 2 can accept a new connection. If thread 1 reads exit on stdin, it passes a message to all threads to stop and shutdown.

Maybe you can implement such a short program in C with pthreads on your embedded system, which has no socat.

The EOF problem:
I tried to google for a program that escapes a special character or reencodes a data stream from ASCII to ANSI or base64 or whatever.... If you can find such a program or write it also in C you can pipe it in between

Server <=> reencode <=> socat <--serial--> socat <=> reencode <=> client

---

Related Topics