I'm working on a custom yocto Linux for a Raspberry PI 3 and try to get the WIFI connection working with SSH. However when trying to connect from my PC (Ubuntu 19.10, SSH OpenSSH_8.0p1 Ubuntu-6build1, OpenSSL 1.1.1c 28 May 2019) to the PI on which Dropbear v2019.78 runs, the connection attempt times out. But only when I try this via SSH, and via wlan0. Other TCP/IP traffic works, and also using the same participants but with eth0. As this is for a robot, I would prefer to not use a tether though...
To try & debug this, I
enabled a serial console so I can work on the PI
disabled eth0
started a tcpdump on the PI (ip.host == 192.168.0.105)
started a tcpdump on the PC (ip.host == 192.168.0.106)
used a dirt-simple TCP/IP socket example written in Python (taken from https://realpython.com/python-sockets/#echo-server) to verify I can in fact communicate. The transmission is successful. I am aware that the example is lacking (no proper protocol etc), but that's not the point of it. It just works enough. The PI runs the server listening on port 2222.
attempted a SSH connection, it timed out.
I filtered the resulting PCAP down to contain just TCP, as there is other information (e.g. Dropbox discovery) that I don't think matters and might potentially be information leaking. On the host side (enp4s0-tcp-and-pi.pcap) I also filtered with ip.host == 192.168.0.105 to only contain any traffic to the PI.
Another note on my setup here: I use a TP-Link router which LAN ports the PC is connected to, and who provides the 2.4GHz WIFI for the PI. So both are part of the same subnet, and no special routing or anything is configured.
Also I stopped the dropbear daemon and adapted my Python code to use port 22. It works.
I'm only broadly aware of the inner workings of TCP, so I can't really make much sense of the things I see here. Any insights are more than welcome.
https://www.dropbox.com/s/5o4rqr5zdws2wq7/wlan0-tcp-only.pcap?dl=0
https://www.dropbox.com/s/amypjtk1nvja4qb/enp4s0-tcp-and-pi.pcap?dl=0
so I made a script that logs into my schools vpn automatically by entering my username and password for me in my raspberry pi. Now I am trying to see if there is a way I can have a script running in the background that detects that I am connected to my vpn and also to my local wifi. If it detects there is no connection, then it will run my script of logging into the vpn automatically.
Below is the script I use to login to my vpn automatically my login.sh file:
#!/usr/bin/expect
spawn sudo openconnect vpn.ucr.edu/engineering
expect -r "\[sudo] .*\: " {
send "pw_for_my_linux\n"
}
expect "Username:" {
send "my_vpn_username\n"
}
expect "Password:" {
send "vpn_password\n"
}
interact
Perhaps you can use ethtool and check the connection status by looking at network interfaces.
ifconfig
(view network interface names, select network interface known to be associated with working vpn)
sudo ethtool eth0
Where 'eth0' is replaced by the name of the network interface that your vpn software is using
OUTPUT should look something like this if it's communicating (replace example net interface name eth0 with relevant one you can see in ifconfig):
Current message level: 0x00000007 (7)
drv probe link Link detected: yes
OUTPUT if down?:
Settings for eth0:
Link detected: no
In your bash code you can poll the 'link detected' status, parse out the answer to determine if you try reconnecting. Warning, haven't been able to test this on a vpn connection -- I have to use a special client other than openconnect, and for me I know the VPN is down if I run
ifconfig | grep "tun0"
If that returns something, VPN is up. If my network interface called tun0 is missing, VPN is not up.
Hope this gets you moving in the right direction!
I have tried to connect wired network connection using modem of ISP provider in Linux but could not see the option for Ethernet/Broadband in network connection.
While i choose add (+) option, there has been list of
VPN
Bridge
Bond
VLAN
I am ex-window user where i setup the internet connection using setup new network or connection using broadband/Adsl option in window network connection without router(only use modem provided by ISP provider).
On Ubuntu you can use the program pppoeconf (available through apt-get) which will walk you through inputting the settings necessary to establish a pppoe connection through your ISP. More documentation on this procedure is available for Ubuntu here: https://help.ubuntu.com/community/ADSLPPPoE.
This is a more constrained version of this question:
I have an embedded ARM device running a custom image with a Linux 3.10.0 kernel.
The only physical interface (no, USB, no Ethernet) is the default Linux shell which is connected one of the serial interfaces.
My question is: Is there any built-in or external tool that opens an IP tunnel over this connection?
I see some general issues:
The device is already use by Linux, so it must use stdin/out to communicate instead of accessing the device directly.
After starting the tunneling application, the application must wait for a tunnel client to connect because I need to close the serial connection on my computer and then start the tunnel client.
There should be a way to close the connection and go back to the normal shell
The actual requirement is, that I can access a REST interface that is running on the embedded device from a computer connected to the embedded device via serial cable.
This already works on devices with a physical Ethernet or Ethernet-over-USB but this device does not offer that.
[UPDATE]
As explained, socat is currently not available on our embedded device so as a first attempt, I used the following:
A Linux (Ubuntu) laptop with a physical serial interface
A Windows Laptop with a physical serial interface and cygwin+socat installed
Both connected via Null-modem cable
Note: I'm using a Windows laptop on one side because we will have the socat client running on Linux (unfortunately).
Direct STDIO Connection
Server
socat stdio file:/dev/ttyS0,b115200
Client
socat file:/dev/ttyS4,b115200 stdio
In cygwin, ttyS0 is COM1, ttyS4 in this case is COM5.
Using these, socat works like a little chat program. Why I type on one side is output on the other and vice-versa.
TCP Connection
The next step is to use a TCP connection.
Server
socat /dev/ttyS0,b115200,crtscts=1,raw,echo=0 tcp-connect:localhost:80
Client
socat -T2 file:/dev/ttyS4,b115200,crtscts=1,raw,echo=0 tcp-l:7777,reuseaddr
I specified the baud rate (115200), used raw transmission, no echo (The HTTP request would otherwise be sent back to the requester) using hardware flow control. Pus I had to use a timeout -T2 wich terminates the connection after 2s. Otherwise, curl does not terminate either and waits for more data.
When I use curl on the windows computer, it successfully transmits the request over serial connection and returns the complete HTTP response of the HTTP server on the Linux computer:
curl localhost:7777/index.html
However, it works only once. After the request is completed, both socatclient and server terminates.
Moreover, when I use a browser (Chorme), it uses g-zip encoding which most probably sends binary characters. And one of these characters will be a EOF character which again terminates socat before completing the request/response.
Then I tried to add fork to the server:
socat /dev/ttyS0,b115200,crtscts=1,raw,echo=0 tcp-connect:localhost:80,fork
This keeps the server alive, but curl returns a 400 Bad Request. So it seems as if the socat server initiated a request for each line or chunk since it does not understand HTTP.
IP Connection
Then I thought about going a layer below and using a TUN connection. However, this is not implemented on the Windows version of socat.
HTTP connection
Correct me if I'm wrong, but as far as I understand, socatdoes not provide a connection type that actually understands HTTP and is able to serialize it properly over a serial connection.
So, I couldn't find any stable way to start both client and server and run multiple HTTP requests over the serial connection.
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
We've now solved the problem halfway using pppd. As it turns out, even Windows supports ppp. In contrast to socat, pppd actually uses a protocol that will have error detection included and it automatically creates network devices on the Linux and Windows system.
The only problem is, that pppd requires to have access to the serial device. There is no direct mode like the ppp tool provides.
We are now disabling the shell on demand, rebooting into IP-over-serial mode. When we are done, we reboot the system which automatically switch back to getty using the serial line.
The is not the prettiest solution but right now, it seems to work.
I have a black-box device with a modem attached (which I can send commands to), and would like to be able to connect to send data to a server from it. What connectivity options do I have, is PPP the protocol I need to use or is there a better option?
ppp is certainly the most common solution for getting an IP connection over a modem. There are other solutions, but there's no reason not to use PPP if what you need is an IP connection.
If you don't need an IP connection and you're writing both the client and the server, you could also do a straight serial connection from one modem to another, but that's kind of old-school.
PPP is probably your best option, if you also want an IP gateway and routing. If you only need terminal access to the device, and it runs some form of *nix, you probably have getty+serial communication as an option. You can use any number of modem terminal clients on the other side.