Setting up VPN tunnel over SSH to your robot
This guide will demonstrate how to setup a VPN tunnel (tun0) over SSH to your robot using Formant's port-forwarding capabilities over our peer-to-peer communication channel. Before starting with this guide, make sure you have setup a device with the agent, and have setup on your client machine fctl and configured ssh. This guide is based on the existing SSH VPN community guide.
Using any editor, open
/etc/ssh/sshd_config and change the "PermitRootLogin" line and add the "PermitTunnel" line:
PermitRootLogin without-password PermitTunnel yes
These commands will enable Network Address Translation (NAT) without the need to reboot (NAT will be persistent). This may already be enabled on your system.
sudo sysctl -w net.ipv4.ip_forward=1
To set as default, using any editor, open
/etc/sysctl.conf and add:
# Needed to add for forwarding net.ipv4.ip_forward = 1
tun0 network interface by adding a network interface. Create the file /etc/network/interfaces.d/tun0 and add:
iface tun0 inet static pre-up sleep 5 address 10.0.0.100 pointopoint 10.0.0.200 netmask 255.255.255.0 up arp -sD 10.0.0.200 eth0 pub
The Formant agent runs with it's own user and group (formant:formant) that, by default, has very limited permissions. To enable the agent to create a tun interface we need to add it to the device's sudoers group:
sudo usermod -aG sudo formant sudo systemctl restart formant-agent
Note: the formant user has no shell or login by design.
Generate a ssh key, here we call it formant-vpn:
ssh-keygen -f formant-vpn -b 4096
Put the private key formant-vpn in /root/.ssh and set permissions:
# create this directory if it doesn't exist sudo mkdir -p /root/.ssh sudo cp formant-vpn /root/.ssh/formant-vpn sudo chown root:root /root/.ssh/formant-vpn sudo chmod 400 /root/.ssh/formant-vpn
Copy the public key formant-vpn.pub onto the device. Once there add it to the authorized keys (Run this ON the device):
# if the root ssh folder doesn't exist, create it sudo mkdir -p /root/.ssh sudo bash -c "cat formant-vpn.pub >> /root/.ssh/authorized_keys"
Setup the root user ssh_config by adding this snippet to /root/.ssh/config:
Host *.formant ProxyCommand fctl port-forward $(echo %h | sed "s/\.formant$//") -r 127.0.0.1 -p %p
SSH Commands on client
Open a new terminal and run this command to stand up the tunnel
sudo ssh -i /root/.ssh/formant-vpn -Cf -w 0:0 nano.001.formant 'ifdown tun0; ifup tun0'
This is running ssh with tunneling (-w) as well as using compression on the channel (-C) and forking it to the background (-f). Additionally, it tells our device to run ifdown tun0; ifup tun0
Note: You may see RTNETLINK answers: Cannot assign requested address which can happen if you rerun this command (the device may already have it's addresses setup.)
Next we need to setup tun0 on our client machine:
sudo ip link set tun0 up sudo ip addr add 10.0.0.200/32 peer 10.0.0.100 dev tun0 sudo ip route add 10.0.0.0/24 via 10.0.0.200
Which configures tun0 on the client machine and routes traffic on 10.0.0.0/24 back to our device.
You can check the tunnel is established with:
and you should see something like the following on the client machine:
tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST> mtu 1500 inet 10.0.0.200 netmask 255.255.255.255 destination 10.0.0.100 inet6 fe80::45f3:9856:2ef0:9b50 prefixlen 64 scopeid 0x20<link> unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 txqueuelen 500 (UNSPEC) RX packets 4 bytes 192 (192.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 1 bytes 48 (48.0 B) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
and on the device:
tun0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST> mtu 1500 inet 10.0.0.100 netmask 255.255.255.255 destination 10.0.0.200 inet6 fe80::1fc:7f5f:6948:9e8d prefixlen 64 scopeid 0x20<link> unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 txqueuelen 500 (UNSPEC) RX packets 80 bytes 12604 (12.6 KB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 90 bytes 13785 (13.7 KB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Try pinging the device from your client machine:
To tear down the connection get the pid of the ssh command:
ps aux | grep ssh
Once you have the pid you can kill it:
sudo kill -9 $pid
The following is a short script to automate the client process. It accepts one input parameter which is the name of the device you are connecting to:
#! /bin/bash -e device=$1 echo "setting up ssh tunnel..." sudo ssh -i /root/.ssh/formant-vpn -Cf -w 0:0 $device.formant 'ifdown tun0; ifup tun0' echo "ssh tunnel setup." sudo ip link set tun0 up sudo ip addr add 10.0.0.200/32 peer 10.0.0.100 dev tun0 sudo ip route add 10.0.0.0/24 via 10.0.0.200 echo "tun0 configured" sleep infinity
Exiting the script will also tear down the ssh tunnel.
If you plan on keeping long-running ssh tunnels to your devices you may want to also set the following in your ssh config:
Host * ServerAliveInterval 120 ServerAliveCountMax 10
The ServerAliveInterval will send a ping every 120 seconds if there is no activity on the tunnel. The ServerAliveCountMax defines how many consecutive pings are sent before disconnecting.
Updated 10 months ago