Installing tinc

OpenWrt already comes with a package for tinc, which you can easily install via the web interface. You will also need the “kmod-tun” package, which is not installed by default.
After installing the packages, ssh into your router and create the configuration for your VPN. We will name our VPN “myvpn”, but you can change the name to whatever you want. We will create a VPN between two hosts, and assume the following configuration:

node1: 1.2.3.4 (external), 192.168.100.1 (internal)
node2: 2.3.4.5 (external), 192.168.101.1 (internal)

Creating the keys

Connect to node1 via ssh and create the key pair.

mkdir -p /etc/tinc/myvpn/hosts
tincd -n myvpn --generate-keys
mv /etc/tinc/myvpn/hosts/myvpn /etc/tinc/myvpn/hosts/node1

Edit /etc/tinc/myvpn/hosts/node1 and add the following lines above the key:

Address = 1.2.3.4
Subnet = 192.168.100.0/24
-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----

You also need to create a key on node2:

mkdir -p /etc/tinc/myvpn/hosts
tincd -n myvpn --generate-keys
mv /etc/tinc/myvpn/hosts/myvpn /etc/tinc/myvpn/hosts/node2

Edit /etc/tinc/myvpn/hosts/node2 and add the following lines above the key:

Address = 2.3.4.5
Subnet = 192.168.101.0/24
-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----

Exchanging keys

Copy the public definition of each node (/etc/tinc/myvpn/hosts/noden) to every node in the network. You should have the files node1 and node2 in /etc/tinc/myvpn/hosts on every router.

Configuring tinc

After you have all the necessary keys, configuring tinc itself is quite easy. Create the configuration file /etc/tinc/myvpn/tinc.conf with the following content:

On node1:

Name = node1
ConnectTo = node2
Address = 1.2.3.4
Subnet = 192.168.100.0/24

On node2:

Name = node2
ConnectTo = node1
Address = 2.3.4.5
Subnet = 192.168.101.0/24

Adjusting firewall rules

To allow connections to tinc from the internet, and allow routing traffic through tinc into your internal network, you need to create some rules for your firewall. We will adjust firewall rules in a script which will be called by tinc on startup.

node1: /etc/tinc/myvpn/tinc-up

#!/bin/sh
ifconfig $INTERFACE 192.168.100.1 netmask 255.255.0.0
iptables --append input_wan --protocol tcp --dport 655 --jump ACCEPT
iptables --append input_wan --protocol udp --dport 655 --jump ACCEPT
iptables --append forwarding_rule -i myvpn -o br-lan -s 192.168.0.0/16 -d 192.168.100.0/24
iptables -A forwarding_rule -o myvpn -j ACCEPT
iptables -A forwarding_rule -i myvpn -j ACCEPT

node2: /etc/tinc/myvpn/tinc-up

#!/bin/sh
ifconfig $INTERFACE 192.168.101.1 netmask 255.255.0.0
iptables --append input_wan --protocol tcp --dport 655 --jump ACCEPT
iptables --append input_wan --protocol udp --dport 655 --jump ACCEPT
iptables --append forwarding_rule -i myvpn -o br-lan -s 192.168.0.0/16 -d 192.168.101.0/24
iptables -A forwarding_rule -o myvpn -j ACCEPT
iptables -A forwarding_rule -i myvpn -j ACCEPT

This file needs to be executable:

chmod +x /etc/tinc/myvpn/tinc-up

Starting tinc

On all nodes, create the file /etc/init.d/tinc and make it executable:

#!/bin/sh
tincd -n myvpn

Then create a symlink to automatically start tinc when you power up your router:

ln -s /etc/init.d/tinc /etc/rc.d/S70tinc

After starting /etc/init.d/tinc (or rebooting) on both nodes, your VPN should be up and running.

Troubleshooting

If you experience problems, you can read tinc’s debug log with logread.

logread    # read syslog
logread -f # read log as it grows

To increase the debug level of tinc, send it a SIGINT signal:

kill -SIGINT `pidof tincd`

Sending the signal again, will revert to the original log level.

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