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4.6 Example configuration

Imagine the following situation. Branch A of our example ‘company’ wants to connect three branch offices in B, C and D using the Internet. All four offices have a 24/7 connection to the Internet.

A is going to serve as the center of the network. B and C will connect to A, and D will connect to C. Each office will be assigned their own IP network, 10.x.0.0.

A: net 10.1.0.0 mask 255.255.0.0 gateway 10.1.54.1 internet IP 1.2.3.4
B: net 10.2.0.0 mask 255.255.0.0 gateway 10.2.1.12 internet IP 2.3.4.5
C: net 10.3.0.0 mask 255.255.0.0 gateway 10.3.69.254 internet IP 3.4.5.6
D: net 10.4.0.0 mask 255.255.0.0 gateway 10.4.3.32 internet IP 4.5.6.7

Here, “gateway” is the VPN IP address of the machine that is running the tincd, and “internet IP” is the IP address of the firewall, which does not need to run tincd, but it must do a port forwarding of TCP and UDP on port 655 (unless otherwise configured).

In this example, it is assumed that eth0 is the interface that points to the inner (physical) LAN of the office, although this could also be the same as the interface that leads to the Internet. The configuration of the real interface is also shown as a comment, to give you an idea of how these example host is set up. All branches use the netname ‘company’ for this particular VPN.

Each branch is set up using the ‘tinc init’ and ‘tinc config’ commands, here we just show the end results:

For Branch A

BranchA would be configured like this:

In /etc/tinc/company/tinc-up:

#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.1.54.1 netmask 255.255.0.0

ifconfig $INTERFACE 10.1.54.1 netmask 255.0.0.0

and in /etc/tinc/company/tinc.conf:

Name = BranchA

On all hosts, /etc/tinc/company/hosts/BranchA contains:

Subnet = 10.1.0.0/16
Address = 1.2.3.4

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----

Note that the IP addresses of eth0 and the VPN interface are the same. This is quite possible, if you make sure that the netmasks of the interfaces are different. It is in fact recommended to give both real internal network interfaces and VPN interfaces the same IP address, since that will make things a lot easier to remember and set up.

For Branch B

In /etc/tinc/company/tinc-up:

#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.2.43.8 netmask 255.255.0.0

ifconfig $INTERFACE 10.2.1.12 netmask 255.0.0.0

and in /etc/tinc/company/tinc.conf:

Name = BranchB

Note here that the internal address (on eth0) doesn’t have to be the same as on the VPN interface.

On all hosts, in /etc/tinc/company/hosts/BranchB:

Subnet = 10.2.0.0/16
Address = 2.3.4.5

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----

For Branch C

In /etc/tinc/company/tinc-up:

#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.3.69.254 netmask 255.255.0.0

ifconfig $INTERFACE 10.3.69.254 netmask 255.0.0.0

and in /etc/tinc/company/tinc.conf:

Name = BranchC

C already has another daemon that runs on port 655, so they have to reserve another port for tinc. It knows the portnumber it has to listen on from it’s own host configuration file.

On all hosts, in /etc/tinc/company/hosts/BranchC:

Address = 3.4.5.6
Subnet = 10.3.0.0/16
Port = 2000

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----

For Branch D

In /etc/tinc/company/tinc-up:

#!/bin/sh

# Real interface of internal network:
# ifconfig eth0 10.4.3.32 netmask 255.255.0.0

ifconfig $INTERFACE 10.4.3.32 netmask 255.0.0.0

and in /etc/tinc/company/tinc.conf:

Name = BranchD

D will be connecting to C, which has a tincd running for this network on port 2000. It knows the port number from the host configuration file.

On all hosts, in /etc/tinc/company/hosts/BranchD:

Subnet = 10.4.0.0/16
Address = 4.5.6.7

-----BEGIN RSA PUBLIC KEY-----
...
-----END RSA PUBLIC KEY-----

Key files

A, B, C and D all have their own public/private keypairs:

The private RSA key is stored in /etc/tinc/company/rsa_key.priv, the private Ed25519 key is stored in /etc/tinc/company/ed25519_key.priv, and the public RSA and Ed25519 keys are put into the host configuration file in the /etc/tinc/company/hosts/ directory.

Starting

After each branch has finished configuration and they have distributed the host configuration files amongst them, they can start their tinc daemons. They don’t necessarily have to wait for the other branches to have started their daemons, tinc will try connecting until they are available.


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