Mesh VPN

This guide provides detailed instructions for configuring ZeroTier VPN within Clan. Follow the outlined steps to set up a machine as a VPN controller (<CONTROLLER>) and to include a new machine into the VPN.

Concept

By default all machines within one clan are connected via a chosen network technology.

Clan 
    Node A
    <-> (zerotier / mycelium / ...)
    Node B

If you select multiple network technologies at the same time. e.g. (zerotier + yggdrassil) You must choose one of them as primary network and the machines are always connected via the primary network.

1. Set-Up the VPN Controller

The VPN controller is initially essential for providing configuration to new peers. Once addresses are allocated, the controller's continuous operation is not essential.

Designate a Machine: Label a machine as the VPN controller in the clan, referred to as <CONTROLLER> henceforth in this guide.
Add Configuration: Input the following configuration to the NixOS configuration of the controller machine:
```
clan.networking.zerotier.controller = {
  enable = true;
  public = true;
};
```
Update the Controller Machine: Execute the following:
```
clan machines update <CONTROLLER>
```
Your machine is now operational as the VPN controller.

2. Add Machines to the VPN

To introduce a new machine to the VPN, adhere to the following steps:

Update Configuration: On the new machine, incorporate the following to its configuration, substituting <CONTROLLER> with the controller machine name:

{ config, ... }: {
  clan.networking.zerotier.networkId = builtins.readFile (config.clan.core.clanDir + "/machines/<CONTROLLER>/facts/zerotier-network-id");
}

Update the New Machine: Execute:
```
$ clan machines update <NEW_MACHINE>
```
Replace <NEW_MACHINE> with the designated new machine name.
For Private Networks
1. Retrieve the ZeroTier ID: On the new_machine, execute:
```
$ sudo zerotier-cli info
```
  Example Output:
```
200 info d2c71971db 1.12.1 OFFLINE
```
  , where d2c71971db is the ZeroTier ID.
2. Authorize the New Machine on the Controller: On the controller machine, execute:
```
$ sudo zerotier-members allow <ID>
```
  Substitute <ID> with the ZeroTier ID obtained previously.
Verify Connection: On the new_machine, re-execute:
```
$ sudo zerotier-cli info
```
The status should now be "ONLINE":
```
200 info d2c71971db 1.12.1 ONLINE
```

Congratulations!

The new machine is now part of the VPN, and the ZeroTier configuration on NixOS within the Clan project is complete.

Further

Currently you can only use Zerotier as networking technology because this is the first network stack we aim to support. In the future we plan to add additional network technologies like tinc, head/tailscale, yggdrassil and mycelium.

We chose zerotier because in our tests it was a straight forwards solution to bootstrap. It allows you to selfhost a controller and the controller doesn't need to be globally reachable. Which made it a good fit for starting the project.