wireguard

Wireguard-based VPN mesh network with automatic IPv6 address allocation

Wireguard VPN Service

This service provides a Wireguard-based VPN mesh network with automatic IPv6 address allocation and routing between clan machines.

Overview

The wireguard service creates a secure mesh network between clan machines using two roles: - Controllers: Machines with public endpoints that act as connection points and routers - Peers: Machines that connect through controllers to access the network

Requirements

• Controllers must have a publicly accessible endpoint (domain name or static IP)
• Peers must be in networks where UDP traffic is not blocked (uses port 51820 by default, configurable)

Features

• Automatic IPv6 address allocation using ULA (Unique Local Address) prefixes
• Full mesh connectivity between all machines
• Automatic key generation and distribution
• IPv6 forwarding on controllers for inter-peer communication
• Support for multiple controllers for redundancy

Network Architecture

IPv6 Address Allocation

• Base network: /40 ULA prefix (deterministically generated from instance name)
• Controllers: Each gets a /56 subnet from the base /40
• Peers: Each gets a unique 64-bit host suffix that is used in ALL controller subnets

Addressing Design

• Each peer generates a unique host suffix (e.g., :8750:a09b:0:1)
• This suffix is appended to each controller's /56 prefix to create unique addresses
• Example: peer1 with suffix :8750:a09b:0:1 gets:
• fd51:19c1:3b:f700:8750:a09b:0:1 in controller1's subnet
• fd51:19c1:c1:aa00:8750:a09b:0:1 in controller2's subnet
• Controllers allow each peer's /96 subnet for routing flexibility

Connectivity

• Peers use a single WireGuard interface with multiple IPs (one per controller subnet)
• Controllers connect to ALL other controllers and ALL peers on a single interface
• Controllers have IPv6 forwarding enabled to route traffic between peers
• All traffic between peers flows through controllers
• Symmetric routing is maintained as each peer has consistent IPs across all controllers

Example Network Topology

graph TB
    subgraph Controllers
        C1[controller1<br/>endpoint: vpn1.example.com<br/>fd51:19c1:3b:f700::/56]
        C2[controller2<br/>endpoint: vpn2.example.com<br/>fd51:19c1:c1:aa00::/56]
    end

    subgraph Peers
        P1[peer1<br/>designated: controller1]
        P2[peer2<br/>designated: controller2]
        P3[peer3<br/>designated: controller1]
    end

    %% Controllers connect to each other
    C1 <--> C2

    %% All peers connect to all controllers
    P1 <--> C1
    P1 <--> C2
    P2 <--> C1
    P2 <--> C2
    P3 <--> C1
    P3 <--> C2

    %% Peer-to-peer traffic flows through controllers
    P1 -.->|via controllers| P3
    P1 -.->|via controllers| P2
    P2 -.->|via controllers| P3

    classDef controller fill:#f9f,stroke:#333,stroke-width:4px
    classDef peer fill:#bbf,stroke:#333,stroke-width:2px
    class C1,C2 controller
    class P1,P2,P3 peer

Configuration

Basic Setup with Single Controller

# In your flake.nix or inventory
{
  services.wireguard.server1 = {
    roles.controller = {
      # Public endpoint where this controller can be reached
      endpoint = "vpn.example.com";
      # Optional: Change the UDP port (default: 51820)
      port = 51820;
    };
  };

  services.wireguard.laptop1 = {
    roles.peer = {
      # No configuration needed if only one controller exists
    };
  };
}

Multiple Controllers Setup

{
  services.wireguard.server1 = {
    roles.controller = {
      endpoint = "vpn1.example.com";
    };
  };

  services.wireguard.server2 = {
    roles.controller = {
      endpoint = "vpn2.example.com";
    };
  };

  services.wireguard.laptop1 = {
    roles.peer = {
      # Must specify which controller subnet is exposed as the default in /etc/hosts, when multiple controllers exist
      controller = "server1";
    };
  };
}

Advanced Options

Automatic Hostname Resolution

The wireguard service automatically adds entries to /etc/hosts for all machines in the network. Each machine is accessible via its hostname in the format <machine-name>.<instance-name>.

For example, with an instance named vpn: - server1.vpn - resolves to server1's IPv6 address - laptop1.vpn - resolves to laptop1's IPv6 address

This allows machines to communicate using hostnames instead of IPv6 addresses:

# Ping another machine by hostname
ping6 server1.vpn

# SSH to another machine
ssh user@laptop1.vpn

Troubleshooting

Check Wireguard Status

sudo wg show

Verify IP Addresses

ip addr show dev <instance-name>

Check Routing

ip -6 route show dev <instance-name>

Interface Fails to Start: "Address already in use"

If you see this error in your logs:

wireguard: Could not bring up interface, ignoring: Address already in use

This means the configured port (default: 51820) is already in use by another service or wireguard instance. Solutions:

1. Check for conflicting wireguard instances:

   sudo wg show
   sudo ss -ulnp | grep 51820
   

2. Use a different port:

   services.wireguard.myinstance = {
     roles.controller = {
       endpoint = "vpn.example.com";
       port = 51821;  # Use a different port
     };
   };
   

3. Ensure unique ports across multiple instances: If you have multiple wireguard instances on the same machine, each must use a different port.

Key Management

Keys are automatically generated and stored in the clan vars system. To regenerate keys:

# Regenerate keys for a specific machine and instance
clan vars generate --service wireguard-keys-<instance-name> --regenerate --machine <machine-name>

# Apply the new keys
clan machines update <machine-name>

Security Considerations

• All traffic is encrypted using Wireguard's modern cryptography
• Private keys never leave the machines they're generated on
• Public keys are distributed through the clan vars system
• Controllers must have publicly accessible endpoints
• Firewall rules are automatically configured for the Wireguard ports

Roles

The wireguard module has the following roles:

• controller
• peer

Options for the controller role

domain

Domain suffix to use for hostnames in /etc/hosts. Defaults to the instance name.

Type: null or string

Default:

instanceName

Declared in: clanServices/wireguard/default.nix

endpoint

Endpoint where the controller can be reached

Type: string

"vpn.clan.lol"

Declared in: clanServices/wireguard/default.nix

port

Port for the wireguard interface

Type: signed integer

Default:

51820

51820

Declared in: clanServices/wireguard/default.nix

Options for the peer role

controller

Machinename of the controller to attach to

Type: string

"controller1"

Declared in: clanServices/wireguard/default.nix

domain

Domain suffix to use for hostnames in /etc/hosts. Defaults to the instance name.

Type: null or string

Default:

instanceName

Declared in: clanServices/wireguard/default.nix

port

Port for the wireguard interface

Type: signed integer

Default:

51820

51820

Declared in: clanServices/wireguard/default.nix