sixnix/README.md

# sixnix

NixOS module for IPv6 networking with WireGuard tunnels and optional BGP failover.

## Motivation

My ISP gives me a single `/64` and it's dynamically assigned. Can't have multiple networks with functional autoconfiguration. Tunnel brokers like [Hurricane Electric](https://tunnelbroker.net/) would work but my ISP uses CGNAT which makes that setup tricky if not impossible. They also do not have any exit nodes in the region I want.

Linode provides a routed `/56` for free with their cheapest $5/month VPS. That's 256 `/64` subnets. You get 1TB traffic at 1Gbit (40Gbit input but that's kind of irrelevant for our use case). Good enough.

## Solution 1: Simple WireGuard setup

Just a plain WireGuard tunnel to route the `/56` to your home network.

With a `/56` you can carve out a `/60` for WireGuard endpoints and you're left with 15 `/60` subnets. Share it with friends!

| Client subnet      | WireGuard subnet     |    |
|--------------------|----------------------|----|
| 2001:db8::/60      | 2001:db8:0:f0::a/127 | 1  |
| 2001:db8:0:10::/60 | 2001:db8:0:f1::a/127 | 2  |
| 2001:db8:0:20::/60 | 2001:db8:0:f2::a/127 | 3  |
| 2001:db8:0:30::/60 | 2001:db8:0:f3::a/127 | 4  |
| 2001:db8:0:40::/60 | 2001:db8:0:f4::a/127 | 5  |
| 2001:db8:0:50::/60 | 2001:db8:0:f5::a/127 | 6  |
| 2001:db8:0:60::/60 | 2001:db8:0:f6::a/127 | 7  |
| 2001:db8:0:70::/60 | 2001:db8:0:f7::a/127 | 8  |
| 2001:db8:0:80::/60 | 2001:db8:0:f8::a/127 | 9  |
| 2001:db8:0:90::/60 | 2001:db8:0:f9::a/127 | 10 |
| 2001:db8:0:a0::/60 | 2001:db8:0:fa::a/127 | 11 |
| 2001:db8:0:b0::/60 | 2001:db8:0:fb::a/127 | 12 |
| 2001:db8:0:c0::/60 | 2001:db8:0:fc::a/127 | 13 |
| 2001:db8:0:d0::/60 | 2001:db8:0:fd::a/127 | 14 |
| 2001:db8:0:e0::/60 | 2001:db8:0:fe::a/127 | 15 |

### Basic configuration

```nix
{
  inputs.sixnix.url = "git+https://code.planet-express.in/konarak/sixnix.git";

  outputs = { nixpkgs, sixnix, ... }: {
    nixosConfigurations.tunnel-server = nixpkgs.lib.nixosSystem {
      modules = [
        sixnix.nixosModules.default
        {
          sixnix = {
            enable = true;
            hostname = "tunnel-server";
            domain = "example.com";
          };

          wireguard.interfaces = [{
            interface = "wg0";
            serverPort = 51820;
            serverAddress = "2001:db8:a7c4:0:f0::a/127";
            clientAddress = "2001:db8:a7c4:0:f0::b/127";
            clientSubnet = "2001:db8:a7c4::/60";
            serverPrivateKeyFile = "/run/secrets/wg0-server-private";
            clientPublicKeyFile = "/run/secrets/wg0-client-public";
          }];
        }
      ];
    };
  };
}
```

How it works:
- Your router uses the ISP-provided IPv6 to connect to the WireGuard server
- Interfaces get `/64`s from the delegated `/60` with router advertisement enabled
- All traffic from clients goes out to the internet via Linode

## Solution 2: BGP failover (ultra advanced)

Want redundancy? Run two Linodes in the same datacenter and use BGP to share a single `/56` between them. If one server goes down, BGP automatically fails over to the other.

Cost: $10/month + tax for two Linodes with pooled 2TB bandwidth quota.

### BGP configuration

```nix
{
  sixnix = {
    enable = true;
    hostname = "tunnel-primary";
    domain = "example.com";

    bgp = {
      enable = true;
      peers = [
        "2001:db8:9f2b::1"  # BGP peer addresses (e.g., Linode route servers)
        "2001:db8:9f2b::2"
        "2001:db8:9f2b::3"
        "2001:db8:9f2b::4"
      ];
      advertisedSubnets = [ "2001:db8:a7c4::/56" ];
      routeMap = "primary";  # or "secondary" for the backup server
    };
  };

  wireguard.interfaces = [{
    interface = "wg0";
    serverPort = 51820;
    serverAddress = "2001:db8:a7c4:0:f0::a/127";
    clientAddress = "2001:db8:a7c4:0:f0::b/127";
    clientSubnet = "2001:db8:a7c4::/60";
    serverPrivateKeyFile = "/run/secrets/wg0-server-private";
    clientPublicKeyFile = "/run/secrets/wg0-client-public";
  }];
}
```

The BGP setup creates:
- A shared dummy interface with a VIP that both servers announce
- Route servers configured automatically based on datacenter ID
- Blackhole routes for the advertised subnet
- Primary/secondary route maps for failover priority

## Notes

- BGP peers and advertised subnets are fully configurable
- The FRR configuration template may need adjustments for providers other than Linode (AS numbers, communities, etc.)
- For Linode: use route servers `2600:3c0f:<dcId>:34::{1,2,3,4}` where `<dcId>` is your datacenter ID (e.g., 25 for in-maa)
- See Linode's [BGP documentation](https://techdocs.akamai.com/cloud-computing/docs/configuring-ip-failover-over-bgp-using-frr-advanced) for more details
- See [`modules/network.nix`](modules/network.nix) and [`modules/wireguard.nix`](modules/wireguard.nix) for all available options