Sample IPv6 configuration for `k3s-ansible`

This scenario contains a cluster configuration which is IPv6 first, but still supports dual-stack networking with IPv4 for most things. This means:

The API server VIP is an IPv6 address.
The MetalLB pool consists of both IPv4 and IPv4 addresses.
Nodes as well as cluster-internal resources (pods and services) are accessible via IPv4 as well as IPv6.

Network design

All IPv6 addresses used in this scenario share a single /48 prefix: fdad:bad:ba55. The following subnets are used:

fdad:bad:ba55:0::/64 is the subnet which contains the cluster components meant for external access. That includes:
- The VIP for the Kubernetes API server: fdad:bad:ba55::333
- Services load-balanced by MetalLB: fdad:bad:ba55::1b:0/112
- Cluster nodes: fdad:bad:ba55::de:0/112
- The host executing Vagrant: fdad:bad:ba55::1
In a home lab setup, this might be your LAN.
fdad:bad:ba55:4200::/56 is used internally by the cluster for pods.
fdad:bad:ba55:4300::/108 is used internally by the cluster for services.

IPv4 networking is also available:

The nodes have addresses inside 192.168.123.0/24. MetalLB also has a bit of address space in this range: 192.168.123.80-192.168.123.90
For pods and services, the k3s defaults (10.42.0.0/16 and 10.43.0.0/16) are used.

Note that the host running Vagrant is not part any of these IPv4 networks.