First things first: Figure out what the IPv6 subnet is assigned to you by your provider or hoster. For demonstration purposes, I’ll use 2001:DB8::/32, you probably got a /64 subnet, but it makes no difference for the setup. Just REMEMBER: change the IP address to the one you got assigned.

Next, you need to decide on an IP address to use. I’ll use 2001:DB8::5/32 as my server IPv6 address. After that, you need to identify what the address for your default gateway is. It will almost always be fe80::1; However, check with your provider or hoster.

Temporary setup

To test the IPv6 setup, you can assign the IP address manually to the interface and add the route.

1. Set the IP address on the vio0 interface ifconfig vio0 inet6 2001:DB8::5/32
2. Add the default route route add -net ::/0 fe80::1%vio0

Permanent setup

To make the changes permanent, you need to create/edit a /etc/hostname.<interface> file (hostname.if(5)) mine for example would be /etc/hostname.vio0. In this file, you can specify the IP addresses associated with interface as well as defining the route(s):

inet6 2001:DB8::5/32
!route add -inet6 ::/0 fe80::1%vio0

Update

[2023-11-22]
If you use PF firewall and have, for example a web server, you most likely want to allow ICMPv6: pass proto ipv6-icmp from any to any

[2024-07-10]
Update the Permanent setup section, and improve the example with the proper configuration.