ipv6 at hetzner

2a01:4f8:221:181:: / 64
2a01:4f8:221:181:0000:0000:0000:0000 / 64

fe80::1

https://www.tunnelsup.com/subnet-calculator/
https://www.calculator.net/ip-subnet-calculator.html

https://www.crucial.com.au/blog/2011/04/15/ipv6-subnet-cheat-sheet-and-ipv6-cheat-sheet-reference/

2a01:4f8:221:181:0000:: / 64
2a01:4f8:221:181:0001:: / 64
2a01:4f8:221:181:0002:: / 64
2a01:4f8:221:181:0003:: / 64
2a01:4f8:221:181:0004:: / 64
2a01:4f8:221:181:0005:: / 64
2a01:4f8:221:181:0006:: / 64
2a01:4f8:221:181:0007:: / 64
2a01:4f8:221:181:0008:: / 64
2a01:4f8:221:181:0009:: / 64
2a01:4f8:221:181:000A:: / 64
2a01:4f8:221:181:000B:: / 64
2a01:4f8:221:181:000C:: / 64
2a01:4f8:221:181:000D:: / 64
2a01:4f8:221:181:000E:: / 64
2a01:4f8:221:181:000F:: / 64
2a01:4f8:221:181:0010:: / 64
2a01:4f8:221:181:0011:: / 64
2a01:4f8:221:181:0012:: / 64
2a01:4f8:221:181:0013:: / 64
2a01:4f8:221:181:0014:: / 64
2a01:4f8:221:181:0015:: / 64
2a01:4f8:221:181:0016:: / 64
..

We have successfully setup the following IPv6 subnet for your server.

IPs: 2a01:4f8:221:181:: /64

Gateway: fe80::1

Useable IP addresses: 2a01:4f8:221:181::2 
to 2a01:4f8:221:181:ffff:ffff:ffff:ffff

http://www.subnetonline.com/pages/ipv6-network-tools/online-ipv6-ping.php

# rc.conf
ifconfig_re0_ipv6="inet6 2a01:4f8:221:181::2 prefixlen 64"
ifconfig_re0_alias1="inet6 2a01:4f8:221:181::3 prefixlen 64"

curl -v https://[2a01:4f8:221:181::2]:443/