Enable IPv6 on Unifi Gateway Networks
I was not able to SSH into any IPv6 servers. Simple test commands were not working
ping6 ipv6.google.com ping6: connect: Network is unreachable
The issue was that I had not configured my home network to know what to do with IPv6. Here is how I solved it.
1) Connect to local UI of Unifi Controller - Go to its local address (e.g., 192.168.1.2:8443) and then into Settings.
2) Enable IPv6 Delegation on Controller - Go to Settings -> Internet. There edit the WAN, go to IPv6 Connection settings, and select "DHCPv6" as "IPv6 Connection" and try 56 for the "Prefix Delegation Size".
3) Enable IPv6 on Network - Go to Settings -> Networks and edit the network that you desire to make IPv6-enabled. Select "Prefix Delegation" for "IPv6 Interface Type". I left the other settings untouched.
Once you have done that you may need to restart the network on the devices you want to make IPv6 capables but once things work both ping6 ipv6.google.com and ip -6 route should succeed.