If you have to ask that question, you do not need it. And because I am still not happy with the current state of IPv6 in OpenWrt as LAN client, I do not recommend to do it except you have a reason.
mpa explained already what is needed. There is an OpenWrt wiki with more details (and for future vistitors perhaps with more up-to-date information). However, as of today, that wiki entry is not complete as you should also delete the
ula_prefix in the globals section of
That answers how to do it. Your questions is whether you need it.
You need a global IPv6 address on your OpenWrt, if you use a service which is external to your home network and is IPv6-only. In other words, a IPv6-only service on the Internet. This rare for public services. However, more and more residential Internet Service Providers (ISP) tend to offer just global IPv6 to their customers (terms are DS-Lite or CG-NAT). If you have such a ISP or a friend of yours has such an ISP, you need IPv6 on your OpenWrt.
You need a global IPv6 address on your OpenWrt if you offer a service (on your OpenWrt) to the Internet and you have such a IPv6 ISP or the local network of your user(s) is IPv6-only.
You need a global IPv6 address on your OpenWrt if you offer a service (on your OpenWrt) to the Internet and the local network of your user(s) is IPv6-only.
The latter sound esoteric today. However, I faced that already several times: In a hotel, where the DHCP server for IPv4 crashed, sometimes, IPv6 connectivity still works. Then all you have is IPv6-only. And then it is very handy to offer a VPN via IPv6 from home because you use whole Internet in that hotel.
So, yes, if you have the time and interest, go for IPv6 on your LAN client. It does not hurt, except that OpenWrt has not that one big switch to enable IPv6 but requires several changes (as mpa, the wiki and I explained). By the way, IPv6 on your OpenWrt is not required if you want to access/configure it. For that, you still use IPv4. I hope this clarifies IPv6 a bit. It is nice to have, in some cases it is a must have.