IPv6 question regarding wan6 interface assignment length

[egc]

My provider finally is supporting public IPv6 addresses on the router (when the modem is in bridge mode)

So I started implementing it, I have a complicated network (used for testing and playing around with multiple daisy chained routers running DDWRT and OpenWRT)

That all seems to work with PD down the chain, possible as my ISP delegates me a /56 prefix

I can of course post anything you want but for starters I have a simple question, but first some assumptions I made while setup and please correct me if I am wrong:

My wan6 interface gets the PD delegated, I enable Delegate IPv6 prefixes which makes it possible that my LAN interface can get an IPv6 address (is this correct?)

I assign a /60 address to my LAN and also enable PD on the LAN interface, so my downstream router can get a PD of /62 and that also works wonderfully (amazing that all the required routing is made automatically)

Now my question: the WAN6 interface has its own /128 address from the ISP.
By default it also gets a /64 from the PD but if I disable this (set IPv6 assignment length to disabled) it still seems to work.

So the question is does the WAN6 interface needs a /64 address from the PD or is the /128 address from the ISP sufficient ( I know it also has LL addresses which are used for routing an communicating)

[mk24]

The WAN only needs a /128. It is used for Internet access that originates inside the router device such as NTP and forwarded DNS. Some ISPs have every customer's basic WAN IP within the same /64 with each customer using one /128. This is acceptable as long as they are also providing routable prefixes.

Internet access from any of your LAN PCs originates with an IP inside the /56. Return traffic to all of the /56 is forwarded to your line, and then your router will further route it into one of the LANs or to the next one of your routers and ultimately back to the originating PC.