* Ian Zimmerman:

> The first reason [...] was that my router does _not_ assign fe80::1 to
> itself, but rather some other arbitrary address in the fe80 prefix

I found an article[1] that I first read years ago. "One method to make
things easier is to manually assign the link-local address to the
upstream router’s interfaces." That's one of the firmware-dependent
things, it may happen automatically. I know that my favourite data
center has its routers set up this way as well. One does not have to use
this method, of course.

[1] 
https://blogs.infoblox.com/ipv6-coe/fe80-1-is-a-perfectly-valid-ipv6-default-gateway-address/

> while the router seems to obtain a delegated prefix from upstream, it
> doesn't assign any address from that range to the internal
> interface. The only ipv6 addresses on the internal interface are the
> link-local address and the ULA address.

I think that, as long as the clients use link-local routing to connect
to the router, and the router correctly passes IPv6 traffic in both
directions, it should work without a global-scope address on the
router's LAN-facing NIC.

> I did enable the router advertisement feature, and I checked that the
> daemon is running on the router. But I can see no output related to
> that when I run tcpdump on the desktop system.

Anything that might be interfering with ICMPv6 ? That would prevent all
NDP, including router advertisement.

> so  you _do_ self-assign a static ipv6 address after all. How do
> you know it is the right one?

I only use a static IPv6 address for hosted machines, because I need DNS
AAAA records. The individual subnets are statically assigned by the data
center to each machine.

At home, I don't configure clients with static IPv6, because it is not
necessary for me. In fact, I'm happy to have the lowest 64 address bits
scrambled (IPv6 Privacy Extensions) to make traffic analysis more
difficult. All local clients can use NDP to locate each other anyway.

> https://openwrt.org/docs/guide-user/network/ipv6/start

Sadly I have no practical experience with OpenWrt. Hopefully somebody
else here can help with that.

-Ralph

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