[ale] IPv6 local devices with a prefix that may change

[James Sumners]

I'll answer in my limited capacity based upon what I have done.

First, forget about knowing all of your local addresses. And forget 
about static assignments. Each host should be addressed by hostname, and 
each host should work out its IPv6 addresses (of which it will have 
several).

Second, if you _really_ need to know your local addresses _and_ want 
them to be IPv6, look into Unique Local Addresses (ULA)[1]. Be 
forewarned, though, that smarter people than me have discovered issues 
with those[2].

I actually do have a use case for ULAs that is described in 
https://jrfom.com/posts/2022/09/29/unifi-udm-pro-at-home/

In short, all you really should care about is the prefix delegation so 
that your devices can be assigned addresses correctly by the discovery 
protocols. Let them then register their name in some way.

[1] -- https://en.wikipedia.org/wiki/Unique_local_address
[2] -- https://twitter.com/jsumners79/status/1576186161063944193

On 2022-11-04 13:04, Alex Carver via Ale wrote:
> This is a purely academic question and thought experiment. It is not
> tied to anything I'm doing specifically or at this time.
> 
> Every website/how-to/explainer I've ever run across talks about
> issuing an IPv6 address to each device with the prefix provided by the
> router and that you don't use the equivalent of NAT because IPv6
> reasons.
> 
> Great, fine, all well and good except no one ever discusses what
> happens when your whole network suddenly has its prefix change.  These
> sites just seem to assume the prefix is static for all time. Well that
> works if you're a company or maybe you're never going to change ISP or
> move to another area. Well that's fine for them but it doesn't really
> apply precisely to me. I've moved several times in the last ten years
> and changed ISPs three times so that prefix would not have been
> stable.
> 
> So suppose this premise:
> 
> I write and/or use software for remotely monitoring and controlling
> devices (doesn't matter what they are, IoT, computers, printers,
> anything) and that software, when it starts up, is going to connect
> out to each device it needs to handle. So there's probably a
> configuration file that contains all the IP addresses.
> 
> Now, under IPv4 they likely would have all been behind NAT and
> therefore all have private address range IPs which would be stable no
> matter what happened to the NAT device's WAN. But if everyone is now
> IPv6 and getting their prefix from the router a change on the WAN
> affects everyone downstream.
> 
> Suddenly my software has an out-of-date configuration because all the
> devices changed out from underneath it.
> 
> If one is supposed to do things "The IPv6 Right Way(tm)"/"NAT is bad
> mmm-kay?" using the issued prefixes and such, how do I keep my
> internal network stable so my software can safely work through WAN
> changes?
> 
> _______________________________________________
> Ale mailing list
> Ale at ale.org
> https://mail.ale.org/mailman/listinfo/ale
> See JOBS, ANNOUNCE and SCHOOLS lists at
> http://mail.ale.org/mailman/listinfo