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

[Derek Atkins]

This is what mDNS (e.g. Avahi) is for -- to be able to query the local
network based on a name and get the machine to respond back with its
address(es).  This is how you reach e.g. your printer, speakers, TV, etc.
If you get renumbered, they get renumbered, and the next lookup will
return the new number.  Done.

It's of course a BIGGER issue if you want to have remotely accessible,
DNS-named servers.  In that case, yes, you will need to update your DNS
AAAA records if you ever do get renumbered.  One potential approach would
by DynDNS, where hosts can update your zone if they change addresses.

In my experience, however, the /60 I got from AT&T (and the /48 I have
from HE, and the /48 I have from my other ISP) are all pretty stable.

-derek

On Fri, November 4, 2022 1:04 pm, 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 Suddenly my software has an out-of-date configuration because all the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?
>
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-- 
       Derek Atkins                 617-623-3745
       derek at ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant