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

[Alex Carver]

I was being generic to capture a lot of different cases but one where I 
think this has an issue is smaller microcontroller devices. They're not 
likely going to have lots of RAM and OSes that can handle services to be 
able to respond to things we take for granted on larger computers.

So if I'm to address by hostname only then you're saying I'll need to 
operate a DNS server but how do I establish that DNS server to point at 
those devices when the prefix changes without having to reconfigure it 
at every prefix change? Or is this where you're applying ULA as well?

On 2022-11-04 10:33, James Sumners wrote:
> 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?
>>
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