Doesn't that mean if you move, or if your ISP changes your IP, all your local devices will end up with different addresses?

I have an internal DNS server and it would be annoying if it could randomly break and require me to update all the IPs.

You can add ULA addresses to devices and use those in local DNS. Or just use the automatic link-local ones, One of the best things about IPv6 is support for multiple addresses per host and using them in different contexts.

I stopped maintaining local DNS and use mDNS instead which updates automatically.

My local devices end up with new ipv6 addresses daily.

> My local devices end up with new ipv6 addresses daily.

Isn't that a pain in the butt?

You’d think so, but dns magically works for me. Wish I had a better answer ha ha.

I assume it's possible to prevent machines from changing their IP address? I have a few where DNS cannot reasonably be used and I use raw IP addresses instead.

You can disable IPv6 privacy extensions. The exact process depends on the operating system you use.

IPv6 not just allowing, but expecting multiple scoped addresses relieves this quite nicely.

The most common setup for this is that you have a static link-local address, and a static global address. And listening processes should listen to these static addresses.

Then you have a temporary global address, and outbound connections should use the youngest temporary global address (because temporary addresses don't disappear when they age out, they disappear when they age out AND no existing connection is still using them).

The net effect is that the address you leave in example.com's httpd logs is a temporary address that has no listening processes. And the address you use in dns, mdns, when connecting intentionally, etc is a static address.

I add a specific static ip where I care (dns resolver). The machines usually give themselves a few other routable ips I guess for fun? No idea why they don’t go away.

So if I'm checking local server log files to debug a problem that started a few days ago, I can't easily tell where the incoming connections are coming from?

You can configure a static ip if you use IP addresses as an identifier. You can also keep track of who had what ip address.

I use ULA addresses in my local dns, the global address can change, privacy addresses can cycle and my local DNS keeps working. This also guarantees that the data you are pushing locally stays local since ULAs will never be sent out of the local network.

Agreed. My favorite part is that you don’t need any special consideration for local/WAN splits in DNS. Your DNS address for your homelab server is the same address on your LAN as it is on the WAN, so your DNS can just be the same. Thus “ssh hostname.fqdn” works whether you’re on the local network or remote, and your packets just automatically stay on your LAN when you’re local (they don’t even have to hit your router… they can directly unicast if you’re on the same switch. No “hairpin NAT” or anything like that needed.)