this post was submitted on 18 Jun 2024
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[–] [email protected] 10 points 4 months ago* (last edited 4 months ago) (12 children)

On one hand you definitely don't want to be assigning manual/static IPv6 to all your devices because if your prefix ever changes you'll have to update it everywhere. IPv6 doesn't really have a concept of private address space (with a few exceptions). ~~On the other hand most modern IPv6 stacks support dynamic protocols like SLAAC while also assigning a static suffix to the published prefix (e.g. You want :0:0:1234:1 to go to your server, and SLAAC gets the prefix 200x::5678/64 your server would assign itself 200x::5678:0:0:1234:1).~~

DHCPv6 fixes a lot of these headaches for managed networks by allowing you to reserve specific IPv6 for a given DUID.

IMO, your network, do what you want. ~~I have two jump Raspberry PIs that I have static suffixes so I always know where they are without relying on DNS or whatever.~~ Edit: I apparently misremembered how I had these setup. I use a custom interface up script to take the SLAAC prefix and append the custom suffix to it as a secondary IP.

[–] [email protected] 6 points 4 months ago (4 children)

IPv6 does have private spaces. Any prefix beginning with fd is 'private,' and (IIRC) there's a formula to generate the next 40 bits of prefix to minimize the chance of intersections. i.e., you can generate your own internal /48 functionally equivalent to 192.168/16 or 10/8

Don't know if you can use that with SLAAAC, but it works if you run a dhcpv6 and makes ipv6 feel a lot like ipv4. You have to NAT everything inside &c, but if you already have a functioning internal IPv4 network, IPv6 is just a matter of figuring out which config options need to be changed (eg, dhcp6.name-servers for option domain-name-servers)

[–] [email protected] 0 points 4 months ago (2 children)

Yes, ULA are one of the exceptions I mentioned. It covers fc00::/7 which is fc00 to fdff, though I believe most use just the top half. I use one for an intermediate network between my edge router and my primary firewall to not consume one of my limited /64 networks.

I haven't played with IPV6 NAT much. I know its use is a bit discouraged as NAT was always designed as a stopgap measure for IPV4 exhaustion. It might be a good option if you need additional space and your ISP doesn't support additional prefixes. Just keep in mind that if you use these in DNS, they won't be accessible externally.

[–] [email protected] 1 points 4 months ago* (last edited 4 months ago)

The downside with ULA is that ipv4 is given preference, which is annoying on dual stack networks. I believe there is a draft RFC to change this but it will take a while for it to be approved and longer still for OSes to change their behaviour. I workaround it by using one of the unused (but not ULA) prefixes.

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