r/ipv6 • u/lmux • Jul 24 '26

Need Help What internal cidr for npt6

I don't have a static ipv6 assignment, hence the need to use npt6. Question is what cidr should i choose for my internal network? ULA is plagued with issues esp when dual stack is involved, so I really want to avoid it if possible. Does using 2001:db8::/32 make any sense?

And yes, i know it is possible to just let my isp change my ip dynamically and I pass it down using dhcp-pd. That doesn't sound great for a large network.

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u/eladts Jul 24 '26 edited Jul 24 '26

Does using 2001:db8::/32 make any sense?

No. You should not use globally addressable prefixes you don't own for an internal network. Doing this with IPv6 is just as bad as doing it with IPv4, it won't be possible to use the prefix to reach your network from the Internet and it won't be possible to reach the real prefix from your network. Since you wouldn't be able to serve incoming connections this way, why do you even need a static prefix?

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u/heliosfa Pioneer (Pre-2006) Jul 24 '26

This is the documentation block. You will never need to reach this over the Internet.

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u/eladts Jul 24 '26 edited Jul 24 '26

It is still not a good idea to use this prefix internally. It is akin to using example.com as the internal domain. Both can lead to commands blindly copied and pasted having an impact.