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I am running a private cloud server and I am facing the problem that my DNS provider does not support dynamic update of the IPv6 address. I know that every IPv6 device has a 'default' IPv6 address which is derived from the MAC address. Therefore, I wonder whether I could use this address to globally identify my server? If that is true, how can I find it out? ifconfig gives me the global address which changes about every 24 hours and the fe80 address which is only valid locally, if I'm not mistaken.

E. Sommer
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    "_I know that every IPv6 device has a 'default' IPv6 address which is derived from the MAC address._" That is incorrect. The original SLAAC specified several ways to create an IID for an interface, but that is not normally used anymore, and it is not even a complete IPv6 address, only a 64-bit IID appended to a 64-bit network address, to get a full IPv6 address. The 64-bit network address must be assigned by an authority to be a global network address. – Ron Maupin Nov 11 '19 at 22:21
  • Do you get a stable (/static) network prefix from your ISP? Your computer controls (mostly) the lower 64 bits of its address, and by default will change them regularly for privacy. That's easy to turn off. But your ISP controls the higher 64 bits, and if they change that -- even if it's only every few months -- you have a much more difficult problem. – Gordon Davisson Nov 12 '19 at 00:59
  • I'm pretty sure the prefix is constant. Do I turn off changing the last bit in the router? – E. Sommer Nov 12 '19 at 05:53
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    @E.Sommer It depends a little on your network setup, but usually the last 64 bits are completely controlled by the computer itself. How you set a static address there depends on the OS it's running. – Gordon Davisson Nov 12 '19 at 08:12

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Configure the interface to use stable addressing. EUI-64, rfc7217 stable opaque, or static addressing. Bring the interface up and get its global scope address.

Anything in fe80::/10 is link local. Not routable, only use those on the same LAN.

By the way, on Linux, use the ip command. Not ifconfig, which has been unmaintained for many years. However, some UNIX call the manage an interface command ifconfig.

John Mahowald
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  • Do you mean I should configure the router to give the server a fixed IPv6? – E. Sommer Nov 12 '19 at 05:54
  • Up to you. I said "stable addressing", a few ways exist to implement that. DHCPv6 can provide address assignments. (But you still need RAs to assign the default gateway anyways.) – John Mahowald Nov 12 '19 at 12:58