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Comments on How is the IPv6 link-local address calculated?

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How is the IPv6 link-local address calculated?

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I was told that an IPv6 link-local address — typically starting with fe80:: — is derived from the interface's MAC address. Here are some instruction on how to do the conversion.

But the conversion result doesn't match my actual IPv6 link-local address according to ip a. My IPv6 link-local addresses and MAC addresses don't seem related at all.

How is the IPv6 link-local address really calculated?

I'm on Arch Linux using NetworkManager 1.42.6.

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1 comment thread

Direct use of MAC addresses for IPv6 SLAAC is discouraged (1 comment)
Direct use of MAC addresses for IPv6 SLAAC is discouraged
Canina‭ wrote over 1 year ago

I'm not up to writing an actual answer, and if someone wants to take this and turn it into an answer before I have a chance to then that's fine by me; but actually using the MAC address directly to generate an IPv6 address, as that page seems to do, has been broadly discouraged for a good while.

See for example https://datatracker.ietf.org/doc/html/rfc7721#section-3

My guess is that your system is configured to use some variation of IPv6 privacy extensions, for example https://datatracker.ietf.org/doc/html/rfc4941 or https://datatracker.ietf.org/doc/html/rfc7217.