ipv6 duplicate address detection

I am a bit confused about the DAD process. When a device connected to an IPv6 network, it will self-assign an ipv6 address with fe80::/64 and an EUI address by integrating its MAC address. Now the MAC address is unique in the whole world. Correct? If yes then why do we need DAD? Thanks
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IPv6 doesn't have to include a MAC address. For security reasons, it's a bad idea to broadcast your machine's MAC pver the internet, so a "temporary" address can be used instead. Windows uses those temporary addresses by default. Here's a good write-up about the process.

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Dave BaldwinFixer of ProblemsCommented:
MAC addresses were supposed to be unique... a long time ago.  Since then, MAC address cloning in routers and manufacturers trying to save on MAC addresses by assigning the same MAC address to multiple NICs have essentially killed that idea.
leblancAccountingAuthor Commented:
I see. So Windows use a random number to generate the link-local address. Will this vary from one OS to another?

So the EUI process will take effect if you don't configure the host part manually or using of a random number. Correct?
I'm not sure what other OSes do by default, but there is defeinitely a command in Linux and MacOS to generate the IPv6 address based on a ramdom string instead of the MAC address.

And yes, the EUI will take effect if the manual/random host isn't specified.
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