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Why flip the 'u' bit when creating the EUI-64 ID?

Hello anyone,

I've done some study of the RFC 4291 where the IPv6 addressing is required. There are two issues that puzzle me:

1.) When creating the 64-bit Interface ID from the MAC address or from the original EUI-64, the U/L bit (the 7th bit of the topmost byte) is inverted. Why is this done? The RFC tries to explain it in a few words but I do not find the explanation sufficient.

2.) If I am specifying the Interface ID of the IPv6 address manually, should I take care that the U/L bit is set to a specific value (in this case, 0)?

Any hints are heartily welcome!

Best regards,

Peter

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