RFC 4291:IP Version 6 Addressing Architecture
RFC-Ref

set to zero


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... EUI-64 format, the "u" bit is set to one (1) to indicate universal scope, and it is set to zero (0) to indicate local scope. The first three octets in binary of an IEEE EUI-64 ...
... link with the interface identifier set to zero. Packets sent to the Subnet ...



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