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universal/local bit in an EUI 64 format in an IPV6 address
smcclenaghan
Member Posts: 139
in CCNA & CCENT
The wording is a little funny in Odom's ICND2 regarding this.
From what I understand, the 7th bit in a typical burned-in MAC address should be 0, which the EUI-64 calculation will switch to a 1, meaning a universal address (versus an address which had a 1 as a 7th bit, which would be inverted to a 0 to indicate a locally administered address). Is this right?
Assuming so, what exactly is the point of the inversion? If 0 means burned-in for a typical MAC, why can't it also mean burned-in (or universal) for EUI-64?
From what I understand, the 7th bit in a typical burned-in MAC address should be 0, which the EUI-64 calculation will switch to a 1, meaning a universal address (versus an address which had a 1 as a 7th bit, which would be inverted to a 0 to indicate a locally administered address). Is this right?
Assuming so, what exactly is the point of the inversion? If 0 means burned-in for a typical MAC, why can't it also mean burned-in (or universal) for EUI-64?
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powmia
Users Awaiting Email Confirmation Posts: 322
The bit is inverted, but so is the meaning. It is still technically considered global after the conversion.
RFC 2373 - IP Version 6 Addressing Architecture
"The motivation for inverting the "u" bit when forming the interface identifier is to make it easy for system administrators to hand configure local scope identifiers when hardware tokens are not available. This is expected to be case for serial links, tunnel end- points, etc. The alternative would have been for these to be of the form 0200:0:0:1, 0200:0:0:2, etc., instead of the much simpler ::1, ::2, etc" -
Optionssmcclenaghan
Member Posts: 139
Thanks, Powmia. That paragraph was extremely helpful. I appreciate your time.