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EUI-64

Hi everybody,

someone knows why in the process of building IPV6 unicast address through EUI-64 the seventh bit from left must be complemented ?? I can't understand .....

thanks

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4 REPLIES
Cisco Employee

EUI-64

Paolo,

You are refrring to 7th bit of mac address the U/L bit not the 7th bit of IPv6 address I guess :-)

You need to look at bit side of things. It makes thing easier in notation.

It's described here:

http://en.wikipedia.org/wiki/IPv6_address#Modified_EUI-64

Take a very simple MAC address and convert it to EUI-64 with and without the bit flipped.

You will see that it's "easier" to write it down when it's flipped.

M.

Re:EUI-64

You may also want to check on the theory behind the U/L bit in mac addresses. Wikipedia is an excellent source.

Regards,

Leo

Silver

EUI-64

Hi Paolo,

hope this helps you

Understanding IPv6 EUI-64 Bit Address

Regards,

Sunil Khanna

PS: Please rate the helpful post.

Regards, Sunil Khanna
Cisco Employee

EUI-64

This is explained in RFC4291 Section 2.5.1.  In short, it is so that the implicit modified EUI-64 portion of manually assigned addresses (such as 2001:db8::1) will be recognized as locally administered.

http://tools.ietf.org/html/rfc4291#section-2.5.1

Relevant text:

   The motivation for inverting the "u" bit when forming an interface
   identifier is to make it easy for system administrators to hand
   configure non-global identifiers when hardware tokens are not
   available.  This is expected to be the case for serial links and
   tunnel end-points, for example.  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 0:0:0:1, 0:0:0:2, etc.
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