Determining if address is locally or globally unique

binaryhat

Hello,

I'm on chapter 13 of lammle's book and I don't understand this:

How is 0260.d6FF.FE73.1987 a global unique address when looking at the seventh bit. my book says 1 is for global and 0 is local.

The book states:

You see, part of the process of padding (called modified eui-64 format) changes a bit to specify if the address is locally unique or globally unique. And the bit that gets changed is the seventh bit in the address.

wolfinsheepsclothing

0260.... (8 4 2 1 8 4 2 1) The seventh bit is on.

CaySpekko

Well, according to Odom "the seventh bit reading from left to right is called the universal/local bit. Set to binary 0, it means that the MAC address is burned-in MAC address. Set to 1, it means that the the MAC address has been configured locally. EUI-64 says that the U/L bit should be set to 1 meaning local."

also from Microsoft:"
The U/L bit is the seventh bit of the first byte and is used to determine whether the address is universally or locally administered. If 0, the IEEE, through the designation of a unique company ID, has administered the address. If 1, the address is locally administered. The network administrator has overridden the manufactured address and specified a different address.
( IPv6 Interface Identifiers )

Also another good explanation: http://packetlife.net/blog/2008/aug/4/eui-64-ipv6/

So in the case of 0260.d6FF.FE73.1987

look at the first byte '02'

0000 0010 <---notice the seventh bit is set to 1, thus the address is locally administered, and not assigned by ieee.

melcredo

binaryhat wrote: »

Hello,

I'm on chapter 13 of lammle's book and I don't understand this:

How is 0260.d6FF.FE73.1987 a global unique address when looking at the seventh bit. my book says 1 is for global and 0 is local.

The book states:

sir this is for ccna right?? not for ccent... thanks

SdotLow

melcredo wrote: »

sir this is for ccna right?? not for ccent... thanks

I would think so. That's not a mac address, unless the "1987" at the end is something added to it that's not covered in CCENT, which could be the case. Doesn't look like an IPv6 address the way it's displayed either though.