IPV6 Addressing EUI - 64
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I was wondering on your IFCONFIG it showed your MAC address (ether) as 68:5b:35:c6:01:62 making your example come out as below.
EUI-64
FE80:0000:0000:0000:xxxx:xxxx:xxxx:xxxx
Original MAC: 68:5b:35:c6:01:62
Padded MAC: 68:5b:35:FF:FE:c6:01:62
EUI-64 Address: FE80:0000:0000:0000:685b:35FF:FEc6:0162
I fully thought I understood this simple use of MAC addressing adoption into IPV6 formate for EUI - 64, but then I noticed in your IFCONFIG and mine, 1 hexadecimal unit off.
FE80:0000:0000:0000:6a5b:35FF:FEc6:0162
My ifconfig shows similar;
ether 4c:8d:79:f4:1d:40
inet6 fe80::4e8d:79ff:fef4:1d40
Is this important at this level of learning to understand why the difference? Or is theory more important to know right now, than why in reality it is different?
My GUESS is it they are different because of multiple devices on the same router, so EUI-64 has to choose one just a little off, so they aren't duplicate? -
Michael,
On EUI-64, we take a MAC and change it fill the 64 bit (HOST ID-"interface identifier")
xx-xx-xx-xx-xx-xx-xx (sample MAC) to xx-xx-xx-FF-FE-xx-xx-xx (EUI-64 interface identifier)
What also happens is that the 7 bit: (xX-xx-xx-FF-FE-xx-xx-xx) 0000 00X0 also gets turned on 0000 0010...
So for example, if my MAC address was: 00:00:5f:9a:8b:7a then we converted for EUI-64
the first octet would also change: 02:01:5f:FF:FE:9a:8b:7a.
So in your example...
Where you show the original MAC beginning with 68:5b we convert the 68h to binary: 0100 1000 and if you do what I have said above and change the 7th bit to "ON" 0100 1010 now the hex conversion is 6A:5b... the same would be true of your MAC as well.
The 7th bit is changed to insure, as you've stated a uniqueness in interface identifiers among a single machine with multiple interfaces.
Hope this answers your question!
Cordially,
Ronnie Wong
Host, ITProTV -
Thank you, Ronnie. Figured it had to be simple.
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Michael,
I wanted to add a little more to Ronnie's answer. You can read about what Ronnie is describing in RFC 4291 Section 2.5.1. The problem with the 7th bit is it functions differently between MAC addresses and IPv6 addresses. In a MAC address "0" means it is assigned by the IEEE (and therefore globally unique) and "1" means it was locally generated (like with VMs). It is the opposite in IPv6 addresses (0 is locally generated and 1 is globally unique). Thus the need for inversion.
Hope that helps,
Don Pezet
Host, ITProTV -
I figured it was above my need to know at this point, but when I see a discrepancy....The only dumb question is the one not asked.
Thanks again.