From: Scott Morris (smorris@internetworkexpert.com)
Date: Wed Dec 24 2008 - 14:20:58 ARST
Well, it still indicates the host portion of the address... So it's KIND OF
following the same logic... But it's really one of those "well, DUH!"
things when you think about it.
Made perfect sense to someone though! Definitely an academic exercise
though!
HTH,
Scott
-----Original Message-----
From: Bit Gossip [mailto:bit.gossip@chello.nl]
Sent: Wednesday, December 24, 2008 2:51 AM
To: smorris@internetworkexpert.com
Cc: 'ccielab'
Subject: RE: IPv6 EUI-64 local/global bit
Ok,
so the U/L bit is correctly set (1=local) to generate the host part of the
link-local address; and I am perfectly happy with this..
But then it is bluntly copied over to the global address loosing the
semantic of the bit :-(
On Tue, 2008-12-23 at 17:35 -0500, Scott Morris wrote:
> EUI-64 is used to derive your host address. This is assigned to your
> link-local address. From there it is merely COPIED to any other
> address calling for EUI-64 information.
>
> Your host address given there on your linux box is 021c.bfff.fe85.3cea
>
> From that we can figure out your MAC address part (take out FFFE) as
> 021c.bf85.3cea... Oh yeah, change that "02" back to "00" for your
> unicast MAC! :)
>
> The second least significant bit of the most significant byte of your
> MAC address is used for U/L (Universal or Local). It is changed with
> EUI-64 formatting just to signify some academic sense of adjustment.
> IMHO, it goes beyond the sense of logic because if you can't figure
> out that a 48 bit number doesn't become a 64-bit number without any
> sort of intervention, you need help! But the spec says that bit gets
> flipped during the EUI-64 process, therefore everyone does it! :)
>
> I think your confusion is more of why do we have changes in BOTH the
> link-local AND global addresses, and that's merely from the copying.
>
> On your router, if you went to the interface and put "ipv6 address
> fe80::22 link-local" and then looked at "show ipv6 interface" you'd
> see your global address is now 2001:1111:1111:A::22
>
> HTH,
>
>
> Scott Morris, CCIE4 #4713, JNCIE-M #153, JNCIS-ER, CISSP, et al.
> CCSI/JNCI-M/JNCI-ER
> Senior CCIE Instructor
>
> smorris@internetworkexpert.com
>
>
>
> Knowledge is power.
> Power corrupts.
> Study hard and be Eeeeviiiil......
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of Bit Gossip
> Sent: Tuesday, December 23, 2008 4:32 PM
> To: ccielab
> Subject: IPv6 EUI-64 local/global bit
>
> Experts,
> I don't understand why both cisco routers and also my linux box set
> the local bit both in the link local address but also in the global
address.
> The global address is derived from NIC OUI where it is 0 (=global) by
> definition; so does it become local in the interface ID?
>
> Thanks,
> Bit.
>
> r1#show ipv6 interface brief f0/0
> FastEthernet0/0 [up/up]
> FE80::204:DDFF:FE11:620
> 2001:1111:1111:A:204:DDFF:FE11:620
>
>
>
> wlan0 Link encap:Ethernet HWaddr 00:1C:BF:85:3C:EA
> inet addr:192.168.255.231 Bcast:192.168.255.255
> Mask:255.255.255.224
> inet6 addr: 2001:1111:1111:a:21c:bfff:fe85:3cea/64 Scope:Global
> inet6 addr: fe80::21c:bfff:fe85:3cea/64 Scope:Link
>
>
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