From: Bit Gossip (bit.gossip@chello.nl)
Date: Wed Dec 24 2008 - 05:50:36 ARST
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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