From: Scott Morris (smorris@internetworkexpert.com)
Date: Tue Dec 23 2008 - 20:35:35 ARST
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
Blogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Thu Jan 01 2009 - 12:53:09 ARST