RE: IPv6 Question flipping the 7th bit conversions

Correct. In reality it's arbitrary whether that bit is 0 or 1 but technically it means that the address MUST be unique if the value is "Universal" (0) while the address SHOULD be unique if the value is "Local" (1). The same is true of your NIC card's MAC address. If the address is vendor assigned (i.e. Universal) then the MAC address MUST be unique, but if you change it yourself (i.e. Local) then it SHOULD be unique but it won't necessarily be. I've seen some corner cases in the past though where a shipment of a particular vendor's NIC cards *did* have the same MAC address (probably an accident) but the end result was that there was unpredictable connectivity on the LAN because the ARP cache and CAM tables kept getting poisoned. That was a fun problem to troubleshoot ;)

HTH,

Brian McGahan, CCIE #8593 (R&S/SP/Security)
bmcgahan_at_INE.com

Internetwork Expert, Inc.
http://www.INE.com

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of Kyle Byrne
Sent: Wednesday, December 26, 2012 12:39 AM
To: Cisco certification
Subject: IPv6 Question flipping the 7th bit conversions

I'm asking this question to clear up my own insanity, because it just dawned on me while reading deeper into frames bits. My question is the reason you have to flip the bit in the 7th bit when converting an IPv6 address using the Mac address, because that bit is the U/L bit and in the U/L bit a 1 means that it was administratively assigned, instead of a 0 which meant that the address was vendor assigned?

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Received on Wed Dec 26 2012 - 20:50:03 ART