North American Network Operators Group
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Re: IPv6 Address Planning

  • From: Iljitsch van Beijnum
  • Date: Thu Aug 11 03:49:39 2005 
On 11-aug-2005, at 2:23, Kevin Loch wrote:
And on that vein perhaps it's prudent for people using network
prefixes longer than /64 to take care to ensure that the bit positions
in the IPv6 address that should correspond to the u and g bits in the
modified EUI-64 interface ID (according to RFC 3513) are both set to


Is there any known use for those bits?




The universal/local bit is copied from the EUI-64/MAC address and
flipped, and indicates whether the address is derived from something
(supposedly) globally unique or not. Both occur frequently, non-
unique stem from manual configuration or RFC 3041 temporary/privacy
addresses. The group bit isn't relevant, although you won't see MAC-
derived addresses with this bit set, of course.



There is no real reason to preserve these bits when the prefix length
is > 64.