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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.




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