IPV6 planning

Karl Auer kauer at biplane.com.au
Mon Mar 7 03:01:53 UTC 2016

On Mon, 2016-03-07 at 02:57 +0100, Baldur Norddahl wrote:
> But the most popular OS (Windows) completely ignores all of that and
> makes up an identifier not based on EUI-64. Everyone are happy 
> anyway. The RFC should have let identifier selection as an 
> implementation detail as the risk of collision is almost non existent 
> given a sufficient random selection and we have duplicate address
> detection as a safeguard.

Privacy and temporary addresses are two of the three SLAAC types. One
critical requirement for the original SLAAC is that the address doesn't
change; for devices without writable storage, that requires a
deterministic algorithm to generate the address. A further critical
requirement was that devices be able to get connected with zero host co
nfiguration - globally and locally.

For temporary and privacy addresses, where permanence is not an issue,
you can use any prefix length, though as I said in my original
response, your protection diminishes the longer the prefix gets.

I'm not trying to be an apologist for those who designed IPv6, but I
really don't think they were stupid, and it's not as simple a situation
as people seem to think.

My initial response was to someone who said they thought Cisco
supported varying prefix lengths with SLAAC. I said it wan't just up to
Cisco, the hosts had to play ball too, and I don't think they do. But,
as already noted, I could be wrong :-)

Regards, K.

Karl Auer (kauer at biplane.com.au)

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