[ppml] [address-policy-wg] Those pesky ULAs again

[Iljitsch van Beijnum]

On 29-mei-2007, at 17:04, Kevin Loch wrote:

>> - IPv6 space is not infinite.  It's a 64-72 bit address space.   
>> That's
>>   right, subnets with > 256 hosts are very uncommon today, so  
>> we've wasted
>>   64 bits to number 256 things.  That makes the space effectively  
>> on the
>>   long end 72 bits.

> Excellent point.  I never understood why they didn't just use say 16
> bits for the host portion, randomly assign an address and check for
> collisions before use.

Eh... Last time I checked, that's exactly what IPv6 does. Except that  
the number of bits for the host portion is 64.

Now 64 is a bit on the large side of course, but it does have the  
advantage that if the host randomly assigns itself an address where  
"randomly" means "borrowed from the ethernet MAC address" it will  
have the same exact address every time it boots without the need for  
anyone or anything to keep track of that address.

>> When your doorknob automatically requests a ULA-C
>>   /64 when you bring it home, and your house has 2,000 of them as  
>> every
>>   individual system talks to each other we'll be looking at this  
>> quite
>>   differently.

> Why can't your doorknob select a ULA-L /64 and check for collisions
> before use?

So what happens when one hotel chain merges with another and suddenly  
all those addresses that seemed to be unique before aren't anymore?