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

Iljitsch van Beijnum iljitsch at muada.com
Sat Jun 2 11:35:59 EDT 2007

On 2-jun-2007, at 2:02, Paul Vixie wrote:

> smaller private connectivity domains would only depend on  
> uniqueness among
> their participants.  are you trying to make a definition of  
> "routable" that
> depends on which connectivity domain the observer is actually in?   
> or would
> it be enough to say "the connectivity domain that ARIN's members  
> all share"?

How did we get from routability tto uniqueness?

"uniqueness among their participants" doesn't sound so bad until  
people start participating in multiple connectivity domains. I don't  
want to fumble the math so I'll spare you (and myself), but you get  
in the situation where there is overlap really fast. Also, in  
computer science there are only three numbers: 0, 1 and many. If we  
need more than one block of private space to avoid collisions, the  
obvious choice is to have as many blocks as there are domains.

>> ULA fails this test because it falls outside the global unicast block
>> and because announcing it to one ISP isn't enough to receive packets
>> from all over the world because people will filter.

> so the routability of an address block can also depend on filters?   
> (and
> perhaps on firewalls?)  and is an address block that's "routable"  
> today
> capable of being "unroutable" tomorrow?  and if it's "routable"  
> according
> to network X, can it be "unroutable" according to network Y?

Don't pretend this is news to you. Ever tried to cat herd? Herding  
network operators is even worse.

> i can't imagine how a policy with these dependencies would be  
> implemented.

Hence the "routability not guaranteed" disclaimer.

> which is precisely the point i'm trying to make.  the RIR system can
> guaranty uniqueness among RIR allocations, but can make no assertions
> either way as to "routability".  since any definition of ULA  
> depends on
> a definition of "routable", i think this slope is too slippery for us.

As I said before, if ARIN feels it should only give out "hopefully  
routable" address space like it does today, no problem, let other  
people give out ULA-C space. But ARINs definition issues don't  
preclude the usefulness of ULA-C.

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