[arin-ppml] IPv6 Non-connected networks

michael.dillon at bt.com michael.dillon at bt.com
Mon Feb 22 12:05:06 EST 2010

> It seems like we're back to ULA again.  It seems that we all 
> want the same thing, "unroutable" address space for internal 
> use only.  There are any number of reasons to have RFC 
> 1918'ish space in v6 and the real difference now is that, 
> given the size of the v6 address space, we don't have to 
> allocate blocks to be used by all providers.  Instead, we're 
> in a position where we *can* give everyone their own block.
> We could even do the old multicast thing and auto-assign a 
> ULA (or whatever it's called) block to each ARIN allocation.  
> In thinking about it, I do agree that having a defined block 
> for filtering purposes is preferred.

GLOP addressing uses the 16-bit ASN to specify a /24 block 
of multicast addresses, if I remember correctly. So, if we
used the 32-bit ASN to specify a /48 block of private use
addresses, we could probably fit it in. 

I don't believe that this has ever been proposed before
so it may be worthwhile writing a draft to see what happens.
And why not also include the "assigned ULA" addresses in 
the draft as well. If people like one idea better than the
other, then simplify the draft.

So we would have

16 bits defined prefix for private use IPv6 addresses
32 bits ASN number
16 bits subnetting space
64 bits IIDs
Total 128 bits of IPv6 address.

And given that there are some private-use ASNs defined, that
gives everyone the option to use those private-use addresses
whether or not they have an assigned ASN. That is essentially
the same as RFC 1918 addresses in IPv4.

--Michael Dillon

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