Re: draft-ietf-ipv6-ula-central-02.txt

james woodyatt wrote:
> On Jun 21, 2007, at 15:26, Templin, Fred L wrote:
>>
>> Maybe I am missing the point, but there seems to be an implication 
>> that ULA-C necessarily implies IPv6 NAT; am I misinterpreting? If 
>> not, then I don't quite understand why this implication is being 
>> drawn. Can someone please explain?
>
No, ULA-C doesn't require NAT, any more than RFC 1918 or ULA-L space does.

> I'm not going so far as to say the implication is there.  I'm just 
> have a very difficult time taking seriously the concern about merge 
> risks associated with renumbering due to the birthday paradox in a 
> 2^40 number space without something more substantial to go on than a 
> bald-faced assertion that any small but non-zero probability of 
> collision is unacceptable.

That assertion has been made, but I don't think we can treat it as 
anything more than a preference by non-technical business people.

>   The alternative explanation that makes the most sense to me is that 
> some influential organizations, which are too small to warrant their 
> own PI space, are resisting migration to IPv6 unless they can use NAT 
> with private addresses, and they won't [or can't] explain why the 
> arguments in RFC 4864 and 
> draft-ietf-v6ops-scanning-implications-03.txt are failing to persuade 
> them.
>
Whether people end up using NAT or not, RFC 4864 specifically states 
that "When changing ISPs or ISPs readjust their addressing pool, DHCP-PD 
[12] can be used as an almost zero-touch external mechanism for prefix 
change in conjunction with a ULA prefix for internal connection 
stability."  This implies, as I have argued previously, that it is 
appropriate in some cases, particularly the absence of PI space, to use 
a ULA prefix for numbering internal infrastructure like router 
interfaces.  If I am a network operator doing so, I would like my 
internal infrastructure addresses to have valid PTRs, which requires DNS 
delegation, which requires ULA-C.

To my mind, the main advantage of ULA-C over ULA-L is the ability to 
register your space and delegate reverse DNS authority to the 
appropriate name servers, such that anyone on your network or any 
privately-connected network can resolve PTR requests for addresses in 
your ULA block.

-Scott

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