Re: NAT64 in RA, draft-ietf-6man-ra-pref64

[David Farmer <[e-mail]>]

On Tue, Jul 2, 2019 at 5:53 AM Lorenzo Colitti <lorenzo=
[e-mail]> wrote:

> On Tue, Jul 2, 2019 at 9:49 AM Jen Linkova <[e-mail]> wrote:
>
>> > The question boils down to - imagine I had only IPv6 to work with.
>> Could we communicate? An IPv6-only host, or IPv6-only network, could
>> communicate with that restriction. Everything else is noise - and if I have
>> to deal with noise, it's not IPv6-only.
>>
>> I totally agree. it was my understanding of IPv6-only as well.
>> So - back to the original problem of excluding some addresses from
>> DNS64 synthesis/NAT64 translation - I've been told that an IPv6-only
>> host might want to exclude some addresses from synthesis and use IPv4
>> to reach them, so I'm trying to understand how *an IPv6-only* host
>> (which, IMHO, can only use IPv6) reach anything using IPv4.
>>
>
> Right. That was the gist of my earlier comment. I believe we all agree
> that in the most common deployment scenario (i.e., an IPv6-only host with
> no IPv4), an exclusion list is not useful, because the host really can't
> reach anything that's not reachable via IPv6.
>

I mostly agree, but there is a scenario I've been thinking about;

What if the network operator doesn't want RFC1918 and RFC 6598 IPv4
addresses synthesized at all? I suppose the NAT64 function could block
these addresses. However, for a large enough population that could be a lot
of useless traffic going to the NAT64 function. While on the other hand
some network operators, especially enterprise operators, will probably want
these addresses synthesized.

Now a complicated APL capability isn't probably needed to handle this, a
simple one-bit option flag or two would suffice, I believe.


> If so, then I really think that an exclusion list should be a separate
> option.
>

I agree that a generalized highly configurable exclusion list should be a
separate option, but I can see the need to exclude or not synthesis for
RFC1918 and RFC 6598 IPv4 addresses being part of this option.

Thanks

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