[ipv6hackers] Dynamic prefixes & privacy (was: IPv6 prefix changing)

Owen DeLong owend at he.net
Fri Mar 16 13:29:34 CET 2012

On Mar 16, 2012, at 4:48 AM, Markus Reschke wrote:

> On Fri, 16 Mar 2012, Alex List wrote:
> Hi Alex!
>>> Not exactly, but yes. IPv6 privacy extensions alone would be sufficient to
>>> make IP based tracking a lot harder and too inaccurate for the marketing
>>> company.
>> Due to the /64 bits left I don't agree, but from the discussion so far
> For dynamic prefixes:
> The 64 bits of the interface address is "randomized" by privacy extensions and the other 64 bits tell us your ISP and your area. That's not much data. The marketing company needs additional sources to be able to track you.

Not really true.

The other 64 bits tell the careful observer quite a bit more...

The first 32 (or less) bits tell us your ISP.
The next 16 bits should narrow it down to an end-site in most cases (yes, some ISPs will do stupid things and give less than /48 to some customers unfortunately, at least initially). Admittedly, which end-site will change every once in a while, but, it will be stable enough in almost every case to be usable for limited marketing purposes, especially when correlated through other means such as cookies.

It's not perfect, but, ti's definitely good enough to be useful to the marketing companies. They don't seem to have too much trouble obtaining additional sources and they're getting better and better ad putting the pieces together even in realtime.

> For fixed IPv6 prefixes:
> You would get a nice whois entry in the RIPE database :-) I haven't checked it yet for IPv6, but there's some lower limit you don't need to add the assignment. Any specific number known?

Only if you are in Europe. Outside of Europe, likely your nice entry would be in some other RIRs database or in some ISPs RWHOIS server.

As to the lower limit, I believe it varies by region. In the ARIN region, I think it is /64.

>> But wait, aren't ULA prefixes random? If CGNs were here to stay[1],
>> why couldn't they provide a "network layer privacy" [2] service? If
>> they claim to be so good at NATPT44, NPTv6 should be a piece of cake.
> Just half of them :-) But CGN wouldn't help. Since the access routers would perform CGN we have the same prefixes. So we know your ISP and area again.

Actually, all currently defined ULA prefixes are supposed to be random. There is a reservation for future RFC work on ULA-registered, but, I believe that all of the drafts languished into expiration and it never came to fruition. Personally, I think that's a good thing. I would like to deprecate ULA altogether as an unnecessary and poorly conceived waste of address space. (Not that I'm concerned about the use of the space nearly so much as the possibility that someone might actually deploy ULA in a myriad of harmful ways and that there aren't actually any good use cases for it that I have seen as yet).


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