[ppml] Paul Vixie: Re: draft-ietf-ipv6-ula-central-02.txt use cases

[Scott Leibrand]

Randy,

Paul's reasoned and thoughtful response was quoting my message, which 
is included below.  I'll Cc: ppml when I've had a chance to draft a reply, 
as we're starting to discuss the similarities and differences between 
ULA-C and a possible new kind of private PI.

-Scott

On 06/25/07 at 7:39pm -0700, Scott Leibrand <sleibrand at internap.com> wrote:
> 
> Date: Mon, 25 Jun 2007 19:39:51 -0700
> From: Scott Leibrand <sleibrand at internap.com>
> Cc: IETF IPv6 Mailing List <ipv6 at ietf.org>
> Subject: Re: draft-ietf-ipv6-ula-central-02.txt use cases
> 
> Apparently people are still having a hard time visualizing use cases for ULA-C, so let me try again
> to lay one out:
> 
> Let's say I build a somewhat ad-hoc wireless mesh network covering a residential area to provide
> Internet service.  For my Internet connectivity, I get service from several different ISPs, each of
> which gives me an IPv6 subnet (PA space).  As this is a wireless network based on inexpensive
> hardware often deployed in a residential setting (and possibly involves some mobility), I can't
> count on any portion of my network to maintain reachability to any particular ISP uplink.  In
> addition, I am likely to change ISPs over time, and I'm too small to qualify for PI space, so I
> choose to number my internal network infrastructure out of private (ULA) space.  In parallel, I also
> use DHCP, DHCP-PD, etc. to assign subnets of my various PA space to users on various portions of my
> network (thereby giving them IPv6 address(es) of whichever Internet uplinks are available to them).
> (I may also use some form of DHCP to assign PA space to my router interfaces, or I may choose to
> hide that detail by doing my mesh networking below layer 3, or I may choose to use ULA space there
> and rewrite the source address of any ULA-sourced packets leaving my network for the Internet.)
> 
> Now let's say I am thinking a little bit bigger than just my neighborhood, and would also like my
> network to connect to neighboring mesh networks.  (This could fairly easily evolve into an
> arbitrarily large internetwork enabling disaster-resistant connectivity across neighborhoods,
> cities, or entire regions.)  In order to facilitate troubleshooting, I elect to use ULA-C space for
> my network infrastructure, including router interfaces, (and either rewrite source addresses of any
> packets (presumably ICMP) my routers send out to the Internet, or also assign PA space to each
> interface with something like DHCP-PD, so that the router can use IPv6 address selection to use a
> public address for packets destined for public Internet addresses).  As before, I would give out PA
> subnet(s) to users for Internet connectivity, but I might also elect to give them ULA addresses to
> communicate with other hosts on my mesh network and neighboring ones.
> 
> In a situation like this, I need to be able to resolve PTRs for hosts using my neighboring networks'
> ULA space without any prior knowledge about the neighboring wireless network.  If both networks are
> numbered out of ULA-C space, this is easy: I send my PTR queries to my regular DNS resolver, which
> has a PA address and Internet connectivity, and can resolve the PTR from the DNS server
> authoritative for my neighboring wireless network's ULA-C block.
> 
> So, again, I see that ULA-C is a very simple solution to fill a very useful function that cannot be
> filled by local ULAs alone (at least without adding additional complexity to DNS).  Importantly,
> this functionality does not depend on ULA-C providing an additional assurance of uniqueness, but on
> the fact that my block (and its authoritative DNS servers) can be registered, and others can query
> the registered data.
> 
> As IPv6 adoption takes hold and dynamic wireless networking becomes cheaper and more widespread, I
> would see this kind of use case, and its many permutations, becoming more and more common.  Can you
> describe a way to use existing address types available to small networks (PA and ULA-L) and existing
> DNS technologies to support the requirements listed above?  If not, I would argue that we should
> complete the process of ULA-C standardization, as it represents the simplest available solution to
> the problem.
> 
> 
> -Scott
>

On 06/25/07 at 10:28pm -0700, Randy Bush <randy at psg.com> wrote:

>> Re: draft-ietf-ipv6-ula-central-02.txt use cases
>> From: Paul Vixie <paul at vix.com>
>> Date: Tue, 26 Jun 2007 05:12:56 +0000
>> To: IETF IPv6 Mailing List <ipv6 at ietf.org>
>> To: IETF IPv6 Mailing List <ipv6 at ietf.org>
>>
>>
>>> Apparently people are still having a hard time visualizing use cases for
>>> ULA-C, so let me try again to lay one out:
>
> sure be nice to know to whom you were responding.  and they might like
> the recognition for there words, despite your (and i) disagreeing with them.
>
> randy
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