[arin-ppml] ARIN-prop-127: Shared Transition Space for IPv4 Address Extension

Owen DeLong owen at delong.com
Fri Jan 21 13:22:08 EST 2011

On Jan 21, 2011, at 6:32 AM, Jack Bates wrote:

> On 1/21/2011 4:17 AM, Owen DeLong wrote:
>> This has a lot more to do with content not being accessible on IPv6 and
>> not having a solution for IPv4-only customer devices to reach IPv6
>> content than it does with the access networks not deploying IPv6.
> I suspect content will hard switch to v6 faster than home routers will.
I'll be surprised. Yes, content can move faster, but, I don't think content will
feel the pressure of runout as fast as the residential provider market will.

>> The access providers generally agree that native IPv6 or 6rd can be deployed
>> easier and quicker than NAT444 for the problems that can solve.
> We can provide, doesn't mean customers will switch their home gear.
It's unlikely they will have a choice relatively quickly. It's also unlikely that
faced with a NAT444 environment that any consumer would not prefer
to switch their gear.

>> The difficult comes when they deal with users, even users that have IPv6
>> access, that need to reach IPv4 content for whatever reason. This is where
>> NAT444 is pretty much the only viable alternative currently on the table.
> Agreed. There will still be some v4 content, even if most will switch to v6 as soon as it's viable QOS wise for them to do so.
There will also be MANY consumer devices that don't support IPv6
that must be considered.

>> I will note that even the people asking for this /10 are saying that they
>> really don't want to use it, but, they don't see any alternative.
> Reuse their existing space. A single /18 of all my address space would be fine for me to handle NAT444, and not a big deal to duplicate it around the different network areas. I suspect I'll actually go with something smaller, and probably from the DHCP pools which don't utilize static addressing (perhaps that /20 in use by the cell phones).
You are running a much smaller network than many of these guys.

They are planning to duplicate this /10 around their different network areas.

>>> The proposal doesn't mention another source of unique IPv4 addresses
>>> that could be used for this purpose - the ISPs' existing assignments.
>> That's really a non-starter.
> Why? We have address space already. Why not duplicate it around the network? What does some arbitrary /10 give me that my existing space doesn't?
In a given region, deploying NAT444 requires you to have the following:

	1 public IP address per N customers
	1 NAT box intermediate address for each CGN/LSN -- part of the proposed /10 or from where?
	1 intermediate address for each customer -- part of the proposed /10 or from where?

To do this from existing space, you would basically need to turn off 2 regions and renumber
all of the subscribers in one to match the addresses of the other. Then you would need
to come up with additional addresses for all of the LSN/CGN boxes on the interior side
and for the shared external addresses. I suppose you could use the addresses recovered
from the second region, but, if your region contains more than 1,000,000 customers, it
seems to me like it would be pretty difficult to do this juggling without significant down

Instead, it's much easier to write up a use-case for the addresses you need for this
and submit it to the RIR. Sure, probably nobody gets a /10 for this, but, not hard
to imagine ways several /14s, possibly a few /12s, and certainly a number of
/15s and /16s go out the door that way. If it goes that way, none of the ISPs have
any incentive to share those intermediate addresses with the other ISPs and
a few downsides to doing so.

>> On the other hand, what I think you will see if this policy does get bogged
>> down is a situation where many of the larger providers that are asking
>> for this will each go apply for their own allocations and they may or may
>> not coordinate sharing that with others. I think that is a far less desirable
>> alternative than getting this policy through.
> They will apply for allocations anyways. They will ask for address space for as long as they possibly can. The fact is, most of the networks who need NAT444 run vast amounts of dynamic space, and we can easily reuse that space for NAT444.
I am unconvinced that it is as easy as you think in many of the scenarios I have

>> I find myself having to agree with Bill here. I'm not 100% convinced this is
>> the right thing to do, and, I was pretty opposed to it from the understanding
>> I had of the issue when it was presented to IETF. However, at this time, I'm
>> leaning more towards the belief that this is one of the three things in the
>> IPv4 end game that we really need to just hold our noses and do.
> I think ARIN should push for education of NAT444 address reuse with existing address space. Once an ISP does decide to shift to NAT444, they will quit hitting up the freepool for more space. I expect the major shift of NAT444 as soon as v6 is the mainstream protocol, reducing the load and problems associated with NAT.

I think many providers are goint to hit the wall with need for NAT444 well before IPv6 is the mainstream protocol and not before we have run out of IPv4.


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