Slashdot: UK ISP PlusNet Testing Carrier-Grade NAT Instead of IPv6

Joe Maimon jmaimon at
Fri Jan 18 15:57:19 UTC 2013

Owen DeLong wrote:

>> Clearly we have run out of trickery as multiple layers of NAT stumps even the finest of our tricksters.
> Yes, we can dedicate thousands more developer hours to making yet more extensions to code to work around yet more NAT and maybe make it sort of kind of work almost as poorly as it does now. Or we could pour a fraction of those developer hours into implementing IPv6 in those same applications and have the problem solved in perpetuity.

There is no "we"

People will follow their personal motivations. If that includes 
improving their application experience in the face of prevalent CGN 
technology, I expect many of them to decide to put in the effort no 
matter what either your or I have to say about it.

> My hope is that we will realize at some point that this is a badly loosing proposition, but, my fear is that we will actually find ways to make it work and worse yet, dedicate resources to doing so.
> IMHO, having it fail miserably is the best case scenario. The alternatives are far worse.

See above. The internet is not top down. It is a potpourri of 
interacting influences. Nobody takes marching orders from either of us.

> I'd believe 50% or maybe even 65%, but 75% stretches credibility. See above for a partial list of the various things I expect they are doing with those addresses.

So a provider to have a one to one relationship between infrastructure 
addresses and subscribers is somehow plausible to you? Anyone else?

Not to me. Not even if you count every single employees and every single 
corporate server and device, of which the vast majority are not even 
using globally unique addresses. Which is what we are discussing.

And suppose they are. A corporation like that can re-use 50% of their 
IPv4 by converting internally to NAT (and IPv6 we hope).

>> How about much simpler math. Assume 75% IP in any provider organization are for subscribers. Assume an average 5-10 subscribers per CGN IP.
> I don't believe the first assumption and I think that more than about 3 is rather optimistic for the second one, actually. Especially in the face of dedicated port range CGN proposed by most of the ISPs I know have real plans to implement CGN rather than just a "yeah, we'll do that when we have to" approach.

Most NAT44 implementations have absolutely no issue scaling to low 
hundreds of users with ONE IP address.

3 is absolutely ridiculously low. 3 of the above, maybe.

However, even at 3, that means that they can double their subscriber 
base with their existing addresses. So unless their existing base took 2 
months to acquire, that is a deal more than 4 month stop gap you claim.

And since you believe that it is plausible for such an organization to 
have a one to one infrastructure/subscriber relationship, going private 
(and we hope ipv6) internally, gives them another 3x subscriber base.

Clearly, CGN can provide enough address re-use to stave off exhausting 
in a provider's subscriber base for years.

But only if the technology scales and is not immediately rejected by 
30-60% of the subscriber base.

This is why we view the testing of CGN as newsworthy.

>> Clearly, that organization's subscriber growth will be limited by CGN technology, not by address scarcity.
> Why? Does it not scale linearly? If not, why not?

I dont particularly like a multilayered NAT internet any more than you.

However it is coming and will stay for as long as it is needed and 
useful for those who operate it. Which is likely to be far longer then 
either of us like.

We only differ in one point. You believe it will be so bad that it will 
immediately drive ipv6 adoption and be viewed as a short term expensive 
boondoggle of a misguided experiment. I am not so confident in its failure.

I think we are heading toward a new norm.

>> Think locally for a bit. Addresses are not instantaneously fungible across the internet. Any provider who can pull this off will have far more then a 4-month stop-gap. They may even have enough to peddle on the market.
> I think that's very optimistic.

With your numbers, a provider can double or triple (actually quadruple 
or sextuple using your ratio) their subscriber base by converting to 
CGN. Were you being overly optimistic?

Or were my estimates, starting at quadrupling or more, overly optimistic?

> I'm not sure why you say they are not instantaneously fungible.
 > Owen

Because nobody deploying CGN is going to flag day convert entire 
subscriber bases. Because the addresses they free up will be reused 
internally. Because if you are not one of these entities with low 
hanging fruit such as easily convertible to CGN subscriber bases, you 
are NOT going to directly benefit from the efforts of those who do.

Unless they peddle it (or return it).


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