The Internet Protocol Journal, Volume 14, No. 2

Letters to the Editor

Hi Geoff,

Thanks you for your contribution to the March 2011 issue of The Internet Protocol Journal. Your description in "A Rough Guide to Address Exhaustion" and the article on "Transitional Myths" were very insightful into the whole issue of IPv4 to IPv6, and the issues concerning migration. Some of your thoughts on the migration hit home, as I am speaking to customers about the planning for the transition and I see a lot of "Got You" that I must now incorporate in my discussions with my customer.

If you do have a means of updating the technical community with activities in the area of IPv6 and how to move customers to this protocol platform, can you please point me in that direction? I like your approach and so would like to stay close to what you are doing in this area. Again, thank you for your contribution!

Ole, thanks for getting this type of information out to the technical community. Great work.


—Joel Smith, Verizon Business, Toronto, Ontario, Canada

The author responds:

Hi Joel,

Thank you for your comments.

Running IPv6 in a dual-stack configuration certainly presents some issues, some of which are unique to particular networks and configurations, some of which appear to be common to particular roles (such as content delivery platform, Internet Service Provider, Enterprise Provider, and end user), and some of which are common across most, if not all, circumstances.

In assisting to set up some dual-stack services a year ago, I wrote down some of the issues that I found helpful in an article: "Two Simple Hints for Dual Stack Servers" ( You may find those hints to be of some value to your work. Some other sites that have a good collection of information are: and the community site, which also contains a wealth of information of a technical nature.

The basic guideline is to approach adding IPv6 to a network like any other engineering project: exercise care and attention to detail, and you will find it to be very straightforward!

Kind regards,

—Geoff Huston

Geoff and Ole,

Many thanks for your excellent papers in the March 2011 issue of IPJ. You have brought all the issues together in one place. They are clearly explained. Now Iíll do my small part by suggesting to one and all that they read it. My IPv6 service comes from a manually configured tunnel from Hurricane Electric.

—Dan Cotts

The author responds:

Thanks, Dan, for this feedback. It's certainly the right time for both users and content providers to act now to ensure that we continue to enjoy an Internet that still operates with a coherent end-to-end architecture into the future. The only way we can ensure that this happens is to act now and insist on IPv6—everywhere!

—Geoff Huston, APNIC


I enjoyed the recent IPv6 issue (Volume 14, No. 1, March 2011), but was dismayed by the lack of any frank discussion of the IPv6 "any-to-any" mantra versus the benefits of IPv4 Network Address Translation (NAT).

Internet purists don't hide their desire to rid the world of NAT and return to an any-to-any Internet where they could use FTP to/from any host. But for the past 15 years, NAT, RFC 1918, and perimeter security have been great for the Internet and for home and enterprise networking. When dealing with billions of endpoints, the implicit security of NAT far outweighs any alternative. Just think back to the pre-broadband/NAT days when hosts were attacked within seconds of dialing into an ISP.

Of the Ã1.7 billion publicly addressed Internet devices, the vast majority would be perfectly happy behind Carrier-Grade NAT (CGN). In fact, as ISPs begin introducing NAT offerings, millions will stampede to them for their lower cost. Mobile phone networks are the lowest-hanging fruit, followed by residential broadband. ISPs will still offer public IP products, of course, just at a higher price point.

The IETF needs to stop pussy-footing around the issue. CGN is not just an IPv6 transitional technology; it could very well become the de facto operating standard for the next decade.

The IETF desperately needs to:

  • Amend RFC 5382 ("NAT Behavioral Requirements for TCP") to allow endpoint-independent mapping. This will improve CGN scalability by several orders of magnitude. For example, rather than 2000 hosts per public IP mentioned in Mr. Huston's "Rough Guide" on address sharing, CGN could support 200,000 or more hosts per public IP.
  • Develop an IETF standard for P2P connection establishment. It took 8+ years for the IETF to take an interest in P2P mechanics (RFC 5128). Now it's time to show leadership. If a CGN-compatible P2P establishment standard were drafted, it would be adopted by P2P libraries overnight. While they're at it, look at standards for tying Universal Plug and Play (uPnP) into CGN.
  • Help coordinate a discussion of operational issues with ISP administration, law enforcement, DMCA enforcement, geolocation ser- vices, black/white lists, etc. Perhaps itís time to extol the benefits of millisecond-accurate IPFIX logs with NAT extensions, or develop a new TCP option to embed NAT details?
  • Legitimize common ISP self-preservation tactics, such as restricting SMTP, metering connections/sec, and so on.

Most importantly, IPv6 proponents should stop taking CGN as a personal affront. There is no malice; it's simply the path of least resistance for the IPv4 conundrum.

—Craig Weinhold, Madison, Wisconsin

The author responds:

Thank you for your note, Craig.

The discussion of how far the Internet could scale with integration of NATs into the interior of the network as well as the current pattern of NATs at the edge is not a new discussion. The Realm Specific IP (RSIP) Working Group was active over a decade ago in the IETF, looking at how a network would operate that consisted of a union of distinct realms, each of which was, in address terms, a discretely addressed IP network. With the benefit of hindsight, the outcomes of that effort in supporting a case for infrastructure NATs as a long-term architectural direction for the Internet were not overly encouraging.

From the perspective of the technology community, it reinforced the conclusion that IPv6 represented the best possible response to the recognized problem of IPv4 address exhaustion. NATs were a poor compromise in so far as, at the most basic level, NATs add state into the interior of the network. This imposition of state into the network infrastructure imposes a cost in terms of service fragility and network robustness that cannot be avoided.

There was an assumption some years ago that the industry would grapple with the transition to IPv6 well before the exhaustion of IPv4 addresses, and we would never have to deal with a dual-stack transition where one-half of the dual stack, the IPv4 part, would need to operate in a mode that included infrastructure NATs. We now appear to be beyond choice here—for the Internet to continue to grow by a further 300 million new services per year at present, and grow by yet more in the coming years, there is no choice but to operate the IPv4 part of the dual-stack environment with infrastructure NATs.

But this is a short-term hack, as distinct from a tenable longer-term position. The address pool of IPv4 is not getting any larger, and as more and more new services are added into a dual-stack network, the growth in the IPv4 part of the network can be absorbed only by progressive reduction of the number of available ports to each client of the infrastructure NAT. Services become more fragile and the network becomes less resilient. The inevitable next step in progressive scarcity of IPv4 addresses in the face of such inexorable growth is to drop the entire notion of end-to-end service and introduce application-level proxies into the IPv4 network. At this point we lose any ability to further sustain an open IPv4 Internet. The only applications that could be supported are those that are supported by the application-level proxies, and all other applications simply fail. The segregation of one Internet into a number of effectively disconnected "walled gardens" of networking is a rapid outcome in such a scenario.

One of the strengths of the Internet is its openness and neutrality. The open architectural model allows novel services to be added into the network by simply equipping clients and services with the service, leaving the interior of the network untouched. The interior of the network is entirely neutral to such innovations, as it is unaware of the content or intent of the packets that are passed through its switching infrastructure.

So the long-term path of greatest common benefit to all in the Internet is a network that, as far as possible, simply vanishes! It is an Internet where content and services can rendezvous with users without having to negotiate with any network elements. It is a network that is free of toll gates. And the network has now grown to such an extent that the only path from here that can sustain that architectural simplicity and sustain yet more growth is one that shifts determinedly and rapidly to IPv6. With the limited time and resources available, attempting to improve upon NATs is, in my opinion, not the best use of the resources we can apply to this problem.


—Geoff Huston, APNIC