A Layman’s Guide to the IPv6 Transition

The Internet uses what’s called the TCP/IP protocol. The IP part of that technology, called IPv4, is running out of addresses, and the telecommunications industry is moving to a new standard, called “IPv6.” In some cases, this may require new home equipment, a new router, and possibly other consumer electronics, if you elect to upgrade. Here’s what you need to know.

Editor’s note: This is not intended to be a detailed, technical article. Instead, it’ll be restricted to the essentials, general simplifications, and some links for more details. Also, this first article on the subject focuses on Comcast and its IPv6 efforts. I asked Century Link about their plans, but they weren’t forthcoming about their IPv6 transition.

Global Internet

What is TCP/IP?

TCP stands for Transmission Control Protocol. Basically it’s the technology that defines data packets and how they’re routed on the Internet. All of the data you send and receive on the Internet is divided into small, digital data packets, and each packet may travel a different route than another one. The job of the network interface card in your computer is to reassemble the packets, which are sequentially numbered, and request a retransmission if one goes missing. That’s how data, say Web pages, e-mail, etc., get transmitted, and that’s how delays can occur. TCP is designed for accuracy, not speed.

IP stands for Internet Protocol. It’s the method we use to identify devices on the Internet and give them an address. Every device on the Internet has a unique identifier, called a MAC address (Media Access Control, nothing to do with Macintoshes), which you may have seen. In turn, that unique device can be given a “dotted decimal” IP address, like That address can occasionally change on a device, but during the lifetime of a transmission and receipt, it’s relatively constant.

When packets are sent on the Internet, the packet contains both the origin and destination IP address. In order to keep devices from having duplicated addresses, the old IP protocol, version, IPv4, has a provision for 232 addresses. That’s about 4.294 billion unique IP addresses.

Why is IPv4 Inadequate?

Even though IPv4 allows for over 4 billion different devices, the world is running out of addresses. That’s not to say that every address is used up. There are technical reasons why some addresses aren’t yet used. The point is that, as far as the telecommunications companies are concerned, the number of available addresses they can assign to, say, your cable (or DSL) modem are dwindling. Something has to be done.

What Is The Industry Planning?

The telecommunications industry has been planning a migration to a new version of IP, called IPv6, for many years. In addition, the Consumer Electronics Association (CEA) has been working with the consumer eletronics industry including equipment makers to facilitate the transition. One main distinguishing characteristic of IPv6 is that that there are 2128 addresses. That’s 3.4028 x 1038. To put that in perspective, there are only about 1019 grains of sand on all the beaches of the world. If you assigned an IPv6 address to each grain of sand, each one could have more than a billon billion addresses.

That seems to be enough for now.

Here is a summary of some basic IPv6 differences.

IPv6 chart

How Will the Change Affect Your Computer?

Apple’s Mac OS X has been ready for IPv6, in principle, since version 10.3, “Jaguar.” However, as IPv6 has developed, new requirements have been imposed, namely, DHCPv6 [specified by RFC3315] specifically stateful DHCPv6. As a result, users must have at least OS X 10.7 “Lion,” Windows Vista or Windows 7 to operate on most modern IPv6 networks. The latest version of each Linux distribution should work as well, but a complete list is beyond the scope of this article.

The modern versions of OS X and Windows can operate in what’s called a “dual stack” mode. IPv4 and IPv6 protocols are both supported and enabled simultaneously. If the OS sees an IPv4 packet, identified by its header, it will route it accordingly. The same goes for IPv6. In general, then, if you have a fairly modern Mac or PC, you should be fine. The dual stack is already enabled, so there’s nothing you need to do.

You can verify that IPv6 is set up automaticaly in System Preferences -> Network -> Advanced… -> TCP/IP.


The dual stack mode extends to iOS devices like your iPhone, iPad, and iPod touch. Most Android devices also support IPv6, however, you will need to check with the manufacturer to verify that IPv6 is enabled.

How Will the Change Affect Your Cable Modem?

If you have Comcast as your ISP, you have a cable modem. The technical descriptor for the level of technology it uses is called DOCSIS. Most of us have what’s called a DOCSIS 2.0 or earlier cable modem. IPv6 is supported by all DOCSIS 3.0 cable modems and a subset of pre-DOCSIS 3.0 cable modems that are firmware upgradable to fully support IPv6. That’s something you need to discuss with Comcast, if they’re your ISP. Here’s a list of Comcast cable modems that shows which ones support IPv6.

It is important to note that this list is expected to change and grow frequently so be sure to check it as you go along. The new (or upgraded) Comcast cable modems will support dual stack operations for devices connected to it. It is important to note that if both IPv4 and IPv6 are enabled and the content being accessed is also enabled over IPv4 and IPv6, IPv6 will generally be preferred. Comcast says that they selected this approach to simplify the transition and help make the introduction of IPv6 seamless for end-users.

How Will the Change Affect Your Home Router?

That leaves your IPv4 home router in the middle, between the cable modem and your home network. If you elect to upgrade to IPv6, it will need to be upgraded or replaced. Comcast told me that they started working with router vendors over three years ago and that as part of their IPv6 rollout they will be providing a list of compatible home routers that have been tested to work on their network. The list will include those that can be upgraded. Newer devices from Apple, including the Airport Extreme and Time Capsule, support IPv6 today. Users may need to enable support for IPv6 manually, however.

IPv6 logo

What About Your Other Home Devices?

Many of us have other IPv4 devices on our home network, such as Blu-ray players, AV receivers, Apple TV, Roku boxes, even modern HDTV sets. Because there are no fundamental changes to IPv4 yet, your upgraded home router will continue to publish IPv4 addresses via DHCP, using Network Address Translation (NAT), to these devices as before. They’ll just keep on working, and there’s nothing you need to do at this time.

Comcast noted that some service providers will likely have to deploy alternate transition technologies, which may have an impact within your home network.

IPv6 doesn’t use NAT. It’s a needless complication and not required. Instead, your IPv6 device gets an IPv6 address, one of the 3.4 x 1038 available. Hostile scans for specific IP addresses are no longer practical because the address space is so vast.

IPv6 and Security

Even though you’ll have a considerable amount of security through obscurity in IPv6, it is expected that there will still be IPv6 firewalls built into your new home networking and consumer electronics. It is important to note that OS X Lion’s firewall also supports IPv6. You can run them both, depending on how you want to configure your system, but that’s a more advanced topic for a later discussion.

Will There be an Extra Charge for IPv6?

Comcast said that they do not plan to charge customers extra at this time as their network is upgraded to include IPv6. However, you may encounter other personal charges, not related to Comcast, for new hardware if you upgrade. For example, a new router (perhaps), upgrading your Mac or PC, etc.

What if You do Nothing?

When Comcast rolls out IPv6, the upgrade won’t be mandatory. They’ll be enabling IPv6 automatically in addition to existing IPv4 services. For the time being, you can just carry on with your old equipment. That’s in recognition of the fact that there are so many household devices that currently use only IPv4 and can’t be upgraded. But how long IPv4 will be supported is undetermined at this time. While IPv4 won’t be turned off just yet, as I mentioned in the introduction, a full depletion of the address space is inevitable. My own surmise is that, as time goes on, new consumer electronics devices will introduce support for IPv6, and then IPv4 traffic will dwindle and fade naturally.

What? Me Worry?

The goal for Comcast is to ensure the transition to IPv6 is seamless and as transparent as possible. You’ll just plug in your new equipment, and expect everything to “just work,” thanks to the dual stack approach.

Why should you upgrade then? The most compelling reason is to avoid some of the less desirable transition technologies and approaches that could adversely impact your user experience if you stick with IPv4. For example, carrier grade NAT, a stop-gap designed to mitigate address exhaustion. Also, IPv6 improves the efficiency of IPSEC. Finally, there are so many IPv6 addresses available that not even a galaxy of hostile supercomputers could find you amidst the vast space of IPv6 addresses.

If Comcast is your ISP, look for this transition in 2012. As I find out more about other major ISPs, I’ll add to the discussion with follow-on articles. Finally, here is Comcast’s IPv6 FAQ and the Comcast IPv6 home page.


I’d like to extend my thanks to Mr. John Jason Brzozowski, Chief Architect, IPv6 and Distinguished Engineer at Comcast for his assistance with this article. Mr. Brzozowski works closely with CableLabs on DOCSIS and PacketCable specifications, and is very involved with the IETF, where he is co-chair of the DHC working group. John also is chair of the Consumer Electronics Association (CEA) IPv6 Working Group and the Society of Cable Telecommunications Engineers (SCTE) IPv6 Deployment Working Group as well as an active contributor on a range of IPv6 issues globally.


IPv6 logo: The Internet Society