Deploy360 19 November 2013

Skype On Android Works Over IPv6 On Mobile Networks Using 464XLAT

By Jan ŽoržFormer Operational Engagement Programme Manager

Mobile operators are running out of excuses why they can’t roll out IPv6 for their users and phones! The deployment of IPv6 in mobile networks has been possible for a long time now. Slovenian operators Mobitel and Tušmobil implemented it as a test in 2010 and Simobil did it a year later, but none of the operators has  yet decided to start selling a special “package” that would offer an Android phone and IPv6-only data access (in addition to the voice service). This is due to the fact that until now “legacy” applications that works solely and exclusively on IPv4 – such as Skype – does not work if the phone is not connected with IPv4 connection …

Such a decision is understandable, since it would cause a problem with the users to whom certain applications would not work.

This is now the past, Google has added a mechanism in Android 4.3 called 464XLAT and solves the fundamental issue of such legacy applications on the phone, which has only IPv6 connection.

In Paris World IPv6 Congress meeting, Lorenzo Colitti from Google and myself showed how the system works and how 464XLAT solves the problem of Skype and other legacy v4-only applications.

The mechanism shown was a prototype, existing only on the Lorenzo’s phone, so I lent him my Simobil test SIM card, we connected over IPv6 roaming (thanks Simobil for roaming traffic for demo purposes) and Skype and other applications started working right away.

How 464XLAT works? You can find it here and on the ISOC web portal D360, where the event in Paris is briefly described.

Lorenzo mentioned to me at the IETF meeting in Berlin that this mechanism is now already included in Android 4.3 and the first device to be sold with this version pre-loaded is Nexus7 LTE.

A few weeks ago the announcement was made that this model of Nexus7 tablet was available in our country and I ordered from one of our major online stores.

After two weeks of waiting the postman brought me a package. 🙂

I wanted to see what the user experience of a regular customer is, so I did not complicate it much. I took the tablet out of the box, turned it on, went through the initial classical procedure to set basic parameters and inserted a Simobil test SIM card that has IPv6 enabled (the only one that has been “cut” to the microSIM, the same would work equally well Mobitel and Tušmobil test SIM cards with enabled IPv6) and installed Skype.

If the package would be sold by mobile operator, the settings of a mobile network connections would be pre-set to IPv6, but in this case I had to configure the network connection to use IPv6-only.

A moment later, when the connection was established I ran Skype, logged in with my username and called my other test account, which I set on another device – and the whole thing worked right away 🙂


In the picture you can see the “screenshot” from Nexus7 tablet where I called the device that also had a camera focused on me, so that I can check the quality of the videocall – and I was more than surprised of how well it worked!

Then I went to a “core” of the Android system and tried to find out what interfaces are there – and found a brand new clat4 interface that was not there before.


You can see that the mobile interface had only IPv6 address and the interface CLAT had address, which is reserved for the ” IPv4-to-IPv6 translation by IANA .”

This means that in the Android 4.3 464XLAT functionality is already included and enabled by default, you don’t have to ask for it specifically. It’s in there, waiting for legacy and archaic v4-only apps to send v4 packets.

The beauty of this new mechanism is that the operator does no longer need to assign an IPv4 address to each mobile phone. This can help significantly in the IPv4-depletion crisis that is coming. In short:

  • CLAT interface simulates the IPv4 address
  • Skype is convinced that this is the right interface and it starts sending packets
  • 464XLAT converts them into IPv6 packets that are sent over mobile network
  • the NAT64 in the core then converts them back to IPv4 and send to the Internet.

T- Mobile USA has already started to sell and ship to the users pre-set IPv6-only phones, especially because Android has the option to setup different APN protocols for home network and roaming. Moreover, T- Mobile USA has made a change in the profile APN settings in Android and set up IPv6 as a “default” 🙂

Hope that other mobile operators in my country and around the world follow this example, it is about time 🙂

Disclaimer: Viewpoints expressed in this post are those of the author and may or may not reflect official Internet Society positions.

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