Two years ago, the Chinese government adopted a controversial approach known as network address translation to bridge the gap between IPv4, the Internet's main communications protocol, and an emerging Internet standard known as IPv6.
Now, the Chinese are proposing their NAT approach — dubbed IVI — as a possible solution to other governments and carriers grappling with the looming depletion of IPv4 addresses and the long-anticipated upgrade to IPv6.
IPv4 uses 32-bit addresses and can support 4.3 billion devices connected directly to the Internet. IPv6 uses 128-bit addresses and can support a virtually limitless number of Internet-enabled devices, such as PCs, printers, gaming systems, cell phones and appliances.
IPv6 was designed a decade ago but hasn't been widely deployed outside of Asia, where IPv4 addresses are scarce. The Chinese government leads the world in IPv6 deployment, with the U.S. government working hard to catch up.
Usually, the Chinese are quiet about their Internet operations because they closely monitor and censor Web surfing by their citizens. However, details about the Chinese IPv6 network have trickled out over the years. (View a slideshow on how the Chinese Internet is different.)
Earlier this month, Chinese researchers outlined their IVI approach to the Internet's leading standards body, the Internet Engineering Task Force. In a document published July 6, engineers from the China Education and Research Network (CERNET) and Tsinghua University described their approach for co-existence and transition between IPv4 and IPv6.
To bridge between its IPv4-only CERNET and IPv6-only CERNET2, the Chinese developed IVI, a mechanism that embeds subsets of IPv4 addresses in prefix-specific IPv6 addresses. IVI allows these IPv6 addresses to communicate directly with global IPv6 networks and through stateless gateways to IPv4 networks.
The IVI scheme supports end-to-end address transparency, incremental deployment of IPv6 and performance optimization in networks that use multiple carriers, according to the document.
The Chinese are pitching IVI as a better way for IPv6 hosts to communicate with IPv4 networks than the IETF's current approaches. Existing standards propose running dual-stack hosts that support both IPv4 and IPv6 and tunneling, which involves encapsulating IPv6 packets to send over IPv4 networks.
The Chinese say a mechanism such as IVI is needed to translate between the different addressing structures used in IPv4 and IPv6. IVI can handle either IPv6 to IPv4 mapping or IPv4 to IPv6 mapping, the document says. It also can be used for client-server or peer-to-peer applications.
IVI "can satisfy most of the basic and advanced requirements for the IPv4 to IPv6 transition," the document says.
In the Chinese approach, carriers deploy gateways that are connected to both IPv6 and IPv4 networks. These gateways handle the IVI mapping and translation mechanism. The gateway runs an algorithm known as SIIT (for stateless IP/ICMP translation), which handles the translation between IPv4 and IPv6 packet headers.
The Chinese say they have successfully deployed IVI.
"The IVI gateway based on the Linux implementation has been deployed between CERNET (IPv4 and partially dual-stack) and CNGI-CERNET2 (pure IPv6) since March 2006," the document says. "The pure IPv6 Web servers using IPv6 addresses behind IVI gateways can be accessed by the IPv4 hosts and also by the global IPv6 hosts."
Several IETF working groups, including IPv6 Operations and Behavior Engineering for Hindrance Avoidance, plan to discuss IVI at a meeting in Dublin scheduled for later this month.
IVI is one of several NAT approaches under consideration for standardization by the IETF.
Fred Baker, co-chair of the IPv6 Operations working group and former chair of the IETF, says the fact that the Chinese have deployed IVI gives it a leg up over alternatives that are on paper only. "That makes it a strong contender in a world of rough consensus and running code," Baker says of IVI.