Service providers are compelled to move to IPv6 to accommodate new customers and content providers need to ensure that their contents are accessible irrespective of the protocol their customers are using. Governments across the world are regulating the move to IPv6 as well. This brings in the challenge of ensuring that new IPv6 enabled devices are able to access any content – hosted on IPv4 or IPv6.  NAT64 is technology that provides the bridge between IPv6 and IPv4 by doing the protocol transformation that the other side understands.

NAT64 does the translation from IPv6 to IPv4 based on a pre-assigned /96 prefix that is carried in the destination IPv6 address of packets. Last 32 bits of the IPv6 address carry the
IPv4 address of the destination IPv4 host. As the traffic passes through the NAT64 device, it looks for the prefix match – if the match is found, the device knows that the destination is IPv4 host and needs translation. Unlike the good old NAT devices, NAT64 devices need to perform protocol transformation – creating an IPv4 header based on the information in the IPv6 header. There are additional requirements to make sure that two disparate networks can talk to each other like ICMP translation along with translation of traditional applications that embed Layer 3/4 information in the packets (e.g. FTP, SIP etc).

Now the question is – how does the connection initiating IPv6 host knows the destination address? This gap is filled by DNS64 device. Whenever DNS64 device gets a query (AAAA) to resolve a name – it first tries to fetch the IPv6 address. If the address is found, it is returned to the host but if there is no IPv6 address – DNS64 device gets the IPv4 address prepends it with the preconfigured 96 bit prefix and returns to the host. Following diagram shows the sequence of events when an IPv6 host tries to connect with an IPv4 server.

In early stages of IPv6 transition content providers are primarily providing access to web content hosted on IPv4 servers. In such scenarios SLB64 offer advantages over pure NAT64 technology. SLB64 is Server Load Balancing by exposing IPv6 connection points for IPv4 servers – so SLB64 devices not only provide translation but also provide other benefits that come along with advanced ADCs like NetScaler.

There are many detractors of NAT yet there is no denying that NAT has been in use for years and is not going away anywhere soon. For IPv6 transition it is emerging as a very strong enabling technology.