Owen DeLong is an IPv6 Evangelist and Director of Professional Services at Hurricane Electric , a large provider of IPv6-native Internet backbone and colocation services.
Most data center operators know that a failure to transition to IPv6 will eventually restrict access to connected resources and degrade communications efficiency. But one lesson of World IPv6 Day 
(held June 8, 2011) is that IPv6 adoption can bring immediate benefits in the form of improved network topologies and security today.
In determining when to transition to IPv6, the most common concern is the dwindling availability of IPv4 addresses to support additional devices. This limited thinking is a pity, as IPv4 suffers from a host of limitations beyond its address capacity, including inefficient routing and packet processing, indirect data flows, overly complex network configuration, and feeble security. Yes, IPv6’s nearly infinite supply of addresses (340 undecillion) could accommodate an intergalactic deployment of connected devices, but of equal importance is IPv6’s ability to improve routing efficiency, reduce router processing, enable true peer-to-peer connectivity, and eliminate complex layers of indirection like NAT.
IPv6 Transition Strategy: Dual Stack
Despite the clear benefits of IPv6, telecom companies, service providers and enterprises with large data centers struggle to determine the least disruptive IPv6 transition strategy. The key element of maintaining backward compatibility with IPv4 systems during the transition is to encourage a “dual-stack” mentality. All devices along the communication path, including endpoint devices, data-center routers and switches, ISPs, and backbone providers must simultaneously support IPv4 and IPv6.
Although the dual-stack model may appear to add complexity, it has the benefit of ensuring that no matter which protocol an endpoint application wishes to use, there will be support for it in the underlying network substrate. Nearly all modern operating systems support both IPv4 and IPv6, so in many cases, enabling IPv6 is simply a matter of turning it on (or, even better, just making sure that no-one has turned it off). Indeed, the majority of infrastructure behind the global Internet is now dual-stacked. Root name servers (fundamental to how we convert names like he.net into address numbers) have been IPv6-enabled for years, and Top Level Domains (TLDs) like .com, .net and .gov are serviced by domain name servers that are dual-stacked. Presently at least 256 of the 306 TLDs are enabled for IPv6.
Once dual-stack operating systems are deployed and enabled throughout an enterprise, there are a few technologies (6in4, 6to4 and Teredo) that ensure that IPv6 traffic can traverse pathways where only IPv4 is supported. Tunnelbrokers, which leverage the 6in4 protocol, allow IPv6 traffic to be tunneled inside IPv4 packets. The 6to4 protocol provides IPv6 connectivity over an IPv4 network by mapping IPv4 addresses into IPv6 addresses using the special 2002::/16 prefix. A 6to4 relay router at the network edge is required to encapsulate and decapsulate IPv6 traffic sent to and from site nodes. Another means to connectivity, Teredo, encapsulates IPv6 packets within IPv4 UDP packets that can be routed through NAT devices. Close consideration and understanding of these temporary measures is critical to filling the gaps in IPv6 connectivity.
The transition to IPv6 takes time and effort, and a carefully managed transition is better than one done in a panic. An organization’s network is a strategic asset that should not be neglected. Like roses and children, networks reflect their care.
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 World IPv6 Day: http://www.worldipv6day.org/
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