In this case, a single router can be deployed in the testbed subnet and a tunnel used for connectivity from the testbed to an upstream IPv6 provider.

The choice for the site is which tunnel mechanism to use. The options include:

• Manually configured tunnel
• Tunnel broker
• 6to4

While 6to4 is convenient and automatic, it can lack reliability (depending on the 6to4 relays being used). It also means the site does not use production address space, or its own allocated address space.A manual tunnel or tunnel broker would generally be preferred.

If the site is using IPv4 NAT, a tunnel can still be established, but may need specific forwarding of (for example) Protocol 41 on the NAT device, or use of a protocol such as TSP to establish a NATfriendly tunnel method such as UDP tunnelling.