Planning for Tunnel Use in the Network

The IPv6 implementation supports a number of tunnel configurations to serve as transition mechanisms as your network migrates to a mix of IPv4 and IPv6. Tunnels enable isolated IPv6 networks to communicate. Because most of the Internet runs IPv4, IPv6 packets from your site need to travel across the Internet through tunnels to destination IPv6 networks.

Here are some major scenarios for using tunnels in the IPv6 network topology:

• The ISP from which you purchase IPv6 service allows you to create a tunnel from your site's boundary router to the ISP network. Figure 2-1 shows such a tunnel. In such a case, you would run a manual, IPv6 over IPv4 tunnel.

• You manage a large, distributed network with IPv4 connectivity. To connect the distributed sites that use IPv6, you can run an automatic 6to4 tunnel from the edge router of each subnet.

• Sometimes, a router in your infrastructure cannot be upgraded to IPv6. In this case, you can create a manual tunnel over the IPv4 router, with two IPv6 routers as endpoints.

For procedures for configuring tunnels, refer to Configuring Tunnels (Task Map). For conceptual information regarding tunnels, refer to Overview of IP Tunnels.