The IPv6 over IPv4 tunnel is applied to IPv4 networks to connect IPv6 islands (also called isolated IPv6 domains).
During the initial phase of the evolution from IPv4 networks to IPv6 networks, IPv4 networks are deployed on a large scale but IPv6 networks are scattered similar to islands. It is uneconomical to connect these islands with private lines. Therefore, through tunneling technologies, you can create tunnels over IPv4 networks to connect IPv6 islands.
The IPv6 over IPv4 tunnel connects IPv6 islands over IPv4 networks. To put this tunnel into practice, border devices on both IPv4 networks and IPv6 networks should support IPv4/IPv6 dual stack. You can set IPv4 addresses for the interfaces through which border devices connect to IPv4 networks and IPv6 addresses for the interfaces connecting IPv6 networks.
IPv6 over IPv4 tunnels are classified into manual tunnels and automatic tunnels based on whether manually configuring the destination addresses of the tunnels is required. All tunnels are configured with tunnel interfaces.
Manual tunnels include:
You need to manually specify the source and destination IPv4 addresses of the tunnel.
Carries IPv6 packets along the IPv4 GRE tunnel.
Automatic tunnels include:
Enables isolated IPv4/IPv6 dual-stack hosts or border devices to access remote IPv6 networks over IPv4 networks.
Connects multiple IPv6 islands over IPv4 networks.
As an extended 6to4 tunnel, the 6RD tunnel connects multiple IPv6 islands over IPv4 networks.
Enables IPv4/IPv6 hosts on IPv4 networks to access IPv6 networks.
Table 1 lists the application scenarios for different types of IPv6 over IPv4 tunnels.
| Tunnel Type | Application Scenario | Features |
|---|---|---|
| IPv6 over IPv4 manual tunnel | Such tunnels are configured between border devicesa on different IPv6 domains. | Simple P2P tunneling. An IPv6 over IPv4 manual tunnel is easy to configure but with less scalability. |
| IPv6 over IPv4 GRE tunnel | Such tunnels are configured between border devices on different IPv6 domains. | Simple P2P tunneling. A GRE tunnel can be configured with authentication on GRE packet headers and tunnel keywords to enhance its security. |
| IPv6 over IPv4 automatic tunnel | Such tunnels are configured between border devices on different IPv6 domains. | Point-to-multipoint tunneling. An IPv6 over IPv4 automatic tunnel does not support forwarding and can be applied only to simple application scenarios. Therefore, the RFC about automatic tunnels has already been aborted. |
| 6to4 tunnel | Such tunnels are configured between border devices on different IPv6 domains. | Point-to-multipoint tunneling. A 6to4 tunnel uses the 6to4 address that consists of fixed prefixes. |
| 6RD tunnel | Such tunnels are configured between border devices on different IPv6 domains. | Point-to-multipoint tunneling. The IPv6 prefix for a 6RD tunnel can be configured at will, therefore forming a 6RD delegated prefix. Tunnel of this type is the most widely applied tunneling technology currently. |
| ISATAP tunnel | Such tunnels are configured between border devices and hosts. | Point-to-multipoint tunneling. An ISATAP tunnel is applied to an IPv6 domainb. |
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