The dynamic tunnels are point to multipoint, virtually treating the underlying IPv4 network as NBMA. This is because the destination IPv4 address is dynamically discovered from the destination IPv6 address. Thus if a protocol uses the destination of multicast address, they will get mapped to an IPv4 address which cannot be routed, there by dropped.
Because of this reason we have to trick the protocol to use unicast IPv6 destination addresses. The implementation of this depends on the routing protocol itself. In this blog I will be demonstrating using OSPFv3 over different tunnel types.
In the above topology R2 which will be the hub is configured for following tunneling methods:
- Automatic 6to4 tunneling towards R1.
- ISATAP tunneling towards R3, where it acts as a client.
- ISATAP tunneling towards R4 where both R2 and R4 are servers.
Caveats: The most important point to take into account is the IPv6 address itself. The transport IPv6 destination address will be automatically discovered with help of the IPv6 destination address. So we must make take care that the IPv6 destination could be properly mapped to the IPv4 destination.