Tunneling Technologies: Automatic 6to4 Tunnels

6to4 tunnels are inherently multipoint by nature, these tunnels treat IPv4 networks as NBMA cloud.  In 6to4 tunnels, the tunnel itself operates on a per packet basis to encapsulate traffic to the correct destination.  These tunnels determine the appropriate destination address by combining the IPv6 prefix with the globally unique destination 6to4 border routers IPv4 address, beginning with 2002::/16 prefix

2002:border-router-IPv4-address::/48

The method leaves 16 bits in the 64bit prefix for numbering networks at each site.

IOS supports only one auto 6to4 tunnel on a given router.  Configuratoin is exactly the same as before except for the tunnel mode type:

tunnel mode ipv6ip 6to4

Tunnel destination is also not explicitly configured because of the automatic nature of the per packet destination method this tunnel type uses.

Routing over this tunnel type is also required, this is typically done using static routing.

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