Cisco Certified Internetwork Expert (CCIE) Practice Test

Which statement is true regarding 6to4 tunneling?

1. It provides a /128 address block.

2. The prefix address of the tunnel is determined by the IPv6 configuration on the interface.

3. It supports static routing only.

4. It provides a /48 address block.

The correct answer is: It provides a /48 address block.

6to4 tunneling is a method that allows IPv6 packets to be transmitted over an IPv4 network by encapsulating them within IPv4 packets. This tunneling technique uses a special IPv6 prefix, specifically the 2002::/16 prefix, which is derived from the IPv4 address of the device that is the tunnel endpoint. When a device that supports 6to4 tunneling is configured, it automatically generates a /48 address block for its interior IPv6 addresses. This means that the device can have up to 65,536 subnets, each with a /64 prefix. The use of a /48 address block maximizes the potential for subnetting and allows for efficient address allocation for multiple networks. The other statements do not correctly represent the 6to4 tunneling method. For instance, stating that the prefix address of the tunnel is determined by the IPv6 configuration on the interface does not hold true, as it is predefined by the 2002::/16 prefix based on the underlying IPv4 address. Furthermore, 6to4 tunneling does not solely support static routing; it is compatible with dynamic routing protocols as well. Lastly, it indeed provides a /48 address block rather than a /128 address block