When you create a 6to4 tunnel you need to apply suitable IPv6 addresses to the tunnel interfaces.
To do this you can take your IPv4 IP address which will be the source IP and convert it to an IPv6 address.
1) Using a Global address you know 2 things A) the high order bits always start 001 = 2000::/3 and generally end with 0001 in the first 16bits and B) a Global prefix is 48 bits long ( or /48). With this in mind you know your first 16 bits, 0010 0000 0000 0001: X:X:X:X:X:X:X, so you are looking for the remaining 32 bits to form the address
2) Copy out into binary the IPv4 address of the physical interface the tunnel will be be associated with then convert it to hex, e.g.) 192.168.99.1
1100 0000. 1010 1000. 0110 0011. 0000 0001
c 0 a 8 6 3 0 1
3) Combine this with your first 16 bits and you have your Global IPv6 to apply to your tunnel interface
2001:c0a8:6301::/48
Practise doing this quickly, again I've not taken the exam, but just like subnetting and Multicast MAC addresses it strikes me as an obvious exam question and an easy mark to pick up quickly leaving you time to work on the harder questions.
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