求 ipv6 分配 subnet 問題

你好,本人遇到一條題目是關於ipv6分配 subnet, 內容如下:

your company get a global address by ASP which prefix is 3FFA:FF2B:4D:B000::/41. your company has four departments. You have to assign a subnet to each department. In this way, which subnetted address prefix will you assign to the fourth department?

A. 3FFA:FF2B:4D:C800::/43
B. 3FFA:FF2B:4D:B400::/43
C. 3FFA:FF2B:4D:C000::/43
C. 3FFA:FF2B:4D:F000::/45
E. None of the above

Answer:A

關於subnet那部份我知道為什麼是43, 由於他有4個department, 而2的2次方等於4化成bit等到11,所以他的subnet由41擴充到43.

但是關於header部分,我不知道怎樣分配,例如由分配給第一個department的subnet時候應該是 3FFA:FF2B:4D:xxxx:://43,那個xxxx是怎樣計算呢?我不知道了

我查了很多關於ipv6的網站也没有這方面的知識==

x0