DRAG DROP
You are configuring a multi-subnet IPv6 network for a regional office.
The corporate network administrator allocates the 2001:0db8:1234:0800: :/54 address space for
your use.
You need to identify network IDs of the first and last subnets that you will be able to create at the
office.
Which network IDs should you identify?
To answer, drag the appropriate network IDs to the correct subnets. Each network ID may be used
once, more than once, or not at all. You may need to drag the split bar between panes or scroll to
view content.
Answer: 
IPv6 addresses have 128 bits. 2001:0db8:1234:0800::/54 is showing you the first 64 bits of the address. With a /54, the first 54 bits are “2001:0db8:1234:08”. So your answers will definitely begin with “2001:0db8:1234:08”. That eliminates the last two answers.
Since all of the possible answers show 64 bits, anything with /54 will not be correct, so that eliminates half the answers.
The last two remaining are: 2001:0db8:1234:0800::/64 and 2001:0db8:1234:08ff::/64.
I know this explanation is kinda confusing, but it’s the only way I can put it into words.
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Actually, /54 is not exactly “2001:0db8:1234:08”, let’s switch the last two digits to binary and see. ‘2001:0db8:1234’ has taken 48 bits, then 08 is
Hex 0 8
Bin 0000 1000
/54 = 0000 10, not 0000 1000, that would be /56. So for the last subnet in binary:
0 B F F
0000 1011 1111 1111
Therefore 2001:0db8:1234:0bff::/64 would be the right answer.
Checkout older posts for other explanation http://www.aiotestking.com/microsoft/which-network-ids-should-you-identify/
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I agree.
Assuming what the best practice is to keep last 64 bits for the host (to support auto configuration):
first subnet will be 2001:0db8:1234:08::/64 [0000 10 00 0000 0000]
last subnet will be: 2001:0db8:1234:0bff::/64 [0000 10 11 1111 1111]
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first subnet will be 2001:0db8:1234:08::/64 ====== [0000 10 00 0000 0000]
last subnet will be: 2001:0db8:1234:0bff::/64 ====== [0000 10 11 1111 1111]
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