Please compress the address 2001:0DB8:0000:C030:0000:0000:09A0:CDEF. ()

Question

Options

• A2001:DB8:0:C030::9A0:CDEF
• B2001:DB8::C030::9A0:CDEF
• C2001:DB8:0:C030:0:0:9A0:CDEF
• D2001:DB8:0:C030::9A0:CDEF

• A
  74% (17)
• B
  13% (3)
• C
  4% (1)
• D
  9% (2)

Explanation

Option A is correct because IPv6 compression follows two rules: drop leading zeros from each group, and replace the longest single consecutive run of all-zero groups with "::". Applying both rules to 2001:0DB8:0000:C030:0000:0000:09A0:CDEF yields 2001:DB8:0:C030::9A0:CDEF, where the two consecutive zero groups (positions 5 and 6) become "::" and all leading zeros are stripped.

Option B is invalid because it uses "::" twice (once after DB8 and once after C030), which is forbidden -- a double colon may appear only once in an address, since two occurrences would make it impossible to determine how many zero groups each one represents. Option C removes leading zeros correctly but fails to apply the "::" compression to the consecutive zero groups, leaving them as explicit "0:0", so it is valid but not fully compressed. Option D appears identical to A as written, suggesting a typo in the original exam; any version of D that differs would fail for the same reasons as B or C above.

Memory tip: think of "::" as a one-time coupon -- you only get to use it once per address, and it always collapses the longest run of consecutive all-zero groups you can find.

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