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Difficulty: MediumIPv6 Addressing Concepts and Header Structure

During a configuration audit of an enterprise router, a network engineer notices several IPv6 addresses entered by junior administrators. The engineer must ensure all addresses conform to standard IPv6 formatting rules (RFC 5952). Which of the following IPv6 addresses represents a syntactically valid shorthand compression of the uncompressed address 2001:0db8:0000:0000:00ab:0000:0000:0001?

  1. 2001:db8::ab:0:0:1Answer
  2. B
    2001:db8::ab::1
  3. C
    2001:db8:0:0:ab::1
  4. D
    2001:db8::b:0:0:1

Answer

2001:db8::ab:0:0:1 is the correct, syntactically valid compressed IPv6 address.
The address '2001:db8::ab:0:0:1' correctly applies RFC 5952 IPv6 representation rules. Leading zeros within hextets are removed (0db8 -> db8, 00ab -> ab, 0001 -> 1), and the first longest sequence of contiguous zero hextets is replaced with a single double-colon (::). The second zero sequence is represented with single zeros to avoid using multiple double colons.

Step-by-Step Solution

1
Identify leading zero suppression rules for each 16-bit hextet.
2001 remains 2001; 0db8 becomes db8; 0000 becomes 0; 00ab becomes ab; 0001 becomes 1.
Leading zeros in any 16-bit hexadecimal group must be omitted, but trailing zeros within a hextet must be preserved.
2
Apply the double-colon (::) zero compression rule to contiguous blocks of zero hextets.
The address contains two blocks of zeros: two consecutive 0000 hextets (positions 3–4) and two consecutive 0000 hextets (positions 6–7).
When zero sequence lengths are equal, RFC 5952 specifies compressing the first sequence of zero hextets with a single double-colon (::).
3
Assemble the compressed address using only a single double-colon (::).
2001:db8::ab:0:0:1
Using :: more than once in an address introduces ambiguity during parsing.

Key Concept

IPv6 Address Compression Rules (RFC 5952)
Estimated Time:1m 30s
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Topics

IPv6 Addressing Concepts and Header Structure

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