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Difficulty: HardIPv6 Addressing Concepts and Header Structure

A network administrator is configuring an IPv6 static route on an enterprise core router. The target next-hop interface requires the preferred compressed representation of the uncompressed 128-bit IPv6 address fe80:0000:0000:0056:0000:0000:0000:0010fe80:0000:0000:0056:0000:0000:0000:0010 following official RFC 5952 rules. Which of the following represents the correct compressed format?

  1. fe80:0:0:56::10Answer
  2. B
    fe80::56::10
  3. C
    fe80::56:0:0:0:10
  4. D
    fe80:0000:0000:56::10

Answer

fe80:0:0:56::10
The correct representation fe80:0:0:56::10 correctly applies RFC 5952 rules: all leading zeros within fields are stripped (0056 becomes 56, 0010 becomes 10, and 0000 becomes 0), and the double colon replaces the longest contiguous sequence of zeros (three consecutive zero fields on the right, rather than the two on the left).

Step-by-Step Solution

1
Suppress leading zeros in all 16-bit fields
The uncompressed address fe80:0000:0000:0056:0000:0000:0000:0010 becomes fe80:0:0:56:0:0:0:10.
RFC 5952 requires removing all leading zeros inside each 16-bit hexadecimal hextet, reducing 0056 to 56, 0010 to 10, and 0000 to 0.
2
Identify all contiguous sequences of zero fields
Sequence 1 consists of two zero hextets (hextets 2 and 3). Sequence 2 consists of three zero hextets (hextets 5, 6, and 7).
To determine where to apply the double colon (::), the lengths of all zero runs must be evaluated.
3
Apply the double colon to the longest zero sequence
The three-hextet zero sequence (hextets 5-7) is replaced with ::, yielding fe80:0:0:56::10.
RFC 5952 explicitly specifies that :: must replace the longest contiguous run of zero fields, and :: cannot be used more than once.

Key Concept

RFC 5952 IPv6 Address Text Representation Rules
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Topics

IPv6 Addressing Concepts and Header Structure

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