From what range are 16-bit private AS numbers selected?

Question

Options

• A64496 64511
• B1-63100
• C64512-65534
• D64513-65535

• A
  3% (1)
• C
  94% (29)
• D
  3% (1)

Explanation

Private 16-bit AS numbers are defined in RFC 6996 as the range 64512–65534, making option C correct. This range sits at the top of the 16-bit AS space (which spans 0–65535), reserved specifically for private use - similar in concept to RFC 1918 private IP addresses.

Why the distractors are wrong:

• A (64496–64511): This range is reserved for documentation and examples (per RFC 5398), not private use - commonly seen in tutorials and RFCs themselves.
• B (1–63100): This is a fabricated range with no standard definition; public AS numbers actually run from 1–64495.
• D (64513–65535): Off by one at both ends - the private range starts at 64512 (not 64513), and 65535 is a reserved value, not a valid private AS number.

Memory tip: Think of the private range as the "last mile" of 16-bit AS space - it starts at 64512 (≈ 64K + 512) and stops one short of the absolute maximum (65535), which is reserved. If you remember 64512 to one-before-max, you've got it locked in.

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