Option 82 in the DHCP message is called the relay agent information option, and the administrator can obtain a lot of client information from it. Option 82 can contain at most () Sub-Options.

Question

Options

• A255
• B1
• C2
• D4

• A
  83% (15)
• B
  11% (2)
• D
  6% (1)

Explanation

Option 82 uses a single octet (8 bits) to identify each sub-option, giving a possible range of 0-255; since sub-option code 0 is typically reserved, codes 1 through 255 are available for use, yielding a maximum of 255 sub-options. Option B (1) is wrong because Option 82 is specifically designed to carry multiple pieces of client context, not just one; in practice, sub-options 1 (Circuit ID) and 2 (Remote ID) are the most commonly deployed. Option C (2) is the most tempting distractor because Circuit ID and Remote ID are the two best-known sub-options, but the standard does not limit the field to just those two. Option D (4) has no technical basis in the RFC 3046 specification that defines Option 82.

Memory tip: Sub-option identifiers in Option 82 are encoded in one byte (8 bits), and the maximum value a single byte can hold is 255 -- so the ceiling on sub-options is 255, matching the upper limit of an 8-bit unsigned integer.

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