Which statement correctly describes how to derive the header length from the IHL value?

Which statement correctly describes how to derive the header length from the IHL value?

• A. IHL is expressed in bytes; header length in bytes equals IHL times 4.
• B. IHL is expressed in 32-bit words; header length is equal to IHL.
• C. IHL is expressed in 16-bit words; header length equals IHL times 2.
• D. IHL is unrelated to header length.

Answer: (D)

The value in the IHL field represents the header length in 32-bit words, not in bytes. To get the header length in bytes, multiply IHL by 4 (since each 32-bit word is 4 bytes). For example, an IHL of 5 means a 20-byte header (5 × 4). If options are present, IHL increases accordingly, up to a maximum of 15 (60 bytes). This conversion—IHL × 4—is what you use to derive the actual header length from the IHL value.

The value in the IHL field represents the header length in 32-bit words, not in bytes. To get the header length in bytes, multiply IHL by 4 (since each 32-bit word is 4 bytes). For example, an IHL of 5 means a 20-byte header (5 × 4). If options are present, IHL increases accordingly, up to a maximum of 15 (60 bytes). This conversion—IHL × 4—is what you use to derive the actual header length from the IHL value.