What is the maximum value of the IP header length (IHL) value when multiplied by 4 to obtain bytes?

What is the maximum value of the IP header length (IHL) value when multiplied by 4 to obtain bytes?

• A. 60 bytes
• B. 40 bytes
• C. 64 bytes
• D. 20 bytes

Answer: (A)

The IHL value is the header length expressed in 32-bit words, and to get the size in bytes you multiply by four. Since IHL is a 4-bit field, its maximum value is 15, which equals 15 × 4 = 60 bytes. So the largest IPv4 header can be 60 bytes long. A header without options is 5 words (20 bytes); with options you can go up in 4-byte steps up to the 60-byte maximum. The other options correspond to smaller header sizes or, in the case of 64 bytes, would require an IHL of 16, which isn’t possible with a 4-bit field.

The IHL value is the header length expressed in 32-bit words, and to get the size in bytes you multiply by four. Since IHL is a 4-bit field, its maximum value is 15, which equals 15 × 4 = 60 bytes. So the largest IPv4 header can be 60 bytes long. A header without options is 5 words (20 bytes); with options you can go up in 4-byte steps up to the 60-byte maximum. The other options correspond to smaller header sizes or, in the case of 64 bytes, would require an IHL of 16, which isn’t possible with a 4-bit field.