Which IPv4 header fields appear in the standard header order up to and including the Protocol field? (Include DSCP/ECN in the Type of Service field)

• A. Version, IHL, Type of Service (DSCP/ECN), Total Length, Identification, Flags/Fragment Offset, TTL, Protocol
• B. Version, IHL, Type of Service, Total Length, Identification, Flags/Fragment Offset, TTL, Protocol
• C. Version, IHL, Time to Live, Protocol, Checksum
• D. Version, IHL, Type of Service, Time to Live, Protocol

Answer: (A)

In IPv4, the header fields follow a fixed order, and the Type of Service field now includes DSCP and ECN bits for quality of service and congestion signaling. After Version and IHL, the next field is Type of Service (DSCP/ECN), then Total Length, followed by Identification, Flags/Fragment Offset, Time to Live, and finally Protocol to indicate the next header. So the sequence up to Protocol is: Version, IHL, Type of Service (DSCP/ECN), Total Length, Identification, Flags/Fragment Offset, Time to Live, Protocol. Other options either omit DSCP/ECN within the Type of Service field or place fields in a different order, which doesn’t match the standard header layout.