Which of the following fields in the IPv4 header checks for integrity of the header information?

The checksum field in the IPv4 header is specifically designed to ensure the integrity of the header information. It serves as a safeguard against errors that may occur during the transmission of the packet across the network. By computing a checksum value based on the header's contents, the sender can create a checksum that is included in the packet.

When the packet reaches its destination, the receiving device calculates the checksum of the received header. If the computed checksum matches the one sent with the packet, it indicates that the header has not been corrupted during transmission. If there is a mismatch, this suggests that an error has occurred, prompting the receiving device to discard the packet or take appropriate error handling steps.

Other fields, like the header length, source IP address, and protocol, are crucial for the proper processing and routing of packets but do not contribute to the integrity checking of the header itself. The header length indicates the size of the header, the source IP address identifies the packet's origin, and the protocol specifies the upper-layer protocol that should handle the packet, but none of these serve a function in verifying that the header has remained unaltered during transit.