Which field in the IPv4 header is responsible for holding the checksum?

The field in the IPv4 header that holds the checksum is indeed the Checksum field. This field is crucial for error-checking within the IPv4 header. When a packet is transmitted over a network, the checksum is calculated based on the contents of the header, and it helps verify the integrity of the data. If the packet is received and the header has been altered in transit, the calculated checksum at the receiving end will not match the value stored in the Checksum field, signaling that an error has occurred.

Other fields in the IPv4 header serve different purposes: the Protocol field indicates the next level protocol carried in the payload (such as TCP or UDP), the Header Length field specifies the length of the header itself, and the TTL (Time to Live) field determines the lifespan of the packet in the network, helping prevent infinite loops by decrementing at each router hop. Thus, while all these fields are vital for packet processing, only the Checksum field directly addresses error detection for the header.