Solution

EXPLANATION:

When an IP datagram is transmitted from Host A to Host B, some fields in the IP header may change, while others remain the same. Here's the breakdown of each field mentioned:

• (A) TTL (Time-to-Live):
  • The TTL field is decremented by each router the datagram passes through. This ensures that packets don't loop indefinitely in the network. Therefore, the TTL will differ when the packet reaches Host B.
• (B) Checksum:
  • The IP header checksum will change as the packet travels through the network, especially when the TTL field is decremented. Since TTL changes, the checksum needs to be recalculated by each router to account for this change. Hence, the checksum will be different.
• (C) Fragment Offset:
  • If the datagram was fragmented during transmission, the Fragment Offset field may change. This field is used to indicate where a particular fragment belongs in the original datagram. If no fragmentation occurred, this field remains unchanged, but if fragmentation occurs, it will differ.
• (D) Source IP:
  • The Source IP address remains unchanged throughout the journey of the datagram because it identifies the sender of the packet. It will not change during transmission.
• (E) Destination IP:
  • Similarly, the Destination IP address also remains unchanged because it specifies the intended recipient of the packet. It will not change during transmission.

Thus, the correct answer is Option 2: (A), (B), and (C) Only.