What is the primary purpose of the sequence number in IP packets?

What is the primary purpose of the sequence number in IP packets?

• A. It ensures the IP addresses are unique.
• B. It helps the receiving computer reassemble the packets.
• C. It encrypts the payload.
• D. It determines the path the packet should take.

Answer: (B)

When IP fragments a large packet, the system needs a way for the destination to put all the pieces back together in the right order. The relevant header information marks which fragments belong to the same original datagram and where each fragment fits in that original message. The Identification field groups fragments, and the Fragment Offset indicates each piece’s position within the original packet. With those together, the receiving host can collect all the fragments with the same identifier and reassemble them into the complete datagram. That’s why this option is the best choice: it directly supports reconstructing the original data after fragmentation. It’s not about making IP addresses unique, encrypting the payload, or choosing the route—the addressing, security, and routing processes handle those things, not the fragment reassembly mechanism.

When IP fragments a large packet, the system needs a way for the destination to put all the pieces back together in the right order. The relevant header information marks which fragments belong to the same original datagram and where each fragment fits in that original message. The Identification field groups fragments, and the Fragment Offset indicates each piece’s position within the original packet. With those together, the receiving host can collect all the fragments with the same identifier and reassemble them into the complete datagram.

That’s why this option is the best choice: it directly supports reconstructing the original data after fragmentation. It’s not about making IP addresses unique, encrypting the payload, or choosing the route—the addressing, security, and routing processes handle those things, not the fragment reassembly mechanism.