Host A (on TCP/IPv4 Networks) send an IP Datagram D to host B (also on…
2024
Host A (on TCP/IPv4 Networks) send an IP Datagram D to host B (also on TCP/IPv4 network). Assume that no error occurred during transmission of D, when D reaches B. Which of following header field may differ from that of original datagram D? (A) TTL
(B) Checksum
(C) Fragment offset
(D) Source IP
(E) Destination IP
Choose the correct answer from the options given below :
- A.
(A) and (B) Only
- B.
(A), (B) and (C) Only
- C.
(A), (B), (C) and (D) Only
- D.
(A), (B), (C) and (E) Only.
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Correct answer: B
Answer: TTL, Header Checksum, and Fragment Offset may differ.
Time To Live (TTL): routers decrement the TTL at each hop, so the value received by the destination is usually lower than the original.
Header Checksum: because the TTL (a header field) changes at each hop, the IP header checksum must be recomputed, so it can differ from the original.
Fragment Offset: if a router performs fragmentation due to MTU constraints along the path, fragment-related fields (including fragment offset) will be set or changed by that router.
Source and Destination IP addresses: normal IP forwarding does not alter these addresses, so they remain the same end-to-end. (They can be changed by NAT or certain tunneling mechanisms, which are special cases.)
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