Which of the following fields of an IP header is/are always modified by any…
2024
Which of the following fields of an IP header is/are always modified by any router before it forwards the IP packet?
- A.
Source IP Address
- B.
Protocol
- C.
Time to Live (TTL)
- D.
Header Checksum
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Correct answer: C, D
Answer: Time to Live (TTL) and Header Checksum
Time to Live (TTL): Routers decrement the TTL by at least 1 for each forwarded packet to prevent indefinite circulation.
Header Checksum: The IPv4 header checksum covers header fields. Because TTL is changed, the header checksum must be updated to match the modified header.
Why not Source IP or Protocol: The Source IP Address is not altered by normal routers (only by NAT devices), and the Protocol field is an identifier for the payload protocol and is not changed during forwarding.
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