Question

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

Hint:

The TTL field prevents infinite loops, and any modification to the header requires recomputing the checksum.

Answer 1

The Correct Option is C

Option (A): The source IP address is not modified by routers. It remains the same throughout the packet's journey. Hence, Option (A) is incorrect.
Option (B): The protocol field indicates the higher-level protocol (e.g., TCP, UDP) and is not modified by routers. Hence, Option (B) is incorrect.
Option (C): The Time to Live (TTL) field is decremented by 1 by each router to prevent infinite loops in the network. This field is always modified by routers. Hence, Option (C) is correct.
Option (D): Since the TTL field is modified, the Header Checksum is recomputed by routers to ensure integrity. Hence, Option (D) is correct. Final Answer: \[ \boxed{\text{(C), (D)}} \]