Consider the following statements about the functionality of an IP based router. I. A router does not modify the IP packets during forwarding. II. It is not necessary for a router to implement any routing protocol. III. A router should reassemble IP fragments if the MTU of the outgoing link is larger than the size of the incoming IP packet. Which of the above statements is/are TRUE?

Let us analyze each statement:

• Statement I is FALSE: During forwarding, a router modifies several fields in the IPv4 packet header, such as decrementing the TTL (Time to Live) field and updating the Header Checksum. If fragmentation occurs or NAT is applied, other header fields are also modified.

• Statement II is TRUE: A router does not necessarily have to run a dynamic routing protocol (e.g., RIP, OSPF, BGP). It can operate purely based on statically configured routes (static routing) or default routes.

• Statement III is FALSE: Intermediate routers do not reassemble fragmented IP packets; reassembly is done exclusively at the final destination host. Routers may further fragment packets if necessary, but they never reassemble them even if the outgoing link MTU is larger than the fragment size.

Therefore, only statement II is TRUE, making D the correct option.