Question 25

Statement I: 'A router does not modify the IP packets during forwarding.'

• When forwarding an IP packet, a router must decrement the Time-to-Live (TTL) or hop limit field and update the header checksum. If the outgoing link MTU is smaller than the packet size, the router may also fragment the packet and update fragment offset flags.
• Hence, routers routinely modify IP packets. Statement I is FALSE.

Statement II: 'It is not necessary for a router to implement any routing protocol.'

• A router requires a forwarding table to direct packets. This forwarding table can be statically configured by an administrator or populated with default routes. While dynamic routing protocols (such as OSPF, BGP) automate table updates, they are not mandatory for router operation.
• Hence, it is not strictly necessary for a router to implement a routing protocol. Statement II is TRUE.

Statement III: 'A router should reassemble IP fragments if the MTU of the outgoing link is larger than the size of the incoming IP packet.'

• In IP architecture, fragment reassembly is performed exclusively at the destination host, not at intermediate routers. Reassembling at intermediate routers would require excessive buffering and would fail if different fragments traversed different paths.
• Hence, routers do not reassemble fragments. Statement III is FALSE.

Therefore, statement II only is TRUE.