GATE CS 2024 Set 2 Q18 — Fragmentation and IP Addressing, IPv4, CIDR

To determine the correct statements about $\text{IPv4}$ fragmentation and reassembly, let's analyze each option:

• Statement A & B (Fragmentation): In $\text{IPv4}$, fragmentation can be performed by the source host or by any intermediate router along the path when the size of the outgoing IP datagram exceeds the Maximum Transmission Unit ($\text{MTU}$) of the next-hop link (provided the Don't Fragment ($\text{DF}$) flag is not set to 1).
  Therefore, Statement A is FALSE and Statement B is TRUE.


• Statement C & D (Reassembly): Reassembly of fragmented IP datagrams is performed only at the destination host. This design choice is made because:
  1. Different fragments of the same datagram can take different paths to the destination, meaning an intermediate router might never see all the fragments.
  2. Performing reassembly at intermediate routers would put a significant computational and buffering burden on them, degrading network performance.
  Therefore, Statement C is TRUE and Statement D is FALSE.

Thus, the true statements are B and C.