To understand which statements about IPv4 fragmentation are true, it's important to delve into the mechanics of IPv4 fragmentation and reassembly.

IPv4 fragmentation occurs when an IP datagram is too large to be transmitted over a network with a smaller Maximum Transmission Unit (MTU) than the size of the datagram. This process helps ensure that datagrams can travel across diverse networks with varying MTU sizes.

Let's analyze each option:

Option A: The fragmentation of an IP datagram is performed only at the source of the datagram

This statement is FALSE. In IPv4, fragmentation can be performed by routers, not just the source. When a router encounters a datagram that is too large for the next network segment based on its MTU, it can fragment the datagram.

Option B: The fragmentation of an IP datagram is performed at any IP router which finds that the size of the datagram to be transmitted exceeds the MTU

This statement is TRUE. Any intermediate router that discovers a datagram larger than the MTU of the next hop network can fragment the datagram. This ensures that the datagram can continue to be transmitted to its destination.

Option C: The reassembly of fragments is performed only at the destination of the datagram

This statement is TRUE. In IPv4, fragment reassembly is performed only by the destination host. Intermediate routers do not reassemble fragments; they only participate in forwarding the individual fragments to the destination.

Option D: The reassembly of fragments is performed at all intermediate routers along the path from the source to the destination

This statement is FALSE. Intermediate routers do not perform reassembly of fragments. They forward the fragments to the destination, where reassembly takes place.

Therefore, the statements that are TRUE are:

Option B: The fragmentation of an IP datagram is performed at any IP router which finds that the size of the datagram to be transmitted exceeds the MTU

Option C: The reassembly of fragments is performed only at the destination of the datagram