Question

Suppose a message of size 15000 bytes is transmitted from a source to a destination using IPv4 protocol via two routers as shown in the figure. Each router has a defined maximum transmission unit (MTU) as shown in the figure, including IP header. The number of fragments that will be delivered to the destination is ___________. (Answer in integer) 

 

Hint:

When calculating the number of fragments, always consider both the payload size and the MTU, as the fragmentation process depends on the smallest MTU along the transmission path.

Answer 1

Correct Answer: 7

As the packet travels across the network, its size must always conform to the smallest MTU encountered so far. Each router therefore limits the maximum payload that can be carried forward without further splitting.

After accounting for the IP header, the first router allows chunks of \(4980\) bytes of data. Carrying \(15000\) bytes of data thus requires four such chunks, which are forwarded independently.

The next router imposes a stricter size limit, permitting only \(2980\) bytes of data per packet. Each of the earlier chunks therefore needs to be split further so that no piece exceeds this limit.

When these constraints are applied across all incoming packets, the data finally arrives at the destination in a total of seven separate fragments.

Hence, the number of fragments delivered to the destination is \(\boxed{7}\).