We can understand about Fragmentation – if big size packet is broken into a small size (1500 byte) of packet its called fragmentation.

Data packets have two main parts: the header and the payload. The header contains information about the packet’s source and destination addresses, while the payload is the actual contents of the packet

Note:- MTU almost always is used in reference to layer 3* packets

Example to understand the fragmentaion –

Imagine a shipping company E-Kart is handling a package that exceeds the weight limits of one of their facilities. Instead of refusing to deliver the package, the shipping company divides the package contents into three smaller packages. It also duplicates the shipping label for each package and adds a note indicating that each package is one part of a series that must arrive together — the first package is 1 of 3, the second is 2 of 3, etc

Fragmentation not work into below condition –

1- Fragmentation is not permitted in IPv6

2- Fragmentation is also not possible when the “Don’t Fragment” flag is activated in a packet’s IP header.

What is the ‘Don’t Fragment’ flag