There is no fragmentation is done at Layer-2 (Data Link Layer)
Layer 2 does not do any fragmentation. It is up to L3 to pass data to L2 in a packet/frame size that will already match L2's MTU (maximum transmission unit). In fact, the reason L3 does fragmentation in the first place is is because of the limitations of the L2 Protocol.
Actually breaking up of PDUs(Protocol Data Unit) takes place only at two layers:1)At transport layer called SEGMENTATION. 2)At network layer called FRAGMENTATION.
The need for fragmentation due to restrictions upon on L-2 interfaces(E.g:for Ethernet it is 1500 bytes).This value is called MTU (Maximum Transmission Unit).If Ethernet interfaces receive frames larger than this default MTU value they will drop those frames.Hence it has to be decided at L-3 level whether or not to fragment the IP datagram as per L-2 requirement.All the process of fragmentation and re-segmentation are done using multiple fields in IP HEADER.
