According to IPV4 Header format ,
Here Total length field is of 16 bit which specifies the entire packet size in bytes, including header and data. The minimum size is 20 bytes (header without data) and the maximum is 65,535 bytes. so according to your question network layer can only send a packet of maximum size 65,535 byte to DLL.
notify me if there is any mistake.
hope it helps.
Because Maximum IP packet size is 65535 B then fragmentation is done in DLL .which is converted according to Medium.