MTU & MSS

Maximum Transmission Unit & Maximum Segment Size

                    <--------------------------- IP MTU ------------------->
                    <--------------------- Ethernet MTU ------------------->
                                               <--------- TCP MSS --------->
       +------------+------------+-------------+---------------------------+------------+
FRAME  | Eth-Header |  IP-Header |  TCP-Header |        Data payload       | Eth-trailer|
       +------------+------------+-------------+---------------------------+------------+
BYTES        14           20            20                 1460                  4

Packet Unit Size

Packet Unit	Minimum Size	Maximum Size	Reasons
IPv4 packet	20 Bytes	65535 Bytes	16-bit Total Length field in an IPv4 header can store values from 0 to 65535. As IP header is 20 bytes which defines the minimal.
Ethernet frame	64 Bytes	1518 Bytes	In the original Ethernet standard (10 Mbps), the minimal ethernet frame size is 64 bytes and Ethernet MTU is 1500 bytes.