Size of MTU depends on the network topology and conventions. On most Ethernet networks it's actually a bit larger.
MTU on Ethernet is (mostly) 1500 (1518 bytes/frame - 18 bytes header&checksum). UDP overhead reduces this by 16 bytes, TCP by 32 bytes.
Sending large packets over unknown territory can lead to fragmentation and reassembly:
MTUThe values you've stated are the largest packets guaranteed not to be fragmented, regardless of layer and topology - if that's what you were looking for. ;-)
